Non-Ferrous Metals

Nonferrous metals offer a wide variety of mechanical properties and material characteristics.

Nonferrous metals are specified for structural applications requiring reduced weight, higher strength, nonmagnetic properties, higher melting points, or resistance to chemical and atmospheric corrosion. They are also specified for electrical and electronic applications.

Material selection for a mechanical or structural application requires some important considerations, including how easily the material can be shaped into a finished part and how its properties can be either intentionally or inadvertently altered in the process. Depending on the end use, metals can be simply cast into the finished part, or cast into an intermediate form, such as an ingot, then worked, or wrought, by rolling, forging, extruding, or other deformation process. Although the same operations are used with ferrous as well as nonferrous metals and alloys, the reaction of nonferrous metals to these forming processes is often more severe. Consequently, properties may differ considerably between the cast and wrought forms of the same metal or alloy.

To shape both nonferrous and ferrous metals, designers use processes that range from casting and sintered powder metallurgy (P/M) to hot and cold working. Each forming method imparts unique physical and mechanical characteristics to the final component.

Though light in weight, commercially pure aluminum has a tensile strength of about 13,000 psi. Cold working the metal approximately doubles its strength. In other attempts to increase strength, aluminum is alloyed with elements such as manganese, silicon, copper, magnesium, or zinc. The alloys can also be strengthened by cold working. Some alloys are further strengthened and hardened by heat treatments. At subzero temperatures, aluminum is stronger than at room temperature and is no less ductile. Most aluminum alloys lose strength at elevated temperatures, although some retain significant strength to 5000F.

Besides a high strength-to-weight ratio and good formability, aluminum also possesses its own anticorrosion mechanism. When exposed to air, aluminum does not oxidize progressively because a hard, microscopic oxide coating forms on the surface and seals the metal from the environment. The tight chemical oxide bond is the reason that aluminum is not found in nature; it exists only as a compound.

Aluminum and its alloys, numbering in the hundreds, are available in all common commercial forms. Aluminum-alloy sheet can be formed, drawn, stamped, or spun. Many wrought or cast aluminum alloys can be welded, brazed, or soldered, and aluminum surfaces readily accept a wide variety of finishes, both mechanical and chemical. Because of their high electrical conductivity, aluminum alloys are used as electrical conductors. Aluminum reflects radiant energy throughout the entire spectrum, is nonsparking, and nonmagnetic.

Wrought aluminum: A four-digit number that corresponds to a specific alloying element combination usually designates wrought aluminum alloys. This number is followed by a temper designation that identifies thermal and mechanical treatments.

To develop strength, heat-treatable wrought alloys are solution heat treated, then quenched and precipitation hardened. Solution heat treatment consists of heating the metal, holding at temperature to bring the hardening constituents into solution, then cooling to retain those constituents in solution. Precipitation hardening after solution heat treatment increases strength and hardness of these alloys.

While some alloys age at room temperature, others require precipitation heat treatment at an elevated temperature (artificial aging) for optimum properties. However, distortion and dimensional changes during natural or artificial aging can be significant. In addition, distortion and residual stresses can be introduced during quenching from the solution heat-treatment cycle. These induced changes can be removed by deforming the metal (for example, stretching).

Wrought aluminum alloys are also strengthened by cold working. The high-strength alloys -- either heat treatable or not -- work harden more rapidly than the lower-strength, softer alloys and so may require annealing after cold working. Because hot forming does not always work harden aluminum alloys, this method is used to avoid annealing and straightening operations; however, hot forming fully heat-treated materials is difficult. Generally, aluminum formability increases with temperature.

Recently developed aluminum alloys can provide nearly custom-engineered strength, fracture toughness, fatigue resistance, and corrosion resistance for aircraft forgings and other critical components. The rapid-solidification process is the basis for these new alloy systems, called wrought P/M alloys. The term wrought P/M is used to distinguish this technology from conventional press-and-sinter P/M technology. Grades 7090 and 7091 are the first commercially available wrought P/M aluminum alloys. These alloys can be handled like conventional aluminum alloys on existing aluminum-fabrication facilities.

Other significant new materials are the aluminum-lithium alloys. These lightweight metals are as strong as alloys now in use and can be fabricated on existing metalworking equipment. Although impressive structural weight reductions (from 7 to 10%) are possible through direct substitution, even greater reduction (up to 15%) can be realized by developing fully optimized alloys for new designs. Such alloys would be specifically tailored to provide property combinations not presently available. Producing an alloy that will provide these combinations is the object of second and third-generation low-density alloy development efforts.

Operating economy is still an important consideration in vehicle design despite fluctuating fuel prices. Downsizing to save fuel has reached its practical limits; now, reducing the weight of individual components is taking over. One significant change being implemented by designers of automobiles and military vehicles today is converting driveshafts, radiators, cylinder heads, suspension members, and other structural components to aluminum.

Cast aluminum: Aluminum can be cast by all common casting processes. Aluminum casting alloys are identified with a unified, four-digit (xxx.x) system. The first digit indicates the major alloying element. For instance, 100 series is reserved for 99% pure aluminum with no major alloying element used. The second and third digits in the 100 series indicate the precise minimum aluminum content. For example, 165.0 has a 99.65% minimum aluminum content. The 200-900 series designate various aluminum alloys, with the second two digits assigned to new alloys as they are registered. The fourth digit indicates the product form. Castings are designated 0; ingots are designed 1 or 2.

Letter prefixes before the numerical designation indicate special control of one or more elements or a modification of the original alloy. Prefix X designates an experimental composition. The material may retain the experimental designation up to five years. Limits for the experimental alloy may be changed by the registrant.

Commercial casting alloys include heat-treatable and nonheat-treatable compositions. Alloys that are heat treated carry the temper designations 0, T4, T5, T6, and T7. Die castings are not usually solution heat treated because the temperature can cause blistering.

Permanent-mold casting technology involves several variations having to do with how the metal gets into the mold cavity. Initially, molds were simply gravity filled from ladles, in the same manner as sand molds. Subsequently, low pressure on the liquid-metal surface of a crucible was used to force the metal up, through a vertical tube, into the mold cavity. This refinement produces castings with higher mechanical properties and is more economical than gravity filling because extensive gates and risers are unnecessary.

More recently, the process was modified to use a low level of vacuum drawn on the mold cavity, causing atmospheric pressure to force the molten metal up into the mold. This process variation, together with controlled and rapid solidification, increases properties further because it produces castings that are almost entirely free of porosity.

Although both variations improve properties and speed casting cycles, the added equipment complexities limit the casting size that can be handled. Consequently, all three perrnanent-mold processes are in use today, turning out aluminum castings weighing from less than one pound to several hundred pounds.

Aluminum matrix composites: Metal matrix composites (MMCS) consist of metal alloys reinforced with fibers, whiskers, particulates, or wires. Alloys of numerous metals (aluminum, titanium, magnesium and copper) have been used as matrices to date.

Recent MMC developments, however, seem to thrust aluminum into the spotlight. In the NASA space shuttle, for example, 240 struts are made from aluminum reinforced with boron fibers. Also, aluminum diesel-engine pistons that have been locally reinforced with ceramic fibers are eliminating the need for wear-resistant nickel-cast iron inserts in the automotive environment.

Fabrication methods differ for both products. Monolayer tapes in the space shuttle struts are wrapped around a mandrel and hot isostaticafly pressed to diffusion bond the layers. For the pistons, a squeeze-casting process infiltrates liquid metal into a fiber preform under pressure. Other fabrication methods for MMCs include: hot pressing a layer of parallel fibers between foils to create a monolayer tape; creep and superplastic forming in a die; and spraying metal plasmas on collimated fibers followed by hot pressing.

Superplastic aluminum: Superplastic forming of metal, a process similar to vacuum forming of plastic sheet, has been used to form low-strength aluminum into nonstructural parts such as cash-register housings, luggage compartments for passenger trains, and nonload-bearing aircraft components. New in this area of technology is a superplastic-formable high-strength aluminum alloy, now available for structural applications and designated 7475-02. Strength of alloy 7475 is in the range of aerospace alloy 7075, which requires conventional forming operations. Although initial cost of 7475 is higher, finished part cost is usually lower than that of 7075 because of the savings involved in the simplified design/assembly.

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Among structural metals, beryllium has a unique combination of properties. It has low density (two-thirds that of aluminum), high modulus per weight (five times that of ultrahigh-strength steels), high specific heat, high strength per density, excellent dimensional stability, and transparency to X-rays. Beryllium is expensive, however, and its impact strength is low compared to values for most other metals.

Available forms include block, rod, sheet, plate, foil, extrusions, and wire. Machining blanks, which are machined from large vacuum hot pressings, make up the majority of beryllium purchases. However, shapes can also be produced directly from powder by processes such as cold-press/sinter/coin, CIP/HEP, CIP/sinter, CIP/hot-press and plasma spray/sinter. (CIP is cold-isostatic press, and HIP is hot-isostatic press.) Mechanical properties depend on powder characteristics, chemistry, consolidation process, and thermal treatment. Wrought forms, produced by hot working, have high strength in the working direction, but properties are usually anisotropic.

Beryllium parts can be hot formed from cross-rolled sheet and plate as well as plate machined from hot-pressed block. Forming rates are slower than for titanium, for example, but tooling and forming costs for production items are comparable.

Structural assemblies of beryllium components can be joined by most techniques such as mechanical fasteners, rivets, adhesive bonding, brazing, and diffusion bonding. Fusion-welding processes are generally avoided because they cause excessive grain growth and reduced mechanical properties.

Beryllium behaves like other light metals when exposed to air by forming a tenacious protective oxide film that provides corrosion protection. However, the bare metal corrodes readily when exposed for prolonged periods to tap or seawater or to a corrosive environment that includes high humidity. The corrosion resistance of beryllium in both aqueous and gaseous environments can be improved by applying chemical conversion, metallic, or nonmetallic coatings. Beryllium can be electroless nickel plated, and flame or plasma sprayed.

All conventional machining operations are possible with beryllium, including EDM and ECM. However, beryllium powder is toxic if inhaled. Since airborne beryllium particles and beryllium salts present a health hazard, the metal must be machined in specially equipped facilities for safety. Machining damages the surface of beryllium parts. Strength is reduced by the formation of microcracks and "twinning." The depth of the damage can be limited during finish machining by taking several light machining cuts and sharpening cutting tools frequently or by using nonconventional metal-removal processes. For highly stressed structural parts, 0.002 to 0.004 in. should be removed from each surface by chemical etching or milling after machining. This process removes cracks and other surface damage caused by machining, thereby preventing premature failure. Precision parts should be machined with a sequence of light cuts and intermediate thermal stress reliefs to provide the greatest dimensional stability.

Beryllium typically appears in military-aircraft and space-shuttle brake systems, in missile reentry body structures, missile guidance systems, mirrors and optical systems, satellite structures, and X-ray windows. The modulus-to-density ratio is higher than that of unidirectionally reinforced, "high-modulus" boron, carbon, and graphite-fiber composites. Beryllium has an additional advantage because its modulus of elasticity is isotropic.

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Copper conducts electricity at a rate 97% that of silver, and is the standard for electrical conductivity. Copper provides a diverse range of properties: good thermal and electrical conductivity, corrosion resistance, ease of forming, ease of joining, and color. In addition, however, copper and its alloys have relatively low strength-to-weight ratios and low strengths at elevated temperatures. Some copper alloys are also susceptible to stress-corrosion cracking unless they are stress relieved.

Copper and its alloys -- the brasses and bronzes -- are available in rod, plate, strip, sheet, tube shapes, forgings, wire, and castings. These metals are grouped according to composition into several general categories: coppers, high-copper alloys, brasses, leaded brasses, bronzes, aluminum bronzes, silicon bronzes, copper nickels, and nickel silvers.

Copper-based alloys form adherent films that are relatively impervious to corrosion and that protect the base metal from further attack. Certain alloy systems darken rapidly from brown to black in air. Under most outdoor conditions, however, copper surfaces develop a blue-green patina. Lacquer coatings can be applied to retain the original alloy color. An acrylic coating with benzotriazole as an additive lasts several years under most outdoor, abrasion-free conditions.

Although they work harden, copper and its alloys can be hot or cold worked. Ductility can be restored by annealing or heating incident to welding or brazing operations. For applications requiring maximum electrical conductivity, the most widely used copper is C11000, "tough pitch," which contains approximately 0.03% oxygen and a minimum of 99.0% copper. In addition to high electrical conductivity, oxygen-free grades C10100 and C10200 provide immunity to embrittlement at high temperature. The addition of phosphorus produces grade C12200 -- the standard water-tube copper.

High-copper alloys contain small amounts of alloying elements that improve strength with some loss in electrical conductivity. In amounts of 1%, for example, cadmium increases strength by 50%, with a loss in conductivity to 85%. Small amounts of cadmium raise the softening temperature in alloy C11600, which is used widely for printed circuits. Tellurium or sulfur, present in small amounts in Grades C14500 and C14700, has been shown to increase machinability.

Copper alloys do not have a sharply defined yield point, so yield strength is reported either as 0.5% extension under load, or as 0.2% offset. On the most common basis (0.5% extension), yield strength of annealed material is approximately one-third the tensile strength. As the material is cold worked or hardened, it becomes less ductile, and yield strength approaches tensile strength.

Copper is specified according to temper, which is established by cold working or annealing. Typical levels are: soft, half-hard, hard, spring, and extra-spring. Yield strength of a hard-temper copper is approximately two-thirds of tensile strength.

For brasses, phosphor bronzes, or other commonly cold-worked grades, the hardest available tempers are also the strongest and represent approximately 70% reduction in area. Ductility is sacrificed, of course, to gain strength. Copper-beryllium alloys can be precipitation hardened to the highest strength levels attainable in copper-base alloys.

The ASME Boiler and Pressure Vessel Code should be used for designing critical copper-alloy parts for service at elevated temperatures. The code recommends that, for a specific service temperature, the maximum allowable design stress should be the lowest of these values as tabulated by the code: one-fourth of the ultimate tensile strength, two-thirds of the yield strength, and two-thirds of the average creep strength or stress-rupture strength under specified conditions. Silicon bronzes, aluminum brasses, and copper nickels are widely used for elevated-temperature applications.

All copper alloys resist corrosion by fresh water and steam. Copper nickels, aluminum brass, and aluminum bronzes provide superior resistance to saltwater corrosion. Copper alloys have high resistance to alkalies and organic acids, but have poor resistance to inorganic acids. One corrosive situation encountered, particularly in the high-zinc alloy, is dezincification. The brass dissolves as an alloy, but the copper constituent redeposits as a porous, spongy metal. Meanwhile, the zinc component is carried away by the atmosphere or deposited on the surface as an insoluble compound.

Designating alloys: Originally developed as a three-digit system by the U.S. copper and brass industry, the designation system for copper-based alloys has been expanded to five digits preceded by the letter C as part of the Unified Numbering System for Metals and Alloys (UNS). The UNS designations are simply an expansion of the former designation numbers. For example, Copper Alloy No. 377 (forging brass) becomes C37700. Numbers C10000 through C79900 are assigned to wrought compositions, and numbers C80000 through C99900 to casting alloys.

The designation system is not a specification; rather, it is a method for identifying and defining the chemical composition of mill and foundry products. The precise requirements to be satisfied by a material and the temper nomenclature that applies are defined by the relevant standard specifications (ASTM, Federal, and Military) for each composition.

There are approximately 370 commercial copper and copper-alloy compositions. Brass mills make wrought compositions in the form of rod, plate, sheet, strip, tube, pipe, extrusions, foil, forgings, and wire. Foundries supply castings. The following general categories apply to both wrought and cast compositions.

Coppers, high-copper alloys: Both wrought and cast compositions have a designated minimum copper content and may include other elements or additions for special properties.

Brasses: These alloys contain zinc as the principal alloying element and may have other designated elements. The wrought alloys are comprised of copper-zinc alloys, copper-zinc-lead alloys (leaded brasses), and copper-zinc-tin alloys (tin brasses). The cast alloys are comprised of copper-zinc-tin alloys (red, semired and yellow brasses), manganese bronze alloys (high-strength yellow brasses), leaded manganese bronze alloys (leaded high-strength yellow brasses), and copper-zinc-silicon alloys (silicon brasses and bronzes).

Bronzes: Wrought bronze alloys comprise four main groups: copper-tin-phosphor-us alloys (phosphor bronzes), copper-tin-lead-phosphorus alloys (leaded phosphor bronzes), and copper-silicon alloys (silicon bronzes). Cast alloys also have four main families: copper-tin alloys (tin bronzes), copper-tin-lead alloys (leaded and high-leaded tin bronzes), copper-tin-nickel alloys (nickel-tin bronzes), and copper-aluminum alloys (aluminum bronzes).

Copper-nickels: These are either wrought or cast alloys containing nickel as the principal alloying element.

Copper-nickel-zinc alloys: These are known as nickel silvers, from their color.

Leaded coppers: These are cast alloys containing 20% lead or more.

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Not only is lead the most impervious of all common metals to X-rays and gamma radiation, it also resists attack by many corrosive chemicals, most types of soil, and marine and industrial environments. Although lead is one of the heaviest metals, only a few applications are based primarily on its high density. Main reasons for using lead often include low melting temperature, ease of casting and forming, good sound and vibration absorption, and ease of salvaging from scrap.

Nearly three-fourths of all U.S. lead consumption is for chemical applications such as paint pigments, gasoline additives, and storage batteries. This chapter, however, discusses only its mechanical applications.

With its high internal damping characteristics, lead is one of the most efficient sound attenuators for industrial, commercial, and residential applications. Sheet lead, lead-loaded vinyls, lead composites, and lead-containing laminates are used to reduce machinery noise. Lead sheet with asbestos or rubber sandwich pads are commonly used in vibration control.

The natural lubricity and wear resistance of lead make the metal suitable, in alloys, for heavy-duty bearing applications such as railroad-car journal bearings and piston-engine crank bearings. Lead is also widely used as a constituent in solders. Most common solders are the lead-tin alloys; melting temperature can be as low as 361oF.

In its unalloyed form (defined by ASTM B29 as 99.85% minimum lead), lead is soft and weak; it requires support for mechanical applications. This "chemical lead" is used primarily in corrosive chemical-handling applications such as tank linings.

"Hard lead" -- lead alloyed with 1 to 13% antimony -- has sufficient tensile strength, fatigue resistance, and hardness for many mechanical applications. These alloys can be cast, rolled, or extruded and are especially suited for castings requiring good detail and moderate strength. Rolled antimonial alloys are harder and stronger than the cast alloys. Battery-plate lead contains 7 to 12% antimony.

Calcium (0.03 to 0.12%) forms another series of mechanically suitable alloys with lead. These alloys age harden naturally at room temperature -- usually for 30 to 60 days -- after being cast or worked. Properties of wrought Pb-Ca alloys are somewhat directional, being greater in the longitudinal direction. Uses include cable sheathing and grids in storage batteries.

Tin, added to Pb-Ca alloys in amounts to about 1.5%, raises tensile strength and stress-rupture resistance but increases aging time to 180 days. Tin is also used to reduce coefficient of friction for bearing applications. Higher tin-bearing alloys are primarily used in solders, which normally contain from 40 to 60% tin.

Lead alloys are castable by most methods. Intricate details can be reproduced, and the surface can be readily painted. Lead alloys can be extruded into pipes, bars, channels, and rods. Cold-rolled lead sheet is available in thicknesses ranging from foil to 2 in., in widths to 11 ft, and in lengths to 60 ft. Sheet thicknesses are specified by weight: Generally, each 1/64 in. of thickness corresponds to 1lb/ftA2.

Lead often requires support by other materials. For example, lead sheets can be clad or fastened (mechanically or with adhesives) to plastic or steel panels and pipe. Lead-clad steel, in a range of thicknesses, is produced by cold-rolling lead sheet on terne-coated steel. Other clad combinations are produced by spot welding, spraying, hot dipping, and electroplating. These laminates are particularly useful in noise and vibration-absorption applications.

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As the lightest structural metal available, magnesium's combination of low density and good mechanical strength results in a high strength-to-weight ratio.

Because of their low modulus of elasticity, magnesium alloys can absorb energy elastically. Combined with moderate strength, this provides excellent dent resistance and high damping capacity. Magnesium has good fatigue resistance and performs particularly well in applications involving a large number of cycles at relatively low stress. The metal is sensitive to stress concentration, however, so notches, sharp corners, and abrupt section changes should be avoided.

Magnesium parts are generally used from room temperature to about 2000F or, in some cases, to 3500F. Some alloys can be used in service environments to 7000F for brief exposures.

Magnesium is widely recognized for its favorable strength-to-weight ratio and excellent castability, but deeply ingrained misconceptions often prevent designers from specifying it as a die-cast material. However, what is true of magnesium as a generic material is not true of today's die-casting alloy. The new high-purity alloy, combined with advances in fluxless, hot-chamber die-casting processing, has altered the traditional guidelines for evaluating the cost and performance of magnesium die castings.

Fabrication: Magnesium alloys are the easiest of the structural metals to machine. They can be shaped and fabricated by most metalworking processes, and they are easily welded. At room temperature, magnesium work hardens rapidly, reducing cold formability; thus, cold forming is limited to mild deformation or roll bending around large radii. Pure magnesium is usually alloyed with other elements to develop sufficient strength for structural purposes. Some alloys are heat treated to further improve properties.

Cast magnesium alloys are dimensionally stable to about 2000F. Some cast magnesium-aluminum-zinc alloys may undergo permanent growth if used above that temperature for long periods. Permanent-mold castings are as strong as sand castings, and they generally provide closer dimensional tolerances and better surface finish. Typical applications of magnesium gravity castings are aircraft engine components and wheels for race and sports cars.

Design of die-cast magnesium parts follows the same principles established for other die-casting metals. Maximum mechanical properties in a typical alloy are developed in wall thicknesses ranging from 0.078 to 0.150 in. Chain-saw and power-tool housings, archery-bow handles, and attache-case frames are typical die-cast applications.

Magnesium is easy to hot work, so fewer forging steps are usually required than for other metals. Bending, blocking, and finishing are usually the only operations needed. Typical magnesium forgings are missile fuselage connector rings.

Standard extruded shapes include round, square, rectangular, and hexagonal bars; angles, beams, and channels; and a variety of tubes. Luggage frames and support frames for military shelters are examples of magnesium extrusions.

Methods used for joining magnesium are gas tungsten-arc (TIG) and gas metal-arc (NUG) welding, spotwelding, riveting, and adhesive bonding. Mechanical fasteners can be used on magnesium, provided that stress concentrations are held to a safe minimum. Only ductile aluminum rivets should be used, preferably alloy 5056-H32, to minimize galvanic-corrosion failure at riveted joints.

The first two letters of the designation identifies the two alloying elements specified in the greatest amount. The letters are arranged in order of decreasing percentages or alphabetically if the elements are present in equal amounts. The letters are followed by respective percentages rounded off to whole numbers, followed by a final serial letter. The serial letter indicates some variation in composition of minor alloying constituents or impurities.

The letters that designate the more common magnesium alloying elements are:
A    Aluminum
E    Rare earths
H    Thorium
K    Zirconium
L    Lithium
M    Manganese
Q    Silver
S    Silicon
Z    Zinc

For example, magnesium alloy AZ3 1B contains 3% aluminum (code letter A)
and 1% zinc (code letterZ).

Resisting corrosion: A problem with magnesium has been its lack of sufficient corrosion resistance for many applications, particularly in the alloys used for die and sand casting. The problem has been solved by the two major supplies, Dow and AMAX; both have developed corrosion-resistant, high-purity AZ91 alloys for die casting, and both also offer a sand-casting grade.

The die-casting grade is now designated by ASTM as AZ91D and will, for all practical purposes, replace AZ91B. The sand-casting grade received the designation AZ91E from ASTM. The high-purity alloys are said to be as much as 100 times more corrosion resistant than standard magnesium alloys, and more resistant to saltwater than die-cast 380 aluminum alloy or cold-rolled steel, tested according to ASTM B117. Research in magnesium metallurgy has shown that the ability of magnesium to resist corrosion in a service environment of salt-laden air or spray depends heavily on keeping contaminants (iron, nickel, copper) below their maximum tolerance limits during all production operations.

The high-purity magnesium die-casting alloy has already replaced other metals as well as a number of plastics in a variety of U.S. passenger-car and lightweight-truck components. Examples include valve and timing-gear covers, brackets, clutch and transfer-case housings, grille panels, headlamp doors, windshield-wiper motor housings, and various interior trim parts.

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Structural applications that require specific corrosion resistance or elevated temperature strength receive the necessary properties from nickel and its alloys. Some nickel alloys are among the toughest structural materials known. When compared to steel, other nickel alloys have ultrahigh strength, high proportional limits, and high moduli of elasticity. Commercially pure nickel has good electrical, magnetic, and magnetostrictive properties.

Common nickel alloy families include: commercially pure nickel; binary systems, such as Ni-Cu, Ni-Si, and Ni-Mo; ternary systems, such as Ni-Cr-Fe and Ni-Cr-Mo; more complex systems, such as Ni-Cr-Fe-Mo-Cu (with other possible additions); and superalloys. Nickel content throughout the alloy families ranges from 32.5 to 99.5%.

At cryogenic temperatures, nickel alloys are strong and ductile. Several nickel-base superalloys are specified for high-strength applications at temperatures to 2,0000F. High-carbon nickel-base casting alloys are commonly used at moderate stresses above 2,2000F.

Alloy characteristics: Commercial nickel and nickel alloys are available in a wide range of wrought and cast grades; however, considerably fewer casting grades are available. Wrought alloys tend to be better known by tradenames such as Monel, Hastelloy, Inconel, Incoloy, etc. Casting alloys are identified by Alloy Casting Institute and ASTM designations. Wrought and cast nickel alloys are often used together in systems built up from wrought and cast components. The casting alloys contain additional elements, such as silicon and manganese, to improve castability and pressure tightness.

Commercially pure nickels and extra high nickel alloys: Primary wrought materials in this group are Nickel 200 and 201, both of which contain 99.5% Ni. The cast grade, designated CZ- 100, is recommended for use at temperatures above 600'F because its lower carbon content prevents graphitization and attendant ductility loss. Both wrought grades are particularly resistant to caustics, high-temperature halogens and hydrogen halides, and salts other than oxidizing halides. These alloys are particularly well suited for food-contact applications.

Duranickel 301, a precipitation-hardened, 94% nickel alloy, has excellent spring properties to 6000F. During thermal treatment, Ni3AITi particles precipitate throughout the matrix. This action enhances alloy strength. Corrosion resistance is similar to that of commercially pure wrought nickel.

Binary nickel alloys: The primary wrought alloys in this category are the Ni-Cu grades known as Monel alloy 400 (Ni-3l.SCu) and K-500 (Ni-29.SCu), which also contain small amounts of Al, Fe, and Ti. The Ni-Cu alloys differ from Nickel 200 and 201 because their strength and hardness can be increased by age hardening. Although the Ni-Cu alloys share many of the corrosion characteristics of commercially pure nickel, their resistance to sulfuric and hydrofluoric acids and brine is better. Handling of waters, including seawater and brackish water, is a major application. Monel alloys 400 and K-500 are immune to chloride-ion stress-corrosion cracking, which is often considered in their selection.

Other commercially important binary nickel compositions are Ni-Mo and Ni-Si. One binary type, Hastelloy alloy B-2 (Ni-28Mo), offers superior resistance to hydrochloric acid, aluminum-chloride catalysts, and other strongly reducing chemicals. It also has excellent high-temperature strength in inert atmospheres and vacuum.

Cast nickel-copper alloys comprise a low and high silicon grade. M-35-1 and QQ-N-288, Grades A and E (1.5% Si), are commonly used in conjunction with wrought nickel-copper in pumps, valves, and fittings. A higher silicon grade, QQ-N-288, Grade B (3.5% Si), is used for rotating parts and wear rings because it combines corrosion resistance with high strength and wear resistance. Grade D (4.0% Si) offers exceptional galling resistance.

Two other binary cast alloys are ACI N-12M-1 and N-12M-2. These Ni-Mo alloys are commonly used for handling hydrochloric acid in all concentrations at temperatures up to the boiling point. These alloys are produced commercially under the tradenames Hastelloy alloy B and Chlorimet 2.

Ternary nickel alloys: Two primary wrought and cast compositions are Ni-Cr-Fe and Ni-Cr-Mo. Ni-Cr-Fe is known commercially as Haynes alloys 214 and 556, Inconel alloy 600, and Incoloy alloy 800. Haynes new alloy No.214 (Ni- 16Cr-2.5Fe-4.5Al-Y) has excellent resistance to oxidation to 2,2000F, and resists carburizing and chlorine-contaminated atmospheres. Haynes patented alloy No.556 (Fe-2ONi-22Cr-18Co) combines effective resistance to sulfidizing, carburizing, and chlorine-bearing environments with good oxidation resistance, fabricability and high-temperature strength. Inconel alloy 600 (Ni-15.5Cr-8Fe) has good resistance to oxidizing and reducing environments. Intended for severely corrosive conditions at elevated temperatures, Incoloy 800 (Ni-46Fe-21 Cr) has good resistance to oxidation and carburization at elevated temperatures, and it resists sulfur attack, internal oxidation, scaling, and corrosion in many atmospheres.

A cast Ni-Cr-Fe alloy CY-40, known as Inconel, has higher carbon, Mn, and Si contents than the corresponding wrought grade. In the as-cast condition, the alloy is insensitive to the type of intergranular attack encountered in as-cast or sensitized stainless steels.

Significant additions of molybdenum make Ni-Cr-Mo alloys highly resistant to pitting. They retain high strength and oxidation resistance at elevated temperatures, but they are used in the chemical industry primarily for their resistance to a wide variety of aqueous corrosives. In many applications, these alloys are considered the only materials capable of withstanding the severe corrosion conditions encountered.

In this group, the primary commercial materials are C-276, Hastelloy alloy C-22, and Inconel alloy 625. Hastelloy alloy C-22 (Ni-22Cr- 13Mo-3W-3Fe) has better overall corrosion resistance and versatility than any other Ni-Cr-Mo alloy. Alloy C-276 (57Ni- 15.5Cr- 16Mo) has excellent resistance to strong oxidizing and reducing corrosives, acids, and chlorine-contaminated hydrocarbons. Alloy C-276 is also one of the few materials that withstands the corrosive effects of wet chlorine gas, hypochlorite, and chlorine dioxide. Hastelloy alloy C-22, the newest alloy in this group, has outstanding resistance to pitting, crevice corrosion, and stress-corrosion cracking. Present applications include the pulp and paper industry, various pickling acid processes, and production of pesticides and various agrichemicals.

Two grades of cast Ni-Cr-Mo alloys, ACI CW-12M-1 and CW-12M-2, are used in severe corrosion service, often involving combinations of acids at elevated temperatures. The two versions of CW- 12M are also produced as Hastelloy C and Chlorimet.

Complex alloys: Ni-Cr-Fe-Mo-Cu is the basic composition in this category of nickel alloys. They offer good resistance to pitting, intergranular corrosion, chloride-ion stress-corrosion cracking, and general corrosion in a wide range of oxidizing and reducing environments. These alloys are frequently used in applications involving sulfuric and phosphoric acids.

Important commercial grades include Hastelloy alloys G-30 and H, Haynes alloy No.230, Inconel alloys 617, 625, and 718, and Incoloy alloy 825.

Haynes alloy No.230 (Ni-22Cr-14W-2Mo) has excellent high-temperature strength, oxidation resistance, and thermal stability, making it suitable for various applications in the aerospace, airframe, nuclear, and chemical-process industries.

Hastelloy alloy G-30 (Ni-3OCr-6Mo-2.5W-15Fe) has many advantages over other metallic and nonmetallic materials in handling phosphoric acid, sulfuric acid, and oxidizing acid mixtures. Hastefloy alloy H (Ni-22Cr-9Mo-2W-18Fe) is a patented alloy with localized corrosion resistance equivalent or better to alloy 625. Alloy H also has good resistance to hot acids and excellent resistance to stress-corrosion cracking. It is often used in flue gas desulfurization equipment.

Inconel alloy 617 (Ni-22Cr-12.5Co-9Mo-1.5Fe-1.2Al) resists cyclic oxidation at 2,0000F, and has good stress-rupture properties above 1,8000F.

Inconel alloy 625 (Ni-21.5Cr-2.5Fe-9Mo-3.6Nb+Ta) has high strength and toughness from cryogenic temperatures to 1,8000F, good oxidation resistance, exceptional fatigue strength, and good resistance to many corrosives. Furnace mufflers, electronic parts, chemical and food-processing equipment, and heat-treating equipment are among a few of the many applications for alloy 615.

Inconel alloy 718 (Ni-18.5Fe-19Cr-3Mo-5Nb+Ta) has excellent strength from -423 to 1,3000F. The alloy is age hardenable, can be welded in the fully aged condition, and has excellent oxidation resistance up to 1,8000F.

Incoloy 825 (42Ni-3OFe-21.5Cr-3Mo-2.25Cu) offers excellent resistance to a wide variety of corrosives. It resists pitting and intergranular corrosion, reducing acids, and oxidizing chemicals. Applications include pickling-tank heaters and hooks, spent nuclear-fuel-element recovery, chemical-tank trailers, evaporators, food-processing equipment, sour-well tubing, hydrofluoric-acid production, pollution-control equipment, and radioactive-waste systems.

Superalloys: One class of Ni-based superalloys is strengthened by intermetallic compound precipitation in a face-centered cubic matrix. The strengthening precipitate is gamma prime, typified by Waspaloy (Ni-19.5Cr-13.5Co-4.3Mo-3.OTi-1.4Al-2.OFe), Udimet 700 (Ni-15Cr-18.5Co-5Mo-3.4Ti-4.3AI-< lFe), and the modern but complex Rene 95 (Ni-14Cr-8Co-3.5Mo-3.5W-3.5Nb-2.5Ti-3.5Al).

Another type of Ni-based superalloy is represented by Hastelloy alloy X (Ni-22Fe-9Mo-22Cr-1.5Co). This alloy is essentially solid-solution strengthened, but probably also derives some strengthening from carbide precipitation through a working-plus-aging schedule.

A third class includes oxide-dispersion-strengthened (ODS) alloys such as IN MA-754 (Ni-2OCr-0.6yttria) and IN MA-6000 (Ni-15Cr-2Mo-4W-2.5Ti-4.5Al), which are strengthened by dispersions such as yttria coupled (in some cases) with gamma prime precipitation (MA-6000).

Nickel-based superalloys are used in cast and wrought forms, although special processing (powder metallurgy/isothermal forging) often is used to produce wrought versions of the more highly alloyed compositions (U-700, Astroloy, IN-100).

An additional dimension of Ni-based superalloys has been the introduction of grain-aspect ratio and orientation as a means of controlling properties. In some instances, grain boundaries have been removed. Wrought powder-metallurgy alloys of the ODS class and cast alloys such as MAR M-247 have demonstrated property improvements due to grain morphology control by directional crystallization or solidification. Virtually all uses of the cast and wrought nickel-base superalloys are for gas-turbine components.

Fabrication: Most wrought-nickel alloys can be hot and cold worked, machined, and welded successfully. The casting alloys can be machined or ground, and many can be welded and brazed.

Nearly any shape that can be forged in steel can also be forged in nickel and nickel alloys. However, because nickel work hardens easily, severe cold-forming operations require frequent intermediate annealing to restore soft temper. Annealed cold-rolled sheet, not stretcher leveled, is best for spinning and other manual work. In general, cold-drawn rods machine much more cleanly and readily than hot-rolled or annealed material.

Nickel alloys can be joined by shielded metal-arc, gas tungsten-arc, gas metal-arc, plasma-arc, electron-beam, oxyacetylene, and resistance welding; silver and bronze brazing; and soft soldering. Resistance welding methods include spot, seam, projection, and flash welding.

Special nickel alloys, including superalloys, are best worked at about 1,800 to 2,2000F. In the annealed condition, these alloys can be cold worked by all standard methods. Required forces and rate of work hardening are intermediate between those of mild steel and Type 304 stainless steel. These alloys work harden to a greater extent than the austenitic stainless steels, so they require more intermediate annealing steps.

Both cold-worked and hot-worked Ni-Cu require thermal treatment to develop optimum ductility and to minimize distortion during subsequent machining. Stress relieving before machining is recommended to minimize distortion after metal removal. Stress equalizing of cold-worked Cu-Ni increases yield strength without marked effects on other properties.

Many Hastelloy alloys can be upset forged if the length of the piece is no greater than twice its diameter. However, upsetting should never be attempted on a cast ingot. Cast ingots must be reduced at least 75% before hot upsetting.

Most wrought nickel-based alloys can be formed from sheet into complex shapes involving considerable plastic flow. These alloys are processed in the annealed condition.

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Precious metals may seem unlikely as engineering materials, but the same expensive metals used for coinage and jewelry also satisfy applications requiring the ultimate in corrosion resistance or electrical conductivity. Three subgroups make up the entire family of precious metals: silver and silver alloys; gold and gold alloys; and the platinum metals, which are platinum, palladium, rhodium, ruthenium, iridium, and osmium. The six platinum metals are so grouped because they occur naturally in the same ore.

Most precious metals are available as sheet, tape, foil, wire, tubing, gauze, discs, electrodes, cathodes, crucibles, catalysts, and salts or solutions for plating and coating. All precious metals are nearly completely corrosion resistant; platinum metals withstand service up to 3,2000F without any evidence of erosion or corrosion.

Gold: An extremely soft, ductile metal, gold undergoes very little work hardening. A gram of pure gold can be worked into leaf covering 6ft^2 and only 0.0000033 in. thick. Because pure gold is too soft for large, freestanding components, it is used chiefly for linings or electrodeposits and is often alloyed with other metals such as copper or nickel to increase strength or hardness.

Gold is extremely inert. It is not attacked by nitric, hydrochloric, or sulfuric acid, but is dissolved by aqua regia and is attacked by sodium and potassium cyanide plus oxygen.

Silver: The least costly of the precious-metal group, silver is also very malleable, ductile, and corrosion resistant. Because it is not attacked by alkaline solutions, it is used to contain caustic soda and potash in all concentrations. Silver has the highest thermal and electrical conductivity of all metals.

Alloyed with copper, and sometimes with zinc, silver is used in high-melting temperature solders. These silver solders are used where more than ordinary joint strength -- or sometimes, electric conductivity -- is required.

Platinum: A silver-white metal, platinum is extremely malleable, ductile, and corrosion resistant. When heated to redness, it softens and is easily worked. It is nearly nonoxidizable and is soluble only in liquids that generate free chlorine such as aqua regia. Because platinum is inert and stable, even at high temperatures, the metal is used for high-temperature handling of high-purity chemicals and laboratory materials. Other applications include electrical contacts, resistance wire, thermocouples, and standard weights. In gauze form, platinum is used as a catalyst in air-pollution control systems.

Palladium, iridium, and rhodium: These metals resemble and behave like platinum. All can be worked but, because they work harden, require annealing between forming operations. Rhodium and iridium are more brittle than palladium, however, and must be forged or swaged above 1,4720F. Iridium cannot be cold rolled at all.

Palladium, which is harder and lighter than platinum, is used as an electrically conductive coating. It is easily applied to printed-circuit boards and various types of contacts. Palladium is often alloyed with silver or copper.

Iridium has the best corrosion resistance of all metals. Because of its excellent resistance to attack by leaded fuels, iridium is used for spark-plug electrodes in aircraft engines and in similar applications where extreme reliability is required. It is also used as an alloying agent for increasing the corrosion resistance and hardness of platinum. Iridium-tungsten alloys are used for springs operating at temperatures as high as 8000C.

Rhodium has the highest electrical and thermal conductivity of the platinum-metals group and is the hardest. It has high reflectivity, which makes it ideal for mirrors and reflectors in high-temperature or highly corrosive applications. It is also used with platinum in thermocouple wire.

Ruthenium and osmium: Although they worked successfully and have no structural applications, these metals are used as alloying elements to increase hardness and electrical resistivity of platinum or other metals in this group. Typical applications for these alloys include electrical contacts and wire for electronic products.

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Refractory metals are characterized by their extremely high melting points, which range well above those of iron, cobalt, and nickel. They are used in demanding applications requiring high-temperature strength and corrosion resistance. The most extensively used of these metals are tungsten, tantalum, molybdenum, and columbium (niobium). They are mutually soluble and form solid-solution alloys with each other in any proportion. These four refractory metals and their alloys are available in mill forms as well as products such as screws, bolts, studs, and tubing.

Although the melting points of these metals are all well above 4,0000F, they oxidize at much lower temperatures. Accelerated oxidation in air occurs at 1900C for tungsten, 3950C for molybdenum, and 4250C for tantalum and columbium. Therefore, protective coatings must be applied to these metals if they are to be used at higher temperatures. Tensile and yield strengths of the refractory metals are substantially retained at high temperature.

Columbium and tantalum: These metals are usually considered together because most of their working characteristics are similar. They can be fabricated by most conventional methods at room temperature. Heavy sections for forging can be heated, without protection, to approximately 4250C.

Out of several commercial-grade tantalum alloys, those containing tungsten, columbium, and molybdenum generally retain the corrosion resistance of tantalum and provide higher mechanical properties. Columbium is also available in alloys containing tantalum, tungsten, molybdenum, vanadium, hafnium, zirconium, or carbon. Alloys provide improved tensile, yield, and creep properties, particularly in the 1,100 to 1,6500C range.

Most sheet-metal fabrication of columbium and tantalum is done in the thickness range of 0.004 to 0.060in. Columbium, like tantalum, can be welded to itself and to certain other metals by resistance welding, tungsten inert-gas (TIG) welding, and to itself by inert-gas arc welding. Electron-beam welding can also be used, particularly for joining to other metals. However, surfaces that are heated above 3150C during welding must be protected with an inert gas to prevent embrittlement.

Principal applications for tantalum are in capacitor anodes, filaments, gettering devices, chemical-process equipment, and high-temperature aerospace engine components. Columbium is used in superconducting materials, thin-film substrates, electrical contacts, heat sinks, and as an alloying addition in steels and superalloys.

Molybdenum: Probably the most versatile of the refractory metals, molybdenum is also a natural resource of the United States. It is an excellent structural material for applications requiring high strength and rigidity at temperatures to 3,0000F where it can operate in vacuum or under inert or reducing atmospheres.

Unalloyed molybdenum and its principal alloy, TZM, are produced by powder-metallurgy methods and by vacuum-arc melting. Both are commercially available in ordinary mill product forms: forging billets, bars, rods, wire, seamless tubing, plate, strip, and thin foil. Compared to unalloyed molybdenum, the TZM alloy (Mo-0.5%Ti-O.1%Zr) develops higher strength at room temperature and much higher stress-rupture and creep properties at all elevated temperatures. At 1,800 to 2,0000F, TZM can sustain a 30,000-psi stress for over 100 hr,three times that for unalloyed molybdenum.

Molybdenum and TZM are readily machined with conventional tools. Sheet can be processed by punching, stamping, spinning, and deep drawing. Some parts can be forged to shape. Molybdenum wire and powder can be flame sprayed onto steel substrates to salvage worn parts or to produce long-wearing, low-friction surfaces for tools.

In nonoxidizing environments, the metal resists attack by hydrochloric, hydrofluoric, sulfuric, and phosphoric acids. Molybdenum oxidizes at high temperatures to produce volatile, nontoxic, molybdenum trioxide; however, parts such as gimbled nozzles have been used successfully in rocket and missile-guidance systems when exposure time to the very-high temperatures of ballistic gases was brief.

Molybdenum parts can be welded by inertia, resistance, and spot methods in air; by TIG and NEG welding under inert atmospheres; and by electron-beam welding in vacuum. The best welds are produced by inertia (friction) welding and electron-beam welding; welds produced by the other techniques are less ductile. Generally, arc-cast metal develops better welds than do powder-metallurgy products. Heavy sections of molybdenum should be preheated and postheated when they are welded to reduce thermal stresses.

Because molybdenum has a modulus of elasticity of 47 x 10^6 psi at room temperature, it is used for boring bars and the quills for high-speed internal grinders to avoid vibration and chatter. Its relatively high electrical conductivity makes unalloyed molybdenum useful for electrical and electronic applications. It is used in the manufacture of incandescent lamps, as substrates in solid-state electronic devices, as electrodes for EDM equipment and for melting glass, and as heating elements and reflectors or radiation shields for high-temperature vacuum furnaces.

Because it retains usable strength at elevated temperatures, has a low coefficient of thermal expansion, and resists erosion by molten metals, the TZM alloy is used for cores in die casting of aluminum, and for die cavities in casting of brass, bronze, and even stainless steel. Dies of the TZM alloy weighing several thousand pounds are used for isothermal forging of superalloy components for aircraft gas turbines, and die inserts made of TZM have been used for extruding steel shapes. Piercer points of TZM are used to produce stainless-steel seamless tubing.

Tungsten: In many respects, tungsten is similar to molybdenum. The two metals have about the same electrical conductivity and resistivity, coefficient of thermal expansion, and about the same resistance to corrosion by mineral acids. Both have high strength at temperatures above 2,0000F, but because the melting point of tungsten is higher, it retains significant strength at higher temperatures than molybdenum does. The elastic modulus for tungsten is about 25% higher than that of molybdenum, and its density is almost twice that of molybdenum. All commercial unalloyed tungsten is produced by powder-metallurgy methods; it is available as rod, wire, plate, sheet, and some forged shapes. For some special applications, vacuum-arc-melted tungsten can be produced, but it is expensive and limited to relatively small sections.

Several tungsten alloys are produced by liquid-phase sintering of compacts of tungsten powder with binders of nickel-copper, iron-nickel, iron-copper, or nickel-cobalt-molybdenum combinations; tungsten usually comprises 85 to 95% of the alloy by weight. These alloys are often identified as heavy metals or machinable tungsten alloys. In compact forms, the alloys can be machined by turning, drilling, boring, milling, and shaping; they are not available in mill product forms because they are unable to be wrought at any temperature.

The heavy-metal alloys are especially useful for aircraft counterbalances and as weights in gyratory compasses. Heavy-metal inserts are used as the cores of high-mass military projectiles. Tungsten alloys are widely used for counterbalances in sports equipment such as golf clubs and tennis racquets. X-ray shielding is another important application of the tungsten alloys.

Filaments for incandescent lamps are usually coils of very fine unalloyed tungsten wire. Electronic tubes are often constructed with tungsten as the heaters; some advanced tubes use heaters made from a tungsten alloy containing 3% rhenium. A thermocouple rated to 4,3500F consists of one tungsten wire alloyed with 25% rhenium and another wire alloyed with 5% rhenium.

Nozzle throats of forged and machined unalloyed tungsten have been used in solid-fuel rocket engines; at one time, throats were machined from porous consolidations of tungsten powder that were infiltrated with silver for exposure to gases at temperatures near 3,5000C. Unalloyed tungsten is used for X-ray targets, for filaments in vacuum-metallizing furnaces, and for electrical contacts such as the distributor points in automotive ignition systems. Tungsten electrodes form the basis for TIG welding. Water-cooled tungsten tips are used for nonconsumable electrode vacuum-arc melting of alloys.

Cutting tools and parts that must resist severe abrasion are often made of tungsten carbide. Tungsten-carbide chips or inserts, with the cutting edges ground, are attached to the bodies of steel tools by brazing or by screws. The higher cutting speeds and longer tool life made feasible by the use of tungsten-carbide tools are such that the inserts are discarded after one use. Tungsten-carbide dies have been used for many years for drawing wire. Inserts of tungsten carbide are used in rotaty bits for drilling oil and gas wells and in mining operations. Fused tungsten carbide is applied to the surfaces of mining machinery that is subjected to severe wear.

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Tin is characterized by a low-melting point (4500F), fluidity when molten, readiness to form alloys with other metals, relative softness, and good formability. The metal is nontoxic, solderable, and has a high boiling point. The temperature range between melting and boiling points exceeds that for nearly all other metals (which facilitates casting). Upon severe deformation, tin and tin-rich alloys work soften.

Principal uses for tin are as a constituent of solder and as a coating for steel (tinplate, or terneplate). Tin is also used in bronze, pewter, and bearing alloys. Tin and tin alloys can be cast, rolled, extruded, or atomized. Because pure tin is too weak to be used alone for most mechanical applications, it is usually alloyed with elements such as copper, antimony, lead, bismuth, and zinc.

Tin and its alloys are cast using most conventional techniques, including gravity die casting, pressure die casting, and centrifugal casting. Tin-alloy castings are sound and dimensionally accurate because little shrinkage occurs on solidification. Essential to the casting of tin-rich alloys is the need to reduce microstructure segregation, which occurs during solidification. Part and mold designs should be such that ample metal is fed to remote regions of the mold cavity. Because of their low-melting points, tin-rich alloys can be cast in carbon-steel or rubber molds.

Pewter: Alloys contain from 1 to 8% antimony and 0.5 to 3% copper, and have excellent castability and workability. For spun pewter products, antimony content is usually below 7%, and pewter casting alloys contain 7.5% antimony and 0.5% copper. Because of the excellent drawing and spinning properties of tin, wrought parts are usually made from pewter that is first cast into slabs, then rolled into sheet.

Bearing alloys: These low-friction materials may contain high percentages of antimony (to 10%), copper (to 10%), or aluminum (to 80%). They include babbitt metal, bronze, and aluminum-tin. Although soft, conformable, and corrosion resistant, their low mechanical strength must be boosted by bonding to steel, cast iron, or bronze backing materials.

Die-casting tin-based alloys: Historically, these were the first materials to be die cast. Low melting point and extreme fluidity of these alloys produce sound, intricate castings inexpensively and with little wear on molds. Antimony, copper, and lead are the principal additions to tin in die-casting alloys. These alloys are mainly gravity or centrifugally die cast. Cast tin-ahoy parts can be held to tolerances of 0.0005 in./in., with wall thicknesses down to 1/32 in. Shrinkage is negligible.

Fusible tin alloys: Melting temperatures for these alloys are usually below the solidus of eutectic-base tin-lead solders (3610F). Primary alloying elements include bismuth, lead, cadmium, and indium. Most of these alloys provide electrical or mechanical links in safety devices. Other applications include low-temperature solders, seals for glass and other heat-sensitive materials, foundry patterns, molds for low-volume production of plastic parts, internal support for tube bending, and localized thermal treatment of parts.

Tin and tin-alloy powders: Produced by atomization techniques, these powders are available in a number of mesh sizes. They are used in the manufacture of powder-metallurgy parts, in tinning and solder pastes, and in the spray metallization of surfaces.

In small amounts, tin is also combined with titanium, zirconium, and other metals to provide special properties. It is used as an alloy in nodular and gray irons to provide greater strength, increased and uniform hardness, and improved machinability. Tin-nickel and tin-zinc coatings are used in the braking systems of automobiles. The tin-nickel alloy is coated on disc-brake pistons because of its good resistance to wear and corrosion. Tin-zinc is used to plate master cylinders in automotive braking systems.

Noncritical parts such as costume jewelry and small decorative items such as figurines can be made by casting pewter and other low-melting tin-based alloys in rubber molds. Tin die-casting alloys are suitable for low-strength precision parts and bearings for household appliances, engines, motors and generators, and gas turbines. These bearings perform well even at start-up and run-down periods of operation, at which times they carry a heavy, unidirectional load without the benefit of a fully formed hydrodynamic film. Other applications for tin-based die castings include parts for food-handling equipment, instruments, gas meters, and speedometers.

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Depending on the predominant phase or phases in their microstructure, titanium alloys are categorized as alpha, alpha-beta, and beta. This natural grouping not only reflects basic titanium production metallurgy, but it also indicates general properties peculiar to each type.

The alpha phase in pure titanium is characterized by a hexagonal close-packed crystalline structure that remains stable from room temperature to approximately 1,6200F. The beta phase in pure titanium has a body-centered cubic structure, and is stable from approximately 1,620OF to the melting point of about 3,0400F.

Adding alloying elements to titanium provides a wide range of physical and mechanical properties. Certain alloying additions, notably aluminum, tend to stabilize the alpha phase; that is, they raise the temperature at which the alloy will be transformed completely to the beta phase. This temperature is known as the beta-transus temperature.

Alloying additions such as chromium, columbium, copper, iron, manganese, molybdenum, tantalum, and vanadium stabilize the beta phase by lowering the temperature of transformation from alpha to beta. Some elements, notably tin and zirconium, behave as neutral solutes in titanium and have little effect on the transformation temperature, acting instead as strengtheners of the alpha phase.

Alpha alloys: The single-phase and near-single-phase alpha alloys of titanium have good weldability. The generally high aluminum content of this group of alloys ensures good strength characteristics and oxidation resistance at elevated temperatures (in the range of 600 to 1,1000F). Alpha alloys cannot be heat treated to develop higher mechanical properties because they are single-phase alloys.

Alpha-beta alloys: The addition of controlled amounts of beta-stabilizing alloying elements causes the beta phase to persist below the beta transus temperature, down to room temperature, resulting in a two-phase system. These two-phase titanium alloys can be strengthened significantly by heat treatment consisting of a quench from some temperature in the alpha-beta range, followed by an aging cycle at a somewhat lower temperature. Beta-phase transformation, which would normally occur on slow cooling, is suppressed by the quenching. The aging cycle causes the precipitation of some fine alpha particles from the metastable beta, imparting a structure that is stronger than the annealed alpha-beta structure. Although heat-treated alpha-beta alloys are stronger than the alpha alloys, their ductility is proportionally lower.

Beta alloys: The high percentage of beta-stabilizing elements in these alloys results in a microstructure that is substantially beta. The metastable beta can be strengthened considerably by heat treatment.

Titanium is used in corrosive environments or in applications that require light weight, high strength-to-weight ratio, and nonmagnetic properties. While commercially available in many alloys, most requirements can be met by a grade of commercially pure titanium, titanium-0.2% palladium alloy, or by the high-strength Ti-Al-V-Cr (beta type) alloys. These grades, which are available in most common wrought mill forms, are covered by ASTM-AMS specifications and, in most cases, by a similar ASNM specification.

Beta-21S is a new beta alloy developed as an oxidation-resistant aerospace material and as a matrix for metal-matrix composites. Composition is Ti-15Mo-2.7Nb-3AI-0.2Si, with molybdenum and niobium working synergistically to raise corrosion resistance to very high levels. It also offers one of the lowest hydrogen uptake efficiency levels of any titanium alloy. The combination of high strength and high corrosion resistance make it an ideal candidate for orthopedic implants, deep sour oil wells, and geothermal brine wells.

Like stainless steel, titanium sheet and plate work harden significantly during forming. Minimum bend-radius rules are nearly the same for both, although springback is greater for titanium. Commercially pure grades of heavy plate are cold formed or, for more severe shapes, warm formed at temperatures to about 8000F. Alloy grades can be formed at temperatures as high as 1,4000F in inert-gas atmospheres. Tube can be cold bent to radii three times the tube OD, provided that both inside and outside surfaces of the bend are in tension at the point of bending. In some cases, tighter bends can be made.

Despite their high strength, some alloys of titanium have superplastic characteristics in the range of 1,500 to 1,7000F. The alloy used for most superplastically formed parts is the standard Ti-6Al-4V alloy. Several aircraft manufacturers are producing components formed by this method. Some applications involve assembly by diffusion bonding.

Titanium plates or sheets can be sheared, punched, or perforated on standard equipment. Titanium and Ti-Pd alloy plates can be sheared subject to equipment limitations similar to those for stainless steel. The harder alloys are more difficult to shear, so thickness limitations are generally about two-third those for stainless steel.

Titanium and its alloys can be machined and abrasive ground; however, sharp tools and continuous feed are required to prevent work hardening. Tapping is difficult because the metal galls. Coarse threads should be used where possible.

Titanium castings can be produced by investment or graphite-mold methods. Casting must be done in a vacuum furnace, however, because of the highly reactive nature of titanium in the presence of oxygen. Typical applications for titanium castings are surgical implants and hardware for marine and chemical equipment such as compressors and valve bodies.

Generally, titanium is welded by gas-tungsten arc (GTA) or plasma-arc techniques. Metal inert-gas processes can be used under special conditions. Thorough cleaning and shielding are essential because molten titanium reacts with nitrogen, oxygen, and hydrogen, and will dissolve large quantities of these gases, which embrittles the metal. In all other respects, GTA welding of titanium is similar to that of stainless steel. Normally, a sound weld appears bright silver with no discoloration on the surface or along the heat-affected zone.

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Zinc, a crystalline metal with moderate strength and ductility, is seldom used alone except as a coating. In addition to its metal and alloy forms, zinc also extends the life of other materials such as steel (by hot dipping or electrogalvanizing), rubber and plastics (as an aging inhibitor), and wood (in paints). Zinc is also used to make brass, bronze, and die-casting alloys in plate, strip, and coil; foundry alloys; superplastic zinc; and activators and stabilizers for plastics.

Casting alloys: Zinc-casting alloys can be grouped into two general categories: standard zinc die-casting alloys, and the newer ZA (zinc-aluminum) casting alloys.

Standard die-casting alloys: For pressure die casting, the established zinc alloys are the No. 3, 5, and 7 Zamak alloys. As die castings, they have good general-purpose tensile properties and can be cast in thin sections and with good dimensional accuracy. The alloys are often selected for plated or highly decorative applications because of their excellent finishing characteristics. Three major end-use areas for zinc die-cast components are automotive, building hardware, and electrical.

Zamak alloys contain approximately 4% aluminum with low percentages of magnesium, copper, and sometimes nickel. impurities such as tin, lead, and cadmium are carefully controlled. These alloys are not recommended for gravity casting. They are cast by the hot-chamber die-casting process, which is different from, and more efficient than, the cold-chamber die-casting process commonly used for aluminum. In addition, a specialized process is used for efficient production of miniature die-cast components, using these alloys as well as ZA-8.

Typical tolerances of zinc die-cast parts are +/-0.0015 in./in. for the first inch with an additional +/-0.002 in./in. for larger parts. New zinc-casting technology allows for thin walls down to 0.025 in., improved internal soundness, and surface finishes that range typically from 32 to 64 rms.

Part dimensions change slightly when zinc die castings are aged. Zamak alloys No. 3 and 7 can shrink about 0.0007 in./in. after several weeks at room temperature. Alloy No. 5 responds similarly, but total shrinkage can be 0.0009 to 0.0024 in./in., followed by expansion of 0.0020 in./in. over a period of years. When it is necessary to bring these changes to completion within a short time after casting, a stabilizing treatment of 3 to 6 hr at 2120F is recommended.

ZA casting alloys: Designated as ZA-8, ZA-12, and ZA-27 (the numerical suffix represents the approximate percent by weight of aluminum), the high-aluminum alloys differ radically from the standard Zamak alloys in composition, properties, and castability. Although the ZA alloys were first introduced for gravity casting (sand and permanent mold), they have expanded into pressure die castings as well as the new, precision graphite-mold process. Important: Alloys ZA- 12 and ZA-27 must be cold-chamber die cast; alloy ZA-8 is hot-chamber castable.

Gravity casting into low-cost graphite permanent molds provides high-quality ZA castings with excellent precision, eliminating much machining. It is particularly competitive for production quantities of 500 to 15,000 parts/year, where die casting or plastic injection molding would be prohibitive because of tooling costs.

ZA alloys combine high strength and hardness (up to 60,000 psi and 120 Bhn), good machinability with good bearing properties, and wear resistance often superior to standard bronze alloys. ZA castings are now competing with cast iron, bronze, and aluminum because of various property and processing advantages.

Of the three alloys, ZA- 12 is preferred for most applications, and particularly for gravity casting. However, ZA-27 offers the highest mechanical properties regardless of casting method. Both are excellent bearing materials. ZA-8, on the other hand, gives the best plating characteristics. Because of its hot-chamber die castability and high mechanical properties, ZA-8 is also used for high-performance applications where standard zinc alloys may be marginal. All ZA alloys offer superior creep resistance and performance at elevated temperatures compared to the Zamak alloys.

Wrought alloys: Wrought-zinc alloys are available in rolled sheet, strip, foil, and as drawn rod or wire. With controlled rolling, zinc alloys can be tailored to meet a wide range of hardness, luster, and ductility requirements. Rolled zinc can be worked by common fabricating methods, and then polished, lacquered, painted, or plated.

When zinc alloys are formed in progressive presses, as in battery-shell manufacture, they are self annealing. After successive forming operations in nonprogressive presses, however, the alloys work harden and break. This can be overcome, in copper-free alloys, by intermediate annealing for 5 min in boiling water to which 20% glycerine has been added. Copper-bearing alloys should be heated 5 to 10 min at 3500F. The copper and titanium-containing alloy should be held at 3900F for about 15 min to bring about crystallization. Excessive exposure to higher temperatures should be avoided, however, to prevent grain growth, cleavage cracks, and property deterioration.

Highly workable and highly forgeable wrought-zinc alloys containing Ti, Al, Pb, Cd, Cu, or Fe in various quantities are easily machined. Forged or extruded parts are free from porosity and have good detail.

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In addition to resisting HCI at all concentrations and at temperatures above the boiling temperature, zirconium and its alloys also have excellent resistance in sulfuric acid at temperatures above boiling and concentrations to 70%. Corrosion rate in nitric acid is less than 1 mil/year at temperatures above boiling and concentrations to 90%. The metals also resist most organics such as acetic acid and acetic anhydride as well as citric, lactic, tartaric, oxalic, tannic, and chlorinated organic acids.

Relatively few metals besides zirconium can be used in chemical processes requiring alternate contact with strong acids and alkalis. However, zirconium has no resistance to hydrofluoric acid and is rapidly attacked, even at very low concentrations.

Zirconium alloys can be machined by conventional methods, but they have a tendency to gall and work harden during machining. Consequently, tools with higher than normal clearance angles are needed to penetrate previously work-hardened surfaces. Results can be satisfactory, however, with cemented carbide or high-speed steel tools. Carbide tools usually provide better finishes and higher productivity.

Mill products are available in four principal grades: 702, 704, 705, and 706. These metals can be formed, bent, and punched on standard shop equipment with a few modifications and special techniques. Grades 702 (unalloyed) and 704 (Zr-Sn-Cr-Fe alloy) sheet and strip can be bent on conventional press-brake or roll-forming equipment to a 5t bend radius at room temperature and to 3t at 2000C. Grades 705 and 706 (Zr-Cb alloys) can be bent to a 3t and 2.5t radius at room temperature and to about 1.5t at 2000C.

Zirconium has better weldability than some of the more common construction metals including some alloy steels and aluminum alloys. Low distortion during welding stems from a low coefficient of thermal expansion. Zirconium is most commonly welded by the gas-tungsten arc (GTAW) method, but other methods can also be used, including gas metal-arc (GMAW), plasma-arc, electron-beam, and resistance welding.

Welding zirconium requires proper shielding because of the metal's reactivity to gases at welding temperatures. Welding without proper shielding (argon or helium) causes absorption of oxygen, hydrogen, and nitrogen from the atmosphere, resulting in brittle welds. Although a clean, bright weld results from the use of a proper shielding system, discoloration of a weld is not necessarily an indication of its unacceptability. However, white deposits or a black color in the weld area are not acceptable. A bend test is usually the best way to determine acceptability of a zirconium weld.

Major uses for zirconium and its alloys are as a construction material in the chemical-processing industry. Applications include heat exchangers (for producing hydrogen peroxide, rayon, etc.), drying columns, pipe and fittings, pump and valve housings, and reactor vessels.

Materials Table of Contents.