1.3 Nonferrous Metals and Alloys
Nonferrous metals and alloys cover a wide range of materials, from common metals such as aluminum, copper, and magnesium to high-strength, high-temperature alloys, such as those of tungsten, tantalum, and molybdenum. Although generally more expensive than ferrous metals, nonferrous metals and alloys have important applications because of properties such as corrosion resistance, high thermal and electrical conductivity, low density, and ease of fabrication.
Aluminum (Al). Typical examples of the applications of nonferrous metals and alloys are aluminum for cooking utensils and aircraft bodies, copper wire for electricity, copper tubing for residential water supply, zinc for galvanized sheet metal for car bodies, titanium for jet-engine turbine blades and for orthopedic implants.
The principal uses of aluminum and its alloys are in containers and packaging (aluminum cans and foil), in buildings and other types of construction, in transportation (aircraft and aerospace applications, buses, automobiles), in electrical applications (economical and nonmagnetic electrical conductor), in consumer durables (appliances, cooking utensils, and furniture). Nearly all high-voltage transmission wiring is made of aluminum. In its structural (load-bearing) components, 82% of a Boeing 747 aircraft (and 79% of a Boeing 757 aircraft) is aluminum.
Porous Aluminum. Blocks of aluminum have recently been produced that are 37% lighter than solid aluminum and have uniform permeability (microporosity). This characteristic allows their use in applications where a vacuum or differential pressure has to be maintained. Examples are the vacuum holding of fixtures for assembly and automation and the vacuum forming or thermoforming of plastics.[7] These blocks are 70% to 90% aluminum powder; the rest is epoxy resin. They can be machined with relative ease and can be joined together using adhesives.
Magnesium (Mg) is the lightest engineering metal available, and it has good vibration-damping characteristics. Its alloys are used in structural and nonstructural applications wherever weight is of primary importance. Magnesium is also an alloying element in various nonferrous metals. A variety of magnesium alloys have good casting, forming, and machining characteristics.
Typical uses of magnesium alloys are in aircraft and missile components, material-handling equipment, portable power tools (such as drills and sanders), ladders, luggage, bicycles, sporting goods, and general lightweight components.
Copper (Cu), first produced in about 4000 B.C., and its alloys have properties somewhat similar to those of aluminum and its alloys. In addition, they are among the best conductors of electricity and heat, and they have good corrosion resistance. They can be processed easily by various forming, machining, casting, and joining techniques.
Copper alloys are often attractive for applications where a combination of electrical, mechanical, nonmagnetic, corrosion-resistant, thermally conductive, and wear-resistant qualities are required. Applications include electrical and electronic components; springs; cartridges for small arms; plumbing; heat exchangers; marine hardware, and consumer goods, such as cooking utensils, jewelry, and other decorative objects.
Titanium (Ti), named after the giant Greek god Titan, was discovered in 1791, but it was not produced commercially until the 1950s. Although it is expensive, its high strength-to-weight ratio and its corrosion resistance at room and elevated temperatures make it attractive for many applications including aircraft, jet-engine, racing-car, chemical, petrochemical, and marine components, submarine hulls, and biomaterials, such as orthopedic implants. Titanium alloys have been developed for service at 550°C (1000 °F) for long periods of time and at up to 750 °C (1400 °F) for shorter periods.
The properties and manufacturing characteristics of titanium alloys are extremely sensitive to small variations in both alloying and residual elements. These elements cause embrittlement of titanium and, consequently, reduce toughness and ductility.
Superalloys are important in high-temperature applications; hence, they are also known as heat-resistant or high-temperature alloys. Major applications of superalloys are in jet engines and gas turbines; other applications are in reciprocating engines, in rocket engines, in tools and dies for hot-working of metals, and in the nuclear, chemical, and petrochemical industries. Superalloys generally have good resistance to corrosion, to mechanical and thermal fatigue, to mechanical and thermal shock, to creep, and to erosion at elevated temperatures.
Most superalloys have a maximum service temperature of about 1000 °C (1800 °F) in structural applications. The temperatures can be as high as 1200 °C (2200 °F) and above and a major application for the superalloys of rapidly-solidified powders is consolidation into near-net shapes for parts used in aerospace engines.
Low-melting alloys are so named because of their relatively low melting points. The major metals in this category are lead, zinc, and tin and their alloys.
Lead (Pb) has properties of high density, resistance to corrosion (by virtue of the stable lead-oxide layer that forms to protect the surface), softness, low strength, ductility, and good workability. Lead is also used for damping sound and vibrations, in radiation shielding against x-rays, in ammunition, as weights, and in the chemical industry. An additional use of lead is as a solid lubricant for hot-metal forming operations. Because of its toxicity, however, environmental contamination by lead (causing lead poisoning) is a major concern.
Zinc (Zn), bluish-white in color, is the metal fourth most utilized industrially, coming after iron, aluminum, and copper. Zinc is also used as an alloying element. Brass, for example, is an alloy of copper and zinc. Major alloying elements in zinc-based alloys are aluminum, copper, and magnesium. Zinc-based alloys are used extensively in die casting, for making such products as fuel pumps and grills for automobiles, components for household appliances such as vacuum cleaners, washing machines, and kitchen equipment, and various machinery parts and photoengraving equipment.
Although used in small amounts, tin (Sn) is an important metal. The most extensive use of tin, a silvery-white, lustrous metal, is as a protective coating on the steel sheet (tin plate) that is used in making containers (tin cans) for food and for various other products. Unalloyed tin is used in such applications as lining material for water distillation plants and as a molten layer of metal over which plate glass (float glass) is made. Tin-based alloys (also called white metals) generally contain copper, antimony, and lead. The alloying elements impart hardness, strength, and corrosion resistance.
Precious Metals. Gold, silver, and platinum are the most important precious (that is, costly) metals; they are also called noble metals.
1. Gold (Au) is soft and ductile, and it has good corrosion resistance at any temperature. Typical applications include jewelry, coinage, reflectors, dental work, electroplating, and electrical contacts and terminals.
2. Silver (Ag) is a ductile metal, and it has the highest electrical and thermal conductivity of any metal. It does, however, develop an oxide film that affects its surface characteristics and appearance. Typical applications for silver include tableware, jewelry, coinage, electroplating, photographic film, electrical contacts, solders, bearing linings, and food and chemical equipment.
3. Platinum (Pt) is a soft, ductile, grayish-white metal that has good corrosion resistance even at elevated temperatures. Platinum alloys are used as electrical contacts, for spark-plug electrodes, as catalysts for automobile pollution-control devices, in filaments, in nozzles, in dies for extruding glass fibers, in thermocouples, in the electrochemical industry, as jewelry, and in dental work.