Machinery's Handbook, 31st Edition
NONFERROUS CASTING MATERIALS 1487 Aluminum-Copper (Al-Cu) Cast Alloys (2xx.x series): These alloys contain 4–4.6% copper, along with small impurities of iron, silicon, and magnesium. Characteristics are heat-treatable, high strength, low fluidity, low ductility, susceptibility to hot cracks, and low corrosion resistance. Aluminum-copper cast alloys are used for cylinder heads for automotive and aircraft engines, pistons for diesel engines, and exhausting system parts. Aluminum-Silicon-Copper (Al-Si-Cu) Cast Alloys (3xx.x series): Aluminum-silicon- copper alloys contain 5–17% silicon and 2–4.5% copper. Characteristics of these alloys are heat-treatable, high strength, good fluidity, low ductility, good machinability, good wear resistance, and decreased corrosion resistance. The copper contributes to strength, and the silicon improves castability and reduces hot shortness; thus, higher silicon alloys are suitable for more complex castings and for permanent mold and die casting processes, which cannot tolerate hot-short alloys. They are used for automotive cylinder blocks and heads, car wheels, aircraft fittings, casings, and other parts of compressors and pumps. Aluminum-Silicon (Al-Si) Cast Alloys (4xx.x series): These alloys contain 5–12% silicon but no copper. Characteristics are non-heat-treatable, moderate strength, moderate duc- tility, very good cast properties, and good wear and corrosion resistance. Rapid cooling to increase strength and ductility can refine the microstructure. These alloys are used for pump casings, thin wall castings, and cookware. Aluminum-Magnesium (Al-Mg) Cast Alloys (5xx.x series): Containing 4–10% magne- sium, characteristics of these alloys are non-heat-treatable, good machinability, and good appearance when anodized. The moderate to relatively poor castability of such alloys and the tendency of magnesium to oxidize increase handling difficulties and, therefore, cost. In general, these alloys are used for sand cast parts. Aluminum-Tin (Al-Sn) Cast Alloys (8xx.x series): Aluminum-tin alloys usually contain about 6% tin and a small amount of copper and nickel to improve strength. Though these compounds are not heat treatable, castability and machinability are good, and wear re- sistance is very good. They are used for cast bearings, due to tin’s excellent lubrication characteristics. Aluminum-Zinc (Al-Zn) Cast Alloys (7xx.x series): With the addition of 6.2–7.5% zinc, these alloys can be heat treated and have good dimensional stability, good machinability (if the alloy contains copper), and good corrosion resistance. They are used for abrasion- resistant parts under various operating conditions, such as axle bushes, shaft sleeves, and worm gears. Copper (Cu).—Copper is a reddish-yellow material with a melting point of 1984.6°F (1084.6°C) and a density of 556.85 lb/ft 3 (8920 kg/m 3 ). Usually a good conductor of elec- tricity and heat, copper is one of the most ductile metals, but it is not especially strong or hard. Pure copper is extremely difficult to cast. As copper forms alloys more freely than most metals, casting and other characteristics can be improved by adding small amounts of various elements, including beryllium, chromium, nickel, silicon, silver, tin, and zinc. Brass: This generic term refers to a range of copper-zinc (Cu-Zn) alloys with differing combinations of properties, including strength, hardness, ductility, machinability, resis- tance to wear and corrosion, and electrical and thermal conductivity. Bronze: Bronze made from copper and tin (Cu-Sn) was the first manmade alloy used thousands of years ago. In modern times, wrought bronzes have been developed with 4–8% tin. These alloys are harder, stronger, and stiffer than wrought brasses and, in strip and wire form, produce a combination of high yield strength and good corrosion resistance. Copper-Nickel (Cu-Ni) Alloys: This combination offers high conductivity, excellent resistance to marine corrosion, and low susceptibility to attachment of marine macro- organisms. The addition of nickel to copper improves strength and corrosion resistance, but good ductility is retained. The two main alloys are 90/10 (90% copper, 10% nickel) and 70/30 (70% copper, 30% nickel). Copper-Nickel-Silver (Cu-Ni-Zn) Alloys: Made from copper, nickel, and zinc but no silver, these alloys can be regarded as special brasses. Containing 10–20% nickel, they
Copyright 2020, Industrial Press, Inc.
ebooks.industrialpress.com
Made with FlippingBook - Share PDF online