NONFERROUS CASTING MATERIALS Nonferrous Casting Metals Machinery's Handbook, 31st Edition
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Nonferrous metals include metal elements and alloys not based on iron. Offering a wide variety of material characteristics and mechanical properties, these casting materials are commonly specified for structural applications that require reduced weight, increased strength, higher melting points, nonmagnetic properties, and/or resistance to chemical and atmospheric corrosion. They also are suitable for electrical and electronic applica- tions. Such metals include aluminum, copper, magnesium, nickel, titanium, zinc, refrac- tory metals (molybdenum and tungsten), and noble metals. Important considerations in selecting material for a specific mechanical or structural application include how easily the material can be shaped into a finished part and how its properties may be altered in the process—either intentionally or inadvertently. De- pending on the end use, metal can be cast into a part and finished. Or it can be cast into an intermediate form (such as ingots), worked, or wrought, by forging, extruding, rolling, or applying other deformation processes, and then finished as needed. Following are the primary nonferrous metals and alloys used in casting. For more information on specific alloys, see NONFERROUS ALLOYS starting on page 510. Aluminum (Al).—Aluminum, also spelled aluminium, is a lightweight, silvery-white metal. It has a melting point of 1220°F (660°C) and a density of 163.55 lb/ft 3 (2700 kg/ m 3 ). The most abundant metallic element in the Earth’s crust, aluminum is the most widely used nonferrous metal. While it is thermodynamically the least stable of the main engi- neering metals, it has the advantage of forming a dense, highly protective alumina film only 20 μin.–60 μin. (0.5 μm–1.5 μm) thick. This film can be reinforced by anodizing and destroyed by salt. Aluminum is one of the few metals that can be cast by all of the processes. When alloyed with other metals, numerous properties are obtained that make such alloys useful over a broad range of applications. Many organizations publish specific standards for the manu - facture of aluminum alloy, including ASTM International and SAE International (specifi - cally, its aerospace standards subgroups). Alloys composed mostly of aluminum have been important in aerospace manufacturing since the introduction of metal-skinned aircraft. Classification of cast aluminum alloys is developed by the Aluminum Association of the United States. Each cast alloy is designated by a four-digit number with a decimal point separating the third and fourth digits: 1. The first digit indicates the alloy group, according to the major alloying element: 1xx.x aluminum (99.0% minimum) 2xx.x copper (4% to 4.6%) 3xx.x silicon (5% to 17%) with added copper and/or magnesium 4xx.x silicon (5% to 12%) 5xx.x magnesium (4% to 10%) 7xx.x zinc (6.2% to 7.5%) 8xx.x tin 9xx.x others 2. The next two digits indicate the alloy purity or identify the alloy: In the alloys of the 1xx.x series, these digits indicate the level of purity of the alloy—the same as the two digits to the right of the decimal point in the minimum concentration of aluminum (in percent): 150.0 means a minimum 99.50% of aluminum in the alloy, 120.1 means a minimum 99.20% of aluminum. In all other groups of aluminum alloys (2xx.x through 9xx.x), the second and third digits together signify different alloys in the group. 3. The last digit indicates the product form: casting (designated by 0) or ingot (designated by 1 or 2, depending on chemical composition limits). A modification of the original alloy or impurity limits is indicated by a serial letter before the numerical designation. The serial letters are assigned in alphabetical order, starting with A, but omitting I, O, Q, and X. (The letter X is reserved for experimental alloys.)
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