Machinery's Handbook, 31st Edition
Aluminum Alloy Series Groups 541 conditions they may be subject to intergranular corrosion. Therefore, these alloys in the form of sheet are usually clad with a high-purity alloy or a magnesium-silicon alloy of the 6000 series, which provides galvanic protection to the core material and thus greatly increases resistance to corrosion. Alloy 2024 is perhaps the best known and most widely used aircraft alloy. 3000 series: Manganese is the major alloying element of alloys in this group, which are generally non-heat-treatable. Because only a limited percentage of manganese, up to about 1.5 percent, can be effectively added to aluminum, it is used as a major element in only a few instances. One of these, however, is the popular 3003, used for moderate- strength applications requiring good workability. 4000 series: The major alloying element of this group is silicon, which can be added in sufficient quantities to cause substantial lowering of the melting point without producing brittleness in the resulting alloys. For these reasons aluminum-silicon alloys are used in welding wire and as brazing alloys where a lower melting point than that of the parent metal is required. Most alloys in this series are non-heat-treatable, but, when used in weld ing heat-treatable alloys, they will pick up some of the alloying constituents of the latter and so respond to heat treatment to a limited extent. The alloys containing appreciable amounts of silicon become dark gray when anodic oxide finishes are applied and hence are in demand for architectural applications. 5000 series: Magnesium is one of the most effective and widely used alloying elements for aluminum. When it is used as the major alloying element or with manganese, the result is a moderate to high strength non-heat-treatable alloy. Magnesium is considerably more effective than manganese as a hardener, about 0.8 percent magnesium being equal to 1.25 percent manganese, and it can be added in considerably higher quantities. Alloys in this series possess good welding characteristics and good resistance to corrosion in marine atmospheres. However, certain limitations should be placed on the amount of cold-work and on safe operating temperatures permissible for the higher magnesium content alloys (over about 3 1 ⁄ 2 percent for operating temperatures over about 150°F or 66°C) to avoid susceptibility to stress corrosion. 6000 series: Alloys in this group contain silicon and magnesium in approximate proportions to form magnesium silicide, thus making them capable of being heat treated. The major alloy in this series is 6061, one of the most versatile of the heat-treatable alloys. Though not as strong as most of the 2000 or 7000 alloys, the magnesium-silicon (or mag nesium-silicide) alloys possess good formability and corrosion resistance, with medium strength. Alloys in this heat-treatable group may be formed in the -T4 temper (solution heat treated but not artificially aged) and then reach full -T6 properties by artificial aging. 7000 series: Zinc is the major alloying element in this group, and when coupled with a smaller percentage of magnesium results in heat-treatable alloys of very high strength. Other elements, such as copper and chromium, are usually added in small quantities. A notable member of this group is 7075, which is among the highest strength aluminum alloys available and is used in air-frame structures and for highly stressed parts. Type Metal.— Antimony gives to metals the property of expansion on solidification. Hence, it is used in type metal for casting type for the printing trades to insure the molds are completely filled. Type metals are generally made with from 5 to 25 percent of anti - mony, and with lead, tin and sometimes a small percentage of copper as the other alloying metals. The compositions of a number of type metal alloys are as follows (figures given are per centages): lead 77.5, tin 6.5, antimony 16; lead 70, tin 10, antimony 18, copper 2; lead 63.2, tin 12, antimony 24, copper 0.8 ; lead 60.5, tin 14.5, antimony 24–25, copper 0.75; lead 60, tin 35, antimony 5; and lead 55.5, tin 40, antimony 4.5. A high grade of type metal is composed of the following percentages: lead 50; tin 25; and antimony 25.
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