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Features of Hard Aluminum Alloy Parts

November 30, 2022

Silicon material is also present as an impurity in hard aluminum. When the iron content in the alloy is low, silicon and magnesium preferentially form the Mg2Si compound, which consumes part of the magnesium and reduces the reinforcing phase S(Al2CuMg) phase. This reduces the natural aging-strengthening effect of hard aluminum. Silicon does not have much effect on the plasticity of hard aluminum, rather when there is iron in the alloy, silicon and iron form Fe2SiAl2 phase, which can be reduced due to the formation of coarse flakes of (FeMn)Al2 phase is a harmful element, the role. The content of silicon in hard aluminum is generally controlled at 0.5% to 0.7%.

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Nickel is also a harmful impurity in hard aluminum alloys. Nickel can form AlCuNi insoluble compounds with copper, which reduces the number of strengthening phases θ(CuAl2) and S(Al2CuMg) phases and makes the aging strengthening effect of hard aluminum lower, so the nickel content should be limited to less than 0.1%.

Zinc exists as an impurity in hard aluminum, which has no effect on the room temperature mechanical properties of hard aluminum, but reduces the thermal hardness of hard aluminum and increases the tendency to form cracks during welding, which also needs to be strictly controlled.

Hard aluminum alloys can be divided into three types according to their alloy element content and performance: namely, low-strength hard aluminum, such as 2A01, 2A03, 2A10, and other alloys; medium-strength hard aluminum, such as 2A11 and other alloys; and high-strength hard aluminum, such as 2A12 and other alloys.

1. Low-strength hard aluminum alloy This kind of hard aluminum alloy has low magnesium content (2A10) or contains a relatively low amount of both copper and magnesium (2A01). Its main strengthening phase is the theta (CuAl2) phase, so the aging strengthening effect is small, the strength is relatively low, with high plasticity, and the aging hardening speed is relatively slow. It has high shear resistance after aging and strengthening and is suitable for riveting material.

2. Medium-strength hard aluminum Medium-strength hard aluminum is also called standard hard aluminum. This type of alloy has high copper and magnesium content. Such as the 2A11 alloy in α (Al) + θ (CuAl2) + S (Al2CuMg) phase area on the left, the main strengthening phase is also θ (CuAl2) phase, followed by S (Al2CuMg) phase. However, the total amount of Cu and Mg is higher and the amount of Mg is lower, so it has higher strength and better plasticity. After the annealing process performance is good and can be cold bending, stamping, and other processes welding performance is good, and corrosion resistance is medium. The machinability in the annealed state is poor, but the age-hardened state is good machinability. Mainly used as a medium load structural parts.

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3. High-strength hard aluminum In order to improve the strength and yield limit of hard aluminum alloy, on the basis of medium-strength hard aluminum, while increasing the content of copper and magnesium or increasing the content of magnesium alone and form high-strength hard aluminum. For example, 2A12 alloy. It is on the right side of the α(Al)+θ(CuAl2)+S(Al2CuMg) phase region in Figure 6-9. Its main strengthening phase is the S(Al2CuMg) phase, followed by the θ(CuAl2) phase. Because the natural aging strengthening effect of the S phase is stronger than that of θ phase, 2A12 alloy has higher strength and yield limit and good heat resistance than 2A11, but plasticity and some process properties are poorer. 2A12 alloy is one of the most widely used high-strength hard aluminum alloys in industry. The corrosion resistance of the hard aluminum alloy is much worse than that of rust-proof aluminum, especially in seawater. Therefore, any hard aluminum alloy parts that need to work in a corrosive environment, its surface should be wrapped with a layer of high-purity aluminum to improve its corrosion resistance, but the mechanical properties of the hard aluminum material after heat treatment are lower than those of uncoated aluminum. Hard aluminum quenching and heating sensitivity to overburning, in order to obtain the maximum solid solution degree of supersaturated solid solution, 2A12 alloy has the most ideal quenching temperature of 500 ± 3 ℃, but the actual production conditions are difficult to do, so 2A12 alloy commonly used quenching temperature of 495 ~ 500 ℃.

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Hard aluminum alloys quenched with an artificial aging state have a greater tendency to intergranular corrosion than quenched with natural aging, so natural aging is generally used except for components working at high temperatures. relationship between natural aging and mechanical properties of 2A12 alloy after quenching. The quenching and cooling rate have a strong effect on the strength and corrosion resistance of hard aluminum alloys. When the quenching cooling rate is low, the natural aging strengthening effect and the tendency of intergranular corrosion will be reduced due to the precipitation of reinforcing phases such as θ(CuAl2) phase along the grain boundaries during the quenching process. Therefore, the quenching of hard aluminum alloys, under the premise of ensuring that no deformation and cracking, the faster the cooling rate, the better. For 2A11 and 2A12 alloy, quenching and cooling rate of not less than 20 ℃ / s and 14 ℃ / s, respectively, usually using water as a quenching medium.