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The function of various elements in aluminum alloy

Copper Element
When the aluminum-copper alloy temperature is 548, the maximum solubility of copper in aluminum is 5.65%. When the temperature drops to 302, the solubility of copper is 0.45%. Copper is an important alloying element and has a certain solid-solution strengthening effect. In addition, CuAl2 precipitated during ageing has strengthening effect. The content of copper in aluminum alloy is usually between 2.5%-5%, and the copper content is between 4%-6.8% with the best strengthening effect. Therefore, the copper content of most hard aluminum alloy falls within this range.
Silicon Element
Al-Si alloy has a maximum solubility of 1.65% in solid solution at a temperature of 577. Although the solubility decreases with decreasing temperature, such alloys are generally not heat-treatable. Al-Si alloys have excellent casting properties and corrosion resistance. If magnesium and silicon are simultaneously added to aluminum to form an aluminum-magnesium silicon alloy, the strengthening phase is MgSi. The mass ratio of magnesium to silicon is 1.73:1. When designing Al-Mg-Si-based alloy composition, magnesium and silicon are disposed on the substrate in this ratio. In some Al-Mg-Si alloys, in order to increase the strength, an appropriate amount of copper is added and an appropriate amount of chromium is added at the same time to offset the adverse effect of copper corrosion resistance.
Mg2Si has a maximum solubility of 1.85% in aluminum and slows down as temperature decreases.
In the deformed aluminum alloy, added silicon alone to the aluminum is limited to the welding material. The addition of silicon to the aluminum also has a certain strengthening effect.
Magnesium Element
Although the solubility curve of Al-Mg alloy shows that the solubility of magnesium in aluminum is greatly reduced as the temperature decreases, in most industrial deformed aluminum alloys, the magnesium content is less than 6%, and the silicon content is also low. Alloys are not heat-treatable, but have good weldability, good corrosion resistance, and moderate strength. The enhancement of magnesium by aluminum is obvious. With every 1% increase in magnesium, the tensile strength increases by about 34MPa. If 1% or less of manganese is added, it may supplement the strengthening effect.
Manganese Element
When the Al-Mn alloy temperature is 658, the maximum solubility of manganese in the solid solution is 1.82%. The alloy strength increases with increasing solubility, and the elongation reaches a maximum when the manganese content is 0.8%. Al-Mn alloys are non-aging hardened alloys, it means non-heat treatable.
Manganese can prevent the recrystallization process of aluminum alloys, increase the recrystallization temperature, and can significantly refine the recrystallized grains. The refinement of the recrystallized grains is mainly hindered by the growth of recrystallized grains through the disperse particles of the MnAl6 compound. Another role of MnAl6 is to dissolve the impurity iron and form (Fe, Mn)Al6, reducing the harmful effects of iron.
Manganese is an important element of aluminum alloys and can be added separately to form Al-Mn binary alloys, and more is added together with other alloying elements. Therefore, most aluminum alloys contain manganese.
Zinc Element
At the temperature of 275, the solubility of Al-Zn in aluminum is 31.6%, while the temperature decrease to 125, the solubility is 5.6%.
Zinc alone added to aluminum, under the deformation conditions of the aluminum alloy strength is very limited, there is stress corrosion cracking, tend to limit its application.
Simultaneous addition of zinc and magnesium to aluminum forms a strengthening phase Mg/Zn2, which produces a significant strengthening effect on the alloy. When the Mg/Zn2 content is increased from 0.5% to 12%, the tensile strength and yield strength can be significantly increased. Magnesium content exceeds that of superhard aluminum alloys required to form Mg/Zn2 phases. When the ratio of zinc and magnesium is controlled to about 2.7, stress corrosion cracking resistance is the highest.
If Al-Zn-Mg is added to the base of copper to form Al-Zn-Mg-Cu alloy, the base strengthening effect is the largest in all aluminum alloys, and it is also an important aluminum alloy material in the aerospace, aerospace and power industries.