Copper element
When the aluminum-rich part of the aluminum-copper alloy is 548, the maximum solubility of copper in aluminum is 5.65%, and when the temperature is reduced to 302, the solubility of copper is 0.45%. Copper is an important alloying element, which has a certain solution strengthening effect, and the CuAl2 precipitated by aging has obvious aging strengthening effect. The copper content in aluminum alloy is usually 2.5% ~ 5%, and the strengthening effect is best when the copper content is 4% ~ 6.8%, so the copper content of most duralumin alloys is in this range.
Silicon element
The maximum solubility of silicon in the solid solution is 1.65% when the eutectic temperature of the aluminum-rich part of the Al-Si alloy is 577. Although solubility decreases with decreasing temperature, these alloys are generally not heat-treatable and strengthened. Aluminum-silicon alloys have excellent casting properties and corrosion resistance. If magnesium and silicon are added to aluminum at the same time 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 the composition of the Al-Mg-Si alloy, the magnesium and silicon content is configured on the substrate in this ratio. In some Al-Mg-Si alloys, in order to improve the strength, an appropriate amount of copper is added, and at the same time, an appropriate amount of chromium is added to offset the adverse effects of copper on corrosion resistance. The maximum solubility of Mg2Si in aluminum is 1.85%, and the deceleration is small with the decrease of temperature. In deformed aluminum alloys, silicon alone is only limited to welding materials, and silicon added to aluminum also has a certain strengthening effect.
Magnesium
Although the solubility curve shows that the solubility of magnesium in aluminum decreases greatly with the decrease of temperature, the content of magnesium in most industrial deformed aluminum alloys is less than 6%, and the silicon content is also low. The strengthening of magnesium to aluminum is obvious, and for every 1% increase in magnesium, the tensile strength increases by about 34MPa. If less than 1% manganese is added, it may supplement the strengthening effect. Therefore, the addition of manganese can reduce the magnesium content, and at the same time can reduce the tendency of hot cracking, and manganese can also make the Mg5Al8 compound evenly precipitate, improving the corrosion resistance and welding performance.
Manganese
The maximum solubility of manganese in the solid solution is 1.82% at the eutectic temperature of 658. The strength of the alloy increases with the increase of solubility, and the elongation reaches the maximum value when the manganese content is 0.8%. Al-Mn alloy is a non-age-hardening alloy, that is, it cannot be strengthened by heat treatment. Manganese can prevent the recrystallization process of aluminum alloys, increase the recrystallization temperature, and significantly refine the recrystallized grains. The refinement of recrystallized grains is mainly hindered by the dispersion of particles of MnAl6 compounds. Another function of MnAl6 is to dissolve impurity iron to form (Fe, Mn)Al6 and reduce the harmful effects of iron. Manganese is an important element of aluminum alloy, which can be added separately to form Al-Mn binary alloy, and more often added together with other alloying elements, so most aluminum alloys contain manganese.
Zinc element
The solubility of zinc in aluminum is 31.6% at 275, but decreases to 5.6% at 125. Zinc is added to aluminum alone, and the improvement of aluminum alloy strength under deformation conditions is very limited, and there is a tendency to stress corrosion cracking and tendency, thus limiting its application. Zinc and magnesium are added to aluminum at the same time to form the strengthening phase Mg/Zn2, which has 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. The content of magnesium exceeds that of the superduralumin alloy required for the formation of Mg/Zn2 phase, and the stress corrosion cracking resistance is the greatest when the ratio of zinc and magnesium is controlled at about 2.7. If copper is added on the basis of Al-Zn-Mg to form Al-Zn-Mg-Cu alloy, the base strengthening effect is the largest among all aluminum alloys, and it is also an important aluminum alloy material in the aerospace, aviation industry and power industry.
