Cu

The maximum solubility of copper in aluminum is 5.65% when the aluminum-rich portion of aluminum-copper alloy is 548, and the solubility of copper is 0.45% when the temperature drops to 302. Copper is an important alloying element and has a certain solid solution strengthening effect. In addition, Cu Al2 precipitated with aging has a significant 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 hard aluminum alloys is in this range.
Aluminum-copper alloys may contain fewer elements such as silicon, magnesium, manganese, chromium, zinc, and iron.

Si

The maximum solubility of silicon in solid solution is 1.65% at the eutectic temperature of 577 Al-Si alloy-rich aluminum part. Although solubility decreases with decreasing temperature, such alloys are generally not heat strengthened. Al-Si alloy has 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 an Al-Mg-Si-based alloy composition, the content of magnesium and silicon is arranged on the substrate in this proportion. In some Al-Mg-Si alloys, in order to increase 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 effect of copper on corrosion resistance.
Al-Mg2Si alloy alloy equilibrium phase diagram The maximum solubility of aluminum-rich part Mg2Si in aluminum is 1.85%, and the deceleration decreases with decreasing temperature.
In deformed aluminum alloy, the addition of silicon to aluminum alone is limited to welding materials, and the addition of silicon to aluminum also has a certain strengthening effect.

Mg

Al-Mg alloy equilibrium phase diagram Al-rich part Although the solubility curve shows that the solubility of magnesium in aluminum decreases greatly with temperature, in most industrially deformed aluminum alloys, the magnesium content is less than 6%. The silicon content is also low. These alloys cannot be strengthened by heat treatment, but have good solderability, good corrosion resistance, and medium strength.
The strengthening of magnesium on aluminum is obvious. For every 1% magnesium added, the tensile strength increases by about 34MPa. If manganese is added below 1%, the strengthening effect may be supplemented. Therefore, after adding manganese, the magnesium content can be reduced, and at the same time, the tendency of thermal cracking can be reduced. In addition, manganese can also uniformly precipitate the Mg5Al8 compound, improving the corrosion resistance and welding performance.

Mn

At the eutectic temperature of 658, the maximum equilibrium solubility of manganese in solid solution is 1.82%. The strength of the alloy increases with increasing solubility. When the manganese content is 0.8%, the elongation reaches a maximum. Al-Mn alloy is a non-aging hardening alloy, that is, it cannot be strengthened by heat treatment.
Rhenium manganese can prevent the recrystallization process of aluminum alloy, increase the recrystallization temperature, and can significantly refine the recrystallized grains. The refining of the recrystallized grains is mainly caused by the dispersed particles of the MnAl6 compound, which hinders the growth of the recrystallized grains. Another function of MnAl6 is to dissolve the impurity iron to form (Fe, Mn) Al6 and reduce the harmful effects of iron.
Hafnium manganese is an important element of aluminum alloys, and can be added separately to form Al-Mn binary alloys. Most are added with other alloy elements, so most aluminum alloys contain manganese.

Zn

The Al-Zn alloy equilibrium phase diagram shows that the solubility of zinc in aluminum is 31.6% when the aluminum-rich part is 275, and its solubility decreases to 5.6% when it is 125.
Rhenium zinc is added to aluminum alone, and the improvement of aluminum alloy strength under deformation conditions is very limited. At the same time, there is a stress corrosion cracking and tendency, which limits its application.
When zinc and magnesium are added to aluminum at the same time, a strengthening phase Mg / Zn2 is formed, 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. When the content of magnesium exceeds the super-hard aluminum alloy required to form the Mg / Zn2 phase, the stress corrosion cracking resistance is greatest when the ratio of zinc to magnesium is controlled at about 2.7.
For example, if copper is added on the basis of Al-Zn-Mg to form an Al-Zn-Mg-Cu series 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 and power industries.