Copper element
When the aluminum-copper alloy is rich in aluminum 548, the maximum solubility of copper in aluminum is 5.65%, and when the temperature drops to 302, the solubility of copper is 0.45%. Copper is an important alloying element with a certain solution strengthening effect, and the aging precipitated CuAl2 has an obvious aging strengthening effect. The copper content in aluminum alloys is usually 2.5% ~ 5%, and 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 solid solution is 1.65% at the eutectic temperature of 577 for the aluminum-rich part of Al-Si alloys. Although the solubility decreases with the decrease of temperature, this type of alloy generally cannot be strengthened by heat treatment. 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 Al-Mg-Si alloys, the content of magnesium and silicon is allocated in this ratio on the matrix. In some Al-Mg-Si alloys, in order to improve strength, an appropriate amount of copper is added, and an appropriate amount of chromium is added to offset the adverse effects of copper on corrosion resistance.
The maximum solubility of the aluminum-rich part of the Al-Mg2Si alloy system in aluminum is 1.85%, and the deceleration is small with the decrease of temperature.
In deformed aluminum alloys, silicon is only added to aluminum alone for 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.
Magnesium strengthens aluminum significantly, 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 reduce the tendency to thermal cracking, and the manganese can also make the Mg5Al8 compound precipitate evenly, improving the corrosion resistance and welding performance.
Manganese element
The maximum solubility of manganese in solid solution is 1.82% at eutectic temperature 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-aging 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 recrystallization grains. The refinement of recrystallized grains is mainly hindered by the diffusion of particles by MnAl6 compounds. Another function 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, which can be added alone to form Al-Mn binary alloys, 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, while its solubility drops to 5.6% at 125.
Zinc alone added to aluminum has limited improvement in the strength of aluminum alloy under deformation conditions, and there is a tendency to stress corrosion cracking and tendency, which limits its application.
Zinc and magnesium are added to aluminum at the same time to form the reinforcing 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. In superduralumin alloys where the content of magnesium exceeds the required for the formation of Mg/Zn2 phase, the ratio of zinc and magnesium is controlled at about 2.7, and the stress corrosion cracking resistance is the largest.
For example, copper is added to the basis of Al-Zn-Mg to form Al-Zn-Mg-Cu alloys, which have the largest base strengthening effect among all aluminum alloys, and are also important aluminum alloy materials in the aerospace, aviation industry and power industry.
