copper
The maximum solubility of copper in aluminum is 5.65% when the aluminum rich part is 548, and 0.45% when the temperature drops to 302. Copper is an important alloying element, which has a certain solution strengthening effect. In addition, the aging precipitated CuAl2 has an obvious aging strengthening effect. Aluminum alloy copper content is usually 2.5% ~ 5%, copper content in 4%~6.8% when the best strengthening effect, so most of the duralumin copper content in this range.
silicon
When the eutectic temperature is 577, the maximum solubility of silicon in the solid solution is 1.65%. Although the solubility decreases with decreasing temperature, such alloys are generally not heat-treatable. Al - si alloy has excellent casting property and corrosion resistance.
If magnesium and silicon are added to aluminum at the same time to form al-Mg-Si 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 alloy, the content of magnesium and silicon in the matrix should be proportioned accordingly. Some Al-Mg-Si alloys, in order to improve the strength, add appropriate amount of copper, while adding appropriate amount of chromium to offset the adverse effect of copper corrosion resistance.
The maximum solubility of Mg2Si in aluminum is 1.85%, and decreases with the decrease of temperature.
In the deformed aluminum alloy, the addition of silicon to aluminum is only a welding material, and the addition of silicon to aluminum also has a certain strengthening effect.
magnesium
Al - Mg alloy system equilibrium phase diagram rich aluminum part though the solubility curve shows that the solubility of magnesium in aluminium greatly decreases with temperature drop, but in most of the deformation of industrial aluminum alloy, magnesium content are less than 6%, and silicon content is low, this kind of alloy can't heat treatment to strengthen, but good weldability, corrosion resistant, with moderate intensity.
The enhancement of magnesium to aluminum is obvious, and the tensile strength increases by about 34MPa per 1% increase of magnesium. If less than 1% manganese is added, the strengthening effect may be supplemented. Therefore, the addition of manganese can reduce the magnesium content and reduce the hot cracking tendency. In addition, manganese can also precipitate Mg5Al8 compound uniformly and improve the corrosion resistance and welding performance.
Manganese element
When the eutectic temperature is 658, the maximum solubility of Mn in the solid solution is 1.82%. 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 of aluminum alloy, increase the recrystallization temperature, and refine the recrystallized grain significantly. The refinement of recrystallized grain is mainly hindered by MnAl6 dispersion particles. Another function of MnAl6 is to dissolve impurity iron and form (Fe, Mn) Al6, reducing the harmful effects of iron.
Manganese is an important element of aluminum alloy. It can be added separately to form Al-Mn binary alloy, and more of them are added together with other alloy elements. Therefore, most aluminum alloys contain manganese.
zinc
The solubility of zinc in aluminum in equilibrium phase diagram of Al-Zn alloy system is 31.6% at 275, but decreases to 5.6% at 125.
When zinc is added to aluminum alone, the strength of aluminum alloy under deformation condition is very limited, and there is a tendency of stress corrosion cracking, so its application is limited.
The strengthening phase Mg/Zn2 is formed by adding zinc and magnesium into aluminum, which has obvious strengthening effect on the alloy. When Mg/Zn2 content is increased from 0.5% to 12%, the tensile strength and yield strength can be obviously increased. When the content of magnesium exceeds that of Mg/Zn2 phase, the stress corrosion cracking resistance reaches the maximum when the ratio of zinc to magnesium is about 2.7.
If copper element 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 aerospace, aviation and electric power industries.
