Copper element

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 alloy element (aluminum alloy element analysis), which has a certain effect of solution strengthening. In addition, the aging precipitated CuAl2 has a significant effect of aging strengthening. The strengthening effect is the best when the copper content is usually 2.5% ~ 5% and 4% ~ 6.8%, so the copper content of most duralumin alloys is in this range.

Aluminum copper alloy can contain less silicon, magnesium, manganese, chromium, zinc, iron and other elements.

Silicon element

The maximum solubility of Si in solid solution is 1.65% at the eutectic temperature of 577. Although the solubility decreases with the decrease of temperature, these alloys can not be strengthened by heat treatment. Al Si alloy has excellent casting performance 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 system alloy, the content of Mg and Si in the matrix is arranged according to this proportion. In order to improve the strength of some Al Mg Si alloys, a proper amount of copper and chromium are added to counteract the adverse effect of copper on corrosion resistance.

The maximum solubility of Mg2Si in aluminum is 1.85% in the equilibrium phase diagram of Al Mg2Si alloy system, and its deceleration decreases with the decrease of temperature.

In the 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.

Magnesium element

Although the solubility curve of the aluminum rich part of the equilibrium phase diagram of Al Mg alloy system shows that the solubility of magnesium in aluminum decreases greatly with the decrease of temperature, the content of magnesium is less than 6% and the content of silicon is also low in most of the industrial wrought aluminum alloys. This kind of alloy can not be strengthened by heat treatment, but it has good weldability, corrosion resistance and medium strength aluminum alloy element analysis.

The strengthening effect of magnesium on aluminum is obvious. For every 1% increase of magnesium, the tensile strength increases about 34 MPa. If less than 1% manganese is added, the strengthening effect may be supplemented. In addition, manganese can make mg5al8 compound precipitate uniformly, improve corrosion resistance and welding performance.

Manganese

The maximum solubility of Mn in solid solution is 1.82% at the eutectic temperature of 658. The strength of the alloy increases with the increase of solubility. When the manganese content is 0.8%, the elongation reaches the maximum value. Al Mn alloy is a non age hardening alloy, that is, it can not be strengthened by heat treatment.

Zinc element

The solubility of zinc in aluminum is 31.6% in the equilibrium phase diagram of the aluminum rich part 275 of the Al Zn alloy system, while it decreases to 5.6% in the aluminum alloy element analysis at 125.

When zinc is added to aluminum alone, the strength of aluminum alloy is limited under the condition of deformation. At the same time, there is stress corrosion cracking and tendency, which limits its application.

The strengthening phase mg / Zn2 is formed by adding zinc and magnesium into aluminum simultaneously, 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 increased obviously. When the ratio of zinc to magnesium is about 2.7, the stress corrosion cracking resistance is the largest.