The influence of various elements in aluminum alloys on the properties of aluminum

The influence of various elements in aluminum alloys on the properties of aluminum

Copper element

When the aluminum-rich part of the aluminum-copper alloy is 548, the maximum solubility of copper in aluminum is 5.65%. When the temperature drops to 302, the solubility of copper is 0.45%. Copper is an important alloy element and has a certain solid solution strengthening effect. In addition, the CuAl2 precipitated by aging has an obvious aging strengthening effect. The copper content in aluminum alloys is usually between 2.5% and 5%, and the strengthening effect is best when the copper content is between 4% and 6.8%, so the copper content of most duralumin alloys is within this range.

Silicon

When the aluminum-rich part of the Al-Si alloy system has a eutectic temperature of 577, the maximum solubility of silicon in the solid solution is 1.65%. Although solubility decreases with decreasing temperature, these alloys generally cannot be strengthened by heat treatment. Aluminum-silicon 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 the composition of the Al-Mg-Si alloy, the contents of magnesium and silicon are configured in this ratio on the matrix. In order to improve the strength of some Al-Mg-Si alloys, 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 Mg2Si in aluminum in the aluminum-rich part of the equilibrium phase diagram of the Al-Mg2Si alloy system is 1.85%, and the deceleration is small as the temperature decreases.

In deformed aluminum alloys, the addition of silicon alone to aluminum is limited to welding materials, and the addition of silicon to aluminum also has a certain strengthening effect.

Magnesium

Although the solubility curve shows that the solubility of magnesium in aluminum greatly decreases as the temperature decreases, the magnesium content in most industrial deformed aluminum alloys is less than 6%. The silicon content is also low. This type of alloy cannot be strengthened by heat treatment, but has good weldability, good corrosion resistance, and medium strength.

The strengthening of aluminum by magnesium is obvious. For every 1% increase in magnesium, the tensile strength increases by approximately 34MPa. If less than 1% manganese is added, the strengthening effect may be supplemented. Therefore, adding manganese can reduce the magnesium content and reduce the tendency of hot cracking. In addition, manganese can also uniformly precipitate Mg5Al8 compounds, improving corrosion resistance and welding performance.

Manganese

When the eutectic temperature of the flat equilibrium phase diagram of the Al-Mn alloy system is 658, the maximum solubility of manganese in the solid solution is 1.82%. The strength of the alloy increases with the increase in 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 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 caused by the dispersed particles of MnAl6 compounds, which hinder the growth of recrystallized grains. Another function of MnAl6 is to dissolve impurity iron to form (Fe, Mn)Al6, reducing the harmful effects of iron.

Manganese is an important element in aluminum alloys. It can be added alone to form an Al-Mn binary alloy. More often, it is added together with other alloying elements. Therefore, most aluminum alloys contain manganese.

Zinc element

The solubility of zinc in aluminum is 31.6% at 275 in the aluminum-rich part of the equilibrium phase diagram of the Al-Zn alloy system, while its solubility drops to 5.6% at 125.

Adding zinc alone to aluminum has very limited improvement in the strength of the aluminum alloy under deformation conditions. At the same time, there is a tendency for stress corrosion cracking, thus limiting its application.

Adding zinc and magnesium to aluminum at the same time forms 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. In superhard aluminum alloys where the magnesium content exceeds the required amount to form the Mg/Zn2 phase, when the ratio of zinc to magnesium is controlled at around 2.7, the stress corrosion cracking resistance is greatest.

For example, adding copper element to Al-Zn-Mg forms an Al-Zn-Mg-Cu series alloy. The base strengthening effect is the largest among all aluminum alloys. It is also an important aluminum alloy material in the aerospace, aviation industry, and electric power industry.