Analysis of the role of common elements in aluminum alloys (1)

Here we are going to analyze the role of common elements in aluminum alloys, focusing on Cu, Si and Mg, which is related to 2 series aluminum alloy, 4 series aluminum alloy and 5 series aluminum alloy respectively.

Copper Cu: 2 series aluminum alloy

When the aluminum-rich part of the aluminum-copper alloy is 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 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 the aluminum alloy is usually 2.5% to 5%, and the strengthening effect is the best when the copper content is 4% to 6.8%, so the copper content of most hard aluminum alloys is in this range.

Aluminum-copper alloys can contain less elements such as silicon, magnesium, manganese, chromium, zinc, and iron.

Silicon Si: 4 series aluminum alloy

When the aluminum-rich part of the Al-Si alloy system is at the eutectic temperature of 577, the maximum solubility of silicon in the solid solution is 1.65%. Although solubility decreases with decreasing temperature, these alloys are generally not heat-treatable. 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 the Al-Mg-Si alloy, the content of magnesium and silicon should be arranged in this proportion on the substrate. In some Al-Mg-Si alloys, in order to improve the strength, an appropriate amount of copper is added, and an appropriate amount of chromium is added to offset the adverse effect of copper on corrosion resistance.

The equilibrium phase diagram of Al-Mg2Si alloy system alloy shows that the maximum solubility of Mg2Si in aluminum in the aluminum-rich part is 1.85%, and the deceleration decreases with the decrease of temperature. In deformed aluminum alloys, 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 Mg: 5 series aluminum alloy

Although the solubility curve of the Al-rich part of the equilibrium phase diagram of the Al-Mg alloy system shows that the solubility of magnesium in aluminum decreases greatly with the decrease of temperature, the content of magnesium in most industrial wrought aluminum alloys is less than 6%. The silicon content is also low, and these alloys cannot be heat-treated to strengthen, but they have good weldability, good corrosion resistance, and moderate strength.