What are the functions of magnesium and manganese in aluminum alloys?

What are the functions of magnesium and manganese in aluminum alloys?

Magnesium element Mg

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

The strengthening of magnesium to aluminum is obvious, 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 reinforcing effect. Therefore, manganese addition can reduce the magnesium content, while reducing the tendency to hot cracking, in addition, manganese can also make Mg5Al8 compound uniformly precipitate, improve corrosion resistance and welding performance.

Manganese element Mn

At the eutectic temperature of 658, the maximum solubility of manganese in the solid solution is 1.82%. The strength of the alloy increases with increasing solubility, and the elongation reaches a maximum at a manganese content of 0.8%. Al-Mn alloys are non-age-hardened alloys, i.e. they cannot be strengthened by heat treatment.

Manganese can stop the recrystallization process of aluminum alloys, increase the recrystallization temperature, and significantly refine the recrystallization grains. The refinement of recrystallized grains mainly hinders the growth of recrystallized grains through the dispersion of MnAl6 compounds. Another function of MnAl6 is to dissolve impurity iron to form (Fe, Mn)Al6 and reduce the harmful effects of iron.

Manganese is an important element of aluminum alloy, which can be added separately to form Al-Mn binary alloy, and more is added with other alloying elements, so most aluminum alloys contain manganese.