Al-Si-Cu-Mg casting alloys which are commonly used contain several other elements, some of which are beneficial and others not. The effects of iron, manganese, zinc and titanium on mechanical properties and microstructures of Al-9.2Si-4Cu-0.5Mg alloy were investigated and the experimental results were analyzed statistically. The following results were obtained.
(1) Zinc content up to 2 percent and titanium content up to 0.2 percent have little effects on tensile properties and hardness of permanent mold castings of this alloy.
(2) With increasing iron content, hardness increases but tensile strength and elongation decrease.
(3) Tensile strength markedly decreases when iron content exceeds 0.5 percent.
(4) Manganese addition reduces the harmful effect of iron since the needle type structure of K compound and FeAl₃ compound is replaced by aluminum-manganese-iron compound.
(5) A small addition of manganese is usually considered to be desirable. Whereas in larger quantities, it has a harmful effect.
(6) A manganese addition of about 0.5 percent results in improved properties of this alloy.