Microstructure refinement of Mg–Al–Zn–Si alloys

Magnesium alloys containing Mg ₂Si particles, as a promising cheap heat-resistant magnesium alloy for automobile engine applications, are attracting more and more attention of both material scientists and design engineers. Refinement of the Chinese script Mg ₂Si particle is a key for using this alloy in sand casting or permanent mould casting. In the present work, the refinement effect of antimony(Sb) or calcium(Ca) on the microstructure was investigated. The study shows that Sb or Ca addition promotes the formation of fine polygonal type Mg ₂Si particles by providing the nucleation sites. Moreover, the grain sizes of Sb or Ca modified Mg–Al–Zn–Si alloys are much finer than that of base alloy. The effect of modification and refinement with Sb addition is more effective than that with Ca addition. Such improved microstructure of the modified alloys results in large improvement in tensile properties and toughness as compared to the base alloy.