Mechanical Properties and Microstructure of Mg-Al-Zn-Si-base Alloy

Abstract

Magnesium alloys containing Mg₂Si particles, as a promising low cost 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 Mg₂Si particle is a key for using this kind of alloy in sand casting or permanent mould casting. In the present work, a new type of heat-resistant magnesium alloy with low cost based on Mg–Al–Zn–Si was developed. The effect of Sb addition and mischmetal (MM, a mixture of rare-earth, RE elements) microaddition to a Mg–Al–Zn–Si alloy was investigated systematically from the viewpoints of microstructure, solidification process, mechanical properties and corrosion resistance. Microstructure observation revealed that Sb promoted the formation of fine polygonal type Mg₂Si particles by providing the nucleation sites. Meanwhile, the grain sizes of modified Mg–Al–Zn–Si–Sb alloy are much finer than those of base alloy. Such improved microstructure brings about the significant improvement in tensile properties, toughness and creep resistance at elevated temperatures up to 200^°C, which is superior to or comparable to AE42 alloy. Moreover, the corrosion resistance of the new alloy is improved significantly by the MM microaddition.