Effect of modification on microstructure and properties of AZ91 magnesium alloy

Refinement of α-Mg solid solution grains has a significant influence on the improvement of mechanical properties of cast magnesium alloys. In the article, the effects of three modifiers on microstructure and properties of AZ91 magnesium alloy casted to a sand mould were described. Overheating, hexachloroethane and wax-CaF₂-carbon powder were applied. The research procedure comprised microstructure analysis by means of light microscopy, scanning electron microscopy and quantitative analysis with AnalySIS Pro® software and mechanical properties’ investigation. The microstructure of AZ91 alloy in the as-cast condition consists of α-Mg solid solution with precipitates of Mg₁₇Al_12, Mg₂Si and Al₈Mn₅ phases. It was reported that all applied modifiers cause refinement of α-Mg solid solution grains and a decrease of the volume fraction of α-Mg+Mg₁₇Al₁₂ compound discontinuous precipitates. The best results were obtained in the case of wax-CaF₂-carbon powder.