Effect of Modification on Microstructure and Properties of AZ91 Magnesium Alloy

Refinement of alpha-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 withAnalySIS Pro(R)software and mechanical properties' investigation. The microstructure of AZ91 alloy in the as-cast condition consists of alpha-Mg solid solution with precipitates of Mg17Al12,Mg2Si and Al(8)Mn(5)phases. It was reported that all applied modifiers cause refinement of alpha-Mg solid solution grains and a decrease of the volume fraction of alpha-Mg+Mg(17)Al(12)compound discontinuous precipitates. The best results were obtained in the case of wax-CaF2-carbon powder.