| Summary: | 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-CaF<sub>2</sub>-carbon powder were applied. The research procedure comprised microstructure analysis by means of light microscopy, scanning electron microscopy and quantitative analysis with <i>AnalySIS Pro<sup>®</sup></i> software and mechanical properties’ investigation. The microstructure of AZ91 alloy in the as-cast condition consists of α-Mg solid solution with precipitates of Mg<sub>17</sub>Al<sub>12,</sub> Mg<sub>2</sub>Si and Al<sub>8</sub>Mn<sub>5</sub> 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+Mg<sub>17</sub>Al<sub>12</sub> compound discontinuous precipitates. The best results were obtained in the case of wax-CaF<sub>2</sub>-carbon powder.
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