Abstract: Microstructural studies have been made on the Mg-0.54Zr,Mg-5.68Zn and Mg-5.65Zn-0.50Zr alloys in the as-cast and homogenized states.The lenticular plates of {012}twins were found in three alloys.After homogenization,ZrH_2 phase formed in the Mg-0.54Zr alloy.The Mg_7Zn_3 phase of cubic structure with a=1.417 nm distributes at the grain boundaries of the Mg-5.68Zn alloy in the as-cast state and after homogenization,the Mg_7Zn_3 phase dissolves and the MgZn_2 phase occurs.The as-cast Mg-5.65Zn-0.50Zr al- loy consists of MgZn_3 phase and Zn-Zr compounds.After homogenization,the dispersed acicular MgZn_2 phase may precipitate.

Key words: Mg-Zn-Zr alloy, phase structure, twin