中文摘要：

本文应用扫描背散射电子（SEM-BSE）像和透射电子显微（TEM）像观察的方法,研究了铸态Mg96 Zn3Y1（at.%）合金经过500℃高温热处理后显微组织结构的变化。结果表明铸态Mg96 Zn3Y1（at.%）合金中的初生相为网格状形貌,其中多数为面心立方W（Mg3Zn3Y2）相,少数为二十面体准晶I（Mg3Zn6Y）相。经过500℃＋4h高温热处理后,初生相整体网格状形貌不发生明显的变化,但准晶I相消失。同时,Mg基体中析出大量弥散分布的具有面心立方结构的片状W’相,高分辨电子显微（HREM）像表明W’相沿基体（001）Mg面以台阶方式生长,并与Mg基体具有半共格界面关系。取向关系满足：[233]W’∥[110]Mg,（311）W’∥（110）Mg,（022）W’∥（001）Mg。

英文摘要：

SEM-BSE,TEM and HREM observations have been carried out to characterize the microstructural variations for the as-cast Mg96Zn3Y1（at.%） alloys subjected to high-temperature heat treatment at 500℃.The results show that the characteristic network structure formed in the as-cast Mg96Zn3Y1 alloy is constructed with most primary W-phase（fcc,Mg3Y2Zn3 type） and a small amount of coexisting icosahedral quasicrystal phase（I-phase）.After heat treated at 500℃ for 4 h,the network structure retained without apparent morphological variation even through the I-phase melted down and disappeared.In addition,a large number of platelet-shaped fcc W＇-phases were observed to precipitate in the matrix due to the heat treatment,and relative increase of Zn-concentration in the Mg matrix was also detected.These variations are responsible for the significant hardness enhancement of the heat-treated alloy.HREM observations indicate a ledge growth mechanism for the platelet-shaped W＇-phase whose interface exhibits a semi-coherent relationship with the Mg-matrix.The orientational relationships between the W＇ precipitate phase and the Mg-matrix have been determined to be as follows： W＇∥Mg,（311）W＇∥（110）Mg,（022）W＇∥（001）Mg.