中文摘要：

研究了高强高韧Mg-8．5Gd-2．0Y-1．0Ag-0．4Zr（wt．％）合金的显微组织和力学性能。结果表明，该合金铸态组织细小，主要由α-Mg固溶体、晶界析出相Mg5（GdY）以及分布在晶粒内部的Zr核组成；T4态时晶界析出相基本完全消失，但出现了一些方块相丫；合金具有明显的时效硬化效果，且随着时效温度的提高，合金的峰值时效硬度下降，峰值时间相应缩短。经200℃峰值时效处理后表现出极为优异的室温力学性能，抗拉强度（UTS）和延伸率分别达到396MPa和9．1％，显著的时效强化是该合金具有优异力学性能的主要原因。如此优异的强度和塑性在常规铸造镁合金中是极为罕见的，对于推广镁合金的应用具有重要意义。

英文摘要：

The microstructure and mechanical properties of Mg-8.5Gd-2.0Y-1. 0Ag-0.4Zr （wt. % ） were investigated. The results show that this ascast alloy has fine microstructure and consists of a-Mg solid solution, grain boundary precipitates Mg5（GdY）, and intracrystalline zirconium-rich cores. After solution treatment, the grain boundary precipitates almost disappear completely and some cubic shaped 7 compounds are observed. The alloy shows remarkable age hardening response, and the age hardness, as well as the time to peak decrease with the increasing age temperature. After peakaged at 200℃, the alloy exhibits very attractive mechanical properties, whose ultimate tensile strength （UTS） and elongation reach 396MPa and 9.1% respectively at room temperature, with the remarkable precipitation strengthening being the major contributor to its excellent mechanical properties. Such excellent combination of strength and ductility is peculiar for ordinary casting Mg alloys, and would be of great significance for the extensive applications of Mg alloys.