中文摘要：

镁合金由于其具有密度小，比强度、比刚度高，减振性、导热性、电磁屏蔽和抗辐射能力强，易切屑加工，易回收，资源丰富等一系列优点，成为21世纪最具开发前景的轻质结构材料，但由于镁合金合金系列少、强度低，限制了镁合金应用的范围。概述了近几十年AZ91镁合金的增强改性研究进展状况，分析了变质、机械震动、熔体混合等物理改性方法和添加Ca＋Si（Re）、Cd＋MM、Y、Sc等化学改性方法的原理及其优缺点，讨论了各种物理及化学改性后对AZ91镁合金组织性能的影响。

英文摘要：

The magnesium alloy has its most developing prospect in the 21st century because of its lower density, high of specific strength and specific stiffness, high modulus, good heat conductivity, well electromagnetic shielding, superior damping characteristic, good machinability and rich in natural resources. However, its continuous application is limited because of fewer alloy series and lower strength. This paper summarizes the condition of AZ91-magnesiurn-alloy strengthen by modification, analyzes the principle of physical and chemical modifications such as alteration,mechanical vibration, special molten liquid heat treatment, alloying agent Ca＋Si（ Re）,Cd＋ MM, Y and Sc, and evaluates the merits and demerits of modification methods. The paper also discusses the influence of physical and chemical modifications on the AZ91-magnesium-alloy performance.