摘要
Microstructures of as-cast and extruded ZK60-xRE （RE=Dy, Ho and Gd, x=0-5, mass fraction） alloys were investigated. Meanwhile, the impact toughness was tested and then the relationship was discussed. The results show that as-cast microstructure is refined gradually with increasing the RE content. Mg-Zn-RE new phase increases gradually, while MgZn2 phase decreases gradually to disappear. Second phase tends to distribute along grain boundary in continuous network. Extruded microstructure is refined obviously to reach the micron level. Broken second phase tends to distribute along the extrusion direction in zonal shape. Impact toughness value -nK increases from 9-17 J/cm2 for as-cast state to 26-54 J/cm2 for extruded state. With increasing the value of -nK, fracture macro-morphology changes from a rough plane via multi-plane with step to V-type plane; and from single radiation zone to two zones of fiber and shear lip, respectively. Fracture micro-morphology changes from the brittle fracture to the ductile fracture. Fine grain and few fine dispersed second phase can enhance the impact toughness of magnesium alloys effectively.
分析铸态和挤压态ZK60-xRE（RE=Dy、Ho和Gd,x=0-5）合金的显微组织,测试其冲击韧性,并讨论两者间的关系。结果表明,随着RE含量的增加,铸态组织逐渐细化;Mg-Zn-RE新相逐渐增多,而MgZn2相逐渐减少直至消失,第二相趋于连续网状分布于晶界处。挤压态组织显著细化至微米级,破碎的第二相沿挤压方向趋于带状分布。冲击韧性值-nK由铸态时的9~17J/cm2提高至挤压态时的26~54J/cm2。随着-nK值的增加,断口宏观形貌由一粗糙平面经台阶多面向V型面转变,同时由单一放射区向纤维区和剪切唇区组成的两区转变;断口微观形貌由脆性断裂向韧性断裂转变。细小晶粒和细小弥散的第二相将有效提高镁合金的冲击韧性。
基金
Projects(2010A090200078,2011A080403008)supported by the Major Science and TechnologyProject of Guangdong Province,China
