研究了微量添加Zn和Nd元素对于砂型铸造Mg-5Gd-4Y-Zr(mass％)镁合金显微组织,时效硬化行为和力学性能的影响规律.结果表明:Zn或者Nd元素的微量添加可以明显改变铸态Mg-5Gd-4Y-Zr合金的晶粒尺寸和第二相的种类、形貌、数量,进而提升其室温拉伸力学性能.对3种合金的固溶处理工艺进行优化,发现Mg-5Gd-4Y-0.8Nd-Zr合金在二级固溶处理条件时会发生铸造表皮附近晶粒异常长大的现象,该现象可以通过改为单级固溶消除;此外,该微合金化还可以显著提升Mg-5Gd-4Y-Zr合金的时效硬化响应能力以及合金峰值时效态的室温和高温强度,而且Nd元素的强化效果更好,其中Mg-5 Gd-4Y-0.8Nd-Zr合金的室温和250℃下的抗拉强度、屈服强度、断裂伸长率分别可以达到303 MPa、215 MPa、1.2％和283 MPa、200 MPa、7.2％.
Effect of trace addition of Zn and Nd on microstructure,age hardening response and mechanical properties of sand casting Mg-5Gd-4Y-Zr magnesium alloys was investigated.The results show that the trace addition of Zn and Nd obviously refines the grain size and changes the kinds,morphology and quantities of the precipitation phase of the as-cast Mg-5Gd-4Y-Zr alloy,and improves its tensile mechanical properties at room temperature.The solution treatments of the alloys are optimized based on experiments,and it is found that the grains near the surface of the casting tensile bar grow up for the Mg-5Gd-4Y-0.8Nb-Zr alloy after two stage solid solution treatment,which can be avoided by single stage solid solution treatment.Moreover,the trace addition of Zn and Nd can significantly improve the aging hardening response of the Mg-5Gd-4Y-0.5Zr alloy as well as its strength at ambient and elevated temperature,and the strengthing effect of Nd addition is better than that of Zn.The ultimate tensile strength,yield strength and elongation of the Mg-5Gd-4Y-0.8Nd-Zr alloy are 303 MPa,215 MPa and 1.2％ at room temperature and 283 MPa,200 MPa and 7.2％ at elevated temperature,respectively.
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