Ca和Al对Mg-Gd-Zn合金中的LPSO相及力学性能的影响

Influence of Ca and Al on LPSO Phase in Mg-Gd-Zn Alloys and Their Mechanical Properties

通过普通重力铸造方法熔炼制备了Mg96.5Gd2.5Zn1、Mg96Gd2.5Zn1Ca0.5和Mg95Gd2.5Zn1Ca0.5Al1(at%,下同)3种合金,考察了合金元素Ca与Al对铸态Mg-Gd-Zn合金中长周期堆垛有序结构相(LPSO)相形成的影响及经固溶热处理和热挤压后微观组织的演变及力学性能变化。结果表明,少量Ca添加到铸态Mg96.5Gd2.5Zn1合金中促进W相偏聚长大、结成网状,经固溶处理炉冷后形成粗大14H-LPSO胞结构和弥散分布于胞内的块状18R相,经挤压后形成长纤维状,显著提高了合金的强度和塑性。铸态Mg95Gd2.5Zn1Ca0.5Al1合金由等轴状a-Mg晶粒及分布于晶界的大量网状18RLPSO相、少量网状共晶Al2Gd相组成;经固溶处理后,网状18R相因部分分解转变为14H而形成取向随机、离散分布的条状18R相;其在挤压变形过程中促进14H、a-Mg晶粒发生显著动态再结晶而导致Mg95Gd2.5Zn1Ca0.5Al1合金相比于Mg96Gd2.5Zn1Ca0.5强度略低、塑性略高。

Three alloys of Mg96.5Gd2.5Zn1,Mg96Gd2.5Zn1Ca0.5 and Mg95Gd2.5Zn1Ca0.5Al1 were prepared by a conventional gravity casting method.The influence of Ca and Al alloying elements on long-period stacking ordered structure(LPSO)phase formation in as-cast Mg-Gd-Zn alloy and their microstructural evolution and mechanical properties after solution solution treatment and hot extrusion were investigated.The results show that a small amount of Ca added to the as-cast Mg96.5Gd2.5Zn1 alloy promotes W phase to segregate,grow and connect to networks,which further develops into coarse 14H-LPSO cell structure and block 18R phase dispersed in the cell after solid solution treatment,and into long fibers after extrusion that significantly improves the strength and ductility of the alloy.The as-cast Mg95Gd2.5Zn1Ca0.5Al1 alloy consists of equiaxeda-Mg grains,a large number of network18R LPSO phases distributed in the grain boundary,and a small amount of network eutectic Al2Gd phase.After solution treatment,part of the network 18R is decomposed into 14H to form a randomly oriented,discretely distributed 18R strips,which promote considerable dynamic recrystallization of 14H anda-Mg grains during extrusion deformation and result in the slightly lower strength and higher ductility of Mg95Gd2.5Zn1Ca0.5Al1 alloy compared to those of Mg95Gd2.5Zn1Ca0.5 alloy.