Zn含量对GW93系合金微观组织和力学性能的影响

Effect of Zn Content on the Microstructure and Mechanical Properties of GW93-xZn Alloys

为提高镁稀土合金的强韧性,文中通过铁模铸造法制备了三种Mg-9Gd-3Y-xZn-0.6Zr合金,(质量分数w(Zn)分别为0.5%,1.87%,3.75%)。利用XRD、SEM、TEM和万能试验机等表征了铸态和热处理态合金微观组织与力学性能,分析了Zn含量对Mg-9Gd-3Y-0.6Zr合金非平衡凝固条件下相组成及含量的影响规律。研究结果表明:铸态合金组织由α-Mg基体和分布于枝晶界的Mg24(Gd,Y,Zn)5、Mg5(Gd,Y,Zn)共晶相和18R-LPSO相组成。当Zn含量为0.5%时在晶界处形成少量18R-LPSO,随着Zn含量的增加,18R-LPSO相的含量逐渐增加,形貌由片层状转变为网状分布的块体,Mg-9Gd-3Y-3.75Zn-0.6Zr合金中18R-LPSO相的体积分数为40%。480℃固溶热处理4h后共晶相发生溶解,枝晶界上18R-LPSO相增多;225℃时效处理40 h后在Zn含量为0.5%、1.87%的合金中析出与基体呈半共格位向关系的β′相,实现了棱柱面析出β′与基面形成LPSO相共存的组织结构,且可通过Zn含量调控两相的比例;时效热处理后Mg-9Gd-3Y-3.75Zn-0.6Zr合金的抗拉强度、屈服强度和延伸率分别为218 MPa、129 MPa和9.2%。结论可为Mg-Gd-Y-Zn-Zr合金强度与塑韧性设计与优化提供参考。

The study aims to improve the strength and toughness of magnesium rare earth alloys.Three kinds of Mg 9Gd 3Y x Zn 0.6Zr(w(Zn)=0.5,1.87,3.75%)alloys were prepared by steel mould casting.The microstructures and mechanical properties of the as cast and heat treated alloys prepared were characterized by XRD,SEM,TEM and a universal testing machine.The effects of Zn content on the phase constituents and volume fraction of Mg 9Gd 3Y 0.6Zr alloys under the non equilibrium solidification condition were analyzed.The results show that the as cast alloys were composed of 0x0E䥺SymbolaA@0x0F Mg matrix and Mg 24(Gd,Y,Zn)5,Mg 5(Gd,Y,Zn)eutectic phase and 18R LPSO phase distributing along dendrite boundaries.A small amount of 18R LPSO is formed at grain boundaries when the Zn content is 0.5%.With Zn content increasing,the amount of 18R LPSO phase increased,its morphology changed from lamellar to net like bulk structure,and its volume fraction reached 40%in Mg 9Gd 3Y 3.75Zn 0.6Zr alloy.After solid solution heat treatment at 480℃for 4 hours,the eutectic phase dissolved and the volume fraction of 18R LPSO phase increased.Through aging treatment at 225℃for 40 hours,precipitation ofβ′phase in semi congruent orientation with the matrix in alloys with 0.5%and 1.87%Zn content,the microstructure with both theβ′phase precipitated on the prismatic plane and LPSO phrase formed on the basal plane of Mg matrix was constructed.The ratio of the two phases could be altered by adjusting the content of Zn.After aging treatment,the tensile strength,yield strength and elongation of Mg 9Gd 3Y 3.75Zn 0.6Zr alloys were 218MPa,129MPa and 9.2%,respectively.These results can provide a new approach to optimizing the strength and ductility of Mg Gd Y Zn Zr alloys.