制备了3种成分的Mg-Gd-Zn三元合金, 并对其显微组织和力学性能进行了较系统的研究. 结果表明, Mg-(11-13)Gd-1Zn(质量分数, %)三元合金的铸态组织由 α-Mg, (Mg, Zn)3Gd和具有14H结构的长周期堆垛有序相(14H-LPSO)组成; (Mg, Zn)3Gd呈现典型的网状共晶形貌, 其体积分数随Gd含量的增加而增大. 热挤压过程中(Mg, Zn)3Gd相破碎, 其颗粒沿挤压方向排列, 而14H-LPSO相则分布于条状分布的(Mg, Zn)3Gd颗粒之间. 铸态和挤压态合金在高温固溶处理后, 14H--LPSO相的体积分数增加, 大部分(Mg, Zn)3Gd相溶入基体. 挤压态合金经固溶和时效(T6)处理后, 显微组织中14H--LPSO相的体积分数大幅度增加, 而且出现了β'和β1沉淀颗粒. 对挤压后的合金直接进行时效处理(T5)过程中也形成了β'和β1沉淀, 但14H-LPSO相没有显著增加. 3种合金中 Mg-11Gd-1Zn合金在T6态的性能最好, 抗拉强度高达 416 MPa.
Three ternary alloys with composition of Mg-(11-13)Gd-1Zn (mass fraction, %) have been prepared and their microstructures and mechanical properties have been also investigated. The results showed that the as cast microstructure of the three alloys consists of α-Mg matrix, (Mg, Zn)3Gd eutectic and a 14H long--period stacking ordered (14H--LPSO) phase. With the increase of Gd content the volume fraction of the (Mg, Zn)3Gd eutectic increases. After extrusion the (Mg, Zn)3Gd eutectic networks are destroyed and its broken particles are arranged in strips along the direction of extrusion, and the 14H--LPSO phase is distributed between (Mg, Zn)3Gd strips. Solid solution treatment at high temperature above 500 ℃ results in the dissolution of (Mg, Zn)3Gd phase into the matrix and the increase of the 14H-LPSO phase. After solution treated alloys are aged at temperature of 225 ℃ (T6 treatment) the volume fraction of the 14H-LPSO phase is further increased and both β' and β1 precipitates appear in the microstructure. Aging of as extruded alloys (T5 treatment) also causes the formation of β' and β1 precipitates but the volume fraction of the 14H--LPSO phase in the T5 treated specimens is lower than that in specimens after T6 treatment. High tensile strength combined with good ductility is obtained from the Mg--11Gd--1Zn alloy after T6 aging.
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