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采用光学显微镜、扫描电镜和X射线衍射仪研究了Sr对Mg-8Zn-5Al-1Si合金铸态组织和力学性能的影响。结果表明:Sr对初生相α-Mg枝晶,第二相类型、数量、大小和形貌均有影响。铸态合金主要由离异共晶τ-Mg32(Al,Zn)49相、规则共晶φ-Al2Mg5Zn2相和连续块状Mg2Si相组成。Sr的加入,抑制了Mg2Si相的形成,τ和φ减少,杆状或针状Al4Sr相和Mg17Sr2相增多。在Sr为2%时,合金在铸态下具有最佳的力学性能,其拉伸强度和屈服强度分别达到了185.85 MPa和147.68 MPa。从凝固过程和断口形貌角度讨论了α-Mg枝晶、第二相析出过程及其对力学性能的影响。
The effects of Sr on the as-cast microstructure and mechanical properties of Mg-8Zn-5Al-1Si alloy were studied by optical microscopy, scanning electron microscopy and X-ray diffraction. The results show that Sr has influence on the α-Mg dendrites, the type, number, size and morphology of the second phase in the primary phase. The as-cast alloy is mainly composed of divorced eutectic τ-Mg32 (Al, Zn) 49 phase, regular eutectic φ-Al2Mg5Zn2 phase and continuous massive Mg2Si phase. The addition of Sr suppresses the formation of Mg2Si phase, the decrease of τ and φ, and the increase of rod-shaped or acicular Al4Sr phase and Mg17Sr2 phase. When Sr is 2%, the alloy has the best mechanical properties in as-cast state, and the tensile strength and yield strength reach 185.85 MPa and 147.68 MPa respectively. The effects of α-Mg dendrites, the precipitation of second phase and their mechanical properties were discussed from the perspective of solidification and fracture morphology.