Mg-Al-Sm系耐热镁合金的显微组织和力学性能

摘要

The microstructures and phase compositions of the as-cast and die-cast Mg−6.02Al−1.03Sm, Mg−6.05Al−0.98Sm−0.56Bi and Mg−5.95Al−1.01Sm−0.57Zn alloys were investigated. Meanwhile, the tensile mechanical and flow properties were tested. The results show that the as-cast microstructure of Mg−6.02Al−1.03Sm alloy is composed ofα-Mg matrix, discontinuousβ-Mg17Al12 phase and small block Al2Sm phase with high thermal stability. Rod Mg3Bi2 phase precipitates when Bi is added, while the added metal Zn dissolves intoα-Mg matrix andβ-Mg17Al12 phase. The as-cast alloys exhibit the excellent tensile mechanical property. The tensile strength (σb) and elongation (δ) can reach 205−235 MPa and 8.5%−16.0%at ambient temperature, respectively. Meanwhile, they can also exceed 160 MPa and 14.0%at 423 K, respectively. The die-cast microstructures are refined obviously, and meanwhile the broken second phases distribute dispersedly. The die-cast alloys exhibit better tensile mechanical properties with the values ofσb andδof 240−285 MPa and 8.5%−16.5%at ambient temperature, respectively, and excellent flow property with the flow length of 1870−2420 mm. The die-cast tensile fractures at ambient temperature exhibit a typical character of ductile fracture.%分析铸态和压铸态Mg−6.02Al−1.03Sm、Mg−6.05Al−0.98Sm−0.56Bi和Mg−5.95Al−1.01Sm−0.57Zn合金的显微组织和相组成，测试其拉伸力学性能与流动性能。结果表明，Mg−6.02Al−1.03Sm合金铸态组织由α-Mg基体、半连续的β-Mg17Al12相和高热稳定性的小块状 Al2Sm 相组成。添加 Bi 后生成杆状 Mg3Bi2相，而添加的 Zn固溶于α-Mg基体和β-Mg17Al12相中。铸态合金呈现优异的拉伸力学性能，室温时其抗拉强度(σb)和伸长率(δ)分别达到205~235 MPa和8.5%~16.0%，而423 K时分别超过160 MPa和14.0%。压铸态组织明显细化，第二相发生破碎，且弥散分布。压铸态合金呈现更高的拉伸力学性能和优异的流动性能，室温σb和δ分别达到240~285 MPa和8.5%~16.5%，流动长度可达1870~2420 mm。压铸态室温拉伸断口呈现明显的断裂特征。