Mg-5Al-0.8Ca-0.2La-xSr合金的显微组织及高温力学性能

Microstructure and high temperature mechanical properties of Mg-5Al-0.8Ca-0.2La-xSr alloy

采用真空熔化、精炼和无氧化重力铸造工艺，制备了不同Sr含量的Mg-5Al-0．8Ca-0．2La镁合金试样。研究了Sr对该镁合金的显微组织、室温与150～200℃温度区间内力学性能的影响。结果表明：基体合金组织除含α-Mg相外，主要由骨骼状和条状的Al2Ca相、点状的Al11La3颗粒相以及少量的β-Mg17Al12相组成；Sr的加入显著细化了基体合金的显微组织，抑制β-Mg17Al12相的析出，并在晶界上析出Mg-Al-Sr三元耐热相，提高了合金的高温力学性能；随着Sr含量的增加，虽然合金的室温抗拉强度和伸长率呈下降趋势，但合金的高温抗拉强度（σb）和屈服强度（σ0．2）得到明显提高；当Sr含量在0．5％时，合金的综合力学性能最佳。

The Mg-5Al-0.8Ca-0.2La-xSr alloys with different Sr contents were melted, refined and non-oxygen-cast under vacuum environment. The effects of addition of Sr on the microstructures and mechanical properties at both room and elevated temperature of 150-200 ℃ for the magnesium alloys were investigated. The results show that the base alloy is composed of Al2Ca and Al11La3 phases, which looks like bones and stripes and small points, respectively, and a small quantity of β-Mg17Al12 phase except α-Mg phase. With addition of Sr, the base alloy is refined remarkably, β-Mg17Al12 phase is restrained, a new heat-resistant phase （Mg-Al-Sr） forms at the grain boundary, which improves the high temperature mechanical properties of alloy. With increasing mass fraction of Sr, the tensile strength and elongation at room temperature decrease. Whereas the tensile strength and yield strength at elevated temperature are improved remarkably. When the mass fraction of Sr is 0.5%, the alloy has the best general mechanical properties.