真空压铸Mg-7Al(-2Sn)合金组织性能研究及第一性原理计算

利用光学显微镜、扫描电子显微镜、能谱分析、X射线衍射、差热分析及拉伸试验比较分析了2%Sn(质量分数)对真空压铸和固溶态Mg-7Al合金的组织与力学性能的影响。结果表明,向Mg-7Al合金中添加2%Sn元素后,能够细化晶粒,抑制Mg17Al12相的生长,在组织中形成新相Mg2Sn,其以颗粒状弥散分布于基体中;固溶处理后Mg-7Al合金中第二相数目明显减少,AT72合金基体中仍存在细小颗粒状Mg2Sn。由于合金组织细化、第二相数量的增加,Mg17Al12相形貌改善以及具有良好热力学性质的Mg2Sn相的析出的综合作用,使得AT72合金表现出比Mg-7Al合金更好的室温及高温拉伸力学性能;固溶处理后的AT72合金表现出更为优异的力学性能,主要强化机制包括:固溶强化和弥散强化。此外,利用第一性原理计算从微观理论角度探讨了Sn合金化Mg-7Al合金力学性能改善的原因。

Microstructure, Mechanical Properties and First Principle Calculation of Mg-7Al (-2Sn) Alloys Prepared by Vacuum Die-casting

The effects of 2 wt% Sn on the microstructures and the mechanical properties of the die-cast Mg-7Al alloy and the solution-treated alloy were studied by optical microscope (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and tensile tests. The results show that after 2 wt% Sn is added into the Mg-7Al alloys, the grains are refined, the growth of Mg17Al12 phase is suppressed and a few dispersed Mg2Sn particles with granular morphology are formed. After solution treatment the second phases of Mg-7Al alloys drastically decrease while fine granular Mg2Sn phases are still on the AT72 alloy matrix. AT72 alloy exhibits better tensile properties at both room and elevated temperature than Mg-7Al alloys due to the refinement of grains, increase of second phases, optimum morphology of Mg17Al12 and precipitation of Mg2Sn with better thermodynamic properties. The mechanical properties are improved after solid-solution treatment, which is attributed to solid-solution strengthening and dispersion strengthening. In addition, from the view of microscopic theory, the effect of Sn on the improvement of the mechanical properties of Mg-7Al alloy at elevated temperatures was discussed by first-principle calculation.