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利用光学显微镜、扫描电子显微镜,能谱分析仪、X射线衍射分析及差热分析研究了T4和T6热处理对真空压铸Mg-7Al-2Sn(AT72)合金组织和力学性能的影响。结果表明,真空压铸使得AT72合金组织更加致密,进而通过热处理可以进一步提高合金的力学性能。特别是T4固溶处理(400℃×20 h)后,晶粒尺寸变化较小,Al、Sn元素固溶到基体中产生固溶强化;同时,由于Mg17Al12相分解,使得高熔点的Mg2Sn颗粒相的析出强化效果更加明显。T4处理后的AT72合金的抗拉强度、屈服强度和伸长率达到276 MPa,202.6 MPa和10.6%,其比压铸态合金分别提高了18.2%,7.0%,24.7%。T6(400℃×20 h+200℃×15 h)处理后由于脆性相Mg17Al12的非连续析出以及Mg2Sn相粗化,使得合金的强度和塑性均有所下降。由于耐热相Mg2Sn的存在,提高了Mg17Al12相的开始熔化温度,使得AT72合金表现出比商用AZ91合金具有更好的高温力学性能。
The effects of heat treatment of T4 and T6 on the microstructure and mechanical properties of vacuum-cast Mg-7Al-2Sn (AT72) alloy were investigated by optical microscope, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis and differential thermal analysis. The results show that vacuum die-casting makes the structure of AT72 alloy more compact, and further improves the mechanical properties of the alloy by heat treatment. In particular, T4 solution treatment (400 ℃ × 20 h), the smaller changes in grain size, Al, Sn element solid solution into the matrix to produce solid solution strengthening; the same time, due to decomposition of Mg17Al12 phase, making the melting point Mg2Sn particle phase The precipitation hardening effect is more obvious. The tensile strength, yield strength and elongation of AT72 alloy reached 276 MPa, 202.6 MPa and 10.6% after T4 treatment, which were respectively 18.2%, 7.0% and 24.7% higher than that of the as-cast alloy. T6 (400 ℃ × 20 h +200 ℃ × 15 h) after treatment due to the non-continuous precipitation of brittle phase Mg17Al12 and Mg2Sn phase coarsening, making the alloy strength and ductility decreased. Due to the presence of Mg2Sn, the melting temperature of Mg17Al12 phase is increased, which makes AT72 alloy show better mechanical properties at higher temperature than commercial AZ91 alloy.