固溶温度对挤压态Mg-13Al-6Zn-4Cu合金组织与性能的影响

采用不同的固溶温度对挤压态Mg-13Al-6Zn-4Cu(质量分数,%)合金进行热处理,然后在(150℃/10 h)条件下进行时效处理,通过金相显微镜、扫描电镜及能谱分析、维氏硬度与极化曲线测试,研究固溶温度对挤压态合金显微组织、硬度与腐蚀性能的影响。结果表明:固溶处理促进晶界处的β-Mg_(17)Al_(12)相充分溶入α-Mg基体中。提高固溶温度使基体晶粒再结晶长大,逐渐缩小T-MgAlCuZn相心部的Cu元素富集区,改变β析出相的形态和分布,促进层片状β相在α-Mg晶界析出,从而提高时效态合金的硬度。但固溶温度超过420℃时,合金晶粒粗化并发生过烧。固溶温度升高导致合金腐蚀电位负移,腐蚀电流增大,腐蚀速率加快。

Effects of solid-solution temperature on microstructure and properties of as-extruded Mg-13Al-6Zn-4Cu alloy

As-extruded Mg-13Al-6Zn-4Cu alloy (mass fraction, %) was heat treated at different solid-solution temperature, and then aged at 150 ℃ for 10h. The effects of solid-solution temperature on the microstructure, hardness and corrosion property of the alloy were studied using optical microscope, scanning electronic microscopy (SEM) equipped with energy dispersive spectroscope (EDS), Vickers hardness tests and electrochemical measurements. The results show that theβ-Mg17Al12 phase distributed along grain boundary can dissolve intoα-Mg through solid-solution. With increasing solid-solution temperature, recrystallization grains grow up and the size of Cu-rich area in inner of T-MgAlCuZn phase decreases gradually. The morphology and distribution ofβ-Mg17Al12 phase varies; and a large number of lamellarβ phase precipitates alongα-Mg grain boundary, improving the hardness of aging alloy. However, the grain of as-extruded alloy will be coarsened and over sintering when the solid-solution temperature is higher than 420 ℃. As solid-solution temperature increases, the corrosion potential of alloy shifts to a more negative orientation with a higher corrosion current, resulting in a higher corrosion rate.