低合金化镁合金熔化焊接组织调控的研究进展

低合金化镁合金因其可加工性好、耐蚀性优异和成本低等优势,成为变形镁合金发展的重要趋势之一。焊接连接已成为推广应用这类材料的关键。然而,低合金化镁合金在焊接过程中存在焊缝晶粒粗大、有效强化相较少等组织软化问题,导致焊接强度不匹配等。本文基于镁合金焊接冶金学的相关理论,重点总结了调控低合金化镁合金焊缝组织的方法,并系统论述了焊缝组织演变过程和机理。最后,针对这类合金在焊接方面的应用需求,对该领域的发展趋势进行了展望。

Effect of addition temperature on dispersion behavior and grain refinement efficiency of MgO introduced into Mg alloy

The effect of addition temperature of MgO particles(MgOp)on their dispersion behavior and the efficiency of grain refinement in AZ31 Mg alloy was investigated.In addition,the grain refinement mechanism was systematically studied by microstructure characterization,thermodynamic calculation,and analysis of solidification curves.The results show that the grain size of AZ31 Mg alloy initially decreases and then increases as the MgOp addition temperature is increased from 720 to 810℃,exhibiting a minimum value of 136μm at 780℃.The improved grain refinement efficiency with increasing MgOp addition temperature can be attributed to the reduced Mg melt viscosity and enhanced wettability between MgOp and Mg melt.Furthermore,a corresponding physical model describing the solidification behavior and grain refinement mechanism was proposed.

铸造Mg-5Cu-3Zn合金第二相表征及细晶机理研究

以铸态Mg-5Cu-3Zn合金为对象、Mg、Mg-5Cu和Mg-3Zn为参照,对显微组织(尤其是第二相)进行了表征,并探讨了Cu和Zn的细晶机理。结果表明:向纯Mg中加入Cu、Zn和Cu、Zn复合添加后,晶粒依次由柱状晶转变为等轴晶。Mg-3Zn中第二相呈颗粒状分布于基体中,物相组成为α-Mg+MgZn;Mg-5Cu中第二相形貌呈网状,物相为α-Mg+CuMg_(2);Mg-5Cu-3Zn晶界上的第二相呈现出2种不同的形貌:连续的块状CuMg_(2),不连续的鱼骨状CuMgZn。Zn对Mg的晶粒细化机理主要是Zn在固液界面前沿偏聚引起的“成分过冷效应”;Cu对Mg的晶粒细化机理主要是Cu在固液界面前沿偏聚引起的“成分过冷效应”和CuMg_(2)对晶界的钉扎作用;Cu与Zn复合添加的细晶效果更好,是由于Cu和Zn的复合添加导致“成分过冷效应”及第二相对晶界的钉扎作用更为强烈。