Wire and arc additive manufacturing (WAAM), using cold metal transfer (CMT) as heat source, exhibits a great potential for additive manufacturing of magnesium alloys due to low heat input. With the purpose of revealing the relationship between the microstructure and mechanical properties of WAAMed AZ31 material, the present study has been carried out. The manufactured AZ31 thin-walled deposit is mainly composed of columnar dendrite arrays, including dendritic α-Mg matrix, interdendritic eutectics (α-Mg and β-Mg₁₇Al₁₂) and some dispersive η-Al₈Mn₅ phases. The average primary dendrite arm spacing increases from 17 μm at the bottom to 39 μm at the top of the deposit, and the volume fraction of the interdendritic eutectic decreases from 52.1% to 39.3%. The microstructure of each layer except the top layer consists of vertical columnar dendrites and direction-changed columnar dendrites in sequence. The top layer appears equiaxed dendrites due to columnar to equiaxed transition (CET). The tensile properties present obvious anisotropic characteristics because of the epitaxial columnar dendritic growth along the building direction. The tensile properties also show obvious variation from the bottom to the top of the deposit because of the differing microstructures in different regions. The results are further analyzed in detail through the microstructure evolution resulted from the new manufacturing method.

使用冷金属转移（CMT）作为热源的电弧焊和电弧增材制造（WAAM）由于热量输入少，具有很大的潜力用于镁合金的增材制造。为了揭示WAAMed AZ31材料的微观结构和力学性能之间的关系，进行了本研究。所制造的AZ31薄壁沉积物主要由柱状晶阵列，包括树突α-Mg基体，枝晶间共晶体（α-Mg和β-Mg系的₁₇的Al ₁₂）和一些分散η-Al系₈的Mn ₅阶段。平均一次枝晶臂间距从沉积物底部的17μm增加到沉积物顶部的39μm，树突间共晶的体积分数从52.1％降低至39.3％。除顶层以外的各层的微观结构依次由垂直的柱状树枝状体和方向变化的柱状树枝状体组成。由于柱状到等轴转变（CET），顶层出现等轴树突。拉伸性能表现出明显的各向异性特征，这是由于沿构造方向的外延柱状枝晶生长。由于在不同区域的微观结构不同，所以拉伸性能从沉积物的底部到顶部也显示出明显的变化。