Microstructure and mechanical properties of wire and arc additive manufactured AZ31 magnesium alloy using cold metal transfer process

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.