Improvement of the Microstructure and Mechanical Properties of Welded Joint of Wire Arc Additive Manufacturing-AZ31B Magnesium Alloy by Using AC/DC Mixed Current Waveform in Tungsten Inert Gas Welding

In this paper, a new waveform of AC/DC mixed waveform (MIX) is proposed to weld CMT-WAAM-AZ31B magnesium alloy components. CMT-WAAM-AZ31B magnesium alloy welded joints were prepared by AC-TIG and MIX-TIG. Welding parameters are scanning speed 3mm/s, current 180A, voltage 16V. The results show that the dendrites in the MIX weld are transformed into equiaxed grains under the stirring of the MIX current waveform, and the grain size in the weld is reduced from 33.95 to 26.03 mu m; at the same time, the multiple of uniform density (MUD) in the MIX weld is reduced from 9.67 to 5.36 compared with the AC weld, and the anisotropy of the MIX weld is reduced; the tensile strength and elongation of the MIX welded joint are increased by about 21 and 28%, compared with the AC welded joint; the hardness of AC weld is about 6HV higher than that of MIX weld. After the current waveform changes from AC to MIX, the dendrites in the weld are broken and the grain refinement is the main reason for the enhancement of the mechanical properties of the welded joint.