Effect of Welding Speed on Microstructure and Mechanical Properties of AE-CMT-Welded AZ31B Magnesium Alloy Joints

In order to verify the reliability and engineering applicability of the AE-CMT welding technology for magnesium alloy joining, AE-CMT welding experiments were conducted at welding speeds ranging from 0.5 to 3.0 m/min on 1.5 mm-thick H24-temper AZ31B magnesium alloy sheets using imported 1.2 mm-diameter WE-33M welding wire. Within the welding speed range of 0.5–3.0 m/min, increasing the welding speed progressively reduces heat input, thereby refining grains and homogenizing the microstructure. The welding heat input of the AE-CMT process ranges from 0.47 KJ/mm to 1.07 KJ/mm, and the grain sizes of the weld zone and HAZ are 9.61–14.18 μm and 6.35–12.22 μm, respectively. In the range of 0.5–2.0 m/min welding speed, increasing welding speed progressively enhances the tensile strength of the welded joint. Notably, joints fabricated at a welding speed of 2.0 m/min deliver the maximum tensile strength, equivalent to 98.0% of the base metal. Well-defined dimples are also detected on the corresponding fracture surfaces. A further increase in welding speed leads to a gradual reduction in the tensile strength of the welded joint. It is demonstrated that welding speed acts as a critical process parameter for tailoring the microstructure and mechanical properties of AE-CMT-welded AZ31B magnesium alloy joints.