Exploring the impact of multiple parameter combinations with constant heat input on weld integrity of Mg alloy welded joints prepared by cold metal transfer technology

Abstract

Reasonably controlling heat input is crucial for optimizing the weld quality of Mg alloys with thermal sensitivity. But it falls to meet diverse requirements of industrial welded structures. This study synchronously adjusts welding current, voltage and speed with constant heat input to achieve further regulation on weld quality of Mg alloy thin plate welded joints. Increasing three parameters significantly expanded melting width and area, with a lower heat-affected zone under full penetration. And equiaxed grains gradually replaced columnar grains at the fusion line. More precipitate phases formed in the weld zone at the same time, inducing a greater hardness. Moreover, higher arc energy promoted recrystallization, weakening the crystallographic texture and internal stress of welded joints. Especially at a wire feed rate of 7 m/min, the subgrain boundary content and kernel average misorientation were far lower than other joints. Although these evolutions had minimal impacts on tensile strength, elongation and yield strength exhibited a fluctuating state that initially decrease then raise. A superior tensile behavior was achieved at a wire feed rate of 6 m/min. The findings highlight significant impacts of varying welding parameters on weld quality under constant heat input, offering new insights for optimizing Mg alloy welding to meet diverse structural needs.