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

• Various parameter combinations were performed for welding Mg alloy thin plates based on constant heat input, which offers flexibility to meet the diverse welding requirements. • Greater melting widths and areas were obtained after increasing welding current, voltage and speed synchronously. • Columnar grains transformed into equiaxed grains at fusion line as the increase of parameters, and lower stress and HAZ were obtained. • Increasing parameters contributed to the formation of precipitate phases along grain boundaries, enhancing the hardness. • Elongation and yield strength of weld joints first fell and then raised with rising three welding parameters. 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.