Determination and Characterization of Heat Input, Microstructure and Performance in Cold Metal Transfer Weld-Brazing of Dissimilar AA6061-T6 to SS304 Sheets

Aluminum-steel hybrid structures have great application prospects in lightweight vehicles. In this study, AA6061-T6 and SS304 with 3 mm thickness and 10 mm lap width were welded-brazed by Cold Metal Transfer process. Both electric parameters and droplets transfer were monitored. An improved discretization method was employed to calculate the equivalent welding parameters. Macro and microstructures were characterized by OM, SEM with EDS and XRD, and the tensile-shear strength, Vickers and nanohardness were measured to evaluate the mechanical properties of the joints. CMT welding process is a short-circuit transfer mode with one pulse one droplet. With the increase in heat input, welding cycle and interfacial layer thickness increased. Al9Fe2Si2 and FeAl5 or FeAl3 were found in the interfacial reaction zone. The intermetallic compounds whose hardness is 1.7 times of SS304 are the main reason for the fracture failure to appear at the interfacial layer.