Joining of dissimilar metals between magnesium AZ31B and aluminum A6061-T6 using galvanized steel as a transition joining layer

A galvanized steel is used to join Mg AZ31B alloy and Al A6061-T6 alloy as a joining transition layer by cold metal transfer (CMT) method. Firstly, to optimize the process variables, extensive welding tests were performed by a design of experiment method. Then, microstructures, joining mechanisms and tensile properties were characterized and analyzed. Results indicated that Mg and Al alloys can be joined by using galvanized steel as a joining transition layer and cold metal transfer welding method. The formed joint is called as a Mg–steel–Al CMT joint. By using galvanized steel transition joining layer, Mg–Al brittle intermetallics Al₁₂Mg₁₇ and Al₃Mg₂ were inhibited. The properties of Mg–steel–Al CMT joints have been improved after optimizing the welding variables. The strength of Mg–steel–Al CMT joint is comparable to those of Al–Al joint and Mg–Mg joint. The strength of Mg–steel–Al CMT joint can reach 100% that of Al–Al joint and Al–steel joint, and reach 90% that of Mg–Mg joint and Mg–steel joint. The optimized Mg–steel–Al CMT welded joint with galvanized steel transition layer is fractured at the heat affected zone of Al base metal rather than at the weld-brazed interface, due to softening of Al base metal.