Microstructure and mechanical properties of magnesium alloy to galvanized steel dissimilar lap joints fabricated by CMT weld-brazing process

Mg/steel dissimilar material joining structure can effectively reduce the vehicle weight, which is one of the ways to realize automotive lightweight. In this work, Mg/galvanized steel joints were joined by CMT welding method. The macroscopic morphology, microstructure, interface and mechanical properties of welded joints were investigated. Results indicate that the wetting and spreading properties of molten metal on the surface of steel plate could be improved by Zn coating. Zn coating reacted with the molten filler material and formed Zn-rich zones at weld toe (both ends) of the joint. An uneven reaction layer was generated by the interfacial formation of Mg 32 (Al, Zn) 49 . The Al element in molten metal reacted with Fe and Mn elements at the liquid-solid interface to form Fe-Al/Al-Mn phase, which enhanced the metallurgical bonding of the inter-face. The joint strength reached a maximum value of 323.5N/mm. The fracture modes and behaviour of the joints were discussed.