Weld formation, microstructure and mechanical properties of magnesium alloy and Al-Si-coated steel dissimilar lap joints fabricated by the CMT weld-brazing process

Magnesium alloy and Al-Si-coated steel dissimilar lap joints were joined using the CMT welding process. The weld formation, microstructure and mechanical properties of Mg/steel CMT weld-brazing joints were investigated. The wetting and spreading behaviour of the molten magnesium alloy filler material on the steel substrate were evidently improved owing to the presence of the Al-Si coating. The Fe-Al intermetallic reaction layer formed at the interface and enhanced metallurgical bonding between the magnesium alloy and steel. The effects of the Al-Si coating and welding heat input on interface layer characteristics were particularly assessed. When the heat input was 178.1 J/mm, the tensile shear strength of the Mg/steel welded joints reached 359.3 N/mm. The fracture modes and failure mechanism for tensile shear specimens were analysed and discussed in detail.