Effects of welding parameters on microstructure and mechanical properties of resistance spot welded magnesium alloy joints

Effects of welding parameters on spot welded magnesium alloy joints have been investigated. With increasing welding time, the weld nugget diameter increased and the nugget microstructure became coarser. The joint strength (shear load at failure) of 2930-3050 N was obtained when welding time was longer than six cycles. Increasing welding currents from 15 to 23 kA resulted in an increase in the joint strength due to an increase in the nugget diameter. In the range of 1.5-4.5 kN electrode force, lowering the electrode force favours increasing the weld nugget diameter and improving the joint strength, but too low electrode force (1.5 kN) easily causes metal expulsion. The joints have two failure modes (interfacial failure and button pullout failure) under tensile shear loading conditions. For the button pullout failure, the crack initiates at cellular dendritic structure of nuggets and propagates along the cellular dendritic structure, heat affected zone (HAZ) and base metal in sequence.