Hot cracking of resistance spot welded magnesium alloy

Crack features of resistance spot welded magnesium alloy joint and effects of welding parameters on susceptibility of the joint to hot cracking have been investigated. In the spot welded joints, solidification cracking in weld nugget and liquation cracking in heat-affected zone (HAZ) were often observed. The formation of solidification cracking is related to low melting point liquid films between dendrites due to segregation of Al and Mn atoms and tensile stress developed during cooling. In HAZ, the grain boundary melting occurred and grain became coarser. The liquation cracking appears in HAZ just adjacent to weld nugget and may be induced by solidification cracking at the edge of weld nugget. The welding parameters (heat input) have an obvious effect on susceptibility of weld nugget to hot cracking. The results show that relatively high heat input (i.e. relatively high welding current, long welding time or low electrode force) increase the hot cracking tendency. It is favorable to select relatively low heat input for reducing susceptibility of spot welded magnesium alloy joint to hot cracking.