3D multi-scale multi-physics modelling of hot cracking in welding

A 3D multi-scale and multi-physics numerical model has been developed and validated to predict the occurrence of hot cracking during fusion welding of Al-Mg-Si alloys. The new model consists of four modules: (I) a welding solidification module that creates the desired weld microstructure consisting of both columnar and equiaxed grains and varies as a function of welding conditions; (II) a thermo-mechanical analysis module that predicts the deformation of the weld mushy zone due to solidification contraction and the response of the base metal; (III) a fluid flow module that calculates the variation in fluid velocity and pressure within the micro liquid channels of the semisolid; and (IV) a crack initiation module that applies Kou's hot cracking criterion [1] to identify cracked liquid channels based on inputs from the solidification, thermo-mechanical and fluid-flow modules. The results identify the underlying mechanisms by which welding process parameters (current and travel speed) and external restraining conditions influence hot cracking susceptibility during Gas Tungsten Arc welding. Interestingly, micro hot cracks seem to initiate near the fusion zone but then localize and form a macroscopic hot crack at the core of the weld.