Solidification Microstructure of Aluminum AA 6016-T4 Resistance Spot Welds Using a Short-Pulse Technique

The influence of the duration of the current pulse on the solidification microstructure of resistance spot welded (RSW) samples of aluminum alloy 6016-T4 with the short-pulse technique was investigated through experiments and numerical modeling. Microstructure was analyzed in terms of morphology and size, and primary and secondary dendrite arm spacing were measured on experimental samples. A reduction in pulse width resulted in a fine, columnar-dendritic microstructure in the outer regions of the fusion zone as well as a larger equiaxed-dendritic zone in the fusion zone center. A two-dimensional, axisymmetric finite element model of the spot welding process with new methods for calculation of the solidification parameters G (thermal gradient in the solid behind the solid–liquid interface) and R (velocity of the solid–liquid interface) was used for investigation of influence of pulse time on solidification microstructure and comparison to experimental results. Morphological trends in the solidification structure showed good agreement between experiments and simulations, and the influence of the pulse duration on the solidification parameters evolved because of changing heat transfer conditions. Simulated solidification data suggest that the solidification of aluminum during RSW falls in the regime of rapid solidification.