Zinc-coated advanced high strength steels (AHSS) used in automotive applications are susceptible to liquid metal embrittlement (LME) during resistance spot welding (RSW). This study examines the impact of multiple pulse welding schedules on LME severity in welds of TRIP1100. Two different types of pulsing methodologies have been proposed to reduce LME severity: applying a pre-pulse before the welding current to remove the zinc coating and pulsing during the welding current to manage heat generation. However, the mechanisms by which these methods affect LME severity have not been fully explored. This work showed that a welding schedule consisting of two equal length pulses resulted in the least severe LME because it reduced the amount of free zinc available for LME without creating too much tensile stress. The majority of pre-pulse welding schedules caused an increase in LME cracking due to the additional heat introduced into the weld. However, a 4 kA (low current) pre-pulse applied for 3 cy (low time) reduced LME cracking by almost 30%. The pre-pulse allowed zinc to diffuse into the coating and stabilize the zinc, without introducing too much additional heat into the weld. These results indicate that multiple pulse welding schedules may be successfully used to reduce LME cracking, although the mechanisms by which they impact LME are more complicated than previously thought.

Tool offset is one the most significant parameters in joining of dissimilar materials by friction stir welding (FSW) process. An investigation is carried out on the effect of tool offset toward thermal history, material flow pattern, mechanical properties, welding force, and weld joint morphology. It was found that offsetting toward aluminum side along with a plasma-assisted heat source is an efficient approach to address one of the most important apprehensions in aluminum-copper solid-state welding process. The offset influences the amount of intermetallic at the joint interface and in-effect impacts on final strength and material flow behavior. The optimum and continuous layer of intermetallic produces the maximum weld joint strength. The specimen welded with optimum tool offset shows the highest strength using 55 A plasma current in hybrid friction stir welding process.

The friction stir welding (FSW) process is often associated with various defects, which may develop due to the inappropriate choice of process parameters. The visualisation of the defects is often impossible by means of simple experiments. The present work develops a finite element model using a coupled Eulerian–Lagrangian (CEL) approach to investigate commonly occurred defects in the FSW process. The numerical model is framed, in general, to predict multiple defects such as the improper joining of substrates, formation of tunnel defect, excessive flash, voids and other surface irregularities. In principle, the flow of material within and out of the solution domain allows predicting both the surface and subsurface defects. A suitable comparison between simulation and experiments shows the robustness of the developed model.