Mechanical and microstructural characteristics of the dissimilar materials butt joints by hybrid CO2 laser-gas metal arc welding

This paper intends to present the applicability of hybrid [CO2 laser+gas metal arc (GMA)] welding process to dissimilar materials AH32 and STS304L by clarifying the mechanical and microstructural characteristics of hybrid welded joints. In order to observe the mechanical phenomena on dissimilar material hybrid welded butt joints, two-dimensional thermal elastoplastic numerical analysis has been carried out. For this, the quasistate heat source model for simulation has been determined considering the hybrid welding characteristics. Based on the thermal history obtained by using this heat source model, the residual stress distribution in welded joints is predicted and found to be in reasonable agreement with the experimentally measured values. The result shows that maximum welding residual stress in longitudinal direction (σzz) in dissimilar material (AH32-STS304L) welded joints has occurred in the STS304L side by about 5% than in the AH32 side of welded joints. However, the equivalent stress of dissimilar material welded joints shows almost identical values as those of similar material (AH32 and STS304L) welded joints. The microstructures of weld metal exhibit well distributed platelike shaped ferrite in the matrix instead of dendritic structure. No weld defect has been detected and the second phase strong in brittleness is not observed on the interface between head affected zone (HAZ) and base metal as the scanning electron microscope-energy dispersive spectrometer (SEM-EDAX) analysis shows.