Abstract
The aim of this article is the in-depth analysis of material behavior during underwater friction stir welding (UFSW) of Al-Mg alloy. A thermo-mechanical model was employed to find the relation between physical changes during UFSW and mechanical properties of the final joint. To better understand the effects of the water environment, the results were compared with conventional friction stir welding (FSW) conditions. Thermal profile and surface heat flux results revealed that lower preheated area (PHA) at the leading edge (LE) decreased the total amount of frictional heat generation in the UFSWed joint. According to the simulation results, the strain rate in the stir zone (SZ) at the FSW sample was more than that of the UFSW specimen. Rapid cooling on submerged welding can result in finer grain structure at the UFSWed joint. The applied compression pressure on the workpiece at the trailing edge (TE) of the tool was more in the UFSW sample compared to the FSW, which led to higher compact joint line in the UFSWed specimen. These phenomena increased the joint line hardness and tensile properties at the UFSWed joint compared with the FSWed sample.