Enhancement of microstructure, corrosion, tribology, and mechanical properties of GMAW joints under various welding positions by post-weld refinement FSP

In this study, the weldability of ST-37 mild steel using the Gas Metal Arc Welding (GMAW) method was investigated under both flat and vertical-up welding positions. Additionally, the effects of the Friction Stir Process (FSP) on the microstructure, mechanical properties, corrosion behavior, and tribological performance of double-sided butt-welded samples from both positions were analyzed. The results showed that FSP effectively refined the microstructure, leading to a uniform distribution of fine grains within the weld zone (WZ) and a significant enhancement in the mechanical performance of the welds. FSP also eliminated metallurgical defects such as porosities. However, it is noteworthy that while hardness and strength generally improved by post-FSP, a localized decrease in these properties may occur depending on process parameters and initial weld conditions. Corrosion testing revealed that FSP enhanced the corrosion resistance of weld samples produced in the vertical-up position, while a slight reduction was observed for samples welded in the flat position. This contrast is attributed to differences in gravitational effects, cooling rates, and resulting metallurgical structures between the two welding positions. Furthermore, FSP-treated samples exhibited superior wear resistance compared to those produced by conventional welding. This improvement is primarily due to stress relief, grain refinement, enhanced mechanical properties, and the reduction of metallurgical imperfections. FSP also influenced the dominant wear mechanisms, altering them from adhesive wear to abrasive wear, depending on the welding orientation (flat or vertical-up).