Laser wobble welding (oscillating laser beam) experiments were performed on high-strength micro-alloyed steels (HSLA) in both a low-carbon state (top plate) and carburized state (lower plate) using various process parameters. The welds were characterized regarding microstructure and microhardness. The cross sections of the welds had a predominantly symmetric geometry and were free of defects. Repeatable heating along an oscillating path resulted in a gradual transformation along heat-affected (HAZ) region of the top HC380LA plate from partial recrystallization through acicular and Widmanstätten ferrite formation to bainite. The microstructure of the lower 16MnCr5 plate experienced self-tempering of HAZ martensite along with bainite formation. The microhardness distribution across the entire fusion zone (FZ) of the dissimilar joint exhibited relatively consistent value, with the most significant variation of 80 HV attributed to the carburized layer of the lower plate.

In the present study, AA2024 aluminum alloy and AISI304 stainless steel were welded in a lap joint configuration by Probeless Friction Stir Spot Welding (P-FSSW) with a flat surface tool. A full factorial DOE plan was performed. The effect of the tool force (4900, 7350 N) and rotational speed (500, 1000, 1500, 2000 RPM) was analyzed regarding the microstructure and microhardness study. A two-dimensional arbitrary Eulerian–Lagrangian FEM model was used to clarify the temperature distribution and material flow within the welds. The experimental results for the weld microstructures were used to validate the temperature field of the numerical model. The results showed that the tool rotation speed had an extensive influence on the heat generation, whereas the load force mainly acted on the material flow.

This paper presents the experimental and numerical results of the influence of dwell time (30, 60, 90 s), down force (2450, 4900, 7350 N), and rotational speed (1000, 1500, 2000 RPM) on microstructure, microhardness, and material flow during solid-state welding. Probeless friction stir spot welding (P-FSSW) with a flat tool shoulder was assisted to form a metal compound of AA2024, AA6082, and AA5754 aluminium plates with different thicknesses in lap configuration. The analysis of the experimental data and numerical results showed that down force had a significant influence on the material flow and the quality of the welds. High friction energy, and subsequent intensive material flow, promoted the vortexes formation, which improve metals mixing and grain refinements.