Tool Pin Profile and B4C Reinforcement Influence on the Microstructural and Mechanical Characteristics of Friction-Stir-Welded Joints

In this study, Al5052 was friction-stir-welded using boron carbide (B₄C) as the reinforcement, with three tool probe profiles: tapered, threaded, and hexagonal. The influence of reinforcement particles on the microstructural and mechanical characteristics of the samples welded using different pin profiles was then investigated. A tool rotational speed of 800 rpm and an 80 mm/min welding speed were maintained throughout the process. Optical microscopy analysis was performed for microstructural characterization. Tensile testing, fractography analysis, and Vickers micro-hardness measurements were also conducted on both the welded samples and the base metal. The base metal exhibited coarse, elongated grains, while the welded samples had much finer grains. Boron carbide particles were distributed almost uniformly throughout the welding zone, although some agglomeration was observed in the welded area of the hexagonal probe sample. The threaded probe tool-welded specimen exhibited a very high tensile strength of 194 MPa, while the hexagonal probe tool samples had the least strength of 108 MPa. The presence of deep dimples from the fractography analysis indicated that ductile-type fractures had occurred for all the specimens. The base metal exhibited lower hardness compared to the nugget zone, primarily due to grain refinement and the particle pinning effect occurring in that zone. XRD and EDS analysis indicated the presence of intermetallic compounds—Al-Mg, Mg₂Al₃, and Al₃Fe.