The effect of friction stir welding parameters on the mechanical properties of the α/β brass plates was investigated. The microstructures of the joints were characterized using optical microscopy, scanning electron microscopy (SEM), and scanning transmission electron microscopy (STEM). The tensile and Vickers hardness tests were conducted to measure the mechanical properties of the processed materials. The results showed that the most effective parameter on the ultimate tensile strength (UTS) and hardness was rotation speed, whereas in the case of tensile elongation it was axial force. Optimizing the parameters revealed that the maximum UTS, hardness, and elongation of 357.4 MPa, 116.3 HV, and 29.1% can be achieved at a rotation speed of 629.2 rpm, a traverse speed of 107.24 mm/min, and an axial force of 2.3 kN. It was observed that α was undergone dynamic recrystallization, which resulted in formation of finer equiaxed grains with high dislocation densities of tangle and cell structures. β fragmented into finer parts between the α grains without any dynamic recrystallization characteristics.
