Unravelling the microstructural origin of strength–ductility synergy in friction stir welded dual-phase brass

The microstructural evolution and mechanical behavior of friction stir welded Cu–37Zn brass were investigated for both single-phase (α) and double-phase (α + β) conditions. Friction stir welding (FSW) resulted in significant grain refinement within the stir zone due to dynamic recrystallization, leading to improved mechanical properties. The ultimate tensile strength increased from 310 to 330 MPa and elongation from 47% to 63% in the single-phase alloy, while in the double-phase alloy, the strength increased from 362 to 385 MPa and elongation from 38% to 60% after welding. Electron backscattered diffraction analysis revealed that in the double-phase brass, the initial coarse β phase was fragmented during FSW into nano-scale regions located primarily along α grain boundaries, accompanied by elevated local misorientation. After tensile deformation, a pronounced increase in BCC-indexed regions was observed in the stir zone, together with higher kernel average misorientation values. This behavior indicates deformation-induced microstructural evolution within pre-existing heterogeneous regions. The combined effect of grain refinement and deformation-driven structural changes contributes to the enhanced strength–ductility balance of the welded joints.