Friction stir processing of wire arc additively manufactured Al-Zn-Mg-Cu alloy reinforced with high-entropy alloy particles: Microstructure and mechanical properties

Wire arc additive manufacturing (WAAM) of Al-Zn-Mg-Cu alloys often leads to poor strength and ductility due to microstructure defects, significantly limiting its application. This study employed friction stir processing (FSP) to reduce porosity and break up continuous coarse second phases along the grain boundaries. By adding high-entropy alloy (HEA) particles with good wettability during FSP, Al-Zn-Mg-Cu alloy components with simultaneously improved strength and ductility were produced. The results indicated that the grain structure transformed from columnar to equiaxed and was refined to 2.3 μm owing to the dynamic recrystallization of FSP and the particle-stimulated nucleation of HEA particles, while the continuous second phase was fragmented into nanoscale precipitates uniformly distributed in the matrix, acting as dislocation movement barriers. The newly formed Ni₃Al precipitates second phases ensure good ductility due to its low lattice mismatch with Al matrix. Additionally, the HEA particles maintained strong interfacial bonding with Al matrix, with an interfacial layer thickness of ~400 nm. The FSP-HEA treated components showed increased hardness (151.8 HV), ultimate tensile strength (374.3±20.4 MPa), and elongation (10.6%±1.6%) compared to the WAAM as-deposited state. This study provides guidance for the improvement of microstructural defects and the simultaneous enhancement of the strength and ductility of high-strength Al alloy WAAM components.