Enhanced strength-plasticity of 2319 Al-Cu alloy formed by hybrid interlayer friction stir processing and wire-arc additive manufacturing

Friction stir processing (FSP) technology can significantly improve the performance of components prepared using wire-arc additive manufacturing (WAAM). In this study, a hybrid method combining WAAM and interlayer FSP (WAAM–IFSP) was used to prepare multilayer 2319 aluminum alloy samples. The resulting periodic microstructures with alternating bimodal and columnar grain regions were investigated in detail. The formation mechanism and influence of the microstructure on the alloy mechanical properties were revealed by analyzing the texture, grain morphology and distribution, grain boundary orientation angle, and dislocation density. The use of WAAM–IFSP refines the grains in the deposited alloy layers, reduces the defect density, increases the internal dislocation density, and results in a random distribution of precipitates in the matrix via the crushing and mixing action of the stirring tool. Compared with samples prepared by WAAM alone, the top layer of the WAAM–IFSP sample showed the best performance, with the ultimate tensile strength increasing from 297 to 378 MPa and the elongation increasing from 16.2% to 30.6%. Furthermore, in the vertical direction, the elongation increased nearly threefold, from 7.9% to 23.2%, which is attributed to a higher interfacial bonding strength and the bimodal grain structure formed by a heat-source coupling effect during WAAM–IFSP. These findings are expected to provide new insights into the further development of methods for enhancing the performance of WAAM components by introducing IFSP, thereby extending the engineering applications of additive manufacturing methods.