Synergistic optimization of strength–ductility matching in wire arc additively manufactured Ti–6Al–4V alloy by hot isostatic pressing + solution treatment and aging

During the wire arc additive manufacturing (WAAM) process of Ti-6Al-4V alloy, repeated thermal cycles tend to the form inhomogeneous microstructures and porosity defects, resulting in poor overall performance. In this study, a combined post heat treatment strategy involving hot isostatic pressing + solution treatment and aging (HIP+STA) was proposed, and its effects on the microstructure, defect characteristics, and mechanical properties of WAAMed Ti-6Al-4V samples were systematically investigated. The results show that HIP treatment (920 °C/120 MPa/2 h/furnace cooling) effectively closed pores to below 40 μm and increased the elongation (EL) to 15.2%. However, the α laths nearly doubled in width, leading to a substantial decrease in the strength of the sample. Further STA treatment (930 °C/1 h/water quenching + 600 °C/4 h/air cooling) also maintained a low porosity. The fine αs + β transformed microstructure restored the ultimate tensile strength (UTS) and yield strength (YS) to 986.8 MPa and 891.5 MPa, respectively, while the EL decreased to 11.5%. Analysis of the strengthening mechanisms indicates that the strength improvement of the HIP+STA sample was mainly attributed to solid solution and dislocation strengthening, while pore closure effectively delayed crack initiation, thereby achieving an optimized strength–ductility balance. This study provides a basis for microstructural regulation and performance optimization in the fabrication of highly reliable WAAMed Ti-6Al-4V load-bearing components.