Microstructure amelioration and strength-ductility improvement of WAAM-LDM hybrid additive manufacturing Ti-6Al-4 V alloy by solution treatment and aging

WAAM-LDM hybrid additive manufacturing can achieve high efficiency and high precision preparation of Ti-6Al-4 V alloy. However, the inhomogeneous microstructure of WAAM-LDMed Ti-6Al-4 V samples results in overall poor tensile properties. Therefore, this paper attempts to ameliorate the inhomogeneous microstructure of the hybrid sample by STA, and simultaneously improve the strength and plasticity. The results showed that the WAAM zone and HAZ were composed of α colonies, the RZ and LDM zone were distributed with fine basketweave structure of the AD samples. With the introduction of STA, the microstructure of each zone of the hybrid sample changes and transformed into a ‘dual-phase’ structure with bi-modal αp and βt. With the increase of aging temperature, the volume fraction of βt increased and the volume fraction of αp phase decreased, accompanied by the formation of bulk α phase and the coarsening of αs phase. It is worth noting that the strength of WAAM zone was obviously improved by STA, and the fracture positions of the STA samples were randomly distributed in the WAAM and LDM zones. Additionally, with the aging temperature increased, the strength of WAAM-LDMed samples was weakened, and the ductility was improved because the coarsened bulk α played a role of coordinating deformation in the tensile process. The excellent strength and ductility (UTS = 976 MPa, YS = 876 MPa, EL = 13.57%) of WAAM-LDMed samples was achieved at aging temperature 750 °C, compared with the AD samples (UTS = 860 MPa, YS = 767 MPa, EL = 12.5%). Finally, by optimizing the STA (940 °C/1 h/WQ + 750 °C/4 h/AC), the amelioration of the microstructure and the improvement of the strength-ductility of the hybrid samples were achieved.