Effect of post heat treatment on microstructure and mechanical properties of Ti-6Al-4V jointing parts proceeded by laser additive manufacturing

Laser Deposition Manufacturing (LDM) provides a novel jointing method to realize metal parts fabrication, which is one of the key research directions for preparing large integral titanium alloy components. Based on LDM, pairs of forged Ti-6Al-4V titanium alloy parts with special designed V shape groove were jointed, followed by post heat treatments which implemented effective adjustment of tensile properties of the joints, to investigate the mechanical performance. Optical microscope (OM), XRD diffraction and transmission electron microscope (TEM) analysis were performed to analysis microstructure in the deposition zone and substrate, the mechanism that evokes mechanical properties variation concerning about heat treatments was also proposed. Lamellar a cluster distributed in the original beta column crystal was the overall feature for the deposition zone of the joint pieces. Due to the heat flux of the melting pool, heat-affected zone was introduced about 0.3-0.5 mm in thickness. The postheat treatment process significantly changed the mechanical properties of both the substrate and the deposition zone. As-deposited and solution thorn aging treatment gave rise to the joint pieces at higher tensile strength relative to aging and annealing treatment, which reduced the strength of the pieces, and the annealing treatment weakened the strength of the deposition area lower than that of the substrate. Post heat treatment processes effectively changed the ratio, size and distribution of alpha and beta phases in the deposition zone, i.e., the increase of lamellar structure in width, length, and beta T portion in the whole structure were the main factor that leading to the decline of strength performance of the junction area.