Microstructures and Mechanical Properties of Thick Ti–6Al–3Nb–2Zr–1Mo Joint by Magnetron-Controlled Narrow Gap TIG Welding

The butt joint of 30 mm-thick Ti–6Al–3Nb–2Zr–1Mo titanium alloys were achieved by the magnetron-controlled narrow gap TIG welding. Microstructure and mechanical properties of joint were comprehensively explored. Ti6321 base metal (BM) was composed of primary α (accounting for 55%) and structure of β transformation (secondary α + β phase). Fine grained heat affected zone was composed of primary α, acicular α and β phase. Coarse grained heat affected zone was composed of acicular α and clusters of α phase with different orientations. The fusion zone (FZ) was composed of acicular α phase, lath α phase and a few β phase. The ratio of high-angle grain boundaries in the HAZ reached the maximum of 94.5% while those of the FZ and BM were 78.1% and 59.4%, respectively. Due to the differences in microstructures and grain orientation, the hardness of FZ (286 HV) was lower than those of BM (304 HV) and HAZ (306 HV). The tensile strength of the welding joint (838 MPa) reached 95% of the BM (883 MPa), and the joint showed excellent impact performance with great impact energies of FZ (72 J) and HAZ (75 J), higher than that of BM (51 J). It was owing to the greater ratio of high-angle grain boundaries in FZ and HAZ that could store more grain boundary energies. Thicker phases hinder the growth of cracks, and, therefore, improve the impact performance of the joint. Graphical Abstract The butt joint of 30 mm-thick Ti–6Al–3Nb–2Zr–1Mo titanium alloys were achieved by the magnetron-controlled narrow gap TIG (MCNG-TIG) welding. Adding magnetic field can refine weld grain. The joints have good mechanical properties, especially impact properties.