Effect of post-weld heat treatment on microstructure and mechanical properties of linear friction welded TC11 titanium alloy joints

Abstract

Post-weld heat treatment(PWHT) could improve the microstructure and properties of linear friction welded joints. The linear friction welded joints of TC11 titanium alloy were double annealed at 950 ℃ and 530 ℃. The effect of double annealing on the microstructure of the joints was studied by microscopic analysis techniques such as optical microscopy(OM) and scanning electron microscopy(SEM). The results show that the dynamic recrystallization grains in the weld zone(WZ) completely disappear after PWHT, and are replaced by coarse needle, strip, and spherical α-phase grains; the degree of deformation of the thermos-mechanically affected zone(TMAZ) decreases. The grains grow, and some α structures are spheroidized. The secondary α phase in the base metal(BM) grows up in the shape of coarse needle and short rod. The grain orientation of the WZ and the TMAZ is more random after heat treatment, and the preferred orientation is significantly reduced. The mechanical properties tests indicate that the double annealing treatment after welding eliminates the high hardness zone in the center of the joint, and the center hardness is about 50HV lower than that of the as-welded joint. The hardness of TMAZ is about 30HV higher than that of the as-welded joint. No significant decrease in tensile strength presents after PWHT. The impact toughness of the joint reaches 61.3 J·cm-2 after PWHT, about 80% higher than that of the as-welded joint and close to that of the BM.

Keywords

• tc11 titanium alloy
• linear friction welding
• post-weld heat treatment
• microstructure
• mechanical property