Damage is inevitably induced in titanium alloy laser-welded (LW) joints after prolonged service, making weld repair an economical and effective restoration method. This study employed gas tungsten arc welding (GTAW) to repair pre-damaged TC4 LW joints, with a systematic investigation on the microstructural and mechanical properties of the repaired joints. The results indicate that both the LW and the GTAW-repaired (GTAW-R) joints exhibit acicular α′ martensite in the fusion zone (FZ). However, the maximum length and width of the α′ phase in the FZ of the GTAW-R joint are 67% and 78% larger than those in the LW joint, respectively. The heat-affected zone (HAZ) of both types of joints comprises α′, α, and β phases. Similarly, due to the higher heat input in GTAW, the α′ phase in the HAZ of the GTAW-R joint is coarser. Differences in acicular martensite size result in an average microhardness of 356.3 HV in the FZ of the GTAW-R joint, which is 15.2 HV lower than that of the LW joint. The higher heat input of GTAW leads to a prolonged duration at elevated temperatures in the HAZ, promoting the formation of acicular α′ phase and, consequently, a slightly higher microhardness compared to the HAZ of the LW joint. The average tensile strength of the GTAW-R joint is 1032 MPa, equivalent to 98.4% of the LW joint strength (1049 MPa) and 96.8% of the BM strength (1066 MPa). Tensile fracture in the LW joint occurs in the BM region, whereas the coarser microstructure in the repair weld leads to fracture in the FZ for the GTAW-R joint. This study demonstrates that when the damage length in an LW joint is less than 20%, GTAW repair can effectively restore the joint strength.
Li et al. (Tue,) studied this question.