Effects of deep cryogenic treatment on the residual stress and mechanical properties of electron-beam-welded Ti-6Al-4V joints

The effects of deep cryogenic treatment (DCT) on the residual stress and mechanical properties of electron beam (EB)-welded Ti-6Al-4V(TC4) joints were investigated. In addition, the effect of different DCT soaking times was analyzed to obtain the optimal time. The results indicated that with a soaking time of 24 h, perpendicular to the welding direction, the residual stress declined by 31.2% for the longitudinal stress and 46.5% for the transverse stress, and along the welding direction, the residual longitudinal and transverse stress declined by 25.1% and 17.2%, respectively. More than 24 h, the effect of increasing the soaking time on eliminating residual stress is not obvious. Meanwhile, the effect of DCT on the tensile strength of the EB-welded TC4 joint was also investigated, which showed that the strength increased by 4.3% and the elongation rate increased by 46.8% when the soaking time was longer than 24 h. The hardness test indicated that values at the weld were higher than that in the base metal, and the average values of hardness increased with DCT. Particular focus was given to the changes in the quantity, size, and morphology of the α and β phases as the main reasons for the above results.