Abstract
Welding thick plate has become a topic of interest for multiple industrial sectors for many years. However, there are plenty of difficulties on the joining technology of medium-thickness titanium alloy plate waiting to be solved urgently. In this paper, the microstructure and residual stress distribution of 7.5-mm-thick TC4 titanium alloy jointed by laser-multi-pass-narrow-gap welding are investigated by simulated and experimental methods. It is demonstrated that the columnar crystals in the lower molten pool are significantly finer than that in the upper molten pool, of which the growth direction is consistent with the direction of the maximum temperature gradient of simulation results. Results also indicate that multiple heat effect is the main cause of the acicular martensite coarsening. In addition, stress field simulation results reveal that high transverse tensile stress appears near the interlayer. There is a stress concentration phenomenon occurring at the weld toe and weld root, and the stress concentration coefficient of the weld root reaches 2.13.
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