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.

多年来，焊接厚板已成为多个工业领域的关注话题。但是，中厚钛合金板的连接技术存在很多困难，亟待解决。通过模拟和实验方法研究了厚度为7.5mm的TC4钛合金的激光多道窄缝焊接工艺的组织和残余应力分布。结果表明，下部熔池中的柱状晶体比上部熔池中的柱状晶体细得多，其生长方向与模拟结果的最大温度梯度方向一致。结果还表明，多重热效应是针状马氏体粗化的主要原因。此外，应力场模拟结果表明，夹层附近出现了较高的横向拉伸应力。在焊趾和焊缝根部均出现应力集中现象，焊缝根部的应力集中系数达到2.13。