Liu Xing, Ling Wanli, Li Yue, Wang Jianfeng, Zhan Xiaohong
College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China.
Materials (Basel). 2022 Nov 3;15(21):7742. doi: 10.3390/ma15217742.
Narrow gap laser welding (NGLW) is a common solution for the welding of thick structures. NGLW was carried out on narrow-gap butt joints of 40 mm-thick Ti-6Al-4V alloy plates with a U-shaped groove. The distribution characteristics of the interlaminar microstructure in different height ranges of the joint were investigated, and the evolution behavior and formation mechanism of the interlaminar microstructure of the joint were also revealed. This showed that a large amount of short needle martensite nucleated and grew up near the fusion line and the upper boundary of the remelting zone. The "softening" phenomenon occurred in all welds except the cover layer weld. The microstructure evolution and defect migration, induced by multiple welding thermal cycles in the upper weld forming process, were the main reasons for the "softening" of the lower weld. The tensile strength of each sample changed in the range of 920~990 MPa; the fracture mode of the sample belongs to a transgranular ductile fracture. In addition, compared with the upper part of the joint, the plasticity and toughness of the weld area in the lower part of the joint was improved.
窄间隙激光焊接（NGLW）是厚结构焊接的常用解决方案。对厚度为40mm的Ti-6Al-4V合金板的U形坡口窄间隙对接接头进行了窄间隙激光焊接。研究了接头不同高度范围内层间组织的分布特征，揭示了接头层间组织的演变行为及形成机制。结果表明，大量短针状马氏体在熔合线和重熔区上边界附近形核并长大。除盖面层焊缝外，所有焊缝均出现“软化”现象。上焊缝成形过程中多次焊接热循环引起的组织演变和缺陷迁移是下焊缝“软化”的主要原因。每个试样的抗拉强度在920~990MPa范围内变化；试样的断裂模式属于穿晶韧性断裂。此外，与接头上部相比，接头下部焊缝区的塑性和韧性得到了提高。
