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.
The welding sequence has an important influence on the formation of stress and deformation in multi-layer and multi-pass welding (MLMPW). In this paper, a 3D finite element model of Invar alloy welding that can calculate the welding stress and deformation has been established using MSC. Marc. The simulation results show that there is high residual tensile stress in the welding zone. For six-layer twelve-pass welding, the welding sequence has little effect on maximum stress value. Meantime, welding deformation is mainly distributed far from the weld metal area and is mainly affected by welding sequence under similar other welding conditions. It is found that the deformation angle of welding sequence D is the smallest, with a value of [Formula: see text].
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