采用光纤激光-熔化极稀有气体保护(MIG)复合焊对不同对接间隙下的3 mm厚低合金高强钢进行焊接。在焊接速度恒定的条件下,研究了不同对接间隙下焊缝的成形过程,并与零间隙下相同工艺参数的激光-MIG复合焊的焊缝形貌进行对比。结果表明:在有对接间隙时,焊缝及其热影响区的上下宽度基本一致(呈U形),而在零间隙下,焊缝及其热影响区的宽度均呈上宽下窄(Y形)的形态。焊缝成形机理如下:在激光-MIG复合焊进行有对接间隙的焊接时,电弧等离子体的形态有三种不同的变化(与任一侧试板起弧燃弧形成的“分叉电弧”以及与两试板同时起弧燃弧形成的“十字电弧”),电弧的三种形态不断变化,形成“摆动”态;“摆动”态电弧等离子体的作用是预热和熔化工件侧壁,激光热源作用在熔池上起到加大熔深、稳定电弧和消除电弧热源导致的侧壁未熔合的作用;对接间隙下电弧热源作用的范围较大,使得母材受热更加均匀;与零间隙焊缝相比,有间隙下的焊缝组织更均匀。

In this study, 3-mm thick low-alloy high-strength steels with different butt gaps were welded by optical fiber laser-metal inert gas (MIG) protection hybrid welding. The forming processes of weld seams with different butt gaps at a constant welding speed were studied and the formed shapes were compared with the morphology of laser-MIG hybrid welding with the same process parameters under zero gap conditions. The results demonstrate that the upper and lower widths of the weld seam and its heat-affected zone are basically same under butt gaps (U-shaped), while the weld-seam width and its heat-affected zone are up-wide and down-narrow under zero-gap (Y-shaped) conditions. The formation mechanism of weld seams is as follows: when laser-MIG hybrid welding is conducted with a butt gap, three different arc plasma shapes exist, i.e. bifurcated arc shapes formed by arc striking/arcing with either side of the test plate and the cross arc shapes formed by arc striking/arcing with both test plates at the same time. The three forms of arc shapes change continuously to form a swing arc pattern. The effect of the swing arc plasma is to preheat and melt the side wall of the workpieces. The laser heat source operates on the molten pool to increase the penetration, stabilize the arc, and eliminate incomplete fusion of the side wall caused by the arc heat source. The arc heat source with a butt gap has a large effective range, and the base metal is heated more evenly. The microstructures of the butt gap welds are more homogeneous than that of the zero-gap welding seams.