Abstract

5A06 aluminum alloy plates with a thickness of 6.9 mm are welded by laser-metal inert gas (MIG) hybrid welding. To investigate the influence of laser heat input on grain size and microhardness, optical microscope observation, scanning electron microscope (SEM) and microhardness test are conducted. According to the microstructure distribution characteristics, the weld seam can be divided into arc-affected zone and laser-affected zone. The crystalline morphology from the weld boundary to the weld center is coarse columnar dendrites, finer columnar dendrites and equiaxed dendrites. In addition, the calculation and comparison of the grain size indicate that, the grain size Z_l of the coarse columnar dendrites and the fine columnar dendrites in the laser-affected zone has increased, compared to both of the arc-affected zone. Due to the mechanical stirring effect on the upper molten pool, the finer equiaxed dendrites are formed at the center of arc-affected zone. It is worth noting that the grain size inhomogeneity has been significantly improved due to the decrease of laser heat input. The average microhardness of the arc-affected zone in case 1 is significantly lower than that of the other three cases due to the higher laser heat input. The laser line energy of 90 J/mm is more suitable for achieving the excellent microhardness property of laser-MIG hybrid welded joint for the 6.9 mm 5A06 aluminum alloy.

摘要

采用激光-金属惰性气体（MIG）复合焊焊接厚度为6.9 mm的5A06铝合金板。为了研究激光热输入对晶粒尺寸和显微硬度的影响，进行了光学显微镜观察、扫描电子显微镜（SEM）和显微硬度测试。根据组织分布特征，焊缝可分为电弧影响区和激光影响区。从焊缝边界到焊缝中心的结晶形貌为粗大的柱状枝晶、细小的柱状枝晶和等轴状枝晶。此外，晶粒度的计算和比较表明，晶粒度Z _l与电弧影响区相比，激光影响区粗柱状枝晶和细柱状枝晶的数量增加。由于上部熔池的机械搅拌作用，在电弧影响区的中心形成了较细的等轴枝晶。值得注意的是，由于激光热输入的减少，晶粒尺寸不均匀性得到了显着改善。由于较高的激光热输入，案例 1 中电弧影响区的平均显微硬度明显低于其他三种情况。90 J/mm的激光线能量更适合实现6.9 mm 5A06铝合金激光-MIG混合焊接接头优异的显微硬度性能。