双相钢/镁合金添加Sn箔激光热传导焊及数值模拟

Laser heat-conduction welding and numerical simulation of double phase steel/magnesium alloy with Sn foil

采用光纤激光器作为焊接热源,对1.4 mm厚DP600双相钢和1.8 mm厚AZ31镁合金平板试件进行钢上、镁下搭接、钢/镁层间添加Sn箔的激光热传导焊试验,通过试验调整优化焊接工艺参数,获得最佳焊缝成形,采用卧式金相显微镜、带有能谱仪(EDS)的扫描电镜、X射线衍射仪(XRD)等观察添加Sn箔钢/镁接头的显微组织、界面元素分布和相结构组成;利用ANSYS有限元软件,考虑材料物性参数的温度相关性、初始条件、边界条件等因素影响,建立钢/镁异种金属激光焊接非线性三维传导有限元模型,模拟计算钢/镁焊接接头的温度场分布。结果表明:添加Sn箔可实现钢/镁之间的有效连接,焊接模式为激光热传导焊,模拟计算获得熔池形状、尺寸与实际焊缝基本吻合,验证采用高斯体热源模型用于模拟双相钢/镁合金焊接接头温度场的合理性;由于添加Sn箔减缓从上层钢板向下层镁合金的热量传递,起到一定程度的隔热效果,利于熔沸点差异大的钢、镁同时熔化,此外上层钢侧冷却速度降低,延长钢板与Sn箔中Fe、Sn元素的相互扩散时间,导致钢/镁界面中钢侧过渡区域生成FeSn、Fe_(1.3)Sn、Fe_3Sn等Fe-Sn相,镁侧过渡区域生成Mg_2Sn相。因此,添加Sn箔有助实现双相钢/镁合金异种金属的有效连接。

Laser welding test with Sn foil addition was carried out on DP600 double steel with thickness of 1.4 mm and AZ31 magnesium alloy with thickness of 1.8 mm by using fiber laser beam and the method of laser heat-conduction welding in an overlap steel-on-magnesium configuration. The best welding was achieved based on the optimization of welding parameters, and microstructure, elements distribution and phase compositions of the welding joint were studied by the horizontal microscopy, SEM with EDS and XRD. Considering the temperature dependence of material properties, initial conditions, boundary conditions and other factors, the nonlinear 3-D conduction finite element model of the steel/magnesium dissimilar metal laser welding was established by ANSYS finite element software. The results show that the effective connection between steel and magnesium can be realized in the heat-conduction welding mode with addition of Sn foil. The simulation calculation results of the weld pool shape, size are basically consistent with those of the actual weld, which verifies the rationality of the Gauss body heat source model for simulating the temperature field of the dual phase steel/magnesium alloy welded joints. Because of the addition of Sn foil to slow down the heat transfer from steel to the magnesium alloy, the effect of heat insulation of Sn foil is beneficial to the steel and magnesium plates melting at the same time. In addition, the cooling speed of the upper steel decreases and prolongs the diffusion time of Fe and Sn element, resulting in FeSn, Fe_（1.3）Sn, and Fe_3Sn phases in the transition zone of steel and Mg_2Sn phase in transition region of magnesium. Therefore, the addition of Sn foil can help to realize the effective connection of dissimilar metals between double phase steel and magnesium alloy.