采用光纤激光器对厚度为1.4 mm的DC56D+ZF镀锌钢和厚度为1.2 mm的6016铝合金平板试件进行了添加Sn粉的激光搭接焊实验,利用卧式金相显微镜、扫描电镜、X射线衍射和微机控制电子万能试验机等研究了添加Sn粉前后焊接接头各区域的金相组织、断口形貌、界面元素分布、主要物相与接头力学性能, 采用基于密度泛函理论的第一性原理方法,计算了添加Sn后新形成物相FeSn和FeAl化合物的模量和热力学性能. 结果表明, 在激光功率为2000 W,焊接速度45 mm/s, 离焦量+2.0 mm, Ar气为保护气体且流量为15 L/min的条件下,添加Sn粉焊接试样的焊缝表面成形性良好, 焊缝区晶粒细小, 焊接接头的平均剪切强度为62.17 MPa,与没有添加Sn相比, 剪切强度提高1.46倍. 由于细晶强化, 提高熔池金属的流动性,利于钢/铝合金界面结合, 减少Fe--Al金属间化合物层厚度, 新形成的FeSn的金属间化合物具有较好延性,高温下结构稳定, 抑制或减少了Fe--Al脆性金属间化合物的生成, 因而添加Sn粉改善了焊接接头的力学性能.

The laser welding test with Sn powder addition was carried out on DC56D+ZF galvanized steel with thickness 1.4 mm and 6016 aluminum alloy with thickness 1.2 mm. By using optical microscopy, scanning electron microscopy, X-ray diffraction and tensile test, the microstructure, fracture morphology, interface element distribution, main phase and mechanical properties of joints were studied. Elastic moduli and thermodynamic properties were calculated by using first-principles method based on density functional theory for FeAl and FeSn compounds. The results indicate that the morphology of welding surface can be improved and grain size is fine when the welding power is 2000 W, welding speed is 45 mm/s, the defocus distance is +2.0 mm, and Ar gas acts as the protection gas with flow rate 15 L/min. The average shear strength of the welding sample with Sn powder reaches 62.17 MPa. Compared to that without Sn powder addition, the average shear strength of weld joint increases by 1.46 times. Because of fine-grain strengthening and the improvement of the fluidity of the molten pool metal with Sn addition, it promotes the combination of the steel and aluminum interface and decreases the thickness of the intermetallic layer. FeSn intermetallic compounds has better ductility and is more stable than that of FeAl at high temperature that retard and reduce the generation of Fe-Al intermetallic compound, which can improve the mechanical properties of weld joint with Sn addition.