Abstract: 22MnB5 hot-formed steel and 6061 aluminum alloy are generally used in the automobile industry. Realizing the connection of these two materials and giving full play to the excellent properties of both materials will no longer only achieve the purpose of lightening the vehicle, but also make certain automobile safety. The low strength of aluminum/steel dissimilar welded joint has been a significant issue restricting their use. The CMT (cold metal transfer) Advanced Pulse (CMT+A+P) welding approach and ER4043 welding wire with a diameter of 1.2 mm were used in this work to achieve effective joining of dissimilar joints in 6061 aluminum alloy and 22MnB5 hot-formed steel with low heat input. The macroscopic morphology, microstructure, and interfacial properties of the fusion brazed joints were analyzed, and the fracture location and fracture morphology were observed by the usage of metallographic microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that when welding heat input increased, the melt width of fusion brazed joint grew steadily and the wetting angle rose initially and fell subsequently. The welding zone was arranged as α-Al equiaxed and Al-Si eutectic, with the Al-Si eutectic equally distributed on the α-Al grain boundary. The grain became coarse because the heat affected zone on the side of the aluminum alloy was subjected to thermal cycling during the welding process. Al and Fe atoms near the interface zone diffuse with each other along the interface layer, and generate various Fe-Al intermetallic compounds. When the heat input increases from 41.8 J/mm to 127.6 J/mm, the thickness of the interface layer grew from 1.49 to 2.85 μm. The fracture appeared at the aluminum alloy base material, the welded joint, and the interface layer, which were ductile fracture, ductile/brittle mixed fracture, and brittle fracture, respectively. The specimen with the highest tensile strength fractured at the aluminum alloy base material, exhibiting ductile fracture, and the tensile and shear loading is 3.88 kN.

Key words: CMT Advanced Pulse, fusion brazing, interface features, microstructure, properties

摘要： 22MnB5热成形钢和6061铝合金是汽车工业中常用的材料，两种材料的连接能够同时实现汽车轻量化和安全性的要求，本工作利用CMT Advanced Pulse (CMT+A+P)焊接方法，选用直径为1.2 mm的ER4043焊丝，通过改善工艺实现了6061铝合金和22MnB5热成形钢异种接头有效连接。通过使用金相显微镜(OM)、扫描电子显微镜(SEM)和能谱仪(EDS)，研究了熔钎焊接头宏观形貌、界面特征及拉伸性能。研究结果表明，随着焊接热输入的增加，熔钎焊接头熔宽增加，润湿角先增加后减小。铝合金侧热影响区晶粒有粗大倾向；焊缝区组织为α-Al等轴晶和Al-Si共晶，Al-Si共晶均匀分布在α-Al晶界上；界面区附近Al和Fe原子沿着界面层相互扩散，生成多种Fe-Al金属间化合物。当热输入由41.8 J/mm 增加至127.6 J/mm时，界面层厚度从1.49 μm增加至2.85 μm。熔钎焊接头断裂位置分别位于铝合金母材处、焊缝处及界面层三个区域，其断口形貌分别呈现为韧性断裂、韧脆混合断裂和脆性断裂；拉伸强度最高的试样断裂于铝合金母材处，呈韧性断裂，拉剪载荷达3.88 kN。

关键词: CMT Advanced Pulse, 熔钎焊, 界面特征, 微观组织, 性能