Ti/Al搭接结构“搅拌摩擦点焊-钎焊-扩散焊”复合接头形成机理及力学行为研究

Lightweight manufacturing is an urgent need for the development of high-tech equipment in China. The dissimilar metal welded structure parts can take maximum advantage of their preponderances and obtain better economic and social benefits and it is an effective method to realize lightweight manufacturing. This project targets to develop a novel hybrid welding method, namely “friction stir spot welding-soldering-diffusion welding” (FSSW-S-DW)for reliable connection of titanium to Aluminum dissimilar metals, because the lightweight manufacturing of high-tech equipment such as aircraft, spacecraft and rail vehicles has potential needs for Ti/Al dissimilar metal welded structure. The weld formation mechanism, microstructure, mechanical behavior of Ti/Al welded joints and welding process will be researched in this project. Through these researches, the mechanism and influence factor of the soldering and diffusion welding under the effect of instantaneous heat and stress during frictions stir spot welding could be revealed and the correspondence between mechanical properties of the FSSW-S-DW welded joints, welding parameters and the weld formation mechanism will be established, which is the theoretical base for process optimization and improving mechanical properties of welded joints. The favorably implements of this project on one side will realize high quality and reliable connection of the Ti/Al dissimilar metal and establish the base of industrial applications such as new aircraft and high-speed rail vehicles, on the other side can play a certain role in promoting the development of lightweight manufacturing technology for high-tech equipment

轻量化制造是我国高端装备研发的迫切需求。异种金属复合焊接构件能最大限度利用材料各自的优点，获得更好的经济效益和社会效益，是实现轻量化制造的重要途径。项目针对航空、航天、轨道车辆等高端装备轻量化制造对高性能Ti/Al异种金属复合焊接结构的潜在需求，发展一种能用于Ti/Al搭接结构可靠连接的“搅拌摩擦点焊-钎焊-扩散焊”复合焊接新工艺。通过对复合焊接接头形成机理、微观组织结构、力学行为以及焊接工艺进行深入研究，阐明在搅拌摩擦点焊过程中瞬时热、力作用下同步实现钎焊和扩散连接的机制及其影响因素，揭示复合焊接接头力学性能与焊接工艺、接头形成机理之间的相关性，并以此为基础来优化工艺、提高接头力学性能，实现Ti/Al异种金属的优质、可靠连接，为其在新型飞机、高铁车辆等装备研发中的应用奠定基础，并对推动我国高端装备轻量化制造技术的发展起到一定的促进作用。

项目发展了一种能用于Ti/Al搭接结构可靠连接的“搅拌摩擦点焊-钎焊-扩散焊”复合焊接新技术，采用复合焊接技术对3mm厚2A14铝合金和TC4钛合金进行了焊接，探索了钎料添加方式对复合焊接接头性能的影响，分析了复合焊接接头组织性能、界面结构和力学性能，得到如下主要结论：. (1)对于直接添加Zn箔钎料、钛合金表面喷涂预置Zn85Al钎料和钛合金表面焊前渗铝后添加Zn箔钎料这三种方式，在前两种方式下的轴肩界面区，钎料层与铝合金结合良好，与钛合金之间存在间隙，钎料与钛合金未发生润湿反应；第三种钎料添加方式下的轴肩区界面结合紧密，接头在轴肩区域的断裂方式为混合型断裂，靠近匙孔周围区域断裂位于渗铝层与钛合金结合面，轴肩边缘区域断裂位于界面下的渗铝层表层。. (2)钛合金表面焊前渗铝后添加Zn箔钎料的复合焊接接头形成过程可分为三个阶段，第一阶段为搅拌针下压时Hook的形成，第二阶段为钎料受热熔化在轴肩力作用下被挤出，第三阶段为剩余钎料在轴肩界面区的溶解、扩散反应。Zn钎料受热熔化在轴肩力的作用下被大量挤出，剩余的液态Zn填充了铝合金和渗铝层之间的间隙，在温度和压力作用下，两侧的Al不断向Zn中溶解，同时也伴随着Zn向Al中扩散，直到最后形成无缺陷和间隙的界面。 . (3)复合焊接接头抗拉剪力随着搅拌头转速的增加先增加后减小，随着焊接时间的增加先增加后减小再基本保持不变。在搅拌头转速为1200rpm，焊接时间为18s时，复合焊接接头的抗拉剪力达到最高，为13.87kN/点，是相同焊接条件下常规FSSW接头的最大抗拉剪力的2.1倍。. (4)复合焊接接头中钎焊界面的存在改变了裂纹在接头中的扩展方式使得疲劳载荷和疲劳寿命比常规FSSW大幅提高。在对应疲劳循环次数为2×106时，常规FSSW焊接接头与FSSW-S复合焊接接头的疲劳载荷分别为1.45kN和3.65kN。