Ti/Al无针搅拌摩擦搭接点焊接头组织特征

Microstructure characteristics of Ti/Al lap joints with pinless friction stir spot welding

采用无针搅拌摩擦搭接点焊对Ti6Al4V钛合金和2A12铝合金异种金属进行焊接,焊后低熔点铝合金受摩擦热影响发生熔化,而高熔点钛合金在焊接过程中始终保持固态,同时与处于液态的铝合金相互作用,最终Ti/Al界面形成熔钎焊接头且接头拉伸剪切力达19.20 kN。研究了Ti/Al熔钎焊接头钛合金和铝合金的组织变化以及连接界面的特征形貌。结果表明由于摩擦热及搅拌头下压的影响,焊点处钛合金和铝合金组织发生明显变化。钛侧主要形成热力影响区和母材区;铝侧形成熔核区、热影响区和母材区3个区域,热影响区和熔核区的晶粒尺寸相对母材区变粗大,其组织经历了受热长大、部分熔化到完全熔化3个过程。在搭接接头界面处形成均匀致密且微薄的金属间化合物层,主要成分为TiAl_(3);接头界面区组织变化明显,中间部位有均匀的TiAl_(3)界面层,随着向接头两边延伸界面层逐渐消失且Cu元素聚集在边缘。相对其他Ti/Al搭接点焊的焊接方法,无针搅拌摩擦搭接点焊获得的接头抗拉伸剪切力得到了明显的提升。

The dissimilar metals of Ti6 Al4 V titanium alloy and 2 A12 aluminum alloy were joined by pinless friction stir lap spot welding. After welding, the low melting point aluminum alloy was melted by friction heat. The high melting point titanium alloy remained solid during the welding process and interacted with the aluminum alloy in the liquid state. Finally, at the Ti/Al interface formed a welded joint, and the tensile shear force of the joint reaches 19.20 kN. This paper studied the microstructure changes of the titanium alloy and aluminum alloy, and the characteristic morphology of the joint interface. The results indicate that due to the influence of friction heat and the downward pressure of the stirring head, the structures of the titanium alloy and aluminum alloy at the welding point changed significantly. On the titanium side mainly formed the thermal mechanically affected zone and the base material zone. Three areas formed on the aluminum side: the nugget zone, heat-affected zone, and base material zone. The grain size of heat-affected zone and nugget zone was larger than that of the base material zone, and its structure underwent a process from being heated for a long time to melt to complete melting. A uniform, dense and thin intermetallic compound layer formed at the interface of the lap joint, with the main component being TiAl_(3). The interface area of the joint changed obviously. There was a uniform interface layer in the middle part, and the layer gradually disappeared as it extended to both sides of the joint with the gathering of Cu at the edge. Compared with that by other Ti/Al lap joint welding methods, the tensile and shear strength of the joint obtained by pinless friction stir spot welding has been significantly improved.