预置焊丝对Al/Cu异种FSW T-搭接接头组织和性能影响

在FSW过程中，T型接头的内角热输入低、塑性流动差导致其易出现虫洞、隧道、交界线等缺陷，造成应力集中，很难实现具有良好力学性能的Al/Cu异种焊缝。创新性地将圆角处预置焊丝应用于4 mm厚的6061-T6铝合金和纯铜异种FSW T-搭接接头的连接，以期改善T型接头的内角材料塑性流动，获得具有良好力学性能的接头。分析了3种预置焊丝对Al/Cu异种 FSW T-搭接接头显微组织和力学性能的影响。结果表明，保持焊接速度35 mm/min不变，旋转速度在700~800 r/min条件下，3种预置焊丝接头大针搅拌区都表现出“洋葱环”。阶梯状搅拌头有效抑制了大量筋板材料向壁板的迁移，减少了Al/Cu互混。大针搅拌区由于少量Cu颗粒被搅拌，流动路径长，不易形成金属间化合物。Al/Cu形成了有效的冶金结合，其交界面处金属间化合物厚度小于1 μm。预置Cu的Al/Cu T-接头沿壁板方向像同种材料对接接头，呈韧性断裂；预置Al的Al/Cu T-接头改变交界线缺陷走向，筋板方向获得一定高度的Al/Cu混合区，机械互锁结合效果达到最优，断裂多在交界面处，抗拉伸强度达157 MPa，呈混合断裂。预置焊丝是一种适用于Al/Cu异种FSW T-搭接接头焊接的良好方法。

Effect of Pre-set Welding Wire on Microstructure and Mechanical Properties of Al/Cu Dissimilar FSW T-Lap Joints

It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for T-lap joints, due to the low heat input and poor plastic flow of the inner corner of the T-joint in friction stir welding (FSW), which leads to easy occurrence of wormholes, tunnel, bonding line defects, etc, and thus further causes stress concentration. Therefore, pre-set welding wires at the fillet were innovatively applied to 6061-T6 aluminum alloy (4 mm in thickness) and pure copper dissimilar plate FSW T-lap joints, in order to improve the internal plastic flow of T-joints, reduce defects, and obtain joints with good microstructure and properties. The effect of three types of pre-set wires on the microstructure and mechanical properties of Al/Cu dissimilar FSW T-lap joints was analyzed. Results reveal that three types of pre-set wire joints exhibit onion ring-like pattern in the large pin stirring zone at a constant travel speed of 35 mm/min and a rotation speed of 700?800 r/min. The progressive tool at all rotation speeds effectively inhibits migration of large amounts of stringer material to the skin and avoids base materials mixing. Small amounts of Cu particles are mechanically stirred and have a long flow path in the large pin stirring regions, which inhibits the formation of brittle Al/Cu intermetallic compound (IMC) phases during welding. Al/Cu forms effective metallurgical bonding, and the IMC thickness of the Al/Cu interface is less than 1 μm. The Al/Cu T-joints with pre-set Cu are similar to butt joints of the same material in the skin direction, showing a typical ductile fracture. In Al/Cu T-joints with pre-set Al, the direction of the bonding line defects is changed, a certain height of Al/Cu mixing zone is obtained in the direction of the stringer, achieving optimal mechanical interlocking bonding, and break mostly occurs at the intersection, with a tensile strength of 157 MPa, showing hybrid fracture. The pre-set welding wire is proved to be a good method for Al/Cu dissimilar FSW T-lap joints.