Aluminium to Copper Lap Joining Using Friction Stir Welding

Al/Cu joints are very interesting for electric power industry in applications where transition pieces are used to transmit electricity. Nevertheless, Al/Cu joints are hardly weldable by using fusion welding techniques due to its remarkably different physical properties as well as to its chemical affinity at fusion welding temperatures. In this context, Friction Stir Welding (FSW), which is a relatively novel solid-sate welding process, is regarded as a technique with strong potential for Al/Cu joining. However, in the recent years, only a few studies have been reported regarding FSW Al/Cu lap joining. Elrefaey et al.^[1] and Abdollah et al.^[2] investigated the performance of Al/Cu friction stir welded lap joints and the metallurgical phenomena occurring at the base materials interface. They reported that high rotation speeds can lead to brittle failure modes due to the formation of intermetallic compounds. In both studies the Al sheet was placed in the upper side of the lap joint and the Cu sheet at the bottom.

In the present work Al/Cu lap joining has been attempted by putting a 1 mm thick sheet of Cu DHP over a 7 mm thick plate of AA5083 H111. Then, the rotating tool was plunged from the copper surface into the aluminium plate and lap joints were produced, in forge force control, using varying rotational and welding speeds. It was noticed that excessive heat input lead to the deformation of the upper Cu sheet, resulting in defective welds. Mechanical and microstructural analyses enabled to correlate the strength of the joints with the formation of IMCs.