Joining of LPBF-printed AlSi10Mg to AA7075-T6 wrought alloy by Refill Friction Stir Spot Welding

Laser Powder Bed Fusion (LPBF) is fundamental for producing lightweight, high-performance parts in the aviation industry. Currently, the produced LPBF parts are assembled with wrought alloy parts using rivets and bolts. Whenever disassembling the printed parts is not needed, permanent joints could be produced by Refill Friction Stir Spot Welding (RFSSW). In addition to the weight reduction due to absent bolt and rivet heads, costs can be reduced, since no pre-drilling is necessary when using spot welding techniques. RFSSW is a solid-state welding process, which enables the joining of 2000 and 7000 series aluminium alloys hardly weldable with fusion-based welding technologies. This work focuses on joining LBPF-printed AlSi10Mg with AA7075-T6 alloy sheets by RFSSW. Besides finding a suitable parameter window for welding these alloys, the correlation of the RFSSW process parameters with microstructure and mechanical properties was investigated. While welding time (WT) and plunge depth (PD) have been kept constant, the rotational speed (RS) and the travel factor (FT) have been varied in this study. Temperature measurements have been carried out, to determine the heat input in the performed spot welds. Lap-shear tests, microhardness measurements as well as SEM and EDS investigations have been conducted to investigate the microstructure and fracture surface of the welds. Defect-free and strong RFSSW welds were successfully achieved.