Enhancing mechanical properties of additively manufactured AlSi10Mg joints via friction stir welding with Cu interlayer and post-weld heat treatment

Friction stir welding (FSW) is widely used for joining lightweight automotive and aerospace materials such as AlSi10Mg, but the process often produces softened weld zones that limit joint performance. This study demonstrates that employing a Cu interlayer together with post-weld heat treatments provides an effective route to enhance the strength of 3D-printed AlSi10Mg components for such applications. Ageing at 170 °C for 2 h increased joint strength by 22% through Cu diffusion, while cryogenic treatment at −190 °C for 24 h produced an additional 54% improvement driven by grain refinement. Microstructural analysis shows that the enhanced performance results from Cu-solute strengthening, a more favourable Si-phase distribution, and preserved solid-solution content. These findings show that well-designed heat treatments can effectively overcome weld softening and produce high-strength joints suitable for automotive and aerospace applications.