Friction stir welding of additively manufactured CuNiSiCr: effect of post-weld heat treatments on microstructure and mechanical properties

Abstract This study investigates the friction stir welding (FSW) of a CuNiSiCr alloy produced by laser powder bed fusion and the role of post-weld heat treatments in the microstructural evolution and mechanical performance of welded joints. The as-built alloy exhibited columnar grains, porosity, and lack-of-fusion defects. FSW refined the microstructure within the stir zone (SZ) and dramatically reduced porosity, both in pore number and size, as revealed by X-ray tomography. Mechanical testing showed that FSW joints outperformed the as-built specimens, with increased yield and tensile strengths, albeit with reduced ductility. Aging at 500 °C markedly enhanced hardness across both the base material and the SZ, achieving peak values of about 195 HV after 2 h. Peak-aged joints reached yield and tensile strengths that were 17% and 16% higher, respectively, than those of the base alloy. Direct aging proved as effective as conventional solution treatment and aging, simplifying the heat treatment route. These findings show that FSW followed by direct aging offers a promising approach for obtaining high-performance joints, providing a viable pathway for producing large, complex, additively manufactured CuNiSiCr assemblies with improved structural integrity.