Influence of copper interlayer on the mechanical performance of friction stir welded AA2024

This paper investigates the mechanical properties of AA2024 joints welded using the Friction Stir Welding (FSW) process, with a particular focus on comparing joints made with and without the inclusion of a commercially pure copper sheet between the edges being welded. The study aims to understand the influence of weld heterogeneity on the mechanical properties of FSW joints. Various joints were fabricated with a copper interlayer, and optimal process parameters—rotational speed, advancing feed, and tool geometry—were identified. Mechanical tests, including Rockwell B and Vickers hardness (HV) tests, as well as tensile tests, were conducted on both homogeneous and heterogeneous joints. The results showed that the presence of copper significantly affected the hardness distribution, particularly in the weld nugget. Heterogeneous joints demonstrated a notable increase in HV at the nugget and a reduced weld-affected area on both the advancing and retreating sides. The study found a strong correlation between process parameters, tool geometry, and the Ultimate Tensile Strength of the joints. Optimal mechanical properties were achieved in heterogeneous joints welded at 800 rpm and 40 mm/min with an 18 mm tool, resulting in a joint efficiency of 73%. These parameters differed significantly from those optimized for homogeneous joints, which were 1200 rpm and 100 mm/min with a 16 mm tool. It was also observed that exceeding 1000 rpm in rotational speed and 70 mm/min in feed speed is not advisable for heterogeneous welds. Future research should explore varying amount of copper and other materials, as well as different interposition methods, to further understand their effects on the mechanical properties of FSW joints