Microstructural and micro-hardness analysis of friction stir-welded AA6101/C11000 dissimilar joints with a hybrid interlayer

Abstract

In applications like busbars, electrical connectors, and heat exchangers, Al–Cu joints are increasingly popular for their cost-effectiveness and weight reduction. Friction stir welding (FSW) is a promising technique for creating sound Al–Cu joints, which are essential for ensuring the mechanical strength and electrical conductivity required in power systems. Stronger joints can enhance system durability and reduce the risk of failure. This study explores the impact of tool rotational speed (TRS) and tool traverse speed (TTS) on the microstructure and microhardness of friction stir-welded (FSWed) 3 mm thick AA6101/C11000 dissimilar joints with a hybrid interlayer (Ag and Zn). Microstructural examinations using scanning electron microscopy and phase evaluation were performed using X-ray diffraction. The present study carefully derived the optimum weld parameters contributing to the welded specimen's sound welds and microhardness. Varied traverse speeds (0.75, 1.25, and 2.25 mm/sec) exhibit distinct micro-hardness influenced by intermetallic layer thickness and brittleness. This manuscript highlights the influence of TRS (800–1800 rpm) on intermetallic compound (IMC) formation, with higher speeds yielding thicker IMC layers and increased microhardness. The optimal weld surface was achieved at 1200 rpm, indicating excellent material mixing, particle dispersion, and the formation of a composite structure in the stir zone. This resulted in a minimum microhardness of 98.33 ± 11.08 ${\mathrm{HV}}_{0.1}$ . The findings suggest that parametric optimization of FSW can effectively control the morphology and formation of micro constituents, enhancing the strength of Al-Cu joints.