Microstructural Evolution and Mechanical Performance of Plasma‐Assisted Hybrid Friction Stir Welded Dissimilar Aluminum–Copper Joints

Plasma‐assisted hybrid friction stir welding (P‐HFSW) is a modification of conventional FSW that employs a low‐cost plasma torch as a localized preheating source to improve solid‐state joining of dissimilar metals. This study develops a P‐FSW setup for joining AA1100 aluminium to pure copper and examines the influence of plasma current, torch–tool offset, tool rotation, and traverse speed on thermal field, welding forces, microstructure, intermetallic compound (IMC) formation, and mechanical properties. Thermal and force measurements show that plasma preheating increases advancing‐side peak temperatures by 40–110 °C (up to ≈384 °C) while reducing axial and traverse forces by 30%–35% (from ≈8.1 kN to ≈5.3 kN under optimized conditions). Mechanical testing indicates major improvement with plasma: the nonpreheated joint (Experiment 1) achieved ≈42 MPa tensile strength (≈29% of Al), whereas the optimized preheated condition (Experiment 4, 55 A) reached ≈140 MPa (≈96% of Al), a ≈230% increase. Ductility also improved as elongation rose from <4% to >8%, showing a transition from brittle to ductile fracture. Optical, scanning electron microscopy, and X‐ray diffraction analyses confirm refined equiaxed grains, a uniform controlled IMC layer, and CuAl 2 , CuAl, and Cu 9 Al 4 phases. Controlled plasma heating enables balanced diffusion, limits IMC growth, and produces defect‐free, high‐strength AlCu joints for industrial applications.