Process window and mechanical interlocking in friction stir welding of laser-textured Al-7075 and PEEK

Polymer–metal hybrid joints are attractive for lightweight structural applications. However, their practical implementation is often limited by failure at the metal–polymer interface rather than by intrinsic material capability. To address this challenge, this work combines nanosecond laser-surface texturing with pinless Friction Stir Welding (FSW) to establish a controlled interfacial architecture in Al-7075/PEEK lap joints and systematically identify a stable, reproducible FSW processing window for reliable joint formation. Wave-shaped microgrooves are created on the aluminum surface by laser before joining to promote polymer-metal mechanical interlocking. Rotational speed, dwell time, and plunge displacement are varied, while joint integrity, groove preservation, and process stability are used as the evaluation criteria. A stable processing region was established primarily at 3000–4500 rpm, with dwell times of 2–6 s and plunge displacements of 0.1–0.2 mm, where sufficient polymer flow occurred without excessive thermal softening of PEEK or distortion of the microgrooves. Successful joints were obtained under restricted conditions at 6000 rpm, limited to low plunge displacement and short dwell time. Outside this processing window, higher rotational speed and longer dwell time were associated with PEEK over-softening and interfacial degradation, consistent with increased thermal input. In contrast, larger plunge displacement increases applied forging pressure and causes groove deformation, reducing interlocking efficiency. Statistical and post-failure analyses show that joint performance is governed primarily by mechanically driven interlocking arising from the interaction between the laser-defined microgrooves and the FSW parameters. The results provide a process-oriented framework for selecting FSW conditions that enable stable and repeatable fabrication of laser-textured polymer–metal load-bearing hybrid joints.