Influence of Surface Finish and Energy Director on Ultrasonic Welding Process of PAEK/Metal Hybrid Structures

The demand for lightweight, multifunctional, and durable hybrid structures is rapidly increasing in aerospace, biomedical, and advanced engineering sectors. Ultrasonic welding (USW) offers a promising route to assemble thermoplastic polymers with dissimilar materials such as stainless steel, aluminium, and ceramics, without adhesives or additional fasteners. This study investigates the ultrasonic joining of high-performance thermoplastics, including carbon fibre-reinforced polyetheretherketone (PEEK), and polyetherimide (PEI) as energy director (ED), with aluminium alloys. Improvement of manufacturing efficiency and weld attributes such as welded area, strength, and failure mechanisms are essential for industrial adoption. In this work, particular attention was given to the effect of metal surface preparation and ED film on weld quality. Weld attributes were analysed in terms of joint area continuity, interfacial morphology, tensile shear strength, and observed failure modes. Whereas not all parameter sets led to successful joining, the findings provide insight into the role of surface finish and ED in determining weldability. These results contribute to the ongoing development of reliable welding for hybrid joining between thermoplastics and metals, highlighting opportunities for thermal process innovation beyond conventional approaches.