Enhancement of Ultrasonically Welded CF / PEEK ‐ Al Hybrid Joints via Multiscale Interfacial Engineering of Aluminum Substrates

ABSTRACT The intrinsic interfacial incompatibility between Polyetheretherketone (PEEK) and aluminum (Al) severely limits the performance of ultrasonically welded aerospace‐grade CF/PEEK‐Al hybrid joints. To address this challenge, a multi‐scale surface engineering strategy is developed for aluminum substrates by integrating laser micro‐texturing, sandblasting, and resin spray coating, enabling deliberate regulation of the welding interface. The optimized combination of laser texturing and spray coating markedly enhances joint performance, leading to a maximum lap‐shear strength of 23.6 MPa. Microstructural characterization reveals that laser‐generated micro‐cavities facilitate the formation of highly embedded resin anchor‐column structures, thereby promoting robust mechanical interlocking across the interface. As a result, the dominant failure mode transitions from brittle interfacial debonding to ductile cohesive fracture within the PEEK matrix. This mechanically governed interfacial bonding mechanism effectively compensates for the intrinsic thermophysical mismatch between Al and CF/PEEK during ultrasonic welding, ensuring enhanced joint stability suitable for aerospace fastening applications. The proposed surface modification approach thus offers a viable pathway toward reliable ultrasonic joining of metal–thermoplastic composite hybrid structures.