Enhancing Resistance‐Welded Joints Between 7075 Al Alloy and <scp>CF</scp> / <scp>PEEK</scp> via Thermoplastic Interface Strengthening

ABSTRACT This study demonstrates effective resistance welding between 7075 aluminum (Al) alloy and carbon fiber/polyether ether ketone (CF/PEEK) composites by combining chemical etching and silanization surface treatments with a polyetherimide (PEI) thermoplastic layer. The effects of this hybrid treatment on the bonding at the 7075 Al alloy/PEI thermoplastic layer interface and the mechanical performance of the welded joints are systematically investigated. Chemical etching created a micro‐nano rough surface that enhanced mechanical interlocking and increased hydroxyl group content from 12.7 mol% to 28.5 mol%. Subsequent silanization grafted amino (NH 2 ) groups onto the 7075 Al alloy surface, enabling hydrogen bonding with the PEI thermoplastic layer. Under the synergistic effects of mechanical interlocking and hydrogen bonding, interfacial bonding is significantly enhanced, increasing the lap shear strength (LSS) of the joint from 0.2 to 24.6 MPa. The fracture failure mode of the welded joint changes from the interfacial failure of the 7075 Al alloy and PEI thermoplastic layer to the interlaminar failure of carbon fiber tearing in the heating element.