A multi-level interfacial structure between 304 SSM heating elements and GF-PA66 for synergistic strengthening in resistance welding

Interfacial bonding reliability remains a critical challenge in resistance welding of fiber-reinforced thermoplastic composites (FRTP) for lightweight applications. In this study, to transform the SSM from a passive heating element into an active load-bearing component, a multi-level interfacial structure featuring a roughness-induced discontinuous silane layer was constructed on 304 stainless steel mesh (SSM) via sequential hydrochloric acid (HCl) etching and γ-aminopropyltriethoxysilane (APTES) coupling. The underlying strengthening mechanism was systematically investigated. Results showed that etching created a three-dimensional micro-nano structure on the SSM, enhancing the interfacial bonding strength via anchoring. Simultaneously, the enlarged surface area and the increase in surface hydroxyl (-OH) density facilitated the adsorption of APTES. Critically, the self-condensation of APTES was suppressed on the rough surface, yielding a discontinuous silane layer rich in both amino (-NH₂) and silanol (-Si-OH) groups, which promoted the formation of a dense hydrogen-bonding network with GF-PA66. Consequently, the synergistic reinforcement from micro-mechanical interlocking and molecular-level hydrogen bonding increased the joint strength by 54.16% to 44.43 MPa. The corresponding failure mode shifted to a mixture of cohesive resin tearing and cooperative SSM deformation, confirming the functional transformation of the SSM. This work provides new insights into silane-based interfacial design for high-performance FRTP resistance welding and deepens the understanding of multi-level interfacial interactions in metal-polymer composite systems.