Constructing quasi-vertical epoxy-pins at bonding interface to improve bonding strength of aluminum alloy and carbon fiber reinforced plastics

This study focused on the various surface treatments of grinding, NaOH etching, HCl pickling, micro-arc oxidation and anodic oxidation to strengthen adhesive bonding joint of Aluminum (Al) substrate and Carbon Fiber Reinforced Plastics (CFRP). Different surface conditions were created by these treatments and simple Resin Pre-Coating (RPC) technique was further used to reduce the potential void defects at the root of those micro-cavities. Carbon Nanotubes (CNTs) were guided into the etched micro-cavities to construct quasi-Z-directional fiber bridging and form the "CNT-reinforced epoxy-pins”. The surface performance testing results imply that anodic oxidation of Al substrate created relatively even and continuous channels with higher hardness and better wettability among these treatments, which could provide quasi-vertical spaces for containing epoxy adhesive or CNTs. The single lap shear test results show combined treatments of anodic oxidation and upgraded RPC with CNTs technique on Al substrate yielded the highest bonding strength of 21.8 MPa (up to 243.3% greater than base strength). The constructed through-the-thickness "epoxy-pins” or "CNT-reinforced epoxy-pins” contributed to failure modes changing from complete debonding failure of Al substrate to peeled-off shallow fiber or delamination failure of CFRP panel. The combined treatments could be utilized to manufacture high-performance Al-CFRP composites for aviation industry application.