Enhanced mechanical performances and corrosion resistance of carbon fibre reinforced PEEK-aluminium alloy fiber metal laminates through an innovative two-step electrochemical treatment

This work deals with the assessment of the effect of an innovative anodizing process on the mechanical performance and corrosion resistance of fiber metal laminates (FMLs) composed of 7075-T6 aluminium alloy and carbon reinforced polyether ether ketone (PEEK) for aerospace applications. To this aim, tartaric-sulfuric acid (TSA) and phosphoric-sulfuric acid (PSA) were combined in a novel two-step anodizing process to form an oxide film on the metallic substrate. Additionally, TSA was modified by pore widening in a 0.1 M solution of NaOH. Mechanical abrasion with sandpaper was also employed as a reference. The morphologies of the metallic samples were analyzed using scanning electron microscope (SEM), while their surface wettability was evaluated through contact angle measurements. Furthermore, electrochemical impedance spectroscopy (EIS) was conducted to investigate the corrosion resistance of the metallic samples. To evaluate the impact of the proposed treatment on the mechanical strength of FMLs, their interlaminar shear strength (ILSS) was investigated via short beam shear tests. Overall, experimental results demonstrate that the innovative two-step anodizing technique with TSA followed by PSA (TSA-PSA) exhibits high mechanical improvement over the reference mechanical treatment (comparable to commercial PSA-only), while maintaining good corrosion resistance (comparable to commercial TSA-only).