Assessment of surface treatment methods for strengthening the interfacial adhesion in CARALL fiber metal laminates

Metal and polymer interface bonding significantly influences the mechanical performance of fiber metal laminates (FMLs). Therefore, the effect of surface treatments (mechanical abrasion, nitric acid etching, P2 etching, sulfuric acid anodizing (SAA), and electric discharge machine (EDM) texturing) carried on aluminum 2024-T3 alloy sheets was evaluated considering surface morphology, surface topography, and surface roughness. Further, the influence of surface treatments on interfacial adhesion strength and failure mode between the aluminum alloy and carbon fiber prepreg was investigated. The surface treatments increased the surface roughness of the aluminum substrates. Surfaces treated using SAA, nitric acid, and P2 etchant showed improved wettability, while mechanically abraded and EDM textured substrates showcased hydrophobic behavior. The selected surface treatments significantly affected interfacial adhesion between the epoxy polymer and aluminum alloy. SAA and EDM texturing greatly enhanced the interfacial peel strength of FMLs. In the case of interfacial shear strength, EDM textured substrate showed superior performance, followed by SAA. Moreover, untreated and mechanically abraded specimens exhibited weaker bonding and adhesive failure at the aluminum-epoxy interface, whilst chemical treatments resulted in mixed model failure. EDM textured surface underwent cohesive failure, while a dominant mixed mode failure and fiber adhesion were observed in the SAA-treated specimen.