Surface treatment effects on interfacial fracture behaviour of aluminium-carbon fibre metal laminates

In Fibre Metal Laminates (FMLs), the metal-composite interface plays a crucial role in the stress transfer between the metal and the composite as well as the in the laminate’s overall structural performance. Although many surface treatment methods have been investigated for adhesive bonding, it is not straightforward to apply them directly to FML laminates due to differences in stress distribution and failure behaviour. This study provides a systematic and comparative evaluation of the influence of different aluminium surface treatments including mechanical, chemical and electrochemical methods, as well as sol–gel and primer coatings on the interfacial behaviour of Al–CFRP laminates. A failure-oriented analysis framework combining shear strength measurements, load–displacement response, cohesive failure assessment and fracture analysis using scanning electron microscopy was adopted. This approach enables a direct correlation to be established between surface characteristics, interfacial properties, and dominant failure mechanisms. The obtained results showed that P2 etching and chromic acid anodizing increase the adhesion at the metal − composite interface by approximately 62% and 67%, respectively, compared to sandblasting, due to the advantageous combination of surface structure and morphology. Furthermore, the application of sol–gel coatings enhances interfacial adhesion, improves stress transfer, and shifts crack propagation from the interface into the composite volume.