Influence of aluminum surface pre-treatments on the bonding mechanisms and mechanical performance of metal-composite single-lap joints

Abstract

The use of frictional heat for joining thermoplastic-based materials to metals has grown in importance in recent years. Friction spot joining is a relatively new joining technology suitable to join metal-polymer and composite overlap structures. In this work, the influence of various aluminum surface pre-treatments on the bonding mechanisms and mechanical performance of single-lap shear and cross-tensile joints was studied. Mechanical, chemical, and electrochemical pre-treatments were applied to the aluminum surface prior to the joining process. All surface pre-treatments increased the joint strength to some extent, compared with specimens without surface pre-treatments. Some of the treatments (chemical and electrochemical) led to the formation of strong chemical bonding between the aluminum and composite. Phosphoric acid anodizing with additional primer layer showed the best performance in increasing the joint’s strength. The reason was the strong bond formation between the primer layer and the matrix of the composite during the joining cycle. Moreover, the morphology and chemical composition of the aluminum after surface pre-treatments were analyzed in detail to study the correlation between bonding mechanisms and the mechanical performance of the joints. Finally, fracture surface of the joints was analyzed optically and by SEM, demonstrating parts of the composite remained attached to the aluminum after failure.