Effect of surface treatments on the interfacial strength for metal/composite hybrid joints

Purpose: This study is about determination of adhesive bonding between composite and different metals with various surface treatments and reviews the surface wettability properties and roughness of metals after surface treatments and shear strengths of the hybrid metal/composite joints conducting single lap shear test. Theory and Methods: Within this study, different metal types with various surface treatments such as cold working, laser texturing and sand blasting, are adhesively bonded to one type of composite. Aluminum 2024 T6, AISI 304 Stainless Steel and Titanium Ti-6Al-4V are the metal types that are coupled with polyamide composite material. The hybrid structure of the differently roughed surfaces of Aluminum, Stainless Steel and Titanium metal materials and PA 66 are tested by single lap shear tests. The shear strength values of these adhesive bonded couples are reported in association with their roughness and wettability properties. Results: The results showed that although the wettability values expected to be increased proportionally with roughness on all these surfaces; in fact, it varies according to the roughness type as it was seen on the sandblasting sample. Considering the results of the droplet contact angle, it is not possible to establish a relationship between shear strength and contact angle similar to that of surface roughness and shear strength. Conclusion: It is concluded that Al2024 sample with 15 Ra roughness forming a hybrid joint with PA 66 exhibited the best shear strength (8 MPa) among the metal samples exposed to different surface treatments.