Effects of Surface Treatment and Morphology on Static and Fatigue Strengths of Adhesively Bonded Steel Plate

Both weight reduction and increase in safety of a car body are required in the automobile industry. Therefore, studies on a multi-material car body structure have progressed. To achieve this structure, techniques that can join dissimilar materials are necessary. Adhesive bonding is an effective joining method used for this purpose. However, the strength of adhesively bonded joints is low and should be improved. Treatment of the adherend surfaces is an effective method to increase the strength of adhesively bonded joints. In this study, blasting, atmospheric-pressure plasma irradiation, and their combined treatment were applied to steel plate cold commercial (SPCC) surfaces, and adhesively bonded joints were prepared using the treated SPCC sheets. The effects of the treatments on the characteristics of the SPCC surfaces and strength of the adhesively bonded joints were investigated. The characteristics of the SPCC surfaces were analyzed using laser microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. The static shear strength and fatigue properties of the adhesively bonded joints were examined. Blasting was found to be effective for increasing the static shear strength and fatigue properties of the adhesively bonded joints formed with the SPCC adherends because of the creation of surface asperities and generation of an anchor effect. Although atmospheric-pressure plasma irradiation decreased the contact angle of the SPCC surfaces owing to the elimination of the organic pollution layer, it did not increase the static shear strength and fatigue properties of adhesively bonded joints with the SPCC adherends. Therefore, the effect of the surface morphology on the static shear strength of the SPCC adhesively bonded joints was investigated in detail. Surface asperities with considerable height, narrow width, and several fine valleys were found to be effective for realizing adhesively bonded joints with higher static shear strength.