Influence of Bonding Condition between Galvanized Steel Sheets and Adhesive on Deterioration Behavior of Adhesive Joints

Abstract

Needs for adhesive bonding in automotive production are increasing. One difficulty with adhesive bonded parts is their deterioration over time. Therefore, using steel sheets with different attributes, we investigated the deterioration behavior of adhesive-joined parts. Results demonstrated that deterioration over time is attributable to reduced strength of interfacial adhesion between the metal surface and the adhesive, and that the degree of deterioration depended on the metal coating type. Furthermore, the deterioration behavior was affected by the difference in the bonding state, which depended on the type of metal coating and adhesive. For this study, we estimated the bonding condition between the galvanized steel sheets and the adhesive by examining the work of adhesion and surface free energy. Then we examined the adhesive bonding aging mechanism. That examination, conducted in the early stage of deterioration, revealed that the intermolecular force was cut by water penetrating the adhesion interface, and that the adhesive strength was reduced. In contrast, when the deterioration occurred over a long term, the deterioration was accelerated further by corrosion of the galvanized steel sheet. Additionally, results show that existence of the chemical bonds at the adhesive interface was more important than intermolecular forces for suppressing deterioration.