Effect of thermal exposure on the strength of adhesive-bonded low carbon steel

Recent trends toward economically fabricating lightweight vehicle structures while ensuring structural performance have led to the implementation of crash-toughened adhesive bonding in automotive industry. Adhesive bonding has been shown to offer better fatigue performance and greater flexibility in joining dissimilar materials when compared with resistance spot welding. While a great deal of effort has been focused on studying the performance of adhesive, there is an urgent need to understand the effect of curing conditions encountered in paint baking environment on the mechanical properties of adhesive-bonded workpieces.This study was carried out to determine the effects of curing temperature, curing time and enclosure conditions in the paint oven on the strength of adhesive-bonded structural steels. The enclosure conditions, simulating the exposure of the vehicle interior and exterior parts in paint baking environment, were classified into three types: fully-enclosed, semi-exposed and fully-exposed. Tests were designed and implemented to examine how the adhesive-bonded interior parts would cure in an electro deposition (ELPO) environment. The results showed that enclosure conditions influenced significantly the strength of the bonded steel because of variations in heat convection. The optimum curing temperature and time significantly depend upon the enclosure conditions of the joints. The increase of the curing time or curing temperature is beneficial for improving the strengths of the adhesive-bonded steel joints.