Adhesion of continuously manufactured fusion bonded multi-material structures consisting of steel and carbon fibre reinforced Polyamide 6

In regard to e-mobility and the correlating additional battery storage weight as well as the demand for the reduction of exhaust emissions in the automotive industry the development of lightweight solutions is required. Load-adapted tailored hybrid structures manufactured within a continuous production process offer a high potential for the automotive industry. With focus on high production rates and a high degree of automation, roll forming of multi-material structures is a promising approach. In order to improve strength and stiffness in relation to density, roll formed parts consisting of steel sheets reinforced by carbon fibre reinforced thermoplastic tapes (CFR-TP) are investigated. The evaluation of the adhesion between both materials joined in a continuous manufacturing process still is an important challenge, because the adhesion between both adherends is mandatory to transfer loads between both materials, and thus considered within the present work. To minimize the amount of process steps for a large-scale production of hybrid structures, the steel sheets and the thermoplastic tape are joined by fusion bonding while the surface of the thermoplastic matrix is melted and thus joined to the steel surface. Therefore a defined heating of both materials is required and consequently the effects of various temperatures on the adhesion have to be considered. With focus on achieving sufficiently high joint strength of multi-materials structures, various pre-treatments of steel as well as of CFR-TP were investigated. Hence, the present work focuses on the one hand on the evaluation of the adhesion between steel and CFR-TP dependent on various steel as well as CFR-TP temperatures within continuous manufacturing processes. On the other hand, effects of different surface conditions of both materials, due to surface pre-treatments of steel and CFR-TP, on the adhesion are examined. The continuously manufactured specimens are destructively tested by roller peel testing. In addition, evaluation of fracture patterns was carried out for the destructively tested hybrid joints. The examinations show the improvement of adhesion with increasing steel as well as CFR-TP temperature. Furthermore, additional pre-treatment results in an improved adhesion.