Improvement of the adhesion of continuously manufactured multi-material joints by application of thermoplastic adhesive film

The development of tailored lightweight solutions is especially required for the support of the structural change from combustion to electric driven vehicles, due to the still challenging weight of the currently used lithium-ion batteries. The manufacturing of tailored multi-material structures consisting of steel and carbon fibre reinforced thermoplastics (CFR-TP) within a continuous roll forming process is a promising approach to combine innovative lightweight design and large-scale production capability. Nevertheless, fusion bonding as joining technology for steel and carbon fibre reinforced thermoplastics within a continuous process is still challenging because of not achieving sufficient joint strength. The application of adhesive films, which can be easily integrated in a roll forming line by coil-coating processes, seems to be promising to increase the adhesion between metal and CFR-TP. Therefore, a thermoplastic adhesive multilayer-film, consisting of functionalized polymers in different thermoplastic layers, is used within this study. The most important challenge consists in the even heating and consolidation of the multi-material structure within the limited joining time in a continuous fusion bonding process. To enable a variation in joining time, the existing test set-up is extended to a reversible, continuous process. The manufactured hybrid specimens as well as high pressure blasted references without adhesive film application are tested mechanically by climbing drum peel test to determine the production-related influence. In addition, micrographs of specimens are evaluated analytically by scanning electron microscopy. The examinations show the significant improvement of adhesion between steel and CFR-TP by application of thermoplastic adhesive multilayer-film. Lower steel temperatures in combination with reversing operation result in peel resistances almost comparable to sequential process.