Due to EU regulations on fuel consumption, reducing the weight of vehicles has become one of the most important goals of car manufacturers in Europe. Among them, Toyota Motor Europe is one of the worldwide leaders in the research for a sustainable future. Materials like fiber-reinforced plastics and aluminum play a significant role in the research for lightweight design, thanks to their very good strength-to-weight ratio. However, joining these materials efficiently together is still a challenge. When thermoplastic composites are used, direct joining with the metal substrate can be obtained using welding technologies which melts the thermoplastic at the interface. Ultrasonic welding is well-known for being a fast, reliable and effective technology for metal/metal or plastic/plastic joining. In this study, a collaboration between Toyota and TU Delft, ultrasonic plastic welding was investigated as candidate joining technology for aluminum/thermoplastic joints in automotive applications. The goal was to understand the main mechanisms involved in the adhesion and how they affect the performance of the joint. Initially, the technique proved to be successful, but moderate strengths were obtained. Therefore, several surface pre-treatments of the aluminum were analyzed to improve performance in terms of strength and durability of the joint; mechanical, chemical and physical treatments were carried out. With laser structuring, strengths comparable to adhesive bonded joints were obtained, but in a much shorter process time. Other treatments such as conversion coating, sandblasting and plasma led to considerable improvements as well. The encouraging results achieved represent an important step in the development of ultrasonic plastic welding for multi-material joining in the automotive industry. Additional research could help Toyota and other car manufacturers realizing a better design to further decrease weight and CO2 emissions of vehicles.

Due to environmental challenges and need for action with regard to CO 2 emission, reducing the weight of vehicles has become one of the most important goals of car manufacturers in Europe. Materials like fibre-reinforced plastics and aluminium are the core of the research for lightweight design. However, efficiently joining these materials together is still a challenge. When thermoplastic composites are used, direct joining (i.e. without adhesives or fasteners) with the metal substrate can be obtained using welding technologies which melt the thermoplastic at the interface. In this study, ultrasonic plastic welding was investigated as a candidate technology for joining aluminium and carbon fibre-reinforced thermoplastics. The goal was to understand the main mechanisms involved in the welding process and how they affect the performance of the joint. Initially, the technique proved to be successful, but moderate strengths were obtained. Therefore, several surface pre-treatments of aluminium were analysed to improve the performance in terms of lap shear strength; mechanical, chemical and physical treatments were also carried out. With laser structuring, strengths comparable to adhesive bonded joints were obtained, but in a much shorter process time. Other treatments led to considerable improvements as well. The encouraging results achieved represent an important step in the development of ultrasonic plastic welding for multi-material joining in the automotive industry. @en