The ultrasonic welding technology is an innovative method to produce hybrid joints for multi‐material components. The investigations described in this paper were carried out using the ultrasonic metal welding technique for joining carbon fibre reinforced thermoplastic composites (CFRP) with sheet metals like aluminium alloys or aluminium‐plated steels. The achievable mechanical properties as a function of the process parameters are presented. Additionally, microscopic investigations of the bonding zone are discussed. One important advantage of ultrasonic metal welding is the possibility to realise a direct contact between the load bearing fibres of the reinforced composite and the metallic surface without destroying the carbon fibres.

Current demands on light weight constructions lead to an increasing use of light weight metals such as aluminum or magnesium alloys as well as fiber reinforced polymers (FRP). Suitable welding methods are necessary to join these dissimilar material groups and to integrate them in engineering structures. At the Institute of Materials Science and Engineering the ultrasonic metal welding technique was successfully applied to realize aluminum sheet/carbonfiber-reinforced polymer (CFRP) -joints. The welding during this process occurs in two steps: First the ultrasonic shear waves lead to a softening and displacement of the polymer matrix out of the welding zone. In the second step a direct weld between the load bearing carbon fibers of the CFRP and the aluminum alloy sheet is generated. A welding time of less than 5 s and no damage of the carbon fibers are important advantages of the process. Actually tensile shear strengths of about 30 MPa were achieved for the joints. By means of light microscopic and SEM investigations the bonding mechanisms can be described in detail. Possible application fields of such welds can be seen in the automotive or in the aircraft industry.

To realize multi-material structures, e.g., out of light metals and fiber reinforced polymer (FRP) composites suitable joining methods are required. The ultrasonic metal welding technology was applied to produce high strength joints between different aluminum alloys and carbon fiber reinforced polymers (CFRPs) in the framework of research unit 524 of the German Research Foundation. The bonding mechanisms were characterized by light optical and scanning electron microscopy (SEM). The performed analysis have shown a bonding zone with an intensive contact between the metallic surface and the load bearing carbon fibers of the CFRP as a result of the ultrasonic welding process. Using precipitation hardening aluminum alloy AA2024 tensile shear strengths of up to 58 MPa could be achieved. In comparison to established joining techniques ultrasonic metal welding can be an interesting alternative to realize dissimilar joints for the automotive or aircraft industry.

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