Development of Multi-Material-Joint Made of Copper-Coated FRP and Steel by Innovative Technology Fusion




Several technologies have been developed to join metal and polymer, such as adhesive bonding, clinching or screwing. These have disadvantages in terms of creep tendency of the adhesives or structural damage to the fiber-reinforced plastic (FRP).

An innovative process chain consisting of laser pre-treatment of the FRP before metallization by thermal spraying and the subsequent low-temperature soldering process enable a reliable multi-material bond, without structural damage either of the FRP or the metal part. In addition to a rough joining surface, the laser pre-treatment enables the deep interlocking of the thermally sprayed copper coating with the carbon fibre-reinforced plastic (CFRP) substrate. After the adhesion strength of the copper-coated CFRP could be doubled to 18 MPa compared to grit-blasting, this hybrid was joined to a steel counterpart with a soft solder BiSnAg1 using infrared heating. Additionally, the hybrid achieved a flexural stress of 1128.0 MPa in a 4-point-bending test without coating impairment. The multi-material joint achieved up to 15.5 MPa in the tensile shear test. During fatigue testing, the specimens withstood 5.000.000 load cycles at a maximum stress of 15 MPa and a mean stress of 8.6 MPa without any measurable structural damage. After salt water aging, the joining zone remained unaffected.