Joining of composites with metals becomes more popular across all industries due to their potential in lightweight design applications. Especially thermoplastic fiber reinforced polymer composites (TP-FRPC) are of particular interest for mass production due to the ability to use welding as an appropriate joining technology. For hybrid structures efficient joining is required, whereby induction welding is suitable due to the good heating properties of metals by induction.
In literature, several technologies for hybrid joining are reported and the bond strength is investigated. However, these investigations usually examine the bond strength directly after the joining process even regardless the type of material used. Especially for welding processes with thermoplastic polymers weathering behavior should be taken into account.
The aim of this study is to investigate the influence of welding temperature and weathering on the joint strength of welded hybrid joints by induction welding. The TP-FRPCs used were continuous glass fiber reinforced polyamide 6 (PA6), polypropylene (PP), polycarbonate (PC) and polyphenylene sulfide (PPS). The metal sheets are mild steel (1.0338 and 1.0330). The surface pretreatment of the metal sheets was either laser structuring in line pattern and two different types of functional coating adhesives. First the process parameters were optimized for each material combination by investigating the bond strength at different process temperatures. In a second step for each material combination a set of 21 specimens were manufactured with optimized process parameters for further investigations. To investigate the influence of weathering the cataplasma test (DIN EN 13523-27: 2009) as well as alternating climatic change (BMW PR 308.2) were used.
Each material combination used has a specific joining temperature and the most appropriate surface pre-treatment to achieve the highest bond strength after welding and weathering. It was also shown that surface pre-treatment has a huge influence on joint strength.
The test specimens are wrapped in water-soaked wool and then sealed in foil. The specimens are stored for 7 days at 70 °C. Then, the specimens are removed from the oven and stored in a freezer at -20 °C for 15 hours.
 Temperature ranges from -30°C up to +90°C with relative humidity from 20 % to 80 % with two repetitions