Intrinsic Aluminum CFRP Hybrid Composites Produced in High Pressure Die Casting with Polymer Based Decoupling Layer

Abstract

Combining aluminum and carbon fiber reinforced plastic (CFRP) has been a key focus in realizing lightweight concepts. Manufacturing technologies for high load-bearing and ultra-lightweight CFRP structures have reached a high level of innovation. The same goes for near-net-shape high pressure die casting (HPDC) aluminum components, which can be mass-produced in a highly efficient manner. Yet for hybrid composites of these materials, the solutions to date have relied on conventionally mechanical or adhesive joining techniques. The direct joining of these two materials is problematic, due to their electrochemical intolerance and the resulting corrosive degradation. The joining technology therefore is at the center of this challenge. The DFG-sponsored joint research project of Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Fiber Institute FIBRE, and Bremen Institute for Mechanical Engineering BIME, all three institutes located at the campus of the university in Bremen, aims at combining aluminum and thermoplastic CFRP into an intrinsic hybrid composite. This is to be achieved in a single-step primary shaping process, avoiding conventional joining techniques like adhesive bonding or riveting. To this end, CFRP structures are to be recast with aluminum, creating an electrochemically decoupling layer between the two materials. This decoupling layer can therefore be considered as a key factor for realizing hybrid composites. It also needs to have a high process reliability and be long-term and mechanically stable. Polyetheretherketone (PEEK) thermoplast was identified as a suitable material for that purpose, given its stability at high temperatures and electrochemical insulation effect. First test results show the possibility of incorporating CFRP accordingly by HPDC, resulting in a continuous intact decoupling layer of PEEK. The trend indicated that different thermal treatments as well as different aluminum thicknesses of the hybrid casted sample influence the joint strength. On average, in tensile shear tests a joint strength approximately in the range of current single lap adhesive bonds could be achieved.