Mechanical characterization of integral aluminum-FRP-structures produced by high pressure die-casting

Due to the growing demand for light-weight solutions in a wide range of industrial sectors, the selection and combination of different materials is becoming more and more important. As a result, there is an increasing need for suitable joining technologies. In a new joining process, flexible glass fiber textiles are integrated into aluminum by high pressure die casting in the first production step. These structures are used for the electrochemical insulation between aluminum and carbon fiber textiles, which are connected in the subsequent production step by textile technology. The finished compound is formed in a final resin impregnation process. Challenges faced by Fraunhofer IFAM lie in the positioning, pre-tensioning, and infiltration of the glass fiber textiles in the high pressure die-casting process. The advantage of this joining technology, in addition to the electrochemical insulation between aluminum and carbon fibers, is in a slim and light-weight connection. Therefore, no thickening of the individual joining partners is necessary, and the force flow lines are not deflected. Within mechanical investigations of those hybrid structures it was determined, that the infiltration content of aluminum has only a small influence on the achievable tensile strength. Rather, casting parameters such as the holding pressure have an influence. The subsequent resin infusion process enables an additional infiltration by the resin system of fiber bundles that have been only slightly infiltrated with aluminum. As a result, additional adhesion can be achieved and the infiltration gaps can be closed. Furthermore, an influence on the achievable tensile strength was observed regarding the use of the fiber material. Further increases in tensile strengths were also observed by adapting the textile parameters (e.g. reduction of the fiber undulations). A variety of failure behaviors could be observed in dependence on textile and process parameters. Tensile strength of the hybrid structures was compared to reference samples made of glass fiber reinforced epoxy resin, to determine the loss of strength caused by the joining technology. Further investigations were carried out, including a fracture surface analysis using a scanning electron microscope. Thus it was possible to determine mechanisms of adhesion between encapsulated glass fibers and the surrounding aluminum matrix

Investigation of integral endless fibre reinforced aluminium-polyamide 6 hybrid joints

Joining processes or connecting elements of structural components are generally used for integration into the automotive body structure. Joining operations cause a locally increased tension profile due to local punctual loads. Thus, a continous and homogenous load path of components to be joines is preferred. Therefore, glass fibre fabrics were imbedded in aluminium-polyamide 6 components by various moulding processes. Along the process chain of aluminium casting and injection moulding, integral endless fibre- reinforced aluminium-polyamide-6 vcomposites were manufactured. Tensile tests of Al-PA6 Test specimens with glass fibres were performed. For the aluminium casting process, low pressure die casting (LPDC) was used. The aluminium melt is moved, against gravity by pressurized nitrogen inducing high quality casting with low porosity, depressions and szhrinkage defects. The grip at the aluminium fibre interface results from microscopic undercuts between metal and fibre. In a second process step, glass fibres and aluminium parts were inserted into the injection moulding machine in which the glass fibres were infiltraded with PA6. Present investigations address non-destructive testing by microcomputer tomography (yCT) to investigate the infiltration of the glass fibres. For destructive methods bytensile testing, the breaking load is affected by the number of layers, infiltration behabiour, fibre orientation and AL-PA6- interface

Process concepts for the manufacturing of hybrid composites made from aluminum and CFRP with a polymer-based decoupling layer

Currently, conventional mechanical or adhesive joining technologies are used for the production of hybrid composites consisting of the light construction materials aluminum (Al) and carbon fiber reinforced polymer (CFRP). A direct joining of these materials is, however, problematic due to their electro chemical in compatibility and the resulting corrosive degradation. The aim of the new collaborative research project “Hybrid Casting” funded by the Deutsche Forschungsgemeinschaft (DFG) is to join Al and CFRP in novel ways using the aluminum high pressure die casting (HPDC) process to create an intrinsic hybrid composite with a decoupling and adhesive layer made from thermoplastic polyether etherketone (PEEK). Two process concepts to produce such a hybrid composite are the primary focus in this investigation