Hybrid casting procedures could serially combine the positive properties of fibre composite materials and metals. Elaborate joining processes that influence the material properties would therefore be eliminated.

In an earlier project at the Fraunhofer IFAM the production of a multi-material system between CFRP and aluminium in an HPDC process using the high performance material PEEK as matrix material was investigated. Single-lap and double-lap samples were tested, single-lap-specimen shown in figure 1. As well as different PEEK films with varying thicknesses. For all film thicknesses, only superficial structural damage to the PEEK due to the heat input from the aluminium melt could be determined. The damage manifests itself through increased pore formation (presumably outgassing). The C-fibres never came into contact with the molten aluminium and therefore remained undamaged.

In the case of the double-lap samples, good connection qualities with form-fitting interlocking between aluminium and CFRP organic sheets could be determined. Within the single-lap specimen a good material connection could be realized during the casting process. In tension tests on these samples, adhesive fractures, mixed fractures and delamination in the CFRP could be observed. Due to the knowledge gained continuously from the basic tests on the single lap samples, an application-related hybrid holding element (bracket) from aircraft construction was developed and implemented during the project. Further experiments with the bracket are planned.

Due to the price structure of PEEK, it is mainly suitable for niche applications with high material requirements in use, such as aerospace, chemical or medical technology. [2]

For broad applications with higher volumes, there is a need to use cheaper matrix materials for the CFRP (e.g. epoxy matrices). This requires the use of a thermal insulation material to realize the joint within the Al HPDC process with CFRP materials that have a much lower temperature resistance than the PEEK used so far. The current work deals with investigations regarding the selection and characterization of different insulating layer concepts on the CFRP, as well as an evaluation of the suitability of the insulating layers for realizing the joining technology described above.

References

[1] L. Kroll and D. Nestler, Verbundwerkstoffe und Werkstoffverbunde, in Technologiefusion für multifunktionale Leichtbaustrukturen, L. Kroll, Ed. Berlin: Springer Vieweg, 2019, pp. 11–22.

[2] https://readingplastic.com/peek-plastic-price-per-pound/