Lightweight Design

Joining CFRP and Aluminum without Contact Corrosion

| Author/ Editor: Dorothee Quitter / Alexander Stark

In cooperation with the Faserinstitut Bremen, Fraunhofer IFAM has developed a new joining technology for the combination of aluminum casting and CFRP that is suitable for series production.

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Holding element for aircraft construction manufactured using hybrid casting technology. A temperature-resistant protective layer on the CFRP component prevents electrochemical corrosion processes in the composite material. The layer also ensures a firm bond.
Holding element for aircraft construction manufactured using hybrid casting technology. A temperature-resistant protective layer on the CFRP component prevents electrochemical corrosion processes in the composite material. The layer also ensures a firm bond.
(Source: Fraunhofer LBF)

A material mix of fiber composites and light metals is a particular challenge for all established joining technologies. At the same time, high joint strengths should not result in any significant weight increase caused by joining. Contact corrosion of the two materials must be prevented. In addition to glued or riveted hybrid joints, hybrid die casting offers a new approach to saving weight in joining and permanently preventing problematic contact corrosion.

Only a Few Process Steps Towards a Hybrid Component

As part of the newly developed process, CFRP structures are partially coated with high-temperature stable plastic (PEEK) prior to the casting process. This material only begins to decompose noticeably at temperatures of around 550 °C. The process is also known as the "PEEK" process. In a subsequent casting process step, the CFRP component is placed in the die casting tool where it is encapsulated with aluminum at a temperature of around 700 °C in the plastic area. Due to a targeted control of the die casting process with short cycle times and the selection of further suitable process and material parameters, it is possible to integrate the plastic into the die casting process despite the temperature differences without impairing its properties. In this way, a stable bond between the two materials is created during the primary forming process of the aluminum component. A complex processing or pre-treatment of joining surfaces is therefore not necessary. Optionally, undercuts can also be incorporated in the joining zone to further increase strength. At 20 MPa, the joining strengths achieved to date are already in the range of structural adhesives.

The feasibility study for efficient series production involved the selection of a holding element from the aircraft construction industry that is to be installed in large numbers. The aim of the development team is to use this component to further develop hybrid casting technology in such a way that a process window can be shown for aluminum die casting which allows reproducible mass production of hybrid connections between CFRP and aluminum.

This article was first published by konstruktionspraxis.

Original: Dorothee Quitter / Alexander Stark

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