Beschichtungen für das Druckgießen von stoffschlüssigen Hybridbauteilen aus Aluminiumguss und Stahlblech

• Coatings for high pressure die casting of metallurically bonded hybrid compounds made of cast aluminum and sheet steel

Gerdt, Leonid; Bobzin, Kirsten (Thesis advisor); Bührig-Polaczek, Andreas (Thesis advisor)

Düren : Shaker (2021)
Book, Dissertation / PhD Thesis

In: Schriftenreihe Oberflächentechnik 68
Page(s)/Article-Nr.: XV, 143 Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

The trend towards lightweight construction with simultaneous increase in the performance of components in the modern automotive industry requires innovative engineering of technical materials. One approach here is to combine the unique properties of aluminum and steel as main construction materials. Die casting of aluminum-steel hybrid components is a novel technology that integrates forming and joining processes and enables the production of components with complex geometries. Despite its potential, there are still several challenges involved in die casting of aluminum-steel hybrid components, which limit the widespread application of this technology. First, the establishment of a metallurgical bond between aluminum melt and the steel is strongly suppressed due to short process times and rapid cooling of the melt. The previous solution approaches were therefore based on the form and friction locking between aluminium cast and steel insert. In this case a gap formation between both materials can hardly be avoided and therefore increases the risk of crevice corrosion during the application. Furthermore, metallurgical bonding between aluminum and steel is always associated with the formation of a reaction zone consisting of intermetallic phases. Beyond certain thicknesses, such reaction zones can considerably impair the mechanical properties of the hybrid components. Within this study, innovative coatings were examined to be applied on the steel inserts. The investigated coatings aim to inhibit the formation of gaps during the die casting of aluminum-steel hybrid components and furthermore, to control the formation of reaction zone. Here two different approaches were applied, namely low-melting Al based coatings deposited by cold gas spraying and deposition brazed copper coating were comprehensively analysed. Based on the results, the shear tensile strength of the aluminum-steel hybrid components will be significantly increased and the risk of gap formation considerably minimized by applying each of the coating systems. Moreover, it is possible to realize the adjustment of the metallurgical bond between the aluminum cast and the coatings. However, the aluminum-based coatings deposited by cold gas spraying can be severely damaged by aluminum melt, depending on the process parameters during the die casting process. Nonetheless, the cohesive and adhesive strength of the coatings can be increased by heat treatment of the coated samples and pretreatment of the insert, respectively.