Enhancement of the interface of friction welded steel-aluminium joints

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Enhancement of the interface of friction welded steel‑aluminium joints Bernd‑Arno Behrens1 · Deniz Duran1 · Tim Matthias1 · Ingo Ross1  Received: 31 July 2020 / Accepted: 26 October 2020 © The Author(s) 2020

Abstract Lightweight multi-material components are of great importance for the transport industry. Not only the component’s weight can be decreased, but also its local properties can be adapted to different loading profiles. Tailored Forming is a novel concept for producing multi-material components. By using a joining process, the creation of a bond between different materials takes place in the first step of the process chain. In the subsequent steps, multi-material workpieces are processed in their joined state while maintaining or improving the joint strength. This study focuses on steel-aluminium joints, which were created by friction welding and further processed by induction heating and impact extrusion. A counter pressure superposition mechanism was implemented in the extrusion tooling to control the stress state during plastic deformation. Flow behaviours of steel and aluminium are largely different at a given temperature, which necessitates a near step-function temperature distribution in the hybrid billet to obtain matching flow stresses. An inductive heating strategy was developed which led to a temperature gradient in the billets before extrusion. Extruded billets were analysed by destructive testing methods and metallography. The bond could be maintained after extrusion when counter pressure superposition was used; but no improvement could be obtained. Without counter force superposition, however, cracks were observed in the joining interface and the joint strength decreased. This paper discusses the aforementioned findings in the current process design and makes suggestions on how the involved processes should be reconfigured to improve the joint strength. Keywords  Tailored Forming · Multi-Material Components · Friction Welding · Impact Extrusion

1 Introduction Driven by rising energy and material costs as well as growing environmental awareness, energy and resource efficiency are increasingly becoming the focus of research and industry. Within the automotive industry, efficient lightweight construction enables weight and fuel consumption to be reduced. New materials are constantly being developed to achieve weight savings. Nevertheless, mono-material * Ingo Ross [email protected]‑hannover.de Bernd‑Arno Behrens [email protected]‑hannover.de Deniz Duran [email protected]‑hannover.de Tim Matthias [email protected]‑hannover.de 1



Institute of Forming Technologies an Machines, Leibniz University Hannover, Hanover, Germany

components are reaching their limits. Hybrid concepts can be used to further advance lightweight construction. In addition, hybrid components allow for adapted material properties that are appropriate for the local application purpose. Hybrid components are usually joined in a near-net-shape condition from two or more different materials. This means that the join