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.
Highlights
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
The Tailored Forming approach, developed in Collaborative Research Centre (CRC 1153), consists of a preceding joining step to combine the different materials to a hybrid blank and a subsequent further processing
Steel is not subjected to plastic deformation during the welding process, whilst aluminium is displaced to the welding flash from the rubbing zone
Summary
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. New materials are constantly being developed to achieve weight savings. Hybrid components are usually joined in a near-net-shape condition from two or more different materials. This means that the joining process is located at the end of the process chain. The Tailored Forming approach, developed in Collaborative Research Centre (CRC 1153), consists of a preceding joining step to combine the different materials to a hybrid blank and a subsequent further processing. The simultaneous processing of different materials results in process-specific challenges that must be solved, in order to achieve good and reproducible results. The materials are heated inductively and formed by impact
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