Thermomechanical processing of friction welded steel-aluminum billets to improve joining zone properties

Bi-material machine components are fabricated usually by joining two individual components which are already given their near-final or final form. These are then put into operation either directly or upon a finishing process. Contrary to that, researchers of the Collaborative Research Centre “CRC 1153 Tailored Forming” are investigating novel process chains, in which different materials are joined in the first step and then subjected to further processing, i.e., forming, machining and heat treatment. By this means, the joining zone properties, which are adversely affected due to the joining process, can be treated and improved via thermomechanical processing during forming. On the other hand, process-specific challenges arise especially for workpieces consisting of dissimilar materials, i.e., steel and aluminum. In order to obtain a favorable flow behavior of the materials in the vicinity of the joining zone, a near step-function temperature distribution in the bi-material billet is desirable. Induction heating is viewed as the most promising method to be used for this purpose. At the Heat Treat 2017 conferences, a paper was presented which discussed the strategy for thermomechanical processing and the modeling of the first concept for the induction heating process. The current study builds on the previous paper and presents the modeling of the forming process along with the analysis of the first prototype samples formed using the technology. A comparison will be made of the joining zone properties before and after thermomechanical processing. Additional considerations will be given on how to further improve the process and move towards a production capable process.