Comparison of the joining zone development of hybrid semi-finished products after different extrusion processes

The use of hybrid semi-finished products made of aluminium and steel enables the production of components with locally adapted properties, i.e. high strength and wear resistance combined with reduced weight. Within the scope of this work, different impact extrusion processes for forming friction-welded hybrid semi-finished products consisting of steel (20MnCr5) and aluminium (EN AW-6082) were developed and experimentally implemented. The resulting material flows were intended to generate different joining zone geometries and to allow the influence of thermo-mechanical treatment during impact extrusion on the quality of the joining zone to be assessed. For this purpose, full-forward extrusion, backward-cup extrusion, backward-cup full-forward extrusion, and hollow-forward extrusion processes were investigated at elevated temperatures. The resulting joining zones were analysed based on metallographic images providing detailed microstructural information and further insights into the forming-related influence on the friction-welded joining zone. The backward extrusion processes proved to be the most suitable for significantly enlarging the joining zone interface due to beneficial material flow. In contrast, forward extrusion processes showed no significant influence on the joining zone geometry and resulted in delamination during hollow-forward extrusion. Compared to backward-cup extrusion, a reduced joining zone deformation was evident in the backward-cup full-forward extrusion process.