Influencing the mechanical properties of pre-JOINED hybrid semi-finished products by impact extrusion

Abstract

Hybrid components are made by combining two or more different materials and used in applications where monolithic components are not suitable due to their limited functionality or performance. Combining steel and aluminium in a technical component for power transmission provides the advantages of locally improved strength and reduced weight. However, the joining zone is critical for the component's performance because of brittle intermetallic phases which may develop. Therefore suitable measures must be taken to achieve a sufficient bond strength. The further forming of pre-joined hybrid semi-finished products allows the joining zone to be positively influenced, both geometrically and mechanically. In this study, components consisting of steel (20MnCr5) and aluminium (EN AW-6082) were first joined by friction welding and formed using three different impact extrusion processes to increase the joint interface area in the compound. In order to evaluate the influence on the bond quality, scanning electron microscope (SEM) images, impact bending tests and tensile tests were carried out. Depending on the adjusted interfacial area enlargements, an influence on the formation of the intermetallic compound and on the mechanical bond strengths could be observed. In contrast to specimens with an unaffected joining zone geometry after forming, those with a developed spherical joining zone and thus an enlarged interface (up to 36 %) achieved higher bond strengths (up to 17 % for tensile load; 42 % for impact load) and were characterised by local joint surfaces without a brittle intermetallic compound.