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

Hybrid components are made by combining two or more

different materials and are 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 that 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. To evaluate the influence on

the bond quality, scanning electron microscope images, impact bending tests and

tensile tests were carried out. Depending on the adjusted interface 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 14%) achieved

higher bond strengths (up to 18% for tensile load; 34% for impact load) and

were characterised by local joint surfaces without a thick brittle

intermetallic compound.