Microstructure and mechanical property characterisation of aluminium–steel joints fabricated using ultrasonic additive manufacturing

Abstract

Driven by the interest to weld steel and aluminium in the solid state to prevent intermetallic formation, 9 kW ultrasonic additive manufacturing (UAM) has been used to fabricate Al 6061-4130 steel dissimilar metal builds. In addition, Al 6061-Al-6061 builds were fabricated using similar techniques to provide a baseline for mechanical property measurement. Mechanical testing performed using pushpin testing shows that steel–aluminium dissimilar metal welds fail across multiple layers while Al–Al welds delaminate from the substrate. Multi-scale characterisation indicates that the change in failure morphology is due to the formation of metallurgical bonds in the Al–steel builds. Texture analysis shows identical textures at the interface of Al–steel, Al–Al and Al–Ti joints; showing that the bond formation in all cases relies extensively on plastic deformation across multiple materials. In addition, no changes to the bonding mechanism occurred when the materials used as foils and substrate were swapped.