Magnetic pulse welding of Al/Al and Al/Cu metal pairs: Consequences of the dissimilar combination on the interfacial behavior during the welding process

Abstract

This paper presents a comparison between Al/Al and Al/Cu magnetic pulse welded pairs, which highlights the influence of the dissimilar metal combination on the welded interface with respect to the variation in the initial radial air gap between a flyer and a target part. The welding of the Al/Al pair offers good bonding for a gap between 1mm and 4mm with a constant input voltage of 7.5kV. The Al/Al interfaces show a metal continuity that can either be straight or wavy, and become progressively sheared by the welded parts with the increase in initial gap, so that the nearby grains of the interface evolve from an undeformed equiaxed to a flattened and elongated morphology. The welded joint deteriorated by a formation of fracture and voids which occurs as a result of strong interfacial shearing for large initial air gaps, which also leads to an ejection of fragments. In the welding of an Al/Cu combination, the nature of the interface changes. A formation of intermediate phases in the form of layers or pockets which constitute of a third compound becomes obvious at the Al/Cu interfaces, which may trigger various detrimental phenomena of the joints. Depending on the thickness of the intermediate phase, the interface becomes sensitive to several mode of failures such as formation of radial microcracks, fragmentation, axial propagation of macrocracks in tensile opening mode, fracture due to an interfacial ejection or interfacial separation due to a melting of the intermediate phase. These defects degrade the joint which initiate the formation of cracks at the interface for low initial air gap (g=1mm), even with a thin intermediate phase of few micrometers. The interface becomes completely damaged for an initial air gap of beyond 3mm.