Electromagnetic pulse welding of Al/Cu dissimilar materials: Microstructure and tensile properties

The aim of this study was to characterize detailed interfacial microstructures and evaluate tensile properties of Al6061-to-Cu dissimilar welded joints via electromagnetic pulse welding (EMPW) at different discharge voltages. The EMPWed joints consisted of annular weld zone and central non-weld zone. The outer and inner regions of annular weld zone exhibited mainly diffusion bonding and mechanical interlocking, respectively, representing a well-bonded interface. Distinctive discontinuous "droplet-like" pseudo-eutectic (alpha-Al + Al2Cu) particles or patches were observed to eject in the adjacent transition region in the non-weld zone. The highly non-equilibrium eutectic-like liquid or slurry at the Al/Cu interface was formed due to the ultra-high strain rate experienced by the interface and the ensuing instant temperature rise beyond the eutectic temperature of Al-Cu system, when the high-velocity flyer Al sheet crashed into the fixed Cu sheet driven by the Lorentz force during EMPW. The interfacial diffusion layer was thin in the order of 1-2 mu m. The higher the discharge voltage was, the more obvious the interfacial diffusion layer and mechanical interlocking were, with "wave-like" and "inverted hook-like" interfacial characteristics observed. While interfacial failure occurred during the tensile lap shear tests for the joints made at a discharge voltage of 12 kV, the failure loads were still significantly higher than those specified in the AWS D17.2 standard. The EMPWed joints made at 14 kV and 16 kV remained intact and only base metal failure occurred, with the tensile lap shear failure loads reaching over twice those specified in the AWS D17.2 standard. Thus the well-bonded robust Al/Cu dissimilar welds were successfully achieved via EMPW.