Process analysis for magnetic pulse welding of aluminium-copper joints

Due to the excellent thermal and electrical conductivity as well as the very good chemical stability, copper is one of the most frequently applied materials especially in electrical and HVAC applications. This has been causing a steady rise of the copper demand and consequently of the copper price over the last years. Moreover, copper has high density leading to accordingly high component weight. Especially in applications in the field of transport or aerospace the use of copper contradicts the demand for implementing lightweight concepts, which has been becoming more and more important. As a consequence, industry has high interest in alternative solutions. In order to solve the conflict of interest between the technological advantages resulting from the beneficial properties of copper, on the one hand, and the limits regarding costs and weight, on the other hand, components, which are currently made from copper completely will be substituted by hybrid copper aluminium parts within the JOIN'EM project. Copper will only be applied in regions where it is indispensable e.g. as a thin layer. Since the aluminium price is only about 40% and ist density is only about 30% while ist thermal and electrical conductivities are about 60% of the according values of copper, high saving potential is expected. However, this approach necessitates a suitable technology for the manufacturing of high-quality aluminium copper joints. Here, magnetic pulse welding offers numerous advantages. One important example is that the connection is formed due to high-velocity collision of the static and the dynamic joining partner (Flyer and Target) without noteworthy heating of the part and thus thermally induced problems of conventional processes as heat distortion, strength reduction in the heat-affected zone, formation of brittle intermetallic phases are avoided. Additionally no shielding gases, fluxes of additives are required and the process excels due to good reproducibility, high automation potential, relatively short process times, and low energy consumption. However, industrial implementation of the process for the described manufacturing task is still hindered by missing quantitative guidelines and tools for joint and process design at the moment. To provide the basis for such guidelines, the influence of important process parameters on the collision of the joining partners and the manufacturing result was investigated in detail via a statistically planned combined experimental and numerical process analysis. A coupled electromagnetic and structural mechanical simulation served for quantifying local collision parameters in the joining zone, while the joint characterisation was done via lap shear tests, micrographs, and electrical conductivity measurements of the connection. The results of the analysis are presented and interpreted in the presentation.