Abstract
Abstract The aim of this study was to clarify the influence of inter-metallic compounds (IMCs) on the electrical conductivity of Cu/Al joint. The longitudinal resistance and the lateral current distribution at flash welded and diffusion brazed Cu/Al joint interfaces were investigated using four-point method and conductive atomic force microscopy, respectively. A 2μm Cu9Al4/CuAl2 layer was formed in both joints. The IMCs layer was homogenous and the current distribution interface was planar at diffusion brazed joint. However, the IMCs layer was discontinuous and the current distribution interface was non-planar at flash welded joint. After heat treatment at 350°C for 500h, the thickness of interfacial layer was increased to 50μm. CuAl and a short crack were newly formed in the diffusion brazed joint. CuAl, (Cu,Al)xOy and a long crack were newly formed in the flash welded joint. A multilayer current distribution was found at both heat treated joints. The resistivity of all Cu/Al joints was higher than that of copper and lower than that of aluminum. The resistivity of diffusion brazed joint was the lowest, which was lower than the theoretical value. The resistivity of the heat treated flash welded joint was the highest among all the joints.
Highlights
Cu/Al bimetal joints have been widely used to transmit the electricity in a variety of electrical applications, such as transmission grid[1], high direct-current bus systems[2] and electric vehicles[3,4]
Two homogenous thin inter-metallic compounds (IMCs) layers are found between copper and aluminum in the joint
No obvious current distribution can be found on the surface of IMCs, indicating that the homogenous thin IMCs layer don’t change the current distribution between copper and aluminum
Summary
Cu/Al bimetal joints have been widely used to transmit the electricity in a variety of electrical applications, such as transmission grid[1], high direct-current bus systems[2] and electric vehicles[3,4]. In these applications, the electrical resistance of these Cu/Al joints should be kept as low as possible to minimize the loss of electrical energy. It is easy to form inter-metallic compounds (IMCs) at temperature above 120°C2 These IMCs have higher electrical resistivity than copper and aluminum. It is important to understand the influence of IMCs on the electrical characterization of Cu/Al joint
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