AFM and KPFM investigation of high strength aluminium brazing sheets

High strength aluminum brazing compounds used in car-cooler systems become susceptible to corrosion after brazing. An intermediate layer has to be inserted to separate the 4xxx filler-material from the 7xxx base-material. The effectivity of this layer in preventing corrosion was investigated using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). Samples were subjected to a simulated brazing cycle and exposed to a corrosive medium. The investigations revealed the presence of cathodic inclusions in the Al-matrix. Further, a line of up to 3 µm wide holes is formed at the transition between intermediate layer and base material.