Gradient multi-layered aluminum sheet with excellent corrosion resistance

Diffusion is a very important phenomenon in the thermal processing, including Cu diffusion, Si diffusion and Zn diffusion in the sheet during brazing. Specifically, the migration of Si affects the amount of liquid metal that can be used to form joint, and further affects the solubility of solid substrate at the liquid-solid interface between the clad alloy and core alloy. In addition, Cu accumulates on Al(Fe,Mn)Si precipitates and in Al-Si eutectic at the grain boundaries. Compared with Al matrix, the formation of Al(Fe,Mn,Cu)Si enhances the potential difference between these materials. These events greatly damaged the corrosion resistance of the sheets. Due to the existence of the interlayer, Zn in the interlayer diffuses to the core layer, and the concentration of dissolved zinc decreases with the increase of depth, resulting in an increasing potential of the Al matrix towards the core layer. With depth from the surface to the core layer, the Al matrix is more cathodic, which promoting lateral corrosion within the interlayer region, prevents through failure and which protects the core alloy. Diffusion during brazing leads to microstructure evolution and local electrochemical characteristics of different layers. The optimized potential gradient of the clad layer-interlayer-core layer can greatly improve the corrosion resistance of the alloy.