Influence of final annealing temperature on the microstructural evolution and corrosion resistance of a Sandwich multi-layered aluminum sheet

Abstract

The effects of final annealing temperature on the microstructure and corrosion resistance of a sandwich (4343/3z23a/4343) multi-layered Al sheet were investigated by optical microscopy, tensile test, Scanning electron microscope (SEM), and Glow discharge optical emission spectrometry (GDOES). It was found that high temperature (460 °C) final annealing significantly improves the brazing ability of 4343/3z23a/4343 multi-layers Al sheets, and eliminates erosion of core layer during brazing. During brazing, Si diffuses from the clad layer to the core layer and Cu diffuses from the core layer to clad layer. Si/Cu segregate at the surface of re-solidified clad layer after brazing. The segregations of Si/Cu at the surface of clad layer after brazing lead to that the open-circuit corrosion potential of the Al sheets increases by 25 mV. The main corrosion mechanism of nonbrazed materials is pitting, while the dominant corrosion mechanism for brazed materials is intergranular corrosion.