The effect of post-brazing heat treatment (PBHT) on the microstructure and electrochemical corrosion of AA4343/AA3xxx/AA4343-layered Al sheets were examined by analysing experimental results and using a work function calculation based on density functional theory (DFT). The PBHT at 325 °C results in the homogeneous dispersion of Cu in the re-solidified clad and eliminates the Al2Cu particles. Furthermore, after the PBHT, a large number of α-Al(Fe,Mn)Si particles were precipitated in the diffusion zone. This makes the diffusion zone slightly more anodic relative to the core layer and improves the capability of the diffusion zone to sacrificially protect the core layer.