Improved Corrosion Resistance of Aluminum Brazing Sheet by a Post-Brazing Heat Treatment

This work studies the influence of the microstructure on the corrosion mechanism and susceptibility of as-brazed aluminum sheet.Various microstructures are obtained using post-brazing heat treatments developed to enhance the corrosion resistance of an AA4xxx/AA3xxx brazing sheet.The heat treatment results in a decrease of the matrix Si content within the heat affected zone (HAZ) and an increase of the Si fraction in the α-Al(Fe-Mn)Si phase.Additionally, the effect of the heat treatment on the local electrochemical activity and corrosion properties are studied.The results indicate that the corrosion susceptibility of the as-brazed structure is diminished due to an amendment of the local electrochemical behavior of the outer clad surface after the post-brazing heat treatment.Moreover, the potential difference between the clad material and core is increased resulting in an improved sacrificial cathodic protection of the core by the resolidified clad layer.