P. Taheri

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 postbrazing 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 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 resulting from of 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 re-solidified clad layer.

Corrosion Performance of Composite Galvanic Coatings with Variable Concentration of Polymeric Nanoaggregates and/or Cr(III) Conversion Layers

This paper reports on the corrosion performance of composite zinc layers (~ 8µm) on a steel substrate, considering the influence of nano-aggregates and Cr(III) conversion layers, compared to control (only Zn layers) conditions. The main factors, influencing the corrosion performance of Zn in this study are: a) the effect of two concentrations of polymeric nano-aggregates (0.1g/l and 0.3g/l PEO113-b-PS218 core-shell micelles in the starting electrolyte); b) the effect of Cr(III) conversion layers on both pure Zn and composite Zn layers. For most of the hereby investigated time intervals i.e. treatment in aerated 5% NaCl from 2h until 120h, the composite coatings present higher corrosion resistance, especially within longer treatment. Corrosion current densities are similar to Zn, however, anodic currents are significantly lower. After treatment in NaCl, the composite Zn coatings present a more homogenous product layer, formed as a result of the presence of the nano-aggregates. The additional Cr(III) treatment does not significantly improve the corrosion resistance of the composite coatings for the hereby investigated time intervals.