Depletion depths of inorganic components from a scribe edge in a polyurethane primer containing Li₂CO₃, MgO, BaSO₄ and TiO₂ beneath a topcoat, were determined using a range of techniques including SEM/EDS and proton induced X-ray and γ-ray emission spectroscopies. SEM of sections cut using an ion beam revealed scribe damage penetrating 20–25 μm away from the scribe edge prior to leaching. After neutral salt spray (NSS) exposure a leached zone developing from the scribe edge was observed. For longer NSS exposure times (>96 h) this leached zone of nearly complete Li and Mg depletion did not develop any deeper than the scribe damaged region indicating that the depletion zone was caused by mechanical damage due to scribing. At short times small voids were formed in Li₂CO₃ particles within the primer well away from the scribe (100–260 μm) whereas a mixture of void and detachment in and around Li₂CO₃ particles was observed at longer times. The detachment was assumed to be part of a channel network within clusters of particles. Internal stresses within the primer resulting from buildup of inhibitor dissolution product within the voids were modelled using finite element analysis. It was found that strains related to von Mises stresses were concentrated around the inorganic particles and developed preferentially within the plane of the primer beneath the topcoat with some indication of concentration towards the primer/metal interface. These stresses resulted from osmosis and swelling related to the voids. They were also attributed to the observed cracking of the binder at some locations. Leaching experiments showed that Li was released very rapidly from the primer. The leaching data was modelled using a power law where the mass released is proportional to tⁿ where the n is an index that reflects the kinetic behavior dictated by the evolving primer porosity. In this study n values between 0 and 1 were observed for all species, with Li starting at around 0.7 but rapidly decreasing to close to zero.

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.