The corrosion resistance performance rating as per salt-spray test has been used as response and the optimizations of factors have been worked out using STATGRAPHICS[R] Centurion XV (Statpoint Inc.) and Minitab 15 (Minitab Inc.) software.
For correlation with salt-spray test, 5% NaCl solution in DI water was used as electrolyte (pH-6.6-6.8).
Table 1 shows the results of water boiling test and salt-spray test for various ureasil-based pretreatments and also for commercial systems.
ASTM B117 salt-spray test is a standard lest to determine resistance of films to corrosion under accelerated conditions.
Salt-spray test results showed very interesting trend.
Alodine 1200 S showed very well-defined passivation in the range of -1.0 V to -600 mV and also showed fading/loss of color in the salt-spray test. This can be attributed to the release of chromium (VI) compounds due to their solubility in water.
After application onto AA 2024 T3, panels were cured at room temperature for 7 days and tested for field corrosion performance in salt-spray test for 3 weeks.