Tests and Quantitative Evaluation of Results

The alloy panels with various low-temperature plasma interface-engineered, primer-coated surfaces were evaluated by accelerated corrosion tests. Two kinds of accelerated corrosion tests were conducted on all the samples, including the two 

After completing corrosion testing exposure, the panels were rinsed with distilled water and visual observations were made. The panels were then subjected to Turco 5469 paint stripper solution to strip off the E-coat or spray primers (including the controls) from the scribed surface, so that the effect of corrosion beneath the coatings and away from the scribes could be viewed. These panels were then used to estimate the average corrosion creep widths, in order to compare the corrosion performance of the different sample systems [5]. 

The image of scanned surface of corrosion test specimens as well as calculated corrosion area and corrosion width can be used to see the influence of the interface on the corrosion resistance of the overall system. Methods of pretreatment of substrate sheet, plasma conditions, and the sample identification codes are shown in Table 28.1. 

Although the panel with the plasma deposited film followed by priming with E-coat is visually better, the use of the corrosion width provides a method for quantifying the improvement in the corrosion performance. Also the factor of about 2 difference in corrosion width between the two chromate conversion-coated panels is difficult to obtain from the qualitative difference observed from the scanned images. It can be seen from this comparison of three panels that the use of the measured corrosion width makes the differentiation of corrosion performance much easier. This method of evaluating corrosion test results is used to determine if the combination of the two bests could indeed yield the better corrosion protection of aluminum alloys. 

---