Corrosion Prevention Of Aluminum (1100) Andalloys (5052) In 3.5%NaCl Solution At High Temperature

The condenser pipe which affects the efficiency of the device and the frequency of shutdown plays an important role in the Low-temperature multi-effect distillation. Currently, the selected materials are either expensive or poor corrosion resistance. For the practical applications, we investigated the corrosion resistance properties in 3.5% NaCl solution at 90℃of both aluminum alloy AA5052 and AA1100 before and after surface treatment.Technological process of anodic oxide coating on AA5052 and AA1100 is studied in this paper. The influence of different process parameters on anodic oxide coating is concretely analyzed.The results of weight loss, electrochemical measurements and SEM reveal that general corrosion is easier occurred on alloy 1100 of the untreated samples and the corrosion resistance of anodized samples is increased obviously. The corrosion resistance of anodized and sealed aluminum is much better than unsealed. Meanwhile, the best technical parameters of anodized coating obtained from the comprehensive analyze are as follows: AA1100 treated under 2A/dm² current density for 10 minutes; AA5052 treated under 1A/dm² current density for 20 minutes and further comparison shows that the corrosion resistance of the former is much better than the latter one.Corrosion mechanism and regularity of distinct anodic oxide processes were observed from comprehensive analysis: For AA1100, with the same processing time, the pitting corrosion resistance enhance as the current density rising. Moreover, under same current density, the samples'pitting corrosion was more liable as processing time increasing. For AA5052, with the same processing time, the corrosion resistance capability degraded first and later increased slightly as current density increased. With the same current density while dissimilar processing time, for the pattern under 20 min treated time, the corrosion resistance is enhanced due to the smaller pitting index, broad passive potential range and the impedance, noise resistance. In addition, the samples of best film-forming process are selected to test under 23℃and 90℃. Corrosion resistance of the specimens significantly decreased under high temperature. This can be attributed to the dissolution of oxide film as well as the accumulation of Cl-.We also observed the corrosion product membrane and the surface morphology of the samples that immersed six weeks in the solution by XRD and SEM. The result indicates that there are fewer pits on the surface of aluminum alloys under the best treatment mentioned above while other specimens have been generally corroded and the main corrosion products are Al, Al (OH) ₃, Al₂O₃ and Al (OH)₃·nH₂O.