The protective performances of different coatings for AZ31 Mg alloy have been evaluated in 0.1N NaCl and Na2SO4 solutions by recording the polarization curves and by EIS measurements. These coatings were formed in permanganate-phosphate or stannate baths as well as in hydroalcoholic solutions of silanes with a long alkyl-chain (e.g. octyl and octadecyl-trimethoxy-silane). The influence of different parameters (solution pH, treatment time) were examined and the possibility to increase the permanganate coating performance with a subsequent treatment in water-soluble silanes was also evaluated. All the treatments with inorganic compounds showed protective characteristics similar or better than those of chromate treatment. Furthermore, silanes may enhance the efficiency of permanganate bath. However, the best results were obtained with the 18 carbon atom long alkyl chain silane (hydrolyzed at pH 5). In this case no corrosion attack was observed in 1000 h immersion in the aggressive solutions.
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