Effects of Fe content on corrosion resistance in fluoride surface layers formed on specimens of a magnesium alloy, AZ31B, have been investigated in detail. The specimen was dipped into molten NaBF
4 at 693 K for 10.8 ks to form fluoride layer. Crucibles made with a mild steel and with an alumina were used to prepare the molten NaBF
4. Corrosion resistance was evaluated by
in-situ observations using a laser microscope with dipping the specimen into a 0.02 N HCl solution, and also by an immersion test using a 5% NaCl solution at 308 K for 259.2 ks. Weight loss after the salt immersion tests showed that corrosion resistance of the specimen fluoride treatment in the alumina crucible was superior to that of the specimen treated in the steel crucible. The fluoride layer of the specimen prepared with using the steel crucible was contaminated with Fe, which was shown by SEM-EDX analysis. Significant corrosion was not observed after the salt immersion test on the specimen fluoride-treated in the alumina crucible, even on the cross-cut specimen.
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