Degradation of unconventional fluoride conversion coating on AZ61 magnesium alloy in SBF solution

Abstract The paper offers an analysis of the corrosion process of the AZ61 magnesium alloy protected with the unconventionally prepared fluoride conversion coating using Na[BF4] salt melt. The protection of the magnesium alloy with the coating was shown to vary depending on the preparation temperature (430 and 450 °C) and coating time (0.5, 2 and 8 h). Lower coating temperature and shorter coating times offer lower protection of the material against corrosion. Similar corrosion mechanism was observed for all the damaged specimens. Migration of the species from the SBF to the substrate through the coating resulted in the coating damage due to the H2 evolution and corrosion products creation following with more pronounced corrosion attack of the substrate. However, no signs of the corrosion attack were observed when the coating was prepared at 430 °C for 8 h and at 450 °C for 2 and 8 h even after 168 h of exposure of the specimen to the simulated body fluid solution at 37 ± 2 °C.