Influence of Sodium Dodecyl Sulfate on Structure and Anti-corrosive Properties of Phosphate Coating on AZ31 Magnesium Alloy

Sodium dodecyl sulfate (SDS) was used as an accelerating reagent to replace nitrite in phosphating bath. Effect of this surfactant on the morphology and anticorrosive performance of phosphate coating on AZ31 magnesium alloy was studied. The light grey phosphate coating was formed on AZ31 magnesium alloy from the zinc phosphating bath containing sodium dodecyl sulfate at temperature of 45-50 ºC and in about 5 minutes. SEM and EDX were utilized to investigate the morphology and elemental compositions of the phosphate coatings. In addition, DC polarization was used to reveal the anticorrosive resistance of phosphate coatings. Results showed that, using SDS as an accelerating reagent to replace nitrite in phosphating bath has caused a more uniform formation of hopeite phase at different directions. In addition, a denser and less permeable coating can be obtained at this conditions. The corrosion resistance of phosphate coatings was superiorly improved using higher SDS concentration in the phosphating bath. J. Color Sci. Tech. 4(2010), 183-189© Institute for Color Science and Technology.