Corrosion and nanoindentation studies of MAO coatings

Abstract

Ceramic coatings have been developed on AZ31B Mg alloys by micro arc oxidation (MAO) technique, using a mixture of sodium phosphate and sodium fluoride electrolytes. Further, MAO coatings were sealed by the conventional hot water immersion technique. The coatings were characterised by X-ray diffraction, potentiodynamic polarisation, mechanical as well as optical profilometry and nanoindentation techniques. The results showed that the surface roughness and related parameters were always higher after the corrosion test in comparison to as developed MAO coatings, the corrosion resistance of the sealed MAO coatings were enhanced in comparison to unsealed coatings and the MAO coatings had nanohardness ,10 times and Young's modulus about two times as high as those of the AZ31B Mg alloys. Further, the characteristic scatter in the data was treated by the application of Weibull statistical method. These results are discussed in terms changes in microstructure of the MAO coatings, especially after sealing.

Nanoindentation study of MAO coatings developed by dual electrolytes

“…Nanoindentation measurements gave hardness of about 4?9-6?5 GPa on the plan section of these MAO coatings. 2 8 Further, the nanoindentation measurement on the plan section of these MAO coatings gave a hardness of 2?9-3?3 GPa and Young's modulus in the range of about 80-90 GPa. 8 Thus, the aforesaid survey clearly suggest that the silicates and phosphates are the most common anions used in weak electrolytes for MAO coating developments.…”

“…2 8 Further, the nanoindentation measurement on the plan section of these MAO coatings gave a hardness of 2?9-3?3 GPa and Young's modulus in the range of about 80-90 GPa. 8 Thus, the aforesaid survey clearly suggest that the silicates and phosphates are the most common anions used in weak electrolytes for MAO coating developments. [2][3][4][5][6][7][8] All of the reported nanoindentation studies were conducted 2,3,6,8 on the plan sections of the MAO coatings.…”

“…8 Thus, the aforesaid survey clearly suggest that the silicates and phosphates are the most common anions used in weak electrolytes for MAO coating developments. [2][3][4][5][6][7][8] All of the reported nanoindentation studies were conducted 2,3,6,8 on the plan sections of the MAO coatings. Further, microhardness measurement on the cross section 5 gave a little lower value, e.g.…”

Effects of laser treating on surface morphology of MAO coating on AZ91 magnesium alloy

“…It is one of the lightest metal with excellent physical and mechanical properties such as low density, high specific strength and good castability [3][4]. Unfortunately, biomedical magnesium alloy has poor corrosion resistance when were utilized in actual conditions because of their relatively low chemical stability and high negative potential [5].…”

“…Unfortunately, biomedical magnesium alloy has poor corrosion resistance when were utilized in actual conditions because of their relatively low chemical stability and high negative potential [5]. Therefore, many methods have been developed to offer protection for biomedical magnesium alloy, among which, the surface modification technique of micro arc oxidation (MAO) has become a frequently used method in recent years [1,[3][4]. MAO can prepare corrosion resistance ceramic coatings on Mg and other metals surface through plasma charge in anodic electrolytic process.…”