Payel Bandyopadhyay

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

Abstract The micro arc oxidation (MAO) process is one of the most industrially accepted, prospective methods to design and develop microstruturally integrated, intrinsically generated oxide/ceramic coating over Mg alloys. Here we report, the surface engineering of AZ31 Mg alloy to form MAO coatings by silicate and phosphate based electrolytes. The microstructural examinations of the MAO coatings were carried out by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. Further, the nanoindentation studies revealed that the MAO coatings had nanohardness (H) and Young’s modulus (E) values as high as about 3–7 times and 1·5–2·5 times those of the as received AZ31 Mg alloy respectively. Both H and E values gradually increased from virgin Mg substrate end to the surface coating end. Further, sealing by hot water did not affect the H and E values of the MAO coatings.