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.

Keywords:

• Magnesium
• MAO
• Microstructure
• Corrosion
• Nanoindentation
• Nanohardness
• Young’s modulus

Acknowledgement

Two of the authors (PB and AKM) acknowledge the kind encouragements received from Director, CSIR-CGCRI during the course of the present work.