Residual stress in pulsed dc microarc oxidation treated AZ31 alloy

Abstract

This paper addresses the residual stress in the microarc oxidation (MAO) coating on AZ31 magnesium alloy. The MAO coating was deposited by pulsed direct current (dc) and examined by scanning electron microscopy and X-ray diffraction for its microstructure and composition. The porosity of the coatings was measured by potentiodynamic polarisation tests and found to be in the range of 3–6%. The residual stresses in the MAO coatings prepared at 300, 500, 1000 and 3000 Hz respectively were found to be between −860 and −1272 MPa. Using a high pulse frequency at 3000 Hz can produce a less porous and less stressed MAO coating, a desirable feature in the biomedical applications of MAO coated AZ31. This finding was further verified by establishing a first principle relation between the residual stress and the porosity via Stoney equation, which enables extrapolation of the experimental data measured.

Keywords:

• MAO
• Pulse
• AZ31
• Residual stresses
• Porosity
• Microstructure

Y. H. Gu was supported by the UAF Graduate School Fellowship for the related research initiated by Dr. J. Zhang.