Tuning Corrosion Properties of the Bio-Inspired AZ-Series Mg Alloys Using Electrochemical Surface Treatment under Varying Experimental Regimes

Abstract

Plasma electrolytic oxidation (PEO) is a preferable process applied to optimize the corrosion and wear properties of metals and their alloys, particularly magnesium (Mg) alloys used in highly demanded medical and aerospace applications. In this project, AZ series alloys (AZ31, AZ61, AZ91), which are the major commercial magnesium alloys, were coated using the PEO process under varying experimental conditions involving electrolyte with Si based ionic chemical networks together with hydroxyl and fluoride functionalities. Surface analysis was carried out using scanning electron microscopy (SEM). Data were further simulated and analyzed using imageJ software. SEM results showed that, increasing the concentration of Al as in AZ91 and AZ61, dendrites-dominated the microstructure at shorter processing times; a cratered-dendritic matrix was obtained at longer processing time. From the composition analysis, fluoride complex peaks were obtained for the higher Al-content alloy (AZ91), due to the localized intensive discharges made regular by the stable beta-phases within the Mg matrix. Corrosion analysis was carried out using potentiodynamic polarization. The compact structure, higher growth rate, and stable chemical phases of MgF2 contributed to the highest hardness values similar to 1271.2 HV and corrosion potential similar to-0.18 V for the AZ91 alloy.