Evolution of PEO coatings on AM50 magnesium alloy using phosphate-based electrolyte with and without glycerol and its electrochemical characterization

PEO coatings were synthesized from phosphate-based (bP-PEO) and glycerol added phosphate-based (gP-PEO) electrolytes with different processing times. For both bP-PEO and gP-PEO coatings treated with different processing time its morphology, elemental and phase composition, and electrochemical behaviour has been comparatively investigated. For this, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDXS), X-ray diffraction, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization techniques were employed. The gP-PEO coatings were observed to have higher pore density with reduced pores size, surface porosity, and average coating thickness compared to bP-PEO for all the PEO processing time. XRD studies revealed that glycerol addition resulted in the fostering of crystalline MgO (periclase) phase and promoting Mg3(PO4)2 (farringtonite) phase amorphization. In general, electrochemical behaviour showed improved corrosion behaviour for gP-PEO compared to bP-PEO.