Self-Healing Corrosion Protection Coatings Obtained by Anodization and Sol-Gel Process on Mg AZ31 Alloy

In the present investigation, we explored a combination of porous anodized layer sealed with self-healing sol-gel coatings on Mg AZ31 alloy. Anodization was carried out on Mg AZ31 alloy by varying the voltage from 10 to 80 V and time 5 to 30 minutes. The porous anodized layer was subsequently sealed with a room temperature curable sol-gel coating having inorganic and organic corrosion inhibitors such as, Ce3+ and 8-hydroxy quinoline respectively in order to enhance the corrosion protection ability. The coatings on Mg AZ31 alloy were characterized by field emission scanning electron microscopy attached with energy dispersive X-ray analysis, adhesion and thermal conductivity studies. Increased adhesion strength and reduced thermal conductivities were observed for the sol-gel sealed anodized coatings on Mg AZ31 alloy. Immersion studies for the coatings in 3.5% NaCl solution followed by electrochemical studies up to 336 h was performed to measure the corrosion behavior. Electrochemical impedance spectroscopy analysis and potentiodynamic polarization studies results revealed the gradual enhancement of corrosion resistance, reduction in corrosion currents and corrosion rates for the inhibitor loaded sol-gel coatings on anodized Mg AZ31 alloy. An artificial scribe was made over the coatings followed by salt spray exposure for up to 336 h. Self-healing phenomenon was corroborated through SEM with EDX mapping with the formation of Ce3+ and 8HQ complexes at the scribed regions for the Ce- and 8HQ-based self-healing coatings. Self-healing sol-gel sealant coatings combined with anodization on Mg AZ31 alloy was found to be promising for various applications.