Inhibitor-doped sol-gel coatings for corrosion protection of magnesium alloy AZ31

This work presents new anticorrosive coatings for the AZ31 magnesium alloy, based on hybrid sol-gel films doped with a corrosion inhibitor. The sol-gel coatings were prepared by copolymerization of 3-glycidoxypropyltrimethoxysilane and zirconium (IV) tetrapropoxide. 8-Hydroxyquinoline (8-HQ) was chosen as a corrosion inhibitor to be incorporated into the sol-gel films at two different stages of synthesis, either before or after hydrolysis of the sol-gel precursors. The effectiveness of 8-HQ for corrosion suppression on AZ31 was verified by Scanning Vibrating Electrode Technique. Electrochemical Impedance Spectroscopy was used to monitor the evolution of the substrate/film systems in the course of immersion in 0.005 M NaCl. The morphology and the structure of the sol-gel films were characterized with SEM/EDS and TEM techniques. The sol-gel films exhibit good adhesion to the metal substrate and prevent the corrosive attack during 2 weeks under immersion test. Results showed that addition of inhibitor into the sol-gel films enhances the corrosion protection of the magnesium alloy and does not lead to deterioration of the barrier properties of the sol-gel matrix. (C) 2009 Elsevier B.V. All rights reserved.