Fault-tolerant hybrid epoxy-silane coating for corrosion protection of magnesium alloy AZ31

Abstract

In this work, a hybrid epoxy-silane coating was developed for corrosion protection of magnesium alloy AZ31. The average thickness of the film produced by dip-coating procedure was 14 mu m. The adhesion strength of the epoxy-silane coating to the Mg substrate was evaluated by pull-off tests and was found to be higher than 16 MPa both in dry and wet conditions. The hybrid epoxy-silane coating showed high corrosion resistance both when intact and when punched through by a needle. The low frequency impedance of intact coating was higher than 1 G Omega cm(2) after one month of immersion in 3.5% NaCl solution. Both, artificially induced defects and corrosion sites that appeared on the metal surface did not propagate. Their passivation behavior, that we call fault-tolerance, was observed by EIS, SVET-SIET and SEM-EDS. It was ascribed to the good adhesion, high coating integrity and corrosion inhibiting effect provided by diethylenetriamine used as epoxy hardener. (C) 2014 Elsevier B.V. All rights reserved.