Electrochemical study of tailored sol-gel thin films as pre-treatment prior to organic coating for AZ91 magnesium alloy

The behaviour/resistance of four optimised sol-gel coating systems (inorganic, hybrid organic-inorganic, containing zirconium ions and containing cerium ions) against corrosion of AZ91 magnesium alloy were studied. The coatings obtained by the sol-gel process were evaluated as autonomous protective coatings as well as a pre-treatment prior to acrylic top coat. The coating obtained from tetramethoxysilane (TMOS) and diethoxydimethylsilane (DEDMS) as precursors and doped with Ce3+ was especially effective as pre-treatment for a final acrylic coating. For non-defected coating the impedance modulus has not changed during the time of immersion (7 days) in 0.5 M Na2SO4. An inhibition of coating delamination at the defect of the acrylic coating was recorded by means of LEIS.