Corrosion protection of AZ31 magnesium alloy by means ofZrO2 coatings deposited with sol-gel technique

摘要

Magnesium alloys like AZ31 are susceptible to severe corrosion attack in aggressive solutionsrn(e.g. chlorides). This limits application of magnesium alloys. Conversion coatings likernchromate or rare earth conversion coatings are usually applied in order to improve corrosionrnbehaviour of magnesium alloys. Thin ZrO2 coatings deposited with sol-gel technique mightrnbe an alternative pre-treatment to conversion coatings. Thin ZrO2 pre-treatments shouldrnprovide good barrier properties, promote coating adhesion and possibly introduce self-healingrnability.rnZrO2 pre-treatments were deposited on magnesium alloy AZ31 by means of dip-coatingrntechnique in a sol of zirconium butoxide in an organic solvent. The sol-gel technique enablesrndeposition of films with thickness in the range of 100-200 nm.rnMorphology of ZrO2 pre-treatments was investigated by means of SEM-EDXS. Filmrnthickness and composition were studied by means of glow discharge optical emissionrnspectroscopy (GDOES). Electrochemical behaviour of ZrO2 coatings was characterized byrnmeans of potentiodynamic polarization.rnZrO2 pre-treatments deposited with sol-gel technology are uniform and well adherent on thernsubstrate. Film morphology is dependent on concentration of precursor solution employed forrndeposition. A strong barrier effect is observed for two-layer ZrO2 films on AZ31 magnesiumrnalloy.