Carbon-free SiOx ultrathin film using atmospheric pressure plasma jet for enhancing the corrosion resistance of magnesium alloys

This study describes the use of tetraethylorthosilicate (TEOS) as the precursor to deposit carbon-free silica (SiO2) dense film as the anti-corrosion layer on the surface of AZ91D magnesium alloys using an air atmospheric pressure plasma jet (APPJ). From the contact angle measurements, APPJ-deposited silica film on AZ91D represents a more hydrophobic property with a lower total surface free energy of 31.3 mN/m. XPS depth profile analyses revealed the chemical compositions (O and Si) were uniformly distributed through the bulk of the deposited films with a thickness of 207 nm, which also comprises of carbon-free SiO2 ultrathin films. The electrochemical impedance spectroscopy (EIS) measurements and corrosion morphologies of 14-day immersion test of deposited films and AZ91D samples in 3.5 wt % NaCl solution are also investigated. The results indicate ultrathin silica coating not only alter the surface property, but also improve the corrosion resistance of AZ91D magnesium alloys.