Electrochemical impedance spectroscopy evaluation of the corrosion behaviour of Mg alloy coated with PECVD organosilicon thin film

This paper describes the preliminary results on the utilization of thin film deposited in Plasmas fed with hexamethyldisiloxane-oxygen (HMDSO-O2) mixture for the corrosion protection of Mg alloys. The corrosion behavior of coated substrates has been evaluated by means of impedance measurements performed in aerated 0.1M Na2SO4 solution. Interesting and promising results have been obtained when a suitable plasma pretreatment is performed both with hydrogen and CF4 fed plasmas and therefore when the extent of surface oxidation is reduced or when the magnesium surface is fluorinated. As a matter of fact, the charge transfer resistance, Rct, increases from about 60 Ω cm2 for the uncoated alloy to more than 90 kΩ cm2 after deposition of a 1300 nm thick SiOx film.