Effect of nitrogen incorporated into oxide layer, formed on the magnesium alloys by using r.f. PECVD process, on their corrosion resistance.

Abstract

This paper presents the changes in corrosion resistance of SiO2 coatings generated in the plasma process PECVD (Plasma Enhanced Chemical Vapour Deposition), using RF plasma (13.56 MHz), under the influence of the introduction of nitrogen to their volume. Two magnesium alloys AZ32 and AZ91 were put under the tests. On each of Mg alloys the coating of SiO2 was made with a thickness of 1000 nm, and the coatings of SiOxNy (oxynitride) with a thickness of 60 nm and 500 nm. The obtained results were compiled with the reference samples of these alloys. The corrosion properties of the tested coatings were determined based on the analysis of voltammetric curves. The obtained results show that the introduction of nitrogen to a volume of a thin layer of plasma produced SiO2, which is the formation of the layer of SiOxNy improves the corrosion resistance of both examined magnesium alloys. With a much smaller thickness of SiOxNy layer in relation to the thickness of SiO2 oxide layer the similar corrosion current density decreases were obtained.