Study of the influence of natural and artificial passivation on the corrosion rate of magnesium alloy for surgical implants

Magnesium-based alloys are widely used materials for surgical implants. Considerable efforts of researchers are applied to the development of new magnesium alloys and methods of their surface treatment in order to protect against biocorrosion or to regulate its speed. The idea of the work is to determine the potential of known magnesium alloys as materials for the production of implants. Industrial magnesium based alloys were analyzed from the point of view of suitability for use for surgical biodissolvable implants. It is shown that the ML10 alloy is the most suitable as it does not contain toxic components, namely aluminum, nickel and cadmium. Samples for corrosion tests were made from a billet of ML10 alloy after processing by plastic deformation by pressing through a calibrated die at a temperature of 375 ± 20 °С. Together with the ML10 alloy, comparative studies of the ML5 alloy were conducted. Corrosion tests of ML5 and ML10 alloys without a coating, as well as of the ML10 alloy with a coating applied by the micro-arc oxidation (MAO) method for 30 seconds, were carried out using the volumetric method. The samples were kept in a 3% NaCl solution at a temperature of 38 ± 2 °C. The corrosion rate of the ML5 alloy was at a constant level during the experiment. No significant ability of the ML5 alloy to self-passivate was found. The ML10 alloy turned out to be capable of significant self-passivation under the influence of a corrosive environment. During the experiment, the corrosion rate of the ML10 alloy sample decreased approximately ten times. It was also established that the corrosion rate of ML10 alloy samples with MAO coating was approximately three times lower than that of samples of the same alloy without coating. Preliminary information was obtained on the reduction of the corrosion rate of the ML10 alloy after plastic deformation. Further research can be aimed at confirming this phenomenon, determining its causes, as well as establishing quantitative indicators of the influence of the degree of plastic deformation on the corrosion rate of the ML10 alloy. Keywords: surgical implants, magnesium alloys, corrosion, self-passivation, coating.