**1. Introduction**

The use of magnesium alloys in different industrial fields has increased mainly due to its very high strength-to-weight ratio in comparison to other structural alloys [1]. However, an important limiting factor is their high reactivity and thus, their susceptibility to corrosion [2]. The main objective of the research area has always been to increase the corrosion resistance of metallic substrates [3]. One method to reduce the effect of corrosion is to deposit a protective coating on a metallic substrate. Among the coating techniques, sol-gel process is considered a very efficient and economically viable solution for developing anticorrosion coatings on magnesium alloys. According to Segal [4], the sol-gel process can be defined as the production of inorganic oxides in the form of colloidal dispersion or metal alkoxides.

The sol-gel process was initially developed for producing pure inorganic materials, ceramic, and glass materials. However, pure inorganic sol-gel coatings do not provide

enough corrosion protection due to the presence of micro-cracks or defects [5]. The ability to process organic-inorganic hybrid composites at low temperature opened new opportunities in the design of free-crack sol-gel coatings that enhances the corrosion resistance of metals [6]. The research focused on the polymerization of organic-inorganic hybrid materials by sol-gel process increased significantly near the end of the twentieth century [7]. Thus, sol-gel process has got a strong technological impact on research related to protective and functional coatings because this method allows the surface modification of different materials without changing the substrate properties.

The citation report of the "Web of Science Core Collection" database reveals that the amount of literature containing "sol gel" and "Mg alloys" as keywords was 421 between 2000 and 2021; the research in this field is annually growing because of the new alkoxysilane precursors and functional species now available to obtain silica coatings with novel physicochemical properties.
