Conversion coating process for magnesium alloy

The present invention relates to a process for surface treating a magnesium alloy which comprises the following steps: (i) blasting the substrate; (ii) degreasing the substrate; (iii) pickling the substrate; (iv) activating the substrate; and (v) contacting the substrate with a chemical conversion coating solution comprising potassium permanganate and sodium phosphate and one of the following additives mixture: (a) calcium nitrate and yttrium nitrate or (b) calcium nitrate and sodium vanadate. The invention also relates to a magnesium alloy substrate obtained according to the process of the invention, to its use in the aerospace and automotive sectors, to parts for use in these sectors, and to a chemical conversion coating solution suitable for use in the process comprising potassium permanganate, sodium phosphate, and (a) calcium nitrate and yttrium nitrate, or (b) calcium nitrate and sodium vanadate.