Effect of traces of silicon on the formation of Fe-rich particles in pure magnesium and the corrosion susceptibility of magnesium

Fe-rich particles that contain silicon were observed in commercially pure magnesium, which contained less than 25 ppm Fe. Based on the simulated phase diagram, silicon, even at low ppm levels, promotes the formation and growth of Fe-rich particles. The studied pure Mg showed a high corrosion rate (>2 mm/year) in 3.5 wt.% NaCl solution, although the Fe content is far below the widely accepted corrosion tolerance limit of Fe (170 ppm by weight). The formation of the Si-containing Fe-rich particles is one of the main reasons for the high corrosion rate observed. Consequently and importantly, the corrosion tolerance limit of iron in magnesium is significantly reduced by the presence of traces of silicon.