Effect of Mn Modification on the Corrosion Susceptibility of Mg–Mn Alloys by Magnesium Scrap

The microstructure and anti-corrosion behavior of Mg–Mn alloys by magnesium scrap have been investigated in this study. The results show that the size of the Fe-rich particles in magnesium scrap decreases but the quantity increases with the Mn addition. Although the presence of Mn-containing Fe-rich particles with unique symbiotic structure can effectively weaken the micro-galvanic corrosion, the presence of more free Fe (Fe-rich particles) does not necessarily lead to severe corrosion of the alloy. The corrosion susceptibility of Mg–Mn–Fe alloy primarily depends on the solubility of iron in the Mg matrix, while it can be significantly reduced by suitable Mn addition. Besides, the tolerance limit of the Fe impurity can be expressed as Femax = 0.0083 Mn (relative to the iron solubility). Only when the Fe/Mn ratio is below 0.0083 can the alloy have excellent corrosion resistance, with the corrosion rate changing in the scope of 0.38 ± 0.09 to 0.54 ± 0.15 mg/cm2 day and icorr from 3 to 9 × 10–4 A/cm2.