Formation of Calcareous Deposition Layers on AM50 Magnesium Alloy in Presence of Ca2+ in De-Icing Salt Solutions: Immersion Vs. Salt Spray Test
Furthermore, the influence of the used testing method was investigated. In addition to immersion experiments, salt spray testing was performed up to 13 weeks which resulted in a different morphology of corrosion and deposition products (see Figure 1). Mass gain and mass loss measurements were carried out and showed a 5-times higher mass loss under immersion conditions in comparison to salt spray testing. The presence of a higher amount of carbonates after salt spray testing could be proven. Calcite is present in the surface layers in significant amounts after both testing methods. The increasing OH- concentration during Mg corrosion triggers the deposition of CaCO3 under conditions of low CO2 partial pressure, whilst the carbonate anion derives from the CO2 in the atmosphere.
 Grabowski, M., Bluecher, D., Korte, M., & Virtanen, S. (2014). Influence of Ca2+ in Deicing Salt on the Corrosion Behavior of AM50 Magnesium Alloy. Corrosion, 70(10), 1008-1023.
 Grabowski, M., Bluecher, D., Korte, M., & Virtanen, S. (2015). The influence of Ca 2+ in de-icing salt on the chemistry of corrosion products formed on AM50 magnesium alloy–calcareous deposition. Corrosion (in press, 2015).
Figure 1: Comparison of surface fraction and appearance of corrosion and deposition products after 1 d, 3 d, 7 d and 12 d of salt spray testing and immersion of AM50 Mg-alloy in presence of a Ca2+-containing de-icing salt solution.