Influence of Ca²⁺ in Deicing Salt on the Corrosion Behavior of AM50 Magnesium Alloy

To lower the freezing point of deicing salt, calcium chloride (CaCl₂) is commonly used. The influence of the presence and absence of the deicing salt ingredient Ca²⁺ on the corrosion behavior of die-cast AM50 magnesium alloy was investigated using an electrolyte close to the deicing salt composition with and without Ca²⁺ addition. The goal of the work was to point out the differences in the corrosion mechanism with and with-out Ca²⁺ addition by electrochemical investigations, H₂ evolution, and weight-loss characterization. Under polarizing conditions the resulting current densities are significantly lower in the presence of Ca²⁺. Electrochemical impedance spectroscopy (EIS) measurements up to 4.5 h showed an increasing polarization resistance, R_P, with time, and after 4.5 h, a breakdown of R_P values in the presence of Ca²⁺ combined with the appearance of an inductive loop. Mass-gain, mass-loss, and hydrogen evolution measurements confirmed the inhibiting behavior in the presence of Ca²⁺ up to 1 day. During immersion, the pH does not exceed a value of 10. Therefore, under these experimental conditions it is not possible for the system to reach the passivating pH of 12. The influence of the pH value on the corrosion rate was found to be limited in the pH region of 8 to 11.