Corrosion behaviour of a nominally high purity Mg ingot produced by permanent mould direct chill casting

The corrosion behaviour was characterized using hydrogen evolution, weight loss, electrochemical impedance spectroscopy (EIS) and cathodic polarization curves, in 3.5% NaCl saturated with Mg(OH)2, with tests lasting up to 14 days, and compared with the corrosion behaviour of the HP Mg used in our prior research at UQ. The corrosion behaviour was consistent with the uni-positive Mg+ ion Mg corrosion mechanism, particularly the fact that the corrosion rate measured using electrochemical techniques was consistently lower than that measured independently by weight loss or hydrogen evolution, as predicted by the uni-positive Mg+ ion Mg corrosion mechanism.

► This corrosion behaviour of the HZG Mg ingot was not characteristic of the corrosion of HP Mg. ► The HZG Mg ingot was not high purity, even though the Fe concentration was in the range 26–48 ppm. ► There was strong evidence for the uni-positive Mg+ ion Mg corrosion mechanism.