Temperature dependence of initial passivity breakdown of AZ61 and AZ91D Mg alloys in 0.1 M NaCl solution.

The effects of solution temperature on the initial corrosion characteristics of wrought AZ61 and die-cast AZ91D Mg alloys in 0.1M NaCl were analyzed. Systematic studies indicate that AZ91D exhibits higher corrosion resistance than AZ61 at room temperature. However, at high temperatures of around 55 °C, we observed contradictory corrosion behavior, as demonstrated by cyclic corrosion tests and electrochemical tests including potentiodynamic polarization, potentiostatic polarization, and elecrochemical impedance spectroscopy. As a result, AZ61 rather showed higher corrosion resistance from the point of view of pit initiation during the immersion at 55 °C resulting from the strengthening of surface passivation. These results can be attributed to the microstructure of AZ61 which contains sub-micron scale β-phase particles dispersed effectively within the α-Mg grains whereas AZ91D has many α-Mg that do not containing any β-phases. [ABSTRACT FROM AUTHOR]