The use of microcapillary techniques to study the corrosion resistance of AZ91 magnesium alloy at the microscale

The AZ91 alloy is composed of Mg17(Al, Zn)12 precipitates, an eutectic phase around these precipitates, AlMn intermetallic particles and an α-Mg solid solution (matrix). The corrosion behaviour of AZ91 was investigated at the microscale by means of the electrochemical microcell technique, which uses extremely small capillaries (diameters between 5 and 10 μm). Experiments were conducted in 0.1 M NaClO4 at 25 °C. The β-Mg17(Al, Zn)12 precipitates were found to have the highest corrosion resistance, whereas the eutectic phase was very active (pitting potential of approximately −1400 mV vs. Ag/AgCl). The α-Mg solid solution displayed better corrosion resistance than the eutectic phase.

► α-Mg matrix undergoes pitting corrosion in NaClO4 solution. ► β-Mg17(Al, Zn)12 precipitates are passivated in sodium perchlorate solution. ► Eutectic is more prone to localised corrosion than the matrix. ► AlMn precipitates work as local cathodes.