Electrochemical behaviour assessment of novel Mg-rich Mg-Al-RE alloys (RE = Ce, Er)

The electrochemical behaviour of new Mg-Al-RE (RE = Ce, Er) alloys AE91 was investigated in 0.01 M NaCl electrolyte (pH = 12) and compared with that of the most commonly used Mg alloy in the automotive field, the AZ91D. Scanning electron microscopy and quantitative electron probe microanalysis were used to characterize the samples prior to the electrochemical tests. AE91 alloys showed very similar microstructures characterized by a three-phase appearance: a Mg-based solid solution containing only Al and two intermetallic phases gamma(Mg17Al12) and (Al1-xMgx)(3)Ce or (Al1-xMgx)(2)Er. Free corrosion potential measurements, potentiodynamic polarization curves and electrochemical impedance spectroscopy revealed improved passivity behaviour compared to AZ91D alloy. The apparent presence of trace amounts of rare earth oxides in the passive film is presumed to be the reason for the enhanced corrosion resistance of AE91 alloys in the aggressive environment considered. (c) 2006 Elsevier Ltd. All rights reserved.