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

Abstract 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 γ(Mg17Al12) and (Al1 − xMgx)3Ce or (Al1 − xMgx)2Er. 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.

[1]  P. Miller,et al.  Assessing the Corrosion Resistance of Nonequilibrium Magnesium-Yttrium Alloys , 1995 .

[2]  J. Kruger,et al.  Corrosion Studies of Rapidly Solidified Magnesium Alloys , 1990 .

[3]  C. Blanc,et al.  AC Impedance Spectroscopy in Characterizing Time-Dependent Corrosion of AZ91 and AM50 Magnesium Alloys Characterization with Respect to Their Microstructures , 2001 .

[4]  M. Dabalà,et al.  Cerium based chemical conversion coating on AZ63 magnesium alloy , 2003 .

[5]  Alireza Zolfaghari,et al.  Capacitance of the double-layer at polycrystalline Pt electrodes bearing a surface-oxide film , 2002 .

[6]  O. Lunder,et al.  Effect of Mn Additions on the Corrosion Behavior of Mould-Cast Magnesium ASTM AZ91 , 1987 .

[7]  M. Sluyters-Rehbach,et al.  The analysis of electrode impedances complicated by the presence of a constant phase element , 1984 .

[8]  F. Rosalbino,et al.  Influence of the rare earth content on the electrochemical behaviour of Al–Mg–Er alloys , 2003 .

[9]  J. Kruger,et al.  Repassivation of Rapidly Solidified Magnesium‐Aluminum Alloys , 1992 .

[10]  Y. Lei,et al.  A study of the degradation of the electrochemical capacity of amorphous Mg50Ni50 alloy , 1996 .

[11]  P. Marcus,et al.  Enhanced corrosion resistance of magnesium and its alloys through the formation of cerium (and aluminium) oxide surface films , 2001 .

[12]  F. Froes,et al.  Corrosion behavior of rapidly solidified MgNd and MgY alloys , 1988 .

[13]  A. D. Mercer,et al.  Progress in the understanding and prevention of corrosion , 1993 .

[14]  K. Nisancioglu,et al.  Morphology and Structure of Water‐Formed Oxides on Ternary MgAl Alloys , 1997 .

[15]  O. Lunder,et al.  The Role of Mg17Al12 Phase in the Corrosion of Mg Alloy AZ91 , 1989 .

[16]  Ian J. Polmear,et al.  Light Alloys: Metallurgy of the Light Metals , 1982 .

[17]  P. Steinmetz,et al.  Corrosion Behavior of Rapidly Solidified Magnesium-Aluminum-Zinc Alloys , 1997 .

[18]  N. Pébère,et al.  Investigation of magnesium corrosion in aerated sodium sulfate solution by electrochemical impedance spectroscopy , 1990 .

[19]  A. Saccone,et al.  The Al-Er-Mg ternary system Part I: Experimental investigation , 2002 .

[20]  H. Godard.  The corrosion of light metals , 1967 .

[21]  Y. Li,et al.  Correlation between the corrosion behavior and corrosion films formed on the surfaces of Mg82−xNi18Ndx (x=0, 5, 15) amorphous alloys , 2001 .

[22]  L. Robbiola,et al.  Influence of Homogenization and Artificial Aging Heat Treatments on Corrosion Behavior of Mg-Al Alloys , 1993 .

[23]  J. Kruger,et al.  Corrosion of magnesium , 1993 .

[24]  F. Rosalbino,et al.  Effect of erbium addition on the corrosion behaviour of Mg–Al alloys , 2005 .

[25]  A. Saccone,et al.  The Al-Er-Mg ternary system Part II: Thermodynamic modeling , 2002 .

[26]  N. Munichandraiah,et al.  Ageing of magnesium /manganese dioxide primary cells , 2001 .