Influence of Scandium on Corrosion Properties and Electrochemical Behaviour of Mg Alloys in Different Media

Corrosion behaviour of Mg-xSc (x=0, 3, 5, wt.%) alloys prepared by zone purifying solidification technique has been investigated by immersion test and electrochemical measurement in both 0.9 wt.% NaCl solution and simulated body fluid. The results of immersion test show the corrosion resistance of Mg-3wt.%Sc alloy in both conditions is much higher than that of pure Mg or Mg-5wt.%Sc alloy. Moreover, the released hydrogen gas per day of Mg-3 wt.% Sc alloy is equivalent, which indicates that the corrosion process is homogeneous. Compared with pure Mg and Mg-5 wt.% Sc alloy, the oxide film is more uniform and compact. The oxide film includes Mg(OH)2 and the sediment of Ca (H2PO4)2 in simulated body fluid. The potentiodynamic polarization curves show that a current plateaus is only observed in Mg-3wt.%Sc alloy due to the stable protective corrosion film. The electrochemical impendence spectroscopy curves of Mg-3wt.%Sc alloy are mostly composed of two capacitive loops in high and low frequency regions because of the existence of stable double-layer capacitance controlled by diffusion. It is demonstrated that the improved corrosion properties of Mg-3wt.%Sc alloy are essentially attributed to the reduction of the cores of pitting corrosion.