Characterisation by EIS of ternary Mg alloys synthesised by mechanical alloying

Electrochemical impedance spectroscopy has been used to study the electrochemical behaviour of ternary Mg60Ti10Si30 and Mg88Ti5Si7 alloy samples fabricated by mechanical alloying of the elemental powders in an argon atmosphere. The influence of different milling times up to 25 h and heat treatment on the electrochemical behaviour of the samples, after compacting under pressure into disks, has been investigated in 0.1 M Na2SO4 and 0.01 M NaCl electrolyte solutions. Complementary measurements of open circuit potential, polarisation curves, and surface and microstructural analysis have been carried out. The experimental results revealed that corrosion is greater for Mg88Ti5Si7 which contains free magnesium; however, in sulphate solution a protective oxide layer formed can reduce the corrosion rate. In Mg60Ti10Si30, heat treatment increases corrosion, which is explained through a greater tendency for pitting corrosion. Comparison is made between the electrochemical impedance data and the nanophase structure as well as with the electrochemical behaviour of other magnesium alloys.