The corrosion resistance of ternary Mg88Ti5Si7 and Mg60Ti10Si30 samples made by mechanical alloying, with and without heat treatment, has been investigated by the electrochemical techniques of open circuit potential, polarisation curves and electrochemical impedance. Samples were made with different milling times and were subjected to annealing at increasing temperatures. The experimental results demonstrate that corrosion is up to one order of magnitude higher for Mg88Ti5Si7 than for Mg60Ti10Si30 which is explained in terms of changes in the alloy microstructure occurring during milling and after heat treatment.