Characterisation by EIS of ternary Mg alloys synthesised by mechanical alloying

Abstract

Electrochemical impedance spectroscopy has been used to study the electrochemical behaviour of ternary Mg 60 Ti 10 Si 30 and Mg 88 Ti 5 Si 7 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 Na 2 SO 4 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 Mg 88 Ti 5 Si 7 which contains free magnesium; however, in sulphate solution a protective oxide layer formed can reduce the corrosion rate. In Mg 60 Ti 10 Si 30 , 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.

Effect of heat treatment on corrosion behavior of low pressure sand cast Mg-10Gd-3Y-0.5Zr alloys

“…The polarization curves show that both the as-cast and T6 conditions have positive corrosion potentials, while the corrosion potential of the T4 sample is negative. This indicates that corrosion potentials of the secondary phases in the as-cast and T6 samples are higher than that of the matrix and lead to an increase in corrosion potentials of the alloys, because the potential of an alloy is determined by the potential of the constituent phases and the area fraction covered by each phase [24] .…”

“…In other words, there are two loops of the high-frequency captance and the mediumfrequency captance but without inductive loops, which shows that the low-pressure sand-cast Mg-10Gd-3Y-0.5Zr alloy has a higher resistance to pitting corrosion in different heat treatment conditions. Brett et al [24] also found that the pitting formation leads to the inductive loop in the impedance spectra. According to the studies of Makar and Kruger [25] , Cao Chu'nan [26] , and Song G. et al [27] , the bigger high-frequency capacitive loops are related to the better corrosion resistance.…”

“…It can be seen that the microstructure of the as-cast condition (Fig. 3a) mainly consists of equiaxed α-Mg and the eutectic compounds [Mg 24 (Gd,Y) 5 phase] distributing along the grain boundries, mostly at the triple points, while that of the T4 condition (Fig. 3b) contains α-Mg matrix and some cuboidshaped particles distributed along grain boundaries and inside the grains.…”

“…6(a, b and c), the as-cast and T6 samples have serious and deep corroded area, while the T4 condition has slight corrosion with a small quantity of remaining eutectic compounds (Mg 24 (Gd,Y) 5 ) in local areas, and also visible Zr-rich cores are remained. It can be concluded that the secondary phase (Mg 24 (Gd,Y) 5 ) and Zr-rich cores have more positive corrosion potentials than that of the α-Mg matrix. Mg 24 (Gd,Y) 5 phase and Zr-rich cores act as the cathodes and the α-Mg matrix acts as the anode.…”

Effects of amorphous NiB on electrochemical characteristics of MgNi alloy

“…The semicircle in high frequency region is attributed to the charge transfer or electrochemical reaction resistance (R 1 ) paralleling with double layer capacitance (CPE), and the low frequency straight line is attributed to the diffusion of hydrogen in the material bulk. Based on the circuit, the overall system ohmic resistance (R s ) and the charge transfer resistance (R 1 ) were obtained by ZView EIS fitting program in Sai software set [12,13]. CPE, which is instead of a capacitor to avoid the error arised by non-homogeneity of the system, is constant phase element which is defined by two values CPE-T and CPE-P.…”