Reduction of Experimental Error by Surface Treatment in the Measurement of Polarization Curves of Magnesium Alloys

抄録

To reduce the electrochemical measurement error of magnesium alloys, surface treatment of AZ91 alloys in 0.1 M NaCl solution at pH = 11 at several potential values were investigated. Scanning electron microscope (SEM) was used to observe the surface conditions. Elemental distribution was investigated using an electron probe micro-analyzer (EPMA). The thickness and chemical composition of the coatings could not be accurately determined from the observations. The electrochemical impedance spectroscopy (EIS) results showed that the electrochemical stability and damage of the surfaces treated at −2.2 V were better than those treated at −1.5 V. This result suggests that surface treatment at −2.2 V prior to polarization test measurements results in smaller experimental errors. For the polarization curve measurements, the surface treatment at −2.2 V was effective to reduce the experimental error. This is also reflected in the standard deviation values for each corrosion property. The standard deviation of the corrosion potential of the surface treatment at −2.2 V was 0.009 V, which was clearly smaller than the standard deviation value of 0.0024 V for the surface treatment at −1.5 V. Therefore, it can be concluded that the surface treatment at −2.2 V reduced the experimental error in the measurement of the polarization curve.

Fig. 5 Polarization curves of AZ91 alloy measured after immersion in 0.1 M NaCl (pH = 11) solution for 2 h at surface treatment potentials of −1.5 V (a) and −2.2 V (b).