| In present study, the chunk breakage of precipitate and the negative difference effect which is a typical electrochemical behavior of Mg-alloy was investigated. In order to estimate the effect of precipitate, the calibration curves were obtained by XRD analyses(internal standard method). The chunk breakage of precipitate was observed under open circuit potential and maintained its original morphology. And, it revealed that the fraction of precipitate in corrosion products was approximately same as the fraction of precipitate in as-cast alloy. This is because of the corrosion behavior which the Mg-rich matrix is preferentially dissolved against the precipitate. Therefore, it was considered that the fraction of precipitate has a role of fixed factor on the corrosion rate of as-cast alloy. Also, the negative difference effect is arisen because the corrosion behavior of Mg-rich matrix is varied by the Al content, e. g. corrosion behavior of surface protective film. And, it reveals that the chunk breakage of precipitate operates only as a factor for the variation of the degree of difference effect(Δ). |
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