| During T6 treatment of Mg-(6, 9, 12) wt.%Al alloys, X-ray diffraction analysis and microstructural observation, immersion test was performed in order to investigate the microstructural transformation and the corrosion behavior. At 220℃, the Fournelle & Clark model operates as a dominant nucleation mechanism and the nucleation rate and boundary migration velocity depends upon the solute concentration. Also the single seam nodule is observed as a dominant morphology of transformed phase. At initial precipitation stage, the corrosion rate of heat-treated specimens depends upon the galvanic corrosion between α-Mg matrix and transformed phase, as well as the corrosion behavior of α-Mg matrix itself. The corrosion behavior of α-Mg matrix depends mainly upon the repassivation tendency of exposing surface, which depends upon the Al concentration of α-Mg matrix. Although the corrosion property of solutionized alloy depends upon the corrosion behavior of α-Mg matrix, the corrosion rate of aged alloy is remarkably decreased by the formation of network morphology of transformed phase along grain boundary. |
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