Study on the early surface films formed on Mg-Y molten alloy in different atmospheres

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• 作者：A.R. Mirak^a ; ^{mirak@iust.ac.ir" class="auth_mail" title="E-mail the corresponding author} ; C.J. Davidson^b ; J.A. Taylor^a
• 关键词：Mg-Y alloy ; SEM ; EDX ; Early surface film ; Oxidation ; Fluoridation
• 刊名：Journal of Magnesium and Alloys
• 出版年：2015
• 出版时间：September 2015
• 年：2015
• 卷：3
• 期：3
• 页码：173-179
• 全文大小：2304 K

文摘

In the present study, the non-isothermal early stages of surface oxidation of liquid Mg-1%Y alloy during casting were studied under UPH argon, dry air, and air mixed with protective fluorine-bearing gases. The chemistry and morphology of the surface films were characterized by SEM and EDX analyses. The results indicate a layer of smooth and tightly coherent oxidation film composed of MgO and Y₂O₃ formed on the molten Mg-Y alloy surface with 40–60 nm thickness under dry air. A dendritic/cellular microstructure is clearly visible with Y-rich second phases gathered in surface of the melt and precipitated along the grain/cell boundaries under all gas conditions. Under fluorine-bearing gas mixtures, the surface film was a mixed oxide and fluoride and more even; a flat and folded morphology can be seen under SF₆ with oxide as dominated phase and under 1, 1, 1, 2-tetra-fluoroethane, a smooth and compact surface film uniformly covering the inner surface of the bubble with equal oxide and fluoride thickness, which results in a film without any major defects. MgF₂ phase appears to be the key characteristic of a good protective film.