2010Effect of melt temperature on the oxidation behavior of AZ91D.pdf

M A T E R I A L S C H A R A C T E R I Z A T I O N 6 1 ( 2 0 1 0 ) 8 9 4 – 8 9 8 ava i l ab l e a t www.sc i enced i r ec t . com www.e l sev i e r . com/ loca te /matcha rEffect of melt temperature on the oxidation behavior of AZ91D magnesium alloy in 1,1,1,2-tetrafluoroethane/air atmospheresHukui Chen? Department of Chemistry, Baoji University of Arts and Science, Baoji 721007, ChinaA R T I C L E D A T A? Tel.: +86 917 3364093; fax: +86 917 3364093 E-mail address: hkchen7115@. 1044-5803/$ – see front matter ? 2010 Elsevi doi:10.1016/j.matchar.2010.05.012A B S T R A C TArticle history: Received 12 December 2008 Accepted 30 May 2010The oxidation behaviors of AZ91D magnesium alloy in 1,1,1,2-tetrafluoroethane/air atmospheres at temperatures between 660 °C and 760 °C have been studied. The experimental results show that with the increase of melt temperature, the oxidation rate of molten AZ91D magnesium alloy in 1,1,1,2-tetrafluoroethane/air atmospheres increased and the oxidation kinetics changed from parabolic law to linear law. On the other hand, the amount of MgF2 in the oxide film formed on AZ91D decreased, and the amount of MgO increased. The effect of melt temperature on the oxidation behaviors is primarily related to the relative content of MgO and MgF2 in the film, as well as the diffusion rate and the evaporation rate of magnesium through the film. ? 2010 Elsevier Inc. All rights reserved.Keywords: Magnesium melt Oxidation 1,1,1,2-tetrafluoroethane Temperature1. Introduction Moltenmagnesiumand its alloy are commonly protected from oxidation and burning by the use of protective atmosphere containing SF6 in melting and casting operations. However, the high greenhouse effect of SF6 has caused the magnesium industry to look for its alternatives. In recent years, 1,1,1,2- tetrafluoroethane (HFC-134a) has been considered a most promising alternatives to SF6, and much research has been carried out on the oxidation behaviors of molten magnesium andmagnesium alloy in t