순 마그네슘의 산화저항성에 대한 CaO의 영향

Abstract

Application of magnesium alloys has been rapidly increased due to their excellent properties such as high specific strength and low density. Nevertheless, magnesium alloys have serious problem that it can be easily oxidized when exposed in the high temperature. Thus, SF6 gas such as protective cover gas is generally used for magnesium alloys during melting and casting process, but this gas has significantly baneful influence on global warming. For this reason, many research have been conducted to improve the oxidation resistance of magnesium alloys. It was reported that addition of Be, Ca and CaO in magnesium alloys improved oxidation characteristic. However, Be and Ca are alkaline earth metal so these elements are difficult to handle because of their high reactivity. Especially, Be has been restricted due to emission of toxic materials. On the other hand, CaO is stable and cheaper than other materials. So in this study, it will be confirmed to possibility of manufacturing the magnesium alloy improved in oxidation resistance by addition of CaO which was extracted from oyster shells. Oyster shells were completely decomposed into CaO and CO2 at 765℃. As adding CaO, Ca was converged from matrix to oxide layer and weight change was decreased during oxidation test. It means that addition of CaO prevents the inward transport of oxygen through porous structure of MgO oxide layer. In other words, it would be difficult to react with magnesium and oxygen.