Flame-retardant Magnesium Alloy

As the lightest metal structure material, magnesium alloys are found using widely in automotive, electronic and aeronautical industries because of a number of desirable features, including high specific strength, high specific stiffness, good magnetic-shielding ability, good damping ability, good machinability and recycled easily. Magnesium alloy is prone to be oxidized and burning during the melting process in air for its high oxygen affinity, which limits its large-scale industrial applications. At present, fluxes and protective gases are currently used for the melting and production processes, but both methods still remain many problems such as environmental polluting greatly,devices complicated and product quality unstable, so that we should look for a more effective method as burning prohibitor. Alloying is a promising method of preventing magnesium alloy from burning.According to the metal oxidation theory, the paper has a further study on the oxidation thermodynamic and kinetic, and gets the structure and growth regularity of the oxide film on the ignition-proof magnesium alloy. Alloying is used for preventing magnesium alloy from burning during melting. By the addition of alloying element, a layer of protective film with dense structure is formed on the surface of the molten alloy, increasing its burning temperature. Furthermore, alloying can evidently enhance mechanical properties. Finally we expect to obtain the new-type ignition-proof magnesium alloy, which has not only the excellent ignition-proof characteristic but also excellent mechanical properties.The subject chooses magnesium alloy ZM5 which is widely used as the original alloy. The effects of mischmetal,Ca and Li additions, with different methods and amount, on the burning temperature of ZM5 magnesium alloy are investigated. The effects of alloying element additions on the mechanical properties of ZM5 magnesium alloy are also investigated. New magnesium alloy with both excellent ignition-proof property and acceptable mechanical properties is obtained, moreover, the ignition-proof principle is also analyzed preliminarily. It is discovered that Ca or mischmetal additions to ZM5 alloy can form a layer of dense-film on the surface and heighten the burning temperature obviously. The additions of 1.0% mischmetal and 0.8% Ca has the best result, which heightens the burning point by 240℃, up to 785℃. Furthermore, alloying elements have enhanced the mechanical properties because of grain refinement,solid-solution treatment and the second phases strengthen. The mechanical testing indicates that adding 1.0% mischmetal and 0.5% Ca to ZM5 alloy shows the best mechanical property. According to the above study, the composition of ZM5-1.0%RE-0.8% alloy with both excellent ignition-proof property and nicer mechanical properties was obtained, which has not only been melted without protection but also excellent mechanical properties.The analysis of oxidation process and the composition of oxide film gives us a clear understanding of oxidation at high temperature. It can help the oxidation-proof study of other metals and alloys. Furthermore, the effects of alloying elements additions on microstructure and mechanical properties for ignition-proof magnesium alloy are investigated, which is of great help to find out the best element additions for alloys.