| Magnesium alloys are the lightest metallic structural materials. The density of magnesium alloy is 35% lower than it of aluminum alloy. Magnesium alloys used on many fields which conclude Aerospace, automotive industry, electronic information industry, household appliances and civilian areas such as national defense industry have broad application prospects and important commercial value because of the higher strength, better electromagnetic shielding capability, better damping property and well machinability.At present, Most of magnesium alloy products are mainly obtained through the casting(including the traditional casting process and a new casting process which called semi-solid casting process ) . Magnesium alloy castings can be very complicated shape. Because of the thick crystal and composition segregation , it can not fundamentally solve the problem of brittleness and corrosion, so we can not manufacture the good performance of magnesium alloy castings. Compared with casting magnesium alloy, wrought magnesium alloy has smaller grains, less micro-empty and less segregation and more suitable for the production of large-scale structureDue to the high affinity between magnesium and oxygen, magnesium oxide generated by the structure of osteoporosis, it can not prevent internal oxidation of the metal to continue, and magnesium oxide heat of formation is very poor and causes thermal conductivity profiles in the processing of magnesium alloy easily oxidized in the combustion process. The antioxidant of magnesium alloy will decline, when the temperature of alloy higher than 350℃. So when deformation of magnesium alloy in the processing, production, stockpiling and use of the period, it should be the use of appropriate protective measures to prevent burning. General large-scale magnesium alloy parts will not be caused by burning. But during processing of magnesium alloy produced by the dust, debris and burrs due to its larger surface area, in the air after the heat caused by burning easily. If a large number of dust increase, they will be floating in the air and mixed with air to form explosive mixtures, the event of fire, explosion occurs fierce burning accident. When burning magnesium alloy dazzling light, and the flames spread fast and difficult to fight which make the production more difficult and even dangerous, hindering the magnesium alloy material further. Large-scale use of magnesium alloy in today's, launch of the deformation of magnesium alloy combustion research, in order to find a magnesium alloy to improve the combustion of the ways to reduce the occurrence of fire on the safety profile of magnesium alloy production, stockpiling and use of very importance.Rare-earth as an effective alloying element, because of its affinity with oxygen than magnesium and oxygen affinity, because it has a better affinity with oxygen than that of magnesium, so it can be widely used in the study of flame-retardant magnesium alloy. But there are fewer researches on wrought magnesium alloy antioxidation with adding rare earth elements.In this paper, AZ31 magnesium alloy was chosen for the study with adding rare earth elements when melting. Paper researched the effect of rare earth elements content on magnesium alloy flammability and the effect of rolling process on magnesium alloy flammability. According to the research, paper has some conclusions:(1) Rare earth elements Ce and Gd can increase the ignition point of magnesium alloy obviously. The temperature is higher than that of magnesium alloy without rare earth elements in it. The ignition point of magnesium alloys changed base on the form of Ce and Gd exist in magnesium alloys. When the rare earth elements content under the solid solubility of magnesium alloy, the rare earth elements can increase the ignition point of magnesium alloy chips with the increase of their content. When the rare earth elements content equal the solid solubility of magnesium alloy, the ignition point reaches highest value. When the rare earth elements content above the solid solubility of magnesium alloy, (rare earth elements formed Al4Ce or Al2Gd) the rare earth elements can decrease the ignition point of magnesium alloy chips with the increase of their content.(2)The main reason that Ce and Gd can improve the flammability of magnesium alloy is that rare earth elements which formed solid solution in alloy. In oxidation process, this Ce and Gd formed Ce2O3 and Gd2O3 which can fill in the holes that formed by MgO. And these oxide can form a kind of dense composite oxide film with MgO. So that, it can delay combustion of magnesium alloy and raise the ignition point of magnesium alloy. But Al4Ce and Al2Gd can reduce the ignition point of magnesium alloy. It is because with forming Al4Ce or Al2Gd, in magnesium alloy can appear some areas around them where lack rare earth elements. In these areas, Ce or Gd can nont form oxides because Al4Ce or Al2Gd is thermal stability phase. So these areas will oxidize deeply and decrease the ignition point of magnesium alloy.(3)Rolling process can decrease the ignition point of magnesium alloy. After rolling, the grain boundary structure become looser and the Atomic arrangement become more disorder than before. It makes the oxide film have more channel that allow oxygen go into deeper to reacted with magnesium. Rolling process can cause grain refinement, and increase the quantity of grain boundary. So it also increase the oxidation areas, and make the ignition point of magnesium lower. |
