The magnesium alloy’s production technique has many characteristics that known and mastered well could make the production smoothly, its characteristics are summarized as followed:
Magnesium chemical activity is very strong, which is easy to have chemical reaction with oxygen, nitrogen in a molten state. If the melt surface is without strict protection, it will be oxidized and burnt quickly when approaching 1073K. In order to reduce the scaling loss, ensure the safety of production and the quality of alloys. In the entire casting process, the melt mass always need to be protected by solvents or gases and avoid the contact with furnace gas and oxygen, nitrogen and water vapor in the air.
In addition to several elements (such as CD, Zn, Al, Ag, etc.), other elements solubility in magnesium are very small. In addition, among the insoluble elements, it is also easy to form high melting point compounds, thus separated out, so it is very difficult to join in the process. Because iron is insoluble in magnesium, the iron tools without any paper paste can be used in the casting process of magnesium alloy.
In some magnesium alloy’s cast ingot, local grain size is easy to differ widely. Meanwhile, the crystal size is large, crystal size is prone to be columnar crystals and fan-shaped crystals, seriously affecting pressure processing performance and the mechanical properties of the products. Thus, different alloys take different modification treatment methods to refine the grain, appropriately changing the size of the crystals. Because magnesium alloy’s crystals tend to be coarsening, thus in principle, the size and shape of magnesium alloy ingots crystals are not strictly required.
Magnesium alloy’s oxidation, solvents’ slag inclusion, and gas solubility are more than aluminium alloy, therefore, it need to be purified. At present, solvent refined method is used more in China. Magnesium alloy’s cleaning agent belongs to settlement type, which is different from aluminum alloy and other nonferrous metals, directly affecting the production process and products’ quality.
Therefore, it need adequate rest time after purifying. On the bottom of the boiler, slag discharge port is required to be set. Picking out the low slag should not be overlooked. With the protection of solvents, it need to use large amounts of solvent throughout the casting process. Meanwhile ,a large number of additional auxiliary materials are added, whose quality directly affects the quality of the alloy. Therefore, there exists strict requirements on the solvent.
Hydrogen may also have an impact on magnesium alloys. In addition to the impact of zirconium solubility in zirconium-containing magnesium, but it will appear microscopic pores of various degrees when the hydrogen content exceeds a certain limit. Therefore, the hydrogen content should not be overlooked. Due to the low content of magnesium alloy, the melt temperature will be reduced when adding high melting point elements or auxiliary materials that has large quantities. Therefore, the magnesium alloy’s melting temperature should be higher than the aluminum. Many factors affect the yield, such as process factors, addition methods or operations, batch, melting temperature and the number and quality of solvents, etc., which all should be strictly paid attention to.
