Magnesium alloys have high specific strength, high specific modulus, high damping capacity, high thermal conductivity, Gao Jing electrical shielding, high mechanical processing and very low density, and so on. Starting in 1940s, magnesium alloys have been widely used in automotive, aerospace and other fields, and in the late 90s, magnesium alloy products began to be used in bicycles, electronic products and other civilian areas. When making cars, aircraft parts with magnesium alloy, can greatly reduce the weight, reduce fuel consumption; when the magnesium alloy manufacturing mobile phone, notebook computer and some domestic appliances, can significantly enhance the cooling capacity and the seismic capacity of the product, and can effectively reduce the electromagnetic radiation on the human body and the surrounding environment; when auto parts manufacturing with magnesium alloy, can enhance the vehicle safety and comfort. Therefore, the world's Magnesium Alloys in the automotive and electronic equipment in the amount of 20% of the rate of growth. This is unprecedented in modern metal engineering materials.

In addition, magnesium alloy can be recycled, is conducive to the environmental protection of a green metal, also known as the twenty-first Century green engineering materials".

1 the development of casting magnesium alloy according to the forming process, magnesium alloy can be divided into casting magnesium alloy and wrought magnesium alloy, both in composition, microstructure and properties, there is a great difference. The casting of magnesium alloy is mainly used for automobile parts, mechanical and electrical components such as shell; deformation magnesium alloy sheet, mainly used for extrusion and forging etc.. The application of cast magnesium alloys is much wider than that of wrought magnesium alloys. This paper mainly introduces the development of casting magnesium alloy. Casting magnesium alloy can be roughly divided into three stages:

(1) the first stage is a basic stage mainly in the addition of aluminum and zinc in magnesium, namely Mg-A1-Zn system alloy. This kind of alloy can get the similar tensile strength with the casting aluminum alloy. China's ZM5, L121 and AM80A of the United States in the United States belong to this type of alloy, the main elements to add aluminum, while the zinc content is low, mainly because of the increase in the zinc content, prone to the emergence of micro.

(2) the second stage is an improvement phase in the addition of zirconium in magnesium, Mg-Zn-Zr, Mg-RE-Zr, etc.. The main role of zirconium in the magnesium alloy is to refine the grain of the magnesium alloy, thus increasing the yield strength of the magnesium alloy, and the magnesium alloy has good anti fatigue properties and low notch sensitivity. Disadvantage is still due to the wide crystallization interval, prone to micro porosity and hot cracking tendency. So at present, the most widely used is the non - zirconium - casting magnesium alloy Al Mg-. In addition, in order to improve the creep resistance of the magnesium alloy, the magnesium alloy with rare earth elements as the main component is produced.

(3) the third stage is to improve the stage of adding silver in magnesium alloy, silver alloy after can enhance the age hardening effect, greatly improves the high temperature strength and creep resistance of magnesium alloy, but will reduce the corrosion resistance of alloy.

2 ways of liquid forming of magnesium alloy at present, liquid forming of magnesium alloy is still in pressure casting, gravity casting, magnesium alloy with other casting methods, such as low pressure casting, casting and other forms of less, which cast magnesium alloy forming the main.

2.1 magnesium alloy die casting is the most important and widely used forming technology of magnesium alloy. Because of the good heat flux of magnesium alloy, it is very suitable for the die casting production of thin wall parts. Magnesium alloy die casting began in the mid 1920s of the German VolksWagen automobile company. Later, the United States, the former Soviet Union, Japan and some European countries have adopted in the die casting of magnesium alloy structural parts of the automobile manufacturing industry, such as the crankcase, the drive shaft casing, air conditioner shell, the shell of the gearbox, cockpit panel, wheel, cylinder body, cylinder cover, distribution frame, pump casing, filter shell etc.. Since 1980s, with the continuous reduction of the cost of magnesium alloy, magnesium alloy began to be more and more applications in the automotive, computer, communication equipment, and the vast majority of magnesium alloy die castings. Although the development of magnesium alloy and preparation technology is relatively early in the world, China has begun to have its own magnesium industry after the liberation of China. In recent years, with the rapid development of China's automotive industry, electronic communications industry, the demand for magnesium alloy die castings is increasing, the development of magnesium die casting industry in our country is very fast. China's magnesium alloy die casting production increased by 1562 tons in 2005 to 8960 tons in 1995, 7 years, production increased by more than 4 times, the average annual growth rate of 60%. It is becoming the development trend of manufacturing industry, especially the automobile manufacturing industry, to replace the traditional cast iron and cast steel with the magnesium alloy die casting. There are many factories in the country engaged in the production and research of magnesium alloy die-casting parts, such as Shenzhen, Dongguan and other factories in the production of notebook computer shell, mobile phone shell magnesium alloy die casting parts, etc.. Chongqing Magnesium Industry Co. Ltd., with motorcycle and light car with magnesium alloy and its parts as the focus, while the development of magnesium alloy wrought products; Qingdao Magtech company focus on the development of 3C electronic products using magnesium alloy products. Although magnesium alloy die castings produced by traditional die casting method are widely used, it can not be strengthened by heat treatment and can not be used at high temperature. In order to eliminate these defects and improve the internal quality of casting, to expand the scope of the use of die casting technology, experts in recent years based on the traditional die casting process on the research and development of some new technologies such as: Die Casting of semi solid die casting, vacuum casting, die casting and super high pressure oxygen casting etc.. These new technologies in the elimination of magnesium alloy die casting