Magnesium is one of the most abundant light metal elements on the earth, with a specific gravity of 1.74g/cm3, only 2/3 of aluminum and 1/4 of steel; Magnesium alloy is 36% lighter than aluminum alloy and 77% lighter than steel. Magnesium has the advantages of high strength, high rigidity, good thermal conductivity, and good electromagnetic shielding, damping, vibration reduction, machinability, low processing cost, processing energy only 70% of aluminum alloy and easy recovery. In addition to its low specific gravity, magnesium has many good physical properties, making it sometimes more valuable than aluminum and plastics in the application of automotive structural materials. The physical properties of magnesium are mainly 30 times higher than that of aluminum; The thermal conductivity and thermal expansion performance 200 times higher than that of plastics are only 1/2 of that of plastics.
However, magnesium metal only accounts for 2.5% of the materials used in automobiles at present, and a considerable part of it is used in automobiles in the form of synthetic materials. It is predicted that the future development trend is that the consumption of magnesium will be further increased. In the future special vehicles, such as F1 racing cars, magnesium will account for about 10% of the whole vehicle material.
At present, the raw material manufacturers of magnesium metal are expanding their production capacity. For example, in China, the annual production capacity of magnesium metal has soared from 5000 tons to 150000 tons; In Germany, the annual output of magnesium alloy castings has reached 30000 tons, the highest ever recorded. In addition, many auto parts suppliers and auto manufacturers also have their own magnesium alloy material development projects and plans. For example, there are many such ideas in North America. However, Europe still has the largest plan and the largest growth rate. Table 1 shows the demand for magnesium alloys in the United States, Europe and Japan.
In the field of automobile manufacturing, magnesium alloy materials have more than 60 different uses. These magnesium alloy auto parts can be seen in both high-end cars and ordinary cars. In racing cars, cars and SUVs, expensive magnesium alloy materials can be processed into qualified automobile parts, and can also be made into load-bearing parts of automobiles. All OEM automobile manufacturers use magnesium alloy parts in their products, but the parts made of these magnesium alloy materials are different. For example, Porsche uses magnesium alloy materials to make front wheels of cars.
There are a wide variety of automobile parts made of magnesium alloy materials, from the moving parts of automobiles (such as wheels), to the structural parts of automobiles (such as seat frames), and to the high-temperature resistant parts (such as cylinder blocks) that bear high temperature. The common feature of these parts is that they bear low mechanical and chemical loads. Magnesium alloy materials are often used to manufacture parts such as “bracket”, “shell”, “end cap” or “plug cap”. Due to the excellent casting flow performance of magnesium alloy material, it is very suitable for manufacturing thin-walled structural parts such as tie rods and large area vehicle internal structural parts, such as doors and front and rear hatch covers. The physical and chemical properties of magnesium metal make it more suitable for die-casting large parts than aluminum. The most commonly used magnesium alloy parts are:
-Steering shaft: 50% of the steering shaft in the world is made of magnesium alloy;
-Beam, about 6000t magnesium alloy material is used in European cars;
-Transmission housing: about 600 magnesium alloy transmission housings are used in Volkswagen B-frame cars every day.
In principle, magnesium alloy materials are mainly used in the drive system of the internal structure of automobiles. Magnesium alloy parts and components provided by automobile parts suppliers in large quantities are expected to enter the automobile manufacturing industry in the next five years. At that time, DaimlerChrysler will use magnesium alloy automatic transmission for automobiles; The engine block made of Mg-Al composite material will be used for cars produced by BMW. In the long run, magnesium alloy materials will also be further increased in the manufacturing of frame and chassis, as well as in the manufacturing of high-temperature resistant parts.
In addition to the advantage of reducing the weight by 40%~70% compared with steel and aluminum, magnesium alloy materials also have great advantages in vibration reduction, noise reduction and environmental protection. The rich content of magnesium element on the earth makes it easy to recycle the waste parts of magnesium alloy materials; Compared with aluminum alloy materials, magnesium alloy materials have less energy consumption during melting and casting, and less mechanical wear during machining. Therefore, the overall production cost can be reduced by about 20% compared with aluminum alloy materials. The good weldability of magnesium alloy materials may bring a new revolution to the structural design of automobiles. It can be used to manufacture a large number of structural parts, especially some thin-walled parts and large-area structural parts, thus reducing the total assembly cost of automobiles.
Although the price of magnesium ingot per kilogram is higher than that of aluminum and iron, this disadvantage in price can be compensated by the low cost in the production and processing of magnesium alloy materials. The latent heat of magnesium melting per unit volume is only 2/3 of aluminum, and the specific heat is only 3/4 of aluminum, and the iron solubility is very low. Therefore, the total price is only about 20% higher than that of aluminum alloy materials. In addition, magnesium alloy materials have some shortcomings, such as poor corrosion resistance, poor creep resistance and poor rigidity. In the manufacturing process of magnesium alloy parts, there are many problems to be solved. For example, during casting, the problem of bad (cold) deformation should be overcome; In addition, magnesium alloy materials also have corrosion problems of external exposed parts in practical applications, and attention should be paid to improving the contact corrosion resistance of magnesium alloy and preventing the spontaneous combustion of metal magnesium during the mixing and transportation of parts with different materials.
Compared with steel and aluminum parts, the competitiveness of magnesium alloy parts is increasing, and the recyclability of magnesium alloy materials also plays an important role in this regard. When people make full use of the characteristics of metal magnesium and reasonably design automobile parts according to the characteristics of metal magnesium, magnesium alloy parts have a tendency to replace steel and aluminum parts, and will not lead to an increase in price. Table 2 shows the growth trend of magnesium metal consumption in the next few years.
The increasing number of magnesium alloy parts in the automobile industry provides a new business opportunity for parts suppliers and system suppliers. In the process of producing and processing magnesium alloy automobile parts, the problem of magnesium ablation should be solved first. After adopting appropriate safety protection measures, Volkswagen can effectively prevent spontaneous combustion in the casting, smelting and cutting of magnesium alloy parts. AHC Surface Processing Co., Ltd. and Henkel Safety Technology Co., Ltd. have developed the polishing technology of magnesium alloy parts that will be put on the market. In addition, Henkel Safety Technology Co., Ltd. also obtained the authorization license for the pretreatment process of magnesium alloy materials, which is a process technology for anti-corrosion treatment of magnesium alloy parts according to the principle of anodic surface treatment.
With the continuous improvement of science and technology, the weaknesses of magnesium alloy materials are also being improved, and magnesium alloy materials will have a very broad market prospect.