The hottest magnesium alloy wheel hub and its elec

Magnesium alloy wheel hub and its electromagnetic pump low pressure casting

Abstract: This paper summarizes the characteristics of magnesium alloy wheel hub and its current application in automobile, motorcycle and bicycle industry, introduces the principle and process characteristics of electromagnetic pump low pressure casting, and the feasibility of producing magnesium alloy wheel hub. It is pointed out that the low-pressure casting technology of electromagnetic pump will play an important role in the production of magnesium alloy hub with its unique advantages

key words: magnesium alloy hub electromagnetic pump low pressure casting

magnesium alloy, as the lightest structural material and recyclable green material, has attracted much attention in recent years. Its application in the automotive industry, electronic industry, national defense industry and other fields has a strong growth momentum. At present, there are at least 60 kinds of magnesium alloy parts used in automobiles, mainly including instrument panel, seat frame, steering wheel, hood, gearbox, intake manifold, wheel hub, etc. Volkswagen AG predicts that magnesium consumption per vehicle will reach kg (1) in the next five years. In recent years, with the decline of the price of raw magnesium materials to see whether the failure is eliminated, the improvement of magnesium alloy forming technology and equipment level, and the improvement of magnesium alloy anti-corrosion technology, magnesium alloy wheels will be used more and more in cars, motorcycles and bicycles. This paper summarizes the characteristics and application status of magnesium alloy hub, as well as the process characteristics of low-pressure casting magnesium alloy hub for electromagnetic pump

Figure 3 low pressure casting magnesium alloy wheel hub of electromagnetic pump

I. characteristics and application status of magnesium alloy wheel hub

1. Characteristics of magnesium alloy wheel hub

using magnesium alloy wheel hub on vehicles can achieve the purpose of lightweight, and the weight is reduced by about 30% compared with aluminum alloy wheel hub. In addition, there are other advantages:

① high vibration damping characteristics: magnesium alloy material has a high damping coefficient, which is 15 times that of aluminum alloy and 60 times that of steel (2). The larger the damping coefficient is, the faster the amplitude attenuation is, and the better the damping performance is. Using magnesium alloy wheel hub can reduce the vibration of automobile engine, suspension bracket and gearbox, and improve its service life; At the same time, it also improves the stability, safety and comfort of the car during driving. It is reported (3) that a magnesium alloy automobile hub developed in the United States can still drive at a speed of no more than 48km/h after the tire is punctured, and the car will not be damaged, which can prevent personal accidents. For people who ride motorcycles or drive by themselves, lower vibration means higher value enjoyment

② high thermal conductivity: for cars, magnesium alloy wheels have high thermal conductivity (slightly worse than aluminum alloy wheels), which can reduce the temperature of the brake system and prolong the service life of the brake wheels

③ improve vehicle performance: the lighter magnesium alloy wheel hub is conducive to improving the acceleration and braking performance of the vehicle

④ improve fuel efficiency and reduce pollution: the use of magnesium alloy wheels can reduce 1 5% of the vehicle weight, improve fuel efficiency and reduce pollution

⑤ high rigidity: compared with aluminum alloy hub, the rigidity is greatly improved, because although the wall thickness of magnesium alloy hub increases, it has little effect on the weight. Therefore, when impacted by obstacles, the shape of the wheel hub can be maintained, so as to improve the service life of the tire

2. Application status of magnesium alloy wheels

many advantages of magnesium alloy wheels can not only meet the requirements of vehicle lightweight, but also improve the performance of some aspects of the vehicle. Therefore, magnesium alloy wheels are used in racing cars and some high-end vehicles

the use of magnesium alloy wheels in automobiles is not new. As early as 1967, Austin cars in Britain began to use magnesium alloy wheels on the Mini Cooper 1275s, while the 911T of German luxury car Porsche also first used magnesium alloy wheels in 1973. Due to the high price and corrosion problems, magnesium alloy wheels have not been widely used in cars, but only in racing cars and a few high-end cars. However, with the decline of the price of raw magnesium materials, the improvement of corrosion prevention technology of magnesium alloy and the improvement of forming technology of magnesium alloy, magnesium alloy wheels will be used more and more in cars, motorcycles and bicycles

at present, in the automotive industry, magnesium alloy wheels are widely used in racing cars. In addition, magnesium alloy wheels are also equipped on concept cars launched by major automobile manufacturers, but they are not widely used in mass-produced models. See Table 1 for the automobile companies and their models that currently use magnesium alloy wheels. Among them, the Corvette C5 model of General Motors is equipped with aluminum alloy wheels as standard, but at the same time, it also provides the cast magnesium alloy wheels produced by dymag company for consumers to choose. In addition, in the retail market of wheels, there are magnesium alloy wheels suitable for Hyundai, Citroen, Mazda, Mitsubishi, BMW, Audi, Mercedes, Volvo and other models for users to choose, but at present, its price is about twice that of aluminum alloy wheels. Table 1 some automobile companies using magnesium alloy wheels and their models

automobile companies

models

wheel production companies

Ferrari

F355 and F50

-

Porsche

911GT (2001) Carrera GT (2003)

forged magnesium alloy wheel hub produced by BBS company

BMW

Z22

-

GM

Corvette C5

cast magnesium alloy wheel hub produced by dymag company

Mazda

RX-7

Mazdaspeed is certainly applied to ms-01 MAG forged magnesium alloy wheel

automobile jointly developed by Mazdaspeed and rays company.It is an important field of magnesium alloy wheels, However, its application in motorcycles and bicycles cannot be ignored

in the motorcycle industry, nearly 90% of racing motorcycles use magnesium alloy wheels. Not only that, the application models of magnesium alloy wheels have also been extended to sports motorcycles, mopeds and concept motorcycles, covering more than a dozen major motorcycle brands in Europe, America and Japan, of which dymag wheels in Britain alone are used in as many as 400 models. See Table 2 for some motorcycle manufacturers and their models using magnesium alloy wheels. In China, Chongqing magnesium industry has developed the LX150 magnesium alloy green concept motorcycle, of which 12 parts are made of magnesium alloy materials, including the front and rear wheels of the motorcycle, the engine crankcase, the case cover, the tail cover and the rear armrest. The magnesium alloy consumption of the whole motorcycle is 12 kg, with a total weight reduction of about 6 kg. In September, 2003, the road condition test was compared with the aluminum alloy motorcycle. The results showed that (4) the fuel consumption of magnesium alloy motorcycle was 2.827l per hundred kilometers, and that of aluminum alloy motorcycle was 3.243l per hundred kilometers. Compared with the former, the fuel consumption of the two vehicles was about 0.416l per hundred kilometers, and the fuel consumption was reduced by about 10%. At the same time, the emission limits of CO, HC and NOx can reach and exceed Europe Ι Emission Standard No. In addition, in terms of the degree of bump damage, magnesium alloy motorcycles are also less damaged than aluminum alloy motorcycles, which is closely related to the lightweight characteristics of magnesium alloy materials and the excellent vibration damping performance of magnesium alloy wheels. Table 2 some motorcycle manufacturers and their models with magnesium alloy wheels

motorcycle manufacturers

models

Honda

cbr900rr

yamagha

yzf-r6/r1

Kawasaki

zx12r

Suzuki

gsxr1000/gsxr1100/gsxr750

Ducati

748/916/996

mvagusta

F4 series

Buell

lighting X1

triumph

595/955i

in the application of magnesium alloy wheel hubs for bicycles, the 3-spoke and 6-spoke magnesium alloy wheel hubs produced by Bassano grimeca in Italy have the characteristics of light weight, firmness, vibration reduction, etc., which are not only convenient but also more comfortable to use. Many manufacturers in Taiwan are also engaged in the development and research of magnesium alloy wheels. For example, yimingdong Industry Co., Ltd. developed magnesium alloy welded wheels suitable for bicycles and electric bicycles in 2000, and far east machinery has three specifications of magnesium alloy wheels. Beijing shoute steel Yuandong magnesium alloy products Co., Ltd. launched nearly 20 bicycles made of magnesium alloy materials. The wheel hub of bicycle accounts for a large proportion of the weight of the whole vehicle, so the prospect of using magnesium alloy wheel hub on bicycle is broad

at present, the application of magnesium alloy wheels in mass-produced automobiles, motorcycles and bicycles is still in its infancy. There is still a lot of research work to be done to achieve the current use of aluminum alloy wheels. Especially in China, it does not have the technology and ability to produce magnesium alloy wheels. Therefore, in the "Tenth Five Year Plan" major scientific and technological research project "magnesium alloy development, application and industrialization", the large-scale production technology and commercial application of magnesium alloy automobile wheels and motorcycle wheels are regarded as the technological breakthrough and industrialization goal (5). Among them, the magnesium alloy automobile hub project is carried out within the framework of the 6th EU and the 863 high tech project of the Ministry of science and technology of China. The magnesium alloy motorcycle wheel hub project is mainly carried out through the agreement between the governments of China and Germany

II. Low pressure casting of magnesium alloy wheel hub electromagnetic pump

in addition to the price of raw materials, the quality of the forming process is directly related to the quality of the wheel hub, and the manufacturing cost also determines the price of the wheel hub product. Therefore, the development of high-quality and low-cost magnesium alloy wheel hub forming technology will be the key to the large-scale application of magnesium alloy wheel hub. At present, the reported methods of producing magnesium alloy wheel hubs include gravity casting (6), vacuum die casting (7), oxygen filled die casting (8), low pressure casting (9), etc. In addition, forging method can also be used. Compared with the above methods, electromagnetic pump low pressure casting has special advantages

Figure 1 Schematic diagram of electromagnetic pump technology

Cosworth process (10), which is relatively popular in the world at present, can be applied to the production of Formula One racing engine to obtain very high-quality castings. One of its key technologies is the use of electromagnetic pump filling low-pressure casting technology. The traditional low-pressure casting method mainly uses compressed air to fill the mold, and others are empty talk of maintaining pressure to complete the casting process. Electromagnetic pump is a kind of equipment for conveying conductive fluid. Its basic principle (as shown in Figure 1): the liquid metal with current is subject to the action of Lorentz force in the magnetic field to produce directional movement. Its main parameters are the magnetic induction intensity B (unit T) of the magnetic field gap of the electromagnet, the current density J (unit a/mm2) flowing through the liquid metal, and the length L of the liquid metal in the liquid rising direction between the magnetic gaps. They are related to the main technical performance index of electromagnetic pump - pressure head（ Δ P) There is the following relationship between (11)

when the current and magnetic field are large enough, the generated force can meet the requirements of general low-pressure casting. Figure 2 is the schematic diagram of the low pressure casting process of the electromagnetic pump. First, pour the refined and purified liquid metal into the holding furnace, and conduct secondary refining if necessary. When the liquid metal reaches the pouring temperature, the mold filling can be carried out under the control of the computer. During the mold filling, the liquid metal flow is controlled according to the volume at different sections of the casting, so as to ensure the stable rise of the liquid level at different sections, so as to achieve the purpose of stable mold filling. When the molten metal is filled with the mold and after a certain crusting time, the pressure can be increased and maintained, which can ensure the quality of the "articles of Association for the development of civil aircraft materials industry" reviewed and approved by the casting meeting

Figure 2 Schematic diagram of electromagnetic pump low-pressure casting process

electromagnetic pump low-pressure casting magnesium alloy hub has the following advantages:

① electromagnetic pump filling because it is not filled in a completely sealed environment, it can refine and purify the magnesium liquid in the holding furnace. During the filling process, both electricity and magnetism can be implemented according to the pre-designed process plan, which can ensure the smooth filling process