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2023.2.23
Lightweight and intelligent automobile has become a new trend in the development of global automobile industry technology. In recent years, with the pressure and development trend of global energy conservation and emission reduction, countries have formulated strict standards and regulations on fuel consumption of passenger cars, putting forward stricter requirements on fuel consumption of passenger cars and corresponding CO2 emissions, and the lightweight of cars is the development trend of the world’s automobile. Especially in China, by 2020, the reduction of automobile fuel consumption will be significantly greater than that of other countries, and the pressure of fuel emission will be greater. Reducing the weight of the whole vehicle is the most effective way to reduce the vehicle weight. The purpose of vehicle lightweight is to “slim down” the vehicle. On the basis of ensuring stable and improved performance, energy-saving design of various parts and components, and continuous optimization of the vehicle model. The experiment shows that if the vehicle weight is reduced by 10%, the fuel efficiency can be increased by 6% – 8%; The vehicle weight can be reduced by 1%, and the fuel consumption can be reduced by 0.7%; Every 100 kg reduction in the curb weight of the vehicle will reduce the fuel consumption per 100 kilometers by 0.3 to 0.6 liters.
The development idea of lightweight technology is mainly divided into three stages to realize vehicle weight reduction year by year.
The first stage is from 2016 to 2020, and the weight of the whole vehicle will be reduced by 10% compared with 2015. Focus on the development of ultra-high strength steel and advanced high strength steel technology, including material performance development, lightweight design method, forming technology, welding process and test evaluation method, etc., to achieve the application ratio of high strength steel in automobiles to more than 50%, carry out research on aluminum alloy sheet stamping technology and practice in the body, and study the connection technology of different materials.
The second stage is from 2021 to 2025, and the weight of the whole vehicle will be reduced by 20% compared with 2015. With the third generation of automobile steel and aluminum alloy technology as the main line, realize the wide range of application of steel and aluminum and other materials mixed body and all-aluminum body, realize the mass production and industrial application of aluminum alloy panels and aluminum alloy parts, and increase the development of production and manufacturing technology of magnesium alloy and carbon fiber composite parts, and increase the application proportion of magnesium alloy and carbon fiber parts, with the amount of aluminum used for a single vehicle reaching 350 kg.
The third stage is from 2026 to 2030, realizing 35% weight reduction of the whole vehicle compared with 2015. Focus on the development of magnesium alloy and carbon fiber composite technology, solve the recycling problem of magnesium alloy and composite materials, realize the wide application of carbon fiber composite hybrid body and carbon fiber components, and break through the complex parts forming technology and dissimilar parts connection technology. Magnesium alloy for single vehicle reaches 45kg, and carbon fiber accounts for 5% of vehicle weight.
According to statistics, in 2016, the consumption of magnesium alloy for a single car produced in China was only 7.3kg, which is a huge gap from the target of 45kg for a single car in 2030. Magnesium alloy has a broad market and unlimited potential for lightweight application in the future.
Low density
The density of die-casting magnesium alloy is only 2/3 of that of aluminum alloy and 1/4 of that of steel. The specific strength and specific stiffness of die-casting magnesium alloy are better than that of steel and aluminum alloy and far higher than engineering plastics. Therefore, die-casting magnesium alloy is an excellent lightweight structural material that can compete with the above materials in many application fields.
Good vibration absorption
It is conducive to vibration reduction and noise reduction. For example, under the stress level of 35MPa, the attenuation coefficient of magnesium alloy AZ91D is 25%, and that of aluminum alloy A380 is only 1%. At 100MP stress level, magnesium alloy AZ91D, AM60 and AS41 are 53%, 72% and 70% respectively, while aluminum alloy A380 is only 4%.
High dimensional stability
The dimensional instability of magnesium alloy die castings due to changes in ambient temperature and time is reduced.
High thermal conductivity
The thermal conductivity of magnesium alloy (60-70W/m-1 K-1) is second only to aluminum alloy (about 100-70W m-1 K-1), so the thermal diffusivity is good.
Non-magnetic, can be used for electromagnetic shielding.
Good wear resistance
Magnesium alloy also has a good damping coefficient, and its damping capacity is greater than that of aluminum alloy and cast iron. It can reduce noise when used in the shell, reduce vibration when used in the seat and wheel hub, and improve the safety and comfort of the car. Magnesium alloy has light weight, strong shock-absorbing performance, good casting performance, high automatic production capacity and mold life, and stable size. As the lightest engineering material, magnesium alloy is not only the most suitable material for casting automobile parts, but also the most effective lightweight material for automobiles.
With the development of automobile lightweight, the demand for magnesium aluminum and other light alloy castings has increased year by year. Since 1990, magnesium for automobile has been developing rapidly at an average annual growth rate of 20%, and magnesium alloys have become an important field in the development of automobile material technology. Die casting magnesium alloy material, with its recyclability and progressiveness chip free process, is particularly suitable for the requirements of circular economy, energy saving, low-carbon and clean production, and plays a leading role in the process of lightweight development of automobiles. Major auto parts manufacturers actively seize the development opportunity and have invested in the production and research of magnesium alloy auto die castings.
The global consumption of magnesium for single vehicle is low, and the demand for magnesium alloy for automobile has a strong expansion potential. For a long time, lightweight materials such as high-strength steel, aluminum alloy and engineering plastics have been widely used in all aspects of automobile and automobile parts manufacturing, while magnesium alloy has not been vigorously promoted and used for various reasons. At present, magnesium alloy is mainly used in instrument panel bracket, steering bracket, engine hood, steering wheel, seat bracket, interior door panel, transmission housing, etc.
Vehicle interior structure
Although magnesium alloys have poor corrosion resistance, corrosion prevention is not the main consideration for the internal structure of automobiles. Therefore, magnesium alloys have been widely used in the internal structure of automobiles, especially in the instrument panel and steering structure. It is reported that the first magnesium alloy instrument panel pillar was produced by General Motors in 1961, which saved 4kg of material than the same parts produced by zinc alloy die-casting. Over the past decade, great progress has been made in the use of magnesium alloy die-cast instrument panel struts.
The application of magnesium alloy in seats began in Germany in the 1990s, mainly because Benz used the seat structure with three-point seat belt produced by magnesium die-casting in SL Roadster. Similar to the application of magnesium alloy in instrument panel, seats designed and manufactured with magnesium alloy have also experienced a significant improvement in recent years. Now the seat structure made of magnesium alloy can be as thin as 2mm, which greatly reduces the weight. Although other materials such as high-strength steel, aluminum and composite materials are also used, experts predict that magnesium alloy will become a major material for lightweight and cost-effective automotive seat components in the future.
Body
Magnesium alloy is limited in the application of vehicle body, but also has been applied by vehicle manufacturers. When General Motors introduced the C-5 Corvette in 1997, it used a whole piece of magnesium alloy die-cast roof frame. In addition, magnesium alloy was also applied to the retractable hardtop convertible roof and roof frame of the Cadillac XLR convertible. Ford F-150 trucks and SUVs also used coated magnesium casting as the radiator support. In Europe, Volkswagen and Benz have taken the lead in realizing the application of thin-walled magnesium alloy castings in body panels.
Chassis
At present, cast or forged magnesium alloy wheels have been used in many high-priced racing cars or high-performance sports cars. However, the relatively high cost and the potential corrosion of magnesium alloy wheels prevent their application in mass production vehicles.
In the future, the production of lightweight and low-cost magnesium alloy chassis components, such as wheel hub, engine suspension and control arm, will depend on the improvement of magnesium alloy casting technology. After transformation, various casting processes that have been developed on aluminum alloy wheel hub and chassis components can be successfully applied to magnesium alloy. In addition, the development of low-cost, corrosion-resistant coating and new magnesium alloys with anti-fatigue and high impact strength will also accelerate the application of magnesium alloys in chassis.
Powertrain
Most of the casting parts of the powertrain, such as engine block, cylinder head, transmission case, oil pan, etc., are made of aluminum alloy. At present, pickups and SUVs produced in North America have magnesium alloy transmissions, and magnesium alloy manual transmissions produced by Volkswagen and Audi are also produced in large quantities in Europe and China. At present, effective progress has been made in dynamometer tests on magnesium strengthened engine prototypes, which means that more magnesium alloys will be used in power systems in the future.