Lightweight trends in cars
Professor Ouyang Ming of Tsinghua University represented the Energy Saving and New Energy Vehicle Development Strategic Advisory Committee and published the contents of the energy-saving and new-energy vehicle technology roadmap. The roadmap proposes the idea of lightweight technology development, which is mainly implemented in three stages. Decrease year by year.
The first phase is from 2016 to 2020, achieving a 10% weight reduction for the vehicle compared to 2015. Focus on the development of ultra-high strength steel and advanced high-strength steel technology, including material performance development, lightweight design methods, molding technology, welding technology and test evaluation methods, to achieve high-strength steel in automotive applications to achieve more than 50%, carry out aluminum alloy The board stamping production technology research and practice in the vehicle body, study the connection technology of different materials.
The second stage is from 2021 to 2025, achieving a 20% weight reduction for the vehicle compared to 2015. With the third-generation automotive steel and aluminum alloy technology as the main line, it will realize the application of a wide range of materials such as steel and aluminum alloys and a wide range of aluminum bodywork to achieve mass production and industrialization of aluminum alloy cover parts and aluminum alloy parts. We will increase the development of manufacturing technologies for magnesium alloy and carbon fiber composite parts and components, and increase the application ratio of magnesium alloy and carbon fiber components. The amount of aluminum used in bicycles will reach 350kg.
The third stage is from 2026 to 2030, achieving a vehicle weight reduction of 35% compared to 2015. Focus on the development of magnesium alloy and carbon fiber composite materials technology to solve the problem of recycling of magnesium alloys and composite materials, to achieve a wide range of applications of carbon fiber composite material hybrid car body and carbon fiber components, breaking through complex parts molding technology and dissimilar part connection technology. The single-use magnesium alloy reaches 45kg, and the carbon fiber consumption accounts for 5% of the vehicle weight.
According to statistics, in 2016, the amount of bicycle magnesium alloys produced in China was only 7.3kg. There is still a huge gap between the targeted magnesium alloy usage target of 45kg in 2030 and magnesium alloy will have a vast market for automotive lightweight applications in the future with unlimited potential.
Magnesium alloy properties and advantages
Low density
The density of die-casting magnesium alloy is only 2/3 of that of aluminum alloy, 1/4 of steel, the specific strength and specific rigidity are better than steel and aluminum alloy, and much higher than engineering plastic, so die-casting magnesium alloy is an excellent one in many Lightweight structural materials that can compete with the above materials in the application area.
Good vibration absorption
It is beneficial to damping 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 the stress level of 100 MP, the magnesium alloys AZ91D, AM60, and AS41 were 53%, 72%, and 70%, respectively, while the aluminum alloy A380 was only 4%.
High dimensional stability
Magnesium alloy die castings have reduced dimensional instability due to changes in ambient temperature and time.
High thermal conductivity
Magnesium alloy thermal conductivity (60 - 70W/m-1 K-1), second only to aluminum alloy (about 100 - 70W m-1 K-1), so good thermal diffusivity.
Non-magnetic, can be used for electromagnetic shielding.
Good wear resistance
Magnesium alloy also has a good damping coefficient, vibration damping is greater than aluminum alloy and cast iron, for the shell can reduce noise, for the seat, the hub can reduce vibration, improve the safety and comfort of the car. Magnesium alloy is light in weight, strong in shock absorption performance, good in casting performance, automatic production capacity, high die life and dimensional stability. As the lightest engineering material, magnesium alloy is not only the most suitable material for casting auto parts, but also the most effective light for automobiles. Quantify the material.
Magnesium alloy automotive die casting industry
With the development of lightweight vehicles, the demand for light alloy castings such as magnesium and aluminum has increased year by year. Since 1990, magnesium for automobiles is rapidly growing at an average annual growth rate of 20%. Magnesium alloys have become an important area for automotive material technology development. Die-casting magnesium alloy materials are especially suitable for circular economy, energy-saving, low-carbon and clean production requirements due to their recyclability and less cutting-edge technology. They are dominant in the development of lightweight vehicles. Major auto parts manufacturers actively seize the opportunity for development and have invested in the research and development of magnesium alloy automotive die castings. According to the "China Magnesium Alloy Automotive Die Casting Industry Analysis Report," data show that in 2015, China's magnesium alloy automotive die casting industry demand reached 149,000 tons, an increase of 23.12%. At present, auto companies at home and abroad are devoting themselves to researching the body (about 30%), engine (about 18%), transmission system (about 15%), walking system (about 16%), wheels (about 5%) Magnesium alloying of steel or aluminum parts.
Combined with the use of bicycle magnesium alloys produced in China, the market capacity of China's magnesium alloy automotive die casting industry will reach 229,000 tons in 2017, and the market capacity will reach 660,000 tons by 2022, with an average annual compound growth rate of 23.5%.
The global use of magnesium for motorcycles is low, and there is strong potential for expansion of demand for automotive magnesium alloys. Traditionally, lightweight materials such as high-strength steels, aluminum alloys, and engineering plastics have been widely used in various aspects of automobile and automobile parts manufacturing, while magnesium alloys have not been widely promoted and used for various reasons. Currently, magnesium alloys are mainly used in instrument clusters. Brackets, steering brackets, engine covers, steering wheels, seat supports, interior door panels, transmission housings, etc. At present, each car in North America uses 3.8kg of magnesium alloy, and 9.3kg in Japan. Each car on the European PASSAT and Audi A4 uses 14kg of magnesium alloy, while the average amount of domestic cars is only 1.5kg.
Application of Magnesium Alloy in Automobile Lightweight
Internal structure of the car
Although magnesium alloys have poor corrosion resistance, anticorrosion is not a major concern for automotive interior construction, so magnesium alloys have found wider application in automotive interior construction, especially in instrument clusters and steering structures. It is reported that the first magnesium alloy instrument panel pillar was produced by GM in die-casting in 1961, which saved 4 kg of material compared to the same component produced using zinc alloy die-casting. Over the past decade or so, the adoption of magnesium alloy die-casting instrument panel pillars has made great progress.
The application of magnesium alloys to seats began in Germany in the 1990s, mainly Mercedes-Benz's use of magnesium die-casting seat structures with three-point seat belts in the SL Roadster. Similar to the application of magnesium alloys on the instrument panel, in recent years, the seats designed and manufactured using magnesium alloys have also undergone a significant increase. The magnesium alloy seat structure can be as thin as 2mm, which greatly reduces the weight. Although other materials such as high-strength steel, aluminum, and composite materials have also been used, experts predict that magnesium alloys will become a major lightweight and cost-effective material for automotive seat components in the future.
Car body
Magnesium alloys are limited in body applications, but they are also being used by OEMs. When General Motors introduced the C-5 Corvette in 1997, it used a magnesium alloy die-cast roof frame. In addition, magnesium alloys were also used in the retractable hardtop convertible top and top frames of the Cadillac XLR Convertible. Ford F -150 trucks and SUVs also use coated magnesium castings as a heat sink. In Europe, Volkswagen and Mercedes have taken the lead in realizing the application of thin-walled magnesium alloy castings in body panels.
Chassis
Currently, cast or forged magnesium alloy wheels have been used in many high-priced racing or high-performance sports cars. However, the relatively high cost and potential corrosion problems of magnesium alloy wheels prevent their application in mass production vehicles.
In the future, the production of lightweight, low-cost magnesium alloy chassis components, such as hubs, engine suspensions, and control arms, will depend on the significant improvement of the magnesium alloy casting process, and various types of aluminum alloy hubs and chassis components have been developed. The casting process can be successfully applied to magnesium alloys after modification. In addition, the development of low-cost, corrosion-resistant layers and new magnesium alloys with fatigue resistance and high impact strength will also accelerate the application of magnesium alloys on the chassis.
Powertrain
Most of the castings of the powertrain, such as the engine block, cylinder head, transmission case, and oil pan, are made of aluminum alloy. Currently, pickups and SUVs produced in North America have magnesium alloy transmissions, and Volkswagen and Audi's magnesium alloy manual transmissions are also mass-produced in Europe and China.
Currently, effective tests have been made through dynamometer tests on magnesium-enhanced engine prototypes, which means that more magnesium alloys will be used in power systems in the future.
Main challenges of magnesium alloys in popularization and application
Poor corrosion resistance, high cost, and high scrap rate are the "roadblocks" of magnesium alloys.
Magnesium alloy manufacturing automobile parts do have problems such as high die casting cost, high reject rate, and hidden safety production problems. Du Fangci, an advisor of the China Association of Automobile Manufacturers, said that magnesium is a very active element and has poor corrosion resistance. China's magnesium alloy components have poorer technical capabilities in terms of corrosion resistance. In addition, during the processing of magnesium, it is prone to combustion and explosion, and there is a problem of safe production. The production site needs strict management to ensure safe production.
With the acceleration of urbanization, energy is becoming increasingly scarce and environmental pollution is becoming more and more serious. Energy conservation and emission reduction have become an important event related to the national economy and the people's livelihood. Both traditional cars and emerging new energy vehicles have paid great attention to the lightweight design of the vehicle body in order to achieve energy conservation and environmental protection.
Magnesium alloys for automotive use are booming. At the same time, magnesium alloy die-casting technology is maturing and the scope of application is expanding. Large-scale magnesium alloy die-casting automotive parts will promote the process of automotive lightweighting.
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