Lightweight and intelligent automobiles have become a new trend in the technological development of the global automobile industry. Over the years, with the pressure and development trend of global energy conservation and emission reduction, countries have formulated strict regulations on fuel consumption standards for passenger vehicles, and put forward more stringent requirements for passenger vehicle fuel consumption and corresponding CO2 emissions. It is the development trend of the world automobile.
Especially in China, by 2020, the fuel consumption of automobiles will drop significantly, and the pressure of fuel emissions will be greater. Reducing the weight of the whole vehicle is an effective way to reduce the weight of automobiles. On the basis of ensuring stable performance improvement, vehicle lightweighting is the energy-saving design of various components and continuous optimization of vehicle models. Experiments have shown 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%, the fuel consumption can be reduced by 0.7%; the vehicle curb weight can be reduced by 100 kg, the fuel consumption per 100 kilometers can be reduced by 0.3-0.6 Lift.
Lightweight Trends in Automobiles
Senior Professor Ouyang Ming from Tsinghua University, on behalf of the Energy-Saving and New Energy Vehicle Development Strategy Advisory Committee, released the content of the energy-saving and new-energy vehicle technology roadmap. The light-weight technology development ideas proposed by the roadmap are mainly divided into three stages Lose weight year by year.
The first stage is from 2016 to 2020, and the weight of the whole vehicle is reduced by 10% compared with 2015. Focus on the development of ultra-high-strength steel and advanced high-strength steel technologies, including material performance development, lightweight design methods, forming technologies, welding processes, and testing and evaluation methods, etc. connection technology.
The second stage is from 2021 to 2025, and the weight of the whole vehicle will be reduced by 20% compared with 2015. Taking the third-generation automotive steel and aluminum alloy technology as the main line, realize the large-scale application of the mixed body of steel and aluminum and other materials, the full-aluminum body, and realize the mass production and industrial application of aluminum alloy covering parts and aluminum alloy parts. Increase the development of manufacturing technology for magnesium alloy and carbon fiber composite parts, increase the application ratio of magnesium alloy and carbon fiber parts, and the amount of aluminum used in bicycles reaches 350kg.
The third stage is from 2026 to 2030, and the weight of the whole vehicle will be reduced by 35% compared with 2015. Focus on the development of magnesium alloy and carbon fiber composite material technology, solve the problem of recycling and reuse of magnesium alloy and composite materials, realize the wide-scale application of carbon fiber composite material hybrid body and carbon fiber parts, and make breakthroughs in complex parts forming technology and dissimilar parts connection technology. The magnesium alloy for bicycles reaches 45kg, and the use of carbon fiber accounts for 5% of the weight of the vehicle.
According to statistics, in 2016, the consumption of magnesium alloys for bicycles produced in China was only 7.3kg, which is still a huge gap from the target of 45kg of magnesium alloys for bicycles in 2030. Magnesium alloys have a broad market and unlimited potential for lightweight applications in automobiles in the future.
Magnesium alloy properties and advantages
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. Its specific strength and specific stiffness are higher than those of steel and aluminum alloy, and much higher than that of engineering plastics. Therefore, die-casting magnesium alloy is an excellent A lightweight structural material that competes with the above materials in many applications.
Good vibration absorption: It is beneficial 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 the 100MP stress level, the magnesium alloys AZ91D, AM60, and AS41 are 53%, 72%, and 70%, respectively, and the aluminum alloy A380 is only 4%.
High dimensional stability: reduce the dimensional instability of magnesium alloy die castings caused by changes in ambient temperature and time.
High thermal conductivity: The thermal conductivity of magnesium alloys (60-70W/m-1 K-1) is second only to aluminum alloys (about 100-70W m-1 K-1), so the thermal diffusivity is good.
Non-magnetic, can be used for electromagnetic shielding.
Good wearability: Magnesium alloy also has a good damping coefficient, and the vibration reduction is greater than that of aluminum alloy and cast iron. It can reduce noise when used in the shell, and can reduce vibration when used in seats and wheel hubs, which improves the safety and comfort of the car. Magnesium alloys are light in weight, strong in shock absorption, good in casting performance, high in automated production capacity and mold life, and dimensionally stable. As light engineering materials, magnesium alloys are not only suitable for casting automotive parts, but also effective automotive lightweight materials.
Status Quo of Magnesium Alloy Automotive Die Casting Industry
With the development of lightweight automobiles, the demand for light alloy castings such as magnesium and aluminum has increased year by year. Since 1990, magnesium for automobiles has been developing rapidly with 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 materials are especially suitable for circular economy, energy-saving, low-carbon and clean production requirements due to their recyclability and the advanced nature of less chip-free processes, and take a dominant position in the process of lightweight development of automobiles. Major auto parts manufacturers actively seize the opportunity of development, and have invested in the production and development of magnesium alloy automotive die castings. According to the data of “Analysis of China’s Magnesium Alloy Automotive Die Casting Parts Industry”, in 2015, the demand for China’s magnesium alloy automotive die casting parts industry reached 149,000 tons, a year-on-year increase of 23.12%. At present, domestic and foreign auto companies are working on the research on the body (about 30%), engine (about 18%), transmission system (about 15%), walking system (about 16%), and wheels (about 16%), which account for a large proportion of the vehicle weight. 5%) for magnesium alloying of steel or aluminum parts. Considering the amount of magnesium alloy used in bicycles produced in my country, the market capacity of my country’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 amount of magnesium used in automobiles is relatively low, and the demand for magnesium alloys for automobiles has strong expansion potential. For a long time, lightweight materials such as high-strength steel, aluminum alloys, and engineering plastics have been widely used in all aspects of automobile and auto parts manufacturing, while magnesium alloys have not been vigorously promoted and used due to various reasons. Magnesium alloys are currently mainly used in dashboards. Brackets, steering brackets, engine hoods, steering wheels, seat brackets, interior door panels, transmission housings, etc. At present, each car in North America uses 3.8kg of magnesium alloy, Japan is 9.3kg, and each car in Europe PASSAT and Audi A4 uses 14kg of magnesium alloy, while the average consumption per domestic car is only 1.5kg.
Application of Magnesium Alloy in Automobile Lightweight
car interior
Although magnesium alloys have poor corrosion resistance, for the interior structure of automobiles, anticorrosion is not a major consideration. Therefore, magnesium alloys have been widely used in the interior structure of automobiles, especially in dashboards and steering structures. It is reported that the first magnesium alloy instrument panel pillar was die-casted by General Motors in 1961, saving 4kg of material compared with the same parts produced by zinc alloy die-casting. Over the past decade or so, great progress has been made in the use of magnesium alloy die-cast instrument panel struts.
The application of magnesium alloys in seats began in Germany in the 1990s, mainly because Mercedes-Benz used magnesium die-casting in the SL Roadster to produce seat structures with three-point seat belts. Similar to the application of magnesium alloys on instrument panels, in recent years, seats designed and manufactured with magnesium alloys have also undergone a process of significant improvement. Now the seat structure using magnesium alloy can be as thin as 2mm, which greatly reduces the weight. While other materials such as high-strength steel, aluminum, composites, etc. are also used, experts predict that magnesium alloys will become a major material for lightweight and cost-effective automotive seat components in the future.
body
Magnesium alloys are limited in body applications, but are also used by OEMs. When General Motors introduced the C-5 Corvette in 1997, it used a one-piece magnesium alloy die-cast roof frame. In addition, magnesium alloy is also used in the retractable hardtop convertible roof and top frame of the Cadillac XLR convertible, Ford F -150 trucks and SUVs also use coated magnesium castings as radiator brackets. In Europe, Volkswagen and Mercedes-Benz have taken the lead in realizing the application of thin-wall magnesium alloy castings in body panels.
chassis
Currently, cast or forged magnesium alloy wheels are used in many high-priced racing cars or high-performance sports cars. However, the relatively high cost and potential corrosion problems of magnesium alloy wheels prevent their application in mass-produced vehicles.
In the future, the production of lightweight and low-cost magnesium alloy chassis components, such as wheel hubs, engine suspensions and control arms, will rely on the vigorous improvement of magnesium alloy casting processes. Various types of aluminum alloy wheels and chassis components have been developed. The casting process can be successfully adapted to magnesium alloys after modification. In addition, low-cost, corrosion-resistant coatings and the development of new magnesium alloys with fatigue resistance 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. 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.
Effective progress has been made by dynamometer testing of magnesium-strengthened engine prototypes, which means that more magnesium alloys will be used in powertrains in the future.
The main challenges in the promotion and application of magnesium alloys. Poor corrosion resistance, high cost and high scrap rate are obstacles to the popularization of magnesium alloys.
Magnesium alloy manufacturing auto parts does have problems such as high die-casting cost, high scrap rate, and hidden dangers in production safety. Du Fangci, a consultant of the China Association of Automobile Manufacturers, said that magnesium is a very active element with poor corrosion resistance, and my country’s technical capabilities in terms of corrosion resistance of magnesium alloy parts are poor. In addition, magnesium is prone to combustion during the processing, and there is a problem of safety in production. The production site needs to be strictly managed to ensure safe production.
With the acceleration of urbanization, energy is becoming more and more 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 people’s livelihood. Both traditional vehicles and emerging new energy vehicles pay attention to the lightweight design of the body to achieve the purpose of energy saving and environmental protection.
Magnesium alloys for automobiles are booming. At the same time, the magnesium alloy die-casting process is becoming more and more mature, and the application scope is expanding. Large-scale magnesium alloy die-casting auto parts will promote the process of automobile lightweight.