Automotive lightweight and intelligence have become new trends in the development of global automotive technology. With the global energy saving and emission reduction pressure and development trend, countries have formulated strict passenger car fuel consumption standards and regulations and put forward more stringent requirements for passenger car fuel consumption and corresponding CO2 emissions. The light weight of automobiles is the development trend of the world automobile.
Lightweighting is to “slim down” the car, ensure stable and improved performance based on the energy-saving design of components, and continuously optimize the model. Experiments have proved that if the weight of a car is reduced by 10%, the fuel efficiency can be increased by 6%~8%; if the weight of a car is reduced by 1%, the fuel consumption can be reduced by 0.7%; for every 100 kg reduction in the overall weight of a car, the fuel consumption of 100 km can be reduced by 0.3~0.6 liters.
The lightweight trend of automobiles
The first phase is 2016 ~ 2020, to achieve a 10% weight reduction of the whole vehicle compared with 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, testing and evaluation methods, etc., to achieve the proportion of high strength steel in automotive applications to more than 50%, to carry out research on aluminum alloy plate stamping production technology and practice in the body, and to study the connection technology of different materials
The second phase is from 2021 to 2025, to achieve a 20% weight reduction of the whole vehicle compared with 2015. With the third generation of automotive steel and aluminum alloy technology as the main line, realize the mixed body of steel and aluminum and other materials, the large-scale application of all-aluminum body, the mass production and industrial application of aluminum alloy coverings and aluminum alloy parts, while increasing the development of magnesium alloy and carbon fiber composite parts production and manufacturing technology, increasing the application ratio of magnesium alloy and carbon fiber parts. The amount of aluminum used in a single vehicle reaches 50kg. The third stage is 2026 ~ 2030, to achieve a 35% weight reduction of the vehicle compared to 2015. Focus on the development of magnesium alloy and carbon fiber composite technology, to solve the problem of recycling magnesium alloy and composite materials, to achieve a wide range of applications of carbon fiber composite hybrid body and carbon fiber parts, breakthroughs in complex parts molding technology, and heterogeneous parts connection technology. The magnesium alloy used in a single vehicle reaches 45kg, and the use of carbon fiber accounts for 5% of the vehicle weight.
According to statistics, in 2016, China’s production of single car magnesium alloy used only 7.3kg, and in 2030 single car magnesium alloy use target of 45kg there is a huge gap in magnesium alloy in the future of automotive lightweight application market is vast unlimited potential.
Magnesium alloy performance and advantages
The density of die-cast magnesium alloy is only 2/3 of aluminum alloy, 1/4 of steel, specific strength and specific stiffness are better than steel and aluminum alloy, much higher than engineering plastics, so die-cast magnesium alloy is excellent in many applications and can compete with the above materials of lightweight structural materials.
Good vibration absorption
Good for vibration and noise reduction; for example, in 35MPa stress level, the attenuation coefficient of magnesium alloy AZ91D is 25%, and aluminum alloy A380 is only 1%. Under 100MP stress level, the attenuation coefficient of magnesium alloy AZ91D, AM60, and AS41 are 53%, 72%, and 70%, respectively, while that of aluminum alloy A380 is only 4%.
High dimensional stability
The dimensional instability of magnesium alloy dies casting is caused by ambient temperature and time changes.
High thermal conductivity
Magnesium alloy thermal conductivity (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 abrasion resistance
Magnesium alloy also has a good damping coefficient, vibration damping is greater than aluminum alloy, and cast iron, used in the shell, can reduce noise, is used for seats, wheels can reduce vibration, and improve the safety and comfort of the car. Magnesium alloy is lightweight, has strong vibration absorption, has good casting performance, high automatic production capacity and mold life, and regular size; as the lightest engineering material, magnesium alloy is not only the most suitable material for casting auto parts but also the most effective material for auto lightweighting.
Magnesium alloy automotive die casting industry status
Automotive lightweight development, so the demand for magnesium, aluminum, and other light alloy castings has increased yearly. Since 1990, automotive magnesium has been growing rapidly with an average annual growth rate of 20%; magnesium alloy has become an important area of automotive material technology development. Die-casting magnesium alloy material with its recyclable and less chip-free process of advanced, especially suitable for the circular economy and energy-saving low-carbon and clean production requirements, in the development of automotive to a lightweight dominant position. The major auto parts manufacturers actively seize the opportunity to develop and have invested in producing magnesium alloy automotive die casting research and development. At present, the domestic and foreign automotive enterprises are committed to research, accounting for a large proportion of vehicle weight body ( about 30% ), engine ( about 18% ), transmission system ( about 15% ), walking system ( about 16% ), wheels ( about 5% ) and other steel or aluminum parts of magnesium alloy.
The global automobile use of magnesium per vehicle is low, and the demand for automotive magnesium alloy expansion potential is strong. Has been high-strength steel, aluminum alloy, engineering plastics, and other lightweight materials are widely used in all aspects of automotive and auto parts manufacturing, and magnesium alloy, for various reasons, has not been vigorously promoted and used; magnesium alloy is currently mainly used in the dashboard bracket, steering bracket, hood cover, steering wheel, seat bracket, interior door panels, transmission housing, and other aspects. North America uses 3.8kg of magnesium alloy per car; Japan uses 9.3kg, Europe PASSAT and Audi A4 on each car use magnesium alloy to 14kg, while domestic cars use only 1.5kg on average.
The specific application of magnesium alloy in the light weight of the car
car internal structure
Although the magnesium alloy corrosion resistance is poor, for the car interior structure, anti-corrosion is not the main consideration, so magnesium alloy in the car interior structure has been more widely used, especially in the instrument panel and steering structure. It is known that the first magnesium alloy dashboard pillar in 1961 was die-casting production, then using zinc alloy die-casting production of the same parts to save 4kg of material. In the past decade, magnesium alloy die-casting for the dashboard pillar has made great progress.
Magnesium alloy in the seat application began in Germany in the 1990s, mainly Mercedes-Benz in the SL Roadster using magnesium die-cast seat structure with a three-point seat belt. Similar to the application of magnesium alloy in the dashboard, in recent years, the use of magnesium alloy design and the manufacturing of seats also experienced a significant improvement. Now the magnesium alloy seat structure can reach the thinnest 2mm, greatly reducing the weight. Although other materials such as high-strength steel, aluminum, and combined materials are also used, experts predict that magnesium alloy will become the future of automotive seat parts, a lightweight and cost-effective major material.
Magnesium alloy in the body application is limited, but it also got the application of the whole car factory. General Motors in 1997 when the introduction of the C-5 Corvette, the use of a whole piece of magnesium alloy die-casting roof frame, in addition, magnesium alloy is also used in the Cadillac XLR convertible retractable hardtop convertible roof, and top frame, Ford F-150 truck, and SUV also used coated magnesium castings as radiator support. In Europe, Volkswagen and Mercedes-Benz have pioneered thin-walled magnesium alloy castings in body panels.
At present, a project to improve the application of magnesium alloy in the car body structure is the “magnesium front-end research and development” project funded by the governments of Canada, China, and the United States and USAMP (the United States Automotive Materials Alliance, a consortium of Chrysler, Ford and General Motors). The project brings together a unique international team from the United States, China, and Canada. It has developed some key technologies and knowledge bases for automotive magnesium applications. The technologies and knowledge base developed in this project will not only facilitate the application of automotive magnesium as a front-end structure for testing but also promote the development of raw magnesium production, component manufacturing, basic research, and advanced computational tools.
Cast or forged magnesium alloy wheels have been used in much high-priced racing or high-performance sports cars. However, magnesium alloy wheels’ relatively high cost and potential corrosion prevent their application in mass production vehicles. In the future, the production of lightweight, low-cost magnesium alloy chassis components such as wheels, engine mounts, and control arms will rely on a significant improvement in the magnesium alloy casting process and various casting processes already developed for aluminum alloy wheels and chassis components can be successfully applied to magnesium alloy after modification. In addition, a low-cost, corrosion-resistant layer and new with fatigue resistance and high impact strength of magnesium alloy development will also accelerate the application of magnesium alloy in the chassis.
Most powertrain casting parts, such as engine block, cylinder head, transmission, oil pan, etc., are aluminum alloys. Currently, the North American pickup trucks and SUVs have magnesium alloy transmission; Volkswagen and Audi’s magnesium alloy manual transmission is also in mass production in Europe and China.
Effective progress has been made through dynamometer tests on magnesium-reinforced engine prototypes.
This means that more magnesium alloys will be used in the powertrain. The American Automotive Materials Consortium’s Magnesium Powertrain Casting Project (MPCC) aims to enable magnesium alloys to completely replace the major aluminum alloy components in the V block engine. The project achieved a 25% weight reduction in the cylinder block (29% of all aluminum castings were replaced with magnesium).
The main challenges in the application of magnesium alloys
Poor corrosion resistance, high cost, and scrap rate are “roadblocks” to the popularity of magnesium alloys. Magnesium alloy manufacturing auto parts do have a high cost of die-casting high scrap rate; there are hidden safety production problems. China automobile industry association consultant Du Fangci said magnesium is a very active element; corrosion resistance is very poor, and China’s technical ability in magnesium alloy parts corrosion resistance is poor. In addition to magnesium being prone to combustion and explosion, there are safety production problems. The production site needs strict management to ensure safe production. In recent years, emerged the magnesium alloy safety production management performance of outstanding manufacturers, such as V1Diecast and other manufacturers. If there is policy encouragement and strict weight requirements for the whole vehicle, the promotion and application of magnesium alloy will be developed for a long time.
With the accelerated urbanization, energy becomes more and more shortage; environmental pollution is becoming more and more serious, and energy saving and emission reduction have become an important events concerning the country’s livelihood. Both classic cars and emerging new energy vehicles pay much attention to the lightweight design of the body to achieve the purpose of energy saving and environmental protection.
Magnesium alloy for the automobile is booming; while the magnesium alloy die-casting process is becoming more and more mature, the application range is expanding, and large magnesium alloy die-casting auto parts will promote the process of automotive lightweight.
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