From all-aluminum body to carbon fiber, reveal the application of lightweight materials in automobiles

Reducing the quality of the car itself is one of the most effective measures to reduce fuel consumption. Data shows that for every 10% reduction in vehicle weight, energy consumption under NEDC conditions can be reduced by 6% to 8%, and emissions can be reduced by 5% to 6%. And every 1L reduction in fuel consumption reduces CO2 emissions by 2.45kg. There are three main means to achieve lightweight: lightweight structure design and optimization, application of advanced lightweight materials, and application of advanced lightweight manufacturing technology. The use of new materials is the most direct and effective way to reduce the weight of automobiles. The lightweight of the car is to reduce the quality of the car as much as possible under the premise of ensuring the strength and safety of the car, thereby improving the power of the car, reducing fuel consumption, and reducing exhaust pollution. Experiments have proved that if the weight of the vehicle is reduced by 10%, the fuel efficiency can be increased by 6%-8%; the weight of the vehicle can be reduced by 1%, and the fuel consumption can be reduced by 0.7%; for every 100 kg reduction in the vehicle's curb weight, the fuel consumption per 100 kilometers can be reduced by 0.3-0.6 Rise.

Common lightweight materials are divided into two camps: metal and non-metal. Metallic materials mainly include high-strength steel, aluminum alloy, magnesium alloy, etc.; non-metallic materials include engineering plastics and composite materials. It has been the goal of major manufacturers to improve the weight of automobiles, so aluminum and carbon fiber materials are used more in the overall body.

1. Aluminum alloy

Aluminum alloy is currently the most widely used lightweight material in automotive materials, and various related technologies are relatively mature. Aluminum has good mechanical properties. Its density is about 1/3 of that of steel. It is easy to process, has good thermal conductivity and corrosion resistance. It has high strength and good energy absorption. According to the report of the American Aluminum Institute, every 0.45kg of aluminum used in a car can reduce the weight of the car by 1kg. In theory, aluminum cars can reduce the weight of steel cars by about 40%. At present, many models such as Audi A8, Jaguar XFL, and Tesla have adopted all-aluminum bodies. In recent years, the cost of processing aluminum alloys used in body materials has been reduced. In the past, thick aluminum alloy plates were stamped into thin plates and then processed. At present, the general hot stamping forming technology similar to steel plate stamping is introduced. The requirements for the process are very strict. Due to the effect of friction, the material flows unevenly throughout the section, which is prone to rapid thinning and cracking in the stress concentration area. Coordinating the relationship between blank holder force and pressing force, coupled with good lubrication, is the key to achieving aluminum alloy hot stamping to reduce material costs again. Of course, aluminum alloy is ideal as a lightweight material for large-scale mass production, but it also has its own shortcomings, such as complex processes and high subsequent maintenance costs. In general, aluminum alloy materials may first replace traditional steel as the main material for lightweight cars. However, due to a series of technical problems such as welding that need to be overcome, ordinary car companies cannot maturely apply such materials to car production .

2. Magnesium alloy

The density of magnesium is about 2/3 of that of aluminum, which is the lightest among metals in practical applications. The density of magnesium is about 2/3 of that of aluminum, which is the lightest among metals in practical applications. Magnesium alloy has strong vibration absorption ability, good cutting performance, and good metal mold casting performance, which is very suitable for manufacturing automobile parts. The earliest examples of magnesium castings used in automobiles are wheel rims. Examples of the application of magnesium alloys in automobiles include clutch housings, clutch pedals, brake pedal fixing brackets, instrument panel frames, seats, steering column parts, steering wheel cores, gearbox housings, engine mounts, and cylinder heads And cylinder head cover, etc. Due to the application of magnesium body panels, better body handling, better performance and more economical fuel costs can be obtained. A lighter body will improve the performance of the vehicle on the overall level. Although the application of magnesium alloys in automobiles has started very early, the current magnesium alloys have not been widely promoted. In terms of manufacturing and processing, compared with aluminum sheet parts, the cost of magnesium alloy body panels is 3 To 4 times. In addition, due to the particularity of the magnesium alloy sheet, there may be some differences in the repair process from the traditional steel sheet.

3. High-strength steel

The application of high-strength steel has become an important development direction of automotive lightweight technology. However, due to the increase in the strength of high-strength steel sheets, the traditional cold stamping process is prone to cracking during the forming process, which cannot meet the processing requirements of high-strength steel sheets. In the case that the forming conditions cannot be met, the hot stamping forming technology of ultra-high-strength steel plates is gradually being studied internationally. This technology is a new process that integrates forming, heat transfer and structural phase transformation. It mainly uses the characteristics of increased plasticity of sheet metal and decreased yield strength under high-temperature austenite state, and the process of forming through molds. However, thermoforming requires in-depth research on process conditions, metal phase transition, and CAE analysis technology. Currently, this technology is monopolized by foreign manufacturers and the domestic development is slow. When the material is stamped and formed, it becomes hard, and different steels have different degrees of hardening. Generally, high-strength low-alloy steel only has a slight increase of 20MPa, which is less than 10%. Note: The yield strength of duplex steel has increased by 140MPa, which is an increase of more than 40%! During the forming process, the metal becomes completely different, unlike before the stamping process. The yield strength of these steel materials increases a lot after being stressed. The higher yield stress of the material plus work hardening equals a great increase in flow stress. Therefore, cracking, springback, wrinkling, workpiece size, mold wear, micro welding wear, etc. have become the focus of problems in the high-strength steel forming process. Based on the characteristics and characteristics of high-strength steel, if the metal flow and friction cannot be changed, the cracking and uneven texture of high-strength steel (HSS) may cause the scrap rate of parts to rise. The high kilopound force per square inch (KSI) (a unit of measurement of bending force) that this material has, enhanced springback, work hardening tendency, and operation at elevated molding temperatures are all factors for the mold challenge. However, among the lightweight materials for automobiles, high-strength steel plates are inexpensive and have superior economic efficiency. The use of high-strength steel plates can reduce the plate thickness under equal-strength design conditions, but the thickness of the selected steel plates for body parts is mostly based on the element stiffness. Therefore, the actual plate thickness reduction rate may not reach the increase rate of the steel plate strength, and it is impossible to greatly Reduce vehicle weight. The main purposes of high-strength steel plates in automobiles are to increase the deformation resistance of components, improve energy absorption and expand the elastic strain zone. Due to the economy and relative ease of using high-strength steel, countries are accelerating the use of high-strength steel and ultra-high-strength steel in automobile body, chassis, suspension, steering and other parts. The Automobile Branch of the World Steel Association put forward the idea of ​​a new generation of steel cars: more high-strength steel plates are used, and the quality of the car body will be 35% lower than before.

4. Plastic and non-metal composite materials

The application of plastics simultaneously meets the needs of reducing the weight and cost of the entire vehicle, so it is the most non-metallic material used in automobiles, and related technologies are relatively mature. Plastic has many advantages such as small specific gravity, corrosion resistance, sound insulation, high specific strength, impact energy absorption, low cost, easy processing, and good decorative effect. It can not only reduce weight and cost, but also improve the safety and comfort of the entire vehicle. And the appearance is favorable. The average amount of plastic used in automobiles in the world reached 115 kg as early as 2001, accounting for about 8% to 12% of the total weight of automobiles, and this proportion is constantly increasing. Plastics are widely used in the interior and exterior of automobiles, such as dashboards, side panels, spoilers, fenders, radiator grilles, fenders, etc. In the future, the key development direction is high-performance plastics for structural parts, functional parts and exterior parts.

Non-metallic composite materials mainly refer to carbon fiber reinforced resin matrix composite materials and organic fiber composite materials. It has the advantages of low density, corrosion resistance, fatigue resistance, high specific strength and specific rigidity, easy shaping, energy saving and earthquake resistance. It is currently mainly used in car bodies, lamp covers, bumpers, etc., such as carbon fiber bodies and carbon fiber bumpers.

Carbon fiber is a new type of high-strength, high-modulus fiber with a carbon content of more than 95%. Carbon fiber is a new material with excellent mechanical properties. Its specific gravity is less than 1/4 of that of steel. The tensile strength is generally above 3500Mpa, which is 7-9 times that of steel. The tensile modulus of elasticity is also high at 23000-43000Mpa. Yu Gang. However, carbon fiber materials only show high strength along the fiber axis, but have poor impact resistance and are easily damaged. Therefore, when manufacturing structural components, they often take advantage of their tensile strength and lightness to avoid side impacts. part. At present, there are not many carbon fiber materials used in civil vehicles, and most of them are concentrated in some sports cars. But this is only a toy for the rich after all. Cars with carbon fiber monocoque structure are often very expensive. The carbon fiber material itself is not expensive, but the value of the carbon fiber is to be processed into a finished product suitable for vehicle driving and collision. Although the good shape of carbon fiber reinforced synthetic materials has neither reached the perfect diamond shape pretreated with chemical agents, nor has it reached perfect robustness, the strength of the material obtained by this method is still comparable to that of steel. The key is that the weight is only that of steel. Half. Carbon fiber monocoque is widely used in performance cars as a body structure with light weight, high strength and high safety. Although it is still not popular in civilian vehicles, after solving the problem of raw materials, I believe that the time when its technology is decentralized is not far away.

Above we have listed the applications of some materials in lightweight. For parts using lightweight materials, further layout analysis and motion interference analysis can also be performed, so that lightweight materials can meet the requirements of body design. It is believed that the continuous advancement of technology and manufacturing process will give more room for extension in lightweight.