Latest developments in new materials for automobiles

I. Overview

With the continuous development of China's economy, people's lives are getting better and better, and the automobile industry has ushered in a period of rapid development for decades. However, while the number of cars has increased dramatically, it has also brought a series of problems to the environment and society. One of the major manufacturers of environmental degradation is automobile exhaust. Therefore, the automobile industry needs constant innovation while maintaining rapid development. The technological innovation of the automotive industry involves new materials technology, new information technology, new energy technologies, new equipment technologies, etc. Automobiles are rapidly developing along the direction of intelligence , light weight and low carbon.

In the field of new automotive materials, many of the world's top technology materials companies are vigorously strengthening the research and development of cutting-edge technologies and new materials related to automobiles. This paper summarizes and organizes the application of new materials in automobiles.

The materials used in automobiles reflect the level of technological development of humans in the field of materials. The main materials for vehicles, such as steel, alloy, plastic, aluminum, rubber, glass, etc., account for about 90% of the quality of automobiles. Other materials include paints, non-ferrous metals (nickel, copper, lead, zinc, tin, etc.). Equipped with fuel, automotive batteries (including new energy lithium batteries for automobiles), topcoats, fibers and other polymer composite materials .

In recent years, the research and development and application of new materials in the automotive industry has become a research hotspot. The research and development and application of new materials are mainly divided into the following three aspects, namely, automotive lightweight materials, automotive nanomaterials, and other functional materials.

Second, automotive lightweight materials

According to the "China Motor Vehicle Environmental Management Annual Report (2017)" promulgated by the Ministry of Environmental Protection of the People's Republic of China: China has become the world's largest motor vehicle production and sales country for eight consecutive years. The exhaust gas emitted by motor vehicles has become China's air pollution and smog. Important sources, especially in urban areas where motor vehicles are dense, motor vehicle exhaust pollution accounts for a larger proportion, and the urgency of pollution prevention and control is significant.

An important way to solve the problem of automobile exhaust pollution is the use of lightweight materials for automobiles. At present, the main measure for lightweighting of automobiles is to replace steel with low-density lightweight materials, such as carbon fiber , aluminum, magnesium, titanium, plastic, and other composite materials. The so-called lightweight car refers to reducing the overall quality of the car as much as possible while ensuring the strength and safety performance of the car, improving the power performance of the car, thereby reducing the consumption of automobile fuel and reducing the exhaust pollution of the car. The experimental results show that the vehicle quality is reduced by 10%, the fuel efficiency of the vehicle can be increased by 6% to 8%; for every 100kg of the vehicle's overall quality, the fuel consumption per 100 kilometers can be reduced by 0.3 to 0.6L. In the increasingly serious environmental protection situation and the need for energy-saving vehicles, the use of lightweight materials for automobiles has become a major direction in the development of the world's automobiles.

Carbon fiber

Carbon fiber composite materials are currently the largest material with the highest specific strength in engineering, and have been widely used in the automotive field. Carbon fiber is 50% lighter than ordinary steel, but its strength is more than 7 times that of steel. It was first used in high-tech fields such as aviation, aerospace, shipbuilding and military. It is recognized in the industry that CFRP (carbon fiber reinforced composite material) is currently the best way to solve the weight loss of fuel vehicles and new energy vehicles. The application of carbon fiber can make the vehicle lose weight by 30% to 60%, and is known as the “king of lightweight”. It is the leader of the car “slimming revolution” and plays a key role in car lightweighting.

Carbon fiber composites are currently being used in high-end cars, supercars, racing cars, modified cars, limited edition models and a small number of electric vehicles. At present, the application of carbon fiber composite materials in automotive parts is mainly distributed in automobile bodies, interior and exterior decoration, chassis systems, power systems and the like.

The application of carbon fiber composite materials can reduce the quality of automobile body by 40% to 60%, which is equivalent to 1/3 to 1/6 of the quality of steel structure. At present, most of the racing cars and some modified vehicles use carbon fiber composite body to reduce the quality. Increased safety due to reduced debris generation during composite collisions. The use of carbon fiber composites results in reduced hub quality, helps reduce wheel moment of inertia, and allows the vehicle to have faster start, stop, and steering speeds. The carbon fiber composite brake disc can reduce the speed from 300km/h to 50km/h within 50m. The carbon fiber brake disc can withstand temperatures up to 2 500 ° C and has stable performance. The drive shaft made of carbon fiber not only reduces the mass of 60% [1], but also has better fatigue resistance and durability. The use of carbon fiber interior and exterior materials, in addition to the lightweight of the car, also simplifies the part manufacturing process, reduces parts processing, assembly, maintenance costs, and reduces production costs. As a material for automotive air intake system, carbon fiber composite material can reduce the quality and achieve the light weight effect on the one hand; on the other hand, the carbon fiber material can be easily processed into various curved shapes, and the surface is smooth, which can effectively improve the intake efficiency. The good high temperature performance of carbon fiber makes it suitable for use in the engine field.

GM, Lamborghini and BMW have used a large number of models, of which BMW is a leader in the application of carbon fiber reinforced composites (CFRP).

2. Aluminum alloy material

Compared with automotive steel materials, aluminum alloy profiles have low density (2.72g/cm3), high specific strength, good impact resistance and high recyclability. They have been recognized as lightweight in automobiles by the automotive industry. One of the most promising metal materials in the process, so aluminum alloy has received extensive attention from industry and enterprises.

The main advantages of aluminum alloy are as follows: 1 The quality of the car using aluminum alloy is about 40% lower than that of the car using traditional steel material; 2 The car using aluminum alloy has a higher safety factor; 3 is equivalent to the same level. Compared with cars with traditional materials, the energy consumption is reduced by nearly 50%; 4 aluminum alloy has higher resource recovery rate and recycling rate, effectively reducing resource waste and environmental pollution; 5 using aluminum alloy cars The emission of exhaust gas is significantly reduced, and the new energy vehicles made of aluminum alloy have a longer cruising range. Therefore, accelerating the research on aluminum alloy materials can promote the rapid development of the automotive industry.

3. Magnesium alloy material

Magnesium alloys are another ideal material for lightweight vehicles. It has low density (1.74g/cm3), high specific strength, good toughness, good damping and high castability. By making magnesium alloy into automobile structural parts, it can effectively reduce the quality of automobiles and greatly improve the various types of automobiles. performance. In addition, the damping coefficient of magnesium alloy is much higher than that of steel and aluminum alloy, and it has excellent impact resistance. Magnesium alloy has good heat dissipation, high thermal conductivity and excellent anti-electromagnetic interference characteristics. Magnesium alloy has high automatic production capacity, long die life and stable size. As the lightest engineering material, magnesium alloy is not only the most suitable material for casting automotive parts, but also the most effective automotive lightweight material.

In addition, the reserves of magnesium metal on the earth are very rich, accounting for 2.7% (mass) of the earth's crust, and its mining life is 20 times and 4 times that of iron (Fe) and aluminum (Al), respectively. In addition, China's magnesium reserves are huge, and the proven reserves account for about 70% of the world's reserves. The reserves of dolomite (the basic raw material for the manufacture of magnesium alloys) have exceeded 7 billion tons, far higher than other countries. China has vigorously developed the magnesium alloy industry for China. Significant. The amount of magnesium used in bicycles in China is only 1.5kg, and the amount of bicycles in Europe has reached 14kg, which has huge room for growth.

The countries that use more magnesium alloys in automobiles are mainly developed countries such as the United States, Japan, and Europe. Germany has always been a world leader in the field of automotive magnesium alloys. As early as the 1930s, Volkswagen began using magnesium alloys as structural materials for automobiles. Audi and Mercedes are also using magnesium alloys as automotive materials.

4. High strength steel alloy

At present, most automakers are committed to reducing the quality of the car body. Lightweight is the most effective way to save energy and reduce emissions . However, the strength and safety of the car cannot be ignored. Advanced high-strength steel meets the above requirements of the automotive industry due to its unique advantages. The high-strength steel has high strength and can be reasonably thinned in the design and application of the body, and the weight-reducing effect can be achieved under the premise of ensuring safety.

The high-strength steel plate is a special steel material produced on the basis of ordinary carbon steel and added with a small amount of alloying elements (manganese, Al, etc.) in the manufacturing process. The manufacturing cost of this special steel plate is close to that of ordinary carbon steel, but the strengthening effect of alloying elements (manganese, Al, etc.) makes the tensile strength significantly higher than that of ordinary steel plates.

(1) can reduce the quality of auto parts

If the strength of the steel plate is increased by 40 to 50 MPa, the thickness of the outer body member can be reduced by about 20%.

(2) for exterior structural parts of the body

Under the condition of constant performance requirements, high-strength special steel can reduce the thickness of parts, and high-strength steel has bake hardening performance. When the surface is baked by paint, the surface hardness of parts is partially improved, which greatly increases Anti-sag and impact performance of automotive exterior parts.

(3) The work hardening rate is higher than ordinary steel plate

High-strength steel absorbs more impact energy and is ideal for use in front and rear rails of automotive undercarriages, as well as in automotive applications where high strength and durability are required. As the proportion of high-strength steel sheets in the vehicle body continues to increase, the key body frame members associated with the collision are all made of ultra-high-strength steel sheets, which strengthens the overall strength and crashworthiness of the vehicle body and improves the safety performance of the vehicle body.

5. Plastic

Because of its light density, plastic products can be used in large quantities in automobiles to help reduce the overall quality of the car. With the application of high-performance plastic materials in the automotive industry, the problem of lightweight vehicles has been solved to some extent. At present, the automotive industry has a huge demand for resins (nylon, polypropylene, polyurethane) and other engineering plastics, and the market capacity accounts for more than 29% of the total resin market demand. In the car, the components of the plastic material can be seen on the bumper, the clutch actuator system, the fuel tank of the car, the body cover and the chassis, the engine intake manifold and the like. Plastic parts have many unique advantages over traditional alloy materials.

Plastic products are inexpensive to produce and easy to process into a variety of complex shapes, especially at the junctions of various complex parts of the car, which significantly reduces the number of parts used in the automotive integration process.

The engineering plastic has a large elastic modulus, and can absorb a large amount of energy generated by the collision during the deformation process, which has a great buffering effect on the strong impact, which greatly protects the vehicle and the passenger; the plastic is resistant to acid and alkali and has strong corrosion resistance even if Local damage will not corrode, and if the paint surface is damaged or the pre-corrosion measures are not good, the material is prone to rust corrosion, which affects the beauty of the car body. Cars pose major safety hazards.

Third, automotive nanomaterials

Nanomaterials refer to materials with material sizes ranging from 1 to 100 nm. The technology for studying and processing materials at this size is called nanotechnology. When a substance is reduced to the nanometer level, its physical properties and chemical properties will undergo qualitative changes. These changes can be widely applied to various fields, and the automotive field is no exception.

The addition of a certain amount of nano-materials (usually nano-carbon materials) to rubber tire products for automobiles can greatly improve the wear resistance, temperature resistance and dielectric constant of the tires, which greatly increases the service life of the tires. In the production process of traditional rubber tire products, carbon black is usually used as a reinforcing filler and an anti-wear agent. As a powder material, an important development direction is to develop into the field of nano materials. The special tires produced by using nano-materials instead of carbon black are not only bright in color, but also have various performances. Experimental results show that the folding performance of the side rubber of the tire has been improved from 100,000 times to more than 500,000 times.

The outer surface of the car requires the protection and decoration of multiple layers of paint, which puts higher demands on the automotive coating. In addition to the variable appearance, the coating also has excellent durability and corrosion resistance, including resistance to atmospheric ultraviolet rays, anti-aging, acid rain and other chemical erosion and surface scratch resistance. Some nano materials have unique UV resistance, good electrostatic shielding effect, high strength and high toughness in the substrate, and strong antibacterial deodorization function. Therefore, nano materials are used in automotive coating applications. There is a broad market space. The development and utilization of nanomaterials in coatings has become a hot spot in the research and development of automotive coatings. Nanomaterials can be used in a wide range of coatings in automotive primers, intermediate coatings and topcoats (including clear varnishes).

In automotive exhaust gas purification catalysts, a large number of nanomaterials exist and play a vital role. When conventional rare earth compounds are replaced by rare earth nanomaterials, carbon monoxide (CO) and nitrogen oxides (NOx) in the exhaust gas are greatly improved. Conversion efficiency, conversion efficiency is above 95%.

The addition of nano-material gasoline emulsifier can transform the quality of gasoline to maximize the full combustion of gasoline and reduce pollutant emissions. Adding nano-material emulsifier, these nano-scale micro-emulsifier beads are gasified under high temperature conditions before combustion to cause "micro-explosion", which causes the fuel to form a secondary atomization, which promotes the fuel to burn more fully in the engine. In order to achieve the effect and purpose of energy saving and emission reduction of the automobile, and at the same time increase the output power of the engine.

Japanese research workers have made a new plastic material by processing the wood pulp made of nano-grade cellulose (CNF) with special chemical methods and adding these nano-celluloses to plastics. The strength of the finished plastic can be comparable to that of steel, and the quality is only 20% of the quality of the steel, which can be used for a large number of steel structural parts to replace the car.

Automotive lead-acid batteries and lead-carbon batteries are also developing in nanotechnology. The addition of nano-carbon materials to the positive and negative electrodes in the battery can provide the capacity of lead-acid batteries, make the battery charging time, and greatly extend the battery life.

In the power battery of the core components of new energy vehicles, there are a large number of nano materials in the positive and negative pole pieces, and they play a decisive role in the battery charge and discharge, life and safety characteristics.

Fourth, other functional materials

Ceramic materials are also widely used in the automotive industry, mainly in the form of functional materials. Magnesium aluminosilicate ceramics can be used in diesel particulate filters to filter fine particles generated during diesel combustion. Reasonable selection of the pore size and porosity of the ceramic material in the automobile can make the filtration cleaning efficiency reach over 95%. The filter regeneration temperature is very high, some can reach more than 1 300 °C. If metal or alloy filter is used, special heat-resistant steel or high-temperature alloy is needed, which greatly increases the cost of the filter.

The rapid growth of new energy vehicle production and sales, China's power battery industry has made great progress. The core component of a new energy vehicle is the vehicle's power battery, which is the energy source of the new energy vehicle, which directly determines the cruising range of the car. The power battery is mainly composed of a positive electrode, a negative electrode, an electrolyte, a diaphragm, etc., and requires high energy density, long life, and reliability. The ternary battery and lithium iron phosphate battery are the leading applications in the passenger car and commercial vehicle fields. At present, the passenger car battery is mainly ternary, and the commercial vehicle battery is mainly lithium iron phosphate battery. Among them, the new materials involved in the power battery are wider, such as graphene, silicon carbon negative electrode, ternary positive electrode, solid electrolyte and the like. Among them, graphene, as the only super material, has broad application scenarios in the fields of automotive power batteries, automotive lightweight, automation, and intelligence, which will greatly promote the advancement of the automotive industry.

V. Conclusion

The automotive industry is in the process of rapid development, and new materials for automobiles will occupy a pivotal position. The future development of the automotive industry will mainly depend on the development level and manufacturing level of new materials technology. China currently has many gaps in the development of new materials such as carbon fiber and aluminum alloy from the United States and Japan. Although China's new automotive materials manufacturing industry has developed, the situation of scattered, chaotic and poor has not been effectively solved, and the scale is small. Dispersion has restricted the development of China's auto industry. China needs to strengthen the use of new materials in automobiles and the research and development of new preparation processes to promote the long-term progress of China's automobile industry.

Text / Li Chunxiao

Beijing University of Chemical Technology