Automotive lightweight materials meet new challenges

“2013 is the last year of the implementation of the integrated lightweight automotive technology development and vehicle integration application project. Some key technologies for vehicle weight reduction are expected to be applied.” A few days ago, the National Strategic Alliance for Automotive Lightweight Technology Innovation was held. National "Twelfth Five-Year Plan" Technology Support Plan "Automatic Key Lightweight Technology Development and Integrated Application of Complete Vehicle" project promotion meeting. Participants revealed that at present, China has basically broken through lightweight design techniques and evaluation methods for auto bodies, ultra-high-strength steel parts stamping thermoforming technology, advanced forming technology for high-strength steel parts, modular design and application technology for fiber-reinforced plastics, and deformed aluminum alloys. Parts development and key technologies for automotive lightweighting, such as the integration of lightweight technologies for vehicle weight reduction.

New materials continue to emerge

Wang Zhiwen, deputy secretary-general of the National Automotive Lightweight Technology Innovation Strategic Alliance, believes that cars are not as heavy and safe as cars. Even if very light materials are used in automobiles, if high-strength processing techniques are used, it can achieve very good elasticity and safety. In recent decades, steel plates for automobiles have become thinner and thinner, and the strength and corrosion resistance of steel materials have also been greatly enhanced. The body of the car is welded together by steel plates of different strengths, and steel plates of different strength levels are used in different positions of the stress environment. For safety reasons, some high-strength steels are used in places where stress conditions are severe and where thick steel plates cannot be used (such as anti-collision beams and some reinforcements).

However, the increase in material strength has also brought about some problems, mainly because of the greater difficulty of processing. General car is made by stamping method, that is molding with die extrusion material. The increased strength of automotive steel plates imposes higher requirements on the stamping process, and now many deep-drawn parts are prone to cracks and wrinkles. In order to avoid the above situation, manufacturers must study the deformation of the steel plate during stamping to prevent the steel plate from tearing during stamping. However, the better the steel plate strength, the more difficult it is to stamp the contradiction.

In order to fundamentally solve the stamping problem of high-strength steels, a new type of steel is used in the production of automobile bodies. The base material of this steel is a relatively soft, tough ferrite, in which martensite with a good hardness is embedded, which is easier to be formed during stamping and has considerable strength after molding. Therefore, this new car steel will make the car more secure.

At present, the thickness of automotive steel plates has dropped to 0.6mm. Analyst Luo Baihui said that this may have reached the limit of the thickness of the steel plate. Even if the steel plate is thin, even if its strength is higher, it loses the structural stability of many materials. Nowadays, the challenge of new steel materials for car steel plates is increasing. The atomic weight of iron determines that its density cannot be changed, and the road to reduce weight by thinning seems to have come to an end.

It is understood that the National Strategic Alliance for Automotive Lightweight Technology Innovation is working with Changan Automobile (000625) Group to jointly develop and promote the “Al-Aluminum Steel” hood. Wang Zhiwen introduced that this study is based on the consideration of protecting the safety of pedestrians in the event of an accident. Because the application of aluminum alloy in the hood and other parts can reduce the secondary impact of the impact on the human body. Although the weight of the aluminum plate is approximately 1/3 of the steel plate, its absorbable collision energy is twice that of the steel plate. Aluminum alloys have a higher safety factor in the event of an impact because their material has a very good energy absorption. Now that aluminum alloys are being widely adopted in high-end vehicles, all-aluminum SUVs have emerged, and high-end cars with aluminum as front-end structures are being followed in the industry.

For some steel companies, automotive steel accounts for about 1/3 of current product sales. In order to guarantee its market for automotive steels and respond to the impact of new materials, many steel companies are actively working with auto companies to develop a new generation of lightweight high-strength steels that are expected to compete with aluminum alloys, plastics, and carbon fiber composites.

Composites still take time

According to the data from the American Chemical Industry Association, the total weight of automotive plastic parts is still less than 1/10 of the total weight of automobiles. Therefore, the space for expanding applications is still very broad. The only drawback of composite materials is their poor flame retardancy, but they can be improved after the addition of flame retardant materials. In recent years, in order to enhance the competitive advantage of the market, various car companies have developed and launched lightweight models. BMW will mass-produce BMWi3 pure electric vehicles this fall. The most important feature of this car is that the outer cover material is plastic and the chassis material is aluminum alloy. Compared with the traditional models of the same kind, the car achieves a weight loss of 250kg to 350kg.

Among the local car companies, Great Wall Motor Co., Ltd. and Chery Automobile Co., Ltd. are the two car companies that have gone farthest in this research field. Chery's A3CC coupe front fenders are made of Noryl GTX resin. At the 2012 Beijing Auto Show, the seven window components of the Haval E concept car displayed at the Great Wall were made of Bayer miquelon polycarbonate and equipped with a large panoramic sunroof. This is the first time that Chinese domestic automakers have applied polycarbonate windows so widely. In addition, in addition to the family-car market, the weight of trucks has long been on the agenda. Beiqi Foton has changed the bumpers of its medium- and heavy-duty trucks from steel to plastic materials, and has activated glass-reinforced plastic in some auto parts. It also replaced some steel engine parts with plastic parts.

However, despite the fact that foreign vehicle companies have become increasingly sophisticated in light weight, China's domestic car companies are still learning or catching up. “This is because the domestic composite materials industry is still relatively backward, especially high-end materials are completely monopolized and controlled by some foreign chemical manufacturers. They have mastered material design techniques, analytical techniques, and design technologies for components. Due to high-end materials such as high-strength carbon fiber Material, long-term monopoly by foreign technology has led to high product costs, some companies can only give up the use of high-end materials in the car." Deputy Secretary-General of China Unsaturated Polyester Resin Industry Association Zhao Honghan said.

At the second session of the International Automotive Lightweight Innovative Materials and Molding Technology Application Summit held recently, Jiang Dingfeng, a senior engineer at Haiyuan Machinery (002529), once told the media that his company is investigating the market for complete sets of equipment for carbon fiber auto parts. "The time for the official listing of this equipment is still not accurate. We still need to make some investments in technology and we must find the entry point for the market. Individuals are expected to come out in 2017 and 2018." He said that there are few companies in the world for the time being. It can produce carbon fiber auto parts and components in large quantities. In addition, he said that only carbon fiber materials can reduce vehicle weight by 50% to 60%, while current materials can only reduce vehicle weight by about 25%.

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