The Research of Auto Lightweight Materials and Their Applications (Part One)

1. Automotive lightweight materials
Lightweight materials are the most important lightweight technologies. Automotive lightweight materials mainly include high-impact steel, aluminum alloys, magnesium alloys, titanium alloys and other metals, engineering plastics, non-metal composite materials, and hybrid materials. The newly developed materials are steel aluminum composite materials, steel aluminum and carbon fiber reinforced composite materials (CFRP). In addition, the processing technology of titanium alloys with excellent performance has been improved, and the price has been reduced, which are used more. There are more researches and applications for metal foam and foam plastic with energy absorption, vibration reduction, heat insulation and compression resistance, biodegradable bioplastics and glass fiber composite materials.
 
2. Automobile lightweight materials are still dominated by steel and iron.
China's self-owned car bodies are still mainly made of steel, including alloy structural steel and high-impact steel. According to the 2015 and 2016 China Lightweight Car Body Conference data, taking 10 self-owned passenger car bodies as an example. Among them, 4 have all-steel bodies with a steel content of over 95%, and 1 is made from an aluminum alloy as the main material. Among the 6 non-all-steel bodies, 4 are made from aluminum alloys, with the contents of 85%, 2%, 1.7% and 1.2%. No magnesium alloy is used in the body of the 10 models. The average consumption of high-impact steel of 10 self-owned passenger car body-in-white including traditional high-impact steel, advanced high-impact steel, ultra high-impact steel, and hot formed steel is about 56%, among which traditional high-impact steel is about 33.6%, advanced high-impact steel 19.09 %, ultra-high-strength steel 1.62%, and hot formed steel 6.72%. The consumption of low-strength steel and cast iron has been greatly reduced in the past three years, and the consumption of high-impact steel, ultra high-impact steel, high-performance spring steel and high-performance gear steel has rapidly increased. Automobile steel has developed to the third-generation advanced high-impact steel. The third-generation advanced high-impact steel is martensite-based phase transformation induced plasticity steel. The consumption of the domestically produced body-in-white mild steel is 26%, dual phase steel 34%, high-impact low-alloy steel 24%, bake hardening steel 9%, hot forming steel and martensitic based steel 7%. At present, the research of China's third-generation high-impact steel for automobiles is at the forefront of the world.
 
3. Aluminum alloy is indispensable for automotive lightweight materials.
Aluminum is the earliest lightweight material for automobiles. The density of aluminum alloy is 1/3 that of steel, and the specific energy absorption is twice that of steel. It has good ductility, easy forming and processing, corrosion resistance and easy recycling, and good casting performance. There are plates, profiles, pipes and high-performance cast aluminum. At present, aluminum castings are currently used, accounting for about 80% of all aluminum products. Pistons made of aluminum-based composite materials are 10% lighter than cast iron pistons. Light and middle-sized vehicles use aluminum alloy wheels, which are 30% to 40% lighter than traditional steel. At present, domestic automotive aluminum alloys are mainly concentrated in housings of power systems, anti-collision beams and chassis steering knuckles, with a total of about 153 kg. Compared with 190 kg in the automotive technology formulated in China in 2020, there are still some distance.

The truck frame beam made from aluminum alloy is 25% lighter than that from high-impact steel. There are 5 series aluminum alloys used for the vehicle body, including series 2, series 5, series 6 and series 7. The strength of series 5 is similar to a low carbon steel plate, which has good formability and is used for parts with complex shapes such as inner panels. Series 6 has good overall performance and can be used for the inner and outer panels of the body. The weight of the small ant model of Chery's all-aluminum body is reduced by 19%. The utilization rate of aluminum alloy profiles for some domestic vans can reach more than 60%, and the weight reduction rate of the cargo trunk exceeds 30%. The recycling and reuse of waste aluminum products is as high as 90%, which is beneficial to environmental protection. However, there is still a lack of large-scale squeeze casting equipment in production. Large squeeze casting part like beams can not be manufactured in China. There are also many grades for aluminum alloys, which are not conducive to mass professional production and cost reduction. In addition, aluminum alloys are not easily welded, and the overall use of automotive aluminum alloys is not as good as foreign products. At present, aluminum alloys have not succeeded in replacing steel plates, but steel-aluminum mixing is a development trend.