The Research of Auto lightweight Materials and Their Applications (Part Two)

Paying attention to using magnesium alloys for lightweight and environmentally friendly materials for automobiles
Magnesium can reduce the weight by 15% to 20% on the basis of the weight reduction of using aluminum. Magnesium alloy is currently the lightest metal with features of high specific strength, good specific rigidity, impact resistance, no biological toxicity, reuse, good processing and casting properties. China's magnesium land resources rank first in the world. Magnesium alloys used in automobiles started late, and the magnesium used in automobiles is growing at an average annual rate of 20%. At present, magnesium alloys are mainly used for manufacturing large-area structural parts such as chassis, bodies, steering wheels, seat frames, and wheels and some thin-walled parts. The body of Chery EQ1 adopts high-impact magnesium-aluminum alloys. The front body of steel structure is replaced by magnesium alloys, which reduces the weight by 58.6%. Because magnesium alloy has good die-cast performance, thin-walled parts and complex structural parts can be manufactured by die casting. The number of parts can be reduced from 89 to 50, and the car body's manufacturing process is simplified. Currently, China has rich magnesium minerals, but products made of magnesium alloys are few. The use of magnesium alloys in the whole vehicle is only about 2 kg, and there is a certain distance from the current average of 5 kg in European and American vehicles. There is a great distance from the goal of 15 kg in 2020. The main reason restricting the development of magnesium is its active chemical properties, poor creep resistance and high-temperature fatigue performance. It requires professional magnesium alloy die casting machines and furnaces. There is no self-contained system for die casting magnesium alloys. The die casting technology for magnesium alloy needs to be improved, and the price is 20% higher than that of aluminum alloy. The research and development of magnesium alloys should be enhanced to replace steel and aluminum alloys, which is one of the important measures for lightweight automotive materials.
 

4. A great development for a wide variety of lightweight non-metallic materials for automobiles

The non-metallic materials used in modern automobiles mainly include rubber, ceramics, glass, plastics, and adhesives. Rubber includes natural rubber and artificial rubber, which are used to make tires, hoses, and shock-absorbing blocks. Ceramics can be divided into engineering ceramics and functional ceramics according to performance and applications. Engineering ceramics can be used for spark plugs, cylinder head bottom plates, piston tops, etc., and functional ceramics can be divided into electrical ceramics, piezoelectricity ceramics and optical ceramics according to their functions, which can be used for ultrasonic testing instruments for electronic instruments. In addition to making wind windows and car doors and windows to broaden the field of vision, glass can also be used to make decelerating glass, heat-absorbing glass and anti-frost glass with special functions. There are safety glass, laminated glass, tempered glass and regional tempered glass.  The amount of plastic used in automobiles today is equivalent to that of aluminum alloys, which is 1/6 of that of steel, and continues to grow. In just a few years, the amount of automobile plastics has increased from 8% to 20%. Commonly used plastics for automobiles include polyethylene, polyvinyl chloride, ABS resin and Polyoxymethylene. Engineering plastics are not limited to interior and exterior parts, but can also be used to manufacture functional and structural parts. At present, more and more plastics are used in fuel tanks, water tanks, hood anti-collision systems, and airbags. A variety of high-performance polypropylene and natural fiber composite lightweight, environmentally friendly, and recyclable new automotive materials are widely used in bumpers, instrument panels, air conditioning systems, etc., and are growing rapidly. There are many types of adhesives, including natural adhesives and synthetic adhesives. Epoxy and phenolic resins are commonly used in automobiles to bond friction plates of clutches, repair cylinders and batteries.
 
5. Not underestimating composite materials and mixed materials
Composite materials in automobiles mainly include resin-based (also called fiber-reinforced plastics), metal-based and ceramic-based materials, which are lightweight and elastic. Glass fiber reinforced plastics (commonly known as glass fiber reinforced plastics) and carbon fiber reinforced plastics are the typical resin-based, and metal-based mainly include aluminum, magnesium, copper, and nickel. Fiber-reinforced composite materials with excellent mechanical properties are a hot topic in the research of new lightweight automotive materials. The general density is 1/4 to 1/5 that of ordinary steel, 1/3 aluminum alloy, and low-cost carbon fiber-reinforced resin-based composite materials and natural fiber-reinforced resin-based composite materials will be an important material to promote the upgrading of the automotive industry. Fiber-reinforced composite materials for manufacturing car doors, windows and wheels have already appeared. The fourth-generation plastic tail gate adopts integrated structural design, which reduces weights up to 26% compared to metal doors. The performance of carbon fiber reinforced plastics is generally better than that of glass fiber reinforced plastics, which can be used to make car bodies, tail wings, chassis, engine hoods, etc. The carbon fiber engine hood can reduce the weight of the engine by more than 6 kg. Fuel tanks made of high-density polyethylene are 4 kg lighter than steel fuel tanks, and it is expected that a fully plastic model of "plastics instead of steel" will be developed. The use of resin-based composite materials can greatly reduce weights, especially carbon fiber reinforced plastics. The weight can be reduced by up to 70%. A breakthrough has been made for the application of glass fiber reinforced plastics to trucks, and “using plastics instead of steel” and single plastic is the highlights of the future development of lightweight automobiles. Henan Bingxiong and other professional refrigerated trucks use FRP inner and outer panels with PU foam mixed materials. Some parts and body parts adopt lightweight hybrid materials including aluminum, magnesium, carbon fiber reinforced materials and even fabrics. Most domestic Chery bodies use high-impact magnesium-aluminum alloys to reduce the weight by 40% compared with traditional cars, and at the same time increase stiffness by more than 60%. The weight of the magnesium profile battery box is significantly reduced. Relevant studies have shown that the optimal carbon fiber composite anti-collision beam structure of a certain model weights 0.825 kg, while the steel anti-collision beam has a structural weight of 2.321 kg, which has a lightweight effect of 64.5% and an increase in the energy absorption ratio, as shown in Figure 3.
 

Figure 3 A comparison of energy absorption of anti-collision beam before and after optimization