With the increase of automobile production and sales, the energy consumption and pollutant emissions generated in the process of automobile production and using are increasing, and at the same time, the pollution of the environment is becoming increasingly prominent. Therefore, in order to promote the sustainable development of the automobile industry, on the premise of ensuring the rigidity, strength and safety performance of the automobile, through changing the materials of the automobile structures and parts, to achieve the lightweight of the automobile, which has a very great promotion role in improving the fuel efficiency of the automobile and reducing the emission of pollutants. Car lightweight can not only save energy and reduce emissions, but also improve the stability and dynamic performance of the car during driving. This paper mainly describes the most widely used automotive lightweight materials magnesium alloy and aluminum alloy, analyzes their characteristics, advantages and the future development trends in automotive lightweight.

From the current development trends, in order to protect the environment and save energy and resources, the future automobile researches and developments will pay more attention to the lightweight designs of automobiles. In the automobile manufacturing, the use of lightweight materials such as high-strength steel, aluminum alloy, magnesium alloy and composite materials can effectively achieve the lightweight of automobiles. In addition, the use of advanced manufacturing processes, such as thermal forming, laser welding, hydraulic forming, etc., can also achieve the lightweight of automobiles. Aluminum alloy has been widely used in automobile lightweight by virtue of its low density, good corrosion resistance and easy workability.

1. Aluminum alloy

1.1 Advantages of aluminum alloy

Aluminum is a light metal, with good electrical and thermal conductivity, but also has good corrosion resistance. At the same time, the mechanical properties of aluminum alloy are better than traditional metal materials, the melting point of aluminum is low, the recovery rate of aluminum in the entire use and recycling process is not less than 90%, aluminum alloy has very good renewability, so aluminum alloy is currently the ideal material to achieve automotive lightweight.

The use of aluminum alloy parts on the car can effectively reduce the weight of the car, reduce the center of gravity of the car, and truly realize the lightweight of the car. After the car is lightweight, the acceleration performances of the car will be improved in the car driving, and the car will be more stable and comfortable, and the noise and vibration will also be improved.

1.2 Applications of aluminum alloy in automotive lightweight

The applications of aluminum alloy in automotive lightweight mainly include aluminum alloy forgings, metal die castings, aluminum alloy extrusion and drawing products.

Cast aluminum alloy is used in the current automotive lightweight process, mainly used in the automobile engine, chassis, hub and other structures, the engine has been known as the "heart" parts of the car, in the cylinder head, cylinder block, piston and other parts of the applications of aluminum alloy can not only effectively reduce the overall weight of the engine, it can also dissipate the heat generated in the engine work projects in time to improve the working efficiency of the engine.

1.3 Development trends of aluminum alloy in automotive lightweight

Aluminum alloy sheet in the use of the process of its weldability is worse than steel. The formability and forming quality of aluminum alloy covering were improved by thermoforming, superplastic forming and electromagnetic coincidence forming.

At present, in addition to the traditional aluminum alloy metal materials, aluminum matrix composite materials with low density, high strength, high corrosion resistance and other advantages, in the automotive lightweight manufacturing has been a good application, with aluminum matrix composite materials made of automotive engine piston relative to the traditional cast iron piston, its weight is reduced by about 10%, while the heat dissipation is increased by 4 times. Restricted by price and production quality control, aluminum matrix composites have not yet formed a large scale, but they have shown their excellent performances on some automotive parts.

2. Conclusion

In today's rapid economic and social developments, in the face of new energy crisis and environmental problems, vehicle lightweight can effectively improve the fuel efficiency of vehicles, and then reduce the emission of pollutants. In the process of automobile lightweight, magnesium alloy, aluminum alloy and other metal materials have been widely used by virtue of their advantages and characteristics. In the future, it is also an inevitable trend of automobile lightweight researches and developments to reduce the cost of materials through technological improvements, improve the utilization rate of materials, and develop new materials with both environmental protection and recyclability.