Aluminum alloy forging in automobile manufacturing

With the development of the automobile industry, the global car ownership is increasing year by year, and all kinds of electric vehicles are also emerging. The resulting energy crisis, air pollution and climate warming are becoming more and more serious, and the policies and regulations of governments on automobile emission are becoming more and more stringent. Whether for fuel vehicles or electric vehicles, vehicle lightweight is an important means to effectively improve the competitiveness of products. One of the main ways is to use light metal parts to replace traditional steel parts, so as to reduce the emission of fuel vehicles and improve the endurance of electric vehicle batteries. The density of aluminum alloy is small, and its density is only one third of that of steel. At the same time, its thermal conductivity, processability and corrosion resistance are better than that of steel. The primary weight reduction effect of typical aluminum alloy parts can reach 30% ~ 40%, and the secondary weight reduction effect can be further increased to 50%. The main production processes of aluminum alloy parts are divided into casting and forging. The parts produced by casting process are mainly shell and support, such as engine cylinder head, gearbox shell, steering gear shell, engine bracket, steering gear support, etc; The parts produced by forging process are mainly parts with high mechanical performance requirements, such as wheels, chassis suspension system control arm, steering knuckle, air conditioning compressor scroll, etc.

The standard of aluminum alloy is made by the National Aluminum Industry Association (ISO), and the standard of wrought aluminum alloy (AA) is registered by the International Aluminum Industry Association. The standard for the designation of wrought aluminum alloy in China is GB / T 16474-2011 wrought aluminum and aluminum alloy designation. In addition, relevant national standards include GB / T 3190-2020 wrought aluminum and aluminum alloy chemical composition and GB / T 33910-2017 extruded aluminum and aluminum alloy profiles for automobile. The material grades of typical automotive aluminum forged parts are mainly 6 series, such as 6060, 6061, 6066 and 6082. Some products also need 2 series, 4 series, 5 series and 7 series materials, such as 2014, 4032, 5754 and 7075.

Typical automobile aluminum forged parts and forming process integral wheel aluminum alloy integral forged wheel is a kind of product continuously developed based on the requirements of automobile lightweight, high efficiency and energy saving. It is generally made of 6061 and 6082 aluminum alloy. Compared with the traditional cast wheel, it has better microstructure, light weight, high strength and good surface quality. However, due to the complex process and large equipment investment, As a result, its manufacturing cost remains high, which can only be used in high-end passenger cars and commercial vehicles. The forming process of integrally forged wheels generally selects different process flows according to different product structure characteristics, application scenarios and batches. The commonly used forming processes and their applications in the market are shown in Table 1. The integrally forged wheel usually needs post forging treatment such as heat treatment, machining and surface treatment after forging. T6 heat treatment process (solid solution treatment + artificial aging) is generally adopted for heat treatment to improve the strength of each part of the wheel.

Control arm automobile control arm, also known as swing arm, is an important part of automobile chassis system. Its comprehensive mechanical properties play a vital role in the safety and stability of vehicles. It is generally made of 6082 aluminum alloy. The control arm is divided into front control arm and lower control arm. The front control arm is the guide and support of the suspension. Its deformation will affect the wheel positioning and reduce the driving stability; The lower control arm is mainly used to support the vehicle body, shock absorber and buffer the vibration during driving. The early control arms were mostly made of cast iron, cast steel or steel plate by stamping and welding. With the improvement of material processing technology, the forged aluminum alloy control arm is gradually replacing the steel control arm and realizing batch application on medium and high-end vehicles at home and abroad, such as Japanese Xuanyi, Xiaoke, Qijun, Korean Langdong, American iveo, carnival, European Suteng, Passat, etc. The typical forging process of aluminum alloy control arm generally includes blanking, heating, blank making, forming, trimming, heat treatment and surface cleaning. According to the different shape and structure of products, the billet making process can adopt roll forging, cross rolling and other methods, and some products also need to adopt bending and pre forging to reduce the difficulty of final forging. The heat treatment generally carries out solid solution and aging treatment to improve the mechanical properties of products. Shot blasting or sand blasting can be used for surface cleaning to remove the oxide skin on the workpiece surface and improve the mechanical properties of the workpiece. Steering knuckle steering knuckle is the key structural part in the automobile front axle assembly and front suspension system. It connects the front axle and steering system. It not only carries the whole weight of the automobile and transmits the steering power, but also bears the load generated by the impact from the ground and wheel lateral braking. It is a powerful guarantee for the safety of the automobile during driving. The steering knuckle is a complex security part in the automobile chassis components. The forging process of aluminum alloy steering knuckle generally includes blanking, heating blank making, pre forging, final forging, trimming, heat treatment and surface cleaning. According to the product structure and forming difficulty, one heating or multiple heating can be carried out. The heating process can be before any process of blank making, pre forging and final forging. The heat treatment generally also adopts solid solution and aging treatment. The development process of scroll plate automotive air conditioning compressor has experienced four generations. The first generation of compressor is reciprocating vertical piston compressor, and then evolved into the second generation of swash plate, rocker plate and radial radiation compressor, and then developed into the third generation of rotary compressor, such as rotary vane, rolling piston, screw and triangular rotor. Now the fourth generation of high-efficiency scroll compressor has been developed for more than 20 years, and has realized industrialization and large-scale production. Scroll disk (Figure 5) is the key component of scroll compressor, which can be divided into moving disk and stationary disk. The material is generally 4032 aluminum silicon alloy, with complex structure and high performance requirements. At present, one-step or two-step back pressure forming and forging process is generally used at home and abroad, and some enterprises also use liquid die forging process.

The application of aluminum alloy forging in the automotive industry is gradually increasing. However, due to the high price of automotive aluminum forgings, which are mainly used in high-end models, the total market demand is not large. Moreover, since most vehicle manufacturers in the international market are foreign enterprises, it is difficult to enter their supplier system. For a long time, most domestic enterprises producing aluminum alloy forgings can only provide products for the after-sales market, and the product quality requirements are not high, Lack of power to continuously improve aluminum forging technology. With the continuous development of automobile lightweight and electrification, global automobile manufacturers are facing more and more fierce competition and cost pressure. More and more aluminum forging products will be produced directly in China, which provides unprecedented development opportunities for domestic enterprises with aluminum forging production capacity.