Die Casting

Application of Metal Die Casting Technology in Automobile Field

Compared with other manufacturing processes, the die-casting process has high production efficiency, high dimensional accuracy, excellent mechanical properties, high material utilization, and better economic benefits in mass production. Among the aluminum alloys for automobiles, die-cast aluminum alloys and other cast aluminum alloys account for about 80%, and processed aluminum materials (plates, strips, foils, tubes, rods, shapes, wires, forgings, powders, pastes, etc.) account for only about 20%. The amount of die-casting parts accounts for about 70% of the total amount of casting products, so die-casting aluminum alloy products account for about 54% to 70% of automotive aluminum.

Since 2009, my country's automobile sales have ranked first in the world for eight consecutive years, from 13 million in 2009 to over 27 million in 2019. With the increasingly fierce competition in the automobile market, various manufacturers are developing in the direction of high quality, high reliability, light weight, energy saving and environmental protection, and low cost. With the tightening of automobile emission standards and international environmental protection policies, new energy vehicles It has become the key development direction of the future automotive field, and more and more high-strength, high-quality new energy vehicle structural components (automotive body, column, chassis, shock tower, etc.) need to be manufactured by die-casting forming process. All these show that aluminum alloy die-casting occupies a pivotal position in the die-casting industry and is the mainstream of the die-casting industry.

Process characteristics of die-casting aluminum alloy

In addition to good die-casting process properties and mechanical properties, die-casting aluminum alloys also need to have the following process properties:

①Good thermoplastic rheological properties, it should have good thermoplastic rheological properties when the superheat is not high and near the liquid and solidus temperatures, so as to realize the filling of complex cavities, form a good casting surface, and avoid shrinkage defects. ;

② Smaller linear shrinkage rate to avoid cracks and deformation in the die-casting process, and improve the dimensional accuracy of the product;

③The smaller solidification temperature range is convenient to achieve rapid and simultaneous solidification, and reduce the number of defects such as internal shrinkage holes;

④Good high temperature thermal strength, avoid thermal cracking or serious deformation during mold opening;

⑤Good casting/mold interface performance, no chemical reaction with die-casting molds, low affinity, avoiding sticking and alloying reaction at the casting/mold interface;

⑥Good physical and chemical properties, it is not easy to inhale and oxidize in the high temperature molten state, which can meet the needs of long-term heat preservation in the die-casting process.

Die-casting aluminum alloy classification

According to the alloy composition, die-casting aluminum alloys can be divided into four series: AI-Si (AI-Si-Cu, Al-Si-Mg), Al-Cu, Al-Mq and Al-Zn. Al-Si die-casting alloys are the most widely used because of their small crystallization temperature interval, large latent heat of crystallization and specific heat capacity of silicon phase solidification, small linear shrinkage, good flow properties, mold filling properties, and small tendency of hot cracking and porosity. Although Al-Cu die-casting alloys have high mechanical properties, the addition of Cu element reduces the corrosion resistance of the material, and the service life of die-casting products is greatly reduced, and the die-casting process is prone to segregation and cracking, so the application range is small. . Compared with Al-Si based die-casting alloys, Al-Mg based die-casting alloys have poor casting properties, large fluctuations in mechanical properties and large wall thickness effects, are prone to cracking during die-casting, and have a greater tendency to stress corrosion; Al-Zn based die-casting alloys are naturally Aging can obtain better mechanical properties, but its corrosion resistance is poor, thermal cracking and stress corrosion are prone to occur, and it is used less. Table 1 shows the grades, chemical compositions and mechanical properties of commonly used die-casting aluminum alloys. Among them, Al-Si-Cu alloys are the most widely used, such as AISi9Cu3 (A380) and AlSi11Cu3 (ADC12). As shown in the table below, die-cast aluminum alloys generally add Si, Cu, Mg, Mn, Fe, Ni and rare earth elements.

Alloy series	GB	ASTM	Js	Main Ingredient	Mechanical Properties
	YL101	A360	ADC3	AlSi1l0Mg(Fe)	2220MPa:622.0%
Al-Si	YL102	A413	ADC2	AlSi12(Fe)	279MPa:62.7%
	YL112	A380	ADC10	AlSi9Cu3(Fe)	≥320MPa:623.596
Al-Si-Cu	YL113	1383	ADC12	AlSil1Cu3	a2230MPa:6z1.09%
YL117	B390	ADC14	AlSi17Cu5Mg	a220MIPa:6z1.0%
Al-Mg	YL302	518	ADC5	AlMg5sil	2220MPa:o2.0g

At present, the application scope of aluminum alloy die castings in the domestic and foreign automotive industries is classified according to the function of use, and has been used in structural parts, stress parts, safety parts and decorative parts, mainly including the following aspects:

①Power system: cylinder block, cylinder block cover, cylinder head cover, crankcase, cylinder head cover, oil pan, piston, pump body, pump cover, intake pipe, generator housing, engine gear chamber, six-seat shaker Arm mounts, various engine brackets, etc.;

② Transmission system: transmission housing, transmission oil circuit board, clutch housing, shift fork, gearbox bracket, etc.;

③Steering system: chain cover, rack housing and turbine housing.

④Chassis assembly: suspension bracket and beam;

⑥Other: shock absorber lower end cover, compressor bracket, clutch pedal and brake pedal, etc. The figure below shows the summary and proportion of aluminum alloy die castings for automobiles. As can be seen from the figure, die-casting aluminum alloys have been widely used in the automotive industry.

The future development trend of die-casting aluminum alloy

In recent years, the electric new energy vehicle industry has continuously improved the requirements for technical indicators such as power, safety, comfort, and lightweight, and the required aluminum alloy products are gradually developing towards thin-walled, high-strength, low-cost and integrated structures. The development of die casting technology provides the application basis and source power. In recent years, the development of aluminum alloy die-casting technology in general is to give full play to the technological characteristics of alloy materials by continuously optimizing and adjusting the composition of alloy materials, combining high-vacuum die-casting technology and control of heat treatment process parameters, and using high-pressure injection and low-speed filling. Continuously improve the comprehensive mechanical properties of die-casting alloy materials. With the continuous deepening of military-civilian integration, a large number of ring-shaped projectile and arrow structural products do not have high requirements on fatigue performance. According to the integrated lightweight design of structural integration, die-casting technology can be used for mass production and development, shortening the product development cycle and reducing Its production cost provides a development basis for the promotion and application of die-casting aluminum alloys.

Policy promotion + "mileage anxiety" promotes the rapid development of lightweight, and the aluminum alloy market has a broad space. Facing the reality of energy conservation and emission reduction policies and anxiety about the mileage of new energy vehicles, lightweighting has become an important technical direction. Aluminum alloy materials have become the preferred choice for lightweighting due to their cost-effective advantages. The market space is expected to reach 136.2 billion yuan in 2025. The compound growth rate in 2025 will reach 17.1%.

The increase of aluminum alloy body structural parts has brought about an upgrade in the difficulty of the splicing process. With the continuous increase of aluminum alloy materials, the splicing process of body structural parts is more difficult to adopt the original stamping + welding process, including friction stir welding, laser welding, riveting and other new connection methods, which bring cost increases and splicing efficiency declines.

Equipment/materials/processes have been gradually improved, and cost/efficiency/safety/precision requirements have jointly promoted Tesla's efforts to integrate die-casting. With the continuous increase in tonnage of die-casting equipment + the maturity of heating-free alloy technology + the continuous improvement of high-pressure die-casting injection, molding, cooling and other processes, the integration of aluminum alloys is technically possible. Driven by the multiple demands of cost, efficiency, safety and precision, Tesla took the lead in trying integrated die-casting technology to complete the integrated die-casting of the rear floor of the Model Y model, and will gradually expand to the front floor and front wall modules.

The market space is broad, and new forces + supply chains are following up one after another. As the integrated die-casting technology continues to mature, it is expected to be applied to body structural parts such as front floor, rear floor, A/B/C/D pillar, front wall assembly, and three-electric system products such as battery boxes. The market space is expected to reach 2025. 38.9 billion yuan, with a compound growth rate of 205% from 2021 to 2025.