Application of Heat-Free Aluminum Alloys to Integrated Die-Casting

Since Tesla first proposed the concept of integrated die-casting in 2019 and achieved significant weight reduction, car companies such as NIO, Xiaopeng, Li Auto, Wenjie, Xiaomi, Changan, FAW, and HiPhi are planning integrated die-casting projects following Tesla's example. As of January 2024, few models have been released with integrated die-casting parts.
 
The heat-free alloys used in the models listed above are all Al-Si alloys. Currently, integrated castings are mainly used in the rear floor and front cabin areas, and are expected to expand to more components, such as the middle floor (battery tray) and C/D pillars, in the future. In terms of casting performance, due to the influence of the casting process, defects, and product design, even with the same material, the mechanical properties of castings at different positions may vary. Currently, the yield strength of various materials ranges from 90 to 150MPa, and the strength of castings made from the same material does not differ significantly from the flat plate test results. However, in terms of elongation, the larger the casting size, the more challenging it becomes to achieve 10% elongation across the entire area. Therefore, optimizing the casting design, mold cooling, and casting process are key measures to ensure that the castings possess both high strength and toughness.
 

Al-Si alloys are the primary materials used for integrated die-casting, heat-treatment-free alloys, and their composition design is shifting towards lower cost. In the design of new materials, priority is given to using lower-cost alloy elements to reduce the demand for expensive raw materials, thereby lowering the overall manufacturing cost of castings. For example, although the element Sc has a significant strengthening effect, its high cost limits its large-scale industrial application. Additionally, researching how to improve the tolerance of heat-treatment-free alloys to impurities like Fe and Cu, to lower smelting costs and raw material quality requirements, is also a key strategy for reducing the cost of producing high-strength and tough aluminum alloys. Narrowing the price gap between aluminum and steel will encourage the wider application of cast aluminum in automotive parts. By thoroughly studying the microstructure and phase transformation mechanisms of the alloy, and optimizing its chemical composition and heat treatment process, key properties like strength and toughness can be further enhanced. Given the advantages of Al-Mg alloys in mechanical properties, future research will focus on overcoming the limitations of their casting performance by optimizing composition, making them ideal materials for the next generation of automotive parts.
 
As the use of heat-treatment-free aluminum alloys increases, their price will gradually decline, making this an inevitable trend. Therefore, future research will focus on achieving same-level recycling of return materials generated during the integrated die-casting process and using low-cost, lower-quality raw materials to produce heat-treatment-free aluminum alloys for green, low-carbon, and cost-effective smelting. In terms of production methods, promoting the direct supply of aluminum alloy liquid to die-casting plants, instead of the traditional process of preparing alloy ingots and then remelting them into aluminum liquid, will help reduce smelting losses and save energy. Additionally, fostering collaboration between alloy ingot manufacturers and electrolytic aluminum enterprises, and directly purchasing raw aluminum liquid from electrolytic aluminum plants, is an effective way to reduce smelting losses.
 
At the current stage, various grades of heat-treatment-free aluminum alloys are available. Not only do the main engine manufacturers, but also upstream material factories and midstream die-casting plants, hold the intellectual property rights for relevant heat-treatment-free alloys. As the primary users of new materials, OEMs involved in integrated die-casting in the later stages are more likely to select materials widely used in the market, accelerating the unification of heat-treatment-free alloys in the industry, especially for mainstream Al-Si alloys. Since the variations in material composition are relatively minor, the trend toward unification will be more pronounced. Additionally, some car companies may select various heat-treatment-free alloys to produce different castings in the early stages because different integrated parts have specific mechanical property requirements. From a production and operational perspective, with an emphasis on cost control and management efficiency, materials are likely to become gradually unified in later stages. From a technical perspective, even if alloys with diverse properties are required, the element content in the composition can be fine-tuned to achieve customized performance differences, meeting the needs of different parts. These two factors have jointly promoted the trend of automobile manufacturers using the same heat-treatment-free aluminum alloy across all models and individual components. Heat-treatment-free alloys have emerged in new energy vehicles but are not limited to them. Traditional vehicles can also achieve weight reduction by replacing steel with aluminum. Currently, AlSiOMnMg and A356 heat-treated materials are widely used in cast aluminum structural parts. In the future, more parts will utilize high-strength, tough heat-treatment-free aluminum alloys. This transformation not only aligns with the global trend toward lightweight automobiles but also brings new development opportunities to the automobile manufacturing industry.
 
With the development of lightweight, energy-saving, and environmentally friendly trends in automobiles, the research and application of integrated die-casting heat-treatment-free aluminum alloys are crucial. A comprehensive analysis of the composition characteristics and mechanical properties of high-strength and tough aluminum alloys, both domestically and internationally, reveals that heat-treatment-free aluminum alloys show significant application potential in the field of die-casting due to their unique advantages. The research status and development trends of heat-treatment-free aluminum alloys are reviewed, and their application in integrated die-casting technology is analyzed in detail. The study found that heat-treatment-free aluminum alloys not only exhibit good casting mechanical properties, such as high toughness and good elongation, but can also further improve their strength and thermal stability through refined chemical composition design. In particular, the addition of trace strengthening elements plays a crucial role in optimizing alloy properties. Although heat-treatment-free aluminum alloys have broad application prospects in the field of integrated die-casting, there are still challenges and limitations. For example, the alloy composition design needs to comprehensively account for strength, toughness, casting performance, and corrosion resistance. Additionally, the promotion and popularization of integrated die-casting technology still need to overcome obstacles related to equipment, processes, and cost. Driven by the rapid development of the new energy vehicle manufacturing industry, high-strength and tough heat-treatment-free aluminum alloys are gradually demonstrating excellent performance and broad application prospects. This type of alloy was originally focused primarily on the die-casting application of integrated body structural parts. In the future, it will not be limited to this but will extend to the manufacturing of large and complex structural parts, indicating further expansion and deepening of its application.