The Advantages of Die Casting Technology of Aluminum Alloys

Rheological die-casting technology originated from the Massachusetts Institute of Technology in the United States in the 1970s. After nearly 50 years of development, it has gradually formed a relatively complete technology chain and has been implemented in many fields such as automobiles, engineering machinery, communication equipment, and photovoltaics. industrial application. In rheological die-casting, the metal or alloy melt is directly prepared into a semi-solid slurry, transferred to the injection chamber of the die-casting machine, flows and fills the mold cavity driven by the injection rod, and solidifies under pressure. Compared with thixotropic die-casting, rheological die-casting has the characteristics of short process flow and low cost; compared with conventional die-casting, rheological die-casting has the advantages of high casting density and long mold service life. According to the different solid phase fraction of semi-solid slurry, rheological die casting can be divided into two categories: low solid phase rheological die casting (slurry solid phase fraction less than 40%), which is mainly used to improve the quality of die castings. , representative products include 5G communication base station casings, power converter casings, photovoltaic inverter casings, etc.; high solid phase rheological die casting (slurry solid phase fraction higher than 40%), mainly used to manufacture high-quality High-quality castings, whose product density and performance are comparable to forged products. Representative products include turbocharger impellers, engine brackets, etc. Compared with low solid phase rheology die casting, high solid phase rheology die casting has greater advantages in casting quality control. In recent years, the industrialization process has been accelerating, and automakers such as BYD, Foton Daimler, and General Motors have successively adopted it. High solid phase rheology die-cast aluminum alloy parts.

In order to meet the specific needs of more application scenarios, high solid phase rheology die casting technology is still developing. The research team of Professor Zhu Qiang and Associate Researcher Lu Hongxing of Southern University of Science and Technology summarized the research progress and industrial application of this technology in slurry preparation, materials, simulation and defect control in recent years, and discussed future development.

About the Author

[Zhu Qiang]

Zhu Qiang graduated from the University of Erlgen-Nuremberg in 1994 with a doctorate in engineering in materials science. He once served as deputy chief engineer, chief expert, academic committee member, and national academic committee member of the Beijing Nonferrous Metals Research Institute (now China Youyan Technology Group). Deputy director of the Nonferrous Metal Composite Materials Engineering Technology Research Center, the first director of the Beijing Metal Advanced Forming Manufacturing Engineering Technology Research Center, and an expert in the overall expert group of the Ministry of Science and Technology's 12th Five-Year Plan for "High-Quality Special Steels and High-Temperature Alloys". He is currently a chair professor at Southern University of Science and Technology, a fellow of the British Society of Materials, Mining and Minerals, a member of the International Semi-Solid Technology Committee, the rotating chairman of the Semi-Solid Working Committee of the China Foundry Association, and the founder of Shenzhen Nan Keqiang Zheng Light Alloy Technology Co., Ltd. In the past 10 years, it has successively undertaken national scientific and technological support, international cooperation, key research and development plans, as well as provincial and municipal vertical scientific research projects and enterprise cooperation horizontal projects, with a total investment of over 100 million yuan. He has been invited to give special lectures at famous international academic conferences for many times, published more than 180 papers, edited and published 2 monographs, and applied for more than 60 patents.

About the Author

[Lu Hongxing]

Lu Hongxing graduated from Beijing University of Aeronautics and Astronautics in 2012, majoring in materials science and engineering, and received a bachelor's degree in engineering. In 2017, he graduated from Beijing General Institute of Nonferrous Metal Research, majoring in materials science and engineering, and received a doctorate in engineering. He is currently a research assistant professor at Southern University of Science and Technology, general manager of Shenzhen Nankeqiangzheng Light Alloy Technology Co., Ltd., and deputy secretary-general of the Semi-Solid Working Committee of the China Foundry Association. The main research directions include high-performance aluminum alloy materials for transportation and communications, aluminum alloy semi-solid forming and die-casting forming technology, semi-solid forming intelligent manufacturing systems, etc., focusing on applied basic research and common engineering technology issues. As the project leader or subject leader, he has undertaken 7 provincial and municipal vertical projects and horizontal enterprise cooperation projects, published more than 20 papers, applied for more than 10 patents, and participated in the formulation of 1 national standard.

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Table 1 High solid fraction rheological pulping technology

There are more than 30 reported rheological pulping technologies, but only a few can be used to prepare high solid fraction slurries. These technologies and the aluminum alloy materials used are shown in Table 1. Among them, the Swirled Enthalpy Equilibration Device (SEED) and New Rheocasting (NRC) have been industrialized.

Figure 1 Solid phase fraction of different aluminum alloys changes with temperature

Figure 2 Microstructure of 7108, 6063 and 7050 aluminum alloy high solid fraction semi-solid slurries prepared by the improved SEED method

Figure 3 Comparison of the simulation results of the microstructure growth process with the real solidified structure

At present, the aluminum alloy materials used for industrial application in high solid-phase rheology die-casting are mainly hypoeutectic Al-Si alloys. Commonly used materials include A356, A357, and A319s aluminum alloys. The mechanical properties of some high solid phase rheology die-cast aluminum alloys are shown in Table 2. It can be seen that there is still a certain gap between the mechanical properties of rheological die-casting aluminum alloy and forging 7075 aluminum alloy. In order to meet the specific application needs of more application scenarios, the research and development of high-performance aluminum alloy materials for rheological die-casting has been carried out at home and abroad.

Table 2 Mechanical properties of some high solid phase rheology die-cast aluminum alloys

Figure 4 Applicable identification method for flow forming alloys

Table 3 Properties of some high-performance aluminum alloys used in SEED rheological die casting

Figure 5 Simulation results and experimental results obtained by testing the fitted power law model using SSR, SRS and SSS

Figure 6 Comparison of multiphase flow simulation solid phase distribution simulation and test results

Figure 7 Some high solid phase rheology die-casting aluminum alloy products

【Analysis conclusion】

High solid phase rheology die casting technology has been continuously developed and improved, and progress has been made in slurry preparation, materials, simulation, defect control, etc., and has been industrialized in automobiles, engineering machinery, communications and other fields. However, with the development of society and the advancement of science and technology, the trend of large-scale castings has begun to emerge. Large-size communication equipment shell parts and super-large car body structural parts have come out one after another, which has posed new challenges to high solid phase rheology die-casting forming. . High solid phase rheology die casting technology is involved in the manufacturing of ultra-large castings, and there are two technical paths to choose from. The first is to break through several key issues in integrated manufacturing: ① High-efficiency slurry preparation technology (single slurry mass ≥ 40 kg); ② New aluminum alloy materials with both high fluidity and excellent comprehensive properties; ③ Large casting forming process Accurate and fast simulation technology. The second is to research the welding technology of high-solid-phase rheology die-casting parts. First, high-quality small-size castings are manufactured through high-solid-phase rheology die-casting, and then welding is used to splice small parts to create oversized parts. Among them, the second technical path is easier to realize in the short term, and compared with ultra-high vacuum integrated die-casting technology, it has the advantages of lower technical difficulty and small equipment investment. It is bound to set off a wave of technology research and development and application in the next few years. Push high-solid semi-solid rheological die-casting forming technology to a new stage of development.

[Literature citation]

Lu Hongxing, Hu Xiaogang, Zhu Qiang. Research progress in aluminum alloy high solid phase rheology die casting forming technology [J]. Special Casting and Nonferrous Alloys, 2023, 43(6): 741-746.