Production Technology and Development Trend of Aluminum Alloy Automobile Sheet
Market Overview of Aluminum Alloy Automobile Sheet at Home and Abroad
Application of aluminum alloy automobile sheet in new energy automobile industry
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From January to November 2021, the sales volume of new energy vehicles in my country reached 2.99 million, a year-on-year increase of 1.7 times. The rapid development of the new energy vehicle industry is closely related to the development of technologies such as batteries, automatic control, and new materials. In the absence of major breakthroughs in battery technology, body weight reduction is still an important research topic in the new energy vehicle industry. Aluminum alloy materials have the advantages of high specific strength, corrosion resistance, and high recovery rate (1). Aluminum alloy castings have been used in engine chassis systems for a hundred years, but the development of aluminum alloy automotive panels used in body panels has been relatively slow. Before 2010, there were only a lot of applications in some high-end models (such as Audi A8). As a leading company in new energy vehicles, La Company took the lead in applying all-aluminum body, and its carbon credit management has been very effective. The commissioning of Tesla’s super factory in Shanghai has also led to the rapid development of the domestic new energy vehicle industry. The sales of new energy vehicles with all-aluminum bodies represented by Weilai were once eye-catching.
Supply Status of Aluminum Alloy Automobile Sheets
In the early days, well-known aluminum processing companies such as Alcoa, Alusuisse, and Alcan cooperated with automobile OEMs such as Leyland, Ford, and Jaguar Land Rover. Rover) to develop customized aluminum alloy automotive panels and achieve exclusive supply. With the demand for lightweight automobiles and the development of the new energy automobile industry, as well as the cost pressure of automobile OEMs, the technical requirements of aluminum alloy automobile sheets have a trend of standardization. For example, the European VDA standard has unified the technical indicators of aluminum alloy automobile sheets: currently the world’s largest aluminum alloy Auto sheet supplier Novelis will achieve a total production capacity of 1 million t/a in 2020 at its plants in North America, Europe, and Asia through new additions and mergers and acquisitions. Over the past ten years, China has invested in the construction of aluminum alloy automobile production lines. Due to market and technical constraints, mass production has only begun in recent years. In 2020, domestic aluminum alloy automobile sheet suppliers include Nanshan Aluminum, Nannan Aluminum, and Chalco Ruimin. The total production capacity of companies such as Zhongwang Group and Zhongwang Group is about 400,000 tons, and the new production capacity is expected to be 120,000 tons in 2022. At present, the production capacity of aluminum alloy automotive sheets at home and abroad is still expanding steadily, and the supply and demand have not yet reached a balanced state.
Aluminum alloy automotive sheet production technology and equipment bottlenecks
The main alloy grades of 6xxx series aluminum alloy automotive sheets include 6016, 6014, 6022, etc., which are the main aluminum alloys currently used in body outer panels. Automobile sheets have high requirements on comprehensive performance, surface quality and quality stability. The current mainstream aluminum alloy automotive sheet production process is relatively complex, including several major processes: melting and casting, soaking, machining, hot rolling, cold rolling, and continuous heat treatment. The 6xxx series aluminum alloy automotive sheet needs to have good stamping and flanging performance, natural aging resistance stability, good strength increase of baking paint, and no Luoping line on the surface of the material after stamping. In order to meet the special performance requirements of automotive panels in automotive OEMs, not only qualified cold-rolled billets are required, but also special heat treatment technology and production equipment are required. The production capacity of aluminum alloy automotive panels is mainly limited by the heat treatment technology and equipment.
Main production process
Mainstream automotive sheet production process: semi-continuous casting (direct chill casting, DC) to produce large-size slabs → sawing head and tail → sharpening surface → heating → high-temperature rolling in large wide-width hot rolling mills → coil → cold rolling Processed to the thickness of the finished product → Heat treatment with an air-cushion continuous heat treatment furnace of special heat treatment equipment for automotive panels. If it is necessary to control the microstructure and grain size of the material, an intermediate annealing process can be added in the cold rolling pass.
Heat Treatment Bottleneck Process
The air-cushion continuous heat treatment furnace is the key equipment for producing 6xxx series aluminum alloy automotive sheets. The core unit of the equipment is the air-cushion quenching heat treatment device and the pre-aging heat treatment device. The air cushion furnace equipment in the broad sense of taking other equipment also integrates a surface pretreatment device, which can be customized to remove surface oxidation of aluminum materials according to the subsequent stamping, welding, baking and other process requirements of automobile OEMs such as BMW, Volkswagen, Toyota, Honda, Tesla, etc. Layer, the surface conversion film is formed by chemical agents, and the protective oil is coated on the surface of the material. The 6xxx series aluminum alloy automotive sheet has low strength, easy scratches on the surface and high temperature sensitivity during high temperature heat treatment. The air cushion type continuous heat treatment production line has become the first choice for the heat treatment production process of automobile panels due to the advantages of good temperature control accuracy, high production efficiency, and excellent surface quality. The core unit of the equipment, the air-cushion continuous heat treatment furnace, has been monopolized by foreign companies such as EBNER. Northeastern University has carried out research on air-cushion floating technology and control systems, and is building the first domestically produced set of this type of equipment in Nanning, Guangxi. It is planned to be in August 2022. Started production at Guangxi Nannan Aluminum Processing Co., Ltd.
Discussion on cost reduction process route
In order to reduce production costs and improve efficiency, the aluminum processing industry is also exploring the feasibility of continuous casting and rolling (coutinuous casting, CC) production of aluminum alloy automotive sheets. In this method, a hot rolling mill is arranged behind the continuous casting machine, and the continuous casting slab is rolled and deformed in the hot rolling mill before being cooled below the recrystallization temperature. The United States Federal Aluminum Research confirmed that the 5754 aluminum alloy produced by the CC method can meet the requirements of automobile companies in terms of mechanical properties, corrosion resistance, welding properties, and formability. In 2017, the China Society for Metals held the “National Seminar on Thin Slab Continuous Casting and Rolling Production Technology”. The meeting focused on the exchange of my country’s thin slab continuous casting and rolling technology and thin strip casting and rolling technology. Its QSIE340TM, QStE420TM, DP600, DP780, HF1500 and other products have been applied in different models of BAIC and GAC. However, there are still many technical problems to be solved in the production of 6xxx series aluminum alloy automotive plate cold-rolled blanks by continuous casting and rolling, including microstructure uniformity control, plate shape control, surface quality control, multi-stand equipment automatic linkage control, etc. It is necessary to carry out comprehensive research and development by combining equipment, technology and materials in order to realize industrial production as soon as possible.
Low carbon aluminum alloy automotive sheet
Although the auto industry has not been directly involved in carbon trading, the construction and implementation of carbon trading is closely related to the auto industry. Vehicle companies are manufacturing companies that rely on upstream parts companies and logistics and transportation businesses, and directly connect with customers, so they need to bear greater responsibility for carbon emission reduction. OEMs will impose carbon emission quota requirements on suppliers to promote more carbon reduction in the manufacturing process of parts and components. The largest production links of carbon emissions in the aluminum industry include alumina smelting and primary aluminum electrolysis, accounting for about 9% and 88% of the total emissions, respectively. Emission reduction pathways for low-carbon electrolytic aluminum include the use of renewable energy and low-carbon electrolysis technologies. There are three ways to reduce emissions of low-carbon aluminum alloys, including using renewable energy, optimizing process equipment to reduce energy consumption, and adding recycled aluminum.
Renewable Energy Low Carbon Aluminum
China’s electrolytic aluminum production capacity has reached 48.57 million t/a, of which clean energy production capacity accounts for 20.3% of the total, and hydropower production capacity accounts for 90.1% of clean energy production capacity, mainly concentrated in Yunnan and Sichuan, which are rich in hydropower resources. Represented by Yunnan Aluminum Company, a subsidiary of Chinalco, the hydropower electrolytic aluminum production capacity exceeds 2 million t/a, and the carbon emission is as low as 3 kg CO/(kg Al). In 2021, Emirates Global Aluminum (EGA) will use solar power to produce electrolytic aluminum and supply CelestiAL green aluminum products to BMW Group, enabling BMW Group to “indirectly” reduce carbon emissions by 222,000 tons per year. In 2020, Iceland’s Century Aluminum Company (Century Aluminum) used hydropower and geothermal power to produce electrolytic aluminum and supplied 150,000 tons of Natur-Al aluminum products to Austria’s Hammerer Aluminum Company (HAI).
Carbon-free smelting technology
In May 2018, Alcoa and Rio Tinto announced a carbon-free aluminum smelting process (inert anode ElysisTM technology), with a total carbon emission of less than 4 kg CO 2 / (kg Al). In November 2017, Rusal launched the low-carbon aluminum brand “ALLOW” with a carbon emission of 2.5 kg CO 2 /(kg Al). In June 2020, RUSAL began industrial experiments with a new type of inert anode, reducing carbon emissions to a record 2 kg CO 2 /(kg Al). Norsk Hydro Aluminum plans to achieve zero emissions by 2030 through its self-developed HalZero zero-carbon electrolysis technology, carbon capture and storage (CCS) technology, and waste aluminum sorting and use technology at the consumer end. my country’s carbon anode product quality still has a large room for optimization and improvement, which can further reduce the energy consumption of electrolytic aluminum and reduce emissions.
Scrap Aluminum Recycling Recycled Automobile Board
With the increasing use of aluminum alloy automobile sheets year by year, the implementation of national carbon emission policy requirements, and the accelerated docking of the international carbon trading market, recycled aluminum alloy automobile sheets have also become a common topic for the automobile industry and aluminum processing companies to discuss. There are many studies on recycled aluminum die-casting parts for automobiles. The scrap aluminum recycled in the market is more suitable for aluminum die-casting parts that have higher requirements for pressure resistance and wear resistance because of its complex composition and high impurity content. The technology of using recycled scrap aluminum to produce die-casting parts The main problem lies in the purification of the melt.” The aluminum alloy automobile sheet used for body stamping has high requirements on comprehensive performance, so the requirements for recycled aluminum have been increased accordingly. According to the shape of the part and the stamping capacity of the material, the stamping yield of the automobile sheet blank is generally 40% ~60%, the cleanliness of stamping scraps is high, easy to collect and transport, and it is highly technically feasible to use aluminum alloy automotive panels, especially outer panels, after recycling. Higher. For market consumer waste aluminum such as cans, aluminum wires, building profiles, and other metal or non-metal waste aluminum connected to steel, it should be dismantled and classified. If necessary, it needs to be remelted, refined and filtered to remove impurities. Recycled aluminum ingots with higher purity are used in the production of aluminum alloy automotive sheets.
Conclusion
The growth of demand for aluminum in the new energy automobile industry has accelerated the development of the domestic aluminum alloy automobile sheet industry. The maturity of domestic aluminum alloy automotive sheet technology has been significantly improved, and the product quality can be compared with imported automotive sheets, and some imports have been replaced. With the expansion of new energy vehicle production capacity and the further increase in demand for aluminum materials, the aluminum processing industry needs to promote the localization of key production equipment air cushion continuous heat treatment furnaces. At the same time, under the background of carbon emission policies, it is necessary to speed up the recycling of aluminum alloy automotive sheets The R&D, trial production and verification of the company can realize the recycling of aluminum used in the body, and achieve the purpose of energy saving and emission reduction in the whole life cycle of the car.
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