All aluminum semi-finished products (plates, strips and foils) are widely used in automotive manufacturing, and in addition to these pressure processing materials, aluminum alloy stamping parts are metal materials for automotive manufacturing.In 2018, about 52 million vehicles were produced worldwide, consuming 114 million tons of materials, of which about 82% were metal materials, and 93.4 million tons were in use, of which aluminum and aluminum alloys accounted for only 6.5%, the rest are steel and cast iron, and the amount of other non-ferrous metals is very little.
6000 series aluminum alloy plate in the application of automobile manufacturing
Almost all aluminum materials have been widely used in automobile manufacturing, but the one that is used more is casting aluminum alloy, which is used to produce die-casting and casting, and there is no car that does not use aluminum and aluminum alloy casting parts. The amount of cast aluminum alloy accounts for 65% of the total amount of automotive aluminum, the total amount of semi-finished aluminum is less than 35%, of which more than 70% with the plate, and with the plate China used more than the thickness of ≤ 2mm thin plate, accounting for more than 92%.
Focus on the development of automotive aluminum alloy sheet is: 6016-S, 6016-IH, 6016-IBR, 6A16-S, 6A16-IBR, 5182-RSS, 5754, 6022, etc., typical 6XXX series aluminum alloy plate elongation A50 ≥ 25%, r value ≥ 0.60, 60d after parking yield strength Rp0.2 ≤ 140N/ mm2, baking hardening yield strength increment ≥ 80N/mm2.
Aluminum alloy plates applied in automobiles can be broadly divided into two categories: passenger car, pickup trucks, vans and other coverings with thin plates, namely ABS, all other cars such as buses, tankers with all kinds of plates, with mostly industrial general plates.
The application of 6000 series aluminum alloy sheet in the automobile
In 2018, China produced 27,809,200 vehicles and sold 28,080,600 vehicles; among them, 23,529,400 and 23,709,800 passenger cars were produced and sold; 4,279,800 and 4,370,800 commercial vehicles were produced and sold.
In 2018, about 8.6 million passenger cars in Europe and the United States used aluminum alloy sheets in the manufacture of passenger cars, and nearly 38% of passenger cars in North America used aluminum alloy engine covers; nearly more than 1.5 million passenger cars in Japan used aluminum alloy sheets. Europe and North America mostly use 6XXX series alloy plates, while Europe mostly uses 6016 alloy, while the United States prefers 6111 alloy. The consuming countries are mainly the U.S., Germany, Japan, South Korea, Canada, Switzerland, the U.K., and Italy, etc. Of the approximately 1.05 million tons of ABS consumed in 2018, the U.S. accounted for about 19.5%, Germany for about 13%, and Japan and Switzerland for 7% each.
The BMW 7 series passenger car of BMW AG in Germany has also made an enviable achievement in weight reduction, with its skeleton consisting of carbon fiber reinforced composite material (CFRP), aluminum alloy extrusion, and high strength steel (high tensile steel), which has significantly improved the overall performance of the car and reduced the net mass of the car with improved fuel efficiency due to the clever combination of these three materials.
6000 series aluminum alloy sheet metal parts for automobiles
6000 series alloys are the most popular aluminum alloys for automotive sheet metal parts in the current automotive industry. They have the forming performance, high strength performance, corrosion resistance, edge folding, high surface performance, etc. At the same time, after painting and baking, the strength performance is also improved.
Replacing the steel plate with aluminum alloy plate in the interior and exterior of the car can reduce the body by 40%~50%, which in turn reduces the net mass of the whole car by about 10%. Ford Model T, Ford Prodigy, FORD T-150 pickup truck, Jaguar XJ, Ferrari 360, Chrysler Prowler, Volkswagen 31 Lupo, Audi A2, A8, Honda hybrid sedan (the Honda Insight), Honda NSX, Teste-Model, S, etc. all use aluminum body The body is made of aluminum. ABS is also used to make hoods and trunk lids, and many more.
Properties of typical sheet alloys
6016 alloy is widely used in ABS, but the heat treatment process is complex and pre-aging treatment T4P between solution treatment and baking treatment is required to obtain good performance. Because of the good forming properties before stamping and the rapid increase in strength during the baking process after stamping, which results in high dent resistance, 6016 alloy sheet can take into account both requirements after solution-T4P-painting treatment, but the process parameters have a great impact on the final performance, insufficient solution treatment reduces the precipitation power of T4P and artificial aging during the baking process, and long holding time may lead to Low humidity of pre-aging reduces the performance stability of the plate placement process and the hardening effect of the baking process, and the high temperature affects the forming performance of the stamping process. This shows that the solid solution and T4P process parameters should be optimized in order to obtain the ideal overall performance.
The strength of the plate is mainly affected by the solid solution strengthening, pre-aging and natural aging strengthening: the solid solution treatment solidifies the soluble phase into the α(Al) matrix to produce solid solution strengthening, while the subsequent T4P process, the supersaturated solute atoms will form aging precipitation The size, number and morphology of these phases are dependent on the pre-aging temperature. On the one hand, aging reduces the degree of matrix supersaturation and weakens the solid solution strengthening effect. On the other hand, the pre-aging precipitated phases produce strengthening effect and increase the strength of the plate; the strengthening effect of natural aging increases monotonically with time and stabilizes after reaching time.
Zhang Zedong and other experts' research results show that: 6016 alloy plate in 560 ℃ / 1min solid solution treatment can obtain good results, continue to extend the holding time is not conducive to performance; comprehensive consideration of 6016 automotive plate performance requirements of the industrial production of oil coating process, determine the 6016 alloy ABS solid solution - pre-aging process: 560 ℃ / 1min + 80 ℃ / 6h ("Light alloy processing Technology" 2019, no. 2, pp. 28-32.)
Application of 5000 series aluminum alloy sheet in automobile manufacturing
There are two kinds of 5XXX series alloys in aluminum alloy sheet for automobile: 5754 and 5182-RSS, besides these two alloys, there are also 5022, 5023, 5454, 5154, 5083 and other alloys used.
Mg has the second highest solubility in aluminum after zinc, with an ultimate solubility of 17.4% at 450°C and only 1% at room temperature. In theory Al-Mg alloys should have strong age-hardening effect, but due to the limitation of the tendency of precipitation along the crystal and dispersion of β-phase, this effect cannot be utilized, and they are mostly used in annealed O state or cold work-hardened state H.
The precipitation process of supersaturated solid solution α' of Al-Mg alloy.
α' → GP zone → β' → β(Al8Mg5)
Mg atomic diameter (0.320nm) is much larger than that of Al (0.286nm), although the GP zone can be formed within a few seconds after quenching, but the size is small (1.0nm~1.5nm), surrounded by a dense vacancy cloud, and almost no co-grid strain occurs with the parent phase, so the Mg content ≤ (5%~7%) of the alloy has no obvious age-hardening effect. After a few years, the GP zone can grow to 10 nm, and although there is a large strengthening effect, there is a strong fracture characteristic along the crystal, and the plasticity is sharply reduced to only about 1.5%, which has no practical value.
To Al-Mg alloy plus Mn or Cr, mainly to improve corrosion resistance and weldability, but the solid solution that part of the strengthening effect. ti and V are grain refinement agent, also has the effect of improving the strength and weldability. be can prevent the melt casting and welding oxidation tendency, especially the high magnesium alloy is particularly needed. Trace Sb or Bi mainly to prevent the high Mg alloy "sodium brittle" phenomenon. cu, Zn, Fe, Si is impurities, should be strictly limited, but Si can improve the weldability, so 5A03 alloy contains 0.50% Si ~ 0.80% Si.
Because Al-Mg alloy has only slight age-hardening effect and strong tendency to precipitate along the crystal, it can only work in annealed (300℃~380℃) or cold work-hardened condition, but their corrosion resistance can only be shown if the β-phase is uniformly distributed along the grain boundary within the grain, and the distribution pattern is also strongly influenced by the Mg content. The results of a series of studies show that the stability of alloys with Mg content ≤ 3%, either in the annealed or cold work-hardened state, and heated for a long time at room temperature or sensitization treatment temperature (67°C~177°C), do not form along the crystalline β-phase network film and are not sensitive to stress corrosion cracking (SCC) and spalling corrosion, but after Mg content > 3.5%, especially after cold work-hardening, with the increase of Mg content (≥ 5% Mg), the susceptibility to SCC also increases strongly, and even after long storage at room temperature (20a~30a), a continuous β-phase mesh film can be formed along the grain boundaries. Because the high Mg content (>6%~7%) alloy even in 315℃~330℃ fully annealed, α solid solution can not be decomposed, still in supersaturated state, so the organization is very unstable.
To solve the high magnesium alloy organization performance stability of two ways: one is annealed for large cold deformation (ε = 30% ~ 50%), increase the dislocation density or β-phase nucleation point, and in 200 ℃ above the precipitation treatment, promote the decomposition of solid solution and β-phase uniform decomposition; another way is to reduce the magnesium content ≤ 3%, and add the appropriate amount can improve the strength and recrystallization temperature of Mn and Cr, can also avoid β-phase along the crystal precipitation, get the strength equivalent to the high magnesium content, the United States 5454 alloy (2.7% Mg, 0.7% Mn, 0.12% Cr) can get the same strength as Al-4Mg alloy without SCC and EFC sensitivity, but this method can not make the strength of Al-Mg alloy has greatly improved.
Properties of Alloy 5454
Chemical composition of 5454 alloy (mass %): 0.25Si, 0.40Fe, 0.10Cu, (0.50~1.0)Mn, (2.4~3.0)Mg, (0.05~0.20)Cr, 0.25Zn00.20Ti, other impurities individual 0.05, total 0.15, rest Al.
The shear strength of the plate is about 55% of the tensile strength Rm, and its compressive Rp0.2 is almost equal to the tensile yield strength. The alloy has an elastic modulus of 69.6GN/mm2 and a compressive elastic modulus of 71.0GN/mm2, and a density of 2.680g/cm3 at 20°C. The liquid phase line temperature is 646°C, and the due phase line temperature is 602°C.
The coefficient of linear expansion of the alloy is as follows.
- -50℃~20℃21.9μm/(m.k)
- 20℃~100℃23.7μm/(m.k)
- 20℃~200℃24.6μm/(m.k)
- 20℃~300℃25.6μm/(m.k)
The coefficient of bulk expansion at 20℃ 68×10-6m3/(m3.k); the specific heat capacity at 20℃ 900J/(kg.K); the thermal conductivity at 20℃ 134W/(m.k); the average isovolumetric conductivity of the material at 20℃ is 34%IACS; at 20℃, the average resistivity of the state material is 51nΩ.m and the resistance temperature coefficient is 0.1nΩ.m; at 25℃ containing 53g NaCl and 3g H2O2T per L of aqueous solution, the potential of -0.86V for 0.1N glycerol electrode; annealing temperature of 343°C, no insulation required; thermal processing temperature of 260°C ~ 510°C.
Properties of 5083 alloy
5083 alloy is a typical 5XXX series alloy, is also a typical automotive sheet metal alloy, there are the weldability performance, corrosion resistance, processing and forming properties and low temperature performance, in the Al-Mg system alloy, it has a medium strength performance, welded joint strength can be equal to the annealed state of the base material, and a reliable corrosion resistance, the alloy's mechanical properties are balanced with the temperature drop and rise, fracture toughness is also so, is a good automotive coverings alloy, especially suitable for commercial vehicles, special cars, semi-trailers and other internal and external welded sheet metal structural properties.
5083 alloy characteristics: not heat treatment strengthening; to prevent "aging softening" and stabilization of corrosion resistance, semi-finished products need to be stabilized; to prevent repeated annealing yield strength reduction, the final cold deformation should be > 50%.
The composition of the alloy (mass %): Mg4.0~4.9, Mn0.4~1.0, Cr0.05~0.25, Si0.40, F0.40, Zn0.25, Ti0.15, other impurities individual 0.05, total 0.15, Al remaining. The main phase composition of the alloy: α(Al), β(Al8Mg5), AlMn, Al7Cr, possible impurity phases are Mg2Si, Al3Fe, Al3Ti, Al6(Fe, Mn).
Mg is the main strengthening element, producing solid solution strengthening and increasing the work hardening rate of the alloy. the solid solution degree of Mg in aluminum changes greatly with temperature, but the precipitation transition phase β'(Al8Mg5) does not co-grid with the matrix, so there is no obvious precipitation hardening effect. the Al8Mg5 phase tends to precipitate slowly on the slip zone and grain boundaries, reducing the solid solution strengthening effect, and under corrosive conditions causes Intergranular corrosion and stress corrosion cracking, so after cold working should be stabilized annealing, in order to promote the uniform precipitation of β-phase in the grain and grain boundaries, stabilizing the mechanical properties and corrosion resistance of the alloy.
Manganese and chromium improve the recrystallization temperature of the alloy and have a complementary strengthening effect, titanium can refine the casting organization and weld organization, iron, silicon, zinc as impurities.
The density of 5083 alloy 2.66g/cm3; melting temperature range 574℃~638℃; specific heat capacity 900J/(kg.k); thermal conductivity 120W/(m.k) at 20℃; body expansion coefficient 70×10-6m3/(m3.k) at 20℃; average linear expansion coefficient is as follows.
- -50℃~20℃22.3μm/(m.k)
- 20℃~100℃24.2μm/(m.k)
- 20℃~200℃25.0μm/(m.k)
- 20℃~300℃26.0μm/(m.k)
The positive elastic modulus of 5083 alloy is 71.0 GN/mm2 and the shear elastic modulus is 26.4 GN/mm2.
Electrical properties of 5083 alloy at 20℃: conductivity (isoelectric product) 32% IACS; resistivity 54nΩ.m at 20℃; resistance temperature coefficient 0.1nΩ.m/K at 20℃; potential of -0.86V for 0.1N glycol electrode in aqueous solution containing 53g NaCl with 3g H2O3 per liter at 25℃.
The annealing temperature of 5083 alloy sheet is 343℃ without holding, and the hot rolling temperature is 260℃~510℃.
Stress corrosion cracking resistance of 5XXX series alloys for automobiles
5XXX alloy sheet for automotive use requires not only high strength performance, good weldability, and considerable resistance to stress corrosion cracking in corrosive environments. Thick 1mm 5XXX series of automotive sheet by the Aluminum Association of America Inc. (AA) the standard of its stress corrosion cracking resistance is shown in Table 1. ◎ said in the more severe conditions will not damage; △ said in some conditions may break; ○ said in severe conditions may produce cracks; X said in the relaxed conditions will also be cracked.
It is desirable to phase out diesel vehicles or increase the rate of aluminization
A study published in the United States on February 26 points out that, according to a study by the U.S. NGO International Council on Clean Transportation (ICCT) and two universities, 11 percent of the 3.4 million premature deaths each year due to PM2.5 and ground-level ozone are related to the global transportation industry, and the medical burden caused by traffic pollution (often associated with heart and lung disease, stroke and diabetes) reached $1 trillion dollars.
In the United States 22,000 people died from traffic pollution, 43% of which were diesel-related; 74,000 people died prematurely from vehicle exhaust in India, 13,000 in Germany, 7,800 in Italy and 6,400 in France. However, the situation is worse in Germany, as 17 out of every 100,000 inhabitants in the country die prematurely due to traffic pollution, a rate three times the global average.
This shows that the impact of vehicle emissions on human health must not be ignored, highlighting the need to actively comply with and enforce class emission standards, and the urgency of increasing the amount of aluminum used to reduce its own mass and expand new energy vehicles.
ABS production lines in China
By 2018, there were seven ABS (Auto-Body-Sheet) lines completed and under construction in China, including six in operation with a production capacity of 523 kt/a and one under construction with a production capacity of 100 kt/a (see Table 2).ABS production is key and equipped in a continuous production line consisting of more than 20 processes such as air cushion furnace treatment with its subsequent pure stretch straightening, pre-aging, and surface treatment. The single-layer arrangement can exceed 600m in length, and the double-layer arrangement is more than 300m.
China's first ABS production line - Nobelis (China) Aluminum Products Co., Ltd. is located in Changzhou National High-Tech Development Zone, Jiangsu Province, covering an area of 4,320km2, with an investment of USD 100 million, which was put into operation on October 21, 2014. on May 22, 2018 the company announced another investment of USD 180 million for a new an air cushion continuous production line to increase ABS production capacity by 100kt/a, which will be put into operation in 2020.
Neither Nobelis (China) Aluminum Products Co., Ltd. nor Shinko Automotive Aluminum (Tianjin) Co., Ltd. produce upstream products, with the former's cold-rolled strip coils coming from South Korea and the latter's cold-rolled strip coils coming from Japan's Mamioka Rolling Mill.
China Aili International (Zhenjiang) Aluminum Co., Ltd., Henan Tongren Aluminum Co., Ltd. and Henan Zhongfu Industrial Co., Ltd. have all made plans to build ABS production lines and will start construction as soon as the market allows. In addition, Nanshan Group Light Alloy Company has a more spectacular plan, with the first phase now completed and the second and third phases to be built at an opportune time, all of which will have a production capacity of 600kt/a, thus becoming a large ABS project.
Among the four types of flat rolled aluminum products produced today (pre-stretched thick plate, ABS, can body and lid material, PS and CTP plate base), the first two are more difficult to produce, with higher technical level requirements and higher added value.
Conclusion
Automotive aluminum alloy plate is a huge family, except for passenger car coverings mainly with 5XXX series and 6XXX series alloys, other aluminum materials are also applied.
This paper briefly introduces the implementation of aluminum alloys for automotive sheet metal parts. China has just started to manufacture passenger car sheet metal parts with aluminum alloys, and the gap with foreign countries is very big, and this gap is manifested in two aspects: firstly, the aluminization rate of automobiles is low, and according to the author's investigation and estimation, the aluminization rate of Chinese automobiles in 2018 may be less than 125kg/vehicle, which is too different from 165kg/vehicle in industrial developed countries; secondly, in The gap between the development of new automotive aluminum alloys and the use of scrap aluminum is a bit larger, for example, Nobelis Aluminum Company every three or four years to launch a new alloy, it launched the Advanz 7000 series of products with the current use of aluminum alloy compared to double the strength; it is special in the use of scrap aluminum production ABS automotive sheet, they plan to reach 80% of the scrap aluminum content in automotive sheet in 2020, which But a class of products.
China's aluminum processing industry and auto manufacturing industry should vigorously promote the application of aluminum in automobiles to bring the amount of aluminum used in automobiles to a higher level.