Aluminum alloy sheet processing method
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- HITACHI HIGH TECH CORP
- Filing Date
- 2021-10-12
- Publication Date
- 2026-08-03
Smart Images
Figure 0007898840000001 
Figure 0007898840000002 
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for processing aluminum alloy plates.
Background Art
[0002] Aluminum (aluminum alloy) plates are effective as lightweight alternatives to steel plate products and are used, for example, as automotive parts. Press product applications of aluminum plates include outer plate products such as hoods, trunks, fenders, and doors. In addition, in-vehicle interior product applications of aluminum plates include heat exchanger members (radiators, etc.) around the engine and heat insulators for heat dissipation. Other than these, aluminum plates are not widely adopted for interior product applications. Aluminum plates are significantly inferior in formability compared to steel plates, and in order to obtain the same rigidity, it is required to increase the plate thickness considerably.
[0003] In addition, as products made of aluminum alloy, engine-related parts (aluminum castings) and cases for control and function integration (aluminum die-castings) can be mentioned. These are formed by pouring molten aluminum into a mold and are good at integral molding with complex shapes. The aluminum alloy used is a 4000-series Al-Si material, and the required material properties are different from those of the rolling materials (1000-series, 2000-series, 3000-series, 5000-series, 6000-series, 7000-series) used for processing. In casting aluminum alloys, the fluidity of the molten metal is important and is characterized by a high Si content. Representative examples of casting alloys are AC4A, and ADC12 as a die-casting alloy. Casting technology is excellent in mass productivity regardless of the size of the product. However, there are problems such as issues caused by being a die-cast product (ADC12) or a casting product (internal material defects: shrinkage cavities, etc., dimensional accuracy: machining required), and deterioration of corrosion resistance due to the addition of Cu in the aluminum alloy (to ensure strength).
[0004] On the other hand, in the automotive industry, electric vehicles (PHEV (Plug-in Hybrid Electric Vehicle), E From the perspectives of electric vehicles (V), autonomous driving (equipped with various sensors), and ensuring safety, the lightweighting of the entire vehicle through multi-material construction is being promoted. Furthermore, in recent years, the promotion of carbon neutrality has been demanded, making the inherent properties of the materials themselves important. In other words, it is important whether new metals that consume a large amount of electricity in their manufacture are used as materials, or whether recycled materials that do not consume a large amount of electricity are used. In the case of steel plates, which make up the majority of the vehicle's weight, the adoption of hot stamping technology is becoming increasingly prominent in addition to conventional pressing (cold working) technology. Hot stamping technology is being applied particularly to structural components for cabins (ultra-high-tensile steel plates) for occupant protection. However, while hot stamping technology for aluminum alloy plates is recognized as a prototype at exhibitions, none of them are envisioned for practical use. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2008-92895 [Patent Document 2] Japanese Patent Publication No. 2016-211999 [Patent Document 3] Patent No. 5681631 [Patent Document 4] Japanese Patent Application Publication No. 9-78210 [Patent Document 5] Patent Application No. 2002-80887 [Patent Document 6] Japanese Patent Application Publication No. 9-78210 [Patent Document 7] Japanese Patent Application No. Hei 6-203720 [Overview of the project] [Problems that the invention aims to solve]
[0006] In recent global circumstances, there is a growing demand for carbon-free solutions to combat global warming. Many components require significant energy during the raw material, material, and processing stages. CO2 emissions vary depending on the type of power generation (thermal, hydroelectric, nuclear, solar / wind, etc.), but in the future (after 2050), the use of renewable energy is desirable, and a shift away from fossil fuels will be crucial for carbon-free production. That said, for the time being, promoting recycling and reuse, which are effective in reducing CO2 emissions from raw materials, as well as reducing the use of fossil fuels in manufacturing processes and shortening processing and heat treatment times in component manufacturing, are required.
[0007] Aluminum materials produced in Japan largely utilize imported new aluminum ingots (7V ingots: 99.7% Al) to create materials (composition, strength, etc.) that meet customer needs. Among these, beverage can materials and die-cast material ADC12 are products that are successfully recycled. While other application materials are also recycled without waste, the high proportion of new ingots used means that further improvement efforts are needed to reduce CO2 emissions.
[0008] Incidentally, considering the role of aluminum materials in recent carbon neutrality (2050 target), new aluminum ingots are manufactured using enormous amounts of energy, resulting in significant CO2 emissions. Therefore, it is desirable to reduce the use of new aluminum ingots. Promoting the recycling or reuse of aluminum products is extremely important. Reusing aluminum products requires only about 3% of the energy required for new ingot production, thus contributing to energy conservation, as well as LCA (Life-Cycle Assessment). And it is effective for future carbon neutrality.
[0009] In this context, the electrification of automobiles (especially EVs (Electric Vehicles) and FCVs (Fuel Cell Vehicles)) is predicted to expand rapidly from 2030 onwards. On the other hand, engine-powered vehicles The number of vehicles equipped with engines is expected to decrease drastically. Many engine parts in engine-equipped vehicles are made of cast aluminum, and the future challenges lie in finding a place for the cast aluminum (cast aluminum alloy) that comes from scrapped engine-equipped vehicles (its uses and processing methods). In particular, cast aluminum is mainly 4000 series aluminum alloy with a high Si content (for example, 5% or more by weight), making it difficult to convert to wrought alloys (1000 series, 2000 series, 3000 series, 5000 series, 6000 series, 7000 series aluminum alloys). If it is between wrought alloys, it is easy to convert back to the same type of wrought alloy (composition adjustment: scrap and a small amount of new metal). When converting cast material back to wrought material, a method of diluting the Si content with a large amount of new metal and wrought material scrap can be considered, but the CO2 reduction effect is small. It is desirable that cast aluminum can be used as a wrought alloy without using a large amount of new metal.
[0010] The present invention aims to provide a hot stamping technology for aluminum alloy sheet materials containing Si. [Means for solving the problem]
[0011] To solve the above problems, the following measures will be taken. That is, the first aspect is, A heating process in which an aluminum alloy plate made from an aluminum alloy containing 5% or more but less than 11% Si by weight is held at a temperature of 350°C or more but less than 580°C for a period of 10 minutes or less, The process includes supplying the aluminum alloy sheet to a mold and press-forming it, and cooling the aluminum alloy sheet to 100°C or below at the bottom dead center of the press-forming process, The thickness of the aluminum alloy plate is 1.5 mm or more and less than 5 mm. This is a method for processing aluminum alloy sheets. [Effects of the Invention]
[0012] According to the present invention, a hot stamping technology for aluminum alloy sheet materials containing Si can be provided. [Brief explanation of the drawing]
[0013] [Figure 1] FIG. 1 is a diagram showing a configuration example of a die of a press working apparatus. [Figure 2] FIG. 2 is a diagram showing examples of a cooling water channel 150 and a thermocouple installation hole 160 provided in a lower die set 122 of a die 100. [Figure 3] FIG. 3 is a diagram showing a configuration example of a die of a press working apparatus. [Figure 4] [[ID=1十一]]FIG. 4 is a diagram showing an example of an operation flow of a hot stamping method for an aluminum alloy plate. [Figure 5] FIG. 5 is a diagram showing the strength and formability of a 4000 - series aluminum alloy plate and a 6000 - series aluminum alloy plate. [Figure 6] FIG. 6 is a diagram showing an example of strength characteristics by aging treatment of a 4000 - series aluminum alloy plate and a 6000 - series aluminum alloy plate. [Figure 7] FIG. 7 is a diagram showing an example of strength characteristics of a 4000 - series aluminum alloy plate by short - time baking treatment.
MODE FOR CARRYING OUT THE INVENTION
[0014] Hereinafter, embodiments will be described with reference to the drawings. The configuration of the embodiments is illustrative, and the configuration of the invention is not limited to the specific configuration of the disclosed embodiments. In carrying out the invention, a specific configuration according to the embodiments may be appropriately adopted.
[0015] 〔Embodiment〕 (Configuration example) Figure 1 shows an example of the configuration of a die for a press forming machine. The die 100 includes an upper die 110 and a lower die 120. The upper die 110 includes an upper die set 111, an upper die wrinkle holder 112, and a punch 113. The lower die 120 includes a lower die wrinkle holder 121 and a lower die set 122. Here, Figure 1 is a view of the die 100 from the front. In Figure 1, the direction from left to right is the x-direction, the direction from the front to the back of the paper (the direction from the front to the back of the die 100) is the y-direction, and the direction from bottom to top (the direction from the lower die set 122 to the upper die set 111) is the z-direction. The upper die set 111 and the lower die set 122 are fixed to the press forming machine. The upper die wrinkle holder 112 and the punch 113 are fixed to the upper die set 111. The punch 113 deforms the aluminum alloy plate 200 to be processed into a predetermined shape. The shape of the tip of the punch 113 (on the lower die 120 side) can be, for example, a cone shape, a columnar shape, or any other shape. The upper die wrinkle-holding part 112 and the lower die wrinkle-holding part 121 suppress the formation of wrinkles in the aluminum alloy plate 200 to be processed. The lower die wrinkle-holding part 121 is fixed to the lower die set. The lower die 120 is positioned opposite the upper die 110. The aluminum alloy plate (test material) 200 to be processed is set on top of the lower die wrinkle-holding part 121. The upper die set 111 has a thermocouple mounting hole 140 for installing a thermocouple 310. The lower die set 122 also has a cooling water channel 150 for flowing a cooling refrigerant and a thermocouple mounting hole 160 for installing a thermocouple 320. The cooling water channel 150 is provided with an inlet and an outlet. A coolant such as water is introduced from the inlet to cool the mold 100 and discharged from the outlet. Thermocouples 310 and 320 are installed in thermocouple mounting holes 140 and 160, respectively, to measure the temperature of the mold 100. The material of the mold 100 is, for example, steel (tool steel, high-speed steel, superhard steel, etc.). A wrinkle-holding control mechanism to suppress shrinkage flange deformation is not required here. The configuration of the mold 100 is not limited to that described herein.
[0016] The upper die 110 (or lower die 120) reciprocates vertically between its top dead center and bottom dead center due to the operation of the press working device, causing the upper die 110 and lower die 120 to move closer together and further apart. When the upper die 110 and lower die 120 approach each other, the punch 113 is pressed against the aluminum alloy plate 200, causing the aluminum alloy plate 200 to deform and thus undergo press working. The press working device is also equipped with a mold spray sprayer that sprays water or a water-soluble lubricant in mist form towards the upper die 110 and lower die 120 of the mold 100. The sprayer sprays a predetermined amount of mist-like water or water-soluble lubricant onto the upper mold 110 and the lower mold 120 before the aluminum alloy plate to be processed is set into the mold 100.
[0017] In deep drawing (shrink flange deformation), the die 100 typically has a wrinkle-pressing control mechanism that controls the pressing of a wrinkle-pressing mechanism against the aluminum alloy sheet 200 using a spring or the like. However, when a wrinkle-pressing control mechanism is used, the aluminum alloy sheet 200 and the wrinkle-pressing control mechanism may come into contact during press working, lowering the temperature of the aluminum alloy sheet 200 and leading to a decrease in formability. In this case, the wrinkle-pressing control mechanism is not used. That is, the contact area of the wrinkle-pressing portion 121 of the lower die 120 is minimized as much as possible, and a receiving shape for the punch 113 exists on the lower die 120.
[0018] As the material for the mold 100, for example, aluminum alloys (e.g., 5000 series, 7000 series), tool steel (e.g., SKD61, etc.), high-speed steel, or cemented carbide can be used. 5000 series aluminum alloys are cost-effective. 7000 series aluminum alloys are strong. The material for the mold 100 can be selected according to the required characteristics of the processed product. Aluminum alloys, tool steels, high-speed steel, and cemented carbide may be used only on the surface layer (processed surface) of the mold 100. The surface of the mold 100 may be left as a polished surface, but in order to prevent adhesion of the aluminum alloy plate 200, it is desirable to apply a high-hardness plating process such as chromium plating or nickel plating to form a coating on the surface of the mold 100 that has a low coefficient of friction. For example, electroless nickel plating with a film thickness of 5-10 μm is desirable. Methods for plating the mold 100 include electrolytic, electroless, and thermal spraying, and the appropriate method can be selected depending on the size of the mold 100. The mold 100 is an example of a steel mold. Steel materials such as tool steel, high-speed steel, and cemented carbide have lower thermal conductivity compared to aluminum alloys, but are easy to process and low-cost.
[0019] In addition, a spray dispenser for aluminum alloy sheets is provided near the press working equipment. The spray dispenser for aluminum alloy sheets sprays a predetermined amount of mist-like water or water-soluble lubricant onto the aluminum alloy sheet (molded product) after press working.
[0020] Figure 2 shows an example of a cooling water channel 150 and thermocouple mounting holes 160 provided in the lower die set 122 of the mold 100. The lower die set 122 has a rectangular parallelepiped shape. The cooling water channel 150 has a first part 151, a second part 152, and a third part 153.
[0021] In the example shown in Figure 2, the inlet and outlet of the cooling water channel 150 and the thermocouple input port are provided on the right side of the lower die set 122. The first part 151 of the cooling water channel 150 is a cylindrical channel extending parallel to the x-direction from the inlet. The second part 152 of the cooling water channel 150 is a cylindrical channel extending parallel to the y-direction, connected to the end of the first part 151 opposite to the inlet end. The third part 153 of the cooling water channel 150 is a cylindrical channel extending parallel to the x-direction to the outlet, connected to the end of the second part 152 opposite to the end connecting to the first part 151. For example, hoses or pipes can be connected to the inlet and outlet of the cooling water channel 150. A coolant such as water is introduced into the cooling water channel 150 from the inlet, passes through the first section 151, the second section 152, and the third section 153, and is discharged from the outlet, thereby cooling the lower die set 122. For example, hoses or pipes are connected to the inlet and outlet of the cooling water channel 150. As the lower die set 122 is cooled, the lower die 120, including the lower die wrinkle-holding section 121, is also cooled. The upper die 110, which comes into contact with the lower die 120 during pressing, can also be cooled. The diameter of the cooling water channel 150 is, for example, 10 mm when the thickness (length in the z direction) of the lower die set 122 is 50 mm.
[0022] The thermocouple mounting hole 160 is a cylindrical hole that extends parallel to the x-direction from the thermocouple insertion opening provided on the right side of the lower die set 122. It extends to near the center of 122. The thermocouple 320 is inserted into the thermocouple mounting hole 160 from the thermocouple insertion port. The temperature sensing junction (the part that measures temperature) of the thermocouple 320 is positioned near the center of the lower die set 122 within the thermocouple mounting hole 160. The thermocouple 320 inserted into the thermocouple mounting hole 160 allows the temperature of the lower die set 122 of the mold 100 to be measured.
[0023] The shapes of the cooling water channels 150 and thermocouple mounting holes 160 are not limited to those described herein and can be appropriately modified to suit the shape of the mold 100, etc. Multiple cooling water channels may also be provided. Furthermore, multiple thermocouple mounting holes may be provided, allowing temperature measurement at multiple locations. The thermocouple mounting holes 160 and thermocouple 310 provided in the upper die set 111 are the same as those provided in the lower die set 122. Instead of thermocouples 310 and 320, a thermistor, resistance thermometer, thermal camera, etc., may be used to measure the temperature of the mold 100. The cooling water channels 150 allow refrigerant to flow, cooling the mold 100 and the aluminum alloy plate 200 set in the mold 100.
[0024] Figure 3 shows an example of the configuration of a die for a press working machine. In the die 100 of Figure 3, the upper die set 111 is provided with a cooling water channel 130 similar to the cooling water channel 150 of the lower die set 122. The other configurations of the die 100 of Figure 3 are the same as those of the die 100 of Figure 1. By providing cooling water channels in the upper die set 111 and the lower die set 122, the die 100 can be cooled more effectively. The amount of refrigerant flowing through the cooling water channel 130 is the same as the amount of refrigerant flowing through the cooling water channel 150.
[0025] (Manufacturing method for aluminum alloy sheets) Here, we will describe the method for manufacturing the aluminum alloy sheet used in the hot stamping method of this embodiment. The aluminum alloy sheet used here is made from, for example, scrap of castings (cast products) made of 4000 series aluminum alloy. Castings of aluminum alloy are made by pouring molten aluminum alloy at high temperature into the cavity of a mold and letting it cool and solidify.
[0026] 4000 series aluminum alloys (Al-Si alloys) are aluminum alloys to which silicon (Si) is mainly added. The 4000 series aluminum alloy used here is, for example, an aluminum alloy containing 5% to less than 11% Si by weight. Aluminum alloys containing less than 5% Si exhibit less precipitation hardening due to Al-Mg-Si and Al-Cu-Mg-Si systems, in addition to solid solution strengthening from the Si-added component. Aluminum alloys containing 11% or more Si have low rollability and are prone to edge cracking and rolling fracture. Therefore, aluminum alloys containing 5% to less than 11% Si are preferred in terms of rollability and strength characteristics when made into aluminum alloy sheets. Furthermore, the 4000 series aluminum alloy used here may also be, for example, an aluminum alloy containing 5% to less than 11% Si, less than 0.6% Mn, less than 0.6% Mg, and less than 2.0% Cu by weight. Furthermore, the 4000 series aluminum alloy used here may be, for example, an aluminum alloy containing, by weight, 5% to less than 11% Si, 0.2% to less than 0.6% Mn, 0.2% to less than 0.6% Mg, and 0.05% to less than 2.0% Cu. Mn and Mg contribute to improving the strength of the aluminum alloy. If the amount of Mn or Mg is less than 0.2%, the effect of improving strength is small. If the amount of Mn or Mg is 0.6% or more, the formation of Al-Mn, Al-Fe-Mn-Mg compounds and macrocompounds is promoted, and crack initiation during processing is accelerated. Therefore, Mn of 0.2% to less than 0.6% and Mg of 0.2% to less than 0.6% are preferred. Cu is an element that is particularly effective in improving strength. With less than 0.05% Cu, the effect of improving strength is small. With 2.0% or more Cu, a decrease in corrosion resistance, excessive acceleration of crack susceptibility, and delayed fracture after forming occur. Therefore, Cu content of 0.05% or more and less than 2.0% is preferred. 4000 series aluminum alloys are However, this is not limited to the above. Each aluminum alloy may contain elements other than those listed herein. For example, Fe, Zn, Ti, etc., may be included. Fe, Zn, Ti, etc., are acceptable as long as they do not adversely affect formability. For example, Fe should be less than 0.3% to prevent a decrease in formability due to the formation of large Al-Fe compounds. Zn should be less than 0.5% to suppress precipitation hardening due to Al-Zn-Mg precipitates and prevent stress corrosion cracking. Ti should be less than 0.10% to reduce the nucleation of large compounds. JIS composition standards for castings made of aluminum alloys range from AC1B to AC9B depending on the application. These are examples of 4000 series aluminum alloys.
[0027] Slabs are produced by melting and casting the raw material aluminum alloy (for example, a cast product made from 4000 series aluminum alloy). During this process, degassing and inclusion removal treatments are performed. Degassing treatment removes hydrogen gas and other gases contained in the molten aluminum alloy. Inclusion removal treatment removes inclusions such as oxides, carbides, and nitrides contained in the molten metal. If inclusions are present in the molten metal, problems such as deterioration of castability can occur. Furthermore, segregation removal treatment is performed on the cast slab. Segregation removal treatment removes heterogeneous segregated areas that occur during casting from the slab. In addition, a quantity of less than 100 ppm of P or Na may be added during casting. The addition of P or Na refines the microstructure of the aluminum alloy cast.
[0028] Next, the slab that has undergone segregation removal treatment is subjected to homogenization heat treatment at a temperature of 400°C to less than 530°C. Homogenization heat treatment is a process that eliminates the non-uniform distribution of atoms in the slab obtained by casting. Homogenization heat treatment at temperatures below 400°C leaves the cast structure intact, leading to edge cracking during hot rolling and reduced formability during cold rolling. Homogenization heat treatment at temperatures above 530°C causes burning on the slab surface and surface defects such as charring on the aluminum alloy sheet surface. Therefore, it is preferable to perform the homogenization heat treatment at a temperature of 400°C to less than 530°C. Furthermore, the slab that has undergone homogenization heat treatment is subjected to hot rolling to become a hot coil with a sheet thickness of 2 mm to less than 8 mm. The hot coil is made by winding the aluminum alloy sheet produced by the hot rolling process into a coil shape. In this case, the winding temperature is set to 300°C to less than 400°C. Plate thicknesses of less than 2 mm can cause friction between the inner and outer surfaces during winding, leading to the formation of defects. Plate thicknesses of 8 mm or more can cause defects due to loosening during winding. Therefore, it is preferable that the plate thickness of the hot coil be between 2 mm and 8 mm. Furthermore, at winding temperatures below 300°C, recrystallization is insufficient. At winding temperatures of 400°C or higher, solid solution strengthening increases, resulting in a change in deformation resistance. An inappropriate winding temperature can lead to a change in deformation resistance and cause defects. Therefore, it is preferable that the winding temperature be between 300°C and 400°C.
[0029] After this, roughening is performed at a temperature of 300°C to less than 400°C, and then aluminum alloy sheets with a thickness of 1.5 mm to less than 5 mm are produced by cold rolling. Cold rolling is performed, for example, at room temperature (for example, 0°C to less than 150°C). Cold rolling is performed at a lower temperature than hot rolling. Roughening helps prevent edge cracking during cold rolling. Roughening is appropriately performed at a temperature of 300°C to less than 400°C to soften the aluminum alloy sheet. For example, if the hot rolling temperature exceeds 300°C, roughening may not be performed. After cold rolling, finish annealing and distortion correction may be performed at a temperature of 330°C to less than 400°C. Performing finish annealing at 330°C to less than 400°C stabilizes the strength of the aluminum alloy sheet and reduces residual stress.
[0030] (Example of operation) Figure 4 shows an example of the operation flow of a hot stamping method for aluminum alloy sheets. The aluminum alloy sheet is a sheet of aluminum alloy to be processed. For example, the aluminum alloy sheet is a 4000 series aluminum alloy sheet manufactured by the method described above. The aluminum alloy sheet is processed into cut sheets of an appropriate size for press working. Here, a die 100 is set in the press working apparatus, and a coolant is flowing through the cooling water channel 150 of the die 100. It is assumed that the cooling water channel 150 is supplied with water as coolant at a rate of 3 L / min to 15 L / min. If the die 100 is made of aluminum alloy, for example, a supply rate of 3 L / min to 10 L / min is appropriate. If the die 100 is made of steel such as tool steel, for example, a supply rate of 7 L / min to 15 L / min is appropriate. During press working, the internal temperature and surface temperature of the die 100 are maintained below 100°C by the coolant. The amount of coolant supplied to the cooling water channel 150 may be adjusted according to the temperature of the die 100 measured by thermocouples 310 and 320 so that the internal temperature and surface temperature of the die 100 are below 100°C. When the temperature exceeds 100°C, the amount of Si, Mg, and Cu dissolved in the aluminum alloy sheet 200 being processed decreases, and the cooling time for the aluminum alloy sheet 200 increases, leading to a decrease in productivity. For example, the higher the temperature measured by thermocouples 310 and 320, the greater the amount of coolant supplied to the cooling water channel 150. If the mold 100 is sufficiently cooled by mist spraying, cooling by the cooling water channel 150 is not necessary.
[0031] In S101, the aluminum alloy sheet 200 to be processed is heated in a heating furnace such as an electric heater furnace (electric furnace), induction heating furnace, or infrared heating furnace, for a holding time of less than 10 minutes at a target temperature of 450°C or higher but less than 560°C. That is, the aluminum alloy sheet 200 is heated in the heating furnace to the target temperature, and then heated further for a holding time of less than 10 minutes at that target temperature. During heating, it is desirable that the temperature difference at each location within the aluminum alloy sheet 200 be within a maximum of 40°C. Also, it is desirable that the heating rate be 50°C / min or higher. The heating rate affects the material structure (crystal grains), and if it is less than 50°C / min, it will lead to a decrease in formability due to crystal grain growth, roughness of the processed surface, and a decrease in productivity. On the other hand, if the range of temperature distribution within the material is large, the strength variation will be large, so it is desirable to keep the temperature difference at each location within the aluminum alloy sheet 200 within 40°C. Furthermore, the thickness of the aluminum alloy plate is, for example, between 1.5 mm and less than 5 mm. The temperature reached may vary depending on the type of aluminum alloy.
[0032] The target temperature is preferably 450°C-560°C. If the target temperature is below 450°C, the solid solution of the additive components in the aluminum alloy sheet is insufficient, making it difficult to achieve high strength. Also, if the target temperature is above 560°C, burning (surface melting) occurs due to the alloy additive elements, which is undesirable. The holding time at the target temperature may be 60 minutes or more, but a longer holding time significantly reduces productivity, so it is desirable to hold the sheet at the target temperature for less than 60 minutes. In particular, if the target temperature is 500°C-560°C, a shorter holding time is preferable, and even 10 minutes or less is sufficient. Also, a target temperature of 500°C-560°C contributes to improved formability and strength. A shorter holding time contributes to improved productivity and energy saving. Furthermore, if the thickness of the aluminum alloy sheet is thin (for example, less than 3 mm), a holding time of less than 1 minute at the target temperature is acceptable, and it is desirable to make it as short as possible. If the thickness of the aluminum alloy sheet is less than 1.5 mm, deformation is likely to occur during transportation, etc., which is undesirable. Furthermore, while this processing is possible even if the aluminum alloy sheet is 5 mm or thicker, other methods such as extruded profiles are more convenient. Also, if the aluminum alloy sheet is 5 mm or thicker, heating before pressing and cooling after pressing takes time, reducing productivity. Therefore, the thickness of the aluminum alloy sheet 200 here is preferably 1.5 mm or more and less than 5 mm.
[0033] In S102, the mold sprayer of the press machine sprays mist-like water or water-soluble lubricant toward the upper die 110 and lower die 120 of the die 100. The mold sprayer sprays the area of the aluminum alloy plate 200 to be processed, which is 100 cm², toward the upper die 110 and lower die 120. 2 Spray at least 10 mg of mist-like water or water-soluble lubricant per unit. The spraying of water or a water-soluble lubricant in mist form using a mold sprayer is performed before the aluminum alloy plate 200 to be processed is set in the mold 100. The spray volume covers an area of 100 cm² of the aluminum alloy plate 200 to be processed. 2If the amount is less than 10 mg per unit area, the cooling capacity and lubrication performance will be insufficient, leading to adhesion of the aluminum alloy plate 200 to the mold 100. Also, the amount of spray applied is less than the area of the aluminum alloy plate 200 being processed (100 cm²). 2 If the amount exceeds 3000 mg per unit area, although sufficient cooling occurs, an excess of water or water-soluble lubricant will remain in the mold 100. An excess of water or water-soluble lubricant in the mold 100 necessitates a dewatering process to remove the liquid (water or water-soluble lubricant) from the mold 100, leading to reduced work efficiency and decreased quality. Furthermore, excessive spraying can cause variations in strength due to temperature unevenness in the aluminum alloy sheet 200. Therefore, the spraying amount should be calculated based on the area of the aluminum alloy sheet 200 being processed (100 cm²). 2 A concentration of 10 mg or more and less than 3000 mg per unit is preferred. For example, if sufficient cooling can be obtained with a cooled mold 100, cooling by mist spraying may not be necessary. Mist spraying using a mold sprayer is effective for cooling the aluminum alloy plate 200. The amount of mist sprayed is preferably increased as the thickness of the aluminum alloy plate 200 increases.
[0034] In S103, the aluminum alloy sheet 200 heated in S101 is removed from the heating furnace and quickly (for example, within 5 seconds) set on the lower die wrinkle-holding section 121 of the die 100 of the press working apparatus. The removal of the aluminum alloy sheet from the heating furnace and setting it in the die 100 is performed, for example, by a well-known robot. The robot, for example, has an arm for gripping the aluminum alloy sheet 200, removes the aluminum alloy sheet 200 that has been heated for a predetermined time from the heating furnace, and moves it to the die 100. Alternatively, the robot may remove the press-worked aluminum alloy sheet 200 from the die 100.
[0035] In S104, the press working apparatus moves the upper die 110 of the die 100 to the bottom dead center, bringing the punch 113 and the upper die wrinkle-holding part 112 into contact with the aluminum alloy sheet 200, thereby deforming (pressing) the aluminum alloy sheet 200 into a predetermined shape. Here, it is preferable that the height of the molded product after the drawing process on the aluminum alloy sheet 200 is less than 40 mm. Since a wrinkle-holding control mechanism is not used here, if the height of the molded product exceeds 40 mm, insufficient material flow due to wrinkles in the flange portion will occur. Here, the height of the molded product obtained by shrink flange processing refers, for example, to the dimension of the processed product in the forming direction, i.e., the pressing direction after processing in press working. Therefore, if the height of the molded product exceeds 40 mm, constrictions and other defects may become apparent in the molded product, and the product performance may not be satisfactory.
[0036] In step S105, the upper mold 110 of the mold 100 is maintained at the bottom dead center to cool the aluminum alloy plate 200 to below 200°C. For example, by maintaining the upper mold 110 at the bottom dead center for 1-5 seconds (bottom dead center holding time of 1-5 seconds), the aluminum alloy plate 200 is cooled to below 100°C. If the bottom dead center holding time is less than 1 second, it is difficult to cool the aluminum alloy plate 200 to below 100°C. If the bottom dead center holding time exceeds 5 seconds, productivity is reduced. Since the mold 100 is cooled beforehand by water cooling or the like, the aluminum alloy plate 200 sandwiched between the upper mold 110 and the lower mold 120 of the mold 100 is also cooled. If the temperature of the aluminum alloy plate 200 exceeds 100°C, problems arise such as the precipitation of additive elements that increase strength, making it impossible to ensure high strength, and the molded product being prone to deformation. Furthermore, by cooling the aluminum alloy sheet 200 to below 100°C, the temperature difference (thermal shrinkage rate) between the temperature reached by the aluminum alloy sheet 200 and the cooling temperature at the bottom dead center can be utilized to improve the flatness of the molded product and its release properties from the mold 100. The temperature of the aluminum alloy sheet 200 decreases upon contact with the mold 100, and this temperature difference creates tension in the aluminum alloy sheet 200, contributing to improved flatness. A lower temperature at the bottom dead center is preferable. On the other hand, thermal shrinkage causes the aluminum alloy sheet 200 to stick to the punch 113 side, making release difficult. Therefore, it is preferable to optimize the temperature reached by the aluminum alloy sheet 200 to reduce tension. Also, if there are shapes that are difficult to release even with thermal shrinkage countermeasures for the aluminum alloy sheet 200, for example, the convex side of the mold 100, the punch 113... It is effective to provide a relief angle of several degrees (for example, 1 to 3 degrees) on the side and to reduce deformation resistance during processing. Deformation resistance is seizure. Deformation resistance can be reduced by appropriately combining plating (for example, nickel plating, chromium plating) on the mold 100 and application of water-soluble coolant (lubricant). A well-known mold release agent can be used as a lubricant. Plating on the mold 100 can reduce the coefficient of friction between the mold 100 and the aluminum alloy sheet 200. By providing a relief angle on the convex side of the mold 100 and plating, the dimensional accuracy (flatness, etc.) of the molded product can be improved. Furthermore, the dimensional accuracy of the molded product can be improved by a forced release method. The forced release method is a method of releasing the molded product (aluminum alloy sheet 200) from the mold 100 by applying force to a part of the molded product (aluminum alloy sheet 200) using a mechanical method (knockout bar, stripper, etc.) to the extent that it does not deform.
[0037] In S106, a short-time baking treatment is performed on the aluminum alloy plate 200 using a heating furnace such as an electric heater furnace (electric furnace), induction heating furnace, or infrared heating furnace, by heating it to a target temperature of 190°C or higher but less than 250°C for a holding time of 5 minutes or more but less than 60 minutes. That is, in the heating furnace, the temperature of the aluminum alloy plate 200 is raised to the target temperature, and then it is heated further at that target temperature for a holding time of 5 minutes or more but less than 60 minutes. Below 190°C, precipitation hardening is insufficient, and above 250°C, the precipitates become larger and precipitation hardening is reduced. Therefore, a short-time baking treatment at 190°C or higher but less than 250°C is preferable. Alternatively, a long-time baking treatment may be performed instead of a short-time baking treatment. Long-time baking involves heating the aluminum alloy sheet 200 in a heating furnace such as an electric heater furnace (electric furnace), induction heating furnace, or infrared heating furnace for a holding time of 5 to 20 hours at a target temperature of, for example, 150°C to less than 180°C (e.g., 170°C for 8 hours). The temperature and time of the long-time baking process should be determined under conditions that reliably yield the desired strength, and are not limited to those described herein. Short-time baking and long-time baking processes are examples of artificial aging treatments. The treatment in S106 may be performed after other treatments (such as trimming, piercing, restrike, or cold pressing) following the treatments in S101 to S105 on the aluminum alloy sheet 200. Alternatively, the treatment in S106 may be performed after the treatments in S101 to S105 on the aluminum alloy sheet 200, maintaining a temperature of 100°C-200°C. This promotes the development of high strength through artificial aging. Alternatively, natural aging (leaving at room temperature (around 25°C)) may be used instead of artificial aging treatment.
[0038] (Example 1) Figure 5 shows the strength and formability of 4000 series aluminum alloy sheets and 6000 series aluminum alloy sheets. Here, as the 4000 series aluminum alloy sheet, scrap of AC4A cast parts (Al-8.9%Si-0.1%Cu-0.4%Mn-0.5%Mg) is melt-cast, homogenized at 480°C, then hot-rolled, cold-rolled, and finished annealed at 350°C to produce a 2mm thick aluminum alloy sheet. As the 6000 series aluminum alloy sheet, 6022-T4 material is used. Here, the tensile strength, yield strength, elongation, Erichsen value, and limiting reduction ratio (LDR) of the produced 2mm thick 4000 series aluminum alloy sheet (AC4A material) and 2mm thick 6000 series aluminum alloy sheet (6022-T4 material) are compared.
[0039] AC4A material has lower strength and yield strength compared to 6022-T4 material. Furthermore, AC4A material has lower elongation and Erichsen value than 6022-T4 material. On the other hand, the limiting reduction ratio (LDR) is the same for both AC4A and 6022-T4 material. This is due to the influence of the material structure (crystal grains, eutectic structure, etc.). Moreover, the drawability of both materials is equivalent due to the improved shrinkage flange properties (wrinkle suppression) resulting from the low strength of AC4A scrap material. Therefore, if the strength of AC4A material is the same as that of 6022-T4 material, the formability of AC4A material is inferior.
[0040] (Example 2) In this study, using the AC4A and 6022-T4 test materials from Example 1, forming tests were conducted on an automotive ECU case using cold pressing and the hot stamping method described above. In cold pressing, both test materials cracked 10 mm before the bottom dead center. The degree of cracking was greater in the AC4A material than in the 6022-T4 material. On the other hand, in the hot stamping method described above (achieved temperature 550°C, application of water-soluble lubricant, water-cooled mold, bottom dead center holding time 2 seconds), neither test material cracked, indicating good formability.
[0041] (Example 3) Figure 6 shows examples of strength characteristics of 4000 series aluminum alloy sheets and 6000 series aluminum alloy sheets after aging treatment. Here, the test specimens (JIS No. 5 test pieces) of AC4A and 6022-T4 material from Example 1 were solution-treated at 550°C, water-cooled, and then subjected to either natural aging (left at room temperature for 2 weeks) or artificial aging (long-time baking treatment, 8 hours at 170°C). Tensile strength, yield strength, and elongation were measured for each test specimen. The test specimen of AC4A material treated with artificial aging achieved high strength comparable to steel sheet (high-tensile steel). The test specimen of AC4A material treated with artificial aging also showed higher strength compared to the test specimen of 6022-T4 material treated with artificial aging. AC4A material is a 4000 series aluminum alloy and belongs to the category of non-heat-treatable alloys. While non-heat-treated alloys are generally said not to exhibit precipitation hardening behavior, high strength can be obtained by the hot stamping process described above (heating to a temperature of 450°C or higher, followed by rapid cooling) applied to 4000 series aluminum alloys. In particular, test materials treated with artificial aging on AC4A material showed higher strength than test materials treated with artificial aging on 6022-T4 material, which is used as a panel material for automobiles.
[0042] (Example 4) Figure 7 shows an example of the strength characteristics of a 4000 series aluminum alloy sheet after short-time baking treatment. Here, the AC4A material test specimen (JIS No. 5 test piece) from Example 1 is subjected to solution treatment at 550°C, water cooling, and then artificial aging treatment (short-time baking treatment), simulating hot stamping. Tensile strength, yield strength, and elongation are measured for the test specimen after artificial aging treatment. The baking conditions for the short-time baking treatment are 180°C for 20 minutes, 200°C for 20 minutes, 220°C for 20 minutes, 240°C for 20 minutes, and 260°C for 20 minutes. Here, a tensile strength of 320 MPa or higher and a yield strength of 250 MPa or higher are considered acceptable. When the baking temperature is 200°C, 220°C, and 240°C, the tensile strength is 320 MPa or higher. When the baking temperature is 180°C and 260°C, the tensile strength is less than 320 MPa. Furthermore, when the baking temperature is 200°C, 220°C, and 240°C, the yield strength is 250 MPa or higher. However, when the baking temperature is 180°C and 260°C, the yield strength is less than 250 MPa. Therefore, when the baking time is 20 minutes, it is desirable that the baking temperature be between 190°C and 250°C. Also, the elongation is 8% or higher under each condition, and an elongation of 8% or higher is a sufficient value. With the short-time baking conditions of 200°C and 20 minutes, the tensile strength of the test material is 365 MPa. A tensile strength of 365 MPa is equivalent to 96% of the tensile strength of 380 MPa obtained from the long-time baking treatment (170°C for 8 hours) of the AC4A test material in Example 3. In this way, by performing a short-time baking treatment, it is possible to obtain an aluminum alloy sheet with strength equivalent to that obtained by long-time baking treatment. By performing a short-time baking treatment, it is possible to obtain an aluminum alloy sheet with equivalent strength to that obtained by long-time baking treatment with less energy consumption.
[0043] (Effects and mechanisms of the embodiment) In this embodiment, a cast product of an aluminum alloy such as 4000 series aluminum alloy is used as the raw material. As a material, an aluminum alloy sheet of 4000 series aluminum alloy is produced. In this process, for example, scrap material of cast aluminum alloy products is melted and cast to produce a slab. During this process, degassing and inclusion removal treatments are performed. Furthermore, segregation removal treatment is performed on the cast slab. In addition, a quantity of less than 100 ppm of P or Na may be added during casting. The addition of P or Na refines the cast structure of the aluminum alloy. Next, the slab that has undergone segregation removal treatment is subjected to homogenization heat treatment at a temperature of 400°C to less than 530°C. Furthermore, the homogenized slab is subjected to hot rolling to become a hot coil with a thickness of 2 mm to less than 8 mm. In this process, the winding temperature is set to 300°C to less than 400°C. Furthermore, roughening is performed at 300°C to less than 400°C, and then an aluminum alloy sheet with a thickness of 1.5 mm to less than 5 mm is produced by cold rolling. Hot stamping is performed on the aluminum alloy plate 200.
[0044] The hot stamping method for aluminum alloy sheets in this embodiment involves heating the aluminum alloy sheet 200 in a heating furnace to a temperature of 450°C or higher but less than 560°C for a holding time of less than 10 minutes. The mold 100 is made of aluminum alloy, tool steel, high-speed steel, cemented carbide, etc. The mold 100 is cooled by a coolant flowing through a cooling water channel 150. The mold 100 is also cooled by mist spraying. The heated aluminum alloy sheet 200 is removed from the heating furnace, set in the mold 100, and pressed. During pressing, the aluminum alloy sheet 200 is cooled to below 100°C at the bottom dead center of the mold 100. This allows for the solid solution of Si, Mg, and Cu, which contribute to strength. The hot stamping method for aluminum alloy sheets in this embodiment improves the formability of the aluminum alloy, enables shapes that were previously difficult to create, and reduces the number of mold steps. By cooling the mold 100, the temperature of the mold 100 can be reduced to below 100°C. By cooling the mold 100, the aluminum alloy sheet 200 to be processed can be cooled. By performing a short baking treatment on the aluminum alloy sheet 200 after press working, the aluminum alloy sheet 200 can be made stronger (tensile strength of 320 MPa or more). By introducing a coolant into the mold 100 and spraying mist, the aluminum alloy sheet can be cooled to a predetermined temperature. Furthermore, by cooling the aluminum alloy sheet 200 to below 100°C, molded products with excellent shape retention and flatness can be produced. By using cooling water channels and mist spraying, direct water cooling of the aluminum alloy sheet after press working can be omitted. By not performing direct water cooling, a decrease in press speed, complexity of mold shape, and complexity of processing steps can be suppressed. This improves the productivity and simplicity of the press working process.
[0045] The hot stamping method for aluminum alloy sheets according to this embodiment can produce press-formed products of 4000 series Al-Si alloys with a high Si content. According to this embodiment, it is possible to manufacture press-formed products from 4000 series aluminum alloys that have the same strength as 6000 series aluminum alloys. According to this embodiment, by producing aluminum alloy sheets from cast products made of 4000 series aluminum alloy as raw materials and then manufacturing press-formed products, energy consumption can be reduced compared to manufacturing press-formed products using new aluminum ingots. This reduction in energy consumption can lead to a reduction in CO2 emissions.
[0046] Each of the above embodiments can be implemented in combination whenever possible. [Explanation of symbols]
[0047] 100 molds 110 Upper mold 111 Upper die set 112 Upper mold wrinkle-pressing section 113 Punch 120 Lower mold 121 Lower mold wrinkle-pressing section 122 Lower Die Set 130 Cooling waterway 140 Thermocouple mounting holes 150 Cooling waterway 151 Part 1 152 Part 2 153 Part 3 160 Thermocouple mounting holes 200 Aluminum alloy plate 310 Thermocouple 320 Thermocouple
Claims
1. A heating process in which an aluminum alloy plate made from an aluminum alloy containing 5% or more but less than 11% Si by weight is held at a temperature of 450°C or more but less than 560°C for a period of 10 minutes or less, The process includes supplying the aluminum alloy sheet to a mold and press-forming it, and cooling the aluminum alloy sheet to 100°C or below at the bottom dead center of the press-forming process. The thickness of the aforementioned aluminum alloy plate is 1.5 mm or more and less than 5 mm. The aluminum alloy plate contains, by weight, 5% to less than 11% Si, 0.2% to less than 0.6% Mg, 0.05% to less than 2.0% Cu, 0.2% to less than 0.6% Mn, less than 0.3% Fe, less than 0.5% Zn, and less than 0.10% Ti, with the remainder being unavoidable impurities and aluminum. The aluminum alloy sheet is manufactured by melting and casting the aluminum alloy, performing homogenization heat treatment at a temperature of 400°C to less than 530°C, hot rolling at a temperature of 300°C to less than 400°C to a thickness of 2 mm to less than 8 mm, and cold rolling to a thickness of 1.5 mm to less than 5 mm. Method for processing aluminum alloy sheets.
2. A heating process in which an aluminum alloy plate, made from an aluminum alloy casting, is held at a temperature of 450°C or higher but less than 560°C for a period of 10 minutes or less, The process includes supplying the aluminum alloy sheet to a mold and press-forming it, and cooling the aluminum alloy sheet to 100°C or below at the bottom dead center of the press-forming process. The thickness of the aforementioned aluminum alloy plate is 1.5 mm or more and less than 5 mm. The aluminum alloy plate contains, by weight, 5% to less than 11% Si, 0.2% to less than 0.6% Mg, 0.05% to less than 2.0% Cu, 0.2% to less than 0.6% Mn, less than 0.3% Fe, less than 0.5% Zn, and less than 0.10% Ti, with the remainder being unavoidable impurities and aluminum. The aluminum alloy sheet is manufactured by melting and casting the aluminum alloy, performing homogenization heat treatment at a temperature of 400°C to less than 530°C, hot rolling at a temperature of 300°C to less than 400°C to a thickness of 2 mm to less than 8 mm, and cold rolling to a thickness of 1.5 mm to less than 5 mm. Method for processing aluminum alloy sheets.
3. The aforementioned aluminum alloy plate is to which less than 100 ppm of P or less than 100 ppm of Na is added. The method for processing an aluminum alloy sheet according to claim 1 or 2.
4. The mold has an area of 100 cm² of the aluminum alloy plate. ２ The process includes a spraying step in which a mist of water or a water-soluble lubricant is sprayed in an amount of 10 mg or more but less than 3000 mg per unit. The method for processing an aluminum alloy sheet according to claim 1.
5. The mold has an area of 100 cm² of the aluminum alloy plate. ２ The process includes a spraying step in which a mist of water or a water-soluble lubricant is sprayed in an amount of 10 mg or more but less than 3000 mg per unit. The bottom dead center holding time in the aforementioned press working process is 1 second or more and less than 5 seconds. The method for processing an aluminum alloy sheet according to claim 2.
6. The process includes a baking step in which the aluminum alloy sheet is held at a temperature of 190°C or higher but less than 250°C for a period of 5 minutes or more but not more than 60 minutes, after the pressing process. The method for processing an aluminum alloy sheet according to claim 1.
7. The process includes a baking step in which the aluminum alloy sheet is held at a temperature of 190°C or higher but less than 250°C for a period of 5 minutes or more but not more than 60 minutes, after the pressing process. The method for processing an aluminum alloy sheet according to claim 2.
8. The process includes a baking step in which the aluminum alloy sheet is held at a temperature of 150°C or higher but less than 180°C for a period of 5 hours or more but not more than 20 hours, after the aforementioned pressing process. A method for processing an aluminum alloy sheet according to any one of claims 1 to 5.
9. The aforementioned mold is provided with a relief angle on the convex side, or is plated. A method for processing an aluminum alloy sheet according to any one of claims 1 to 8.
10. The process includes a release step in which force is applied to a portion of the aluminum alloy sheet after the press working step to release the aluminum alloy sheet from the mold, A method for processing an aluminum alloy sheet according to any one of claims 1 to 9.