Thick aluminum sheet material production method and thick aluminum sheet material

Abstract

This thick aluminum sheet material production method is characterized by comprising: a first press-down step for, through hot-forging, pressing down an ingot of aluminum or an ingot of an aluminum alloy in a Z direction which is the longitudinal direction of the ingot to reduce the size of the ingot in the Z direction and to obtain a hot-forged product; and a second press-down step for pressing down the hot-forged product in the Z direction through hot-rolling of the hot-forged product to reduce the size of the hot-forged product in the Z direction and to obtain a thick aluminum sheet material. According to the present invention, it is possible to provide a thick aluminum sheet material production method capable of producing a thick sheet material having low internal porosity in production of a thick sheet material of aluminum or an aluminum alloy having a large sheet thickness.

Description

Manufacturing method for thick aluminum plate material and thick aluminum plate material

[0001] The present invention relates to thick aluminum or aluminum alloy plate material having reduced internal porosity.

[0002] Aluminum or aluminum alloy thick plates have traditionally been widely used as processing materials for vacuum chambers, semiconductor manufacturing equipment, and other applications, and as equipment becomes larger, there is a demand for extra-thick plates. Aluminum alloy thick plates for this application require reduced internal porosity to ensure airtightness, reduce outgassing, improve surface treatment uniformity, and improve mechanical strength (especially fatigue strength). Since extra-thick plates, in particular, tend to have large or numerous internal porosities, finding a solution to this problem has been a technical challenge.

[0003] Furthermore, reducing internal porosity is a common issue for materials used in fields that require high reliability, such as high-speed railways, ships, space and aviation.

[0004] Aluminum alloy thick plates are generally produced by hot rolling a roughly rectangular DC ingot (slab) as the starting material. At this slab stage, the slab has a certain degree of internal porosity. The internal porosity tends to be particularly large and abundant near the center of the slab thickness.

[0005] When a typical slab with a thickness of about 500 mm is hot-rolled to a thickness of 100 mm or less using normal hot rolling at a relatively high reduction rate (80% or more), the porosity is compressed and eliminated due to material deformation up to the center of the plate thickness, resulting in a state with little internal porosity.

[0006] On the other hand, when the plate thickness is reduced to, for example, 200 to 400 mm by hot rolling, there is a problem that the size and number of internal porosity become larger than in the original slab. This is thought to be because light to moderate pressure does not cause deformation enough to compress existing porosity, but rather promotes the expansion and connection of porosity, and also causes the generation of new porosity at grain boundaries and interfaces between intermetallic compound particles. In particular, due to the different deformation state near the center of the plate thickness, porosity that existed in the slab state is not eliminated, and instead usually increases in size and number.

[0007] It is well known that increasing the reduction rate in hot rolling can reduce the internal porosity of hot-rolled plates. However, because there are industrial limitations on the thickness of DC slabs and the maximum material thickness that can be put into a hot rolling mill, there is a limit to how much the reduction rate can be increased in hot rolling, especially when manufacturing thick plates. For this reason, internal porosity tends to remain in extra-thick plates.

[0008] Therefore, Patent Document 1 discloses a technique for reducing the amount of hydrogen gas by degassing during casting and for reducing the porosity of thick aluminum plates by controlling the reduction rate in one pass of hot rolling.

[0009] JP 2009-090372 A

[0010] However, the method of Patent Document 1 was insufficient in improving the reduction of porosity in extra-thick plates.

[0011] Therefore, an object of the present invention is to provide a method for manufacturing thick aluminum plates that can produce thick aluminum or aluminum alloy plates with little internal porosity.

[0012] As a result of extensive research, the present inventors have found that, in the manufacture of thick aluminum or aluminum alloy plates, internal porosity can be reduced by subjecting an ingot to composite hot working, which combines hot forging and hot rolling, to produce thick plates, and have completed the present invention.

[0013] That is, the present invention (1) provides a method for producing an aluminum thick plate, characterized by comprising: a first rolling step of hot forging the ingot to roll it down in the Z direction to reduce the dimension of the ingot in the Z direction, thereby obtaining a hot forged product, when the longitudinal direction of the aluminum ingot or aluminum alloy ingot is defined as the Z direction; and a second rolling step of hot rolling the hot forged product to roll it down in the Z direction to reduce the dimension of the hot forged product in the Z direction, thereby obtaining an aluminum thick plate.

[0014] The present invention (2) also provides a method for producing an aluminum thick plate according to (1), characterized in that the total reduction rate in the first reduction step and the second reduction step is 75.0% or more.

[0015] The present invention (3) also provides a method for producing an aluminum thick plate according to (1) or (2), characterized in that the first reduction rate in the first reduction step is 60.0% or more.

[0016] The present invention (4) also provides a method for producing an aluminum thick plate according to (1) or (2), characterized in that the second reduction rate in the second reduction step is 0.5% or more.

[0017] The present invention (5) also provides a method for producing thick aluminum plates according to (1) or (2), characterized in that the thickness of the thick aluminum plate is 100 mm or more.

[0018] The present invention (6) also provides a method for producing an aluminum thick plate according to (1) or (2), characterized in that the dimension of the ingot in the Z direction is 800 mm or more.

[0019] The present invention (7) also provides the method for producing an aluminum thick plate according to (1) or (2), characterized in that, when the short side direction of the ingot is the X direction, the ratio of the dimension of the ingot in the Z direction to the dimension of the ingot in the X direction (dimension in the Z direction / dimension in the X direction) is 2.0 or more.

[0020] The present invention (8) also provides an aluminum thick plate material obtained by carrying out a first rolling step in which, when the longitudinal direction of an aluminum ingot or an aluminum alloy ingot is the Z direction, the ingot is rolled down in the Z direction by hot forging to reduce the dimension of the ingot in the Z direction and obtain a hot forged product, and a second rolling step in which the hot forged product is rolled down in the Z direction by hot rolling to reduce the dimension of the hot forged product in the Z direction and obtain an aluminum thick plate material.

[0021] The present invention (9) is directed to a sheet made of aluminum or an aluminum alloy containing 80 mass% or more of aluminum, having a plate thickness of 100 mm or more, and in a cross section parallel to the plate thickness direction, when the cross section is divided into three parts in the plate thickness direction by a microscope, the number density of internal porosity having a Feret diameter of 50 μm or more in the central part is 0.15 pieces / mm ２ The present invention provides an aluminum thick plate material characterized by the following:

[0022] The present invention (10) is an Al-Mg alloy containing 1.50 mass% or more of Mg, and has a plate thickness of 100 mm or more, and in a cross section parallel to the plate thickness direction, when the cross section is divided into three parts in the plate thickness direction by a microscope, the number density of internal porosity of 50 μm or more in Feret diameter is 0.15 pieces / mm ２ The present invention provides an aluminum thick plate material characterized by the following:

[0023] According to the present invention, a method for manufacturing thick aluminum plates can be provided that can produce thick aluminum or aluminum alloy plates with little internal porosity.

[0024] FIG. 1 is a schematic perspective view of an example of the form of an ingot to which hot forging according to the present invention is applied. FIG. 2 is a schematic perspective view showing a manufacturing process for a thick aluminum plate according to the present invention. FIG. 3 is a schematic cross-sectional view of a thick aluminum plate according to the present invention when cut parallel to the plate thickness direction. FIG. 4 is an observation result of a cross-section of a thick aluminum plate according to Example 1 by fluorescent penetrant inspection. FIG. 5 is an observation result of a cross-section of a thick aluminum plate according to Comparative Example 1 by fluorescent penetrant inspection. FIG. 6 is an SEM image of a cross-section of a thick aluminum plate according to Example 1. FIG. 7 is an optical microscope image of a cross-section of a thick aluminum plate according to Comparative Example 1.

[0025] The aluminum alloy thick plate of the present invention is a manufacturing method for an aluminum thick plate, comprising: a first rolling step of hot forging the ingot to reduce its dimension in the Z direction by hot forging, where the longitudinal direction of the aluminum ingot or aluminum alloy ingot is the Z direction, thereby obtaining a hot forged product; and a second rolling step of hot rolling the hot forged product to reduce its dimension in the Z direction by hot rolling, thereby obtaining an aluminum thick plate. In the present invention, both thick plates made of pure aluminum and thick plates made of aluminum alloys are collectively referred to as aluminum thick plate.

[0026] The method for producing an aluminum thick plate of the present invention includes a composite hot working process that combines a first rolling step in which forging is performed and a second rolling step in which hot rolling is subsequently performed.

[0027] The first reduction step is a step of performing hot forging to reduce an aluminum ingot or an aluminum alloy ingot.

[0028] The aluminum ingot is the target of hot forging in the first rolling step and is an ingot made of 1000-series pure aluminum. The aluminum alloy ingot is the target of hot forging in the first rolling step and is an ingot made of an aluminum alloy. There are no particular restrictions on the type of aluminum alloy, and examples include 2000-series, 3000-series, 4000-series, 5000-series, 6000-series, 7000-series, and 8000-series aluminum alloys. In particular, 5000-series and 6000-series aluminum alloys are useful for semiconductor manufacturing equipment.

[0029] Examples of ingots to be hot forged (ingots before hot forging) include ingots produced by a conventional semi-continuous casting (DC casting) method. Semi-continuous casting of aluminum or aluminum alloys generally involves supplying molten aluminum or aluminum alloys from above a horizontally positioned mold of a predetermined shape with both ends open, cooling and solidifying the molten aluminum or aluminum alloy in the mold by pouring cooling water below the mold, and then discharging the molten aluminum or aluminum alloy downward. In semi-continuous casting, the horizontal direction of the mold corresponds to the X and Y directions of the ingot, which will be described later, and the casting direction corresponds to the Z direction of the ingot, which will be described later.

[0030] In the first reduction step, the shape of the ingot to be hot forged (the ingot before hot forging) is a rectangular parallelepiped. The dimensions of the ingot to be hot forged will be described with reference to FIG. 1. FIG. 1 is a schematic perspective view of an example of an ingot to be hot forged according to the present invention. In FIG. 1, the shape of the ingot 1 to be hot forged is a rectangular parallelepiped, and the direction in which the longest side of the three sides of the ingot 1 extends is the longitudinal direction, which is referred to as the Z direction. Furthermore, the direction in which the shortest side of the three sides of the ingot 1 extends is the lateral direction, which is referred to as the X direction. Furthermore, the direction in which the second longest side of the three sides of the ingot 1 extends is referred to as the Y direction. The Z direction, Y direction, and X direction are perpendicular to each other.

[0031] In the first rolling step, the dimension in the Z direction of the ingot to be hot forged is preferably 800 mm or more, more preferably 1000 mm or more, and even more preferably 1500 mm or more. In addition, in the first rolling step, the dimension in the X direction of the ingot to be hot forged is about 350 to 700 mm.

[0032] In the first reduction step, the ratio of the Z-direction dimension to the X-direction dimension of the ingot to be hot forged (Z-direction dimension / X-direction dimension) is preferably 2.0 or more, more preferably 3.0 or more, and more preferably 3.5 or more. When the ratio of the Z-direction dimension to the X-direction dimension of the ingot to be hot forged (Z-direction dimension / X-direction dimension) is within the above range, the effect of reducing internal porosity is enhanced, particularly the effect of reducing internal porosity near the center of the plate thickness. Furthermore, to ensure safety, the ratio of the Z-direction dimension to the X-direction dimension of the ingot to be hot forged (Z-direction dimension / X-direction dimension) is preferably 6.0 or less.

[0033] The manufacturing method of the ingot to be subjected to hot forging in the first reduction step is not particularly limited, and for example, conventional molten metal treatment can be used. The molten metal treatment reduces the amount of hydrogen gas contained in the product to approximately 0.2 cc / 100 g or less. Furthermore, the resulting ingot can be subjected to homogenization and facing by conventional methods. The homogenization temperature can be appropriately set for each alloy.

[0034] In the first reduction step, the ingot to be hot forged (the ingot before hot forging) is reduced by hot forging to reduce the dimension of the ingot in the Z direction. The hot forging performed in the first reduction step is free forging, in which the ingot is compressed in the Z direction at a temperature equal to or higher than the recrystallization temperature of the aluminum ingot or aluminum alloy ingot. More specifically, free forging includes upsetting, forging extension, and width widening. In hot forging (free forging), a frictional restraining force acts on the surface in contact with the die, resulting in small deformation. Therefore, unlike rolling, strain in the center is large.

[0035] The hot forging temperature in the first reduction step has an optimal value for each pure aluminum or aluminum alloy and is not particularly limited. For example, the preheating temperature is preferably 300 to 550 ° C., and the material temperature during hot forging is preferably 300 ° C. to 500 ° C.

[0036] In the first reduction step, hot forging is performed on the hot forging target until the thickness in the Z direction of the hot forged product obtained by hot forging reaches the desired thickness. The number of hot forgings may be one, two or more. That is, in the first reduction step, the ingot may be compressed to the desired thickness by one hot forging, or the ingot may be compressed to the desired thickness by two or more hot forgings.

[0037] The first reduction rate in the first reduction step is preferably 60.0% or more, more preferably 70.0% or more, and more preferably 80.0% or more. Since it is determined by constraints such as the equipment, the upper limit of the first reduction rate is not specified here, but it is preferably up to about 95%. When the first reduction rate in the first reduction step is within the above range, the effect of reducing internal porosity is enhanced. In the present invention, the first reduction rate is a value calculated by the following formula: First reduction rate (%) = ((Z-direction dimension of ingot before first hot forging - Z-direction dimension of ingot after final hot forging) / Z-direction dimension of ingot before first hot forging) × 100.

[0038] In this way, a hot forged product is obtained by performing the first reduction step. The hot forged product obtained by performing the first step may be subjected to hot rolling in the second reduction step as is, or the surface of the hot forged product obtained by performing the first step that was in contact with the stamping die may be chamfered before performing the second reduction step, and the chamfered hot forged product may be subjected to hot rolling in the second reduction step.

[0039] After the first rolling step and before the second rolling step, the outer diameter shape of the base material for the second rolling step can be adjusted to a rectangular parallelepiped shape suitable for rolling by machining, cutting, or chamfering the side surfaces, as needed, to adjust the size. At this time, corners and sides may be rounded or chamfered as needed.

[0040] The second rolling step is a step of hot rolling the hot forged product obtained by the first rolling step.

[0041] In the second rolling step, the hot forged product obtained by the first rolling step is rolled down by hot rolling to reduce the dimension of the hot forged product in the Z direction. The hot rolling performed in the second rolling step is a plastic processing in which the hot forged product is rolled down and elongated in the Z direction between rotating rolls at a temperature above the recrystallization temperature of the hot forged product. In the second rolling step, the hot forged product obtained by the first rolling step is compressed in the Z direction of the hot rolled product to the desired thickness. In hot rolling, shear force is generated due to friction between the rolls and the material, and the surface portion of the material is subjected to more severe processing than the center portion.

[0042] In the present invention, the Z direction of the hot forged product corresponds to the Z direction of the ingot before hot forging in the first reduction step, and is the direction in which the ingot is compressed in the first reduction step. The Z direction of the hot forged product will be described with reference to FIG. 2 . FIG. 2 is a schematic perspective view showing the manufacturing process of the thick aluminum plate of the present invention. In FIG. 2 , a first reduction step 11 is performed on an ingot 1 to be hot forged, thereby reducing the Z-direction dimension of the ingot 1. Next, a second reduction step 12 is performed on a hot forged product 2 obtained by the first reduction step 11, thereby reducing the Z-direction dimension of the hot forged product 2 to obtain a thick aluminum plate 3. In this case, the Z direction of the hot forged product 2 corresponds to the Z direction of the ingot 1 before hot forging, and is the direction in which the ingot is compressed by hot forging. In other words, the Z direction of the hot forged product 2 corresponds to the thickness direction of the thick aluminum plate 3 obtained by the second reduction step 12. In other words, when viewed from the perspective of the final aluminum thick plate 3, the thickness direction of the aluminum thick plate 3 is the Z direction of the aluminum thick plate 3, which is also the Z direction of the hot forged product 2, and which is also the Z direction of the ingot 1.

[0043] The hot rolling temperature in the second reduction step has an optimum value for each pure aluminum or aluminum alloy and is not particularly limited, but for example, it is preferable that the material temperature during hot rolling is 400° C. to 500° C. Furthermore, in the hot rolling in the second reduction step, the dimensional accuracy and surface smoothness can be controlled essentially in the same way as in the hot rolling of ordinary plate materials.

[0044] In the second rolling step, the hot rolling target is hot rolled until the thickness in the Z direction of the aluminum thick plate obtained by hot rolling reaches the desired thickness. The number of hot rolling operations may be one, two or more. That is, in the second rolling step, the hot forged product may be compressed to the desired thickness by one hot rolling operation, or the hot forged product may be compressed to the desired thickness by two or more hot rolling operations.

[0045] The second reduction ratio in the second reduction step is preferably 0.5% or more, more preferably 15.0% or more, and more preferably 30.0% or more. There is no particular upper limit, but it is preferably up to about 80%. When the second reduction ratio in the second reduction step is within the above range, the effect of reducing internal porosity is enhanced. In the present invention, the second reduction ratio is a value calculated by the following formula: Second reduction ratio (%) = ((Z-direction dimension of the hot forged product before the first hot rolling - Z-direction dimension of the aluminum thick plate after the final hot rolling) / Z-direction dimension of the hot forged product before the first hot rolling) × 100.

[0046] The total reduction ratio in the first and second reduction steps is preferably 75.0% or more, more preferably 85% or more, and more preferably 90% or more. When the total reduction ratio in the first and second reduction steps is within the above range, the effect of reducing internal porosity is enhanced. In the present invention, the total reduction ratio in the first and second reduction steps is a value calculated by the following formula: Total reduction ratio in the first and second reduction steps (%) = [((Z-direction dimension of ingot before first hot forging - Z-direction dimension of thick aluminum plate after final hot rolling) / Z-direction dimension of ingot before first hot forging))] × 100 When facing (intermediate facing) is performed after hot forging, the total rolling reduction is calculated as follows: Total rolling reduction in the first and second rolling reduction steps (%) = [{Z-direction dimension of ingot before first hot forging - (Z-direction dimension of aluminum thick plate after final hot rolling x Z-direction dimension after hot forging / Z-direction dimension at start of hot rolling)} / Z-direction dimension of ingot before first hot forging)] × 100. In other words, it is expressed by the following formula. Total reduction rate = [{Z0 - Z3 x (Z1 / Z2)} / Z0] x 100 Or, Total reduction rate (%) in the first reduction step and the second reduction step = 100 - (100 - RD1) x (100 - RD2) / 100 Z0: Z direction dimension of the ingot before the first hot forging is performed Z1: Z direction dimension after completion of hot forging Z2: Z direction dimension at the start of hot rolling Z3: Z direction dimension after completion of hot rolling RD1: Reduction rate in the first reduction step (hot forging) RD2: Reduction rate in the second reduction step (hot rolling)

[0047] In the manufacturing method of aluminum thick plate of the present invention, after the first and second rolling steps, cutting to a predetermined shape, annealing, heat treatment (solution treatment and quenching, aging treatment), and shape correction (stretching, compression, etc.) can be performed as necessary. Annealing and heat treatment conditions vary depending on the alloy system and can be performed according to the standard conditions described, for example, on pages 9-11 of the "Aluminum Handbook, 6th Edition." Regarding the final thick plate temper, H112 and O are the main components for non-heat-treatable alloys (3000 series, 5000 series, and pure aluminum = 1000 series). For heat-treatable alloys (2000 series, 6000 series, and 7000 series), in addition to H112 and O, the final thick plate tempers include precipitation-aged T3, T4, T6, T7, and variations thereof (e.g., T651 and T7). The tempers of each alloy are determined in accordance with JIS H0001 and JIS H4000.

[0048] In this way, the method for manufacturing thick aluminum plates of the present invention can produce thick aluminum plates with no internal polishing or with very little internal polishing, if any.

[0049] In hot forging (free forging), the material near the surface in contact with the die is constrained by friction, and material flow near the center in the compression direction prevails. In hot rolling, shear force is generated by friction between the roll and the material, and the surface layer of the material is subjected to more severe processing than the center, resulting in material flow near the surface prevailing. In the manufacturing method of aluminum thick plate of the present invention, hot forging is performed first, followed by hot rolling, thereby combining the above-mentioned actions and effects of hot forging and hot rolling, and reducing internal porosity.

[0050] The thickness of the aluminum thick plate obtained by the aluminum thick plate manufacturing method of the present invention is preferably 100 mm or more, more preferably 150 mm or more. In conventional plate manufacturing methods using only hot rolling, the presence of internal porosity is particularly problematic when the aluminum thick plate manufactured has a thickness of 100 mm or more. The aluminum thick plate manufacturing method of the present invention can also be used to manufacture aluminum thick plates with a thickness of less than 100 mm, but the effect of reducing internal porosity of the aluminum thick plate manufacturing method of the present invention is most effectively manifested when manufacturing aluminum thick plates with a thickness of 100 mm or more. The upper limit of the thickness (final thickness) of the aluminum thick plate depends on the processable range of the hot rolling mill. For example, a rolling mill capable of rolling from 600 mm can also manufacture thick plates with a thickness of 570 mm. This makes it possible to manufacture aluminum thick plates with a thickness greater than the X-direction dimension (slab thickness) of the original ingot, while reducing internal porosity. For example, it is possible to manufacture an aluminum thick plate having reduced internal porosity and a plate thickness of 550 mm using an ingot having a dimension of 500 mm in the X direction.

[0051] The thick aluminum plate obtained by the manufacturing method of the present invention has very little internal porosity of 50 μm or more, and in particular, the number density of internal porosity of 50 μm or more in the center of the plate thickness is very low compared to the number density in the center of the plate thickness of thick plates obtained by conventional manufacturing methods. And because the thick aluminum plate obtained by the manufacturing method of the present invention has very little internal porosity of 50 μm or more, it has higher fatigue strength than thick plates obtained by conventional manufacturing methods.

[0052] For example, by using an ingot with an X-direction dimension of 600 mm and only hot rolling the ingot in the X-direction to a final thickness of about 60 mm or less (approximately a reduction of 90% or more) without hot forging, an aluminum plate with relatively little internal porosity can be obtained. On the other hand, if an ingot with an X-direction dimension of 600 mm is hot rolled to a final thickness of about 100 mm or more (approximately a reduction of 83% or less) without hot forging, an aluminum thick plate with little internal porosity cannot be obtained. In order to obtain an extra-thick plate with a thickness of 100 mm or more by hot rolling with a 90% reduction, similar to the 60 mm plate described above, a slab with an X-direction dimension of 1200 mm or more must be hot rolled in the X-direction. Casting and hot rolling such slabs is difficult to carry out within industrial equipment specifications and normal conditions.

[0053] In contrast, the method for producing an aluminum thick plate of the present invention is fundamentally different from a conventional process in that an ingot having a Z-direction dimension of preferably 800 mm or more, more preferably 1000 mm or more, and even more preferably 1500 mm or more is rolled down in the Z direction. For example, in the case of a slab having a Z-direction dimension of 1200 mm or more, hot forging is performed in the first rolling step, and then hot rolling is performed in the second rolling step to roll down in the Z direction at a total rolling reduction rate of 90% or more, thereby producing an aluminum thick plate with little internal porosity even if the final plate thickness is 100 mm or more.

[0054] A first form of the present invention provides an aluminum thick plate, characterized in that it is obtained by carrying out a first rolling step in which, when the longitudinal direction of an aluminum ingot or an aluminum alloy ingot is defined as the Z direction, the ingot is rolled down in the Z direction by hot forging to reduce the dimension of the ingot in the Z direction and obtain a hot forged product, and a second rolling step in which the hot forged product is rolled down in the Z direction by hot rolling to reduce the dimension of the hot forged product in the Z direction and obtain an aluminum thick plate.

[0055] The first and second rolling steps for the thick aluminum plate of the first embodiment of the present invention are the same as the first and second rolling steps for the manufacturing method of the thick aluminum plate of the present invention. The internal porosity is efficiently compressed and eliminated by the combined hot working of hot forging and rolling.

[0056] The aluminum thick plate material of the second embodiment of the present invention is made of aluminum or an aluminum alloy containing 80 mass % or more of aluminum, has a plate thickness of 100 mm or more, and when a cross section parallel to the plate thickness direction is observed with a microscope, the number density of internal porosity of 50 μm or more in Feret diameter at the center when the cross section is divided into three in the plate thickness direction is 0.15 pieces / mm ２ The thick aluminum plate material is characterized by the following:

[0057] The aluminum thick plate material of the second embodiment of the present invention is aluminum or an aluminum alloy containing 80% by mass or more of aluminum, thereby ensuring the ductility of the material and allowing internal porosity to be efficiently compressed and eliminated by combined hot working of hot forging and rolling. It is even more desirable that the aluminum or aluminum alloy used in the aluminum thick plate material of the second embodiment of the present invention contains 90% by mass or more of aluminum.

[0058] The thickness of the aluminum thick plate material in the second embodiment of the present invention is 100 mm or more, preferably 150 mm or more.

[0059] In the aluminum thick plate material of the second embodiment of the present invention, when a cross section parallel to the plate thickness direction is observed under a microscope, the number density of internal porosity having a Feret diameter of 50 μm or more in the central part when the cross section is divided into three in the plate thickness direction is 0.15 pieces / mm ２ Preferably 0.10 pieces / mm or less ２ When the number density of the internal porosity having a Feret diameter of 50 μm or more in the central part of the cross section parallel to the plate thickness direction is within the above range, the fatigue strength is increased.

[0060] In the present invention, the number density of internal porosity with a Feret diameter of 50 μm or more in the central part when the cross section is divided into three in the thickness direction is an analytical value in scanning electron microscope (SEM) observation of a cross section parallel to the thickness direction. In the scanning electron microscope observation, first, the cross section parallel to the thickness direction is polished appropriately smooth to prepare a cross section to be analyzed, and then the cross section to be analyzed is observed under a scanning electron microscope to obtain an SEM image of the cross section to be analyzed. Next, in the SEM image of the obtained cross section, the central part when divided into three in the thickness direction is partitioned, and the number of internal porosity with a Feret diameter of 50 μm or more present in that partition, the area of ​​that partition (mm ２ ) is obtained, and the number density of internal porosity having a Feret diameter of 50 μm or more is calculated. In addition, in the present invention, when the cross section is divided into three parts in the thickness direction, the number density of internal porosity having a Feret diameter of 50 μm or more is analyzed in the central part, an observation image is obtained using an optical microscope instead of SEM observation, and the number density of internal porosity having a Feret diameter of 50 μm or more can be obtained from the obtained optical microscope observation image by the same method as in the case of SEM observation.

[0061] The central portion and the entire cross section when the cross section is divided into three in the plate thickness direction will be described with reference to Figure 3. Figure 3 is a schematic cross section of a thick aluminum plate 20 cut parallel to the plate thickness direction 13. In Figure 3, when the cross section 11 is divided equally into three in the plate thickness direction 13, the middle portion is the central portion 14, and the portions on either side of it are the outer portions 15a and 15b. Furthermore, the outer portions 15a, the central portion 14, and the outer portions 15b, i.e., the area from one surface 12a to the other surface 12b of the thick aluminum plate 20, constitute the entire cross section 16.

[0062] The aluminum thick plate of the second embodiment of the present invention is suitably produced by carrying out the above-described method for producing an aluminum thick plate of the present invention, using an aluminum or aluminum alloy ingot containing 80 mass % or more, preferably 90 mass % or more, of aluminum as the ingot to be hot forged in the first rolling step.

[0063] A third aspect of the present invention provides an aluminum thick plate material made of an Al-Mg alloy containing 1.50 mass % or more of Mg, having a plate thickness of 100 mm or more, and in a cross section parallel to the plate thickness direction, when the cross section is divided into three parts in the plate thickness direction by a microscope, the number density of internal porosity of 50 μm or more in Feret diameter is 0.15 pieces / mm ２ The thick aluminum plate material is characterized by the following:

[0064] The aluminum thick plate material of the third embodiment of the present invention is made of an Al-Mg alloy containing 1.50% by mass or more of Mg. The Mg content of the Al-Mg alloy related to the aluminum thick plate material of the third embodiment of the present invention is 1.50% by mass or more, preferably 2.2 to 6.0% by mass, and more preferably 3.5 to 6.0% by mass. For example, the Al-Mg alloy related to the aluminum thick plate material of the third embodiment of the present invention is a 5000 series alloy. When the Mg content of the Al-Mg alloy is within the above range, it becomes suitable as a thick plate to be used in parts where stress is applied. On the other hand, even if the Mg content of the Al-Mg alloy is less than the above range, the effect of reducing porosity can be obtained, but it is unsuitable for use as a structural member. The Al-Mg alloy for the aluminum thick plate material of the third embodiment of the present invention may, for example, contain 1.50 mass% or more, preferably 2.20 to 6.00 mass%, and more preferably 3.50 to 6.00 mass% Mg, with the balance being Al and inevitable impurities. The Al-Mg alloy for the aluminum thick plate material of the third embodiment of the present invention may, for example, contain 1.50 mass% or more, preferably 2.20 to 6.00 mass%, and more preferably 3.50 to 6.00 mass% Mg, and further contain 0.05 to 0.35 mass% Cu, 0.05 to 0.35 mass% Zn, 0.05 to 0.35 mass% Cr, 0.05 to 1.0 mass% Mn, 0. % of Zr, 0.05 to 0.35 mass% of Sc, 0.05 to 0.35 mass% of V, 0.05 to 0.35 mass% of Ni, 0.005 to 0.20 mass% of Ti, 0.001 to 0.04 mass% of Be, and 0.001 to 0.02 mass% of B, with the balance being Al and unavoidable impurities.

[0065] The thickness of the aluminum thick plate material according to the third embodiment of the present invention is 100 mm or more, preferably 150 mm or more. The internal porosity is efficiently compressed and eliminated by the combined hot working of hot forging and hot rolling.

[0066] In the aluminum thick plate material of the third embodiment of the present invention, when a cross section parallel to the plate thickness direction is observed under a microscope, the number density of internal porosity having a Feret diameter of 50 μm or more in the central part when the cross section is divided into three in the plate thickness direction is 0.15 pieces / mm ２ Preferably 0.10 pieces / mm or less ２ When the number density of the internal porosity having a Feret diameter of 50 μm or more in the central part of the cross section parallel to the plate thickness direction is within the above range, the fatigue strength is increased.

[0067] The aluminum thick plate of the third embodiment of the present invention is suitably produced by carrying out the above-described method for producing an aluminum thick plate of the present invention, using an aluminum alloy ingot having a Mg content of 1.50 mass % or more as the ingot to be hot forged in the first rolling step.

[0068] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples shown below.

[0069] (Example 1) A DC slab (JIS 5083 alloy, thickness 600 mm (X direction dimension), width 1505 mm (Y direction dimension), length 2090 mm (Z direction dimension)) having the chemical composition shown in Table 1 produced by semi-continuous casting was heated to a temperature of 360 to 420 ° C., which is equal to or higher than the recrystallization temperature (350 ° C.), and then pressed down in the Z direction using a 15,000 tf hot forging press. Hot forging was performed in which the slab was compressed in multiple steps until the Z direction dimension reached 350 mm. The first reduction rate at this time was 83.2%. Next, the slab was faced until the Z-direction dimension was 334 mm, and then reheated again to a temperature of 530 ° C, which is higher than the recrystallization temperature (350 ° C), and rolled in the Z-direction in multiple passes in a hot rolling mill until the Z-direction dimension was 180 mm, to obtain a thick plate material. The second rolling reduction at this time was 45.6%. The total rolling reduction in the first and second rolling steps was 90.9%. The total rolling reduction was calculated as follows. Total rolling reduction (%) = (Z-direction dimension of DC slab before the first hot forging - Z-direction dimension after hot rolling × Z-direction dimension after hot forging / Z-direction dimension at the start of hot rolling) / Z-direction dimension of DC slab before the first hot forging × 100) = (2090 - 180 × 350 / 334) / 2090 × 100 = 90.9

[0070] Comparative Example 1 A JIS 5083 alloy thick plate was prepared as a comparative material by hot rolling a DC slab having the chemical composition shown in Table 1 in a conventional process to reduce the X-direction dimension from 600 mm to 180 mm. The reduction rate of this hot rolling was approximately 70%.

[0071] <Evaluation of Internal Porosity by Fluorescent Penetrant Inspection> A cross section in the thickness direction of a thick plate was observed by fluorescent penetrant inspection. The results are shown in Figure 4 (Example 1) and Figure 5 (Comparative Example 1). The operation and conditions for fluorescent penetrant inspection are as follows. After the rolling direction cross section of the thick plate was chamfered and cleaned, a fluorescent penetrant (Superglow OD-2800N, manufactured by Martec) was applied to the observation surface and allowed to penetrate into the porosity, after which the inspection liquid remaining on the surface was washed away. This was then dried and observed under a black light, and the areas where the fluorescent penetrant was present and seeping out were visually identified as light spots. These light spots can be considered to be the locations of porosity.

[0072] As a result of the observation, it was found that in the 5083 alloy thick plate material of the same thickness of 180 mm, which was hot-rolled only by conventional hot rolling in Comparative Example 1, a cluster of luminescent spots representing internal porosity was present in a region of about 1 / 3 of the plate thickness at the center of the thickness of the cross section. In contrast, no significant luminescent spots or clusters of luminescent spots were observed in the cross section of the thick plate material of Example 1. From these findings, it can be seen that the internal porosity of the thick plate material is almost completely eliminated, and the problem of internal porosity is almost completely resolved according to the manufacturing method of the present invention.

[0073] <Evaluation of internal porosity by microscopic observation> A cross section parallel to the thickness direction of the thick plate material was analyzed using a scanning electron microscope (SEM). The results are shown in Figure 6 (Example 1) and Figure 7 (Comparative Example 1). Furthermore, a cross section in the thickness direction of the thick plate material was analyzed using an optical microscope. The results are shown in Figure 8 (Example 1) and Figure 9 (Comparative Example 1). Note that in Figures 6 to 9, small black spots with a maximum Feret diameter (hereinafter simply referred to as Feret diameter) of less than 50 μm, mostly 5 to 20 μm, are observed. However, these are due to the presence of Mg, which is composed of elements lighter than Al. ２ Many of the Si intermetallic compound particles appear black under the SEM, and analysis has confirmed that they are not internal porosity. However, some of the black spots may be due to the presence of Mg during polishing to prepare the specimen for observation. ２ These include holes formed by the detachment of intermetallic compound particles containing transition elements such as Si and Fe. Of course, in comparative materials in which internal porosity reduction was not possible, fine internal porosity was also present and observed as black spots, making it difficult to distinguish between them. Therefore, in the present invention, the number density of porosity with a Feret diameter of 50 μm or more and porosity with a Feret diameter of 100 μm or more was used as an index for comparatively evaluating the effect of reducing internal porosity. Next, the vicinity of the center of the plate thickness was observed using an SEM, and the resulting SEM image was analyzed to determine the number (number density) of internal porosity with a Feret diameter of 50 μm or more and internal porosity with a Feret diameter of 100 μm or more per unit area in a region of 1 / 3 of the plate thickness (the central part when the plate thickness is divided into three parts) centered on the center in the plate thickness direction. The results are shown in Table 2.

[0074]

[0075]

[0076] As a result of the analysis, the hot-rolled material of Comparative Example 1, which was only subjected to normal hot rolling, contained porosity inside, whereas the internal porosity had disappeared in Example 1. From these findings, it can be seen that according to the manufacturing method of the present invention, the internal porosity of the thick plate material almost completely disappears, and the problem of internal porosity is almost completely solved.

[0077] <Evaluation by Rotating Bending Fatigue Strength> The improvement of mechanical properties due to the elimination of porosity by the method of the present invention will be explained using an example of rotating bending fatigue strength. Rotating bending fatigue tests were conducted in accordance with JIS Z2278. Test specimens (80 mm long, 8 mm parallel diameter) were taken from a region of 1 / 3 of the thickness (the central portion when the plate is divided into three parts in the thickness direction) centered on the center of the thickness direction of the hot-rolled thick plate (5083-H112) of Example 1 and Comparative Example 1, with the rolling direction as the longitudinal direction of the test specimen. Evaluation was performed based on fatigue strength based on 107 repeated stresses. The rotating bending fatigue strength was 152 MPa for Example 1 of the present invention and 69 MPa for Comparative Example 1. In the conventional hot-rolled material of the comparative example, internal porosity near the center of the thickness acts similarly to a notch, reducing fatigue strength. As a result of the elimination of internal porosity, fatigue strength in the examples of the present invention is significantly higher than in the comparative examples.

[0078] (Example 2) A DC slab (JIS 5083 alloy, thickness 600 mm (X-direction dimension), width 1505 mm (Y-direction dimension), and length 2090 mm (Z-direction dimension) of the same chemical composition as in Example 1 produced by semi-continuous casting was heated and reduced in the Z direction using a 15,000 tf hot forging press at a temperature of 360 to 420 ° C., or higher than the recrystallization temperature (350 ° C.). Hot forging was performed in which the slab was compressed in multiple steps until the Z-direction dimension reached 350 mm. The first reduction rate at this time was 83.2%. Next, the slab was faced until the Z-direction dimension reached 334 mm, reheated again to a temperature of 530 ° C., or higher than the recrystallization temperature, and reduced in the Z direction in one pass using a hot rolling mill until the Z-direction dimension reached 331 mm, thereby obtaining a thick plate material. The second reduction rate at this time was 0.9%. The total reduction rate in the first and second reduction steps was 83.4%. Next, the vicinity of the center of the plate thickness was observed with a scanning electron microscope (SEM), and the obtained SEM image was analyzed to determine the number (number density) per unit area of ​​internal porosity with a Feret diameter of 50 μm or more and internal porosity with a Feret diameter of 100 μm or more in a region of 1 / 3 of the plate thickness centered on the center in the plate thickness direction. As a result, the number density of internal porosity with a Feret diameter of 50 μm or more was 0 pieces / mm ２ The number density of internal porosity with a Feret diameter of 100 μm or more is 0 pieces / mm ２ It was.

[0079] (Comparative Example 2) A JIS 5083 alloy thick plate was used as a comparative material. A DC slab with the same chemical composition as Comparative Example 1 was hot-rolled in a conventional process to reduce the X-direction dimension from 600 mm to 331 mm. The reduction rate during this hot rolling was approximately 45%. Next, the vicinity of the center of the plate thickness was observed using a scanning electron microscope (SEM), and the resulting SEM image was analyzed to determine the number per unit area (number density) of internal porosity with a Feret diameter of 50 μm or more and internal porosity with a Feret diameter of 100 μm or more in a region of 1 / 3 of the plate thickness centered on the center in the plate thickness direction. As a result, the number density of internal porosity with a Feret diameter of 50 μm or more was 0.9 pieces / mm ２ The number density of internal porosity with a Feret diameter of 100 μm or more is 0.4 pieces / mm ２ It was.

[0080] The rotating bending fatigue strength of the material in a region of 1 / 3 of the thickness of the 5083 alloy H112 material centered at the center in the thickness direction was 179 MPa in Example 2 and 76 MPa in Comparative Example 2.

[0081] These results show that the manufacturing method of the present invention almost completely eliminates the internal porosity of thick plates, and virtually eliminates the problem of internal porosity. It also shows that the reduction in internal porosity achieved by the manufacturing method of the present invention leads to a significant improvement in fatigue strength.

[0082] (Example 3) A DC slab (JIS 5052 alloy, after cutting and facing: thickness 630 mm (X-direction dimension), width 1505 mm (Y-direction dimension), length 1968 mm (Z-direction dimension)) having the chemical composition shown in Table 3 produced by semi-continuous casting was heated and reduced in the Z direction using a 15,000 tf hot forging press at a temperature of 360 to 420 ° C. above the recrystallization temperature (350 ° C.). The hot forging was carried out in multiple steps until the Z-direction dimension reached 488 mm. The first reduction ratio at this time was 75.2%. Next, the slab was faced so that the Z direction was 457 mm, reheated again to a temperature of 530 ° C. above the recrystallization temperature, and hot rolled in multiple passes in a hot rolling mill until the Z-direction dimension reached 297 mm. The second reduction ratio at this time was 35.0%, and the total reduction ratio was 83.9%. Next, the vicinity of the center of the plate thickness was observed with an optical microscope, and the obtained image was analyzed to determine the number (number density) per unit area of ​​internal porosity with a Feret diameter of 50 μm or more and internal porosity with a Feret diameter of 100 μm or more in a region of 1 / 3 of the plate thickness centered on the center in the plate thickness direction. As a result, the number density of internal porosity with a Feret diameter of 50 μm or more was 0 pieces / mm ２ The number density of internal porosity with a Feret diameter of 100 μm or more is 0 pieces / mm ２ It was.

[0083] (Comparative Example 3) A JIS 5052 alloy thick plate was used as a comparative material, in which a DC slab having the chemical composition shown in Table 3 was hot-rolled in a conventional process to reduce the X-direction dimension from 533 mm to 297 mm. The reduction rate during this hot rolling was approximately 44%. Next, the vicinity of the center of the plate thickness was observed with an optical microscope, and the resulting image was analyzed to determine the number per unit area (number density) of internal porosity with a Feret diameter of 50 μm or more and internal porosity with a Feret diameter of 100 μm or more in a region of 1 / 3 of the plate thickness centered on the center in the plate thickness direction. As a result, the number density of internal porosity with a Feret diameter of 50 μm or more was 0.23 pieces / mm ２ The number density of internal porosity with a Feret diameter of 100 μm or more is 0.05 pieces / mm ２ It was.

[0084]

[0085] The 5052 alloy H112 material of Example 3 clearly had reduced internal porosity compared to the normal hot-rolled material of Comparative Example 3. The rotating bending fatigue strength of the material in the region of 1 / 3 of the plate thickness centered on the center in the plate thickness direction was 115 MPa in Example 3 and 95 MPa in Comparative Example 3, with Example 3 showing a higher value than Comparative Example 3.

[0086] (Example 4) A DC slab (JIS 6061 alloy) with the chemical composition shown in Table 4 was rolled under the same conditions as in Example 3 to obtain a material with a Z-direction dimension of 297 mm. This material was subjected to solution treatment at 525°C for 1 hour and water quenching, and artificial aging treatment at 170°C for 8 hours to obtain a T6 material. Images of this 6061 alloy T6 material were analyzed using an optical microscope, and the number of internal porosity with a Feret diameter of 50 μm or more and internal porosity with a Feret diameter of 100 μm or more per unit area (number density) was determined in a region of 1 / 3 of the thickness of the plate centered in the plate thickness direction. As a result, the number density of internal porosity with a Feret diameter of 50 μm or more was 0 / mm ２ The number density of internal porosity with a Feret diameter of 100 μm or more is 0 pieces / mm ２ It was.

[0087] (Comparative Example 4) A DC slab having the chemical composition shown in Table 4 was hot rolled in a normal process to reduce the X-direction dimension from 533 mm to 297 mm, and a 6061 alloy T6 material was heat treated in the same manner as in Example 4 to prepare a comparative material. In the central region of the thickness of this comparative material, the number density of internal porosity of 50 μm or more in Feret diameter was 0.17 pieces / mm ２ The number density of internal porosity with a Feret diameter of 100 μm or more is 0.04 pieces / mm ２ It was.

[0088]

[0089] The 6061 alloy T6 material of Example 4 clearly had reduced internal porosity compared to the conventional hot-rolled Comparative Example 4. The rotating bending fatigue strength of the material in the region of 1 / 3 of the thickness centered on the center in the thickness direction was 135 MPa for Example 4 and 95 MPa for Comparative Example 4, with Example 4 showing a higher value than Comparative Example 4.

Claims

1. A method for producing thick aluminum plate material, comprising: a first reduction step of hot forging the ingot to reduce its dimension in the Z direction by hot forging, where the longitudinal direction of the ingot is the Z direction, thereby obtaining a hot forged product; and a second reduction step of hot rolling the hot forged product to reduce its dimension in the Z direction by hot rolling, thereby obtaining a thick aluminum plate material.

2. The method for producing thick aluminum plate according to claim 1, characterized in that the total reduction rate in the first reduction step and the second reduction step is 75.0% or more.

3. The method for manufacturing thick aluminum plate material according to claim 1 or 2, characterized in that the first reduction rate in the first reduction step is 60.0% or more.

4. A method for manufacturing thick aluminum plate material according to claim 1 or 2, characterized in that the second reduction rate in the second reduction step is 0.5% or more.

5. A method for manufacturing thick aluminum plates according to claim 1 or 2, characterized in that the thickness of the thick aluminum plates is 100 mm or more.

6. A method for manufacturing thick aluminum plate material according to claim 1 or 2, characterized in that the dimension of the ingot in the Z direction is 800 mm or more.

7. The method for manufacturing thick aluminum plate material according to claim 1 or 2, characterized in that, when the short side direction of the ingot is the X direction, the ratio of the dimension of the ingot in the Z direction to the dimension of the ingot in the X direction (dimension in the Z direction / dimension in the X direction) is 2.0 or more.

8. An aluminum thick plate material obtained by carrying out a first reduction process in which, when the longitudinal direction of an aluminum ingot or an aluminum alloy ingot is the Z direction, the ingot is reduced in the Z direction by hot forging to reduce the dimension of the ingot in the Z direction to obtain a hot forged product, and a second reduction process in which the hot forged product is reduced in the Z direction by hot rolling to reduce the dimension of the hot forged product in the Z direction to obtain an aluminum thick plate material.

9. Made of aluminum or an aluminum alloy containing 80% or more by mass of aluminum, the plate thickness is 100 mm or more, and in a cross section parallel to the plate thickness direction, when observed under a microscope, the number density of internal porosity with a Feret diameter of 50 μm or more in the center when the cross section is divided into three in the plate thickness direction is 0.15 pieces / mm ２ 1. An aluminum thick plate material, comprising:

10. An Al-Mg alloy containing 1.50% or more by mass of Mg, with a plate thickness of 100 mm or more, and in a cross section parallel to the plate thickness direction, the number density of internal porosity with a Feret diameter of 50 μm or more in the center when the cross section is divided into three in the plate thickness direction is 0.15 pieces / mm ２ 1. An aluminum thick plate material, comprising:

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