JP2009090372A - Method for manufacturing aluminum alloy plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an aluminum alloy plate capable of preventing porosity coarsening in the central part of the plate arising in the initial period of hot rolling by a simple method without using complicated equipment. <P>SOLUTION: The aluminum alloy plate with a final plate thickness of 100 to 460 nm is manufactured by subjecting a dissolved aluminum alloy to degassing treatment of ≤0.2 cc/100 g in the content of gaseous hydrogen in a degassing treatment step of reducing the amount of the gaseous hydrogen in the dissolved aluminum alloy; applying homogenization treatment of a holding time for 1 to 10 hours to a slab at a holding temperature of 470 to 530°C; applying a plurality of times of rolling passes to the slab, and rolling the slab at one time rolling with draft (δ) [δ=ä(H1-H2)/H1}×100%] of ≥7%, wherein the plate thickness after rolling is defined as (H2) with respect to the plate thickness (H1) prior to rolling, and repeating the rolling several times, in a rolling step. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a manufacturing method of an aluminum alloy suitable for manufacturing, for example, a vacuum equipment chamber, an electronic component device, a semiconductor device, and an aluminum alloy thick plate product for injection molding automobiles.

  Conventionally, aluminum and aluminum alloy plate materials have been widely used for vehicle body sheet materials, can materials, fin materials, thick plates and the like.

  The slab ingot that is the basis of these plate materials is usually manufactured by solidifying a molten metal by a continuous water cooling method by DC casting using a water-cooled casting mold that is open at the top and bottom. However, since the difference in hydrogen solubility between molten and solidified aluminum and aluminum alloy is extremely large compared to other metals, the hydrogen absorbed in the molten metal during melting is released during solidification. Gas hole).

  In addition, regarding the influence of casting conditions in DC casting of aluminum and aluminum alloys on the generation of porosity in slabs, many researchers have conducted theoretical calculations such as elucidating the generation mechanism and predicting the generation of porosity. (For example, see Patent Document 1).

  Patent Document 1 proposes a method for predicting the generation amount of porosity (holes) that is a casting defect in vertical continuous casting of an Al—Mg-based aluminum alloy slab.

  In particular, the porosity generated in the vicinity of the slab cast skin surface may be directly exposed to the rolling surface by chamfering after casting, resulting in point defects. Also, in the case where porosity exists directly under the slab face, the cause of blistering on the surface of the slab after homogenization (soaking), streaking of the rolled material, blistering on the surface of the rolled coil after annealing, etc. It has become a quality problem.

  The most effective method for reducing the amount of porosity produced in the slab during casting is to reduce the amount of hydrogen gas in the molten metal. Therefore, the so-called degassing process for removing hydrogen gas from the molten metal is an extremely important process as the molten metal process for improving the quality of aluminum and aluminum alloy slab ingots. The amount of hydrogen gas in the molten metal is measured by a method such as a reduced pressure solidification method or a Lansley gas analysis method, and is strictly controlled according to the required quality.

  By the way, when the slab is rolled and used as a plate or foil of about 1 mm or less, if the thickness of the original slab is about 250 to 500 mm, the total rolling reduction from the slab to the final plate is about 99.6% or more. Therefore, the porosity generated in the slab at the time of casting is crushed and pressed in the rolling process. For this reason, with the exception of high-quality foils such as high-purity foils, high-strength fin materials, and automotive materials, the fine porosity present in the center of the plate thickness is a direct problem for normal plate products. There was little to be done.

However, in recent years, for example, thick plates (thickness: 6 to 400 mm) made of aluminum and aluminum alloys have been widely used in vacuum chambers, electronic component devices, semiconductor devices, and injection molds. Thick plates used in these applications are processed by cutting, cutting, welding, etc. before they become final products. Since high airtightness is required when used, the porosity inside the plank is a fatal defect for these products. In particular, in a thick plate having a thickness of 100 to 460 mm, since the number of rolling operations (number of passes) applied to the original slab before rolling is small, the porosity remains inside and is exposed, which is a fatal defect for the product. It becomes.
Japanese Patent No. 3397134

  However, systematic research and analysis have so far been conducted on how the amount of porosity at the center of the thickness generated during slab casting has disappeared and crimped during subsequent homogenization and hot rolling. It wasn't.

  This invention was made in view of the above circumstances, investigated by the operation scale test how the porosity generated during slab casting disappears due to the homogenization treatment conditions and hot rolling treatment conditions, and the results An object of the present invention is to provide a method for producing an aluminum alloy thick plate that obtains an aluminum alloy thick plate with reduced porosity by performing theoretical calculation on the basis of the theoretical calculation.

  In order to solve the above-mentioned problems, a method for producing an aluminum alloy thick plate according to the present invention includes a degassing treatment step for reducing the amount of hydrogen gas in a molten aluminum alloy, a step for casting a slab, A homogenization treatment step in which a crystallized product in the slab structure is diffused into aluminum as a base material by holding it for a predetermined time at a temperature, and a final plate thickness of 100 to 460 mm is applied by a plurality of rolling passes by a hot rolling mill. A method of manufacturing an aluminum alloy thick plate having a hot rolling step of rolling into a thick plate, wherein in the degassing step, the hydrogen gas content in the slab after casting is 0.2 cc / 100 g or less. In the homogenization step, the slab is subjected to a homogenization treatment at a holding temperature of 470 to 530 ° C. and a holding time of 1 to 10 hours. In the rolling step in which the rolling is performed, the rolling reduction ratio (δ) [δ = {(H1-H2) for one rolling when the thickness (H2) after rolling is set to the thickness (H2) before rolling. / H1} × 100%] is rolled over the plurality of rolling passes at 7% or more (claim 1).

  In the present invention, the slab is preferably an aluminum alloy having a composition of 2.0% by weight Mg and the balance Al and inevitable impurities (claim 2).

  According to the present invention, in the degassing process, the degassing process is performed so that the hydrogen gas content in the slab after casting is 0.2 cc / 100 g or less, thereby reducing the porosity of the slab. In the casting process, by casting at a casting speed of 50 mm / min or less, the porosity at the center of the slab can be reduced. In the homogenization process, the holding temperature is 470 to 530 ° C., the holding time is 1 to 1. By performing the homogenization treatment for 10 hours, the area ratio of porosity can be reduced and the number of porosity can be reduced. Further, in the rolling process, the rolling reduction ratio (δ) [δ = {(H1−H2) / H1 for one rolling when the thickness (H2) after rolling is set to the thickness (H2) before rolling. } × 100%] at a rate of 7% or more over a plurality of rolling passes can suppress porosity coarsening by the rolling process. Therefore, according to the present invention, an aluminum alloy thick plate having a rolled structure with few porosity defects near the center of the aluminum alloy thick plate can be easily manufactured.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a flowchart showing a manufacturing process of an aluminum alloy thick plate according to the present invention.

  To manufacture an aluminum alloy thick plate, as shown in FIG. 1, first, the aluminum alloy is melted (step 1-1), and the amount of hydrogen (H) gas in the molten aluminum alloy is reduced (removed). Gas treatment process: Step 1-2). In this degassing process, for example, argon (Ar) gas is blown into the molten aluminum alloy by a rotor-type degassing apparatus to reduce the amount of hydrogen. By this degassing treatment, the hydrogen (H) gas content in the molten aluminum alloy is reduced to 0.2 cc / 100 g or less. Thereby, the amount of porosity of the slab can be reduced. The slab is manufactured by solidifying the molten metal by continuous water cooling by DC casting using a water-cooled mold in which the upper and lower sides of the degassed aluminum alloy molten metal are opened (casting process: step 1-3). The casting speed at this time is 50 mm / min or less, preferably 20 to 50 mm / min. If the casting speed is faster than 50 mm / min, the porosity near the center of the slab becomes coarse, and if it is slower than 20 mm / min, the cooling speed of the entire slab becomes too slow, the amount of porosity increases, and the cast structure becomes rough. This is because the quality of the entire slab deteriorates.

  Next, the cast slab is chamfered to produce a thick plate having a predetermined thickness, for example, 400 to 600 mm (facing process: step 1-4). Next, the slab chamfered to a predetermined thickness (for example, 400 to 600 mm) is placed in a burning furnace and held at a predetermined temperature (for example, 470 to 530 ° C.) for a predetermined time (for example, 1 to 10 hours). Then, these elements are diffused from the crystallized material in the cast structure (the portion where the element concentration of solute atoms such as Fe, Si, Mg, etc. is high) into αAl which is a base material (matrix) (homogenization process: step 1-5). . Here, the reason why the holding temperature is 470 to 530 ° C. is that if the holding temperature is less than 470 ° C., the effect of the homogenization treatment cannot be obtained, and if the holding temperature is higher than 530 ° C., local melting occurs. Because there is a possibility.

  The reason for setting the holding time to 1 to 10 hours is that if the holding time is less than 1 hour, the homogenization process is completed before the entire slab reaches a uniform temperature, and there is a sufficient effect of the homogenization process. If the retention time is longer than 10 hours, the porosity area ratio and number increase rapidly due to the diffusion of hydrogen gas.

  Next, the slab homogenized using a hot rolling mill (plate thickness: 400 to 600 mm) is repeatedly reciprocated, for example, 4 to 10 times reciprocated and rolled through the rolling mill (rolling step: step 1). -6). By this rolling, an aluminum alloy thick plate having a final thickness of 100 to 460 mm, which is used particularly in a vacuum chamber and an electronic component device, is manufactured. When the plate thickness is less than 100 mm, there is no use as a vacuum chamber, and the porosity is similarly crushed by rolling regardless of the rolling history. In addition, when the plate thickness is larger than 460 mm, there is no use for a vacuum chamber or the like, and since the number of rolling passes is reduced, a cast structure (metal structure) remains, and a rolled structure cannot be obtained. The strength requirement cannot be satisfied. In this rolling process, the rolling reduction (δ) of one rolling (one pass) [δ = {(H1-H2) when the thickness (H2) after rolling is set to the thickness (H2) before rolling. / H1} × 100%] is rolled at 7% or more. Thereby, porosity coarsening can be suppressed by a rolling process.

  Hereinafter, conditions and the like in each processing step according to the present invention will be described in detail.

<Examination of rolling conditions>
In general, when a slab is rolled, porosity defects inside the thick plate are presumed to be gradually reduced by receiving pressure. However, according to the results of the operational scale test, a much larger porosity was found near the center of the slab plate with fewer rolling passes than before rolling. As shown in FIG. 2, when a slab having a thickness of 560 mm is rolled by a conventional method with a rolling reduction ratio of 5% in each pass, the porosity becomes coarse at the center of the thick plate. The porosity size was three times larger than before rolling.

  Therefore, in the present invention, in order to suppress the porosity coarsening at the center of the thick plate during hot rolling, the slab after the casting (original slab) {As cast}, the homogenization treatment (soaking), and the thickness during rolling. Observe the porosity distribution and changes in the plate, grasp the change in porosity due to this series of processes, and use general-purpose forging and rolling analysis software FORGE2 (trade name) to determine the deformation and stress inside the plate during the rolling process. A simulation was conducted, and the cause of the coarsening of the porosity was clarified from the comparison between the simulation results and the porosity measurement results.

  Furthermore, in the present invention, a method for preventing porosity coarsening in the vicinity of the center of the thick plate was developed by performing analysis by changing rolling parameters such as rolling speed, rolling reduction, rolling temperature and the like.

  One of the features of the present invention has been obtained by conducting basic experiments and analytical studies on the hot rolling process in order to solve the above problems. That is, slabs in each process in the manufacturing process of aluminum alloy thick plates, slabs after homogenization (soaking), and changes in the internal porosity of the thick plates after rolling are investigated, and the thick plates in the rolling process that are particularly problematic About the cause of the porosity coarsening near the center, general-purpose forging and rolling analysis software FORGE2 (trade name) is used to perform deformation and stress analysis inside the thick plate during the rolling process.

  Further, in the present invention, from the comparison between the simulation result and the measurement result of porosity, the cause of the porosity coarsening is clarified, and further, the rolling speed, the reduction amount {(thickness of thick plate before rolling)-(after rolling) Thickness of thick plate)}, and by changing the rolling parameters such as rolling temperature, analysis is performed to find a method for preventing porosity coarsening near the center of the thick plate.

  And the suppression condition of the coarsening of a porosity is calculated in advance during hot rolling using the said method, and generation | occurrence | production of a porosity coarsening is prevented.

  Furthermore, the minimum porosity and the casting conditions and soaking conditions in the casting process are determined by experiment and analysis, and in combination with the rolling method described above, the maximum length of porosity defects near the center of the thick plate is present in the final product thick plate. The allowable size is 110 μm or less without any influence.

<Examination of homogenization treatment conditions>
There is very little knowledge and research on the change of porosity in the process of homogenization (soaking). Therefore, in this invention, investigation is made on the change in porosity inside the slab due to changes in soaking temperature and soaking time, targeting Al-Mg alloy slabs cast using a small DC caster for testing and slabs cast on an actual operating scale machine. went. The change in porosity during the soaking process was clarified by observing and quantitatively measuring the porosity before and after soaking.

  Specific examples of the present invention will be described below.

<Rolling conditions>
As shown in FIG. 3, the length of the thick plate 1 is 1000 mm, the thickness is 500 mm with a slab after chamfering, and there is no deformation in the width direction of the thick plate 1 as shown in FIG. Was assumed. Using general-purpose software FORGE2 (trade name), the stress and deformation inside the thick plate during the rolling process were analyzed. Further, in consideration of symmetry, the analysis was performed with a 1/2 model as shown in FIG. In the analysis, the element division in the thickness direction of the thick plate 1 was made finer as it was closer to the surface. The physical property values of the rolling analysis object used in the rolling analysis are as shown in Table 1.

  The slab size at the start of rolling was set to 500 × 1000 mm, and the initial temperature of rolling, the rolling reduction, the rotation speed of the roll 2 and the initial temperature of the roll 2 were changed for analysis. In the analysis, the calculation was repeatedly performed with the same reduction amount from the first pass to the plate thickness of 150 mm. Here, the calculation is performed based on the following assumptions.

(1) The thick plate 1 is in a plane strain state.

(2) The roll 2 is a rigid body, and the deformation of the roll 2 is ignored.

(3) Analysis is performed in consideration of heat transfer between the roll 2 and the plate, frictional heat, heat generated in plastic deformation, and heat transfer between the plate and air.

(4) The relationship between flow stress at high temperature, temperature and strain rate is analyzed based on experimental values.

(5) Since the thick plate 1 is vertically symmetric, half of the thickness is the analysis target.

FIG. 4 shows the distribution of thick plate internal pressure in a rolling process, for example, plate thicknesses of 480 mm, 300 mm, and 200 mm, when the reduction rate is 5% / pass analyzed using the general-purpose software FORGE2 (trade name). The pressure (P) here is the sum of stresses σ _X , σ _Y , and σ _Z in the X, Y, and Z directions inside the thick plate, that is, P = σ _X + σ _Y + σ _Z. Incidentally, the pressure of the surface layer portion near the reduction of the thick plate 1 is 9.00 to 7.54 MPa, the pressure near the middle layer portion is 6.09 to 3.17 MPa, and the pressure near the central portion is 1.71 to − 1.20 MPa. A positive value indicates compression, and a negative value indicates tension.

  As shown in FIG. 4, when the number of rolling passes is small, the pressure by the roll acts only near the thick plate surface. Near the center of the plate, negative pressure, that is, tension is applied. That is, when the number of passes is small, the thick plate 1 receives pressure from the roll 2 in the vicinity of the thick plate surface, so the porosity near the surface layer is crushed and reduced. On the other hand, the thick plate is under tension near the center, so it is assumed that the porosity has been stretched and increased. This phenomenon is caused by the porosity distribution in the surface layer and the central portion of the plate thickness of 560 mm shown in FIGS. 5A and 5B, and in the surface layer and the central portion of the plate thickness of 300 mm shown in FIGS. It was in good agreement with the measurement situation of the internal porosity of the thick plate shown in the distribution of porosity of the steel sheet, and the calculation accuracy of the rolling analysis could be confirmed.

  When the number of passes is increased, the tension near the center of the thick plate decreases, and as shown in FIG. 4, when the plate thickness is about 200 mm, the tension near the center disappears and the entire thick plate is under pressure. Therefore, when the number of passes is small, it is presumed that the tension near the center of the thick plate will be increased by the tensile force due to the tension near the center of the thick plate. In addition, when the number of passes increases, the tension near the center disappears and the entire thick plate is subjected to compressive stress, so the porosity size at the center of the thick plate is considered to be small. This is because the original slab of FIG. 6-1, the soaking shown in FIG. 6-2, the post-rolling thickness of 300 mm shown in FIG. 6-3, the post-rolling thickness of 250 mm shown in FIG. As shown in the post-rolling sheet thickness of 200 mm shown in -5, this agrees well with the change in porosity near the center of the thick sheet during the rolling process. That is, as the number of passes increases, the plate thickness decreases and the stress state near the center of the thick plate changes from tension to compression, so the porosity size near the center of the thick plate also changes from increase to decrease.

  FIG. 7 shows the porosity size at the center of the thick plate rolled by the actual machine using the rolling method proposed from the analysis results, the conventional rolling method (rolling rate 5% / pass), the rolling rate 6% / pass, and the rolling rate. A comparison with the internal porosity of a slab rolled at 7% / pass and a rolling reduction of 10% / pass is shown. As shown in FIG. 7, when the rolling reduction rate of each pass becomes 7% or more, the porosity size decreases rapidly. Compared with the conventional method, the porosity size of the central part of the 300 mm thick plate is about 1/4, which is smaller than before rolling, and it is considered that the coarsening of the porosity can be suppressed.

<Casting conditions, homogenization conditions>
Next, in order to reduce the porosity, the experiment was conducted by changing the casting conditions that greatly affect the porosity and the homogenization (soaking) conditions that are the subsequent uniform processing of the structure. The slab after soaking was chamfered and hot rolled to the specified thickness. For the slab and plank obtained in each of the above steps, a sample was cut from the center of the slab and plank, and the generation status of the maximum length and area ratio of porosity was investigated. The results are shown in Table 2.

  As shown in Table 2, soaking with a gas amount of 0.2 cc / 100 g or 0.15 cc / 100 g and a slab cast at a casting speed of 50 mm / min, 45 mm / min or 40 mm / min with a holding time of 10 hours or 1 hour When the one-pass rolling reduction is 7% or 10%, the porosity size near the center of the thick plate is 80 μm or less. In Table 2, test numbers 1 to 16 are values obtained by experiments, and test numbers 17 to 20 indicate values obtained by calculation.

  As a result of the above experiment, in the degassing process step, a degassing process with a hydrogen gas content of 0.2 cc / 100 g or less was performed. In the casting process, casting was performed at a casting speed of 50 mm / min or less, and the homogenization process (soaking) ) In the process, after holding the slab for 10 hours and performing the homogenization treatment, in the rolling process, the one-pass reduction ratio is rolled at 7% or more, so that the porosity size near the center of the thick plate is 80 μm or less. It was found that even if it exists in the thick plate of the final product, it can be made 110 μm or less, which is an acceptable size without any influence.

  The sample is made of aluminum with a purity of 99.9% (hereinafter "%" is mass%) and magnesium (Mg) metal of 99.9%. Casting was performed using a DC casting machine. The dimensions of the slab are 1400 mm in length, 400 mm in width, and 250 mm in thickness. The casting conditions were a casting temperature of 730 ° C., a casting speed of 58 mm / min, an effective mold length of 50 mm, and a cooling water amount of 170 L / min, and no refiner was added.

As shown in FIG. 8, the heat-treated sample was collected from the slab 1 cast at a casting speed of 50 mm / min or less and a gas amount of 0.2 cc / 100 g or less. That is, the front and rear end portions in the casting direction of the slab 1 are chamfered to make them unusable, and the intermediate portions thereof are samples for holding time of 1 hour, non-processed cast products (As cast Metallography), holding time of 10 hours, respectively. Samples and samples for a retention time of 100 hours were collected. A5052, which is a practical alloy, is a slab having a length of 3000 mm, a width of 1480 mm, and a thickness of 600 mm cast under normal casting conditions with an actual machine of an operational scale. The heat-treated sample of A5052 was collected from a slice of 100 mm thickness as shown in FIG. Table 3 shows the chemical composition of each alloy.

  The observation of the grain structure and porosity after solidification is performed on the cross section of the sample cut out from the slab block shown in FIG. 8 (a) in order to investigate the effect of soaking, which is a process before rolling, on the porosity inside the slab. It was. In order to investigate the porosity quantitatively, the obtained sample is polished, and the number of porosity, size, area ratio, maximum length, etc. from the surface layer to the center of the slab are measured using an image analyzer (LUZEX) {product name}. did. However, the porosity measurement target was set to have an equivalent circle diameter of φ6 μm or more observed in the microstructure. The area ratio of porosity was an average value of n = 20 values measured for one measurement sample. The gas content was measured by the Lansley method.

  The Al—Mg alloy was tested under the following soaking conditions (1) to (3). Moreover, about A5052 alloy, experiment was implemented on the soaking conditions of following (1)-(5).

(1) Soaking temperature is 530 ° C. (temperature increase rate: 50 ° C./hr), maintained for 1 hour, and then cooled to room temperature at a temperature decrease rate of 35 ° C./hr.

(2) Soaking temperature is 530 ° C. (temperature increase rate: 50 ° C./hr), maintained for 10 hours, and then cooled to room temperature at a temperature decrease rate of 35 ° C./hr.

(3) The soaking temperature is 530 ° C. (temperature increase rate 50 ° C./hr), kept for 100 hours, and then cooled to room temperature at a temperature decrease rate of 35 ° C./hr.

(4) After holding for 10 hours at a soaking temperature of 500 ° C. (temperature increase rate: 50 ° C./hr), it is cooled to room temperature at a temperature decrease rate of 35 ° C./hr.

(5) After holding for 10 hours at a soaking temperature of 470 ° C. (temperature increase rate: 50 ° C./hr), it is cooled to room temperature at a temperature decrease rate of 35 ° C./hr.

  FIG. 10 shows the gas content of each alloy under each heat treatment condition measured using the Lansley method. As shown in FIG. 10, the gas content in the alloy increases as the amount of Mg added increases. As the soaking time increased, the amount of gas in the alloy tended to decrease slightly, but the change was very small, so no change in the gas amount due to the soaking time was observed.

  11-1 to 11-3 to 16-1 to 16-3, Al-4% Mg, 6% Mg alloy slab is used, soaking temperature is kept constant at 530 ° C., holding time is 1 hour, 10 The porosity distribution inside a slab when changing to time and 100 hours is shown. 11-1, FIG. 11-2, and FIG. 11-3 are the cases where the holding time of the Al-4% Mg alloy slab is 1 hour, and the porosity of 110 to 120 mm, 95 to 105 mm, and 80 to 90 mm from the surface layer, respectively. FIGS. 12-1, 12-2, and 12-3 show the distribution situation, and when the holding time of the Al-4% Mg alloy slab is 10 hours, 110 to 120 mm, 95 to 105 mm from the surface layer, respectively. The porosity distribution situation of 80-90 mm is shown, and FIGS. 13-1, 13-2, and 13-3 are the cases where the holding time of the Al-4% Mg alloy slab is 100 hours, and 110 to 120 mm from the surface layer, respectively. , 95-105 mm, 80-90 mm porosity distribution. FIGS. 14-1, 14-2, and 14-3 show the case where the holding time of the Al-6% Mg alloy slab is 1 hour, and 110 to 120 mm, 95 to 105 mm, and 80 to 90 mm from the surface layer, respectively. 15-1, FIG. 15-2, and FIG. 15-3 are the cases where the holding time of the Al-6% Mg alloy slab is set to 10 hours, and 110 to 120 mm and 95 to 95 mm from the surface layer, respectively. FIGS. 16-1, 16-2, and 16-3 show the porosity distribution of 105 mm and 80 to 90 mm. FIGS. 16-1, 16-2, and 16-3 show the case where the holding time of the Al-6% Mg alloy slab is set to 100 hours. The porosity distribution situation of ˜120 mm, 95 to 105 mm, and 80 to 90 mm is shown.

  As can be seen from the porosity distribution situation, in any of the Al-4% Mg and 6% Mg alloy slabs, the number of porosity and the size tend to increase as the holding time becomes longer. In addition, with respect to the porosity shape, it is observed that as the holding time is longer, a lot of porosity close to a spherical shape is generated. When the porosity inside the 6% Mg alloy was compared with the 4% Mg alloy, it was observed that the size of the porosity was considerably increased. This is because as the amount of Mg added increases, the amount of hydrogen gas absorbed in the alloy increases, so that a lot of porosity is formed.

  17 and 18, the area ratio (the area of porosity per unit area) and the porosity around the center of the Al-4% Mg, Al-6% Mg alloy slab measured using an image analysis apparatus (LUZEX) {product name}. The distribution of density (number of porosity per unit area) is shown. When the holding time of any alloy co-soaking is 100 hours, the area ratio and density of porosity tend to increase suddenly. This is because when the porosity formed during solidification is reheated, it grows due to hydrogen redistribution and gas volume expansion according to the Sieverts law. That is, hydrogen atoms dissolved in supersaturation in an aluminum solid are released into the porosity as hydrogen gas during soaking or rolling. In addition, it is considered that, by holding at a high temperature for a long time, the dissolved hydrogen gas gathers at the grain boundary due to high-temperature diffusion, and a lot of porosity is reformed. However, when the holding time is 10 hours, the area ratio tends to decrease somewhat.

  In FIGS. 19-1, 19-2, 19-3, and 19-4, the holding time is kept constant for 10 hours, and the soaking temperature is changed, for example, 470 ° C., 500 ° C., and 530 ° C. before soaking. The change in porosity near the center of the A5052 alloy slab is shown. As can be seen from FIGS. 19-1 to 19-4, almost no change in porosity due to the soaking temperature is observed. However, when compared with the porosity before soaking in FIG. 19-1, the size was slightly increased, but it was observed that the number of porosity decreased.

  FIG. 20 shows the distribution of area ratio (porosity area per unit area) and porosity density (porosity number per unit area) near the center of the A5052 alloy slab measured using an image analysis apparatus (LUZEX) {product name}. . As shown in FIG. 20, almost no change in porosity due to a change in soaking temperature is observed. However, as with the observation results of FIGS. 19-1 to 19-4, it was found that both the area ratio and the density of the porosity were reduced when compared with any soaking temperature and before soaking.

  FIG. 21 shows changes in the porosity area ratio and density near the center of the A5052 slab measured by an image analyzer (LUZEX) {product name} when the soaking temperature is kept constant at 530 ° C. and the holding time 1, 10, 100 is changed. Show. When the soaking time is 10 hours, both the area ratio and density of the porosity are minimized. On the other hand, as shown in FIG. 21, it was found that when the soaking time was too long, the area ratio and number of porosity increased rapidly due to the diffusion of hydrogen gas.

  From the above observation and measurement results, the soaking time in which both the area ratio of porosity and the number of porosity per unit area are minimized within the range of this experiment was 10 hours. If the holding time is less than 1 hour, the treatment is completed before the entire slab reaches a uniform temperature, and sufficient soaking (homogenization treatment) effect cannot be obtained. Further, if the holding time exceeds 10 hours, the production cost increases and the amount of porosity tends to increase, which is not preferable. From this, the preferable soaking time was set to 1 to 10 hours. Moreover, the preferable temperature range about soaking temperature was 470-530 degreeC.

  In the experiment of the above homogenization treatment (soaking) conditions, the case where the casting speed was set to 58 mm / min was explained. However, even if the casting speed is changed, the holding temperature, holding time, porosity area ratio, and porosity density distribution state are affected. There is not, and the tendency similar to the distribution state shown in FIG.20 and FIG.21 is shown.

The thickness of the original slab before rolling under the conditions of casting speed 50 mm / min, rolling reduction rate 7% / pass, soaking holding temperature 520 ° C., soaking holding time 2 hours, hydrogen gas content 0.2 cc / 100 g or less. When the maximum length (μm) of the porosity of 8 types of thick plates obtained by rolling three types having different thicknesses (thicknesses depending on the size of the casting mold are 560 mm, 508 mm, and 406 mm), the results shown in Table 4 were obtained. was gotten.

  In the above experiment, the thickness of the original slab before rolling depends on the size of the casting mold, and the actual thickness of the original slab is reduced by the surface cutting on both sides. However, when the thickness of the thick plate is 460 mm or less, the porosity is reduced. The maximum length was 110 μm.

It is a flowchart which shows the manufacturing process of the aluminum alloy thick board of this invention. It is a graph which shows the coarsening of the thick plate center part porosity by the conventional rolling method. It is the distribution map which analyzed the stress and deformation inside the thick board of a rolling analysis model. It is a distribution map which shows the thick plate internal pressure in a rolling process. It is a microscope picture figure which shows the porosity distribution situation inside the surface layer of plate | board thickness 480mm. It is a microscope picture figure which shows the porosity distribution condition of the center part of plate | board thickness 480mm. It is a microscope picture figure which shows the porosity distribution condition inside the surface layer of board thickness 300mm. It is a microscope picture figure which shows the porosity distribution condition of the center part of plate | board thickness 300mm. It is a microscope picture figure which shows the porosity distribution condition of the thick plate center part of the former slab (As cast). It is a microscope picture figure which shows the porosity distribution condition of the thick board center part after soaking. It is a microscope picture figure which shows the porosity distribution condition of the thick plate center part of 300 mm thick after rolling. It is a microscope picture figure which shows the porosity distribution situation of the thick plate center part with a sheet thickness of 250 mm after rolling. It is a microscope picture figure which shows the porosity distribution situation of the thick plate center part of 200 mm thick after rolling. It is a graph which shows the relationship between the plate | board thickness and porosity size in rolling reduction 5% / pass, 6% / pass, 7% / pass, 10% / pass. It is a collection conceptual diagram of the sample for Al-Mg alloy slab heat treatment experiment. It is an extraction conceptual diagram of the sample for A5052 alloy slab heat treatment experiment. It is a graph which shows the relationship between soaking time and gas content in an alloy. It is a microscope picture figure which shows the porosity distribution condition of 110-120 mm from the surface layer at the time of holding time of Al-4% Mg alloy slab as 1 hour. It is a microscope picture figure which shows the porosity distribution situation of 95-105 mm from the surface layer at the time of holding | maintenance time of Al-4% Mg alloy slab as 1 hour. It is a microscope picture figure which shows the 80-90 mm porosity distribution state from the surface layer at the time of holding | maintenance time of Al-4% Mg alloy slab as 1 hour. It is a microscope picture figure which shows the porosity distribution condition of 110-120 mm from the surface layer at the time of holding time of Al-4% Mg alloy slab as 10 hours. It is a microscope picture figure which shows the porosity distribution state of 95-105 mm from the surface layer at the time of holding time of Al-4% Mg alloy slab as 10 hours. It is a microscope picture figure which shows the porosity distribution condition of 80-90 mm from the surface layer at the time of holding time of Al-4% Mg alloy slab as 10 hours. It is a microscope picture figure which shows the porosity distribution condition of 110-120 mm from the surface layer when the retention time of Al-4% Mg alloy slab is 100 hours. It is a microscope picture figure which shows the porosity distribution condition of 95-105 mm from the surface layer at the time of making retention time of Al-4% Mg alloy slab into 100 hours. It is a microscope picture figure which shows the 80-90 mm porosity distribution situation from the surface layer at the time of setting the retention time of Al-4% Mg alloy slab to 100 hours. It is a microscope picture figure which shows the porosity distribution condition of 110-120 mm from the surface layer when the retention time of Al-6% Mg alloy slab is 1 hour. It is a microscope picture figure which shows the porosity distribution condition of 95-105 mm from the surface layer at the time of making holding time of Al-6% Mg alloy slab into 1 hour. It is a microscope picture figure which shows the 80-90 mm porosity distribution condition from the surface layer at the time of making the holding time of Al-6% Mg alloy slab into 1 hour. It is a microscope picture figure which shows the porosity distribution condition of 110-120 mm from the surface layer at the time of making retention time of Al-6% Mg alloy slab into 10 hours. It is a microscope picture figure which shows the porosity distribution condition of 95-105 mm from the surface layer at the time of making retention time of Al-6% Mg alloy slab into 10 hours. It is a microscope picture figure which shows the 80-90 mm porosity distribution state from the surface layer at the time of holding time of Al-6% Mg alloy slab as 10 hours. It is a microscope picture figure which shows the porosity distribution condition of 110-120 mm from the surface layer when the retention time of Al-6% Mg alloy slab is 100 hours. It is a microscope picture figure which shows the porosity distribution condition of 95-105 mm from the surface layer at the time of making retention time of Al-6% Mg alloy slab into 100 hours. It is a microscope picture figure which shows the 80-90 mm porosity distribution condition from the surface layer at the time of making retention time of Al-6% Mg alloy slab into 100 hours. It is a graph which shows the relationship between the retention time in a Al-4% Mg alloy slab, a porosity area ratio, and a density. It is a graph which shows the relationship between the retention time in a Al-6% Mg alloy slab, a porosity area ratio, and a density. It is a microscope picture figure which shows the porosity distribution condition before soaking of A5052 alloy. It is a microscope picture figure which shows the porosity distribution condition whose soaking temperature of A5052 alloy is 470 degreeC. It is a microscope picture figure which shows the porosity distribution condition whose soaking temperature of A5052 alloy is 500 degreeC. It is a microscope picture figure which shows the porosity distribution condition whose soaking temperature of A5052 alloy is 530 degreeC. It is a graph which shows the relationship between the soaking temperature in A5052 alloy, a porosity area rate, and a density. It is a graph which shows the relationship of the retention time in a A5052 alloy, a porosity area rate, and a density.

Explanation of symbols

1 Thick plate 2 Roll

Claims (2)

A degassing treatment step for reducing the amount of hydrogen gas in the molten aluminum alloy, a step for casting a slab, and holding the slab at a predetermined temperature for a predetermined time to use a crystallized substance in the slab structure as a base material. A method for producing an aluminum alloy thick plate comprising a homogenization treatment step for diffusing into aluminum and a hot rolling step for rolling a thick plate having a final thickness of 100 to 460 mm by performing a plurality of rolling passes by a hot rolling mill. There,
In the degassing treatment step, degassing treatment is performed so that the hydrogen gas content in the slab after casting is 0.2 cc / 100 g or less,
In the homogenization treatment step, the slab is subjected to a homogenization treatment at a holding temperature of 470 to 530 ° C. and a holding time of 1 to 10 hours,
In the rolling step in which the plurality of rolling passes are performed, the rolling reduction ratio (δ) of one rolling when the thickness (H2) after rolling is set to the thickness (H2) before rolling (δ = { (H1−H2) / H1} × 100%] is rolled over the plurality of rolling passes at a rate of 7% or more. In the manufacturing method of the aluminum alloy thick plate of Claim 1,
In the said casting process, it casts at a casting speed of 50 mm / min or less, The manufacturing method of the aluminum alloy thick board characterized by the above-mentioned.