JP2017061709A - Aluminum alloy sheet excellent in ridging resistance and hem bendability and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet excellent in ridging resistance and hem bendability.SOLUTION: An aluminum alloy sheet composed of an aluminum alloy containing Mg and Si and excellent in ridging resistance and hem bendability, has crystal particle diameter of an L-LT surface at a central vicinity area with 1/2 depth of total sheet thickness in a sheet thickness direction from a sheet surface of 45 to 100 μm, crystal particle diameter of an L-ST surface in a whole sheet of 80 μm or less and Cube direction area percentage in a crystal orientation measured on the L-LT surface of a sheet surface of 10% or more. The present invention also provides a manufacturing method for the aluminum alloy sheet.SELECTED DRAWING: None

Description

  The present invention is suitably used for members, parts of various automobiles such as automobile body seats and body panels, ships, aircraft, etc., or building materials, structural materials, various mechanical instruments, home appliances and parts thereof, and the like. The present invention relates to an aluminum alloy plate excellent in ridging properties and hem bendability and a method for producing the same.

  For example, cold rolled steel sheets have often been used for automobile body sheets. However, recently, in order to suppress global warming and reduce energy costs, there is an increasing demand for reducing the weight of automobiles and improving fuel efficiency. For this reason, the tendency to use an aluminum alloy sheet having a specific gravity of about 1/3 of that of a cold-rolled steel sheet as a body sheet for an automobile is increased in spite of the strength equivalent to that of a conventional cold-rolled steel sheet. It's getting on. In recent years, aluminum alloy plates having characteristics such as high thermal conductivity and specific strength are increasingly used for molded parts other than automobiles, such as panels and chassis of electronic and electrical devices, for example.

  In general, as an aluminum alloy material for an automobile body sheet, an Al—Mg—Si alloy or an Al—Mg—Si—Cu alloy is mainly used in addition to an Al—Mg alloy. The Al—Mg—Si based alloy and the Al—Mg—Si—Cu based alloy are aging alloys, and the strength is improved before and after coating baking by using a heating process of coating baking. In other words, it has a relatively low strength before mold baking and excellent moldability, while it has an advantage that the strength after baking is increased, and thus has recently been applied to automobile materials.

  Moreover, as an aluminum alloy material for automobile body sheets, it is particularly necessary to have excellent surface quality and formability. Regarding the surface quality, the Al—Mg—Si alloy and the Al—Mg—Si—Cu alloy have an advantage that a Ruders mark that is a problem in the Al—Mg alloy is less likely to occur. However, on the other hand, it is often a problem that ridging marks are generated in which streaky irregularities are formed on the plate surface after press molding. With respect to formability, hem bending is generally performed when the outer panel and the inner panel are integrated, and therefore, there is a strong demand for particularly excellent hem bendability among the formability.

  Here, the ridging mark is a fine concavo-convex pattern that appears in a streak pattern in a direction parallel to the rolling direction in the manufacturing process of the raw material plate when the plate is formed. Ridging marks are particularly likely to occur when the press molding conditions become severe, and materials that do not generate ridging marks are strongly demanded along with the recent increase in the shape and thickness of automobile bodies. In the present specification, the property that ridging marks are not easily generated during molding is referred to as “riding resistance”.

  Since the generation of ridging marks is deeply related to the recrystallization behavior of the material, in order to suppress the generation of ridging marks, it is indispensable to control the metal structure in the plate manufacturing process. For this reason, as a conventional technique for improving ridging resistance, for example, as described in Patent Documents 1 to 5, from the viewpoint of controlling a recrystallization state during a hot rolling process of a plate material, a crystal Proposals have been made from the viewpoint of controlling the orientation and from the viewpoint of controlling the crystal grain size of the product plate. Further, for improving hem bendability, for example, as described in Patent Documents 6 and 7, proposals have been made from the viewpoint of crystal orientation.

Japanese Patent No. 2823797 Japanese Patent No. 3590685 JP 2009-263781 A JP 2010-242215 A Japanese Patent No. 5113318 Japanese Patent No. 4939901 JP 2014-234542 A

  Recently, further improvements in materials, particularly surface appearance quality, have been demanded from the viewpoint of design and the like. In particular, Al-Mg-Si-based alloy plates and Al-Mg-Si-Cu-based alloy plates with excellent formability as well as improved strength in the paint baking process have better ridging resistance. It is strongly required to have However, it has been difficult to sufficiently satisfy the required performance with the conventional technology as described above.

  In the method for producing an aluminum alloy sheet described in Patent Documents 1 and 2, since the hot rolling start temperature is in the range of 350 to 450 ° C., the formation of coarse crystal grains during hot rolling is suppressed to some extent. However, the suppression effect was insufficient. In particular, experiments by the present inventors have revealed that coarse crystal grains are formed near the center of the plate thickness, and as a result, sufficient ridging resistance cannot always be obtained.

  Moreover, in the manufacturing method of the aluminum alloy plate described in Patent Documents 3 and 4, in order to eliminate the structure in which the crystal grains close to the crystal orientation causing the ridging mark are grouped in the rolling direction, the aluminum alloy plate is specified. The crystal orientation is controlled. Although this method has a certain effect in improving the ridging resistance, the effect is insufficient for the further demand for improving the ridging resistance recently.

  Patent Documents 5 and 6 propose that the hem bendability, which is an important characteristic as an automobile body sheet material, is greatly improved by the development of the Cube orientation. However, the improvement of ridging marks and the improvement of hem bendability by controlling the crystal orientation require reciprocal texture control, and in order to realize this, it is necessary to use a very complicated and expensive manufacturing process. There is.

  In Patent Document 7, it is proposed to improve ridging resistance by controlling the crystal grain size. However, with this method, it is difficult to obtain sufficient bendability, and there remains a problem that requires a very complicated manufacturing process.

  In recent years, there has been a strong demand for the development of technology for manufacturing automobile body sheet materials at a lower cost while having higher performance than before. One part of the manufacturing process can be omitted as a cost-reducing measure, but this measure is adopted because it causes deterioration in various performances such as ridging resistance, hem bendability and bake hardness required for automobile body sheet materials. Has not reached.

  The present invention has been made in view of the above circumstances, and it is possible to reliably suppress generation of ridging marks even under severe molding conditions, and to provide an aluminum alloy plate excellent in hem bendability and molding having such excellent performance. An object of the present invention is to provide a manufacturing method capable of producing an aluminum alloy plate for processing on a mass production scale reliably and stably at a low cost.

  As a result of intensive studies on the cause of ridging marks, the present inventors have made a band-like structure (stripe) formed by crystal grains stretched in the rolling direction in the hot rolling and cold rolling processes that are the origin of ridging marks. When the crystal structure is recrystallized and decomposed, the recrystallized grain size is coarsened to increase the decomposition force and greatly reduce the strong linearity in the rolling direction, which is a characteristic of ridging marks. It was found that the generation of ridging marks can be suppressed.

  As a result of further studies by the present inventors, it has been found that the band-like structure decomposition effect due to the coarsening of the recrystallized grain size can be increased by making the band-like structure formed during hot rolling fine. In order to make the band-like structure fine, it is effective to lower the hot rolling temperature. By combining the band-like structure decomposition by recrystallization grain size coarsening, ridging marks can be obtained even under severe molding conditions. It was found that can be prevented.

  Furthermore, by lowering the hot rolling temperature, omitting intermediate annealing, and adopting a sufficient cold rolling rate, a rolling texture is developed during hot rolling and cold rolling, and this rolling texture is a solution. It contributes to the development of the Cube orientation during the crystallization treatment, and as a result, the bendability can be greatly improved by improving the Cube orientation density of the product plate. However, as described above, the Cube orientation is generally the orientation that causes ridging marks, and it has been difficult to achieve both improvement of ridging marks and improvement of bendability.

  In order to achieve both the improvement of the ridging mark due to the coarsening of the crystal grain size described above and the improvement of bendability due to the development of the Cube orientation, the present inventors have conducted intensive studies. It has been found that heat treatment can achieve both ridging mark improvement and bendability improvement. In other words, strain relief annealing below the recrystallization temperature makes it possible to reduce the strain energy in the rolled sheet without reducing the rolling texture formed during hot rolling and cold rolling, and subsequent solution treatment. During processing, the crystal grain size increases and the Cube orientation develops. Furthermore, in this manufacturing method, although a strain relief annealing process is required, the intermediate annealing process can be omitted, and thus the manufacturing cost can be reduced.

  As described above, the present inventors have conducted various experiments and studies, and as a result, manufacturing methods for Al—Mg—Si alloys and Al—Mg—Si—Cu alloys include control of hot rolling temperature, intermediate Control the grain size and orientation of the final plate by omitting annealing, adopting a sufficient cold rolling rate, performing strain relief annealing at a temperature where recrystallization does not occur, and solution treatment immediately after strain relief annealing. As a result, it has been found that the ridging resistance and the hem bendability are reliably and significantly improved.

  Specifically, the present invention according to claim 1 is an aluminum alloy plate made of an aluminum alloy containing Mg and Si and having a thickness t, which is along the thickness direction centering on the plate thickness (t / 2). Further, the crystal grain size on the L-LT plane in the range of ± (t / 8) is 45 to 100 μm, the crystal grain size of the L-ST plane is 80 μm or less in the whole plate, and the Cube orientation of the crystal orientation on the plate surface An aluminum alloy plate excellent in ridging resistance and hem bendability characterized by having an area ratio of 10% or more.

  Further, in the present invention according to claim 2, the present invention provides the aluminum alloy according to claim 1, wherein the aluminum alloy contains Mg: 0.20 to 1.50 mass%, Si: 0.30 to 2.00 mass%, and Mn: 0.03 to 0. .60 mass%, Cr: 0.01-0.40 mass%, Zr: 0.01-0.40 mass%, Fe: 0.03-1.00 mass%, Ti: 0.005-0.300 mass% and Zn: One or more selected from 0.03 to 2.50 mass% is further contained, Cu is regulated to 1.50 mass% or less, and the balance is composed of Al and inevitable impurities.

  Moreover, in this invention, in this invention, in the manufacturing method of the aluminum alloy plate of Claim 1 or 2, the casting process which casts the said aluminum alloy, the hot rolling process which hot-rolls an ingot, and intermediate | middle A cold rolling step for cold rolling the hot rolled plate without annealing, a strain relief annealing step for the cold rolled plate, and a solution treatment step for solution treatment of the annealed rolled plate, the heat In the cold rolling step, the hot rolling start temperature is set to 300 to 450 ° C., the hot rolling end temperature is set to 200 to 350 ° C., and in the cold rolling step, the rolling reduction is set to 60.0% or more to reduce the final sheet thickness. A method for producing an aluminum alloy plate excellent in ridging resistance and hem bendability, characterized in that a cold-rolled plate is heat-treated at an ultimate temperature of 200 to 350 ° C. in the strain relief annealing step. .

  Furthermore, the present invention according to claim 4 further comprises a homogenization treatment step of homogenizing the ingot between the casting step and the hot rolling step.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of a ridging mark can be suppressed reliably also on severe forming conditions, and the aluminum alloy plate excellent in hem bendability can be provided. Moreover, the manufacturing method of the aluminum alloy plate excellent in ridging resistance and hem bendability of the present invention can reduce the cost as compared with the conventional manufacturing method.

  Hereinafter, the aluminum alloy plate excellent in ridging resistance and hem bendability according to the present invention will be described in detail.

1. The component composition of the aluminum alloy The component composition of the aluminum alloy plate according to the present invention may be an Al-Mg-Si-based alloy or an Al-Mg-Si-Cu-based alloy, and the specific component composition is particularly Although not limited, it usually contains Mg: 0.20 to 1.50 mass% (hereinafter simply referred to as “%”), Si: 0.30 to 2.00%, and Mn: 0.00. 03 to 0.60%, Cr: 0.01 to 0.40%, Zr: 0.01 to 0.40%, Fe: 0.03 to 1.00%, Ti: 0.05 to 0.30% And Zn: containing one or more selected from 0.03 to 2.50%, Cu: regulated to 1.50% or less, and the remainder consisting of Al and unavoidable impurities is preferably used. .

  Next, the reasons for limiting the above elements will be described.

Mg:
Mg is an alloy element that is the basis of the Al—Mg—Si alloy or Al—Mg—Si—Cu alloy that is the subject of the present invention, and contributes to improving the strength together with Si. The Mg content is preferably 0.20 to 1.50%. If the Mg content is less than 0.20%, G. contributes to strength improvement by precipitation hardening during baking. P. Since the amount of zone formation is reduced, a sufficient strength improvement effect cannot be obtained. On the other hand, if the Mg content exceeds 1.50%, a coarse Mg-Si-based intermetallic compound is generated, and press formability, mainly bending workability, is deteriorated. In particular, in order to improve the bending workability of the final plate, the Mg content is more preferably 0.30 to 0.90%.

Si:
Si is also an alloy element that is the basis of the Al—Mg—Si alloy or Al—Mg—Si—Cu alloy that is the subject of the present invention, and contributes to strength improvement together with Mg. Further, Si is generated as a crystallized product of metal Si particles during casting. Since the periphery of the metal Si particles is deformed by the processing applied during cold rolling and becomes a recrystallization nucleus generation site during the solution treatment, it contributes to refinement of the recrystallized structure. The Si content is preferably 0.30 to 2.00%. If the Si content is less than 0.30%, the above effects cannot be obtained sufficiently. On the other hand, when the Si content exceeds 2.00%, coarse Si particles and coarse Mg-Si intermetallic compounds are generated, and press formability, particularly bending workability, is deteriorated. In order to obtain a better balance between press formability and bending workability, the Si content is more preferably 0.50 to 1.30%.

Mn, Cr, Zr, Fe, Zn:
These elements are effective in improving the strength, refining crystal grains, improving aging (bake hardenability) and / or improving surface treatment properties, and contain one or more of these elements. preferable. Of these, Mn, Cr, and Zr are effective in improving the strength and refining and stabilizing the crystal grain structure. If the Mn content is less than 0.03%, the Cr content is less than 0.01%, and the Zr content is less than 0.01%, the above effects cannot be obtained sufficiently. On the other hand, when the content of Mn exceeds 0.60% and the content of Cr and Zr exceeds 0.40%, not only the above effects are saturated but also a large number of intermetallic compounds are produced, and formability, In particular, hem bendability may be reduced. Therefore, the Mn content is preferably 0.03 to 0.60%, and the Cr and Zr contents are preferably 0.01 to 0.40%. More preferably, the Mn content is 0.03 to 0.40%, and the Cr and Zr contents are each 0.01 to 0.30%.

  Fe is also an element effective for strength improvement and crystal grain refinement. If the Fe content is less than 0.03%, the above effect cannot be obtained sufficiently. On the other hand, when the Fe content exceeds 1.00%, a large number of intermetallic compounds are produced, and press moldability and bending workability may be deteriorated. Therefore, the Fe content is preferably 0.03 to 1.00%. In particular, in order to suppress a decrease in bending workability to a minimum, the Fe content is more preferably 0.03 to 0.50%. Further, Zn is an element that contributes to improvement of strength through improvement of aging properties and is effective in improving surface treatment properties. If the Zn content is less than 0.03%, the above effect cannot be obtained sufficiently. On the other hand, if the Zn content exceeds 2.50%, the moldability deteriorates. Therefore, the Zn content is preferably 0.03 to 2.50. The Zn content is more preferably 0.03 to 1.50%.

Ti:
Ti exhibits the effect of refining the ingot structure. The Ti content is preferably 0.005 to 0.300%. If the Ti content is less than 0.005%, the above effects cannot be obtained sufficiently. On the other hand, when the Ti content exceeds 0.300%, not only the effect of addition of Ti is saturated but also a coarse crystallized product may be generated. The Ti content is more preferably 0.005 to 0.200%. Further, by adding B of 500 ppm or less simultaneously with Ti, the effect of refining and stabilizing the ingot structure becomes more remarkable.

Cu:
Cu may be added to improve strength and formability. If the Cu content exceeds 1.50%, the corrosion resistance (intergranular corrosion resistance, yarn rust resistance) decreases, so the Cu content is preferably regulated to 1.50% or less. Further, when it is desired to further improve the corrosion resistance, it is preferable to limit the Cu content to 1.00% or less, and particularly when corrosion resistance is important, the Cu content is preferably limited to 0.05% or less. .

  In addition to the above elements, B, Ga, V, and the like as unavoidable impurities are each contained in an amount of less than 0.05% and less than 0.15% in total, because they do not affect the material of the present invention. Also good.

  The contents of Mn, Cr, Zr, Fe, Zn, and Ti are shown as ranges when positively added. Accordingly, any of these elements does not exclude the case where an amount less than the lower limit of each content is contained as an impurity. In particular, when an ordinary aluminum ingot is used, Fe of less than 0.03% is usually contained as an inevitable impurity.

2. Crystal grain size control and crystal orientation control of aluminum alloy plate In the aluminum alloy plate according to the present invention, in order to improve the ridging resistance and hem bendability reliably and stably, the alloy composition is adjusted as described above. In addition, it is extremely important to control the crystal grain size and crystal orientation of the final aluminum alloy sheet.

2-1. Specific crystal grain size A band-like structure that has a particularly strong effect on the generation of ridging marks is present in the region near the center of the aluminum alloy plate in the thickness direction, and the crystal grain size in this region is recrystallized to an appropriate size. This promotes decomposition of the band-like tissue and prevents the generation of ridging marks. Here, the region near the center in the plate thickness direction (hereinafter, “region near the center”) refers to the thickness of the aluminum alloy plate as t, and the thickness along the thickness direction around the plate thickness (t / 2). The region in the range of (t / 8) shall be said.

  According to experiments conducted by the present inventors, in order to decompose the band-like structure formed in the manufacturing process, the crystal grain size d1 in the L-LT plane in the vicinity of the center is 45 μm or more, preferably 50 μm or more, More preferably, it is 60 μm or more. When the crystal grain size d1 is less than 45 μm, the band-like structure that causes the generation of ridging marks cannot be sufficiently decomposed, and ridging marks are generated. Further, if the crystal grain size d1 exceeds 100 μm, the elongation and formability are greatly reduced. Therefore, the crystal grain size d1 is set to 100 μm or less, preferably 80 μm or less.

  Further, according to conventional knowledge, increasing the crystal grain size of the final material is thought to lead to deterioration of surface properties and formability. For example, problems related to surface properties such as rough skin and orange peel May cause. It is known that it is effective to reduce the crystal grain size for these suppressions. For this reason, also in the present invention, it is necessary to control the crystal grain size of the entire plate to such an extent that rough skin and orange peel do not occur. For that purpose, the crystal grain size d2 in the L-ST plane of the entire plate thickness is 80 μm or less, preferably 60 μm or less. In the alloy composition and manufacturing method employed in the present invention, it is about 10 μm.

  In order to improve the hem bendability, it is particularly important to control the crystal orientation of the plate surface layer that has a strong influence on the hem bendability. For this purpose, the Cube orientation area ratio C of the crystal orientation on the plate surface is set to 10% or more, preferably 15% or more. In the alloy composition and manufacturing method employed in the present invention, about 60% is the upper limit.

  As described above, in order to improve ridging resistance, the entire plate thickness is obtained while decomposing the band-like structure by increasing the crystal grain size d1 in the L-LT plane near the center during recrystallization to an appropriate size. By controlling the crystal grain size d2 in the L-ST plane, rough skin and the like can be prevented, and further, by controlling the Cube orientation area ratio C of the crystal orientation on the plate surface, the hem bendability can be improved. It is possible to obtain an aluminum alloy plate excellent in surface properties such as ridging resistance and rough skin resistance, and hem bendability.

  Further, the band-like structure in the region near the center that strongly affects the generation of ridging marks is formed from the time of hot rolling, and the thickness of the region near the center with respect to the total sheet thickness t, ie, the thickness (t / 2) is the center. Even if rolling progresses and the plate | board thickness reduces, the area | region over the range of +/- (t / 8) along the length direction maintains the ratio with respect to the whole thickness. Therefore, the plate thickness that can prevent ridging marks by controlling the crystal grain size is not particularly limited, and can be applied to a final rolled plate having a predetermined plate thickness required for a product. A 5.0 mm one is used.

2-2. Specific Measurement Method for Crystal Grain Size and Crystal Orientation Next, a specific measurement method for the crystal grain size and crystal orientation will be described.
First, about d1, after carrying out thickness reduction by caustic etching to the arbitrary L-LT surface in the center vicinity area | region of an aluminum alloy plate, it carries out mechanical polishing, buffing, and electrolytic polishing, and let it be a measurement surface. Next, for d2, mechanical polishing, buffing, and electrolytic polishing are performed on an arbitrary L-ST surface of the aluminum alloy plate to obtain a measurement surface. Further, for C, the surface of the aluminum alloy plate is subjected to mechanical polishing, buffing, and electrolytic polishing to obtain a measurement surface.

  Specifically, the orientation data of the texture is acquired by measuring each measurement surface with a backscattered electron diffraction measurement device (SEM-EBSD) attached to the scanning electron microscope. Next, crystal grain sizes (d1, d2) are obtained from the obtained orientation data using EBSD analysis software (“OIM Analysis” manufactured by TSL). Here, a crystal boundary line having a misorientation of 5 ° or more is regarded as a crystal grain boundary, and a diameter calculated as a circle is defined as a crystal grain size. Further, from the orientation data obtained in the same manner, the crystal orientation area ratio C is measured using EBSD analysis software. For the Cube orientation area ratio C, a crystal orientation within 15 ° from the (001) <100> orientation is calculated as the Cube orientation. The measurement area on each measurement surface is an area of 1000 μm × 1000 μm or more in the case of the L-LT surface, and an area of 1000 μm × 1000 (or the total plate thickness) μm or more in the case of the L-ST surface. Three or more points are measured as about 1/10 of the diameter, and D1, d1, and C are determined by the arithmetic average value.

3. In the method for producing an aluminum alloy plate according to the present invention, as the structure of the aluminum alloy plate for forming the final plate, in order to obtain the above-described structure, hot rolling during the production process, It is necessary to carry out cold rolling, strain relief annealing and solution treatment under specific conditions.

3-1. Necessity of performing each manufacturing process First, the necessity of performing each manufacturing process in the manufacturing method according to the present invention will be described. In order to obtain d1, d2 and C defined in the present invention, various manufacturing methods are conceivable. However, from the viewpoint of cost reduction, the processes generally used as a manufacturing method for automobile body sheet materials are currently used, that is, casting, homogenization treatment, hot rolling, cold rolling, intermediate annealing, cold rolling. It is necessary to carry out the same number of steps as the steps according to the order of the solution treatment.

  In order to obtain the d1, d2 and C defined in the present invention, it is necessary to make the crystal grain size during the solution treatment coarser than that in the conventional process. As this method, “reducing the strain energy introduced into the cold rolled sheet immediately before the solution treatment” is optimal. The dislocations introduced by hot rolling or cold rolling become nucleation sites for recrystallization nuclei during the solution treatment. Therefore, the larger the strain energy, the larger the recrystallization generated. Nuclei increase and recrystallized grains become finer. On the contrary, the smaller the introduced strain energy, the fewer recrystallized nuclei that are generated, and the larger the crystal grain size. Further, in order to obtain C, it is necessary to sufficiently develop a rolling texture during rolling. As this method, it is necessary to reduce the number of recrystallizations during the manufacturing process and to obtain a sufficient rolling reduction.

  Therefore, in order to make the above-mentioned d1, d2 and C specified in the present invention compatible, a rolling texture can be sufficiently developed by increasing the rolling reduction without recrystallization and introduced immediately before the solution treatment. It is necessary to reduce the strain energy generated.

  Here, in order to reduce the strain energy introduced into the cold rolled sheet immediately before the solution treatment, it is easiest to reduce the hot rolling rate and the cold rolling rate. The rolling rate needs to be sufficiently low. In that case, it is known that a Cube orientation effective for improving bendability is not sufficiently developed. This is because the rolling texture formed during rolling plays an important role in the development of the Cube orientation during solution treatment, and the Cube orientation must be developed sufficiently during rolling. Does not develop.

  In order to reconcile such a reciprocal phenomenon with respect to strain energy, the present inventors have found that a strain relief annealing process for reducing strain energy is performed by performing annealing immediately before the solution treatment. In this strain relief annealing, heat treatment is performed at a temperature lower than the recrystallization temperature. Therefore, it becomes possible to reduce only the strain energy while maintaining the rolling texture developed by the high cold rolling rate, and the crystal grain size is appropriately coarsened during the solution treatment immediately after that, and the high Cube. It is possible to obtain an orientation density.

  Therefore, in the cold rolling step before the strain relief annealing, the rolling reduction is set to 60% or more, preferably 70% or more. If the rolling reduction is less than 60%, the rolling assembly necessary for the development of the Cube orientation does not sufficiently develop, and a desired Cube orientation area ratio cannot be obtained in the solution treatment step. Furthermore, by performing the cold rolling process without performing the intermediate annealing process after the hot rolling process, the manufacturing cost can be reduced while further developing the rolling texture.

3-2. Each manufacturing process Next, the typical and optimal manufacturing method for obtaining the aluminum alloy plate which has said d1, d2, and C prescribed | regulated by this invention is demonstrated. In such a production method, a molten aluminum alloy melt is cast, optionally subjected to a homogenization treatment, and then hot rolling, cold rolling, strain relief annealing, and solution treatment are performed in this order.

3-2-1. Casting process An aluminum alloy having the above-described composition is melted in accordance with a conventional method, and a normal casting method such as a continuous casting method (CC casting method) or a semi-continuous casting method (DC casting method) is appropriately selected and cast.

3-2-2. Homogenization treatment process You may perform a homogenization process as needed with respect to the ingot obtained by a casting process. The conditions for the homogenization treatment are not particularly limited, but it is preferable to perform a heat treatment at a temperature of 480 to 590 ° C. for 0.5 to 24 hours.

3-2-3. Hot Rolling Step Hot rolling may be performed on the ingot after the homogenization treatment or on the ingot after casting according to a conventional general method. In the process up to the start of hot rolling, any of the following processing methods can be applied as necessary. That is, when homogenization treatment is performed, after cooling to normal temperature or near normal temperature in the cooling process after homogenization treatment, it is again heated to the start temperature of hot rolling and held, and hot rolling is performed at this temperature. A method of starting, or a method of starting or maintaining hot rolling at a temperature at which the hot rolling is started or cooled in the cooling process after the homogenization treatment and starting the hot rolling at this temperature, or when the homogenization treatment is not performed. Is a method in which after cooling to room temperature or near room temperature after the casting process, it is again heated to the hot rolling start temperature and held, and hot rolling is started at this temperature.

  In hot rolling, the hot rolling start temperature is set to 300 to 450 ° C, and the hot rolling end temperature is set to 200 to 350 ° C. The hot rolling start temperature is preferably 300 to 420 ° C, and the hot rolling end temperature is preferably 200 to 320 ° C. If the starting temperature is less than 300 ° C., rolling will be difficult or the productivity will be significantly reduced. If it exceeds 450 ° C., recrystallization will be repeated during hot rolling, and the rolling texture will not develop. As a result, the Cube orientation will not change during the solution treatment. It will not develop. If the end temperature is less than 200 ° C., rolling becomes difficult, and if it exceeds 350 ° C., recrystallization occurs and the Cube orientation does not develop.

3-2-4. Cold rolling process Following the hot rolling process, the rolled sheet is subjected to cold rolling to obtain a cold rolled sheet having a final thickness (product thickness). The rolling reduction in the cold rolling step is 60.0% or more, preferably 75.0% or more. When the rolling reduction is less than 60.0%, the rolling texture formed during rolling does not sufficiently develop, and the Cube orientation density formed during the solution treatment becomes insufficient. If the rolling reduction exceeds 90%, cold rolling itself becomes difficult, so the upper limit of the rolling reduction is 90%. Here, it is also possible to carry out cold rolling and intermediate annealing following hot rolling. However, in this case, the manufacturing process increases, so that the cost is increased and the rolling texture formed during hot rolling and cold rolling is lowered by recrystallization during intermediate annealing. As a result, it becomes more difficult to obtain a sufficient Cube orientation density at the time of the solution treatment, and therefore intermediate annealing is not performed in the present invention.

3-2-5. Strain relief annealing Strain relief annealing is performed on the cold rolled sheet. Examples of the strain relief annealing include a batch furnace and a continuous annealing furnace. Since the amount of decrease in strain energy during strain relief annealing depends on the heat treatment temperature and time of annealing, conditions must be set so that an appropriate strain energy amount is obtained.

  The heat treatment temperature for strain relief annealing depends on the annealing method to be used, but is 200 to 350 ° C, preferably 230 to 350 ° C. The purpose of strain relief annealing is to reduce strain energy while still in an unrecrystallized state. If recrystallization occurs during strain relief annealing, recrystallization occurs with a high strain energy, so that the crystal grain size becomes fine and the desired coarse crystal grain size cannot be obtained.

  In the case of using a batch furnace for annealing, the processing temperature region is shifted to a lower temperature side than in the case of using a continuous annealing furnace described later, and strain relief annealing is performed for a long time. The annealing heat treatment temperature is 200 to 300 ° C, preferably 230 to 300 ° C. The holding time is preferably 5 minutes to 20 hours, more preferably 1 hour to 10 hours. When the heat treatment temperature is less than 200 ° C., the holding time takes a long time, so the productivity is lowered. On the other hand, when the heat treatment temperature exceeds 300 ° C., the cold-rolled sheet is recrystallized, and the prescribed crystal grain size and Cube orientation density cannot be obtained during the solution treatment in the next step. When the holding time is less than 5 minutes, it becomes difficult to stably manage the holding time. On the other hand, when holding time exceeds 20 hours, productivity will fall.

  When a continuous annealing furnace (CAL) is used for annealing, the processing temperature region is shifted to a higher temperature side than when a batch furnace is used, and strain relief annealing is performed in a short time. The ultimate temperature of the heat treatment is 250 to 350 ° C, preferably 270 to 350 ° C. The holding time is preferably 0 seconds to 5 minutes, and more preferably 0 seconds to 1 minute. When the ultimate temperature is less than 250 ° C., the strain energy cannot be sufficiently reduced by heat treatment in a short time. On the other hand, when the ultimate temperature exceeds 350 ° C., there is a risk of recrystallization by a short heat treatment. If the holding time exceeds 1 minute, productivity may be reduced. The holding time of 0 seconds means that the cooling is performed immediately after reaching the ultimate temperature.

  By applying a solution treatment to the cold rolled sheet with reduced strain energy by such a strain relief annealing process, the grain size is appropriately coarse enough to improve ridging marks and rough skin. (D1, d2) can be obtained, and a high Cube orientation density can be obtained.

3-2-6. Solution Treatment Step Following the strain relief annealing, the rolled plate is subjected to a solution treatment. The material arrival temperature in the solution treatment is 480 to 590 ° C. or lower. If the material arrival temperature is lower than 480 ° C., recrystallization may not occur. On the other hand, if the material arrival temperature exceeds 590 ° C., the plate may melt and stable production may become difficult. The holding time is not particularly limited, but is preferably 0 seconds to 5 minutes, more preferably 0 seconds to 1 minute from the viewpoint of productivity. For cooling after the solution treatment, the cooling rate from the holding temperature to a temperature range of 150 ° C. or lower is preferably 100 ° C./min or higher, whereby sufficient moldability and bake hardenability can be obtained. The cooling rate is more preferably 300 ° C./min or more. The upper limit of the cooling rate depends on the cooling device and the cooling method, but in the present invention, it is set to 10,000 ° C./min from the viewpoint of productivity and operability.

3-2-7. Other Steps In the present invention, in order to obtain good bake hardenability, it is preferable to perform preliminary aging treatment immediately after the solution treatment. However, this preliminary aging treatment does not have an essential influence on the crystal grain size, and therefore the preliminary aging treatment may not be performed in the present invention.

  Examples of the present invention will be described below together with comparative examples. The following examples are for explaining the effects of the present invention, and the processes and conditions described in the examples do not limit the technical scope of the present invention.

  Aluminum alloys having respective component compositions shown in alloy codes A to N in Table 1 were melted in accordance with a conventional method, and cast into a slab by a DC casting method. The ridging resistance and hem bendability, which are the main problems of the present invention, include the above crystal grain sizes d1, d2 and C as means for solving the problems. The above solution is controlled by prescribing. Furthermore, since the rough skin property is also suppressed by d1 and d2, this was also evaluated. On the other hand, strength as a mechanical characteristic in addition to the main problems described above is not listed as a problem of the present invention, but it was also evaluated because it is a characteristic originally required for automobile body sheets and the like.

  Each obtained slab was homogenized at 530 ° C. for 8 hours and then allowed to cool to near room temperature. Then, after heating to the hot rolling start temperature shown in Table 2, preliminary heating was performed by holding at this temperature for 2 hours. Further, after preliminary heating, hot rolling was performed at the start temperature and end temperature shown in Table 2. Table 2 shows the thickness after hot rolling.

  Next, the hot-rolled sheet was cold-rolled to obtain a cold-rolled sheet having a final sheet thickness of 1.0 mm. The cold rolling rate is shown in Table 2.

  Next, after performing strain relief annealing on the cold rolled sheet under the conditions shown in Table 2, solution treatment was performed under the conditions shown in Table 2. For the solution treatment, a continuous annealing furnace was used. Then, after cooling to near room temperature at a cooling rate of 600 to 1000 ° C./min, a preliminary aging treatment was immediately performed at 80 ° C. for 5 hours. This preliminary aging treatment affects the mechanical properties, but does not affect the crystal grain size or crystal orientation. The structure after annealing is also shown in Table 2.

  With respect to each plate material sample having a final plate thickness of 1 mm obtained as described above, the crystal grain size (d1, d2) and crystal orientation (C) were measured by the method described above. The results are shown in Table 3.

  Furthermore, ridging resistance was evaluated for each plate material sample using a conventional simple evaluation method. Specifically, a JIS No. 5 test piece was collected along a direction forming 90 ° with respect to the rolling direction. The test piece was stretched at 5% and 15%, respectively, and a streak pattern (striated uneven pattern) generated along the rolling direction on the surface was used as a ridging mark, and the presence or absence of the occurrence was visually determined. The 5% stretch is the amount of strain assuming normal press forming, and the 15% stretch is the amount of strain assuming particularly severe forming. A circle indicates no streak pattern, and a cross indicates a strong streak pattern. Similarly, the presence or absence of rough skin was also determined. The mark “◯” indicates that no rough skin occurs, and the mark “X” indicates that rough skin that is problematic as a surface texture has occurred. The results are shown in Table 3.

  Furthermore, for each plate material sample, 90 days after the solution treatment, a JIS No. 5 test piece in the direction of 90 ° with respect to the rolling direction was collected, and a hemming test based on JIS 7701 was performed. The pre-strain was 8%, the punch tip radius during pre-hemming was 0.5 mm, and the thickness of the intermediate plate during main hemming was 1.0 mm. After the hemming test, the outer peripheral surface was observed, and 0 to 2 points described in JISH7701 were set to pass (◯), and 3 to 4 points were set to fail (x).

  Finally, strength was also evaluated as mechanical properties. For each plate material sample obtained as described above, 7 days after the solution treatment, a JIS No. 5 test piece was cut out in a direction parallel to the rolling direction, and 0.2% proof stress (ASYS) was obtained by a tensile test. And elongation (ASEL) were evaluated. Further, after the test piece was stretched by 2%, a 0.2% proof stress value (BHYS) after heat treatment in an oil bath at 170 ° C. for 20 minutes was measured as a heat treatment corresponding to the paint baking treatment. As criteria for determining formability and strength, ASYS is 90 MPa or higher, ASEL is 25% or higher, and BHYS is 160 MPa or higher, based on the standards required for automobile body sheet materials. It was. The results are shown in Table 3.

  Examples of production process numbers 1 to 3, 5, 7, 10, 11, 13, and 15 in Table 3 are all within the range defined by the present invention for the component composition of the alloy, and the crystal grain size after solution treatment d1, d2 and Cube orientation area ratio C are within the range defined by the present invention. In these examples, it has been confirmed that 5% and 15% stretches do not cause ridging and do not cause rough skin, neither of which is a problem. As mechanical properties required for automobile materials, ASYA , ASEL and BHYS also satisfactorily fulfilled the performance. Furthermore, the structure after annealing became non-recrystallized.

  On the other hand, in the production process numbers 4 and 14 in Table 3, since the cold rolling rate is low, the Cube orientation area rate is outside the range defined by the present invention, and the hem bendability is required as an automobile material. I was not satisfied. On the other hand, the crystal grain sizes d1 and d2 are within the range defined by the present invention, and ridging did not occur and rough skin did not occur even with 15% stretch simulating severe press molding.

  In manufacturing process numbers 6 and 9, since the temperature of strain relief annealing was low, the strain energy did not sufficiently decrease. As a result, the crystal grain size d1 was out of the range specified in the present invention during the subsequent solution treatment. Since the starting temperature of the hot rolling was within the range specified by the present invention, ridging did not occur in the 5% stretch, but ridging occurred in the 15% stretch that simulated severe press molding.

  In the production process numbers 8 and 12, since the temperature of strain relief annealing was high, the structure after strain relief annealing was a recrystallized structure, and the crystal grain size d1 was outside the range specified in the present invention. Since the starting temperature of the hot rolling was within the range specified by the present invention, ridging did not occur in the 5% stretch, but ridging occurred in the 15% stretch that simulated severe press molding.

  In the production process numbers 16 and 17, since the heating and holding in the strain relief annealing was performed for a long time, the strain energy was excessively reduced, and as a result, the crystal was recrystallized excessively during the subsequent solution treatment. It was out of the range of the prescribed crystal grain diameters d1 and d2. Since d1 was sufficiently coarse, ridging did not occur even with 15% stretch, but rough skin was strongly generated. Moreover, in manufacturing process number 16, ASEL failed.

  In production process number 18, the hot rolling start temperature was as high as 550 ° C., and since strain relief annealing was not performed, ridging occurred strongly, the Cube orientation area ratio was low, and the hem bendability was inferior.

  In manufacturing process number 19, since strain relief annealing was not performed, the crystal grain size d1 was outside the range specified in the present invention, and ridging occurred in 15% stretch simulating severe press molding.

  In production process number 20, since the hot rolling start temperature is as high as 550 ° C., ridging is usually strong, but the crystal grain size after solution treatment is within the range specified in the present invention by strain relief annealing. Therefore, ridging did not occur even with 15% stretch. However, since the starting temperature of hot rolling is high, the development of the rolling texture during hot rolling is small and the Cube orientation area ratio is low, resulting in poor hem bendability.

  In manufacturing process number 21, since the end temperature of hot rolling was high, as a result of recrystallization at the end of hot rolling, the Cube orientation area ratio after solution treatment was low, and the hem bendability was inferior.

  In the examples of production process numbers 22 to 29 in Table 3, the composition of the alloy is out of the range defined by the present invention. The production conditions satisfied the scope of the present invention, and the crystal grain size (d1, d2) and the Cube orientation area ratio (C) were satisfied. As a result, the ridging mark resistance and the hem bendability were acceptable. However, at least one of ASYA, ASEL, and BHYS becomes x, and the mechanical characteristics are not satisfactory.

  As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. This embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. This embodiment and its modifications are included in the scope of the present invention and the gist thereof, and are also included in the invention described in the claims and the equivalent scope thereof.

  The aluminum alloy plate according to the present invention can reliably suppress the generation of ridging marks even under severe molding conditions, and is excellent in hem bendability. Further, the method for producing an aluminum alloy plate according to the present invention enables reliable and stable production at a low cost on a mass production scale.

Claims (4)

  An aluminum alloy plate made of an aluminum alloy containing Mg and Si and having a thickness t, L-LT in a range of ± (t / 8) along the thickness direction centering on the plate thickness (t / 2) The crystal grain size on the plane is 45 to 100 μm, the crystal grain size of the L-ST plane is 80 μm or less in the whole plate, and the Cube orientation area ratio of the crystal orientation on the plate surface is 10% or more. Aluminum alloy plate with excellent ridging resistance and hem bendability.   The aluminum alloy contains Mg: 0.20 to 1.50 mass%, Si: 0.30 to 2.00 mass%, Mn: 0.03 to 0.60 mass%, Cr: 0.01 to 0.40 mass. %, Zr: 0.01-0.40 mass%, Fe: 0.03-1.00 mass%, Ti: 0.005-0.300 mass% and Zn: 0.03-2.50 mass% The aluminum alloy sheet excellent in ridging resistance and hem bendability according to claim 1, further comprising seeds or two or more kinds, Cu: regulated to 1.50 mass% or less, and consisting of the balance Al and inevitable impurities.   The method for producing an aluminum alloy plate according to claim 1 or 2, wherein a casting step for casting the aluminum alloy, a hot rolling step for hot rolling the ingot, and a hot rolled plate without intermediate annealing. A cold rolling step for cold rolling, a strain relief annealing step for the cold rolled plate, and a solution treatment step for solution treatment of the annealed rolled plate, in the hot rolling step, the hot rolling start temperature 300 to 450 ° C., the hot rolling finish temperature is 200 to 350 ° C., and in the cold rolling step, the rolling reduction is 60.0% or more to obtain a cold rolled plate having a final thickness, and the strain relief annealing step. The method for producing an aluminum alloy plate excellent in ridging resistance and hem bendability, wherein the cold-rolled plate is heat-treated at an ultimate temperature of 200 to 350 ° C.   The method for producing an aluminum alloy plate excellent in ridging resistance and hem bendability according to claim 3, further comprising a homogenization treatment step of homogenizing the ingot between the casting step and the hot rolling step.