JP2016098412A - Method for producing aluminum alloy sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aluminum alloy sheet excellent in ridging mark resistance without providing the restrictions of the production method and further without increasing production costs.SOLUTION: The method for producing an aluminum alloy sheet is a method for producing Al-Mg-Si series or Al-Mg-Si-Cu series aluminum alloy sheet for an automobile panel, and the aluminum alloy sheet is produced by performing uniformization treatment, hot rolling and cold rolling using an ingot in which the average crystal grain size in the central part of the ingot is 150 μm or lower. The crystal grain size of the ingot 10 is measured, e.g., at the 5 points of measurement points 11 in the central part of the ingot with a low cooling velocity in general.SELECTED DRAWING: Figure 1

Description

  The present invention is a molding process as a member / part of various automobiles, ships, airplanes, etc., such as body sheets and body panels for automobiles, as a building material or structural material, or as a raw material for various machinery / equipment, home appliances or parts thereof. And an Al-Mg-Si-based or Al-Mg-Si-Cu-based aluminum alloy plate used for coating and baking.

  Conventionally, cold rolled steel sheets have been mainly used as body sheets for automobiles. Recently, however, aluminum alloy sheets have been increasingly used from the viewpoint of weight reduction of the vehicle body. In addition, since body sheets for automobiles are used after being subjected to press molding or high-temperature high-speed molding, they are required to have excellent moldability.

  For such body sheets for automobiles, Al-Mg-Si based alloys and Al-Mg-Si-Cu based aluminum alloy plates having aging properties are mainly used.

  In recent years, the shape of molded products that require severe molding due to productivity and design design has increased, so it is extremely difficult to suppress the occurrence of rough skin and ridging marks at severe molding sites. The problem is difficult. A ridging mark is a streak pattern along the rolling direction that appears during the forming process of a plate, and is particularly likely to occur when the forming conditions become severe, such as an increase in the size of the structure, a complicated shape, or a reduction in thickness.

  Conventionally, the ingot is cooled after homogenization heat treatment at a temperature of 500 ° C. or higher, or reheated after cooling to room temperature, and heated at a relatively low temperature of 350 to 450 ° C. It is known to prevent ridging marks on the excess Si-type 6000 series aluminum alloy sheet by starting hot rolling (see Patent Document 1).

  Also, various methods for improving the ridging mark by controlling the crystal orientation of the 6000 series aluminum alloy plate as in Patent Documents 2 and 3 have been proposed.

Japanese Patent Application Laid-Open No. 08-232052 JP 2009-263781 A JP 2010-242215 A JP 2003-226926 A

  However, the plate obtained by the conventional manufacturing method for the Al-Mg-Si-based and Al-Mg-Si-Cu-based alloy plates for automobile body sheets as described above is required in recent automobile body sheets. It was difficult to sufficiently satisfy the ridging mark resistance.

  That is, in the method shown in Patent Document 1, since the hot rolling start temperature is in the range from 350 ° C. to 450 ° C., the formation of coarse crystal grains during hot rolling is moderately suppressed. However, the suppression effect was still insufficient. In particular, recent automobile body sheet materials are increasingly subjected to more severe molding from the viewpoint of design, and in such cases, it has been difficult to prevent the generation of ridging marks.

  In addition, the method of controlling the specific crystal orientation of the plate as described in Patent Documents 2 and 3 has a certain effect in improving the ridging mark resistance, but in response to the recent strong demand for improving the ridging mark resistance. The effect was still inadequate. In addition, the control of these crystal orientations basically randomizes the crystal orientations and eliminates the collection of crystal grains having similar crystal orientations aligned in the rolling direction that cause ridging marks. Such control of crystal orientation makes it difficult to use a technique for improving characteristics by strongly developing a specific crystal orientation, which is becoming apparent in recent studies. For example, Patent Document 4 proposes improving the bending workability, which is an important characteristic for an automobile body sheet material, by developing a cube orientation, but no improvement in ridging mark resistance has been studied.

  As described above, the conventional method cannot obtain a sufficient effect against the recent strong demand for improving the ridging mark resistance, and in order to improve the ridging mark resistance, In some cases, a process is selected that sacrifices important characteristics.

  In view of the above circumstances, the present invention has not been studied for improving the ridging mark resistance so far, by clarifying the influence of the ingot structure, without restricting the manufacturing method, and manufacturing It aims at providing the manufacturing method of the aluminum alloy plate excellent in ridging mark resistance, without raising cost.

In order to achieve the above object, a method for producing an aluminum alloy plate according to the present invention comprises:
A method for producing an Al-Mg-Si-based or Al-Mg-Si-Cu-based aluminum alloy plate for automobile panels,
Using an ingot having an average crystal grain size of 150 μm or less at the center of the ingot, it is manufactured by homogenization, hot rolling, and cold rolling.
It is characterized by that.

The start temperature of the hot rolling is 400 ° C. or less, and the end temperature of the hot rolling is 300 ° C. or less,
The obtained hot-rolled sheet is cold-rolled to a predetermined thickness without being annealed.
It is good as well.

The aluminum alloy plate contains mass: Mg: 0.20 to 1.5%, Si: 0.30 to 2.0%, Mn: 0.03 to 0.60%, Cr: 0.00. 01-0.40%, Zr: 0.01-0.40%, Fe: 0.03-1.0%, Ti: 0.005-0.30%, Zn: 0.03-2.5% 1 or 2 or more types selected from among them, further Cu is regulated to 1.5% or less, the balance consists of Al and inevitable impurities,
It is good as well.

  The present invention relates to a method for producing an aluminum alloy plate, in which an aluminum alloy is subjected to hot rolling under appropriate conditions using an ingot having a fine crystal structure, regardless of whether an intermediate annealing treatment step is performed or not. When producing a plate and panel-molding the aluminum alloy, ridging marks generated during panel molding are suppressed with good reproducibility. Thereby, in the panel-shaped article of complicated shape, in particular Al-Mg-Si used for an automobile outer plate, Al-Mg-Si-Cu-based alloy, with no restrictions on the manufacturing method, compared to the conventional one, Moreover, the manufacturing method of the aluminum alloy plate excellent in ridging mark resistance can be provided without increasing the manufacturing cost, and the appearance can be improved.

It is sectional drawing which shows typically an ingot and the measurement position of a crystal grain diameter. It is a perspective view which shows typically a casting_mold | template and the insertion position of the horn for ultrasonic vibration application.

  Hereinafter, embodiments of the present invention will be described in detail.

  In order to achieve the above object, the inventors have conducted various experiments and studies, and as a result, an ingot having a fine crystal structure can be obtained as compared with an ingot obtained by a conventional method. Then, homogenization treatment is performed, and recrystallization is suppressed as much as possible in hot rolling, followed by cold rolling and solution treatment, thereby obtaining an aluminum alloy plate having better ridging mark resistance than before. As a result, the present invention has been made.

  That is, using an ingot having an average crystal grain size of 150 μm or less at the center of the ingot, which is an Al—Mg—Si based or Al—Mg—Si—Cu based aluminum alloy plate for automobile panels It is characterized by being manufactured by performing treatment, hot rolling, and cold rolling.

(Chemical composition of aluminum alloy sheet)
The aluminum alloy plate of the present invention may basically be made of an Al-Mg-Si alloy or an Al-Mg-Si-Cu alloy, and its specific composition is not particularly limited. Usually, however, it contains Mg: 0.20 to 1.5%, Si: 0.30 to 2.0% in mass%, and Mn: 0.03 to 0.60%, Cr: 0.00. 01-0.40%, Zr: 0.01-0.40%, Fe: 0.03-1.0%, Ti: 0.005-0.30%, Zn: 0.03-2.5% It is preferable to have a component composition that contains one or more selected from among them, Cu is further regulated to 1.5% or less, and the balance is composed of Al and inevitable impurities.

  Next, the reason for limitation of the preferable range of the composition of each element will be described.

Mg:
Mg is an alloy element which is a basic alloy of the system targeted by the present invention, and contributes to strength improvement in cooperation with Si. If the amount of Mg is less than 0.20%, G. contributes to strength improvement by precipitation hardening during baking. P. Since the amount of zone formation decreases, sufficient strength improvement cannot be obtained. On the other hand, if it exceeds 1.5%, coarse Mg-Si based intermetallic compounds are generated, which is disadvantageous for increasing cube orientation density. As a result, press formability, particularly bending workability, decreases. Therefore, the Mg content is set in the range of 0.20 to 1.5%. In order to improve the press formability of the final plate, particularly bending workability, the Mg content is preferably in the range of 0.30 to 0.90%.

Si:
Si is an alloy element that is a basic alloy of the system of the present invention, and contributes to strength improvement in cooperation with Mg. In addition, since Si is produced as a metal Si crystallized product (hereinafter referred to as Si particles) during casting, when processing is performed, the periphery of the Si particles is deformed by processing and is regenerated during solution treatment. Since it becomes a generation site of crystal nuclei, addition of Si contributes to refining of the recrystallized structure. If the amount of Si is less than 0.30%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 2.0%, coarse Si particles or coarse Mg-Si-based intermetallic compounds are generated to increase the cube orientation density. As a result, the press formability, particularly the bending workability, is reduced. Therefore, the Si amount is set in the range of 0.30 to 2.0%. In order to obtain a better balance between press formability and bending workability, the Si content is preferably in the range of 0.50 to 1.3%.

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 any one or more of them are added. Among these, Mn, Cr, and Zr are elements that are effective in improving the strength, refining crystal grains, and stabilizing the structure. However, the Mn content is less than 0.03% and the Cr content is 0.01%. If the Zr content is less than 0.01% or less than 0.01%, the above effects cannot be obtained sufficiently. On the other hand, if the Mn content exceeds 0.60% or the Cr and Zr contents exceed 0.40%, not only the above effects are saturated, but a large number of intermetallic compounds are produced. This may adversely affect moldability, especially hem bendability. Therefore, Mn is within the range of 0.03 to 0.60%, and Cr and Zr are within the range of 0.01 to 0.40%. Fe is also an element effective for strength improvement and crystal grain refinement, but if its content is less than 0.03%, a sufficient effect cannot be obtained, while if it exceeds 1.0%, many intermetallic compounds are obtained. May be produced, and press formability and bending workability may be reduced. Therefore, the amount of Fe is set in the range of 0.03 to 1.0%. In addition, when it is desired to minimize a decrease in bending workability, the Fe content is preferably in the range of 0.03 to 0.50%. Zn is an element that contributes to improvement of strength through improvement of aging and is effective for improvement of surface treatment. However, if the amount of Zn is less than 0.03%, the above effect cannot be obtained sufficiently. If the content exceeds 5%, the moldability deteriorates, so the Zn content is set in the range of 0.03 to 2.5%.

Ti:
Since the addition of Ti is effective in preventing the rough surface of the final plate through the refinement of the ingot structure and improving the ridging mark resistance, the present invention also adds Ti for refinement of the ingot structure. If the amount is less than 0.005%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.30%, not only the effect of adding Ti is saturated but also a coarse crystallized product may be formed. Therefore, the Ti content is within the range of 0.005 to 0.30%. Ti may be added alone, but by adding a small amount of B together with Ti, the effect of refining and stabilizing the ingot structure becomes more remarkable. Therefore, also in the present invention, it is allowed to add 500 ppm or less of B together with Ti.

Cu:
Cu is an element that may be added to improve strength and formability, but if its amount exceeds 1.5%, corrosion resistance (intergranular corrosion resistance, yarn rust resistance) decreases. The Cu content was regulated to 1.5% or less. In addition, when it is desired to further improve the corrosion resistance, the Cu content is preferably 1.0% or less, and when the corrosion resistance is particularly important, it is desirable to regulate the Cu content to 0.05% or less.

  In addition to the above elements, basically, Al and inevitable impurities may be used. The content may be a range that does not affect the material of the present invention, each less than 0.05%, and may be less than 0.15% in total.

  In addition, said Mn, Cr, Zr, Fe, Zn content range is shown as the range in the case of adding each positively, and excludes the case where all contain less than a lower limit as an impurity. It is not a thing. In particular, Fe of less than 0.03% is usually inevitably contained if a normal aluminum ingot is used.

  Further, in order to reliably and stably improve the ridging mark resistance particularly in the aluminum alloy plate of the present invention, not only the alloy composition is adjusted as described above, but also the crystal grain size of the ingot is appropriately set. It is extremely important to control.

  The ridging mark is a fine uneven pattern generated in a streak pattern on the surface of the rolled plate in a direction parallel to the rolling direction when the rolled plate is formed. According to the inventors' research, such ridging marks originate from a band-like structure (stripe structure) formed by crystal grains stretched in the rolling direction in the hot rolling and cold rolling processes. It is known that the thickness of the mark has a correlation with the thickness of the band-like structure. That is, it is effective for reducing the ridging marks to make the band-like structure finer. As a result of further studies by the inventors, it has become clear that it is effective to reduce the particle size of the ingot in order to refine the band-like structure.

  That is, when an ingot having a fine crystal grain size is used, the structure after the subsequent hot rolling and cold rolling becomes a thin band-like structure that drags the ingot grain size, and the ridging mark after molding becomes thin, It becomes difficult to be visually recognized as a ridging mark. On the other hand, when an ingot having a large crystal grain size is used, the structure after subsequent hot rolling and cold rolling becomes a thick band-like structure, and the ridging mark after forming becomes thick and easily visible. According to the inventors' experiment, ridging marks can be prevented by setting the ingot particle size to 150 μm or less, preferably 100 μm or less, and more preferably 80 μm or less.

  Further, when the hot rolling temperature exceeds 400 ° C. to 450 ° C., it is known that the recrystallized structure at the time of hot rolling tends to be coarse and forms a band-like structure coarser than the ingot particle size. . However, according to experiments by the inventors, when an ingot having a fine crystal grain size is used, a band formed during hot rolling even when the hot rolling temperature is higher than 400 ° C to 450 ° C. It has been found that the texture is likely to become fine and the ridging mark resistance can be improved. In addition, by performing hot rolling at a temperature of 400 ° C. or lower, the band-like structure to be formed can be further refined, and the ridging mark resistance can be further improved. Generation of marks can be prevented. According to the study by the inventors, the band-like structure formed by setting the hot rolling start temperature to 400 ° C. or lower and the hot rolling end temperature to 300 ° C. or lower can be refined.

  In addition, in the ingots other than the present invention, that is, ingots having a crystal grain size of more than 150 μm that are normally manufactured, when preventing ridging marks, ingots having a normal crystal grain size are hot-rolled. Is carried out, the intermediate annealing is performed after hot rolling or subsequent cold rolling. This promotes the decomposition of the band-like tissue and prevents ridging marks. However, when an ingot having a fine crystal grain size is used as described above, this intermediate annealing step can be omitted, and it becomes possible to manufacture at a lower cost.

  As described above, it is possible to prevent the generation of ridging marks by reducing the crystal grain size of the ingot in order to improve the ridging mark resistance. Furthermore, by appropriately controlling the hot rolling temperature, it is possible to produce an aluminum alloy plate that can prevent generation of ridging marks even under severe forming conditions at a lower cost.

Next, the relationship between the generation of ingots and ridging marks will be described. Since the ridging mark is caused by crystal grains extending in the rolling direction, the ridging mark does not occur in the manufacturing conditions in which the crystal grains do not extend in the rolling direction. Since the length of a ridging mark that is a practical problem often exceeds 10 mm, if the ridging mark is defined as having a length of 5 mm or more, the ingot particle size is D (mm), When the ingot plate thickness is T1 (mm) and the product plate thickness after rolling is T2 (mm), the conditions under which the ridging mark may be generated are obtained by the following formula 1.
5 ≦ D × T1 / T2 (Formula 1)

  Next, a method for measuring the crystal grain size of the ingot will be described.

  As described above, to improve the ridging mark resistance, it is required that the crystal grain size of the entire ingot is as fine as 150 μm or less. However, the ridging mark is strongly generated at the coarsest part of the ingot. It is thought that. Ingots generally have the largest crystal grain size at the center of the ingot where the cooling rate is low. Therefore, as shown in FIG. 1, the measurement position 11 of the crystal grain size is, for example, five points of intersections of a line that divides the width direction of the ingot 10 into 6 and a line that bisects the plate thickness direction. A sample for measurement is cut out from the part into a square of several centimeters, and mechanical polishing, buffing, and electrolytic polishing are performed on the ingot length direction-ingot width direction cross section. On the polished surface, texture orientation information is obtained by measuring with a backscattered electron diffraction measurement device (SEM-EBSD) attached to the scanning electron microscope. The measurement is performed in an area of 2000 μm × 2000 μm or more, and the measurement step interval may be about 1/10 of the crystal grain size. When it is difficult to measure 2000 μm × 2000 μm or more in one field of view, the measurement may be performed so that the total area of the plurality of fields of view becomes 2000 μm × 2000 μm or more.

  From the obtained orientation data, the crystal grain size is measured using EBSD analysis software (“OIM Analysis” manufactured by TSL). At this time, 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 an average crystal grain size. Thus, among the five average crystal grain sizes shown in FIG. 1, the largest value is the average crystal grain size at the center of the ingot defined in claim 1.

  Next, the manufacturing method of the aluminum alloy plate for shaping | molding processing of this invention is demonstrated.

(casting)
First, an alloy having the above component composition is melted in accordance with a conventional method. The casting method is not particularly limited as long as the crystal grain size of the ingot satisfies the above-mentioned rules. Although it does not specifically limit as a method for that, For example, the DC (Direct Chill) casting method using the following ultrasonic vibration application is mentioned.

  Ingot refinement using ultrasonic vibration application has been known for a long time and is considered to be an effect of ultrasonic cavitation generated by applying ultrasonic vibration to a molten metal. When applying ultrasonic vibration, a cylindrical nitride horn made of silicon nitride is inserted into the molten metal melted at 700 ° C. or higher, and reaches the solidus temperature from the liquidus temperature at which the primary crystal α starts to form. Until then, miniaturization is achieved by applying ultrasonic waves continuously.

  The crystal grain size of the ingot is also related to the cooling rate during casting. The cooling rate during casting without applying ultrasonic waves is 0.50 ° C./sec or more, preferably 1.0 ° C./sec at the center of the ingot where the cooling rate is the slowest and the crystal grain size tends to be coarse. Control above. If it is less than 0.50 ° C./sec, the cooling rate is slow, so that the crystal grain size of the ingot is likely to become coarse, and it becomes difficult to obtain fine crystal grains of 150 μm or less.

(Homogenization treatment)
The ingot having a fine crystal grain size obtained as described above is subjected to homogenization treatment according to a conventional method and cooled. Homogenization treatment removes segregation of added elements in the ingot, or dissolves coarse second-phase particles and crystallized materials present at the boundary between the ingot cell and crystal grains in the matrix. This is an important process for reducing the variation in the performance of the product plate and for obtaining the required crystal orientation by organically combining with the hot rolling process and the solution forming process. When the temperature of the homogenization treatment is less than 480 ° C., the above-mentioned effects are insufficient. Therefore, it is usually preferable to perform the homogenization treatment at a temperature of 480 ° C. or higher, and 590 ° C. or lower to avoid eutectic melting. Is preferable.

(Hot rolling)
The hot rolling may be performed according to normal conditions. For example, if the hot rolling start temperature is less than 580 ° C. and 250 ° C. or higher, and the hot rolling end temperature is 150 ° C. or higher and controlled to a temperature at which hot rolling is possible. Good. However, if the hot rolling temperature is too high, recrystallization occurs during hot rolling, and a coarse band-like structure is easily formed. Therefore, in order to obtain a product having particularly excellent ridging mark resistance, it is preferable that the hot rolling start temperature is 400 ° C. or lower and 250 ° C. or higher, and the hot rolling end temperature is 300 ° C. or lower and 150 ° C. or higher.

(Cold rolling)
Following hot rolling, cold rolling is performed. The rolling rate of this cold rolling is not particularly limited, but is preferably about 5.0 to 85%. In performing cold rolling, intermediate annealing is performed between passes of cold rolling, that is, hot rolling is followed by primary cold rolling, and then intermediate annealing and secondary cold rolling may be performed. It is preferable to omit from the viewpoint of manufacturing cost. The intermediate annealing conditions in the case of performing the intermediate annealing are not particularly limited, but may be performed under preferable conditions depending on the target alloy type. For example, in the case of batch annealing, the material arrival temperature is preferably 300 ° C. or more and 450 ° C. or less, and the holding time at the material arrival temperature is preferably 0.5 hours or more and 5 hours or less. Is preferably 350 ° C. or higher and 580 ° C. or lower and within 5 minutes. Moreover, the rolling rate of the primary cold rolling and the secondary cold rolling when performing the intermediate annealing is not particularly limited, but is preferably about 5.0 to 85%.

(Solution treatment)
Following the cold rolling, a solution treatment is performed. The solution treatment is performed at a material arrival temperature of 480 ° C. or higher and 590 ° C. or lower, and the holding time is not particularly limited, but is preferably within 5 minutes in consideration of productivity. About cooling after solution treatment, sufficient moldability and bake hardenability can be obtained by cooling to a temperature range of 150 ° C. or less at a cooling rate of 100 ° C./min or more.

  In order to obtain better bake hardenability, it is preferable to perform a pre-aging treatment immediately after the solution treatment for 1 hour or more in a temperature range of 50 to 150 ° C. This preliminary aging treatment does not essentially affect the crystal grain size, and whether or not the preliminary aging treatment is performed is not an essential requirement 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.

  The alloys of alloy symbols A to M within the composition range of the present invention shown in Table 1 were dissolved in accordance with ordinary methods. In Table 1, “-” represents no addition. Next, as shown in FIG. 2, molten aluminum at 700 ° C. is poured into the mold 20 having an open top of 80 mm in thickness, 150 mm in the illustrated example, and 300 mm in width, and continuously at a descending speed of 50 mm / min. DC casted. First, in order to confirm the difference in the cooling rate due to the difference in the ingot thickness, the alloy symbol B was cast with the thermocouple inserted in the center of the ingot, and the cooling rates at the plate thickness of 80 mm and 150 mm were measured. The measured cooling rate is shown in Table 2.

  Next, for those applying ultrasonic vibration, a silicon nitride cylindrical horn having a diameter of 40 mm and a length of 500 mm was inserted into the insertion position 21 in the mold 20 5 minutes after the start of casting, and ultrasonic vibration was applied. . The insertion positions 21 of the horn were two places other than the center where the ½ thickness and ¼ width lines of the mold intersect, and the immersion depth of the horn was 100 mm. The ultrasonic frequency of the horn was 20 kHz, the amplitude of the horn tip was 20 μm, and the output was 500 W. For alloy symbol A, the amount of Ti having a refinement effect was adjusted as shown in Table 3 in order to control the crystal grain size of the ingot.

  In addition, a comparative material cast without applying ultrasonic vibration and without inserting a horn was also manufactured. In Table 3, what was ultrasonically cast was set to "(circle)", and what was not ultrasonically cast was set to "-".

The obtained ingots were each subjected to 5 mm chamfering on the entire surface, homogenized at 530 ° C. for 5 hours, and then allowed to cool to near room temperature. Hot rolling was performed to a sheet thickness of 4 mm at the hot rolling start temperature and hot rolling end temperature shown in Table 3, and then cold rolling was performed to a sheet thickness of 1.0 mm. The solution treatment was performed by holding at 560 ° C. for 30 seconds. After forced air cooling with a fan to near room temperature, a preliminary aging treatment was performed immediately at 80 ° C. for 5 hours.
In addition, after the above hot rolling, the manufacturing process number 23 is cold-rolled to a sheet thickness of 2.0 mm, subjected to an intermediate annealing at a material reaching temperature of 400 ° C. for 2 hours in an atmospheric furnace, and then cold-rolled. Rolling was carried out to a plate thickness of 1.0 mm.

  The ingot obtained as described above and each plate material having a plate thickness of 1 mm were evaluated as follows. The evaluation results are shown in Table 4.

(Evaluation of crystal grain size of ingot)
About the obtained ingot, the crystal grain diameter was measured by the method mentioned above. Of the five points measured under any condition, the crystal grain size at the center position of the plate width was the largest. Table 3 shows the largest value of the crystal grain size.

(Evaluation of ridging marks)
About each board | plate material obtained as mentioned above, the ridging mark resistance was evaluated using the conventional simple evaluation method. Specifically, along the direction forming 90 ° with respect to the rolling direction, a JIS No. 5 test piece having a parallel part of 50 mm including the central part in the plate width direction is sampled, stretched by 5% and 15%, and the rolling direction is applied to the surface. As a ridging mark, the presence or absence of the streak pattern (striated uneven pattern) generated along the line 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. In this example, the evaluation criteria were focused on ridging mark resistance evaluation with 5% stretch assuming a normal press, and it was determined that more effective was obtained with 15% stretch. A circle indicates no ridging mark, and a cross indicates that a ridging mark is generated.

Furthermore, for each plate 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) and elongation (ASEL) were evaluated. Assuming paint baking, after measuring 2% stretch, 0.2% proof stress (BHYS) was measured using an oil bath and heat-treated at 170 ° C for 20 minutes, equivalent to the heating conditions during paint baking. did.
In this specification, as criteria for determining formability and strength, ASYS is 90 MPa or more, ASEL is 25% or more, and BHYS is 160 MPa or more, based on standards required for automobile body sheet materials.

  In any of production process numbers 1 to 7, the crystal grain size of the ingot is within the scope of the present invention. Moreover, as for the manufacturing process numbers 1-7, the hot rolling temperature among the component composition of an alloy and a manufacturing process is in the above-mentioned preferable range, respectively. Since the crystal grain size of the ingot is fine and the hot rolling temperature is low, the band-like structure to be formed is fine, and no ridging marks are generated even under the condition of 15% stretch simulating severe forming. .

  In any of the production process numbers 8 to 11, the crystal grain size of the ingot is within the scope of the present invention. In addition, in the manufacturing process numbers 8 to 11, the component composition of the alloy is within the above-mentioned preferable range, but the hot rolling temperature is out of the above-mentioned preferable range in the manufacturing process. Since the ingot crystal grain size is fine, the band-like structure to be formed is finer than usual, and ridging marks did not occur in 5% stretch simulating ordinary press molding, but 15% stretch Then a ridging mark occurred.

  In any of the manufacturing process numbers 12 to 16, the crystal grain size of the ingot is within the scope of the present invention. In addition, in the production process numbers 12 to 16, the alloy component composition is within the above-described preferable range, and the ingot thickness is 80 mm. As shown in the table, since the cooling rate of the center part of the ingot is high, the crystal grain size of the ingot satisfies the provisions of the present invention both when ultrasonic casting is performed and when it is not performed. Among these, since 12, 13 and 15 have a hot rolling temperature within the above-mentioned preferable range, no ridging marks were generated even under conditions of 15% stretch simulating severe forming. 14 and 16, the hot rolling temperature was out of the above-mentioned preferable range, and no ridging mark was generated in 5% stretch simulating normal press forming, but ridging mark was generated in 15% stretch.

  Production process numbers 17 to 22 did not perform ultrasonic casting, so the crystal grain size of the ingot did not satisfy the provisions of the present invention. In addition, the component composition of the alloy of manufacturing process numbers 17-22 is in the range prescribed | regulated by this invention. As a result of forming a coarse band-like structure regardless of the hot rolling temperature, ridging marks were generated even with 5% stretch.

  The production process number 23 uses the same ingot as the production process number 5 and is subjected to intermediate annealing after hot rolling. As in the case of 5 without intermediate annealing, ridging marks are not generated even with 15% stretch, and there is no problem in mechanical properties. As described above, the present invention can obtain the same characteristics as the case where the intermediate annealing is performed even if the manufacturing cost is reduced without performing the intermediate annealing.

  In any of the production process numbers 24 to 30, the crystal grain size of the ingot is within the scope of the present invention. In addition, in the manufacturing process numbers 24 to 30, the hot rolling temperature in the manufacturing process is within the above-described preferable range, but the alloy component composition is out of the above-described preferable range. These did not generate ridging marks even when stretched 15%, but mechanical properties such as elongation were somewhat low.

10 Ingot 11 Measurement position 20 Mold 21 Insertion position

Claims (3)

A method for producing an Al-Mg-Si-based or Al-Mg-Si-Cu-based aluminum alloy plate for automobile panels,
Using an ingot having an average crystal grain size of 150 μm or less at the center of the ingot, it is manufactured by homogenization, hot rolling, and cold rolling.
A method for producing an aluminum alloy plate characterized by the above. The start temperature of the hot rolling is 400 ° C. or less, and the end temperature of the hot rolling is 300 ° C. or less,
The obtained hot-rolled sheet is cold-rolled to a predetermined thickness without being annealed.
The method for producing an aluminum alloy plate according to claim 1. The aluminum alloy plate contains mass: Mg: 0.20 to 1.5%, Si: 0.30 to 2.0%, Mn: 0.03 to 0.60%, Cr: 0.00. 01-0.40%, Zr: 0.01-0.40%, Fe: 0.03-1.0%, Ti: 0.005-0.30%, Zn: 0.03-2.5% 1 or 2 or more types selected from among them, further Cu is regulated to 1.5% or less, the balance consists of Al and inevitable impurities,
The manufacturing method of the aluminum alloy plate of Claim 1 or 2 characterized by the above-mentioned.

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