JP5415016B2 - Aluminum alloy plate for forming and method for producing the same - Google Patents

Description

  The present invention relates to parts and parts of various automobiles, ships, aircraft, etc., such as automobile body seats and body panels, or building materials, structural materials, various other machinery and equipment, home appliances, parts thereof, and the like. The present invention relates to an Al-Mg-Si-based or Al-Mg-Si-Cu-based aluminum alloy plate used by baking and a method for producing the same, and has a good balance between press formability and bending workability, and is particularly resistant. The present invention relates to an aluminum alloy plate for forming and having excellent skin roughness and ridging resistance, and capable of imparting good bake hardenability and high press formability according to the use, and having a small room temperature change over time, and a method for producing the same. Is.

  Conventionally, as a body sheet of an automobile, a cold-rolled steel sheet has been mainly used, but recently, an aluminum alloy rolled sheet is frequently used from the viewpoint of reducing the weight of the vehicle body. By the way, automobile body sheets are used after being pressed, so that they have excellent molding processability, and are used with hem bending to join and integrate the outer panel and inner panel. Therefore, it is required that the hemmability is excellent among the moldability. Also, since it is usually used after painting and baking, when emphasizing strength in the balance between formability and strength, high strength can be obtained after painting and baking, and conversely when molding is emphasized. It is required that high press formability be obtained instead of sacrificing some strength after coating baking. More recently, severe molding processing has been increasingly applied, and surface appearance quality has become more important, so there is no Luders mark even during severe molding processing. Needless to say, it is strongly required that no rough skin or ridging marks occur.

  Conventionally, as an aluminum alloy for an automobile body sheet, in addition to an Al—Mg alloy, an Al—Mg—Si alloy or an Al—Mg—Si—Cu alloy having aging properties is mainly used. . These aging Al-Mg-Si alloys and aging Al-Mg-Si-Cu alloys have relatively low strength and excellent formability during molding before coating baking, while coating baking. In addition to the advantage that it is aged by heating at the time and the strength after baking is increased, it also has the advantage that the Ruders mark is less likely to occur.

By the way, the ridging mark is a streak pattern along the rolling direction that appears during the forming process of the plate, and the generation of the ridging mark is deeply related to the recrystallization behavior of the material. Control of recrystallization during the plate manufacturing process is indispensable in order to make the property that marks are not easily generated (referred to as “riding resistance”). With respect to such ridging resistance, proposals as shown in Patent Document 1 and Patent Document 2 have been conventionally made.
Japanese Patent No. 2823797 Japanese Patent No. 3590685

  In the plate obtained by the conventional manufacturing method for the aging Al-Mg-Si-based and Al-Mg-Si-Cu-based alloy plates for automobile body sheets as described above, it is required for the recent automobile body sheets. It has been difficult to fully satisfy the properties obtained.

  That is, recently, further improvement in materials has been demanded due to productivity and design of the design, etc. For automobile body sheets, the moldability (especially press formability, hem workability) and strength (bake hardenability, That is, with respect to satisfying various required performances such as BH properties, ridging resistance, room temperature aging suppression performance, corrosion resistance, etc., Al—Mg—Si based, Al— An Mg—Si—Cu alloy plate is still insufficient.

  Here, among the forming processes, the hemming process is a severe bending process of 180 ° bending with a bending inner diameter of 1 mm or less, and it is difficult to achieve both good hemming workability and press formability. There is a problem, and it is extremely difficult to suppress rough skin and generation of ridging marks in a severely molded portion such as a portion where the amount of pressing is large.

  In addition, with regard to paint baking, the baking temperature is lower than before, and the baking time is also shortened from the standpoints of energy saving, productivity improvement, and combined use with materials such as resins that are not preferably exposed to high temperatures. There is an increasing tendency to shorten the time. However, in the case of aging Al-Mg-Si-based and Al-Mg-Si-Cu-based alloy plates obtained by the conventional general manufacturing method, curing at the time of coating baking (baking) There is a problem that it is difficult to obtain sufficient strength after baking.

  Here, in the aging Al-Mg-Si-based and Al-Mg-Si-Cu-based alloy plates obtained by the conventional general manufacturing method, the balance between high press formability and hem workability is bad and severe. There is a problem that it is extremely difficult to suppress the occurrence of rough skin at the molding site (hereinafter referred to as “skin rough resistance”, a property in which rough skin hardly occurs) and the generation of ridging marks.

  By the way, among the above-mentioned patent documents, in the method shown in Patent Document 1, the starting temperature of hot rolling is in the range of 350 ° C. to 450 ° C. In this case, coarse crystals during hot rolling are used. Although the formation of grains is suppressed as such, the suppression is still insufficient, and coarse crystal grains are formed in part, and as a result, sufficient skin resistance cannot be obtained, and ridging resistance is not necessarily obtained. It has been found by experiments by the present inventors that the properties may also be lowered. On the other hand, in the case of the method of Patent Document 2, the hot rolling start temperature is set to 450 ° C. or lower, preferably 350 ° C. or higher, and intermediate annealing is a batch method with a slow temperature increase rate (about 30 ° C./h). As a result, it has been found that, in practice, the crystal grains are likely to be coarse, and as in the method described in Patent Document 1, sufficient rough resistance cannot be obtained, and ridging resistance is also reduced. . Further, as will be described in detail later, the present inventors have found that appropriately and strictly controlling the crystal orientation of the plate is effective for surely improving the rough skin resistance and sufficiently improving the ridging resistance. As found, in these Patent Documents 1 and 2, the crystal orientation is not sufficiently controlled, and it is still insufficient for the recent strong demands for improving the rough skin resistance and improving the ridging resistance.

  This invention was made against the background described above, has an appropriate strength, has low anisotropy such as r value and mechanical properties, and has a good balance between press formability and bending workability, By controlling the recrystallization behavior of the material, it has excellent skin resistance and ridging resistance, and can provide good bake hardenability and higher press formability depending on the application, and also changes over time at room temperature. It is an object of the present invention to provide a method for producing a small aluminum alloy plate for forming and a plate having such excellent performance on a mass-production scale reliably and stably at a low cost.

  As a result of repeated experiments and examinations by the present inventors to solve the above-mentioned problems, as a structure of the final plate of Al-Mg-Si-based or Al-Mg-Si-Cu-based alloy, a specific orientation, In particular, the crystal orientation density of the cube orientation (cube orientation) is appropriately suppressed, and at the same time, the ND rotational cube orientation density and the RD rotational orientation density are also appropriate based on the relationship with the cube orientation density in order to achieve dispersion of the cube orientation. By controlling to a certain level, deterioration of press workability and heme workability caused by anisotropy can be prevented, and good bake hardenability and room temperature aging resistance are not impaired, and rough skin resistance is prevented. And ridging resistance can be reliably and significantly improved. Further, the present inventors have found a process condition capable of manufacturing an aluminum alloy sheet for forming having such excellent performance on a mass production scale reliably, stably and at low cost, and has made the present invention.

Specifically, the aluminum alloy sheet of the invention of claim 1 contains Mg 0.2 to 1.5% (mass%, the same shall apply hereinafter), Si 0.3 to 2.0%, and Mn 0.03 to 0 .6%, Cr 0.01-0.4%, Zr 0.01-0.4%, V 0.01-0.4%, Fe 0.03-1.0%, Ti 0.005-0.3% 1 or 2 or more types selected from the above, Cu is regulated to 1.5% or less, the balance is made of an aluminum alloy consisting of Al and inevitable impurities , and the crystal grain cubes present in the plate The orientation density is C, and the density of the {001} <410> orientation (hereinafter referred to as “ND rotating cube orientation”) among the orientations rotated from the cube orientation about the plate surface normal (hereinafter referred to as “ND”) is N. From the cube orientation around the rolling direction (hereinafter referred to as “RD”) The density of {027} <100> azimuth (hereinafter referred to as “RD rotating cube azimuth”) among the rotated azimuths is represented by G, and the following formulas (1) to (5) (the numerical values of the respective azimuth densities C, N, and G) Are all expressed in multiples of random crystal orientation density)
C ≦ 7.1 (1)
N ≦ 4.6 (2)
0.65 ≦ N / C <1 (3)
G ≦ 3.5 (4)
0.38 ≦ G / C <1 (5)
Further, the ear rate is 7% or less, and the crystal grain size is 5 or more by ASTM number.

Furthermore, in the method for producing an aluminum alloy plate according to the invention of claim 2 , in producing the aluminum alloy plate for forming according to claim 1 , the aluminum alloy ingot is homogenized at a temperature of 480 ° C. or higher. Then, after the homogenization treatment, it is cooled to a temperature range of less than 450 ° C. at a cooling rate of 50 ° C./h or more, and then hot rolling is started in a temperature range of less than 350 ° C. and 200 ° C. or more. The hot rolling is completed at a temperature of less than 350 ° C. at least once during the period from the thickness of 200 mm to the final thickness of the hot rolled sheet, with a one-pass rolling rate of 40% or higher. Thereafter, intermediate annealing is performed at a rate of temperature increase of 100 ° C./min or higher and a material temperature of 430 ° C. or higher with or without cold rolling, and further 30% after cooling. The highest rolling rate After cold rolling to a predetermined plate thickness, after performing solution treatment at a temperature of 480 ° C or higher, cooling to a temperature range of less than 150 ° C at an average cooling rate of 100 ° C / min or higher It is a feature.

  The aluminum alloy sheet for forming according to the present invention can prevent a decrease in press formability due to anisotropy of mechanical properties, has a good balance between press formability and bending workability, and is subjected to intermediate annealing. Can significantly improve rough skin resistance and ridging resistance than before, and can provide good paint bake hardenability, higher press formability according to the application, and also at room temperature. Therefore, it is most suitable for automobile body sheets and the like that are used after press baking and hem processing and after painting and baking. Moreover, according to the manufacturing method of the aluminum alloy plate for forming according to the present invention, the aluminum alloy plate for forming having excellent performance as described above can be manufactured reliably and stably on a mass production scale.

The aluminum alloy sheet for forming according to the present invention is basically made of an Al-Mg-Si-based alloy or an Al-Mg-Si-Cu-based alloy having an alloy composition as defined in claim 1 . The

The reason for limiting the component composition of the material alloy defined in claim 1 as described above will be described.

Mg:
Mg is an alloy element that 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 0.2%, G. contributes to strength improvement by precipitation hardening during baking. P. Since the amount of zone formation is reduced, sufficient strength improvement cannot be obtained. On the other hand, if it exceeds 1.5%, a coarse Mg-Si intermetallic compound is produced, and press formability, particularly bending workability is improved. Since it falls, the amount of Mg was made into the range of 0.2 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 0.3 to 0.9%.

Si:
Si is also an alloy element that is fundamental in the alloy of the present invention, and contributes to strength improvement in cooperation with Mg. In addition, Si is produced as a crystallized product of metal Si at the time of casting, and the periphery of the metal Si particles is deformed by processing and becomes a recrystallization nucleus generation site during solution treatment. It also contributes to When the amount of Si is less than 0.3%, the above effects cannot be obtained sufficiently. On the other hand, when it exceeds 2.0%, coarse Si particles and coarse Mg-Si based intermetallic compounds are produced, and press formability, In particular, bending workability is reduced. Therefore, the Si amount is set in the range of 0.3 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 0.5 to 1.3%.

Mn, Cr, Zr, V, F e, T i:
These elements are effective for improving strength, crystal grain refinement, aging (bake hardenability) and surface treatment, and any one or more of them are added. Among these, Mn, Cr, Zr, and V are elements that are effective in improving the strength, refining crystal grains, and stabilizing the structure, but the Mn content is less than 0.03%, or Cr, Zr, V If the content of each is less than 0.01%, the above effects cannot be obtained sufficiently, while the content of Mn exceeds 0.6% or the contents of Cr, Zr, and V are each 0.4%. If the amount exceeds 50%, not only the above effects are saturated, but also a large number of intermetallic compounds may be produced, which may adversely affect the formability, particularly hem bendability. Therefore, Mn is 0.03 to 0.6%. And Cr, Zr, and V were each in the range of 0.01 to 0.4%. 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 deteriorated. Therefore, the amount of Fe is set within a range of 0.03 to 1.0%. Incidentally, if you want to minimize the deterioration of bending workability, Fe amount is not preferable in the range of 0.03 to 0.5%. Ti in is found, the intensity of the final plate through refinement of ingot tissue enhancement, rough skin prevention, since it is effective in ridging resistance improvement, but added for finer ingot tissue, its content If it is less than 0.005%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.3%, not only the effect of adding Ti is saturated but also coarse crystallized products may be formed. It was made into the range of 005-0.3%. In addition, B may be added simultaneously with Ti, and by adding B together with Ti, the effect of refining and stabilizing the ingot structure becomes more prominent. It is permissible to add B.

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) deteriorates. 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.

  In addition, in an aging Al—Mg—Si alloy or an aging Al—Mg—Si—Cu alloy, a trace amount of Ag, In, Cd, Be, or Sn which is a high temperature aging promoting element or a room temperature aging inhibiting element is added. However, even in the case of the present invention, addition of these elements is permissible as long as it is added in a small amount, and if it is 0.3% or less, the intended purpose is not particularly impaired.

  Furthermore, it is said that the addition of Sc is effective for refining the ingot structure. In the case of this invention, a small amount of Sc may be added, and within the range of Sc 0.01 to 0.2%. There is no particular problem.

  Furthermore, in the aluminum alloy sheet for forming according to the present invention, in order to optimize the balance between press formability and bending workability, it is necessary to suppress the anisotropy to be small, and the resistance to rough skin and ridging resistance For improvement, it is very important not only to adjust the alloy composition as described above, but also to appropriately control the texture of the aluminum alloy plate as the final plate, particularly the crystal orientation density.

In an actual material, there are various crystal orientations. As a result of extensive investigations by the present inventors, the orientation density of cube orientations among various crystal orientations, that is, the ideal orientation of cube orientations {001 } It is effective to suppress the anisotropy to appropriately suppress the orientation density of the <100> orientation, and in order to further appropriately distribute the cube orientation , the ratio between the cube orientation density and the ND rotating cube orientation density , In addition, by appropriately controlling the ratio between the cube orientation density and the RD rotating cube orientation density , a high level of rough skin resistance and ridging resistance could be realized.

That is, as defined in claim 1, the cube orientation density of the crystal grains existing in the plate is C, the ND rotation cube orientation rotated from the cube orientation about the plate surface normal ND, particularly {001} <410. > The density of the orientation is N, the RD rotation cube orientation rotated from the cube orientation about the rolling direction RD, especially the density of the {027} <100> orientation is G, and the equations (1) to (5)
C ≦ 7.1 (1)
N ≦ 4.6 (2)
0.65 ≦ N / C <1 (3)
G ≦ 3.5 (4)
0.38 ≦ G / C <1 (5)
By controlling so as to satisfy the above conditions, it is possible to reliably prevent the occurrence of rough skin and to prevent the generation of ridging marks even in a portion subjected to severe molding.

Here, as described above , the ND rotating cube direction is represented by the {001} <410> direction as the representative direction, and the RD rotating cube direction is represented by the {027} <100> direction as the representative direction . The orientation density is measured with the density of these representative orientations . Here, the numerical values of the orientation densities in the equations (1) to (5) are all expressed as multiples of the random crystal orientation density.

Here, the equation (1) means that the value of the cube orientation density C itself is restricted to a low value, and this cube orientation density C has an effect on hem workability, press formability, anisotropy, ridging resistance, and the like. give. If the value of C exceeds 7.1, it is most advantageous for heme workability, but there is a risk that press formability may be reduced due to strong anisotropy, and such specific orientation density can be increased. In this case, the ridging resistance is also lowered. On the other hand, the formulas (2) and (4) mean that the density N and G of the orientation rotated from the cube orientation about the plate surface normal ND or the rolling direction RD are regulated to a low value. Each of the N and G orientations affects the hemmability, press formability, anisotropy, ridging resistance and the like. If the value of N exceeds 4.6 or the value of G exceeds 3.5, it is not as good as C, but it is advantageous for hem workability, but the anisotropy becomes strong and press formability decreases. If such a specific orientation density increases, the ridging resistance also decreases. Furthermore, formulas (3) and (5) are defined for cube orientation dispersion. If the value of N / C or G / C is 1 or more, the balance between press formability and hemmability is obtained. If the value of N / C is less than 0.65 or the value of G / C is less than 0.38 , the ratio of C is relatively high and ridging resistance is lowered. Note that N and G have almost the same effect on the improvement of azimuth dispersion and ridging resistance. However, if both N and G are regulated, the effect of the regulation can be obtained more reliably and significantly. . Therefore, in the present invention, both N and G are regulated.

  Furthermore, in the aluminum alloy plate for forming according to the present invention, it is also important that the ear rate (0 ° ear, 90 ° ear) is 7% or less over the entire plate. That is, as described above, in the present invention, the crystal orientation density is defined by the formulas (1) to (5), but the orientation density of other crystal orientations is also to some extent anisotropy, rough skin resistance, and ridging resistance. Affects sex. However, in practice, it is difficult to strictly define the orientation density of all crystal orientations other than these orientations. On the other hand, the crystal orientation of the material can be macroscopically evaluated based on the ear ratio of the cup squeezed by the plate cupping test. Therefore, in the present invention, the influence of the density of orientations other than the crystal orientations defined by the formulas (1) to (5) is evaluated and regulated by the ear rate. Specifically, when the ear degree of the 0 ° and 90 ° ears of the cup is 7% or more on the basis of the rolling direction, even if the conditions of the above-mentioned formulas are satisfied, the required anisotropy and good resistance to resistance are obtained. There is a risk that rough skin and ridging resistance may not be obtained. Therefore, in the present invention, the ear rate is regulated as described above. In addition, although the ear | edge rate does not limit the minimum, Usually, the range of 0 to 7% is preferable.

  In order to improve bending workability and prevent rough skin, which is an appearance defect during press molding, it is necessary to make the crystal grain size fine. As a result of repeated experiments and examinations by the present inventors, it has been found that if the crystal grain size is set to 5 or more in the ASTM number, it has the effect of improving bending workability and preventing rough skin (appearance defects), and the conditions Is stipulated. Further, when the appearance is important, the ASTM number is preferably 6.0 or more.

  Next, a method for producing the aluminum alloy plate for forming according to the present invention will be described.

  First, an alloy having the component composition as described above is melted in accordance with a conventional method and cast by a normal casting method such as a DC casting method.

  The resulting ingot is homogenized at a temperature of 480 ° C. or higher, and then cooled to a temperature range of less than 450 ° C. at a cooling rate of 50 ° C./h or higher. The reason why the conditions for the homogenization treatment and the cooling are defined in this way is as follows.

  In other words, the homogenization process removes segregation of added elements in the ingot, or dissolves coarse second-phase particles, crystallized materials, etc. existing at the boundaries between the ingot cells and crystal grains in the matrix. In particular, it is an important process for reducing the variation in product plate performance and for obtaining the required crystal orientation by organically combining with the hot rolling process and the solution forming process. If the homogenization temperature is less than 480 ° C., the above-described effects are insufficient. The upper limit of the homogenization temperature is not particularly limited, but it is usually preferable to perform the treatment at 590 ° C. or lower in order to avoid eutectic melting.

  As for cooling after the homogenization treatment, in general, in order to obtain a high bake hardenability, coarsening of precipitates formed in the cooling process should be avoided, so that a temperature range of less than 450 ° C. is 50 ° C./h or more. It was decided to cool at a cooling rate of. The “cooling rate” mentioned here means the average cooling rate. Note that the size and distribution of the precipitates also affect the recrystallization behavior of the material. Therefore, in order to reliably obtain the effects of the present invention, 150 ° C./h up to a temperature range of 450 ° C. or lower after the homogenization treatment. It is preferable to cool at the above cooling rate.

  After the homogenization treatment as described above, after cooling to a temperature range of less than 450 ° C, hot rolling is performed, but since the start temperature of hot rolling is less than 350 ° C, the process until the start of hot rolling In, any of the following processing methods can be applied as needed. That is, it cools to normal temperature or near normal temperature in the cooling process after the homogenization treatment, and then starts the hot rolling again by heating to the start temperature of the hot rolling, or hot in the cooling process after the homogenization treatment. Cool to the starting temperature of rolling and start hot rolling as it is, or, in the cooling process after homogenization, once stayed and held in a temperature range of less than 450 ° C and more than 350 ° C, and then lowered the temperature The hot rolling may be started in a temperature range of less than 350 ° C.

  Even if any of these processing methods is applied, the effect of the present invention is not impaired. From the viewpoint of productivity and the like, the cooling, staying and holding processes are preferably within 48 hours.

The homogenization treatment and the hot rolling after cooling must be performed so as to satisfy the following conditions (1) and (2).
(1) The hot rolling start temperature is set to a temperature range of less than 350 ° C. and 200 ° C. or more .
(2) In the hot rolling process, at a stage where the plate thickness is 200 mm or more, at least one pass is subjected to a high pressure pass with a rolling rate of 40% or more.

Among these conditions, the condition (1), that is, setting the hot rolling start temperature to less than 350 ° C. and 200 ° C. or more completely suppresses recrystallization of the material during the hot rolling, and the required crystal This is an indispensable condition for improving the roughness resistance and ridging resistance as well as obtaining the orientation density. If hot rolling is started at a high temperature of 350 ° C. or more, partially coarse recrystallized grains are formed, and there is a possibility that sufficient skin resistance and ridging resistance cannot be obtained. Note the hot rolling start temperature is, that the hot rolling itself becomes difficult at 200 ° C. or less because it is usually in the range of less than 200 to 350 ° C..

  Next, the condition (2) is an indispensable condition for obtaining the required crystal orientation density by suppressing recrystallization of the material during hot rolling in combination with the condition (1). That is, the target crystal rotation can be achieved by applying a large deformation under the pressure of one pass to the substantially unrecrystallized on-fiber structure in the stage after the plate thickness of 200 mm in the hot rolling process. It is necessary to apply a high-pressure pass with a rolling rate of 40% or more at the stage after the plate thickness of 200 mm. It is preferable to apply a high-pressure pass with a rolling rate of 50% or more. By applying a pass under a high pressure of 40% or more, preferably 50% or more as described above, by causing two or more recrystallizations together with the intermediate annealing and solution treatment, the cube orientation in the final plate is obtained. By suppressing the development of the cube, dispersion of the cube orientation can be achieved to reduce the anisotropy, and the rough skin resistance and ridging resistance due to the orientation dispersion satisfying the above formulas (1) to (5). It is effective in improving sex.

  If the end temperature of the hot rolling is 350 ° C. or higher, coarse recrystallization occurs and the surface roughness resistance is lowered. Therefore, the end temperature of the hot rolling is limited to less than 350 ° C. In order to actively prevent the generation of coarse recrystallized grains, it is preferable to set the hot rolling end temperature within the range of 150 ° C to 300 ° C.

  Here, if any one of the hot rolling conditions as described above is not satisfied, it is difficult to obtain a final plate that satisfies the required crystal orientation density condition, and various properties of the final plate may be deteriorated.

  After hot rolling is completed as described above, intermediate annealing is performed immediately after cold rolling (primary cold rolling) or without cold rolling. This intermediate annealing has the effect of recrystallizing the material, decomposing and subdividing the structure formed by hot rolling, and also increasing the solid solubility. The temperature rise rate is 100 ° C./min or more and the material arrival temperature is 430 ° C. or more. If the rate of temperature increase is less than 100 ° C./min, coarse crystal grains are likely to be formed, and there is a risk of causing rough skin resistance and deterioration of ridging resistance. If material arrival temperature is less than 430 degreeC, there is little effect which raises a solid solubility and a moldability and bake hardenability will fall. The holding at the material arrival temperature above 430 ° C. is not particularly limited, but it is usually not holding or holding for 5 minutes or less. Further, the cooling rate after the intermediate annealing is not particularly limited, but it is usually desirable to set the cooling rate to 100 ° C./min or more in the same manner as the heating rate from the viewpoint of productivity.

  Although the rolling rate of primary cold rolling is not particularly limited when intermediate annealing is performed with cold rolling (primary cold rolling) sandwiched after hot rolling, it is usually preferably about 5 to 85%.

As described above, after hot rolling, intermediate annealing is performed with or without cold rolling, and then final cold rolling is performed at a rolling rate of 30% or more to obtain a predetermined plate thickness. This final cold rolling not only has an effect on accumulating strain in the plate and refines the crystal grains in the subsequent solution treatment, but also has a certain influence on the formation of crystal orientation of the final plate. If the final cold rolling ratio is less than 30%, the crystal grain size and grain orientation density specified in the present invention may not be obtained. Although the upper limit of the rolling reduction of the final cold rolling is not particularly defined, it is usually about 50%.

After cold rolling, a solution treatment is performed. However, a solution treatment at a temperature of 480 ° C. or higher is required for the Al—Mg—Si-based or Al—Mg—Si—Cu-based alloy targeted in the present invention. is there. This solution treatment is an important step for solid-dissolving Mg ₂ Si, simple substance Si, etc. in the matrix, thereby imparting bake hardenability and improving the strength after paint baking. This process also contributes to lowering the distribution density of the second phase particles by solid solution of Mg ₂ Si, simple substance Si particles, etc., improving ductility and bendability, and finally by recrystallization. This is an important step for obtaining a desired crystal orientation and obtaining good moldability, good skin roughness resistance and good ridging resistance.

  In particular, when emphasizing the solution effect, the solution treatment temperature is preferably 500 ° C. or higher. On the other hand, the upper limit of the solution treatment temperature is not particularly defined, but it is usually preferably 590 ° C. or less in consideration of the possibility of eutectic melting and coarsening of recrystallized grains. The solution treatment time is not particularly limited. However, if it exceeds 5 minutes, the solution effect is saturated, not only the economic efficiency is impaired, but also the crystal grains may be coarsened. Is preferably within 5 minutes.

Regarding cooling after solution treatment, in order to prevent a large amount of Mg ₂ Si or simple substance Si from being precipitated at the grain boundaries during cooling, the cooling rate is 100 ° C./min or higher and the temperature range is 150 ° C. or lower. It needs to be cooled (quenched). Here, when the cooling rate after the solution treatment is less than 100 ° C./min, press formability, particularly bending workability is lowered, and at the same time, bake hardenability is lowered, and sufficient strength improvement at the time of coating baking cannot be expected.

  After the solution treatment, a stabilization treatment may be performed as necessary. That is, when bake hardenability (BH property) is more important than moldability, after solution treatment, after cooling (quenching) to a temperature range of 50 ° C. or more and less than 150 ° C. at a cooling rate of 100 ° C./min or more. The stabilization treatment is preferably performed within this temperature range (less than 50 to 150 ° C.) before the temperature falls to a temperature range (room temperature) of less than 50 ° C. The holding time in the temperature range of 50 to less than 150 ° C. in this stabilization treatment is not particularly limited, but normally it is desirable to hold for 1 hour or longer, and cooling (slow cooling) over 1 hour or more within that temperature range. You may do it.

  On the other hand, when emphasizing formability, particularly press formability, rather than bake hardenability, the solution is cooled to a temperature range of less than 50 ° C. in the cooling process after solution treatment without performing stabilization treatment, and 0-50 It is preferable to leave in a temperature range of ° C.

  Here, after solution treatment, when cooled to a room temperature of less than 50 ° C. at a high average cooling rate of 100 ° C./min or more, a room temperature cluster is generated, and this room temperature cluster contributes to strength. P. Since it is difficult to shift to the zone, it is disadvantageous for paint bake hardenability, but since the decrease in ductility is small, it is advantageous for press formability. On the other hand, when the solution is cooled to a temperature range of 150 ° C. or higher and kept as it is after the solution treatment, P. A zone or a stable phase is generated, the strength of the material before molding becomes too high, and the hemmability and press formability may deteriorate, and the room temperature aging resistance may also deteriorate. Therefore, the solution treatment-quenching, solution treatment-quenching-stabilization treatment under the above conditions is selected from the viewpoint of balance between hemmability, press moldability, paint bake hardenability, and room temperature aging resistance.

  Furthermore, after performing solution treatment and quenching in a temperature range of less than 50 ° C. and leaving it in a temperature range of 0 to 50 ° C., a restoration treatment may be performed again at 180 to 280 ° C. That is, a room temperature cluster formed by cooling to a room temperature of less than 50 ° C. contributes to strength. P. Although it is difficult to shift to the zone, it is disadvantageous for paint bake hardenability, but by applying heat treatment (restoration treatment) for a short time (preferably within 5 minutes) at 180 to 280 ° C, the paint bake hardenability is recovered. Thus, the effect of improving the bending workability can be obtained.

  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.

Alloys having the alloy symbols A1 and A2 within the composition range of the present invention shown in Table 1 were melted in accordance with conventional methods and cast into slabs by DC casting.

  Each obtained slab was homogenized at 530 ° C. for 5 hours. After the homogenization treatment, the slab was cooled to 200 ° C. or lower at an average cooling rate of 5 ° C./min. Then, after subjecting to a hot rolling process and performing hot rolling under the conditions shown in Table 2, after performing primary cold rolling or without performing primary cold rolling, intermediate annealing is performed, and further, the final cold After rolling, solution treatment was performed, and cooling (quenching) was performed at an average cooling rate of 800 ° C./min. Thereafter, some were subjected to stabilization treatment, and some were subjected to restoration treatment.

  The finally obtained aluminum alloy plate (product plate) was examined for texture (crystal orientation density) as follows.

  That is, using a plate having a thickness of 1 mm, the position at a depth of ¼ from the surface is the X-ray measurement surface, and using an X-ray diffractometer, the X-ray diffraction Schertz reflection method is used to {100} , {110}, {111} incomplete pole figures were measured, and based on these, three-dimensional crystal orientation analysis (ODF) was performed and examined. In these analyses, the data obtained by measuring a sample having a random crystal orientation made from aluminum powder is used as a standardized file for analysis of {100}, {110}, {111} pole figures. Thus, various orientation densities were obtained as multiples of the sample having a random orientation. In this invention, the crystal orientation density is all based on three-dimensional crystal orientation analysis (ODF). Also, here, the cube orientation is represented by {001} <100>, the N orientation is represented by {001} <410>, and the G orientation is represented by {027} <100>. Orientation.

  In addition, since there is usually azimuth dispersion having a certain angle centered on the azimuth, in the present invention, the maximum azimuth density in the 5 ° rotation range around the azimuth is taken as a representative value of the azimuth density. .

  Table 4 shows the measurement results of each crystal orientation density.

  The final plate was examined for crystal grain size as follows.

  That is, the ASTM number was calculated by the cutting method based on the image mapped by the EBSP (EBSD) method in the RD-ND cross section constituted by the plate rolling direction RD and the plate surface normal ND. Here, a crystal boundary line with a misorientation of 5 ° or more was regarded as a crystal grain boundary. The results are shown in Table 4.

  Further, each plate obtained as described above was left at room temperature (25 ° C.) for one month in consideration of room temperature aging, and then the strength of the plate before paint baking was evaluated by the tensile test and the ear by the cup drawing test. Rate, ridging mark evaluation, and hemmability evaluation by bending test. Further, after stretching each 2%, a coating baking (baking) treatment was performed at 170 ° C. for 20 minutes, a tensile test was performed, and a 0.2% proof stress value was measured as a mechanical strength. These results are shown in Tables 4 and 5. Each measurement method and evaluation method are as follows.

Ear rate measurement:
After applying lubricating oil to the plate, the cup was squeezed under the conditions of a punch diameter of 32 mm, a blank diameter of 62 mm, and a wrinkle holding force of 100 kg, and the ear ratio of the cup was examined. Here, the direction of the ear rate is indicated by a 0 ° direction and a 90 ° direction based on the rolling direction.

Hem processability evaluation:
Bending specimens are collected in three directions of 0 °, 45 °, and 90 ° within the plate surface relative to the rolling direction of the material, stretched 5%, bent at a bending radius of 0.5 mm and 180 °, and visually cracked. The presence or absence of occurrence was evaluated. Here, a circle indicates that there is no crack, and a cross indicates that there is a crack.

Ridging marks and rough skin evaluation:
A JIS No. 5 tensile test was taken along a direction forming 45 ° with respect to the rolling direction, 10% stretching was performed, and lines (unevenness) along the rolling direction formed on the surface and rough skin were visually determined. ○ indicates no streak and no rough skin, Δ indicates a medium streak and rough skin, and x indicates a strong streak and rough skin. Here, even if the lines and the roughness of the skin are moderate, there is a possibility that the appearance of the outer plate for automobiles becomes unsuitable.

Production numbers 1 and 2 are both within the range specified by the present invention for the component composition of the alloy, and the manufacturing process conditions are also within the range specified by the present invention. The conditions specified in the present invention are satisfied, but in these cases, the strength and elongation anisotropy are small, the heme workability is excellent, and the rough skin resistance and the ridging resistance are good. Also among these, the production number 1, high bake with curability, showed sufficient bake hardenability during baking, while the serial number 2, although low bake hardenability, elongation is an indicator of formability It was excellent. The production number 1 is a temperature range from a quenching temperature of 100 ° C. to 50 ° C. instead of a stabilization treatment, and an average cooling rate of 5.5 ° C./h (that is, a residence time between 100 ° C. and 50 ° C. is 9.1 hours). ).

On the other hand, in production numbers 3 to 6 , all of the alloy component compositions are within the range defined in the present invention, but any of the production process conditions is out of the scope of the present invention. And among these, in the production number 3 , the crystal orientation density and the ear ratio did not satisfy the conditions specified in the present invention, and the rough skin and the anisotropy of strength and elongation were also observed. In the case of production numbers 4 and 5 , the anisotropy of strength and elongation was small, but the hem workability was inferior, and the rough skin resistance and ridging resistance were slightly poor. Further, in the case of production number 6 , since the maximum reduction during hot rolling was small and the final cold rolling rate was low, the crystal grains were rough, the rough skin resistance was remarkably deteriorated, the hemming property was inferior, and The ridging property was not so good.

Claims (2)

Mg 0.2-1.5% (mass%, the same shall apply hereinafter), Si 0.3-2.0%, Mn 0.03-0.6%, Cr 0.01-0.4%, Zr0.01 ~ 0.4%, V 0.01 ~ 0.4%, Fe 0.03 ~ 1.0%, Ti 0.005 ~ 0.3% one or more selected from among, further containing Cu Is controlled to 1.5% or less, and the balance is made of an aluminum alloy composed of Al and inevitable impurities. The cube orientation density of crystal grains existing in the plate is C, and the plate surface normal (hereinafter referred to as “ND”). ) With the density of {001} <410> orientation (hereinafter referred to as “ND rotating cube orientation”) as N, and the rolling direction (hereinafter referred to as “RD”) as the axis. Of the orientations rotated from the orientation, the {027} <100> orientation (hereinafter “ The density of D rotation described as cube orientation ") as G, all of the following (1) to (5) below (the orientation density C, N, figures G represents a multiple for a random crystal orientation density)
C ≦ 7.1 (1)
N ≦ 4.6 (2)
0.65 ≦ N / C <1 (3)
G ≦ 3.5 (4)
0.38 ≦ G / C <1 (5)
An aluminum alloy sheet for forming with excellent skin roughness resistance and ridging resistance, characterized by satisfying the above requirements, having an ear ratio of 7% or less and a crystal grain size of 5 or more in ASTM number. In manufacturing the aluminum alloy plate for forming according to claim 1 ,
The aluminum alloy ingot is homogenized at a temperature of 480 ° C. or higher, and after the homogenization, cooled to a temperature range of less than 450 ° C. at a cooling rate of 50 ° C./h or higher, followed by less than 350 ° C. and 200 ° C. or higher. In the hot rolling process, the rolling rate of one pass is 40% or more at least once from the stage of the sheet thickness 200 mm to the stage of the finished sheet thickness in the hot rolling process. Apply high pressure, finish hot rolling at a temperature of less than 350 ° C., and then reach the material with a temperature increase rate of 100 ° C./min or higher with or without cold rolling. Intermediate annealing at a temperature of 430 ° C. or higher is performed, and after cooling, a final cold rolling is performed at a rolling rate of 30% or higher to obtain a predetermined thickness, and then a solution treatment at a temperature of 480 ° C. or higher is performed. To an average cooling rate of 100 ° C./min or more In up to a temperature range below 0.99 ° C. characterized by cooling, surface roughening resistance and anti-ridging excellent production method of molding an aluminum alloy plate resistance.