JP4200086B2 - Aluminum alloy plate for forming and method for producing the same - Google Patents

Description

  The present invention relates to an Al-Mg-Si-based aluminum alloy plate used as a material for an automobile body sheet, other various automobile parts, various machinery and equipment, home appliances and parts thereof, and the like, and subjected to forming and baking. The present invention relates to a manufacturing method, which has good formability, particularly hem bendability and press workability, has high strength after baking, and has little change over time at room temperature, and its manufacturing method It is about.

  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, since the body sheet of an automobile is used after being pressed, it is required that it has excellent molding processability, that no Ruders mark is generated during the molding process, and that it must have high strength. Since it is usually used after being baked, it is required to obtain high strength after baking. And of course, it is required to have good moldability, but as a body sheet for automobiles, it is used by applying hem bending to join the outer panel and inner panel together. In many cases, it is strongly required that hem bendability is particularly excellent among moldability.

  Conventionally, as an aluminum alloy for an automobile body sheet, an Al—Mg—Si alloy having aging properties is mainly used in addition to an Al—Mg alloy. This aging Al-Mg-Si alloy has a relatively low strength and excellent formability during molding before coating baking, while it is aged by heating during coating baking and has a strength after coating baking. In addition to the advantage that it becomes higher, it has the advantage that a Ruders mark does not occur.

As the prior art relating to the bending workability improvement, such as heme bendability, particle size and the number of Mg 2 _Si compound or grain boundary precipitates, Patent Document 1 that controls the dispersion density of the second phase particles, JP 2 and the techniques of Patent Document 3 and Patent Document 4 for regulating the ratio of crystal grain boundaries whose crystal grain boundary orientation difference is 15 ° or less or 20 ° or less, and the {200} plane or {400} of the texture There are Patent Literature 5, Patent Literature 6, and the like that regulate the integrated intensity of a surface. The present inventors have already made a proposal shown in Patent Document 7.

JP 2003-105471 A JP 2003-268472 A JP2003-171726 JP 2003-166029 A JP 2003-226926 A JP2003-226927A JP 2003-268475 A

  The plate obtained by the conventional manufacturing method for the aging Al-Mg-Si alloy plate for an automobile body sheet as described above sufficiently satisfies the characteristics required for the recent automobile body sheet. Was difficult.

  That is, recently, in order to further reduce the cost and reduce the weight of the automobile body, it has been strongly demanded to further reduce the thickness of the body sheet for automobiles, so that even a thin wall can obtain sufficient strength. In addition to the demand for higher strength, improvement in formability, particularly hem bendability, is strongly demanded. Al—obtained by a conventional general production method in terms of satisfying these performances in a balanced manner. An Mg—Si alloy plate was insufficient. In particular, the hem bending process is a severe bending process of 180 ° bending with a bending inner diameter of 1 mm or less, and thus there is a problem that it is difficult to achieve both good hem bendability and strength.

  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 an aging Al-Mg-Si alloy plate obtained by a conventional general manufacturing method, the coating baking process at a low temperature and a short time lacks the curing at the time of coating baking (baking hardening), and after coating baking There was a problem that it was difficult to obtain a sufficiently high strength.

  Here, in the aging Al-Mg-Si alloy plate obtained by a conventional general manufacturing method, if it is intended to increase the bake hardenability in order to obtain high strength after coating baking, the ductility and bending of the material (Especially hem bendability) decreases, and when it is allowed to stand at room temperature after the plate is manufactured, it tends to be hardened by natural aging, so that the formability, particularly hem bendability, tends to be hindered. .

Of the above patent documents, Patent Document 1 and Patent Document 2 regulate the compound dispersion state, in particular, the particle size and number of Mg ₂ Si, or the grain boundary precipitates and the dispersion state of the second phase particles. Although it has been proposed to improve bending workability, the effect has not been sufficient.

  On the other hand, in Patent Document 3 and Patent Document 4, it is proposed to improve bending workability by regulating the ratio of crystal grain boundaries in which the orientation difference between crystal grains is 15 ° or less or 20 ° or less. Certainly, in this method, a certain degree of improvement in bending workability can be achieved. However, as a result of repeated experiments and examinations by the present inventors, a crystal whose orientation difference between crystal grains is 15 ° or less or 20 ° or less. It has been found that even if the grain boundary ratio exceeds 20%, the bendability in all directions of the rolled sheet is not improved. For example, even if the bendability in the direction parallel to the rolling direction or the direction perpendicular to the rolling direction is improved, the bendability in the direction of 45 ° with respect to the rolling direction is not improved. It turns out that the problem of directionality occurs.

  Further, in Patent Document 5 and Patent Document 6, it is proposed that the integrated strength of the {200} plane and the {400} plane is regulated to improve the flat hem workability as rolling texture control. In Patent Document 7 by humans and others, it is proposed to improve the hem bendability by regulating the cube orientation density, the ND rotating cube orientation density and the ear rate. Even with these methods, it is possible to obtain a certain improvement effect in bendability. However, as a result of further experiments and examinations by the present inventors, these methods have improved the hem bendability, but at the time of molding processing. Anisotropy that n value (working effect index) that is an index of work hardening amount is non-uniform in each direction in the plane (hereinafter, “n value for anisotropy in the plane of such work hardening index n value” Anisotropy), and at the same time, the rankford value (r value; plastic strain value), which is an index of deep drawability, becomes non-uniform in each direction in the plate surface. (Hereinafter, the in-plane anisotropy for such a plastic strain value is simply referred to as “in-plane anisotropy”), and as a result, the formability (press workability) in the press work is improved. It was found that there was a risk of decline. Such problems of n-value anisotropy and in-plane anisotropy were not considered at all in Patent Documents 5 to 7, but press working with deep drawing is frequently used in automobile body sheets and the like. Therefore, even if the bending workability represented by hem bendability is good, if the press workability is lowered, the value as a processing material is lowered, and therefore n-value anisotropy and in-plane It is also extremely important for automobile body sheets and the like to appropriately control the anisotropy so that the material has a good balance between bending workability and press workability.

  This invention was made against the background described above, has a good balance between bending workability and press workability, has good bending workability and press workability, and has low bending anisotropy, Furthermore, it offers excellent bake hardenability, a large increase in strength during baking, and an aluminum alloy plate for forming that has little change over time at room temperature after the plate is manufactured. The object of the present invention is to provide a method capable of reliably and stably producing an aluminum alloy plate for forming having a mass production scale.

  As a result of repeating various experiments and studies by the present inventors in order to solve the above-mentioned problems, not only appropriately adjusting the component composition of the Al-Mg-Si-based alloy, but also a specific orientation, In particular, by increasing the crystal orientation density of the cube orientation (cube orientation) and at the same time appropriately regulating the cube orientation density distribution in the plate thickness direction, it is possible to improve bending workability, especially hem bendability, and at the same time (Bend anisotropy) can be reduced, good bake hardenability and aging at room temperature can be obtained, and not only that, but also in-plane anisotropy is reduced and n It has been found that by appropriately regulating the value anisotropy, good press workability can be obtained without impairing the bending workability. Furthermore, the present inventors have found a process condition capable of stably producing such an aluminum alloy sheet for forming having such excellent performance on a mass-production scale, and have made the present invention.

Specifically, the aluminum alloy sheet for forming according to the invention of claim 1 contains Mg 0.4 to 0.7%, Si 0.8 to 1.2%, and Mn 0.03 to 0.4%, Contains one or more selected from Cr 0.01-0.4%, Fe 0.03-0.5%, Ti 0.005-0.2%, Zn 0.03-2.5% Further, Cu is restricted to 0.1% or less, the balance is made of an alloy composed of Al and inevitable impurities, the cube orientation density on the plate surface is C ₀ , and the plate thickness is 1 / th of the plate thickness in the plate thickness direction. The cube orientation density at the position 4 is C _1/4 , and the cube orientation density at the position ½ of the plate thickness from the plate surface to the plate thickness direction is C _1/2 , and the following equations (1) and (2) C ₀ <C _1/4 > C _1/2 (1)
20 <{(C ₀ + C _1/4 + C _1/2 ) / 3} <200 (2)
In which the work hardening index in the direction parallel to the rolling direction is n _{0 in} the plate surface and 45 ° to the rolling direction in the plate surface. work hardening exponent _{n 45,} as _{n 90} and work hardening coefficient in a direction forming a 90 ° to the rolling direction in the plate surface, the following (3) and (4) _{n 0 <n 45> n 90} · (3)
0 <n ₄₅ − (n ₀ + n ₉₀ ) / 2 <0.40 (4)
In the direction parallel to the rolling direction is r ₀ , the rank ford value in the direction of 45 ° with respect to the rolling direction in the plate surface is r ₄₅ , and the direction in the plate surface is orthogonal to the rolling direction. the Lankford value as _{r 90} of, [Delta] r value _{Δr = (r 0 + r 90} ) which is defined by the following equation (5) _{/ 2-r 45 ··· (5} )
Is less than 1.2.

  An aluminum alloy sheet for forming according to the invention of claim 2 is the aluminum alloy sheet for forming according to claim 1, characterized in that the crystal grain size is 4.0 or more in terms of ASTM number.

Furthermore, the manufacturing method of the aluminum alloy plate for forming according to the invention of claim 3 is the method for manufacturing the aluminum alloy plate for forming according to claim 1 or 2, wherein Mg 0.4 to 0.7%, Si0 0.8 to 1.2%, and Mn 0.03 to 0.4%, Cr 0.01 to 0.4%, Fe 0.03 to 0.5%, Ti 0.005 to 0.2%, Zn 0. For an ingot of an alloy containing one or more selected from 03 to 2.5%, further Cu being restricted to 0.1% or less, and the balance being Al and inevitable impurities , In the range of 490 to 590 ° C., homogenized at a temperature of 450 ° C. or lower at an average cooling rate of 3 ° C./min or higher, and then hot rolled.
(1) Hot rolling temperature in the range of 300-450 ° C,
(2) The maximum reduction amount per pass is 80 mm or less,
(3) The distortion rate of each path is 350 / sec or less,
(4) The temperature of the hot rolled sheet in the stage where the sheet thickness during hot rolling is 150 to 50 mm is within the range of 250 to 430 ° C.
(5) The temperature drop amount of the hot rolled sheet from the start of hot rolling to the stage where the sheet thickness during hot rolling is 150 to 50 mm is 150 ° C. or less,
(6) The hot rolling end temperature is in the range of 200 to 300 ° C.
(7) The average cooling rate from the hot rolling end temperature to 100 ° C. is 100 ° C./hr or less,
After the hot rolling is completed, the hot rolled plate is cold rolled at a rolling rate of 30% or more to obtain a product plate thickness, and further subjected to a solution treatment at a temperature of 480 ° C. or higher. It is characterized by cooling to a temperature range of 50 ° C. or higher and lower than 150 ° C. at an average cooling rate of / min or higher, and then performing a stabilization treatment for 1 hour or longer in that temperature range.

  In the present invention, the cube orientation density means a crystal orientation density of (100) <001> orientation which is a cube ideal orientation. That is, in general industrial materials, the crystal orientation density within the range rotated up to 15 ° around the cube ideal orientation is often referred to as cube orientation density. Orientation density and the orientation density of the peripheral orientation of the ideal cube orientation (the orientation density of the crystal orientation obtained by rotating the cube ideal orientation by 10 ° with reference to the rolling direction axis RD, and the ideal cube orientation based on the plate surface normal axis ND) In order to distinguish clearly from the orientation density of the crystal orientation obtained by rotating the angle of 10 °, the orientation density of the cube ideal orientation is referred to as the cube orientation density.

  In the present invention, the numerical values of the cube orientation density (the numerical values on the right side and the left side of Equation (2)) are expressed as multiples of the random orientation sample.

Furthermore, in this invention, the work hardening index (n ₀ , n ₄₅ , n ₉₀ ) in each direction is represented by an n value when the tensile test is performed on the test piece taken along each direction and the elongation is 10%. Shall. Here, the n value is expressed by the following equation (6) when σ is a true stress, ε is a true strain, F is a coefficient, and n is an n value: σ = Fε ⁿ (6)
Is a value obtained by.

The aluminum alloy sheet for forming according to the present invention is excellent in formability, particularly hem bendability, press workability, bend anisotropy, and paint bake hardenability. strength after baking is high, also less change over time at room temperature is optimal for automotive body sheet or the like used by painted after the flop-less processing and hem bending machining follow. Moreover, according to the manufacturing method of this invention, the aluminum alloy plate for shaping | molding which has the outstanding performance as mentioned above can be obtained reliably and stably on a mass-production scale.

  First, the reasons for limiting the component composition in the aluminum alloy sheet for forming according to the present invention 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 Mg content is less than 0.4%, 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 0.7%, coarse Mg-Si based intermetallic compounds are produced, which is disadvantageous for increasing cube orientation density. Further, since the formability, particularly the bending workability is lowered, the Mg amount is set in the range of 0.4 to 0.7%.

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 If the amount of Si is less than 0.8%, the above effect cannot be obtained sufficiently. On the other hand, if it exceeds 1.2%, coarse Si particles and coarse Mg-Si based intermetallic compounds are produced to increase the cube orientation density. For this reason, it becomes disadvantageous, and the formability, particularly bending workability, is reduced. Therefore, the Si amount is set in the range of 0.8 to 1.2%.

Mn, Cr, Fe, Ti, Zn:
These elements are effective for improving the strength, refining crystal grains, improving aging properties, and improving surface treatment properties, and any one or more of them are added. Among these, Mn and Cr are elements that are effective in improving the strength, refining the crystal grains, and stabilizing the structure, and contribute to increasing the cube orientation density and increasing the ear rate of the 0 ° ear and the 90 ° ear. However, if the Mn content is less than 0.03% or the Cr content is less than 0.01%, the above effects cannot be obtained sufficiently, while the Mn and Cr contents are each 0.4%. If it exceeds, 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 0.4%. Within the range, Cr was within a range of 0.01 to 0.4%. Fe is also an element effective for strength improvement and grain refinement, but if its content is less than 0.03%, sufficient effects cannot be obtained, while if it exceeds 0.5%, the cube orientation density is increased. In addition to being disadvantageous in the above, it is disadvantageous to increase the 0 °, 90 ° ear ratio, and there is a possibility that the formability, particularly bending workability and press formability may be lowered. Within the range of 0.5%. Furthermore, Ti is an element effective for improving the strength and refining the ingot structure, but if its content is less than 0.005%, a sufficient effect cannot be obtained, while if it exceeds 0.2%, the effect of adding Ti In addition to being saturated, there is a possibility that coarse crystallized matter may be formed, so the Ti content is set in the range of 0.005 to 0.2%. 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%.

Cu:
Cu is an element that may be added to improve strength and formability, but if the amount exceeds 0.1%, corrosion resistance (intergranular corrosion resistance, yarn rust resistance) deteriorates. The Cu content is restricted to 0.1% or less. In particular, when emphasizing corrosion resistance, it is desirable to limit the amount of Cu to 0.05% or less.

  In addition to the above elements, basically, Al and inevitable impurities may be used.

  In addition, the above-mentioned content ranges of Mn, Cr, Fe, Ti, and Zn are shown as ranges in the case where each is positively added, and all exclude cases where the content is less than the lower limit as impurities. It is not a thing. In particular, Fe of less than 0.03% is usually inevitably contained if a normal aluminum ingot is used.

  In addition, in an aging Al—Mg—Si 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, may be added. If so, the addition of these elements is allowed, and if the content is 0.3% or less, the intended purpose is not particularly impaired.

  In addition, in a general Al alloy, B may be added at the same time as the above-mentioned Ti for refining the ingot structure. In this invention, addition of 800 ppm or less of B together with Ti is permitted. The

  Further, Zr and V, which are considered to be effective in improving the strength, refining the crystal grains, and stabilizing the structure, may be added. Never give.

  Further, in the aluminum alloy sheet for forming according to the present invention, in order to obtain good bending workability, particularly good hem bendability, and at the same time, to suppress bending anisotropy and in-plane anisotropy, In addition to adjusting the composition as described above, it is extremely important to appropriately control the texture of the plate, particularly the crystal orientation density and its thickness direction distribution.

  In other words, in this invention, the crystal orientation density is controlled not only to control the grain boundary properties (small angle or large angle) but also to control the overall slip deformation of the crystal accompanying the plastic deformation of the aluminum alloy. Is the main purpose. In particular, it is extremely important to increase the degree of accumulation of crystal orientations that are likely to cause cross-slip during bending. By doing so, the increase in dislocation density due to processing is suppressed, and work hardening is suppressed. Is possible. As a result, during hem bending, large strain deformation of the material is possible until the crack limit strength is reached by suppressing work hardening. Here, in order to make the slip deformation behavior greatly different from that of a conventional material having a relatively random crystal orientation, in other words, a conventional material that hardly causes cross-slip, it is necessary to accumulate crystal orientations. On the other hand, there are various crystal orientations in the actual material, but as a result of extensive studies by the present inventors, the orientation density of the cube orientation, that is, the (001) <100> orientation, in particular, among the various crystal orientations. It has been found that by increasing the orientation density, the sliding deformation behavior can be greatly different from that of conventional materials. That is, by increasing the cube orientation density, cross-sliding during work deformation becomes active, work hardening is suppressed, and bending workability is improved.

  Here, simply increasing the cube orientation density may reduce the balance of material properties, for example, press workability may deteriorate. Therefore, when the present inventors conducted further experiments and examinations, the cube orientation density was not simply increased, but by appropriately regulating the cube orientation density distribution in the plate thickness direction, bending was performed without impairing press workability. It has been found that processability can be improved.

That is, the cube orientation density at the position of the plate surface is C ₀ , the cube orientation density at the position of _{1/4 of} the plate thickness in the plate thickness direction from the plate surface is C _1/4 , and the plate thickness is 1 in the plate thickness direction from the plate surface. If the cube orientation density at the position of / 2 is C _1/2 , the following formula (1), formula (2) C ₀ <C _1/4 > C _1/2 (1)
20 <{(C ₀ + C _1/4 + C _1/2 ) / 3} <200 (2)
By satisfying the above, it has been found that the bending workability can be improved without impairing the press workability, and therefore, the equations (1) and (2) are defined.

  Here, the formula (1) indicates that the cube orientation density at a position 1/4 of the plate thickness from the plate surface is higher than the cube orientation density at the plate surface and the cube orientation density at a position 1/2 of the plate thickness from the plate surface. Therefore, this equation (1) means that the cube orientation density is higher in the intermediate portion than in the plate surface side and the plate thickness direction center portion side. Further, the formula (2) means that the average cube orientation density in the thickness direction is more than 20 times and less than 200 times that of the random orientation sample. When these formulas (1) and (2) are not satisfied, a material having an excellent balance between bending workability including bending anisotropy and press workability cannot be obtained.

  Further, in the aluminum alloy plate for forming according to the present invention, it is also important that the ear rate of the 0 ° ear and the 90 ° ear is 5% or more over the entire plate. That is, as described above, in the present invention, in order to ensure good bending workability and to suppress bending anisotropy, the cube orientation density and its thickness direction distribution are defined, but the orientation of other crystal orientations Density also affects bending workability to some extent. 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 orientation density of the crystal orientation other than the cube orientation and the peripheral orientation is evaluated and regulated by 0 ° ear and 90 ° ear. Specifically, when the 0 ° and 90 ° ear ratio of the cup is less than 5% based on the rolling direction, even if the above-mentioned cube orientation density and its thickness direction distribution conditions are satisfied, good bending And bending anisotropy may not be obtained. Therefore, in the present invention, the ear rate is regulated as described above.

In the aluminum alloy plate for forming according to the present invention, the work hardening index (n value) in each direction in the plate surface of the product plate is defined as an index of in-plane work hardening anisotropy. That is, the n value in the direction parallel to the rolling direction is n ₀ , the n value in the direction forming 45 ° with respect to the rolling direction in the plate surface is n ₄₅ , and the direction orthogonal to the rolling direction in the plate surface (90 ° direction). It is defined that the following formulas (3) and (4) are satisfied, where n value of n is n ₉₀ .
n ₀ <n ₄₅ > n ₉₀ (3)
0 <n ₄₅ − (n ₀ + n ₉₀ ) / 2 <0.40 (4)

  The reason why the expressions (3) and (4) are defined in this way is as follows.

The work hardening index (n value) is a value that serves as an index of the degree of work hardening when the material is processed, and is generally closely related to the chemical composition of the alloy, the solid solution amount of the solute element, and the like. However, as a result of repeated experiments and examinations by the present inventors, it has been found that even in the same alloy plate, there is a phenomenon in which the n value varies depending on each direction in the plate surface, that is, n-value anisotropy exists. As a result of further experiments and examinations, it has been found that the value of n in each direction within the plate surface has a strong correlation with the degree of integration of the crystal orientation of the material. Since the n value itself is an index of the degree of work hardening as described above, the magnitude of the n value is related to press formability. Then, n values in each direction in the plane, in particular, three directions representing each direction in the plate plane, that is, n values (n ₀ , n _{45 in the} 0 ° direction, 45 ° direction, 90 ° direction with respect to the rolling direction). , N ₉₀ ), and properly controlling the mutual relationship between the values of n ₀ , n ₄₅ , and n ₉₀ , it is found that stable press workability and hem bendability can be obtained stably. Then, the above formulas (3) and (4) are defined.

In the above formula (3), the n value (n ₀ ) in the direction parallel to the rolling direction (0 ° direction) in the plate surface and the n value (n ₉₀ ) in the direction perpendicular to the rolling direction (90 ° direction) are Both represent lower than the n value (n ₄₅ ) in the direction of 45 ° with respect to the rolling direction. On the other hand, the equation (4) expresses the difference (Δn) between the n value (n ₄₅ ) in the 45 ° direction and the average value of the n value (n ₀ ) in the ₀ ° direction and the n value (n ₉₀ ) in the 90 ° direction. ,
Δn = n ₄₅ − (n ₀ + n ₉₀ ) / 2
This means that Δn is larger than 0 and smaller than 0.40. In other words, the n value in the 45 ° direction is made larger than the n value in the 0 ° direction and the 90 ° direction to allow the n value anisotropy to exist in the plate surface. This means that the degree of directivity (Δn) is regulated within an appropriate range that is not so large.

  Here, the existence of n-value anisotropy is advantageous for improving the bending workability. However, if the n-value anisotropy is too large, the press formability is lowered. Therefore, in order to achieve both press workability and bending workability, it is important that n-value anisotropy exists within an appropriate range. From this viewpoint, the n-value anisotropy is regulated ( 3) and (4). When the n value in each direction does not satisfy the expressions (3) and (4), either the press workability or the bending workability is impaired, and a well-balanced material cannot be obtained. Although the reason why the presence of n-value anisotropy is advantageous in bending workability is not yet clear as described above, it is considered that the accumulation degree of dislocations is relaxed during processing.

In the above equation (4), the value of Δn = n ₄₅ − (n ₀ + n ₉₀ ) / 2 is defined as 0 <Δn <0.40, but the balance between press workability and bending workability is more stable. In order to obtain an excellent material,
0.02 <Δn <0.30
It is desirable to be within the range.

In addition, in the aluminum alloy sheet for forming according to the present invention, in order to obtain a more stable balance between press workability and bending workability represented by hem bendability, an in-plane plastic strain anisotropy is obtained. The anisotropy (Δr value) of the Rankford value (r value) of the product plate as an index is defined. That is, the Rankford value in the direction parallel to the rolling direction is r ₀ , the Rankford value in the direction forming 45 ° with respect to the rolling direction in the plate surface is r ₄₅ , and the Rankford value in the direction orthogonal to the rolling direction in the plate surface. values as _{r 90,} [Delta] r value _{Δr = (r 0 + r 90} ) which is defined by the following equation (5) _{/ 2-r 45 ··· (5} )
Is less than 1.2. That is, Δr <1.2 is required. The reason why Δr value <1.2 is defined as follows.

  The Δr value represented by the equation (5) is an index representing the variation in each direction in the plate surface of the plastic strain value (r value), that is, the in-plane plastic strain anisotropy, and if the Δr value is too large, There may be a difference in plastic deformation in each direction in the plate surface during deep drawing such as press work, which may reduce press workability, etc., and balance of material characteristics, especially balance between press workability and hem bendability. Is not preferable.

  Further, in the aluminum alloy sheet for forming according to the invention of claim 2, it is specified that the crystal grain size is 4.0 or more in terms of ASTM number. The reason for this definition is as follows.

  That is, 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 ASTM number 4.0 or more, there is an effect of improving bending workability and preventing rough skin (appearance defects). Is stipulated.

  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 obtained ingot is homogenized at a temperature in the range of 490 to 590 ° C., and then cooled to a temperature range of 450 ° C. or lower at a cooling rate of 3 ° C./min or higher. The reason why the conditions for the homogenization treatment and the subsequent cooling conditions are defined in this way is as follows.

  In other words, the homogenization treatment has the effect of removing segregation of the additive elements in the ingot, and dissolving the coarse second phase particles and crystallized substances present at the boundaries between the ingot cells and crystal grains in the matrix. In addition, it is an important process for obtaining a required crystal orientation by organically coupling with a reduction in performance variation of the product plate and further organically connecting with a hot rolling process, a cold rolling process, and a solution forming process. If the temperature of this homogenization treatment is less than 490 ° C, the above-mentioned effect is insufficient. On the other hand, if it exceeds 590 ° C, eutectic melting may occur, so the homogenization treatment temperature is in the range of 490 to 590 ° C. did.

  Further, after the homogenization treatment, cooling to a temperature range of 450 ° C. or lower at a cooling rate of 3 ° C./min or more is indispensable for obtaining high bake hardenability. If the cooling rate to a temperature range of 450 ° C. or lower is slower than 3 ° C./min, coarsening of precipitates occurs in the cooling process, and in subsequent hot rolling started at 450 ° C. or lower, the coarsening is eliminated. Not only that, but in the short-time solution treatment process after hot rolling-cold rolling, a sufficient amount of Mg and Si cannot be secured, and as a result, it is difficult to obtain high bake hardenability. It becomes.

  As described above, after cooling to a temperature range of 450 ° C. or lower at 3 ° C./min or higher after the homogenization treatment, hot rolling is started at a temperature within a range of 300 to 450 ° C. as described later. After the homogenization treatment, the steel sheet is cooled at a cooling rate of 3 ° C./min or more to a temperature range of 300 to 450 ° C., and hot rolling is immediately started within the temperature range of 300 to 450 ° C. or homogenization. After cooling to 300 ° C. or less after the treatment at a cooling rate of 3 ° C./min or more, preheating to a temperature in the range of 300 to 450 ° C. may be performed again, and hot rolling may be started within that temperature range, Selecting any of these will not affect the performance.

  The ingot structure after homogenization is desirably as fine as possible. Specifically, the ingot crystal grain size is desirably ASTM number 00 or more. In other words, the refinement of the ingot structure is effective in preventing the occurrence of streak-like appearance defects (riding) on the surface of the product plate during molding, that is, improving the ridging resistance. As already described as the agent, it is desirable to add Ti or Ti and B.

After the homogenization treatment, hot rolling is performed as described above. This hot rolling needs to be performed so as to satisfy the following conditions (1) to (7).
(1) The temperature within the range of 300 to 450 ° C. for the hot rolling start temperature.
(2) The maximum reduction amount per pass is 80 mm or less.
(3) The distortion speed of each path is 350 / sec or less.
(4) The temperature of the hot-rolled sheet in the stage where the plate thickness during hot rolling is 150 to 50 mm is in the range of 250 to 430 ° C.
(5) The temperature drop amount of the hot rolled sheet from the start of hot rolling to the stage where the sheet thickness during hot rolling is 150 to 50 mm is 150 ° C. or less.
(6) The hot rolling end temperature is in the range of 200 to 300 ° C.
(7) The average cooling rate from the hot rolling end temperature to 100 ° C. is 100 ° C./hr or less.

  The reasons for defining these hot rolling conditions are as follows.

  That is, first, setting the condition of (1), that is, the hot rolling start temperature within the range of 300 to 450 ° C., suppresses recrystallization of the material during hot rolling, and at the same time obtains the required crystal orientation density. It is an indispensable condition for improving ridging resistance. When the hot rolling start temperature is 300 ° C. or less, hot rolling itself becomes difficult. On the other hand, if hot rolling is started at a high temperature exceeding 450 ° C., ridging resistance cannot be improved. Was in the range of 300-450 ° C.

  Further, the above conditions (2) to (7), that is, the maximum reduction amount per pass is set to 80 mm or less, the strain rate of each pass is set to 350 / sec or less, and the plate thickness during hot rolling is 150 to 50 mm. The material temperature is controlled within the range of 250 to 430 ° C., the temperature drop of the hot rolled plate from the start of hot rolling to the plate thickness stage is controlled within 150 ° C., and the hot rolling end temperature is 180 ° C. It is also necessary for proper control of crystal orientation density and improvement of ridging property to control within the range of ~ 330 ° C and to further reduce the average cooling rate from the hot rolling end temperature to 100 ° C to 5 ° C / min or less. is there. That is, as a result of repeated experiments and examinations by the present inventors, appropriate control of crystal orientation density and its thickness direction distribution, n value in each in-plane direction, and improvement of ridging by only controlling the hot rolling start temperature. It became clear that it was not possible. After further diligent experiments and examinations, in order to obtain the required crystal orientation density, thickness direction crystal orientation density distribution, n-value conditions by suppressing recrystallization during the hot rolling process, and to improve ridging resistance In addition to the hot rolling start temperature, the maximum reduction amount of each pass, the strain rate of each pass, the temperature of the hot rolled plate at the stage of a plate thickness of 100 to 50 mm during hot rolling, and hot rolling It has been found that it is necessary to appropriately regulate the temperature drop amount of the hot rolled sheet from the start to the sheet thickness stage, and further the hot rolling end temperature. Further, in order to stably obtain a predetermined crystal orientation density distribution in the sheet thickness direction and satisfy the required n-value condition, the average cooling rate from the hot rolling end temperature to the subsequent 100 ° C. is 5 ° C./min or less. It was found that it was necessary to make these, and the conditions (2) to (7) were defined. If any one of these conditions (2) to (7) is not satisfied, the required crystal orientation density and its distribution in the thickness direction or the n-value condition will not be satisfied, or sufficient ridging resistance will be improved. It becomes difficult to plan.

  After hot rolling as described above and winding the coil, cold rolling is performed at a rolling rate of 30% or more without intermediate annealing to obtain a required thickness (product thickness). Thus, by cold rolling at a rolling rate of 30% or more, a product plate having the crystal orientation density conditions as described above can be obtained. Further, here, by setting the cold rolling rate to 30% or more, high strain energy is accumulated in the material, and the crystal grains formed during solution treatment and quenching after hot rolling become finer, after forming processing. Good surface appearance quality can be obtained. If the cold rolling rate is less than 30%, surface defects such as rough skin may occur during molding. In particular, when the appearance quality is important, the cold rolling rate is preferably 50% or more.

After the required product thickness is obtained as described above, solution treatment is performed at a temperature of 480 ° C. or higher. 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 process for obtaining a desired crystal orientation and obtaining good bending workability and press workability.

When the solution treatment temperature is less than 480 ° C., it is considered advantageous for suppressing the change over time at room temperature, but in that case, the amount of solid solution of Mg ₂ Si, Si, etc. is reduced and sufficient bake hardenability is obtained. Not only cannot be obtained, but also ductility and bendability are significantly deteriorated. Therefore, the solution treatment temperature must be 480 ° C. or higher. 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 specified, but it is usually preferably 580 ° 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.

After the solution treatment, it is cooled (quenched) to a temperature range of 50 ° C. or higher and lower than 150 ° C. at a cooling rate of 100 ° C./min or higher. Here, if the cooling rate after the solution treatment is less than 100 ° C./min, Mg ₂ Si or simple substance Si precipitates in the grain boundary during cooling, and at the same time, the formability, particularly the hem bendability decreases, The bake hardenability is lowered, and a sufficient strength improvement at the time of baking is not expected.

  After performing solution treatment at a temperature of 480 ° C. or higher as described above and cooling (quenching) to a temperature range of 50 ° C. or higher and lower than 150 ° C. at a cooling rate of 100 ° C./min or higher, a temperature range of less than 50 ° C. Before the temperature drops to (room temperature), stabilization treatment is performed for 1 hour or longer within this temperature range (less than 50 to 150 ° C.). This stabilization treatment may be held at a constant temperature within a temperature range of 50 to 150 ° C. for 1 hour or longer, or may be cooled (slowly cooled) over 1 hour within the temperature range.

  The reason for performing the stabilization treatment at a temperature of 50 to less than 150 ° C. without cooling to a temperature range of less than 50 ° C. after the solution treatment and quenching to a temperature range of less than 50 to 150 ° C. is as follows. Street. That is, after solution treatment, a room temperature cluster is generated particularly when cooling to room temperature below 50 ° C. at an average cooling rate of 100 ° C./min or more. This room temperature cluster contributes to strength. P. Since it is difficult to shift to the zone, it is disadvantageous for paint bake hardenability. 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. Zones or stable phases are generated, the strength of the material before molding becomes too high, and bending workability and other moldability deteriorate. Therefore, from the viewpoint of the balance between bending workability, press workability and paint bake hardenability, it is necessary that the solution treatment-quenching-stabilization treatment satisfy the above conditions.

  Alloys of alloy symbols A1 to A4 within the component composition range of the present invention shown in Table 1 are melted in accordance with conventional methods, cast into slabs by DC casting method, and homogenized under various conditions for the obtained slabs Was applied. After homogenization, some products (Product No. 2) are cooled to 367 ° C. and then subjected to hot rolling, and others are cooled to 200 ° C. or less at various cooling rates by water cooling. The mixture was allowed to cool to room temperature, then reheated to various temperatures at a heating rate of 2 ° C./hr or higher, and hot rolling was started at that temperature. In the hot rolling, rolling was performed from a slab thickness (250 mm or more) to 5 mm (manufacturing numbers 2, 3) or 3 mm (manufacturing numbers 1, 4-9). In this hot rolling, the material temperature is measured at 100 mm and 60 mm as the representative plate thickness at the stage of intermediate plate thickness of 150 to 50 mm, and the temperature drop from the start of hot rolling at the plate thickness stage is 150 ° C. And the hot rolling end temperature was measured. After completion of hot rolling, the coil was wound up, and then cold rolled to a plate thickness of 1 mm without intermediate annealing during the cold rolling. Further, some of them (manufacturing number 7) are subjected to solution treatment after low-temperature annealing at 250 ° C. × 2 hours, and others (manufacturing numbers 1 to 6, 8, 9) Solution treatment was performed without performing low-temperature annealing. In the solution treatment, after reaching various solution treatment temperatures by heating, the solution is immediately cooled (quenched) to various temperatures at a cooling rate of 100 ° C./min or more without holding time, and subsequently various stabilization treatments are performed. I did it. Detailed conditions of these production processes are shown in production numbers 1 to 9 in Tables 2 and 3.

  In Tables 2 and 3, production numbers 1 to 3, 6, 8, and 9 are those in which the stabilization process was performed at a constant temperature, while production numbers 4, 5, and 7 were the constant temperature as the stabilization process. Instead of holding the temperature, the temperature was gradually cooled from 100 ° C. to 60 ° C. at a cooling rate of 2 to 15 ° C./h.

Each plate obtained as described above is left at room temperature for 3 months, then stretched by 2%, and then subjected to a coating baking (baking) treatment at 170 ° C. for 20 minutes, and the plate before baking in each direction. A tensile test was conducted to examine the work hardening index and Δr value in each direction, and 0.2% proof stress was measured as mechanical strength. Similarly, regarding the plate before baking, the texture (crystal orientation density) at each position in the plate thickness direction was examined, and the crystal grain size was examined. In addition, a tensile test is conducted on the plate after paint baking in each direction to check the 0.2% proof stress, and the edge ratio in the cup drawing test and the corner head drawing height are evaluated for press formability evaluation of the plate before paint baking. In addition, heme bending workability evaluation by hem bending test and ridging mark generation evaluation by punch overhang test were performed. These results are shown in Tables 4 and 5.

  Specific methods for each measurement and test are shown below.

Tensile test (work hardening index n ₀ , n ₄₅ , n ₉₀ , Δr value, yield strength):
JIS No. 5 tensile test pieces were sampled in three directions of 0 °, 45 °, and 90 ° in the plate surface with respect to the rolling direction of the plate, and each was subjected to a tensile test. Then, in addition to examining the 0.2% proof stress value in the 0 ° direction, in each direction, the n value (n ₀ , n ₄₅ , n ₉₀ ) when the elongation becomes 10% is examined, and the Rankford value (r value) As described above, the r value when the elongation is 7.5% in each direction was obtained, and the Δr value was obtained from the r value (r ₀ , r ₄₅ , r ₉₀ ) in each direction according to the above equation (5).

Measurement of texture (crystal orientation density):
A sample having a thickness of 1 mm was etched with a 10% NaOH aqueous solution from the surface toward the center of the plate thickness to various depths, and a sample that was not etched was used as a measurement sample. The cube orientation density (C ₀ ) on the plate surface, the cube orientation density (C _1/4 ) at a position 250 μm from the plate surface, and the cube orientation density (C _1/2 ) at a position 500 μm were obtained. As a measuring device, an incomplete pole figure of {200}, {220}, {111} is measured by the X-ray diffraction Schertz reflection method using the Rigaku Corporation X-ray diffractometer. A three-dimensional crystal orientation analysis (ODF) was performed and examined. In these analyses, data obtained by measuring a sample having a random crystal orientation made from aluminum powder is used as a standardized file used in the analysis of {200}, {220}, {111} pole figures. Thus, the cube orientation density, that is, the density of {100} <001> orientation, was obtained as a multiple of the sample having a random orientation. In this invention, the crystal orientation density is all based on three-dimensional crystal orientation analysis (ODF).

Ear rate:
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:
A material left at room temperature of about 25 ° C. for 3 months is pre-aged in an electric furnace at 100 ° C., and when the 0.2% proof stress in the direction perpendicular to the rolling direction becomes 145 MPa, the material is rolled in the rolling direction. Bending test specimens are collected in three directions at 0 °, 45 °, and 90 ° in the plate surface, stretched by 15%, and then a 180 ° bending test is performed by inserting an intermediate plate having a thickness of 0.5 mm. The presence or absence of cracks was observed visually. Here, a circle indicates that there is no crack, and a cross indicates that there is a crack.

Evaluation of generation of ridging marks:
Overhanging was performed up to a height of 30 mm with a spherical head punch having a diameter of 100 mm, and the streaks (unevenness) along the rolling direction formed on the surface were visually determined. A circle indicates no muscle or a weak muscle, and a cross indicates a strong muscle. If the streak is strong here, the appearance of the automobile outer plate is inappropriate.

Square head drawing height (press workability evaluation):
After applying rust preventive oil to the plate, a square head punch test was performed using a wrinkle presser 3 ton using a square head punch having dimensions of 200 mm × 300 mm and a corner R of 10 mm, and the molding height (moldability) was evaluated.

Final grain size:
The ASTM number was determined based on a photograph taken with an optical microscope in a cross section parallel to the rolling direction of the plate.

  Production numbers 1 to 5 are all within the range specified by the present invention for the component composition of the alloy, and the production process conditions are also within the range specified by the present invention. The conditions specified in this invention are satisfied. In these cases, the hemmability (bending workability) is excellent, and at the same time, the corner head drawing height is sufficiently high and the press workability is excellent. Further, the bake hardenability was high, the bake hardenability was sufficiently exhibited during paint baking, the in-plane anisotropy represented by the Δr value was small, and the generation of ridging marks was not observed.

  On the other hand, in the production numbers 6 to 9, although the component composition of the alloy is within the range specified in the present invention, any of the production process conditions is out of the scope of the present invention, and any of the crystal orientation density conditions, etc. Does not satisfy the conditions defined in the present invention. Among these, in the case of production number 6, ridging resistance is poor, the n-value condition is removed, the hem bendability is inferior, the corner head drawing height (press workability) is also inferior, and the bake hardenability is also inferior. The crystal grains were also coarse. In the case of production number 7, the n-value condition is removed, the corner head drawing height is low and the press workability is inferior, the in-plane anisotropy Δr is large, and the bake hardenability is inferior. It was rough. In the case of production number 8, the ridging resistance was poor and the hem bendability in the 45 ° direction was poor. Furthermore, in the case of production number 9, the hem bendability in the 45 ° direction was inferior and the paint bake hardenability was inferior.

  In addition, the above Example is for demonstrating the effect of this invention, and the process and conditions as described in an Example do not restrict | limit the technical scope of this invention.

Claims (3)

Mg 0.4-0.7% (mass%, the same shall apply hereinafter), Si 0.8-1.2%, Mn 0.03-0.4%, Cr 0.01-0.4%, Fe0.03 ~ 0.5%, Ti 0.005 to 0.2%, Zn contains 0.03 to 2.5% selected from one or more, and further Cu is regulated to 0.1% or less An alloy consisting of Al and inevitable impurities is used as the raw material, the cube orientation density on the plate surface is C ₀ , and the cube orientation density at the position of 1/4 of the plate thickness from the plate surface to the plate thickness direction is C _1/4. The cube orientation density at a position 1/2 of the plate thickness in the plate thickness direction from the plate surface is C _1/2 , and the following formulas (1) and (2) C ₀ <C _1/4 > C _1/2 ... (1)
20 <{(C ₀ + C _1/4 + C _1/2 ) / 3} <200 (2)
In which the work hardening index in the direction parallel to the rolling direction is n _{0 in} the plate surface and 45 ° to the rolling direction in the plate surface. work hardening exponent _{n 45,} as _{n 90} and work hardening coefficient in a direction forming a 90 ° to the rolling direction in the plate surface, the following (3) and (4) _{n 0 <n 45> n 90} · (3)
0 <n ₄₅ − (n ₀ + n ₉₀ ) / 2 <0.40 (4)
In the direction parallel to the rolling direction is r ₀ , the rank ford value in the direction of 45 ° with respect to the rolling direction in the plate surface is r ₄₅ , and the direction in the plate surface is orthogonal to the rolling direction. the Lankford value as _{r 90} of, [Delta] r value _{Δr = (r 0 + r 90} ) which is defined by the following equation (5) _{/ 2-r 45 ··· (5} )
Is an aluminum alloy sheet for forming, characterized by being less than 1.2. In the aluminum alloy plate for forming according to claim 1,
An aluminum alloy plate for forming, wherein the crystal grain size is 4.0 or more by ASTM number. In the method for manufacturing the aluminum alloy sheet for forming according to claim 1 or 2,
Mg 0.4-0.7%, Si 0.8-1.2%, Mn 0.03-0.4%, Cr 0.01-0.4%, Fe 0.03-0.5%, Ti0 Contains one or more selected from 0.005 to 0.2% and Zn 0.03 to 2.5%, further Cu is restricted to 0.1% or less, the balance being Al and inevitable The alloy ingot made of impurities is homogenized at a temperature in the range of 490 to 590 ° C., cooled to a temperature of 450 ° C. or lower at an average cooling rate of 3 ° C./min or higher, and then hot rolled. In doing
(1) Hot rolling temperature in the range of 300-450 ° C,
(2) The maximum reduction amount per pass is 80 mm or less,
(3) The distortion rate of each path is 350 / sec or less,
(4) The temperature of the hot rolled sheet in the stage where the sheet thickness during hot rolling is 150 to 50 mm is within the range of 250 to 430 ° C.
(5) The temperature drop amount of the hot rolled sheet from the start of hot rolling to the stage where the sheet thickness during hot rolling is 150 to 50 mm is 150 ° C. or less,
(6) The hot rolling end temperature is in the range of 200 to 300 ° C.
(7) The average cooling rate from the hot rolling end temperature to 100 ° C. is 100 ° C./hr or less,
After the hot rolling is completed, the hot rolled plate is cold rolled at a rolling rate of 30% or more to obtain a product plate thickness, and further subjected to a solution treatment at a temperature of 480 ° C. or higher. Cooling to a temperature range of 50 ° C. or more and less than 150 ° C. at an average cooling rate of at least / min, and subsequently performing a stabilization treatment for 1 hour or more within the temperature range, to produce an aluminum alloy plate for forming Method.