JP5677193B2 - Aluminum alloy sheet for warm forming - Google Patents

Description

  The present invention relates to an aluminum alloy plate that can be suitably used for warm forming.

As measures for reducing the weight of automobiles in recent years, the use of an aluminum alloy plate having a specific strength higher than that of a steel plate has been studied and put into practical use. However, since the formability of an aluminum alloy plate is inferior to that of a steel plate, its application is limited to applicable parts.
Therefore, conventionally, various special forming methods have been studied in order to improve the formability of the aluminum alloy plate. One example is warm forming, that is, a press forming method in which the die temperature of the die and the wrinkle presser is heated to 150 to 300 ° C. and the punch is cooled (for example, Non-Patent Document 1). Since this forming method can be expected to ensure the formability equivalent to that of a steel sheet, studies for practical use are in progress.

  Since this forming method is deep drawing, the formability depends on the difference between the material strength of the punch portion and the yield strength of the die portion. When the punch is kept at room temperature and the die part is kept at 200 ° C. or 250 ° C., the material strength of the punch part is the tensile strength (TS) at room temperature because it contacts the punch at room temperature. The strength is the yield stress (YS) at high temperature because it contacts the 200 ° C. or 250 ° C. flange. Therefore, a material excellent in warm molding material needs to have a large TS (room temperature) -YS (high temperature).

  Up to now, as a warm forming material, generally an Al—Mg alloy having high formability, particularly JIS 5182 alloy as in Non-Patent Document 1, has been used.

Shinji Abe, Masakatsu Yoshida, “Double sink type warm forming of 5182 aluminum alloy sheet”, light metal, 1994, published by Japan Society of Light Metals, Vol. 44, No. 4, p. 240-245

  However, warm forming has not yet been put to practical use. This indicates that the warm formability of JIS 5182 alloy is still insufficient for practical use. Until now, the development of warm forming materials has not been studied, and the development of warm forming materials having higher formability than JIS 5182 alloy is desired.

  The present invention has been made in view of the above situation, and as a material superior in warm formability to JIS 5182 alloy, the difference between TS at room temperature and YS at the temperature during warm forming is obtained. It provides the material to maximize.

As a result of studying to solve the above-mentioned problems, the present inventors have considered that greatly increasing TS (room temperature) -YS (high temperature) is equivalent to increasing the work hardening amount. In order to increase the work hardening amount, it is necessary to dissolve a large number of atoms that contribute to solid solution strengthening.
In the case of an Al—Mg alloy, these atoms are Mg, Mn, and Cr. Among these, since most of the addition amount of Mg is dissolved, the amount of solid solution strengthening can be controlled by adjusting the addition amount. On the other hand, since Mn and Cr form precipitates with other atoms, adjustment of the manufacturing process for reducing these precipitates, that is, adjustment of heat treatment, is necessary for controlling the amount of solid solution strengthening by these atoms.

  The present inventors tried to invent a material having higher warm formability than before by adding Mn and / or Cr and adjusting heat treatment conditions in addition to control by addition of Mg. In particular, it has been found that the above precipitates can be reduced by increasing the cooling rate within the temperature range in which Mn and / or Cr precipitates are most formed. As a result, the present inventors have found a means for securing solid solution amounts of Mn and Cr and obtaining solid solution strengthening. Furthermore, it has been found that a decrease in the amount of Si added and a decrease in crystal grain size also contribute to an increase in the work hardening amount. The present invention has been made based on the above findings.

In order to achieve the above object, an aluminum alloy plate according to the present invention is characterized by the following.
(1) Mg: 2.0-6.0% (mass%, the same shall apply hereinafter) and Mn: 2.50% or less, Cr: 0.5% or less of 1 or 2 types And the balance consists of Al and inevitable impurities, and {(Mn addition amount (mass%))-(Mn precipitate area ratio (%)) × 0.24} + {(Cr addition amount (mass%)) − (Area ratio of Cr precipitates (%)) × 0.15}
Is an aluminum alloy sheet for warm forming.

(2) The aluminum alloy plate for warm forming according to (1), further containing Cu: 0.3-2.0%.
(3) The warm forming aluminum alloy plate contains Mn, and further, the Si content is restricted to 0.20% or less. Aluminum alloy plate.
(4) The aluminum alloy plate for warm forming according to (1) to (3), wherein the crystal grains are 25 μm or less.

  According to the present invention, the solid solution amount of Mn and Cr contributing to increase in work hardening amount is maximized, TS (room temperature) -YS (high temperature) is larger than that of the conventional JIS 5182 alloy, and warm formability is excellent. It has become possible to provide an aluminum alloy sheet for warm forming.

The present invention is described in detail below.
(Components of aluminum alloy)
First, the component composition of the aluminum alloy plate of the present invention will be described. Here, the unit of content is mass%.

An Al—Mg alloy is suitable for the material of the aluminum alloy plate of the present invention.
In the Al-Mg alloy, the addition amount of Mg is preferably 2.0% or more. High strength is obtained when the Mg content is 2.0% or more. On the other hand, if Mg is added in excess of 6.0%, hot workability may be deteriorated, resulting in an increase in manufacturing cost.

Since Mn and Cr are effective elements for increasing the work hardening amount by solid solution, one or two of them are added.
When Mn is added, the Mn content is 2.50% or less. When the content of Mn exceeds 2.50%, precipitates that are the starting points of fracture increase. Further, since Mn forms an Al—Mn precipitate, not all of the added Mn is dissolved in the Al—Mg alloy. For this reason, when adding Mn, in order to ensure sufficient solid solution amount, it is preferable to contain Mn 0.50% or more. In addition, when Mn is contained as an inevitable impurity in the aluminum alloy, the content of Mn contained in the aluminum alloy is less than 0.01%.

The solid solution amount of Mn is equal to a value obtained by subtracting the amount of Mn contained in the Al—Mn precipitate from the amount of Mn added, but it is difficult to directly analyze. From this, the following formula (1) was defined as an index that approximately indicates the solid solution amount of Mn.
(Mn addition amount (mass%))-(Al-Mn precipitate area ratio (%)) × 0.24 (1)

  The “area ratio of Al—Mn precipitates” in the formula (1) is determined by using a transmission electron microscope with a warm forming material having a constant film thickness of 0.3 μm or less with a focused ion beam (FIB). It calculates | requires from the observed image observed from the following formula | equation (2). “Area ratio of Al—Mn precipitates” is calculated from the observation image of the transmission electron microscope using the image analysis software to calculate the area of the Al—Mn precipitates in the observation image and calculate the following formula (2). You may ask for.

{(Area of Al-Mn precipitate in observed image) / (Area of entire observed image)} × 100 (%) (2)
Al-Mn precipitates are often _al 6 Mn. For this reason, when calculated from the atomic weight, the proportion of the amount of Mn contained in the Al—Mn precipitate is 24 (mass%). Therefore, as shown in the above formula (1), the amount of Mn in the Al—Mn precipitate is obtained by multiplying the area ratio of the Al—Mn precipitate by 0.24.

  Similarly, Cr is an effective element for increasing the work hardening amount by solid solution. The addition amount range in the case of Cr is 0.50% or less. When the Cr content exceeds 0.50%, precipitates are formed that serve as starting points for fracture. Since Cr forms Al—Cr precipitates, not all of the added Cr is in solid solution. Also, the larger the amount of Cr dissolved, the greater the work hardening amount, which is desirable. For this reason, when adding Cr, addition of 0.20% or more is preferable. In addition, when Cr is contained as an inevitable impurity in the aluminum alloy, the content of Cr contained in the aluminum alloy is less than 0.01%.

The amount of solid solution of Cr is equal to a value obtained by subtracting the amount of Cr contained in the Al—Cr precipitates from the amount of added Cr. For this reason, it defines as the following formula | equation (3) similarly to the case of the solid solution amount of Mn.
(Cr addition amount (mass%))-(Al-Cr precipitate area ratio (%)) × 0.15 (3)

  The “area ratio of Al—Cr precipitates” in the formula (3) is determined by the following formula (from the observation image observed with a transmission electron microscope with the warm molding material having a constant film thickness of 0.3 μm or less by FIB or the like. 4). The “area ratio of Al—Cr precipitates” is calculated from the observation image of the transmission electron microscope using the image analysis software to calculate the area of the Al—Cr precipitates in the observation image and to calculate the following formula (4). You may ask for.

{(Area of Al—Cr precipitates in the observed image) / (Area of the entire observed image)} × 100 (%) (4)
The determination of the Al—Mn precipitate and the Al—Cr precipitate in the observation image of the transmission electron microscope may be performed by an elemental analyzer installed in the transmission electron microscope.

Most of the Al—Cr precipitates are Cr ₂ Mg ₃ Al ₁₈ . For this reason, when calculating from the atomic weight, the ratio of the Cr amount contained in the Al—Cr precipitates is 15 (mass%). Therefore, as shown in the above formula (3), the amount of Cr in the Al—Cr precipitate is obtained by multiplying the area ratio of the Al—Cr precipitate by 0.15.

  Sum of solid solution amounts of Mn and Cr represented by the sum of the above formulas (1) and (3) {(Mn addition amount (% by mass))-(Mn precipitate area ratio (%)) × 0. 24} + {(Cr addition amount (% by mass)) − (Area ratio of Cr precipitates (%)) × 0.15} is less than 0.4%, the improvement in warm formability is small. In the invention, the sum of the solid solution amounts of Mn and Cr is set to 0.4% or more. In addition, Formula (1) and Formula (3) are formulas that hold when it is assumed that the specific gravity of the matrix, Mn, and Cr-based precipitates is the same.

  In the above-described alloy, Cu may be added as necessary. Although Cu also contributes to an increase in solid solution strengthening, excessive addition deteriorates formability through formation of a starting point of fracture. Therefore, when Cu is contained, the addition amount is limited to 2.0% or less. On the other hand, the lower limit in the case of containing Cu is determined by the amount at which the effect of improving the solid solution strengthening is achieved, and is 0.3% or more.

  When Si is added, the precipitation of Al—Mn precipitates is promoted, so that the amount of Mn solid solution decreases. Accordingly, when the aluminum alloy plate of the present invention contains Mn, the lower the Si content, the more preferable it is for solid solution of Mn. However, since Si has an effect of increasing the strength due to solid solution, it may be contained in the aluminum alloy plate as necessary. Si is restricted to 0.20% or less in order to suppress precipitation of Al-Mn precipitates even when it is included with Mn as an unavoidable impurity or when Si is included with Mn as necessary. To do. In addition, when a general aluminum ingot is used as a material of an aluminum alloy plate, less than 0.20% Si is inevitably contained.

  Fe may be further added to the component composition of these Al—Mg alloys. Fe is mixed from the melted raw material, and Fe contained as impurities generates a crystallized product. While this becomes a nucleus of recrystallization, when it is added in excess of 0.30%, it becomes a starting point of fracture and deteriorates formability and bending workability. Therefore, the addition amount is preferably 0.30% or less.

  In addition, Zr and V may be further added to the above component composition. These transition elements have the effect of generating dispersed particles during the homogenization heat treatment and suppressing grain boundary migration after recrystallization. However, a large amount of addition produces an intermetallic compound, which becomes a starting point of fracture in warm forming and bending, and deteriorates these characteristics. Therefore, when Zr is added, it is preferable to add 0.25% or less for Zr and 0.9% or less for Ti.

  Since the work hardening amount increases as the crystal grain size becomes finer, a smaller one is preferable. If the crystal grain size is too large, it causes rough skin and impairs the appearance of the molded product. Desirably, when the crystal grain size is 10 μm or less, a part of the material causes a superplastic phenomenon at a high temperature range, and the ductility is improved.

(Aluminum alloy manufacturing method)
Next, the manufacturing method of the said aluminum alloy is demonstrated. An aluminum alloy for warm forming needs to have sufficient strength and ductility.
The ingot of the Al—Mg alloy having the above composition is subjected to homogenization heat treatment, hot rolling, and cold rolling, followed by solution heat treatment and quenching treatment. These steps are the same as in the conventional method. Note that one or more heat treatments may be performed during the cold rolling, or the hot-rolled sheet may be heat treated after the hot rolling. Further, when the molded article does not require sufficient strength, ductility, and recrystallized grains, a cold rolled material may be used.

First, in the melting and casting process, a conventional melting and casting method such as a continuous casting rolling method and a semi-continuous casting method (DC casting method) is selectively performed on the molten alloy having the above-described component composition. In particular, when the continuous casting and rolling method is applied, a significant reduction in manufacturing cost can be expected.
The next homogenization heat treatment is aimed at homogenizing the material. The main purpose of the homogenizing heat treatment is to eliminate segregation of additive elements. In addition, heat treatment at a temperature of 520 ° C. or higher and a melting point or lower is required to sufficiently dissolve fine Al—Mn and / or Al—Cr compounds. Preferably it is higher than the solid solution temperature of Mn and / or Cr.

Although the heat treatment time depends on the amount of added elements, it is sufficient if it is 20 minutes or longer and 8 hours or shorter within the above temperature range. If it is shorter than 20 minutes, it is difficult to sufficiently eliminate segregation. On the other hand, if it is 8 hours or more, the production cost increases.
In addition, after holding the heating time within the above temperature range, it is necessary to cool the temperature range of 180 to 560 ° C. at a cooling rate of 20 ° C./sec or more, and the Mn-based precipitates and Cr-based precipitates are the most It is essential to cool the temperature range of 400 to 560 ° C. to be formed at a cooling rate of 30 ° C./sec or more. When the cooling rate is slower than this, Mn-based precipitates and / or Cr-based precipitates are formed, and the solid solution amount of Mn and / or Cr decreases. Means for increasing the cooling rate include forced air cooling and water cooling, but the means is not particularly limited.

In the subsequent hot rolling, it is necessary to set a starting temperature, which should be 450 ° C. or higher. At temperatures below 450 ° C., the frequency of recrystallization during hot rolling decreases sharply, which increases the possibility of non-recrystallization in the final product. Preferably, when the starting temperature is 520 ° C. or higher, fine Al—Mn and / or Al—Cr-based compounds are dissolved, and the solid solution amount of Mn and / or Cr increases.
It is preferable that the time from the hot rolling start temperature to the hot rolling start is shorter. 20 minutes or less is particularly desirable. When the said time becomes long, an Al-Mn and / or Al-Cr type compound will precipitate, and the solid solution amount of Mn and / or Cr may reduce.

In addition, after hot rolling, it is necessary to cool the hot rolled sheet at a temperature range of 180 to 560 ° C. at a cooling rate of 20 ° C./sec or more, and a temperature range of 400 to 560 ° C. at which Mn and Cr-based precipitates are formed most. It is essential to cool at a cooling rate of 30 ° C./sec or more. When the cooling rate is slower than this, Mn and / or Cr-based precipitates are formed, and the solid solution amount of Mn and Cr decreases.
The final thickness is not particularly limited and is preferably 5 mm or less from the viewpoint of the ease of the subsequent cold rolling process.

  In order to obtain reliable recrystallization, the hot-rolled sheet may be annealed before cold rolling. In that case, 20 minutes or more is sufficient at a temperature of 400 ° C. or higher, and annealing for a long time is a disadvantage of increasing the production cost. Further, in consideration of the entire manufacturing cost, this hot-rolled sheet annealing may be omitted. Also in the cooling after this hot-rolled sheet annealing, it is necessary to cool the temperature range of 180 to 560 ° C. at a cooling rate of 20 ° C./sec or more, and 400 to 560 ° C. that most forms Mn and Cr-based precipitates. It is essential to cool the temperature range at a cooling rate of 30 ° C./sec or more.

Subsequent cold rolling may be performed by a conventional method until cold to a desired thickness.
Moreover, in order to obtain reliable recrystallization similarly to hot-rolled sheet annealing, you may implement one or more heat processing (intermediate annealing) in the middle of cold rolling. If the temperature at this time is equal to or higher than the solid solution temperature of Mn and Cr, the solid solution amount of Mn and Cr increases, which is preferable. Similar to hot-rolled sheet annealing, it is necessary to cool a temperature range of 180 to 560 ° C. at a cooling rate of 20 ° C./sec or more in the cooling after the intermediate annealing, and 400 most forms Mn and Cr-based precipitates. It is essential to cool the temperature range of ˜560 ° C. at a cooling rate of 30 ° C./sec or more.

It is preferable that the cold rolling rate from the intermediate annealing to the final plate thickness is large. By increasing the cold rolling rate, the recrystallized grains at the time of final annealing are refined. Desirably, the cold rolling rate from the intermediate annealing to the final thickness is 75% or more.
After the cold rolling, final annealing is performed. The final annealing temperature is 400 ° C. or higher and the melting point or lower. The temperature is preferably higher than the solid solution temperature of Mn and Cr. The final annealing is preferably performed in a continuous annealing furnace, and it is necessary to cool a temperature range of 180 to 560 ° C. at a cooling rate of 20 ° C./sec or more, and 400 to 560 ° C. that most forms Mn and Cr-based precipitates. It is essential to cool the temperature range at a cooling rate of 30 ° C./sec or more. If the cooling rate is slower than this, Mn and Cr-based precipitates are formed, and the solid solution amount of Mn and Cr decreases.

(Molding method)
Next, the molding method of the present invention will be described.
The warm forming using the above-described aluminum alloy plate is performed by lowering the temperature of the punch than the temperature of the die and the crease presser mold. The greater the temperature difference, the greater the strength difference in the material and the deep drawability improves. The necessary temperature difference between the die and wrinkle holding mold and the punch is 50 to 300 ° C. When the temperature difference is less than 50 ° C., a sufficient strength difference does not appear in the material. In addition, in order to obtain a temperature difference exceeding 300 ° C., a significant equipment cost is required, which is industrially disadvantageous. The heating method may be an electric heater or a method using another heat medium, and is not particularly limited.

  In addition, since the fall of the deformation resistance of a flange part is inadequate if the heating temperature of a die | dye and a wrinkle pressing die is less than 150 degreeC, let the minimum of these temperatures be 150 degreeC or more. The deformation resistance of the flange portion decreases as the heating temperature of the die and the wrinkle holding mold increases. For this reason, it is preferable that heating temperature shall be 200 degreeC or more, and the range of 250-300 degreeC is an optimal range.

  Further, in order to increase the temperature difference between the temperature of the material in contact with the punch and the temperature of the material in contact with the die and the wrinkle holding mold, it is preferable to provide a pipe in the punch and cool it by water cooling. In addition, the cooling water of a punch may be 30 degrees C or less, and cooling is possible at the temperature of normal tap water. The punch temperature is preferably as low as possible, and if it is 10 ° C. or less, the moldability becomes extremely good.

Here, in order to cool the punch, it is preferable to connect a pipe provided in the punch to a cooling device and to circulate a temperature-controlled refrigerant in the punch. When using a refrigerant and a cooling device, considering piping and the like, the temperature of the refrigerant is practically in a range of −50 ° C. or more, and the range of −30 to 0 ° C. is optimal.
In order to efficiently cool the punch, the refrigerant is preferably an aqueous ethylene glycol solution. As the refrigerant, alcohols such as methanol and ethanol, or organic halogen compounds such as methylene chloride may be used.

The cooling device for cooling the refrigerant is not particularly limited, and a general-purpose device may be used.
In order to promote cooling of the punch shoulder portion, a counter punch opposite to the punch may be provided, and in this case, it is preferable to provide the counter punch with water cooling means to cool to the same temperature as the punch.

  Further, the temperature difference between the temperature of the material in contact with the punch and the temperature of the material in contact with the die and the wrinkle holding die is smaller than the temperature difference between the die and the wrinkle holding die and the punch due to the heat conduction of the material. In order to obtain good moldability, as described above, the temperature difference between the material portion in contact with the die and the crease pressing die and the material portion in contact with the punch needs to be 50 ° C. or more. For this purpose, it is preferable that the temperature difference between the die and the crease pressing die and the punch itself is 90 ° C. or more. Thereby, it becomes possible to make the intensity difference of the part equivalent to the flange part and punch shoulder part of an aluminum alloy plate into an appropriate range, and press formability can be improved further.

(Suitable properties of alloy plate)
The alloy plate of the present invention preferably gives the following characteristics. LDR value (limit drawing ratio): It is preferably more than 2.4, more preferably 2.5 or more, and particularly preferably 2.6 or more.

Examples of the present invention will be described below.
Using the alloy of the composition which contains the component of Table 1 and the remainder consists of Al and an unavoidable impurity, the to-be-formed board was manufactured on the basis of Table 2 and the following manufacturing conditions. Thereafter, the obtained plate to be molded was warm-formed under the following conditions, and the LDR value (limit drawing ratio) was measured by the following method.

<Manufacturing conditions of the plate to be molded>
The production conditions for the molded plate are as follows. First, ingots having the compositions of alloy numbers 1 to 24 shown in Table 1 were manufactured by melt casting, and homogenized. The homogenization temperature was 550 ° C. and the heat treatment time was 4 hours. After the homogenization treatment, hot rolling was performed, and the hot rolling start temperature was set to 550 ° C. The hot-rolled sheet was cold-rolled without intermediate annealing to a final sheet thickness of 1.0 mmt. At this time, the thickness of the hot rolled sheet was adjusted, and the final cold rolling rate was changed as shown in Table 2. After the cold rolling, final annealing was performed at 500 ° C. to obtain a molded plate (manufacturing conditions 1 to 31).
In Table 1, (-) indicates that the component is not positively added. In addition, the cooling rates during the heat treatment (homogenization treatment, hot rolling, final annealing) were unified, and the cooling rates in the temperature ranges of 400 to 560 ° C. and 180 to 400 ° C. were controlled as shown in Table 2.

<Warm forming>
For warm forming, a cylindrical punch having a diameter of 75 mm and a die having a diameter of 80 mm were used. The die and wrinkle holding mold were heated by electrothermal heating with a heater embedded in the mold, and the punch was cooled by circulation of cooled ethylene glycol water. The punch temperature was set to 25 ° C., and the temperature of the die and wrinkle holding mold was set to 250 ° C. A general-purpose molybdenum disulfide aqueous solution was used for lubrication.

<LDR value (limit aperture ratio)>
The LDR value is an evaluation value of deep drawing formability, which is a value obtained by dividing the diameter of the largest circular aluminum alloy plate that can be formed until drawing without breaking, by a punch diameter (here, 75 mm). If this value is large, the warm formability is excellent. Under this test condition, the LDR value in the general warm forming of JIS 5182 alloy is 2.4, and the LDR value greater than 2.4 is required for the warm forming material. In addition, BHF (wrinkle pressing load) was set to 1t.

<Calculation of the sum of Mn solid solution amount and Cr solid solution amount>
A method for calculating the sum of the Mn solid solution amount and the Cr solid solution amount will be described. The manufactured plate was processed by FIB so as to have a constant film thickness of approximately 0.3 μm, and observed with a transmission electron microscope. The observation image was read into image analysis software, and the area ratio of Al—Mn or Al—Cr precipitates was measured. The determination of the Al—Mn precipitate and the Al—Cr precipitate was performed with an elemental analyzer equipped with a transmission electron microscope. The sum of the Mn solid solution amount and the Cr solid solution amount was calculated by adding the value of the formula (1) and the value of the formula (3) using the measured area ratio.

<Experimental result>
The molding test results of the molded plates under the manufacturing conditions 1 to 31 shown in Table 2 will be described.
In production conditions 1 to 24, the cooling rate after solution heat treatment is increased to 25 ° C./sec at temperatures below 400 ° C. and 35 ° C./sec from 400 to 560 ° C., thereby increasing the solid solution amount of Mn and Cr. planned.

  The influence of Mg content was investigated by comparison of manufacturing conditions 1-5. In production condition 1, since the Mg content was small, the LDR value was low, and warm formability exceeding that of JIS 5182 alloy could not be obtained. On the other hand, production conditions 2 to 4 are LDR exceeding JIS 5182 alloy, and the warm formability is improved as the Mg content is increased. In manufacturing condition 5, since there was much Mg content, the hot rolling crack was raise | generated and it did not reach evaluation.

  The effect of Mn content was investigated by comparison of production conditions 3 and 6-10. In production conditions 6 to 8, the amount of Mn added was small, and the sum of the Mn solid solution amount and the Cr solid solution amount was small, so that warm formability exceeding that of JIS 5182 alloy could not be obtained. Production conditions 3 and 9 were LDR values exceeding those of JIS 5182 alloy, and as the Mn content increased, the Mn solid solution amount increased and the warm formability improved. However, since the Mn content was too high under production condition 10, a coarse intermetallic compound was produced, and the moldability deteriorated.

  The effect of Cr content was investigated by comparison of production conditions 8, 11-15. Under production conditions 8 and 11, the Cr solid solution amount was small, and the sum of the Mn solid solution amount and the Cr solid solution amount was small, so the LDR value was low, and warm formability exceeding that of JIS 5182 alloy was not obtained. On the other hand, production conditions 12 to 14 were LDR values exceeding those of JIS 5182 alloy, and as the Cr content increased, the Cr solid solution amount increased and the warm formability tended to improve. However, under production condition 15, since the Cr content was too high, a coarse intermetallic compound was produced, and the formability deteriorated. In the manufacturing condition 13, the formability is improved only by the amount of Cr solid solution.

  The influence of Cu content was investigated by comparison of production conditions 3 and 16-20. In the production condition 16, since the Cu content was small, no significant improvement in the LDR value was observed. On the other hand, in the production conditions 17 to 19, the warm formability tended to improve as the Cu content increased. However, since the Cu content was too high under the production condition 20, the moldability deteriorated.

The influence of Si content was investigated by comparison of production conditions 12, 21-23. In production conditions 12, 21, and 22, since the Si content was small, the amount of Al—Mn-based precipitates was small, and the Mn solid solution amount was large. Therefore, good warm formability higher than that of JIS 5182 alloy was maintained. On the other hand, since the manufacturing condition 23 had too much Si content, the Mn solid solution amount decreased and the warm formability deteriorated.
Production condition 24 is such that Mn has a content close to the upper limit at which coarse precipitates are not generated, and Cr has an upper limit content at which coarse precipitates are not generated, but very good warm formability. showed that.

  By comparing the production conditions 12, 25 to 28, the influence of the cooling rate during the heat treatment on the Mn solid solution amount and the warm formability was investigated. In production conditions 12, 25, and 27, the cooling rate was high, the Mn solid solution amount was maintained, and the warm formability was also good. On the other hand, under the production condition 26, the overall cooling rate is 20 ° C./sec or more, but the cooling rate was low in the temperature range of 400 to 560 ° C. where the formation of Al—Mn precipitates was active, so the Mn solid solution amount decreased. Warm formability deteriorated. Moreover, although the cooling rate in the temperature range of 400-560 degreeC was large also in the manufacturing conditions 28, since the cooling rate in the temperature range of 180-400 degreeC was small, the amount of Mn solid solution decreased and the warm formability deteriorated.

  The effects of the cold rolling rate on the crystal grain size and the warm formability were investigated by comparing the production conditions 3, 29, 30 and the comparison of the production conditions 1, 31. By increasing the cold rolling rate, the crystal grains became finer and the warm formability tended to improve. In particular, in the production condition 30, the crystal grain size became 10 μm or less by setting the cold rolling rate to 75%, and the warm formability was greatly improved. On the other hand, in the production condition 31, the cold rolling rate was low, the crystal grain size was larger than 25 μm, the LDR value was good, but the surface appearance of the molded product was rough.

Claims (4)

Mg: 2.0-6.0% (mass%, the same shall apply hereinafter) and Mn: 2.50% or less,
Cr: containing one or two of 0.50% or less,
The balance consists of Al and inevitable impurities, and {(Mn addition amount (% by mass)) − (Mn precipitate area ratio (%)) × 0.24} + {(Cr addition amount (% by mass)) − ( Area ratio of Cr precipitates (%)) × 0.15}
Is an aluminum alloy sheet for warm forming.   Furthermore, Cu: 0.3-2.0% is contained, The aluminum alloy plate for warm forming of Claim 1 characterized by the above-mentioned.   The aluminum alloy plate for warm forming according to claim 1 or 2, wherein the aluminum alloy plate for warm forming contains Mn, and further, the amount of Si is regulated to 0.20% or less. .   The aluminum alloy plate for warm forming according to any one of claims 1 to 3, wherein the crystal grains are 25 µm or less.