JP2009001842A - Aluminum alloy sheet for press forming - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for press forming suitable for press forming by increasing fracture thresholds in equal biaxial deformation, plane strain deformation and uniaxial deformation. <P>SOLUTION: All work hardening index n values (calculated at the two points of nominal strains 0.15 and 0.20) in the 0° direction, 45° direction and 90° direction are ≥0.25. The aluminum alloy sheet for press forming is preferably composed of an Al-Mg-Si based aluminum alloy sheet. The aluminum alloy sheet for press forming preferably has a composition comprising, by mass, 0.2 to 2.0% Si and 0.2 to 1.5% Mg, and the balance aluminum with inevitable impurities. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aluminum alloy plate for press forming particularly suitable for automobile parts such as automobile body panels.

Conventionally, when aluminum alloy sheets are press formed, the texture of the aluminum alloy sheets is controlled according to the type of press forming (for example, deep drawing formability, stretch formability, bending workability, etc.) It has been proposed to improve performance.
For example, in the texture of an Al—Mg—Si-based aluminum alloy plate, it is proposed that at least the orientation density of the Cube orientation can be controlled in accordance with the type of press forming to improve the press formability. (Patent Document 1).

  However, press molding of automobile body panels and the like is a combination of the above-mentioned types of press molding. Therefore, in order to improve the formability when press-molding automobile body panels, it is necessary to improve the fracture limit in equal biaxial deformation, plane strain deformation, and uniaxial deformation of the material (to increase the fracture limit strain) )is required.

JP 2000-319741 A

  The present invention has been made in view of such conventional problems, and is an aluminum alloy plate for press forming that is suitable for press forming by increasing the fracture limit in equal biaxial deformation, plane strain deformation, and uniaxial deformation. Is to provide.

  In the present invention, the work hardening index n values (calculated from two points of nominal strain 0.15 and 0.20) in the 0 ° direction, 45 ° direction, and 90 ° direction with respect to the final rolling direction are all 0.25 or more. It is in the aluminum alloy plate for press forming characterized by being (Claim 1).

  The work hardening index n value is a characteristic value that is a measure of moldability. It is known that when the work hardening index n value is large, the strain easily propagates and is easily deformed uniformly, so that the elongation to the local deformation (uniform elongation) is improved. However, it is known that the work hardening index of an aluminum alloy varies depending on the amount of strain, and tends to decrease particularly in a high strain region (nominal strain of 0.10 or more).

  And when this invention is measured as measurement conditions to calculate from two points of nominal strain 0.15 and 0.20, it is 0 ° direction, 45 ° direction, 90 ° direction with respect to the final rolling direction. It is an aluminum alloy sheet for press forming that is controlled so that all the work hardening index n values are high values of 0.25 or more. It has been found that by having the above-mentioned work hardening index characteristics, the fracture limit in equal biaxial deformation, plane strain deformation, and uniaxial deformation is increased, and press formability can be improved.

  As described above, according to the present invention, it is possible to provide an aluminum alloy plate for press forming suitable for press forming by increasing the fracture limit in equal biaxial deformation, plane strain deformation, and uniaxial deformation.

The aluminum alloy sheet for press forming of the present invention has a work hardening index n value of 0 ° direction, 45 ° direction and 90 ° direction with respect to the final rolling direction (calculated from two points of nominal strain 0.15 and 0.20). Are all 0.25 or more.
Calculation of the work hardening coefficient n value (n) can be calculated from the load P _b when the load P _a nominal strain e _b when the nominal strain e _a using the following equation.

  If any one of the work hardening index n values in the 0 ° direction, 45 ° direction, and 90 ° direction with respect to the final rolling direction is less than 0.25, the fracture limit in each of the above deformations decreases. There is a problem that moldability deteriorates.

  Further, in the method for producing the aluminum alloy plate for press forming, the obtained press forming aluminum alloy plate has all the work hardening index n values of 0 °, 45 ° and 90 ° with respect to the final rolling direction of 0. If it is 25 or more, it is not particularly limited. For example, hot rolling is performed on an ingot made of an aluminum alloy, and then cold rolling is performed in a 90 ° direction with respect to the rolling direction of hot rolling. Further, there is a method in which solution treatment and quenching are performed, and then heat treatment is performed.

However, when an Al—Mg—Si-based aluminum alloy described later is used as the aluminum alloy, it is preferably used in T4 refining in order to impart bake hardness. In order to improve the bake hardness, it is effective to perform preliminary aging (about 1 to 3 hours at 60 to 130 ° C.) immediately after the quenching treatment.
Moreover, it is thought that various future methods will be developed about a manufacturing method, and as long as it has the said work hardening index n value characteristic, it is not necessary to limit to a specific method.

Moreover, it is preferable that the said aluminum alloy plate for press forming consists of an Al-Mg-Si type aluminum alloy plate (Claim 2).
In this case, in particular, a material suitable for an automobile body panel that requires bake hardness can be obtained.

The aluminum alloy plate for press forming contains Si: 0.2 to 2.0% (mass%, the same applies hereinafter), Mg: 0.2 to 1.5%, and the balance is inevitable impurities and aluminum. (Claim 3).
Si is necessary for obtaining bake hardness, and functions to increase the strength by forming an Mg—Si based compound such as Mg ₂ Si.

When the Si content is less than 0.2%, the yield strength is low, and sufficient bake hardness may not be obtained. On the other hand, when the Si content exceeds 2.0%, the yield strength at the time of molding is increased, and there is a risk that the spring back in which the elastic deformation of the material recovers its shape (elastic recovery) due to release. . On the other hand, when the Si content is less than 0.2% or exceeds 2.0%, the work hardening index n value tends to be small, and the moldability may be deteriorated.
The Si content is more preferably 0.8 to 1.2%.

Mg is necessary for obtaining the bake hardness like the above-mentioned Si, and functions to increase the strength by forming a Mg—Si based compound such as Mg ₂ Si.
When the Mg content is less than 0.2%, the yield strength is low, and sufficient bake hardness may not be obtained. On the other hand, if the Mg content exceeds 1.5%, the yield strength during the molding process is increased and the spring back may be increased. On the other hand, when the Mg content is less than 0.2% or exceeds 1.5%, the work hardening index n value tends to be small, and the moldability may be deteriorated.
The content of Mg is more preferably 0.3 to 0.7%.

  Further, the aluminum alloy plate for press forming is further Cu: 0.1% or less (excluding 0%, the same shall apply hereinafter), Mn: 1.0% or less, Zn: 0.5% or less, Cr: 0 .3% or less, V: 0.2% or less, Zr: 0.2% or less, Ti: 0.1% or less, B: 0.005% or less, preferably 1 type or 2 types or more (Claim 4).

Cu functions to increase strength and improve formability. If the Cu content exceeds 1.0%, the corrosion resistance may be deteriorated. The Cu content is more preferably 0.3% or less.
Zn functions to improve the zinc phosphate processability during the surface treatment. If the Zn content exceeds 0.5%, the corrosion resistance may deteriorate.

Fe, Mn, Cr, V, and Zr function to increase strength and refine the crystal grains to prevent rough skin during molding. When the content of Fe, Mn, Cr, V, and Zr exceeds the above range, the work hardening index n value tends to be small, and the moldability may be deteriorated.
Ti and B function to refine the cast structure and improve formability. When the content of Ti and B exceeds the above range, the work hardening index n value tends to be small, and the moldability may be deteriorated.

(Example 1)
In this example, press-molding aluminum alloy plates (sample E1 to sample E7 and sample C1 to sample C7) were manufactured as examples and comparative examples according to the press-molding aluminum alloy plate of the present invention. These examples show one embodiment of the present invention, and the present invention is not limited thereto.
This will be described in detail below.

The manufacturing method of the said aluminum alloy plate for press forming is demonstrated.
First, an ingot (alloy A to alloy G) having the composition shown in Table 1 and the balance consisting of inevitable impurities and aluminum was ingoted by a semi-continuous casting method called a DC casting method (Direct Hill Casting Process). . The resulting ingot was homogenized at 550 ° C. for 8 hours, and then cooled to room temperature.

And the said ingot was reheated to 430 degreeC and hot rolling was started, and the hot rolled sheet of thickness 4.0mm was obtained. The end temperature of hot rolling was 240 ° C.
Subsequently, as shown in FIG. 1 (a), the 0 ° direction (arrow B) with respect to the hot rolling direction (arrow A), or as shown in FIG. 1 (b), the hot rolling direction (arrow C). ) In the 90 ° direction (arrow D) to obtain a 1.0 mm cold rolled plate.

Furthermore, the solution treatment for 30 seconds was performed at 550 degreeC, and it hardened to room temperature with the cooling rate of 30 degreeC / s. Thereby, aluminum alloy plates for press forming (Sample E1 to Sample E7 and Sample C1 to Sample C7) were obtained.
Table 2 shows the types of alloys used and the cold rolling direction relative to the hot rolling direction for the samples E1 to E7 and C1 to C7.

  Next, with respect to Sample E1 to Sample E7 and Sample C1 to Sample C7, the work hardening index n value and the moldability were evaluated by the following method 7 days after the final heat treatment. The results are also shown in Table 2.

ここで、Ｐ_aは公称ひずみｅ_aの時の荷重、Ｐ_bは公称ひずみｅ_bの時の荷重である。 <Work hardening index n value>
The work hardening index n value (n) is obtained by taking JIS No. 5 test pieces in 0 ° direction, 45 ° direction and 90 ° direction with respect to the final rolling direction, and using the load at nominal strain of 0.15 and 0.20. It was calculated using the following formula.

Here, load when the P _a nominal strain e _a, the P _b is the load when the nominal strain e _b.

  Table 2 shows the minimum work hardening index n value in the three directions. For example, in sample E1, the work hardening index n value in the 0 ° direction with respect to the final rolling direction is 0.32, the work hardening index n value in the 45 ° direction with respect to the final rolling direction is 0.35, and in the final rolling direction. On the other hand, the work hardening index n value in the 90 ° direction was 0.33. Therefore, the minimum work hardening index n value in the three directions of the sample E1 in Table 2 shows a work hardening index n value of 0.32 in the 0 ° direction.

<Moldability>
Formability was evaluated by measuring the breaking limit strain of equal biaxial deformation, plane strain deformation, and uniaxial deformation.
(Equal biaxial deformation)
For the breaking limit strain of equibiaxial deformation, using a blank to which a scribed circle of φ6.35 mm was transferred, a punching diameter: φ50 mm, a molding speed: 2 mm / s, a blank size: 100 mm × 100 mm was subjected to a molding test. After this, the fracture limit strain was measured.
As a lubricant, a vinyl sheet coated with high-viscosity mineral oil on both sides was inserted between a punch and a blank and used.
The breaking limit was 0.40 or more as acceptable and less than 0.40 as unacceptable.

(Plane strain deformation)
Plane strain deformation was performed by applying a low-viscosity mineral oil to the blank by changing the lubricant in the above-described method for measuring the breaking limit strain of biaxial deformation. The other molding conditions were the same as the method for measuring the breaking limit strain of the above biaxial deformation.
The breaking limit was 0.30 or more as acceptable and less than 0.30 as unacceptable.

(Uniaxial deformation)
The fracture limit strain in uniaxial deformation was measured by measuring the fracture limit strain after performing a tensile test using a JIS No. 5 test piece to which a scribed circle of φ6.35 mm was transferred.
The breaking limit was 0.40 or more as acceptable and less than 0.40 as unacceptable.
The tensile strength, proof stress and elongation are also shown.
(Evaluation)
Formability is determined to pass (evaluation ○) when it is acceptable in any of biaxial deformation, plane strain deformation, and uniaxial deformation, and rejected (evaluation ×) when any one of them fails. .

As is known from Table 2, Sample E1 to Sample E7 as examples all had a work hardening index n value of 0.25 or more in the 0 ° direction, 45 ° direction, and 90 ° direction with respect to the final rolling direction. .
And the said sample E1-sample E7 showed the favorable result also about the moldability and tensile strength, yield strength, and elongation.
Thereby, according to this invention, the fracture limit in equal biaxial deformation, plane distortion deformation, and uniaxial deformation can be raised, and the aluminum alloy plate for press forming suitable for press forming can be obtained.

  Samples C1 to C7 as comparative examples had at least one of less than 0.25 among the work hardening index n values in the 0 ° direction, 45 ° direction, and 90 ° direction with respect to the final rolling direction. Therefore, all the breaking limit strains of equibiaxial deformation, plane strain deformation, and uniaxial deformation were low, and the formability was unacceptable.

Explanatory drawing which shows the cold rolling direction with respect to the hot rolling direction in Example 1. FIG.

Explanation of symbols

  1 Aluminum alloy sheet for press forming

Claims (4)

  That the work hardening index n values (calculated from two points of nominal strain 0.15 and 0.20) in the 0 ° direction, 45 ° direction, and 90 ° direction with respect to the final rolling direction are all 0.25 or more. A featured aluminum alloy sheet for press forming.   2. The aluminum alloy plate for press forming according to claim 1, wherein the aluminum alloy plate for press forming comprises an Al—Mg—Si based aluminum alloy plate.   In Claim 2, the said aluminum alloy plate for press molding contains Si: 0.2-2.0% (mass%, and the following similarly), Mg: 0.2-1.5%, and the remainder is inevitable. An aluminum alloy plate for press forming, comprising impurities and aluminum.   In claim 3, the aluminum alloy plate for press forming is further Cu: 0.1% or less (excluding 0%, the same shall apply hereinafter), Mn: 1.0% or less, Zn: 0.5% or less, Cr: 0.3% or less, V: 0.2% or less, Zr: 0.2% or less, Ti: 0.1% or less, B: One or more of 0.005% or less An aluminum alloy plate for press forming characterized by the above.

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