JP2001295007A - Method for producing high strength and high formability aluminum alloy sheet and aluminum alloy sheet obtained by the same producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an aluminum alloy sheet by which, as for an Al-Mg alloy containing a relatively small amount of Mg of 3.0 to 5.0%, a sheet material having a fine recrystallized grain structure and excellent in strength and formability can be produced without undergoing recrystallization annealing and to provide an aluminum alloy sheet obtainable by the same method. SOLUTION: An aluminum alloy sheet containing 3.0 to 5.0% Mg, and the balance Al with impurities is cold-rolled at a draft of >=70% to form the structure of the matrix of the same aluminum alloy sheet into the unrecrystalled one, and, after that, the aluminum alloy sheet is stretched at 200 to 300 deg.C at a strain rate of >=1×10-4/sec and a tensile amount of >=10%. By this producing method, the above unrecrystallized structure is dynamically recrystallized, by which the aluminum alloy sheet having the average crystal grain size of <=3 μm can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-formability aluminum alloy sheet, and more particularly, to a high-strength, high-formability aluminum-Mg alloy sheet having a fine recrystallized grain structure and suitable for structural use. The present invention relates to a production method and an aluminum alloy plate obtained by the production method.

[0002]

2. Description of the Related Art JIS (or AA) 5052, 505
Al-Mg based alloys containing a relatively large amount of Mg, such as 6, 5082, 5083, and 5086, are excellent in strength, formability, and weldability, and are therefore used for transportation of railway vehicles, aircraft, ships, automobiles, bicycles, and the like. It is used as equipment, pressure vessels and tanks of chemical plants, and members of buildings and structures.

[0003] These Al-Mg based alloy plates are usually made of D
The ingot was formed by C casting, and the obtained ingot was cast according to a conventional method.
After homogenization, hot rolling and cold rolling are performed to obtain a sheet having a predetermined thickness, and then recrystallization annealing is performed to obtain an aluminum alloy sheet having an average recrystallized grain size of 20 to 30 μm. .

In recent years, particularly in response to demands for miniaturization, weight reduction, and high performance of transportation equipment parts, in order to reduce the thickness of members, an Al—Mg based alloy plate having both excellent strength and formability has been developed. Development has been demanded, and as a means for achieving this demand, a technique for further refining the recrystallized structure of an Al-Mg-based alloy has attracted attention. By having a fine grain structure, not only strength and formability, but also fracture toughness and
Excellent properties such as improved corrosion resistance and stress corrosion cracking resistance can also be exhibited.

Conventionally, Al-M having a fine grain structure
As a method of manufacturing a g-based alloy sheet, for example, while containing not less than 6.0% and up to 7.0% of Mg,
e: 0.1 to 2.0%, Cr: 0.05 to 0.5%, Z
r: Recrystallized grains after recrystallization annealing by adding cold rolling at a rolling reduction of 90% or more to an Al-Mg alloy containing one or more of 0.05 to 0.2%. It has been proposed to make fine particles having a diameter of 5 μm or less (Japanese Patent Application No. 11-268599).

According to this method, the Mg content is extremely increased, and a large reduction is applied in cold rolling to increase the number of dislocations and Fe-containing compound particles serving as nucleation sites for recrystallization. It is intended to suppress the coarse growth of recrystallized grains due to the movement of grain boundaries by dispersing precipitated particles such as Cr and Zr. Actually, after recrystallization annealing, Al-Mg having a fine recrystallized structure of 5 μm or less is obtained. Although it is possible to manufacture an alloy plate, it is necessary to contain a large amount of Mg. Therefore, the amount of Mg is out of the upper limit of the standard of the component of Mg in the ordinary 5000 series (JIS or AA) alloy. Edge cracks occur during rolling, and edge cracks during cold rolling due to large reduction increase, making it difficult to manufacture sheet materials, and even if it can be manufactured, the yield will be extremely low, so practical use There is a problem that it is difficult.

Further, in this method, since the high Mg content aluminum alloy is subjected to cold rolling under high pressure, the amount of work hardening of the obtained aluminum alloy sheet becomes extremely large, and therefore, recrystallization annealing is not performed. When performed at a low temperature, the annealing becomes insufficient, and the elongation and formability required for various uses are often not obtained.

In order to solve such a problem, in the above method, the Mg content is reduced,
When the content is less than 5.0% of the system standard, it is difficult to reduce the recrystallized grain size after final annealing to 5 μm or less, and when the recrystallization annealing temperature is increased to improve the formability, Also, the recrystallized grains became coarse and the recrystallized grain size after final annealing was 5
It is difficult to reduce the size to μ or less.

On the other hand, high strength A such as JIS7075 alloy
The l-Zn-Mg-Cu-based alloy plate is cold-rolled at a rolling reduction of 25 to 67% to produce an aluminum alloy plate having an unrecrystallized structure, and then 4x10 in a warm region of about 350 ° C. ^-3 /
It has been reported that a non-recrystallized structure is dynamically recrystallized by applying a strain at a strain rate of about second and giving a strain of about 40% to obtain a fine recrystallized grain structure (Light Metal, Vol. 49, No. 8). issue,
1999, pp. 383-388), it is known that high strength can be achieved by this method.

The inventor further studied the above-mentioned method of dynamically recrystallizing an unrecrystallized structure obtained by cold rolling by stretching it warmly.
As a result of conducting multilateral tests and studies on the applicability to Al-Mg based alloys of a specific composition contained in a relatively large amount within the component specification of the content, specific warm tensile temperature, strain rate and tensile It has been found that in the combination of the amounts, both properties of strength and cold formability are simultaneously improved.

[0011]

SUMMARY OF THE INVENTION The present invention has been made based on the above-mentioned findings, and its object is to provide a liquid crystal display having a size of 3.0 to 3.0.
For an Al-Mg alloy containing 5.0% Mg, 3
A method for producing a high-strength high-formability aluminum alloy capable of producing a sheet material having a recrystallized grain structure of not more than μm and excellent in strength and formability without performing recrystallization annealing and without going through complicated steps. An object of the present invention is to provide an aluminum alloy plate obtained by the method.

[0012]

According to a first aspect of the present invention, there is provided a method for producing a high-strength, high-formability aluminum alloy sheet, comprising 3.0 to 5.0% of Mg. An aluminum alloy plate comprising the balance of Al and impurities is cold-rolled at a rolling reduction of 70% or more to make the matrix of the aluminum alloy plate an unrecrystallized structure.
It is pulled at a strain rate of 1 × 10 ⁻⁴ / sec or more and a tensile amount of 10% or more at a temperature of 00 to 300 ° C., and the unrecrystallized structure is dynamically recrystallized to have an average crystal grain size of 3 μm or less. It is characterized by obtaining an aluminum alloy plate.

According to a second aspect of the present invention, in the method for manufacturing a high-strength and high-formability aluminum alloy plate, the aluminum alloy plate according to the first aspect further comprises Mn: 0.05 to 0.1.
5%, Cr: 0.05-0.2%, Zr: 0.05-
The method for producing a high-strength and high-formability aluminum alloy sheet according to claim 3, wherein the aluminum alloy sheet comprises 0.2% or more of 0.2% or more. Further, Ti: 0.001 to 0.1
%, B: 1 to 300 ppm.

A high-strength, high-formability aluminum alloy sheet according to claim 4 of the present invention is an aluminum alloy sheet produced by the method according to any one of claims 1 to 3, wherein the average crystal grain size is 3 μm or less. Wherein the proof stress is 250 MPa or more and the elongation is 11% or more.

A high-strength, high-formability aluminum alloy sheet according to claim 5 of the present invention is an aluminum alloy sheet produced by the method according to any one of claims 1 to 3, wherein the average crystal grain size is 3 μm or less. And a proof stress of 260 MPa or more and an elongation of 13% or more.

According to the present invention, as described above,
A relatively large reduction of 70% or more is applied to an Al-Mg-based alloy sheet containing a relatively large amount within the component specification of the Mg content of the system-based aluminum alloy, and the large-angle grains in the crystal grain structure before cold rolling are applied. Unrecrystallized Al with high density of field
An Mg-based alloy sheet is prepared, and then the Al-Mg-based alloy cold-rolled sheet is stretched (stretched) at a temperature of 200 to 300 ° C to dynamically recrystallize an unrecrystallized structure. And the average crystal grain size of the recrystallized structure is 3 μm or less.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The significance of the constituent elements of an Al-Mg based alloy in the present invention and the reasons for limitation will be described.
Mg is an element that functions to improve the strength and formability of the alloy by solid solution strengthening, and the preferred content is 3.0 to 3.0.
It is in the range of 5.0%. If it is less than 3.0%, sufficient solid solution strengthening cannot be obtained. In addition, recovery in the case of performing cold rolling with a relatively large rolling reduction cannot be suppressed, and the dynamic recrystallization of the unrecrystallized structure during warm stretching after cold rolling is insufficient, and the A crystal structure and a dislocation structure remain, a fine recrystallized structure cannot be obtained, and sufficient strength and formability cannot be achieved. If the content exceeds 5.0%, the production of a sheet material becomes difficult due to edge cracks at the time of casting, hot rolling and cold rolling, and even if it can be produced, the yield is remarkably reduced. Not suitable for

Mn, Cr and Zr are Al-Mn type, Al
-Generation of compound particles (crystals) such as Cr-based and Al-Zr-based, and growth of fine crystal grains formed by warm tension;
It functions to suppress coarsening and refine recrystallized grains. The preferred content is Mn: 0.05-0.5%, C
r: 0.05 to 0.2%, Zr: 0.05 to 0.2%, the effect is not sufficient below the lower limit, and the grain size is reduced when the upper limit is exceeded, respectively. Effect is saturated, and coarse crystals are formed during casting, and properties such as fracture toughness, fatigue strength, elongation, and formability are easily deteriorated.

Ti and B have the effect of refining the crystal grains of the ingot. In particular, Ti is an element usually added to an aluminum alloy. The preferred content is Ti: 0.0
01 to 0.1%, B: 1 to 300 ppm,
If the content is less than the lower limit, the effect is small, and if the content exceeds the upper limit, a coarse crystallized substance is easily formed at the time of casting. In the present invention, in addition to the above components, 0.2% or less of Cu, 0.25% or less usually contained in an Al—Mg alloy.
Zn, 0.5% or less of Si, O. F of 5% or less
e, the effect of the present invention is not impaired even if V and the like are contained at 0.05% or less.

The method for producing the aluminum alloy sheet of the present invention will be described. The starting material in the present invention, that is, the Al-Mg alloy sheet to be subjected to cold rolling and warm stretching is as follows:
It can be manufactured by an ordinary method. That is, the Al-Mg alloy having the above composition is melted and semi-continuous casting (DC
The ingot is produced by homogenization, hot rolling after homogenization treatment, intermediate annealing as necessary, or cold rolling after hot rolling, and intermediate annealing.

The ingot is homogenized by an Al—Mn system, Al
430 to 540 in order to precipitate fine and many compound particles such as Fe-based, Al-Cr-based, and Al-Zr-based particles.
It is preferably carried out at a temperature of ° C. If the temperature is lower than 430 ° C., the effect of homogenization itself by diffusion is insufficient.
There is a high possibility that the above compound particles become coarse.

Hot rolling can be carried out by a conventional method. However, since the working ratio (reduction ratio) of hot rolling affects the reduction ratio of cold rolling, it is necessary to increase the reduction ratio of cold rolling. In the case where the final plate thickness is the same, it is preferable that the plate thickness at the end of hot rolling be large. Further, since it is desirable to increase the strain (dislocation density) introduced at the time of hot rolling, the end temperature of hot rolling is preferably lower.

In the present invention, in the casting step, A
l-Mn, Al-Fe, Al-Cr, Al-Zr
It is preferable to promote the solid solution of compounds such as the system and to suppress the precipitation of these compounds. For this purpose, it is desirable to increase the cooling rate during casting. A twin-roll casting method using a rotary water-cooled mold or the like, a belt casting method using a steel belt as a mold, capable of setting a cooling rate from a liquidus temperature to a solidus temperature of 2 ° C./sec to 10 ° C./sec. It is preferable to use a continuous casting method such as a method, a 3C method, or a block caster method using a water-cooled mold block.

The plate material cast by the above casting method is
The above hot rolling, if necessary, intermediate annealing, cold rolling after hot rolling, intermediate annealing, or direct cold rolling without hot rolling, by performing intermediate annealing, the starting material in the present invention, namely Cold rolling-Al for warm tension-
An Mg-based alloy plate is used. The intermediate annealing is performed by a batch type heat treatment furnace or a continuous annealing furnace (CAL).

The cold rolling step-warm stretching step which is a feature of the present invention will be described. First, in the cold rolling step, cold rolling is performed at a rolling reduction of 70% or more. This step is an important step for reducing the recrystallized grain size to 3 μm or less in the subsequent warm stretching step. By cold rolling at a rolling reduction of 70% or more, the large-angle grain boundaries formed before the cold rolling are distributed at a high density. Adjacent sub-crystal grains rotate due to a large grain boundary slip, thereby increasing the grain boundary tilt angle, thereby making it possible to obtain a fine crystal structure.

The subsequent warm tension is 200 to 3
At a temperature of 00 ° C., a strain rate of 1 × 10 ⁻⁴ / sec or more,
This is performed under the condition of a tensile amount of 10% or more, and dynamically recrystallizes the unrecrystallized matrix of the cold-rolled sheet. In this case, a recrystallized structure may be substantially formed, and a slight unrecrystallized structure or dislocation structure which does not affect the effects of the present invention may be present. If the temperature is lower than 200 ° C., it is not possible to sufficiently recrystallize the unrecrystallized crystal, and the unrecrystallized structure and the dislocation structure remain, and a fine recrystallized grain structure having an average crystal grain size of 3 μm or less cannot be obtained. . If the temperature exceeds 300 ° C., the recrystallized grains become coarse, so that a fine recrystallized grain structure having an average crystal grain size of 3 μm or less cannot be formed.

When the strain rate is less than 1 × 10 ⁻⁴ / sec, even if a tensile amount of 10% or more is applied, 200 to 3
Since the time during which the aluminum alloy plate is heated to 00 ° C. becomes long, recrystallized grains become coarse. If the tensile amount is less than 10%, the dynamic recrystallization of the unrecrystallized crystal is insufficient even when the film is stretched at a strain rate of 1 × 10 ⁻⁴ / sec or more at a temperature of 200 to 300 ° C. Structure remains and average grain size 3
A fine recrystallized grain structure of μm or less cannot be obtained.

The warm stretching in the present invention can be performed by using, for example, a tension straightening machine such as a stretcher provided with a heating / heating device or a roll straightening machine such as a leveler.

In the present invention, the crystal grain size is measured by
The cross section in the length direction (rolling direction) of the aluminum alloy plate is cut by a cutting method using an optical microscope and a focused ion beam processing observation device (FIB). Specifically, a straight line is drawn so that the number of crystal grains cut by the straight line becomes 100 or more, and the length of the straight line is divided by the number of cut crystal grains to obtain a recrystallized grain size.

Normally, Al—Mg based alloy sheets are finally subjected to high-temperature annealing to improve formability such as elongation and drawing height required for various applications. This is an alternative to the annealing treatment, and the Al-Mg-based alloy plate that has undergone the warm tensile process has an average crystal grain size of 3 μm.
Since it has the following microstructure, it has high strength and high formability, and ordinary high-temperature annealing is unnecessary. The final high-temperature annealing is harmful because it coarsens the recrystallized grain size. One of the features of the present invention is that a product plate is formed without performing final annealing.

The aluminum alloy sheet produced by the above process has a very fine recrystallized grain structure having an average crystal grain size of 3 μm or less, and has a proof stress of 240 MPa or more, preferably 260 MPa or more, and an elongation of 10% or more. Desirably, it has mechanical properties of 13% or more, and has excellent strength and moldability.

[0032]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples, and the effects thereof will be demonstrated based on them.
It should be noted that these examples are for describing a preferred embodiment of the present invention, and the present invention is not limited thereto.

Example 1 An Al-Mg alloy having the composition shown in Table 1 was formed by DC casting (cooling rate: 5 ° C./sec), and the obtained ingot (thickness: 50 mm) was cooled to 520 ° C. After homogenizing at a temperature of 4 hours (heating rate: 50 ° C./sec), hot rolling was started at this temperature, and hot rolling was completed at 300 ° C. to obtain a sheet material having a thickness of 10 mm.

Next, as shown in Table 2, these hot-rolled sheets were cold-rolled at a rolling reduction of 90% and 80%, and a stretcher provided with a heating device was mounted on the obtained cold-rolled sheets. Then, warm tension was performed under the conditions shown in Table 2.

With respect to the Al—Mg alloy plate (test material) after the warm tension, the average recrystallized particle size was determined by measuring the recrystallized particle size of the cross section in the length direction by the above-mentioned method, and the tensile test (J
ISZ 2241), and the tensile strength (σ _B ), proof stress (σ _0.2 ), and elongation (δ) were measured. Also, in order to evaluate press formability, a blank material was sampled from the test material, and L
Mold for measuring DH ₀ (maximum overhang height) (diameter 50.8
A ball-head overhang test was performed using a ball-head punch (mm), and the LDH ₀ (maximum overhang height) that could be formed without cracking at that time was determined. Table 2 shows the results.

[0036]

[Table 1]

[0037]

[Table 2]

As can be seen from Table 2, the test material No. Nos. 1 to 9 each have a fine recrystallized structure having an average crystal grain size of 3 μm or less, have excellent mechanical properties in a warm tensile state, and have excellent moldability.
Of these test materials, test material No. with a slightly lower rolling reduction in cold rolling was used. 2. Test material N with relatively low strain rate and tensile strength
o. Test materials Nos. 4 and 5 have relatively large recrystallized grain diameters and have relatively low tensile temperatures. In Sample No. 3, since a dislocation structure was slightly mixed in the structure, some of the mechanical properties were slightly inferior to those of the other test materials.

Comparative Example 1 An Al-Mg alloy having a composition shown in Table 3 was formed by DC casting (cooling rate: 5 ° C./sec), and the obtained ingot (thickness: 50 mm) was cooled to 520 ° C. After homogenizing at a temperature of 4 hours (heating rate: 50 ° C./sec), hot rolling was started at this temperature, and hot rolling was completed at 300 ° C. to obtain a sheet material having a thickness of 10 mm.

Next, these hot rolled sheets and alloy No. 1 of Example 1 were used. As shown in Table 4, the hot-rolled sheet A was cold-rolled at a rolling reduction of 90% and 60%, and the obtained cold-rolled sheet was stretched with a heating device in the same manner as in Example 1 And subjected to warm tension under the conditions shown in Table 2,
The same measurement and test as in Example 1 were performed on the plate material (test material) after the warm tension. Table 4 shows the results. Table 3
In Nos. To 4, those which did not satisfy the conditions of the present invention are underlined.

[0041]

[Table 3]

[0042]

[Table 4] << Table Note >> Average crystal grain size *: Unrecrystallized structure

As shown in Table 4, the test material No. No. 10 shows excellent properties, but the content of Mg is large, so that edge cracks are remarkably generated in casting, hot rolling, and cold rolling, and the yield of a plate material obtained as a healthy part is 70%.
%, Which is extremely low, and there is a problem in practical use. Test material No. In No. 11, a structure having an average crystal grain size of 3 μm or less was not obtained because the amount of Mg was small, and the mechanical strength was low. The test material No. In Nos. 12 to 16, the reduction ratio of cold rolling or the conditions of warm tension are out of the conditions of the present invention, so that any of them has a large recrystallized grain size or an unrecrystallized structure, and has mechanical strength and formability (elongation). ) Resulted in inferior results.

[0044]

As described above, according to the present invention, 3.0 is obtained.
For Al-Mg alloy containing relatively small amount of Mg of up to 5.0%, it is possible to manufacture a sheet material having a fine recrystallized grain structure and excellent strength and formability without undergoing recrystallization annealing. Becomes

The aluminum alloy sheet obtained by the present invention has an extremely fine structure having an average crystal grain size of 3 μm or less, and is excellent in strength and formability. It can be expanded and has high industrial value.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C22F 1/00 630 C22F 1/00 630K 685 685Z 685A 691 691B 694 694A (71) Applicant 000004743 Nippon Light Metal Co., Ltd. Shinagawa, Tokyo Furukawa Electric Co., Ltd. 2-6-1 Marunouchi, Chiyoda-ku, Tokyo (71) Applicant 000176707 Mitsubishi Aluminum Co., Ltd. 2-3-3 Shiba, Minato-ku, Tokyo No. 3 (72) Inventor Kazunori Kobayashi 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture Inside Kobe Steel, Ltd.

Claims (5)

[Claims] 1. An aluminum alloy sheet containing Mg: 3.0 to 5.0% (mass%, the same applies hereinafter) and the balance of Al and impurities is cold-rolled at a rolling reduction of 70% or more. The matrix of the aluminum alloy plate is made to have an unrecrystallized structure, and then, at a temperature of 200 to 300 ° C., 1 × 10
An aluminum alloy sheet having an average crystal grain size of 3 μm or less is obtained by dynamically recrystallizing the unrecrystallized structure by pulling at a strain rate of ^-4 / sec or more and a tensile amount of 10% or more. A method for producing a high-strength, high-formability aluminum alloy sheet. 2. The method according to claim 1, wherein the aluminum alloy plate further comprises M
n: 0.05 to 0.5%, Cr: 0.05 to 0.2%,
2. The method for producing a high-strength, high-formability aluminum alloy sheet according to claim 1, wherein one or more of Zr: 0.05 to 0.2% is contained. 3. The method according to claim 2, wherein the aluminum alloy plate further comprises
The method for producing a high-strength and high-formability aluminum alloy sheet according to claim 1 or 2, wherein one or two of i: 0.001 to 0.1% and B: 1 to 300 ppm are contained. . 4. An aluminum alloy sheet produced by the method according to claim 1, having an average crystal grain size of 3 μm or less, a proof stress of 250 MPa or more, and an elongation of 11% or more. A high-strength, high-formability aluminum alloy sheet characterized by the above-mentioned. 5. An aluminum alloy sheet produced by the method according to claim 1, having an average crystal grain size of 3 μm or less, a proof stress of 260 MPa or more, and an elongation of 13% or more. A high-strength, high-formability aluminum alloy sheet characterized by the above-mentioned.