JP2003027172A - Aluminum-alloy sheet for structural purpose having fine structure, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al-Mg alloy sheet for structural purposes having fine structure and capable of attaining high strength without deteriorating formability, and its manufacturing method. SOLUTION: The aluminum-alloy sheet has a composition consisting of 4-7% Mg, 0.4-1.0% Mn, 0.05-0.25% Zr, 0.5-2% Zn and the balance Al with inevitable impurities and further containing Cu. In this aluminum-alloy sheet, average grain size in a final heat treated state is <=7 μm and grain boundaries of 3-10 deg. grain misorientation are contained in amounts of >=25% in a sheet surface. This aluminum-alloy sheet can be manufactured by subjecting an ingot to homogenizing treatment and hot working, carrying out rolling of >=4 passes, after the temperature of the resultant alloy plate after the completion of hot working reaches a value in the neighborhood of room temperature, while controlling mill-roll temperature to >=60 deg.C and holding alloy-sheet temperature at 420-200 deg.C to apply >=70% draft to prescribed sheet thickness, and then applying final heat treatment at 350-420 deg.C for >=30 s.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural aluminum alloy plate suitable as a member for vehicles such as automobiles, a member for ships, etc., in particular, high strength can be obtained without lowering moldability, and the member can be made thinner. The present invention relates to a structural aluminum alloy plate having a microstructure that enables the above and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, a structural aluminum alloy is M
g, Zn as main alloying components, and Mn, C
u, Zr, etc. are combined, and the aluminum alloy sheet material is, for example, worked at a workability of 20 to 60 without being subjected to intermediate heat treatment or hot rolling after homogenizing the ingot. % Cold rolling, and then heat treatment at a temperature of 350 to 480 ° C. as an annealing treatment.

However, since the strength of the conventional structural aluminum alloy plate is limited, there is a limit to the requirement for thinning in application to transportation equipment members for vehicles, ships, etc. Currently, it is not possible to achieve thinning.

It is known that it is desirable to make the crystal grain size fine in order to improve the strength of the metal material. A Hall-Petch relationship is established between the strength of the metal material and the crystal grain size, and there is a positive correlation between the refinement of the crystal grains and the improvement of the strength. It is also known that the strengthening method by refining crystal grains can improve the strength without significantly impairing the elongation of the material, unlike other strengthening methods. Conventionally, as a method for refining crystal grains, it has been attempted to accumulate strain by applying strong working and then recrystallize by performing an appropriate heat treatment, but structural aluminum such as Al-Mg system is used. Even if this method is applied to an alloy, it is difficult to refine the crystal grains to a certain extent.

In order to suppress the generation of coarse recrystallized grains and obtain an aluminum alloy sheet having excellent surface properties without grain streaks or ridging marks, the rolling temperature in hot rough rolling and hot finish rolling, rolling A method of controlling speed, rolling roll temperature, etc. (Japanese Patent Laid-Open No. 2000-119782) has been proposed.
Although the generation of coarse particles of m or more can be suppressed, only the crystal grain size of the final plate is about 20 to 40 μm.

47 using a 5182 aluminum alloy
Material that has undergone 98.3% strong working at a temperature of 3K or less
By annealing at 73K, an ultra-fine grain structure with an average grain size of about 600 nm is formed, and a tensile strength of 380 MPa and 20
% Growth is also reported (Journal of Japan Institute of Metals, No. 6)
3 No. 2 (1999) pp. 243-251), in this case, ultrafine particles having a crystal grain size of 1 μm or less are formed in 70 to 80% of the material, and at most about 90%. However, there is no formation of ultra-fine grains in the remaining region, and 57
When it is annealed at a temperature of 3K or higher, it becomes a normal recrystallization structure,
There are many problems in practical use because high-temperature treatment for stably obtaining high ductility cannot be performed. In order to stably obtain a high-strength and high-ductility material having a fine structure, it is necessary to form a thermally stable fine structure that does not coarsen even when heat-treated at a relatively high temperature.

On the other hand, first, the inventors have controlled the material temperature and the rolling roll temperature in the warm rolling, and at the same time, misorientation of adjacent crystal grains (Note:
As shown in FIG. 1, the orientation difference between adjacent crystal grains indicates how much an angle difference (orientation difference θ) is with respect to the rotation axis common to the crystal grains A and B). The idea was introduced, and an Al-Zn-Mg alloy plate for high strength and high corrosion resistance structure and a method for producing the same (Japanese Patent Application No. 2001-039464) were proposed.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides the above-mentioned method for the Al—Zn—Mg based alloys by the inventors in order to obtain an Al—Mg based alloy plate having a thermally stable microstructure. It was made as a result of further tests and examinations regarding the structure, and the purpose thereof is to provide stable structure properties even after high-temperature treatment, and to achieve high strength without impairing ductility. It is intended to provide an Al-Mg alloy plate for use and a method for manufacturing the same.

[0009]

A structural aluminum alloy having a fine structure according to claim 1 of the present invention for achieving the above object comprises Mg: 4 to 7% and Mn: 0.4 to.
1.0%, Zr: 0.05 to 0.25%, Zn: 0.5
An aluminum alloy plate containing 2% by weight and the balance Al and unavoidable impurities, having an average crystal grain size of 7 μm or less in the final heat treatment state, and a crystal grain orientation difference of 3 to 10 ° on the plate surface. It is characterized by containing 25% or more of grain boundaries.

A structural aluminum alloy plate having a fine structure according to claim 2 is characterized in that, in claim 1, the aluminum alloy plate further contains Cu: 0.1 to 0.5%.

A method of manufacturing a structural aluminum alloy sheet having a microstructure according to claim 3 of the present invention is directed to Mg:
4-7%, Mn: 0.4-1.0%, Zr: 0.05-
Aluminum alloy containing 0.25% and Zn: 0.5 to 2% and the balance Al and unavoidable impurities, or an aluminum alloy further containing Cu: 0.1 to 0.5%. After the homogenizing treatment of the ingot, the hot rolling is performed, and after the temperature of the alloy sheet after the hot working is close to room temperature, the temperature of the rolling roll is set to 60 without performing the intermediate heat treatment or the intermediate heat treatment. After controlling the temperature to ℃ or more and maintaining the temperature of the alloy plate at a temperature of 420 to 200 ° C., rolling is performed for 4 passes or more to give a working ratio of 70% or more to a predetermined plate thickness, and then 350 to 420 ° C. The final heat treatment is performed for 30 seconds or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to an Al-Mg based alloy sheet which is finally heat-treated for recovering ductility and used. First, the meanings of the components contained in the present invention and the reasons for limitation are explained. Then, Mg is a main element that improves strength, and the preferable content range is 4 to 7%. If it is less than 4%, strength equivalent to that of conventional alloys cannot be obtained, and fine graining is also hindered. If it is contained in excess of 7%, hot workability is deteriorated and it becomes difficult to manufacture a plate material.

Mn is an element that functions to form a thermally stable structure. That is, 420 to 2 described later
In warm rolling at 00 ° C, the solid solution Mn is finely precipitated, which has the effect of suppressing the movement of dislocations introduced by working, and further, by repeatedly working, the formation of immobile dislocations results. Becomes a thermally stable organization. The preferable content of Mn is in the range of 0.4 to 1.0%, and
If it is less than 4%, the above effect is not sufficient and it is difficult to form a thermally stable structure. If it exceeds 1.0%, the workability deteriorates and problems such as rolling cracks and poor formability occur. The more preferable content range of Mn is 0.5 to 0.8%.

Zr is an element necessary for forming a thermally stable structure together with Mn, and like Mn, Zr is finely precipitated during the warm rolling at 420 to 200 ° C., which will be described later, It has the effect of suppressing the movement of dislocations introduced by processing, and by further processing it, immobile dislocations are formed and consequently a thermally stable structure is formed. Zr
The preferable content range of is 0.05 to 0.25%,
If it is less than 0.05%, this effect is small, and if it exceeds 0.25%, the contribution to the formation of a thermally stable structure does not change, and rather, a Zr-based giant crystallized product is easily formed during casting. Not preferable. The more preferable content of Zr is 0.10.
Is in the range of 0.20%.

Like Mn and Zr, Zn functions to form a thermally stable structure. That is, 42 described later
It has an action of forming a Mg—Zn-based compound during warm working at 0 to 200 ° C. and suppressing the movement of dislocations introduced by working. Also, it precipitates during the final heat treatment to suppress crystal grain growth. The preferable content of Zn is in the range of 0.5 to 2%, and if it is less than 0.5%, the effect is not sufficient.
If it exceeds 2%, the hot workability deteriorates and problems such as cracking occur.

Cu functions to more reliably form a thermally stable microstructure. That is, 420 to be described later
Al-Cu-Mg-based compound finely precipitates during warm working at 200 ° C to suppress movement of dislocations introduced by working, and, like Zn, precipitates during final heat treatment. Suppresses grain growth. The preferable content of Cu is in the range of 0.1 to 0.5%, and if it is less than 0.1%, this effect is small, and if it exceeds 0.5%, the hot workability is deteriorated and problems such as cracking occur. Occurs.

In the present invention, the Al--Mg system (500
(0 series) Cr, Ti, B, F in an amount enough to be contained in the alloy
Although containing e and Si does not affect the effect of the present invention, it is preferable to limit the content to 0.5% or less from the viewpoint of the formability of the final plate.

The aluminum alloy plate according to the present invention has an average grain size of 7 μm or less, and a structure containing small-angle grain boundaries having a grain orientation difference (misorientation) of 3 to 10 ° in the plate surface in an amount of 25% or more of all grain boundaries. The aluminum alloy plate is characterized by having a property, and by virtue of this structure property, an aluminum alloy plate having a fine structure having practically sufficient formability and high strength can be obtained.

A fine structure containing small-angle grain boundaries having a grain size difference of 3 to 10 ° in an amount of 25% or more of all grain boundaries and having an average grain size of 7 μm or less is thermally stable and has a grain size difference. 3-1
The structure containing 25% or more of the small-angle grain boundaries of 0 ° of all the grain boundaries makes the average grain size fine. When the average crystal grain size exceeds 7 μm, the degree of improvement in material strength decreases.

The crystal grain orientation difference is measured by an automatic measuring device which is a combination of a scanning electron microscope (SEM) and a CCD camera. Specifically, an electron beam is incident on the crystal surface that appears on the sample surface, and the Kikuchi pattern is captured by a CCD camera,
The crystal plane is specified by a computer. For the orientation difference between adjacent crystal grains, if the crystal planes are known, the common rotation axis can be identified, and the angle difference (= orientation difference = misorientation) with respect to the rotation axis is found. . Lower limit of crystal grain orientation difference 3 °
Is defined in consideration of the resolution and error of the measuring device.

Hereinafter, the average crystal grain size is 7 μm or less, and the crystal grain orientation difference (misorientation) is 3 to 3 on the plate surface.
Explaining a method for producing an aluminum alloy plate that stably obtains a fine structure containing small-angle grain boundaries of 10 ° in an amount of 25% or more of all crystal grain boundaries, an aluminum alloy having the above composition is produced by, for example, ordinary DC casting. The obtained ingot is subjected to a homogenization treatment and hot working according to a conventional method.

After the temperature of the alloy sheet after the hot working is close to room temperature, the temperature of the rolling roll is controlled to 60 ° C. or higher and the temperature of the alloy sheet is controlled to 420 ° C. or less without intermediate heat treatment. ~ 200 ° C, more preferably 4
Repeated warm rolling is performed while maintaining the temperature of 00 to 250 ° C.

A thermally stable microstructure is formed by the above steps. When the temperature of the rolling roll is lower than 60 ° C., the processing is concentrated only on the surface of the material and the uniform processing inside the material is not performed, resulting in coarsening of crystal grains in the final heat treatment.

When the temperature of the plate material exceeds 420 ° C., the recovery phenomenon of the structure occurs preferentially, the formation of stationary dislocations is hindered, and as a result, a thermally stable fine structure cannot be formed. When the temperature of the plate material is less than 200 ° C., Mn,
The precipitation of Zr is delayed, and the effect of suppressing the movement of dislocations introduced by working is weakened. As a result, the formation of stationary dislocations is hindered, and coarsening of crystal grains occurs in the final heat treatment.

Repeated rolling is preferably carried out for 4 passes or more. If the number of passes is 3 passes or less, the central portion of the plate thickness is not sufficiently processed and the formation of stationary dislocations is hindered, resulting in a thermally stable fine grain. Since the structure cannot be formed, coarse crystal grains may be formed in the central portion after the final heat treatment.

The workability in the above temperature range is preferably 70% or more. When the workability is less than 70%, the formation of stationary dislocations is insufficient, and a structure in which coarse crystal grains are partially mixed after the final heat treatment. It is easy to become.

After rolling, in order to recover ductility, 35
A final heat treatment is applied at a temperature of 0 to 420 ° C. Conventional Al-
350 ° C for Mg-based hard aluminum alloy plate
When heated to a temperature of about 300 ° C., recrystallization occurs and the ductility is improved but the strength is significantly reduced.
Since the microstructure of the alloy-based alloy sheet is thermally stable, the microstructure is maintained even when heated to a temperature of 350 ° C or higher, the ductility is restored, practically sufficient formability is obtained, and high strength is achieved. it can. At a temperature above 420 ° C., coarse crystal grains are liable to be partially generated, which is not preferable.

[0028]

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

Example 1 An aluminum alloy having the composition shown in Table 1 was cast by a DC casting method, a slice having a thickness of 30 mm was prepared from the obtained slab, and a homogenizing treatment was performed at a temperature of 480 ° C. for 12 hours. It was In Table 1, alloys A and B are invention alloys,
Alloy S is a comparative alloy of 5083 standard composition.

Then, the slices are heated to 480 ° C.,
After hot rolling to a thickness of 30 mm to 8 mm, and after the material temperature has dropped to near room temperature, intermediate heat treatment for 60 s at 450 ° C. is performed in a salt bath furnace, and then warm rolling and final heat treatment according to the conditions shown in Table 2. I went. Rolling was performed by reheating after each pass, and the reheating temperature after each pass was the upper limit temperature of the rolling temperature range.

[0031]

[Table 1]

[0032]

[Table 2]

With respect to each test material after the final heat treatment, the crystal grain orientation difference, the average crystal grain size and the tensile property were evaluated. The evaluation results are shown in Table 3. In addition, the crystal grain orientation difference is SEM manufactured by Hitachi, Ltd. and EBSD (Electronic manufactured by Oxford).
n backscatterdiffraction)
Using a device, the ratio of small-angle grain boundaries showing a tilt angle of 3 to 10 ° was determined from a histogram showing a crystal grain orientation difference (misorientation) distribution.

The average crystal grain size is obtained by a sectioning method from a polarized structure photograph by an optical microscope or a transmission electron microscope photograph, and tensile properties are obtained by taking a test piece in parallel with the rolling direction.
It was determined using an Instron type tensile tester with the gauge length set to 10 mm.

[0035]

[Table 3]

As can be seen in Table 3, the test material Nos. Nos. 1 to 7 each have a high proportion of small-angle grain boundaries, a fine structure with an average crystal grain size of 7 μm or less, a tensile strength of more than 350 MPa, and an elongation of 15% or more showing high strength and high ductility. It was

Comparative Example 1 From a slab having the composition shown in Table 1 obtained in Example 1, a thickness of 3 was obtained.
0 mm slices were prepared and homogenized at 480 ° C. for 12 h.

Then, as in the first embodiment, 48 slices are prepared.
After heating to 0 ° C and hot rolling to a thickness of 30 mm to 8 mm, after the material temperature has dropped to around room temperature, 4 in a salt bath furnace
Intermediate heat treatment was performed at 50 ° C. for 60 s, and then warm rolling and final heat treatment were performed according to the conditions shown in Table 4. Rolling was performed by reheating after each pass, and the reheating temperature after each pass was the upper limit temperature of the rolling temperature range.

[0039]

[Table 4]

With respect to each test material after the final heat treatment, the crystal grain orientation difference, the average crystal grain diameter and the tensile property were evaluated by the same method as in Example 1. The evaluation results are shown in Table 5.

[0041]

[Table 5] << Table Note >> Average grain size Mixed grain: Microstructure in which some coarse grain is mixed

As shown in Table 5, the test material No. 8-9
Since the temperature of the rolling roll was low, the structure after the final heat treatment became a coarse grain structure and the strength was low. Test material N
o. In No. 10, since the rolling start temperature was high, the recovery phenomenon was prioritized and a fine grain structure could not be obtained, resulting in low strength.
Test material No. In No. 11, since the rolling temperature was low, precipitation of Mn and Zr was delayed, and as a result, a fine grain structure was not obtained and the strength was low.

Test material No. 12, rolling degree is 70%
Therefore, the formation of immobile dislocations was not sufficient, and a coarse morphology was present in the microstructure, resulting in low strength. Test material N
o. Since No. 13 had a high final heat treatment temperature, it had a structure morphology in which coarse grains were mixed and the strength was low. Test material N
o. Since No. 14 had a small number of passes, it had a structure in which coarse grains were mixed and the strength was low. Test material No. 1
No. 5 was a conventional 5083 alloy, and no fine crystal structure was obtained.

Example 2 and Comparative Example 2 An aluminum alloy having the composition shown in Table 6 was agglomerated by the DC casting method, a slice having a thickness of 30 mm was prepared from the obtained slab, and the slice was homogenized at a temperature of 480 ° C. for 12 hours. The chemical treatment was performed.

Then, the slices are heated to 480 ° C.,
After performing hot rolling from a thickness of 30 mm to 8 mm and lowering the material temperature to near room temperature, an intermediate heat treatment was performed at 450 ° C. for 60 s in a salt bath furnace, and then the test material Nos. Warm rolling and final heat treatment according to the same conditions as 1
With respect to each test material after the final heat treatment, the crystal grain orientation difference, the average crystal grain size and the tensile property were evaluated by the same method as in Example 1. The evaluation results are shown in Table 7.

[0046]

[Table 6]

[0047]

[Table 7] << Table Note >> Test material No. 25: 5083 alloy soft plate manufactured on a mass production scale

As shown in Table 7, test material N according to the present invention
o. All of 16 to 19 have a high ratio of small-angle grain boundaries, a fine structure with an average crystal grain size of 7 μm or less, a tensile strength of more than 350 MPa, and an elongation of 15% or more, showing high strength and high ductility. It was

On the other hand, the test material No. 20 is Mg,
The content of Mn is small, and the test material No. 21 and 22 are Zr
Of the test material No. 23 is Zr, Zn
The content was low, and no fine grain structure was obtained in either case, resulting in low strength. Test material No. 24 is Mn and Z
Since the content of n was large, the hot rolling property was deteriorated and cracks were generated during the rolling, so that the rolling thereafter could not be performed. Test material No. No. 25 is a conventional 5083 alloy soft plate, which does not have a fine crystal structure and has low strength.

[0050]

EFFECTS OF THE INVENTION According to the present invention, it is possible to achieve a high strength without deteriorating the moldability by providing a stable texture even when subjected to a high temperature treatment. Provided is a structural Al—Mg alloy plate having a fine structure which is suitably used as a member or the like and enables the member to be thin, and a method for producing the same.

[Brief description of drawings]

FIG. 1 is a diagram showing the orientation of crystal grains.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 C22F 1/00 630K 631 631A 683 683 691 691B 694 694A 694B (71) Applicant 000004743 Nippon Light Metal Co., Ltd. Company 2-20, Higashi-Shinagawa, Shinagawa-ku, Tokyo (71) Applicant 000005290 Furukawa Electric Co., Ltd. 2-6-1, Marunouchi, Chiyoda-ku, Tokyo (71) Applicant 000176707 Mitsubishi Aluminum Co., Ltd. Shiba, Minato-ku, Tokyo 2-3-3 (72) Inventor Hiroki Tanaka 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industries, Ltd. (72) Inventor Hiroki Ezaki 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industry Co., Ltd.

Claims (3)

[Claims] 1. Mg: 4 to 7% (mass%, the same applies hereinafter),
Mn: 0.4 to 1.0%, Zr: 0.05 to 0.25
%, Zn: 0.5 to 2%, an aluminum alloy plate consisting of the balance Al and unavoidable impurities, having an average crystal grain size of 7 μm or less in the final heat treatment state, and a crystal grain orientation difference on the plate surface. Is a structural aluminum alloy plate having a fine structure characterized by containing 25% or more of crystal grain boundaries of 3 to 10 °. 2. The aluminum alloy plate further comprises C
u: 0.1-0.5% is contained, The structural aluminum alloy plate which has a microstructure of Claim 1 characterized by the above-mentioned. 3. Mg: 4 to 7%, Mn: 0.4 to 1.0
%, Zr: 0.05 to 0.25%, Zn: 0.5 to 2%
Containing aluminum and the balance Al and unavoidable impurities, or an aluminum alloy further containing Cu:
After homogenizing an aluminum alloy ingot containing 0.1 to 0.5%, hot working is performed, and an intermediate heat treatment is performed after the temperature of the alloy sheet after the hot working is close to room temperature. The temperature of the rolling roll is controlled to 60 ° C. or higher and the temperature of the alloy sheet is 420 to 200 without performing the heat treatment or the intermediate heat treatment.
Rolling for 4 passes or more while maintaining the temperature of ℃, 70
% To give a predetermined plate thickness and then 350-
A method for producing a structural aluminum alloy plate having a fine structure, which comprises performing a final heat treatment at 420 ° C. for 30 seconds or more.