JP2000212673A - Aluminum alloy sheet for aircraft stringer excellent in stress corrosion cracking resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an aluminum alloy sheet for an aircraft stringer in which the average thickness of crystal grains after a stringer stock is subjected to step cold rolling, preheating treatment and solution treatment is <=40 μm even in the part high in a step cold rolling working degree, also aspect ratio is >=4 over the whole length and having excellent stress corrosion cracking resistance of >=250 MPa threshold stress, and to provide a method for producing the same. SOLUTION: This invention is an aluminum alloy sheet having a compsn. contg. 5.1 to 8.4% Zn, 1.8 to 3.0% Mg and 1.2 to 2.6% Cu, moreover contg. one or >= two kinds among <=0.35% Cr, <=0.35% Mn and <=0.25% Zr, and the balance Al with impurities, in which the average thickness of crystal grains is <=25 μm, and aspect ratio is >=4. Even in the case the alloy sheet is subjected to cold rolling at partially different working degrees in the range of <=90% working degrees, is subjected to preheating treatment at 350 to 400 deg.C and is thereafter subjected to solution treatment, the average thickness of the crystal grains is <=25 μm in the case of <30% working degree and <=40 μm in the case of 30 to 90% working degree, and the aspect ratio is maintained to >=4 in both cases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy sheet for aircraft stringers having excellent resistance to stress corrosion cracking and a method for producing the same.

[0002]

2. Description of the Related Art A stringer of an aircraft is a reinforcing material made of a 7000 series aluminum alloy material having a hat-shaped, Z-shaped or J-shaped cross-section, which is attached in the longitudinal direction and the circumferential direction inside the fuselage of the aircraft. Conventionally, many proposals have been made on the material and manufacturing method of this aircraft stringer material (Japanese Patent No. 1405136, 13).
37646-1337649, 1339927, etc.) and typical production steps are as follows.

[0003] An ingot of JIS A7075 alloy is used for about 45 minutes.
After homogenizing at 0 ° C. for about 16 hours, hot rolling is performed at a temperature of about 400 ° C. to obtain a plate having a thickness of about 6 mm,
After the intermediate annealing at 0 ° C. for about 1 hour, the furnace is cooled, and further cold-rolled to a thickness of 3 to 4 mm, and a temperature of 320 to 500 ° C. at an average heating rate exceeding 11 ° C./min. After heating for about 1 hour to soften by holding for about 1 hour, it is cooled.
Reheat to a temperature of 200 ° C and a reheat temperature of 200 ° C or more and 350 ° C.
When the temperature is lower than 30 ° C., the stringer is cooled by air cooling or at an average cooling rate of 30 ° C./hour or less, and when the reheating temperature is 350 to 500 ° C., the stringer is cooled at an average cooling rate of 30 ° C./hour or less. Manufacture materials.

Then, as shown in FIG. 1, for example, as shown in FIG. 1, the rolling degree of the stringer material is changed in the longitudinal direction, and a part A having a degree of working zero, a part B having a relatively low degree of working, and a part having an intermediate degree of working are formed. C, stepwise cold rolling at a working ratio of 0 to 90% for working into a form having a high working degree portion D, etc., and then a solution treatment is performed to obtain a stringer material. Molded into a cross section such as T6
Stringer by refining.

The stringer manufactured by the above process has an average crystal grain size of 25 μm or less in the raw material before the stepped cold working, and is subjected to stepped cold rolling at a working ratio of 0 to 90%. After performing the solution treatment, if the working degree is less than 30%, the working degree is 25 μm or less, and the working degree is 30 to 90%.
In the range, the average crystal grain size of 40 μm or less is maintained, so that rough surface and cracking do not occur during section roll forming, and excellent mechanical properties, elongation, fracture toughness, chemical milling properties, fatigue strength, etc. are obtained. Can be

However, JI used in T6 tempering
7000 series aluminum alloy materials such as SA7075 alloy tend to have lower stress corrosion cracking resistance than T7 temper, and even if it is judged in the laboratory that they have sufficient stress corrosion cracking resistance, If used in an environment that is harsher than expected, problems may occur. Therefore, it is required to further improve the stress corrosion cracking resistance of stringer materials. In the 7000 series aluminum alloy, as shown in FIG. 2, the relationship between the aspect ratio of crystal grains (crystal grain length ÷ crystal grain thickness) and stress corrosion cracking has been clarified. It is known that a material having a large aspect ratio is preferable in providing the stress corrosion cracking resistance because the threshold stress of the stress corrosion cracking increases.

[0007] As a result of examining the aspect ratio of the stringer material manufactured by the above-mentioned conventional manufacturing process, it was found that the aspect ratio was 2.1 to 4.2 after the stepped cold rolling reduction of 0 to 90%. The minimum value of the threshold stress for stress corrosion cracking is about 150 MPa, and there is room for further improvement. A proposal has been made to increase the aspect ratio by performing a preheating treatment step between the stepped cold rolling step and the solution treatment step to improve the effective corrosion cracking resistance. No. 241811), after performing stepwise cold rolling of 0 to 90%, preheating at 350 to 375 ° C. for 1 to 2 hours, and examining the crystal grains of the solution-treated one. Is 25 μm or less when the degree of processing is less than 30%,
Although the workability was as small as 40 μm or less in the range of 30 to 90%, the aspect ratio was in the range of 2.4 to 15.6, and no improvement in the aspect ratio was observed depending on the workability.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems in aluminum alloy sheets for aircraft stringers and to obtain an aluminum alloy sheet with further enhanced resistance to stress corrosion cracking. The purpose of this study was to review the alloying components of the alloys, their combinations, and the manufacturing process of the stringer material, and to conduct various experiments and studies on the relationship between these and the aspect ratio. An object of the present invention is to provide an aluminum alloy plate for an aircraft stringer having an improved aspect ratio after processing and having excellent stress corrosion cracking resistance, and a method for producing the same.

[0009]

According to the first aspect of the present invention, there is provided an aluminum alloy sheet for an aircraft stringer having excellent stress corrosion cracking resistance according to the present invention.
n: 5.1 to 8.4%, Mg: 1.8 to 3.0%, Cu: 1.2 to 2.6%
And further contains one or more of Cr: 0.35% or less, Mn: 0.35% or less, Zr: 0.25% or less, the balance being Al and impurities, and the average thickness of crystal grains is 25 μm. Hereinafter, an aluminum alloy plate having an aspect ratio of 4 or more and a workability of 90%
% Cold rolling of a different degree of work within a range of not more than 30%, and then a solution treatment after a preheating treatment at a temperature of 350 to 400 ° C. , An average thickness of 25 μm or less and an aspect ratio of 4 or more are maintained, and when the workability is in the range of 30 to 90%, an average thickness of crystal grains of 40 μm or less and an aspect ratio of 4 or more are maintained.

An aluminum alloy plate for an aircraft stringer according to a second aspect is characterized in that the aluminum alloy according to the first aspect further contains Ti: 0.2% or less and B: 0.001% or less.

According to a third aspect of the present invention, there is provided a method for producing an aluminum alloy sheet for an aircraft stringer having excellent resistance to stress corrosion cracking, wherein the aluminum alloy according to the first or second aspect is homogenized, hot-rolled and treated in a conventional manner. After cold rolling,
Perform softening treatment at a temperature of 200 to 350 ° C., 5 to 40%
Cold-rolled to a predetermined thickness with a working degree of
It is characterized by heating to a temperature range of 0 to 500 ° C. at an average heating rate exceeding 11 ° C./min and softening by cooling at an average cooling rate of 30 ° C./hour or less.

A method for producing an aluminum alloy sheet for an aircraft stringer according to a fourth aspect of the present invention is a method for homogenizing, hot rolling and cold rolling the aluminum alloy according to the first or second aspect according to a conventional method. A softening treatment is performed at a temperature of 350 ° C., and cold-rolled at a working degree of 5 to 40% to a predetermined thickness.
After softening by heating at an average heating rate exceeding 1 ° C./min, cooling at an average cooling rate exceeding 30 ° C./hour, reheating to a temperature of 200 ° C. or more and less than 350 ° C., air cooling or 30 ° C. Cooling at an average cooling rate of not more than / hour.

According to a fifth aspect of the present invention, there is provided a method for manufacturing an aluminum alloy sheet for an aircraft stringer, comprising the steps of homogenizing, hot rolling and cold rolling the aluminum alloy according to the first or second aspect according to a conventional method. 200-350 ° C
Softening at a temperature of 5%, cold rolling at a working ratio of 5 to 40% to a predetermined thickness, and then heating to a temperature range of 320 to 500 ° C at an average temperature rising rate exceeding 11 ° C / min. And cooled at an average cooling rate exceeding 30 ° C./hour, and then reheated to a temperature of 350 to 500 ° C.,
It is characterized by cooling at an average cooling rate of 30 ° C./hour or less.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The significance of alloy components in an aluminum alloy sheet for aircraft stringers according to the present invention and the reasons for limiting the same will be described. Zn is an element that contributes to strength improvement, and its preferred content is in the range of 5.1 to 8.4%. If it is less than 5.1%, the strength after T6 treatment is not sufficient,
If the content exceeds 8.4%, toughness is reduced and stress corrosion cracking is liable to occur.

Mg, like Zn, is an element that functions to improve the strength, and its preferable content is in the range of 1.8 to 3.0%. If it is less than 1.8%, the strength after T6 treatment is low,
%, The cold workability of the softened material deteriorates, and the toughness of the material after T6 treatment decreases.

Cu, like Zn and Mg, is an element that increases the strength of the alloy, and the preferred content is in the range of 1.2 to 2.6%. If it is less than 1.2%, the strength after T6 treatment is low, and 2.
If it exceeds 6%, the toughness after T6 treatment decreases.

[0017] Ti and B effectively act to refine the casting structure and prevent ingot cracking during casting. The preferred content ranges are 0.2% or less and 0.001% or less, respectively. When Ti and B are contained in excess of the upper limits, a huge intermetallic compound is crystallized and impairs workability.

Each of Cr, Mn and Zr is an element which functions effectively for refining crystal grains. The preferred contents are Cr: 0.35% or less, Mn: 0.35% or less, and Zr:
0.25% or less, a more preferable content is Cr: 0.18 to 0.
25%, Mn: 0.10 to 0.30%, and Zr: 0.05 to 0.25%. If the respective upper limits are exceeded, a huge intermetallic compound is crystallized to impair castability and workability.

In the present invention, Be can be added in a range of 0.005% or less to prevent oxidation of the molten metal. If the content of Fe as an impurity exceeds 0.50%, the amount of insoluble compounds in the alloy material increases, and the toughness tends to decrease. Therefore, the content of Fe is preferably regulated to 0.50% or less, preferably 0.30% or less. If the content of Si exceeds 0.40%, the amount of insoluble compounds in the alloy material increases, and the toughness tends to decrease. Therefore, the content of Si is preferably restricted to 0.40% or less, preferably 0.15% or less.

In order to manufacture the aluminum alloy sheet for an aircraft stringer of the present invention, first, an aluminum alloy ingot having the above composition is subjected to a homogenization treatment, hot rolling and cold rolling according to a conventional method. The homogenization treatment is 400 to 490
The heating is preferably performed at a temperature of 2 ° C. for 2 to 48 hours. By homogenizing treatment, elements such as Zn, Mg, and Cu are sufficiently dissolved, and Cr, Mn, and Zr are precipitated as fine intermetallic compounds. . Heating at a low temperature of less than 400 ° C. or short-time heating results in poor hot workability, lowering of stress corrosion cracking resistance and coarsening of crystal grains. High-temperature heating exceeding 490 ° C. may cause eutectic melting.

Hot rolling is preferably started at a temperature of 350 to 470 ° C. If the temperature is lower than 350 ° C., deformation resistance is increased and rolling workability is reduced. If the temperature exceeds 470 ° C., work cracking is caused due to embrittlement. It is easy to occur.

After the hot rolling, a softening treatment is performed if necessary. After the softening treatment is heated and held at a temperature of 300 to 460 ° C,
This is performed by cooling to a temperature of about 260 ° C. at a cooling rate of 30 ° C./hour or less. This softening treatment is particularly important when the degree of work in the next cold rolling step is increased. The working ratio of the cold rolling is desirably 20% or more. If the working ratio is low, the crystal grains of the stringer material to be produced become coarse, which causes deterioration in workability and performance.

In the present invention, after cold rolling, 200 to
A softening treatment is performed at a temperature of 350 ° C., and cold-rolled to a predetermined thickness at a working ratio of 5 to 40%, and then a thickness of 320 to 50%.
The first characteristic in manufacturing is that the material is softened by heating to a temperature range of 0 ° C. at an average heating rate exceeding 11 ° C./min and cooling at an average cooling rate of 30 ° C./hour or less.

The softening treatment after the cold rolling increases the aspect ratio of the stringer material, and prevents abnormal growth of crystal grains when the workability of the stepped cold-rolled material is relatively small, for example, about 20%. If the temperature of the softening treatment is lower than 200 ° C., it is difficult to obtain a sufficient effect for improving the aspect ratio and suppressing abnormal growth of crystal grains.
If the temperature exceeds 350 ° C., the proof stress after the final softening treatment is increased, easily deviating from the O material standard, and cracks are easily generated by taper roll processing (stepped cold rolling) on stringers.

The cold rolling after the softening treatment is performed at a working ratio of 5 to 40%. When the working ratio is less than the lower limit and exceeds the upper limit, the aspect ratio of the stringer material becomes small,
The desired stress corrosion cracking resistance cannot be obtained.

After the completion of the cold rolling, the steel sheet is rapidly heated to a temperature range of 320 to 500 ° C. at an average heating rate exceeding 11 ° C./min.
The softening treatment is performed by cooling at an average cooling rate of 0 ° C./hour or less. A stringer having recrystallized grains having an average crystal grain thickness of 25 μm or less and an aspect ratio of 4 or more by combining this softening treatment step with the softening treatment step after the cold rolling and the cold rolling step. The material is obtained.

If the heating temperature is lower than 320 ° C., softening and recrystallization are not sufficient, so that cracks are liable to occur in the taper roll processing (cold rolling with steps) on the stringer, and if it exceeds 500 ° C., the material may be melted. There is a possibility that abnormal crystal grain growth occurs and recrystallized grains become extremely coarse.

When rapid heating is performed at a heating rate at which the average temperature rise rate exceeds 11 ° C./min, Mg
-The precipitation of the Zn-based compound is small, and the dislocation structure introduced by cold rolling changes to a uniform cell structure by softening by rapid heating. A material having such a structure may be subjected to a weak taper roll process (working degree 5% or more 3
0%) and then a solution treatment after preheating at 350 to 400 ° C., since recrystallization proceeds with a uniform fine cell structure as a nucleus, the average thickness of recrystallized grains And a uniform fine recrystallized structure with an aspect ratio of 4 or more is obtained. The average thickness of the recrystallized grains is 40 μm even when the taper roll processing is performed at a processing degree of 30% or more and the above-mentioned preheating treatment and solution treatment are performed.
In the following, a uniform fine recrystallized structure having an aspect ratio of 4 or more can be obtained.

On the other hand, when the average heating rate is 11 ° C./min or less, the Mg—Zn-based compound precipitates non-uniformly during heating, and the dislocation structure disappears completely or becomes coarse. In addition, a non-uniform cell structure remains. When the material having such a structure is subjected to a weak taper roll process, followed by a preheating process at 350 to 400 ° C., and then a solution treatment, the crystal grains are significantly coarsened, and the crystal grain thickness is increased. Often exceeds 25 μm. When the taper roll processing is performed at a processing degree of 30% or more and the above-mentioned preheating treatment and solution treatment are performed, the average thickness of the recrystallized grains is 40 μm or less, but the crystal grain length is reduced. Therefore, the aspect ratio tends to be less than 4, and the stress corrosion cracking resistance becomes insufficient.

When the cooling rate after the softening treatment by the rapid heating is high, aging hardens due to quenching, and the strength becomes higher than that of a normal annealed material (O material). However, application to a stringer material requiring a high degree of processing has a problem in terms of the degree of processing.

For this reason, in the present invention, after the softening treatment, the steel sheet is cooled at an average cooling rate exceeding 30 ° C./hour and further reheated to a temperature of 200 ° C. or more and less than 350 ° C. to be air-cooled or 30 ° C./hour or less. Cooling at an average cooling rate of 30 ° C./hour after the softening treatment, and then 350-500.
A third manufacturing feature is to re-heat to a temperature of ° C. and cool at an average cooling rate of 30 ° C./hour or less.

That is, in order to prevent burning after reheating, the cooling rate after reheating is reduced,
Even when the cooling rate after the softening treatment by rapid heating is high, rolling at a high degree of working is enabled.

By the combination of the alloy composition and the manufacturing process described above, in the state of the raw material before the stepped cold rolling, the average thickness of the crystal grains in the thickness direction is 25 μm or less, and the aspect ratio of the crystal grains is 4 or more. 0-90% taper roll processing,
When the crystal grains after the preheating treatment and the solution treatment at a temperature of 350 to 400 ° C. have a workability of less than 30%, the average thickness is 25%.
μm or less, aspect ratio 4 or more, and processing degree is 30 ~
In the range of 90%, it is possible to obtain an aluminum alloy sheet for stringers having an average thickness of 40 μm or less, an aspect ratio of 4 or more, a threshold stress of 250 MPa or more, excellent stress corrosion cracking resistance, and good section roll formability. it can.

[0034]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 An aluminum alloy having the composition shown in Table 1 was ingoted by semi-continuous casting, and after homogenizing at 460 ° C. for 16 hours, 400
Hot-rolled to a thickness of 6 mm at a temperature of 400 ° C., cooled to room temperature, and then cold-rolled to a thickness of 3.7 mm.
After a softening treatment at 50 ° C for 1 hour, the furnace was cooled, and the degree of processing was 1
9% cold rolling was performed to a thickness of 3 mm.

The obtained plate was heated at an average heating rate of 1200 ° C.
/ Min. And heated to 450 ° C for 3 minutes.
It cooled at the cooling rate at the time, and was set as the O material. This is processed 20
%, 40%, 60%, and 80%, and those not processed (0% workability) were pre-heated at 375 ° C. for 1 hour, and then heated at 470 ° C. for 40 minutes in a salt bath. A solution treatment was performed and water quenching was performed. After water quenching,
Natural aging was performed at room temperature for 4 days, and artificial aging treatment was performed at 120 ° C. for 24 hours to obtain a T6 tempered material.

With respect to the obtained O material, the tensile strength at room temperature was measured. The average thickness and the aspect ratio of the crystal grains of the T6 tempered material were measured, and the degree of cold work was 80%.
With respect to the above, the tensile strength at room temperature was measured. The measurement results are shown in Tables 2 and 3. As seen in Table 2,
Test material No. In all of Examples 1 to 6, the aspect ratio of the crystal grains is 4 or more at all the working degrees, and the crystal grain thickness is 25 μm or less when the working degree is 0% and 20% (less than 30%), and the working degree is 40%. , 60% and 80%
(30-90%), it was 40 μm or less, and as shown in Table 3, the tensile strength was also excellent.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

Comparative Example 1 An aluminum alloy having the composition shown in Table 4 was formed by semi-continuous casting, and an O material and a T6 tempered material were produced in the same steps as in Example 1. For the obtained O material, the tensile strength at room temperature was measured, and for the T6 tempered material, the average thickness of crystal grains and the aspect ratio were measured. For those having a cold work degree of 80%, the tensile strength at room temperature was measured. The measurement results are shown in Tables 5 and 6.

As shown in Table 5, the test material No. 7 is Mn
Since the amount, the amount of Cr, and the amount of Zr were less than the lower limit values, the crystal grains did not become finer and became crystals close to equiaxed crystals, so that the aspect ratio was small and the thickness of the crystal grains was large. Test material No. In No. 8, since the amounts of Mn, Cr, and Zr exceeded the upper limits, a huge intermetallic compound was crystallized, and a sound ingot could not be produced. Test material No. 9 is Zn content, Mg
Since the amount and the amount of Cu exceeded the upper limit, the ingot was cracked at the time, and the plate could not be manufactured. Test material No. 10
Is less than the lower limit because Zn content, Mg content, and Cu content are less than the lower limit.
6 The temper is inferior in strength.

[0042]

[Table 4]

[0043]

[Table 5]

[0044]

[Table 6]

Comparative Example 2 Test material Nos. Shown in Table 1 were obtained by semi-continuous casting. An aluminum alloy having the same composition as in Example 1 was ingoted, homogenized at 460 ° C. for 16 hours, and hot-rolled at a temperature of 400 ° C. to a thickness of 6 m.
m, a softening treatment was performed at 250 ° C. for 1 hour without cooling, followed by furnace cooling and cold rolling at a workability of 50% to a thickness of 3 mm.

The obtained plate was heated at an average heating rate of 1200 ° C.
/ Min. And heated to 450 ° C for 3 minutes.
It cooled at the cooling rate at the time, and was set as the O material. This is processed 20
%, 40%, 60%, and 80%, and those not processed (0% workability) were pre-heated at 375 ° C. for 1 hour, and then heated at 470 ° C. for 40 minutes in a salt bath. A solution treatment was performed and water quenching was performed.

With respect to the obtained quenched material, the average thickness and aspect ratio of crystal grains were measured. As shown in Table 7, when the degree of work was 20%, abnormal growth of crystal grains occurred, No stringer material was obtained.

[0048]

[Table 7]

Comparative Example 3 The test material No. shown in Table 1 was obtained by semi-continuous casting. An aluminum alloy having the same composition as in Example 1 was ingoted, homogenized at 460 ° C. for 16 hours, and hot-rolled at a temperature of 400 ° C. to a thickness of 6 m.
m, cooled to room temperature, and then cold-rolled to a thickness of 3.
7 mm, and then softened at 250 ° C. for 1 hour, cooled in a furnace, and cold-rolled at a workability of 19% to a thickness of 3 m.
m.

The obtained plate was heated to 450 ° C. at an average temperature rising rate of 50 ° C./hour, held for 3 minutes, and then cooled at a cooling rate of 25 ° C./hour to obtain an O material. This is processed 20%, 4
Cold-rolled at 0%, 60% and 80%, including those not processed (0% workability), after pre-heating at 375 ° C for 1 hour, and then solutioning at 470 ° C for 40 minutes in a salt bath It was treated and water-quenched.

The average thickness of crystal grains and the aspect ratio of the obtained quenched material were measured. As shown in Table 8, the crystal grain thickness was 25 μm or less in all cases. Some were less than 4.

[0052]

[Table 8]

Comparative Example 4 Test material Nos. Shown in Table 1 were obtained by semi-continuous casting. An aluminum alloy having the same composition as in No. 1 was ingoted, homogenized at 460 ° C. for 16 hours, and hot-rolled at a temperature of 400 ° C. to a thickness of 8 m.
m, then cold-rolled to a thickness of 6.0 mm, softened at 250 ° C. for 1 hour, cooled in a furnace, and cold-rolled to a workability of 50% to a thickness of 3 mm. did.

The obtained plate was heated at an average heating rate of 1200 ° C.
/ Min. And heated to 450 ° C for 3 minutes.
It cooled at the cooling rate at the time, and was set as the O material. This is processed 20
%, 40%, 60%, and 80%, and those not processed (0% workability) were pre-heated at 375 ° C. for 1 hour, and then heated at 470 ° C. for 40 minutes in a salt bath. A solution treatment was performed and water quenching was performed.

With respect to the obtained quenched material, the average thickness and the aspect ratio of the crystal grains were measured. As shown in Table 9, the crystal grain thickness was 25 μm or less in all cases. Less than 4 parts.

[0056]

[Table 9]

Comparative Example 5 Test material Nos. Shown in Table 1 were obtained by semi-continuous casting. An aluminum alloy having the same composition as in Example 1 was ingoted, homogenized at 460 ° C. for 16 hours, and hot-rolled at a temperature of 400 ° C. to a thickness of 6 m.
m, then cold-rolled to a thickness of 3.0 mm, softened at 250 ° C. for 1 hour, and then cooled in a furnace. No subsequent cold rolling was performed.

The obtained plate was heated at an average heating rate of 1200 ° C.
/ Min. And heated to 450 ° C for 3 minutes.
It cooled at the cooling rate at the time, and was set as the O material. This is processed 20
%, 40%, 60%, and 80%, and those not processed (0% workability) were pre-heated at 375 ° C. for 1 hour, and then heated at 470 ° C. for 40 minutes in a salt bath. A solution treatment was performed and water quenching was performed.

With respect to the obtained quenched material, the average thickness and aspect ratio of the crystal grains were measured. As shown in Table 10, the crystal grain thickness was 0% and 20%.
(30% or less), 40%, 60% and 80% (30 to 90%) had a value of 40 μm or less, but the aspect ratio was partly less than 4.

[0060]

[Table 10]

Comparative Example 6 Test material Nos. Shown in Table 1 were obtained by semi-continuous casting. An aluminum alloy having the same composition as in Example 1 was ingoted, homogenized at 460 ° C. for 16 hours, and hot-rolled at a temperature of 400 ° C. to a thickness of 6 m.
m, then cold-rolled to a thickness of 3.7 mm, softened at 410 ° C. for 1 hour, cooled in a furnace, and further cooled for 1 hour.
9% cold rolling was performed to a thickness of 3 mm.

The obtained plate was heated at an average heating rate of 1200 ° C.
/ Min. And heated to 450 ° C for 3 minutes.
It cooled at the cooling rate at the time, and was set as the O material. This is processed 20
%, 40%, 60%, and 80%, and those not processed (0% workability) were pre-heated at 375 ° C. for 1 hour, and then heated at 470 ° C. for 40 minutes in a salt bath. A solution treatment was performed and water quenching was performed. After water quenching, natural aging was further performed at room temperature for 4 days, and artificial aging treatment was performed at a temperature of 120 ° C. for 24 hours to obtain a T6 tempered material.

The tensile strength at room temperature of the obtained O material was measured, and the average thickness and aspect ratio of crystal grains of the T6 tempered material were measured. For those having a cold work degree of 80%, the tensile strength at room temperature was measured.

As shown in Table 11, as shown in Table 11, the thickness and aspect ratio of the crystal grains were satisfactory in all the working ratios, but the proof stress of the O material was as large as 165 MPa, which was outside the JIS standard. The result was. In addition, the tensile strength of the T6 tempered material was 570 MPa.

[0065]

[Table 11]

Examples 2 to 3 By semi-continuous casting, test material Nos. An aluminum alloy having the same composition as in Example 1 was ingoted and, as in Example 1,
After a homogenization treatment at 60 ° C. for 16 hours, a hot-rolled sheet is formed at a temperature of 400 ° C. to a thickness of 6 mm. After cooling to room temperature, the sheet is cold-rolled to a thickness of 3.7 mm. After a softening treatment at a temperature for 1 hour, the furnace was cooled and further cooled for 19 hours.
% Cold rolling to a thickness of 3 mm.

Subsequently, an average heating rate of 1200 ° C./min.
After heating to 50 ° C. and holding for 3 minutes, it was cooled at a cooling rate of 50 ° C./hour. The obtained plate material was reheated to a temperature of 280 ° C. and maintained for 1 hour, and then air-cooled to obtain an O material. Also,
The obtained sheet material was reheated to a temperature of 400 ° C. and maintained for 1 hour, and then cooled at a cooling rate of 25 ° C./hour to obtain an O material.

These O materials were processed at a working ratio of 20%, 40%,
Cold-rolled at 60% and 80%, and those that are not processed (deformation 0%) are also subjected to a preheating treatment at 375 ° C for 1 hour, followed by a solution treatment at 470 ° C for 40 minutes in a salt bath. , Water quenched. After water quenching, natural aging was further performed at room temperature for 4 days, and artificial aging treatment was performed at a temperature of 120 ° C. for 24 hours to obtain a T6 tempered material.

The tensile strength at room temperature of the obtained O material was measured, and the average thickness and aspect ratio of crystal grains of the T6 tempered material were measured. For those having a cold work degree of 80%, the tensile strength at room temperature was measured. Table 1 shows the results
2 and Table 13.

[0070]

[Table 12] 《Table Note》 Test material No.16: Test material reheated to 280 ℃ Test material No.17: Test material reheated to 400 ℃

[0071]

[Table 13]

As can be seen from Tables 12 and 13, the test materials No. 16, test material No. No. 17 has satisfactory characteristics with a crystal grain thickness of 25 μm or less and an aspect ratio of 4 or more.

[0073]

According to the present invention, in the state of the raw material before the stepped cold rolling, the average thickness of the crystal grains in the thickness direction is 25 μm or less, and the aspect ratio of the crystal grains is 4 or more. In the cold-rolled, preheated and solution-treated crystal grains,
When the working degree of the stepped cold rolling is less than 30%, the average thickness of the crystal grains is maintained at 25 μm or less and the aspect ratio is 4 or more. When the working degree is in the range of 30 to 90%, the average thickness of the crystal grains is 40 μm or less. Maintain ratio 4 or more, threshold stress is 250M
Provided is an aluminum alloy plate for a stringer having excellent stress corrosion cracking resistance of not less than Pa and good section roll formability, and a method for producing the same.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a processing state of a stringer material.

FIG. 2 is a diagram showing the relationship between the aspect ratio of crystal grains of a 7000 series aluminum alloy material and stress corrosion cracking resistance.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 686 C22F 1/00 686B 691 691B 691A 692 692A 694 694A (72) Inventor Keiichi Sakai Port of Tokyo 5-11-3 Shimbashi, Ward Sumitomo Light Metal Industries, Ltd. (72) Inventor Minami Ichiro 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industries, Ltd. (72) Inventor Hidetoshi Uchida Tokyo 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industries Co., Ltd.

Claims (5)

[Claims] Claims: 1. A composition comprising: Zn: 5.1 to 8.4% (% by weight, hereinafter the same), Mg: 1.8 to 3.0%, Cu: 1.2 to 2.6%,
Cr: 0.35% or less (excluding 0%, the same applies hereinafter),
Mn: 0.35% or less, Zr: 0.25% or less of one or more of the following, the balance consisting of Al and impurities,
An aluminum alloy plate having an average thickness of crystal grains of 25 μm or less and an aspect ratio (average crystal grain length / average crystal grain thickness) of 4 or more;
Perform cold rolling with different working degrees partially in the following range,
Thereafter, even if solution treatment after preheating at a temperature of 350 to 400 ° C. is performed, if the degree of work is less than 30%, the average thickness of crystal grains is 25 μm or less and the aspect ratio is 4 or more. An aluminum alloy sheet for an aircraft stringer having excellent stress corrosion cracking resistance, wherein the average grain thickness is maintained at 40 μm or less and the aspect ratio is at least 4 in the range of 30 to 90%. 2. An aluminum alloy plate further comprising: Ti: 0.2
% Or less, B: 0.001% or less, The aluminum alloy sheet for aircraft stringers excellent in stress corrosion cracking resistance according to claim 1. 3. After homogenizing, hot rolling and cold rolling the aluminum alloy according to claim 1 or 2 in a conventional manner, the aluminum alloy is softened at a temperature of 200 to 350 ° C.
Cold-rolled at a working ratio of 加工 40% to a predetermined thickness, and then heated to a temperature range of 320 to 500 ° C. at an average heating rate exceeding 11 ° C./min, and an average cooling rate of 30 ° C./hour or less A method for producing an aluminum alloy sheet for an aircraft stringer having excellent resistance to stress corrosion cracking, characterized by softening by cooling at a temperature. 4. After homogenizing, hot rolling and cold rolling the aluminum alloy according to claim 1 or 2, the aluminum alloy is softened at a temperature of 200 to 350 ° C.
Cold-rolled at a working ratio of ４０40% to a predetermined thickness, then softened by heating to a temperature range of 320 to 500 ° C. at an average heating rate exceeding 11 ° C./min. After cooling at an average cooling rate exceeding that, it is further reheated to a temperature of 200 ° C or more and less than 350 ° C, and air-cooled or 30 ° C.
A method for producing an aluminum alloy plate for an aircraft stringer having excellent stress corrosion cracking resistance, wherein the aluminum alloy sheet is cooled at an average cooling rate of not more than / h. 5. The aluminum alloy according to claim 1, which is subjected to a homogenization treatment, a hot rolling and a cold rolling according to a conventional method, and then subjected to a softening treatment at a temperature of 200 to 350 ° C.
Cold-rolled at a working ratio of ４０40% to a predetermined thickness, then softened by heating to a temperature range of 320 to 500 ° C. at an average heating rate exceeding 11 ° C./min. After cooling at an average cooling rate exceeding
A method for producing an aluminum alloy sheet for an aircraft stringer having excellent stress corrosion cracking resistance, comprising reheating to a temperature of 00 ° C and cooling at an average cooling rate of 30 ° C / hour or less.