JPH0734170A - Aluminum alloy material having excellent intergranular corrosion resistance and method for producing the same - Google Patents

Abstract

PURPOSE:To provide an aluminum alloy material free from the generation of intergranular corrosion even if being used in a corrosive environment by subjecting an aluminum alloy material to solution treatment and tempering treatment and precipitating an Mg2Si phase in the matrix. CONSTITUTION:An aluminum alloy is added, e.g., with 0.2 to 1.5% Mg and 0.2 to 1.5% Si as essential components and selectively added with small amounts of Cu, Mn, Cr, Zr, Ti or the like. This is subjected to solution treatment and tempering treatment to precipitate an Mg2Si phase in the matrix and to improve its strength. After the solution treatment, cold working of >3% draft or cold reduction working of >=5% is executed to apply compressive residual stress thereto. After that, tempering treatment is executed. In this aluminum alloy material, the depth from the surface of the alloy to the tip of corrosion is regulated to <=200mum according to an intergranular corrosion test. Thus, the generation of deterioration in its fatigue strength can be prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an aluminum alloy material having excellent intergranular corrosion resistance and a method for producing the same, and more specifically, it is subjected to solution treatment and tempering treatment to form Mg ₂ S in a matrix.
The present invention relates to an aluminum alloy material that provides excellent intergranular corrosion resistance for a 6000 series aluminum alloy that precipitates the i phase, and a method for producing the same.

[0002]

2. Description of the Related Art Mg and Si are contained as main alloying components, and M is contained in a matrix by solution treatment and tempering treatment.
A 6000 series aluminum alloy that precipitates g ₂ Si phase (for example, American Aluminum Association AA6061,6063,606
(6,6351,6082 alloys, etc.) are widely used in various fields as alloys that have appropriate strength and corrosion resistance. However, when intergranular corrosion occurs when a 6000 series aluminum alloy is used in a corrosive environment. There is a problem.

In particular, when the aluminum alloy is applied as a structural member, when the intergranular corrosion progresses, the corroded portion acts as a sharp notch in a use environment where repeated stress is applied, so that the fatigue strength of the alloy increases. Will be reduced. As a method of generally improving the fatigue strength of this alloy, a method of applying compressive stress to the material surface by performing shot peening etc. in the cold after solution treatment and tempering treatment is generally used. It is not effective in preventing corrosion and is not useful for improving fatigue strength in corrosive environments.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Containing Mg as a main alloying component and precipitating a Mg ₂ Si phase in the matrix by solution treatment and tempering treatment 60
It was made in order to solve the above problems in the 00 series aluminum alloy material, and the purpose thereof is an aluminum alloy material excellent in intergranular corrosion resistance in which intergranular corrosion does not occur even when used in a corrosive environment. And a method for manufacturing the same.

[0005]

An aluminum alloy material having excellent intergranular corrosion resistance and a method for producing the same according to the present invention for achieving the above object are obtained by performing solution treatment and tempering treatment, and It is an aluminum alloy material in which a Mg ₂ Si phase is precipitated, and the depth from the surface to the corrosion tip of the aluminum alloy material determined by the grain boundary corrosion test specified in JIS W 1103 is 200 μm or less according to the present invention. In the method for producing an aluminum alloy material in which the solution treatment and the tempering treatment are performed to precipitate the Mg ₂ Si phase in the matrix, a compressive residual stress is applied to the aluminum alloy material after the solution treatment. applying to a first aspect of the manufacturing process configuration of the present invention to tempering treatment, solution heat treatment, subjected to tempering treatment, precipitation of Mg ₂ Si phase in the matrix In the method for producing an aluminum alloy material, the aluminum alloy material is an aluminum alloy plate material, and after the solution treatment, cold rolling is performed at a reduction rate of more than 3% to perform tempering treatment, and solution treatment and tempering treatment. In the method for producing an aluminum alloy material in which the Mg ₂ Si phase is precipitated in the matrix, the aluminum alloy material is an aluminum alloy tube rod material, and cold drawing is performed after the solution treatment at a reduction rate of 5% or more. The tempering treatment is the second and third characteristics of the manufacturing method configuration.

The aluminum alloy to which the present invention is applied is
For example, it contains 0.2 to 1.5% of Mg and 0.2 to 1.5% of Si as main alloying components, and contains a small amount of Cu, Mn, Cr and Z.
r, Ti and other elements are selectively added according to the purpose of use, and Mg is added to the matrix by solution treatment and tempering treatment.
_{2 A} 6000-series aluminum alloy that aims to improve strength by precipitating a Si phase. As the 6000 series aluminum alloy, for example, American Aluminum Association standard AA6061,
AA6063, AA6066, AA6351, AA6082 alloy etc.

Since the 6000 series aluminum alloy material has strength and relatively good general corrosion resistance as described above, it is often used as a structural member. However, intergranular corrosion may occur depending on the corrosive environment. When repeated stress is applied, the corroded portion acts as a sharp notch, which causes deterioration of fatigue strength. In the intergranular corrosion, the Mg ₂ Si phase precipitates at the crystal grain boundaries in the alloy matrix, especially at the high-angle grain boundaries due to solution treatment and tempering treatment, and a potential difference occurs between the Mg ₂ Si phase and the matrix in a corrosive environment Therefore, in order to suppress the occurrence of intergranular corrosion, it is necessary to prevent the Mg ₂ Si phase from precipitating at the crystal grain boundaries during the tempering treatment.

In the present invention, in order to improve the strength of a 6000 series aluminum alloy material, when the solute atoms are precipitated by solution treatment and tempering treatment, a method for preventing the grain boundary precipitation of the Mg ₂ Si phase was intensively studied. As a result, by applying compressive residual stress to the material after the solution treatment and before the tempering treatment, the strain field formed in the alloy structure serves as a nucleation site for the precipitated particles and promotes the precipitation of solute atoms in the crystal grains. Mg ₂ S
This is based on the finding that the grain boundary precipitation of the i phase is prevented.

The method for applying the compressive residual stress is preferably cold rolling in which the reduction ratio exceeds 3% when the aluminum alloy material is a plate material, and when the aluminum alloy material is a tube rod material It is preferable to perform cold drawing at a reduction rate of 5% or more. When the reduction rate of cold rolling is 3% or less and when the reduction rate of cold drawing is less than 5%, the formation of the strain field in the grain boundaries becomes non-uniform, resulting in partial grain Boundary precipitation occurs, and the effect of suppressing grain boundary precipitation tends to be insufficient. In the case of drawing, since tensile stress may remain on the surface of the material when the reduction rate becomes large, the upper limit of the drawing rate is preferably 20% though it depends on the shape and size of the material. The upper limit of the rolling workability is preferably 15%.

Since cold rolling and cold drawing for imparting compressive residual stress are carried out in order to promote precipitation in crystal grains during tempering, solution treatment of alloy material is carried out. However, it must be performed before the tempering process, and there is no effect even after the tempering process. Further, even if it is performed before the solution treatment, there is no effect because the generated strain field disappears due to the recovery of the structure during the solution treatment.

As one of the intergranular corrosion tests of aluminum alloy materials, there is an intergranular corrosion test specified in JIS W 1103 used in the inspection of heat treatment type aluminum alloys for aircraft. Then, regarding the 6000 series aluminum alloy material that has been subjected to the compressive residual stress and tempered as described above, the relationship between the corrosion form and the corrosion depth by the above-described intergranular corrosion test, the corrosion environment, the magnitude of the repeated stress, etc. As a result of examination, if the material has a corrosion depth of 200 μm or less from the material surface when an intergranular corrosion test is performed according to JIS W 1103, it becomes a notch that reduces fatigue strength even in a corrosive environment during actual use. It was clarified that fatigue strength did not decrease because intergranular corrosion did not occur.

[0012]

According to the present invention, which has the above-mentioned structure, when an aluminum alloy material for precipitating a Mg ₂ Si phase in a matrix by performing solution treatment and tempering treatment is produced, after the solution treatment,
Cold working at a specific reduction rate is applied to give compressive residual stress to the material to form precipitation grain generation sites at the crystal grain boundaries, and to crystallize the Mg ₂ Si phase that tends to precipitate at the grain boundaries by tempering. By preferentially precipitating in the grains, the grain boundary precipitation of the Mg ₂ Si phase is suppressed, and the intergranular corrosion resistance in a corrosive environment is improved.

[0013]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 A 6000 series aluminum alloy having the composition shown in Table 1 was melted to cast a slab having a width of 550 mm, a length of 800 mm and a thickness of 170 mm. After homogenizing this slab according to a conventional method, the head and tail of the slab were cut off, the surface was trimmed by 10 mm on each side, and hot-rolled at 500 ° C. to a thickness of 15 mm. After annealing, cold-roll to a thickness of 3 mm, cut out the plate for testing from the cold-rolled material, subject it to solution treatment at a temperature of 530 to 540 ° C for 45 minutes, then quench with water and cool at each reduction rate. Then, it was tempered at a temperature of 175 ° C for 8 hours.

The test plate thus obtained was washed with NaCl in accordance with the intergranular corrosion test (JIS W 1103) used in the inspection of heat-treatable aluminum alloys for aircraft.
After immersing 57 g and 30% H ₂ O ₂ in a test solution adjusted to 1 liter with water at 30 ° C for 6 hours, an intergranular corrosion test was performed to observe the cross section with an optical microscope. For the evaluation, after the intergranular corrosion test, a sample was cut out from the plate material, and after polishing, it was observed with an optical microscope to investigate the corrosion form and how much the corrosion tip reached from the plate material surface in the thickness direction. The results are shown in Table 2.

[0015]

[Table 1]

[0016]

[Table 2]

As shown in Table 2, according to the present invention,
The test materials No. 1 to No. 8 which were cold-rolled with a reduction rate of more than 3% after the solution treatment and before the tempering treatment did not show intergranular corrosion, and the corrosion tip from the plate surface Depth up to 200 μm
It was below.

Comparative Example 1 A plate for testing was cut out from the cold-rolled material produced in Example 1, and solution-annealed at a temperature of 530 to 540 ° C. for 2.5 hours as in Example 1, followed by water quenching. Then, cold rolling was performed at each reduction ratio, and then tempering was performed at a temperature of 175 ° C for 8 hours.
The same intergranular corrosion test as in Example 1 was performed on the obtained test plate material. The test results are shown in Table 3. As shown in Table 3, test material No. 1 in which cold rolling for imparting compressive residual stress is not performed, and the reduction rate of cold rolling is smaller than the lower limit N
In Nos. 2, No. 5, No. 6, and No. 7, intergranular corrosion occurred, and corrosion was caused to a depth of more than 200 μm from the surface of the plate material. In Nos. 3 and 4, the cold rolling time for imparting compressive residual stress did not satisfy the conditions of the invention, so intergranular corrosion occurred and the corrosion depth exceeded 200 μm.

[0019]

[Table 3]

Example 2 An aluminum alloy having the composition shown in Table 4 was melted and a billet having a diameter of 250 mm was cast. After homogenizing this billet by a conventional method, it was hot extruded at 450 ° C. into a round bar having a diameter of 50 mm. Using this round bar as a test material, 530
After solution heat treatment at a temperature of ~ 540 ° C for 2.5 hours, water quenching was performed, cold drawing was performed at each reduction rate, and finally tempering treatment was performed at a temperature of 175 ° C for 8 hours. An intergranular corrosion test similar to that in Example 1 was performed on the obtained drawn bar material, and the corrosion form and the reached corrosion depth were measured. The results are shown in Table 5.

[0021]

[Table 4]

[0022]

[Table 5]

As shown in Table 5, according to the present invention,
After the solution heat treatment and before the tempering treatment, cold drawing of 5% or more was performed, and the test materials No. 9 to No. 16 to which compressive residual stress was applied did not cause intergranular corrosion, It was also less than 200 μm, showing excellent intergranular corrosion resistance.

Comparative Example 2 The hot extruded bar produced in Example 2 was used as a test material, and similarly to Example 2, the solution treatment was performed at a temperature of 530 to 540 ° C. for 2.5 hours, followed by water quenching. Cold drawing at a reduction rate,
Then, tempering treatment was performed at a temperature of 175 ° C. for 8 hours. The same intergranular corrosion test as in Example 2 was performed on the obtained test material, and the corrosion morphology and the corrosion depth from the material surface were measured. The results are shown in Table 6. As shown in Table 6, a test material that is not drawn to give a compressive residual stress
No. 8, test material No. 8 having a drawing ratio smaller than the range of the present invention
In Nos. 9, No. 12, No. 13, and No. 14, intergranular corrosion occurred, and the reached corrosion depth exceeded 200 μm. No.1
In Nos. 0 and 11, the cold drawing process for imparting the compressive residual stress did not satisfy the conditions of the present invention, so intergranular corrosion occurred and the depth from the surface to the corrosion tip exceeded 200 μm.

[0025]

[Table 6]

[0026]

According to the present invention, solution treatment and tempering treatment are performed to precipitate the Mg ₂ Si phase in the matrix.
In the 000-series aluminum alloy material, as a result of suppressing the grain boundary precipitation of the Mg ₂ Si phase, an alloy material that does not cause grain boundary corrosion is provided.

Claims (4)

[Claims] 1. An aluminum alloy material which has been subjected to solution treatment and tempering treatment to precipitate a Mg ₂ Si phase in a matrix, and which is obtained by a grain boundary corrosion test from the surface of the aluminum alloy material to the corrosion tip. An aluminum alloy material having excellent intergranular corrosion resistance, which is characterized by having a depth of 200 μm or less. However, the intergranular corrosion test was performed according to JIS W 1103. 2. A method for producing an aluminum alloy material in which a solution treatment and a tempering treatment are carried out to precipitate a Mg ₂ Si phase in a matrix, wherein a tempering treatment is performed by applying a compressive residual stress to the aluminum alloy material after the solution treatment. A method for producing an aluminum alloy material having excellent intergranular corrosion resistance, which comprises: 3. A method for producing an aluminum alloy material in which a solution treatment and a tempering treatment are performed to precipitate a Mg ₂ Si phase in a matrix, wherein the aluminum alloy material is an aluminum alloy plate material, and 3% after the solution treatment is applied. 3. The tempering process is performed by cold rolling at a reduction rate exceeding the above.
A method for producing an aluminum alloy material excellent in intergranular corrosion resistance as described. 4. A method for producing an aluminum alloy material in which a solution treatment and a tempering treatment are performed to precipitate a Mg ₂ Si phase in a matrix, wherein the aluminum alloy material is an aluminum alloy tube rod material, and 5 after the solution treatment. 3. A temper drawing process is performed by cold drawing at a reduction rate of at least%.
A method for producing an aluminum alloy material excellent in intergranular corrosion resistance as described.