JP6344816B2 - High-strength aluminum alloy extruded thin section and method for producing the same - Google Patents

Description

  The present invention relates to a high-strength aluminum alloy extruded thin-walled material, particularly an Al-Zn-Mg-Cu-based high-strength aluminum alloy extruded thin-walled material suitably used for transport equipment such as aircraft materials and sports equipment such as bats and the like. It relates to a manufacturing method.

  High-strength aluminum alloys, especially Al-Zn-Mg-Cu-based aluminum alloys, are often used as materials for sports equipment such as aircraft, helicopters, and motorcycles, and bats. Development of an extruded thin section of an Al—Zn—Mg—Cu-based aluminum alloy having a yield strength of 700 MPa or more is eagerly desired.

  Until now, for the purpose of increasing the strength of the Al—Zn—Mg—Cu-based aluminum alloy extruded material, a method of obtaining an aluminum alloy by solidifying and forming rapidly solidified powder by an atomizing method has been proposed. For example, an Al alloy containing Zn: 5 to 11%, Mg: 2 to 4.5%, Cu: 0.5 to 2%, and Ag: 0.01 to 0.5%, with the balance being substantially Al. It is disclosed that the tensile strength can be increased to about 900 MPa by treating the molded body produced from the rapidly solidified powder by the powder metallurgy method with T6.

  However, since the rapidly solidified powder is used, the factory production is complicated and expensive, and for that reason, a wrought material produced by rolling or extrusion has been used even if the strength is low. Even in the wrought material, a proof stress of 700 MPa or more is obtained in a round bar-shaped extruded material in which high strength is easily obtained, but there is a problem that it is difficult to obtain a high strength of 700 MPa or more in an extruded thin-walled material.

JP 7-316601 A

Light metal, vol. 60, page 75

  In an Al—Zn—Mg—Cu-based aluminum alloy, an extruded thin profile with a thickness of 5 mm or less tends to have a main orientation in the extrusion direction that is a Brass orientation. Therefore, a high strength of 700 MPa or more cannot be obtained. In order to obtain a material, extrusion was performed in a round bar shape or a thick-walled shape in which the P-direction has a small Brass direction and the P-direction which tends to be high in strength is the main direction, and was cut into a thin-walled material.

  The present invention has been made in order to solve the conventional problems associated with an Al-Zn-Mg-Cu-based high-strength aluminum alloy extruded thin section having a thickness of 5 mm or less, and its purpose is to have a proof stress of 700 MPa or more. An object of the present invention is to provide an Al-Zn-Mg-Cu-based high-strength aluminum alloy extruded thin-walled material capable of obtaining strength and a method for producing the same.

In order to achieve the above object, the high-strength aluminum alloy extruded thin section according to claim 1 has Zn: 9.0 to 13.0% (mass%, the same applies hereinafter), Mg: 2.0 to 3.0% Cu: 1.0-2.0%, Zr: 0.05-0.30%, consisting of the balance Al and unavoidable impurities, fine precipitates having a circle-equivalent diameter of 5-20 nm in the crystal grains It is characterized in that 4000 to 6000 are dispersed per 1 μm ² .

  The high strength aluminum alloy extruded thin section according to claim 2 is characterized in that, in claim 1, the proof stress is 700 MPa or more and the elongation is 9% or more.

The manufacturing method of the high strength aluminum alloy extruded thin section according to claim 3 is Zn: 9.0-13.0%, Mg: 2.0-3.0%, Cu: 1.0-2.0%, Zr: 0.05 to 0.30% of aluminum alloy having a composition composed of the balance Al and inevitable impurities is ingoted, and the resulting ingot is homogenized according to a conventional method, followed by hot extrusion. The solution is subjected to solution treatment, quenching treatment and aging treatment, and the aging treatment is held at a temperature of 100 to 130 ° C. for 6 to 48 hours and then cooled to room temperature. Then, the temperature is raised to a temperature of 160 to 180 ° C. at a temperature rising rate of 0.5 ° C./second or more and held at the temperature for 10 ^X (min) or more and 10 ^Y (min) or less, and then 0.02 Second-stage aging treatment for cooling to room temperature at a cooling rate of ° C / second or more, and 100 to 13 It is characterized by comprising a third-stage aging treatment in which the temperature is kept at 0 ° C. for 6 to 48 hours and then cooled to room temperature. However, X = −0.03 × holding temperature + 5.11 and Y = −0.03 × holding temperature + 7.07.

According to the present invention, a fine precipitate having an equivalent circle diameter of 5 to 20 nm can be obtained by performing three-stage aging treatment even in the case of an extruded thin-walled material having a thickness of 5 mm or less in which the Brass orientation tends to be the main orientation in the extrusion direction. Al-Zn-Mg-Cu-based high-strength aluminum alloy extrusion that has the property that 4000 to 6000 per 1 μm ² are dispersed in the crystal grains, and can obtain properties of proof stress 700 MPa or more and elongation 9% or more Thin wall profiles are provided.

The significance and reasons for limitation of the constituent elements of the aluminum alloy constituting the high-strength extruded thin-walled material according to the present invention will be explained. Zn coexists with Mg to form the η ′ phase and MgZn ₂ and to improve the strength. To do. The preferred content is in the range of 9.0 to 13.0%. If it is less than 9.0%, the strength is insufficient, and if it exceeds 13.0%, the ductility is lowered.

Mg functions to improve the strength by coexisting with Zn to form the η ′ phase and MgZn ₂ . The preferred content is in the range of 2.0 to 3.0%. If it is less than 2.0%, the strength is not sufficient, and if it exceeds 3.0%, the ductility is lowered.

  Cu functions to improve strength. The preferred content is in the range of 1.0 to 2.0%. If it is less than 1.0%, the strength is not sufficient, and if it exceeds 2.0%, the ductility is lowered.

Zr has the effect of precipitating as Al ₃ Zr and suppressing recrystallization, and functions to form a fibrous structure and improve strength. The preferred content is in the range of 0.05 to 0.30%. When the content is less than 0.05%, the strength is reduced. When the content exceeds 0.30%, a coarse crystallized product is produced during casting and ductility is caused. Cause a decline.

  In addition, as inevitable impurities other than the above alloy components, 0.30% or less of Si, 0.30% or less of Fe, or the like may be contained. Further, for refinement of the cast structure, the inclusion of 0.05% or less of Ti and 0.01% or less of B is allowed.

  An aluminum alloy extruded thin section according to the present invention is formed by agglomerating an aluminum alloy having the above composition into a billet for extrusion, preferably by semi-continuous casting, and homogenizing the resulting billet according to a conventional method, followed by hot extrusion. And the obtained hot-extruded material is produced by solution treatment, quenching treatment and aging treatment. The aging process includes a first stage aging process, a second stage aging process, and a third stage aging process.

  The first-stage aging treatment is a heat treatment in which the temperature is kept at 100 to 130 ° C. for 6 to 48 hours and then cooled to room temperature, and sufficient precipitation is obtained by this treatment. When the treatment temperature is less than 100 ° C., sufficient precipitation cannot be obtained, and when the treatment temperature exceeds 130 ° C., the η phase is precipitated and the strength is lowered. The cooling rate to room temperature does not affect the effect of the present invention and is not particularly limited.

In the second stage aging treatment, the temperature was raised to a temperature of 160 to 180 ° C. at a temperature raising rate of 0.5 ° C./second or more and held at the temperature for 10 ^X (min) or more and 10 ^Y (min) or less. Thereafter, the heat treatment is performed to cool to room temperature at a cooling rate of 0.02 ° C./second or more, and is performed for the purpose of re-dissolving precipitates in the grains in the matrix. However, X = −0.03 × holding temperature + 5.11 and Y = −0.03 × holding temperature + 7.07. When the holding time is less than 10 ^X (minutes), re-dissolution of precipitates in the grains does not occur sufficiently, and the strength is lowered. When the holding time exceeds 10 ^Y (minutes), a coarse η phase is precipitated and the strength and ductility are lowered.

  When the treatment temperature is less than 160 ° C., the precipitate is not sufficiently dissolved. Moreover, when it exceeds 180 degreeC, heat processing time will become short and industrial production will become difficult. If the rate of temperature rise to the treatment temperature is less than 0.5 ° C./second, the η phase precipitates during the temperature rise, resulting in a decrease in strength and a decrease in ductility. When the cooling rate from the treatment temperature is less than 0.02 ° C./second, the growth of precipitates progresses during cooling, resulting in a decrease in strength and a decrease in ductility.

  The third stage aging treatment is a heat treatment in which the temperature is kept at 100 to 130 ° C. for 6 to 48 hours and then cooled to room temperature. The second-stage aging treatment leaves a η ′ phase on the grain boundary, and the precipitates in the grains are almost dissolved to form a matrix single-phase, but the third-stage aging treatment is performed by heating the η ′ phase. Is intended to improve the strength by precipitation strengthening. When the treatment temperature is less than 100 ° C., sufficient precipitation cannot be obtained, and when it exceeds 130 ° C., the η phase is precipitated and the strength is reduced. The cooling rate to room temperature does not affect the effect of the present invention and is not particularly limited.

  The aluminum alloy extruded thin section according to the present invention has a 0.2% proof stress of 700 MPa or more as defined in ASTM E9, and even an extruded section in which the Brass orientation is accumulated in the extrusion direction has strength characteristics corresponding to weight reduction. Can be obtained.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects. In addition, these Examples show one Embodiment of this invention, and this invention is not limited to these.

Example 1 and Comparative Example 1
An aluminum alloy having the composition shown in Table 1 was melted and agglomerated into an extrusion billet having a diameter of 90 mm by a semi-continuous casting method, and the obtained billet was homogenized at 470 ° C. for 10 hours. The mixture was cooled to 250 ° C. in 48 minutes (average cooling rate 250 ° C./h) and then cooled to room temperature. The billet was heated to 420 ° C. in an induction heating furnace for 5 minutes with a temperature rising time, held for 1 minute, and then a plate-like extruded shape having a thickness of 4 mm and a width of 60 mm was produced by hot extrusion. The extrusion speed on the die exit side during extrusion was 1 m / min.

The obtained extruded shape was heated to 470 ° C. at a heating rate of 50 ° C./h, held at a temperature of 470 ° C. for 60 minutes, then quenched in water at 20 to 30 ° C., and then at a temperature of 120 ° C. For 24 hours, and then cooled to room temperature by air cooling (cooling rate 25 ° C./sec), heated to 160 ° C. at a rate of 3 ° C./sec and held for 120 minutes, Second stage aging treatment that cools to room temperature by air cooling (cooling rate 25 ° C./sec), third stage aging treatment that cools to room temperature by air cooling (cooling rate 25 ° C./sec) after holding at 120 ° C. for 24 hours The test materials 1-16 were obtained by performing. The holding time at the holding temperature in the second stage aging treatment is a condition of 10 ^X (min) or more and 10 ^Y (min) or less (X = −0.03 × holding temperature + 5.11, Y = −0.03). X Holding temperature + 7.07) In Table 1, those outside the conditions of the present invention are also underlined.

  With respect to the obtained test materials 1 to 16, the tensile performance and the number of fine precipitates were measured by the following methods. The measurement results are shown in Table 2. In Table 2, the number of fine precipitates outside the conditions of the present invention is underlined. Moreover, the underline was attached also to the thing whose tensile performance was not determined to be acceptable.

(Measurement of tensile performance)
Tensile test specimens were collected from the obtained test materials by a method according to ASTM E9, and the tensile strength, proof stress and elongation were measured, and those showing a proof stress of 700 MPa or more and an elongation of 9% or more were regarded as acceptable.

(Measurement of the number of fine precipitates)
About the obtained test material, the center part (part of 2 mm in thickness direction and 30 mm in the width direction) of the cross section perpendicular to the extrusion direction is 50,000 times magnification using JEM-2010 manufactured by JEOL Ltd. The number density (pieces / μm ² ) of fine precipitates having an equivalent circle diameter of 5 to 20 nm among the fine precipitates observed as a dark color contrast in a bright field image was obtained. Observation was carried out with three fields of views ^{(18 * 10 4 nm 2/} 1 field), it was adopted average value.

As shown in Table 2, all of the test materials 1 to 8 according to the present invention show a texture property in which 4000 to 6000 fine precipitates having a circle-equivalent diameter of 5 to ²⁰ nm are dispersed in 1 μm ² in the crystal grains, All of them had a tensile performance of a yield strength of 700 MPa or more and an elongation of 9% or more, and were excellent in strength and ductility.

  On the other hand, the test materials 9 to 16 that do not satisfy the conditions of the present invention did not reach the pass line in either proof stress or elongation. Since the test material 9 had too low Zn content, the strength improvement effect was not fully obtained but the yield strength was inferior. Since the test material 10 had a Zn content that was too high, grain boundary precipitation occurred and sufficient elongation was not obtained. Since the test material 11 had too low Mg content, the strength improvement effect was not fully obtained but the yield strength was inferior. Since the test material 12 had too high Mg content, grain boundary precipitation occurred and sufficient elongation could not be obtained.

  Since the test material 13 had too low Cu content, the strength improvement effect was not fully acquired and the yield strength was inferior. Since the test material 14 had too high Cu content, grain boundary precipitation occurred and sufficient elongation could not be obtained. The test material 15 had a recrystallized structure because the Zr content was too low, and a sufficient strength improvement effect was not obtained, resulting in poor proof stress. Since the test material 16 had a too high Zr content, the ductility was lowered by the coarse crystallized product, and sufficient elongation was not obtained.

Example 2
An aluminum alloy having the composition shown in Table 3 was melted and agglomerated into a billet for extrusion having a diameter of 90 mm by a semi-continuous casting method, and the obtained billet was homogenized at 470 ° C. for 10 hours. The mixture was cooled to 250 ° C. in 48 minutes (average cooling rate 250 ° C./h) and then cooled to room temperature. The billet was heated to 420 ° C. in an induction heating furnace for 5 minutes with a temperature rising time, held for 1 minute, and then a plate-like extruded shape having a thickness of 4 mm and a width of 60 mm was produced by hot extrusion. The extrusion speed on the die exit side during extrusion was 1 m / min.

The obtained extruded shape was heated to 470 ° C. at a heating rate of 50 ° C./h, held at 470 ° C. for 60 minutes, then quenched in water at 20-30 ° C., and then shown in Table 4 Under the conditions (a1 to a13), first-stage aging treatment, second-stage aging treatment and third-stage aging treatment were performed to obtain test materials 17 to 29. In the first stage aging treatment, cooling from the holding temperature to room temperature was performed by air cooling (cooling rate 25 ° C./second), and in the third stage aging treatment, cooling was performed from the holding temperature to room temperature by air cooling (cooling rate 25 ° C./second). . The holding time at the holding temperature in the second stage aging treatment is a condition of 10 ^X (min) or more and 10 ^Y (min) or less (X = −0.03 × holding temperature + 5.11, Y = −0.03). X Holding temperature + 7.07)

  For the obtained test materials 17 to 29, the tensile performance and the number of fine precipitates were measured by the same method as in Example 1. Table 5 shows the measurement results.

As shown in Table 5, all of the test materials 17 to 29 according to the present invention have a texture property in which 4000 to 6000 fine precipitates having a circle-equivalent diameter of 5 to ²⁰ nm are dispersed in 1 μm ² in the crystal grains. All of them had characteristics of proof stress of 700 MPa or more and elongation of 9% or more, and were excellent in strength and ductility.

Comparative Example 2
A plate-like extruded shape having a thickness of 4 mm and a width of 60 mm was produced in the same manner as in Example 2 using an aluminum alloy having the composition shown in Table 3, and the resulting extruded shape was heated at a rate of temperature increase of 50 ° C./h. The temperature was raised to 470 ° C. and held at a temperature of 470 ° C. for 60 minutes, and then quenched in water at 20 to 30 ° C. Then, under the conditions (b1 to b26) shown in Table 6, the first stage aging treatment, The stage aging treatment and the third stage aging treatment were performed to obtain test materials 30 to 55. In the first stage aging treatment, cooling from the holding temperature to room temperature was performed by air cooling (cooling rate 25 ° C./second), and in the third stage aging treatment, cooling was performed from the holding temperature to room temperature by air cooling (cooling rate 25 ° C./second). . In Table 6, those outside the conditions of the present invention are underlined.

  For the obtained test materials 30 to 55, the tensile performance and the number of fine precipitates were measured by the same method as in Example 1. Table 7 shows the measurement results. In Table 7, those in which the number of fine precipitates deviated from the conditions of the present invention were underlined. Moreover, the underline was attached also to the thing whose tensile performance was not determined to be acceptable.

  As shown in Table 7, the test materials 30 to 55 that did not satisfy the conditions of the present invention did not reach the pass line in either or both of proof stress and elongation. Since the test materials 30 and 31 were low in the second-stage aging treatment temperature, the re-solution of fine precipitates was not sufficient, and sufficient precipitation hardening was not obtained in the third-stage aging treatment, resulting in poor proof stress.

  Since the test materials 32, 34, and 36 had a short holding time in the second-stage aging treatment, the η ′ phase did not re-dissolve, so that precipitation hardening in the third-stage aging treatment was not sufficient and the yield strength was inferior. Since the test materials 33, 35, and 37 have a long retention time in the second stage aging treatment, precipitation of coarse η phase proceeds and the ductility is inferior, and the precipitation hardening in the third stage aging treatment is not sufficient and the yield strength is low. It was inferior.

  In the test material 38, the rate of temperature rise in the second-stage aging treatment is slow, so that precipitation of coarse η phase proceeds during the temperature rise, the ductility is inferior, and precipitation hardening in the third-stage aging treatment is not sufficient and the yield strength is low. It was inferior. Since the test material 39 has a slow cooling rate in the second stage aging treatment, precipitation of a coarse η phase progresses during cooling, and the ductility is inferior, and the precipitation hardening in the third stage aging treatment is not sufficient and the yield strength is inferior. It was.

  Since the test material 40 had a short holding time in the first-stage aging treatment, sufficient precipitation hardening could not be obtained and the proof stress was inferior. Since the test material 41 had a long retention time in the first-stage aging treatment, a coarse η phase was formed and the yield strength was inferior. Since the test material 42 had a short retention time in the third-stage aging treatment, sufficient precipitation hardening was not obtained and the yield strength was inferior. Since the test material 43 had a long retention time in the third stage aging treatment, a coarse η phase was formed, and therefore the yield strength was inferior.

  Since the test material 44 had a short retention time in the first-stage aging treatment, sufficient precipitation hardening was not obtained and the yield strength was inferior. Since the test material 45 had a long retention time in the first stage aging treatment, a coarse η phase was formed, and therefore the yield strength was inferior. Since the test material 46 had a short holding time in the third stage aging treatment, sufficient precipitation hardening was not obtained, and the yield strength was inferior. Since the test material 47 had a long retention time in the third stage aging treatment, a coarse η phase was formed, and therefore the yield strength was inferior.

  Since the test materials 48 and 49 had a low holding temperature in the first-stage aging treatment, sufficient precipitation hardening was not obtained and the proof stress was inferior. Since the test materials 50 and 51 had a low holding temperature in the third stage aging treatment, sufficient precipitation hardening was not obtained, and the proof stress was inferior. Since the test materials 52 and 53 had a high holding temperature in the first-stage aging treatment, sufficient precipitation hardening was not obtained and the proof stress was inferior. Since the test materials 54 and 55 had a high holding temperature in the third stage aging treatment, sufficient precipitation hardening was not obtained, and the proof stress was inferior.

Claims (3)

Zn: 9.0 to 13.0% (mass%, the same applies hereinafter), Mg: 2.0 to 3.0%, Cu: 1.0 to 2.0%, Zr: 0.05 to 0.30% High-strength aluminum alloy extruded thin wall characterized in that it contains the balance Al and inevitable impurities, and 4000 to 6000 fine precipitates having a circle-equivalent diameter of 5 to ²⁰ nm are dispersed in 1 μm ² in the crystal grains. Profile material. The high-strength aluminum alloy extruded thin section according to claim 1, wherein the yield strength is 700 MPa or more and the elongation is 9% or more. Zn: 9.0 to 13.0%, Mg: 2.0 to 3.0%, Cu: 1.0 to 2.0%, Zr: 0.05 to 0.30%, the balance Al and An aluminum alloy having a composition consisting of inevitable impurities is ingoted, and the resulting ingot is homogenized according to a conventional method, followed by hot extrusion, and the resulting hot extruded material is solution treated and quenched. The aging treatment is carried out at a temperature of 100 to 130 ° C. for 6 to 48 hours, and then cooled to room temperature, and a temperature rising rate of 0.5 ° C./second or more and 160 to 180 ° C. A second stage aging treatment in which the temperature is raised to a temperature of ℃ and held at the temperature for 10 ^X (min) or more and 10 ^Y (min) or less, and then cooled to room temperature at a cooling rate of 0.02 ℃ / sec or more. And the third stage aging which is kept at a temperature of 100 to 130 ° C. for 6 to 48 hours and then cooled to room temperature. A process for producing a high-strength aluminum alloy extruded thin section characterized by comprising processing. However, X = −0.03 × holding temperature + 5.11, Y = −0.03 × holding temperature + 7.07.