JP2015040320A - High strength aluminum alloy, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength aluminum alloy excellent in surface quality and stress corrosion crack resistance after anodizing, and to provide a method for producing the same.SOLUTION: A high strength aluminum alloy to be anodized has a chemical component comprising by mass% Zn: 5.0% or more and 7.0% or less, Mg: more than 2.2% and 3.0% or less, Cu: 0.01% or more and 0.10% or less, Zr: 0.10% or less, Cr: 0.02% or less, Fe: 0.30% or less, Si:0.30% or less, Mn: 0.02% or less, Ti: 0.001% or more and 0.05% or less and the remainder consisting of Al and inevitable impurities, and having a Zn/Mg ratio of 1.7 or more and 3.1 or less, has a proof stress of 350 MPa or more, and has a metal structure consisting of a recrystallized structure.

Description

  The present invention relates to a high-strength aluminum alloy that is used in a site where at least both appearance characteristics and stress corrosion cracking resistance are regarded as important.

  As a material used for sports equipment, transportation equipment, machine parts, and other applications in which at least strength characteristics and appearance characteristics are regarded as important, aluminum alloys are increasingly used. Since durability is required for these uses, it is desired to use a high-strength aluminum alloy having a proof stress of 350 MPa or more. As an aluminum alloy used for applications in which both strength characteristics and appearance characteristics are important, for example, an aluminum alloy extruded material described in Patent Document 1 has been proposed.

JP 2012-246555 A

  The 7000 series aluminum alloy disclosed in Patent Document 1 has a problem that stress corrosion cracking is likely to occur when T6 treatment is performed by aging treatment. Further, as a countermeasure, overaging treatment can improve the stress corrosion cracking resistance, but there is a problem that the strength is lowered.

As described above, for example, the conventional 7000 series aluminum alloy described in Patent Document 1 has a high yield strength, but it cannot be said that measures against stress corrosion cracking are taken. Therefore, these alloys are not suitable for applications that are used for a long time in a state where stress is always applied in a corrosive environment.
The present invention has been made in view of such a background, and an object of the present invention is to provide a high-strength aluminum alloy excellent in surface quality and stress corrosion cracking resistance after anodizing, and a method for producing the same.

One aspect of the present invention is a high-strength aluminum alloy that is anodized,
In mass%, Zn: 5.0% to 7.0%, Mg: 2.2% to 3.0%, Cu: 0.01% to 0.10%, Zr: 0.10% or less Cr: 0.02% or less, Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less, Ti: 0.001% or more and 0.05% or less, and the balance Having a chemical component having a Zn / Mg ratio of 1.7 or more and 3.1 or less, and consisting of Al and inevitable impurities,
Yield strength is 350 MPa or more,
The high-strength aluminum alloy is characterized in that the metal structure is a recrystallized structure.

Another aspect of the present invention is a method for producing the high-strength aluminum alloy,
In mass%, Zn: 5.0% to 7.0%, Mg: 2.2% to 3.0%, Cu: 0.01% to 0.10%, Zr: 0.10% or less Cr: 0.02% or less, Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less, Ti: 0.001% or more and 0.05% or less, and the balance Is made of Al and inevitable impurities, and ingot having a chemical component having a Zn / Mg ratio of 1.7 or more and 3.1 or less,
A homogenization treatment is performed in which the ingot is heated at a temperature of 540 ° C. to 580 ° C. for 1 to 24 hours,
In the state where the temperature of the ingot at the start of processing is 440 ° C. to 560 ° C., the ingot is hot-worked to obtain a wrought material
After starting the cooling while the temperature of the wrought material is 400 ° C. or higher, the average cooling rate while the temperature of the wrought material is in the range of 400 ° C. to 150 ° C. is 1 ° C./second to 300 ° C./second. Performs a rapid cooling process to cool by controlling to less than a second,
Cooling the temperature of the wrought material to room temperature by the rapid cooling treatment or subsequent cooling;
Thereafter, an artificial aging treatment is performed on the wrought material.

  The high-strength aluminum alloy has the specific chemical component, has a proof stress of 350 MPa or more, and has a metallographic structure composed of a recrystallized structure. As a result, the above high-strength aluminum alloy has high strength, excellent stress corrosion cracking resistance, and excellent surface quality after anodizing treatment, strength characteristics, appearance characteristics and stress corrosion cracking resistance. Can be suitably used for a site where importance is attached.

  That is, the high-strength aluminum alloy can ensure excellent stress corrosion cracking characteristics by having the above specific chemical component, and thus exhibits excellent durability even when used in a corrosive environment. can do.

  The high-strength aluminum alloy has a yield strength equal to or higher than that of the conventional 7000 series aluminum alloy material, that is, a yield strength of 350 MPa or more. Therefore, for example, strength requirements such as ensuring strength characteristics that can cope with thinning for weight reduction can be satisfied relatively easily.

  In addition, the high-strength aluminum alloy has the specific chemical component and the metal structure is composed of a recrystallized structure, so that a streak pattern caused by the fibrous structure is generated after the anodizing treatment. Can be suppressed, and good surface quality can be obtained.

  Next, in the manufacturing method of the high-strength aluminum alloy material, the high-strength aluminum alloy is manufactured by the specific processing temperature, processing time, and processing procedure. Therefore, the above excellent high strength aluminum alloy can be easily obtained.

The drawing substitute photograph which shows the metal structure of the sample 4 in Example 1. FIG. The drawing substitute photograph in Example 1 which shows the metal structure of sample A19.

  The high-strength aluminum alloy is, in mass%, Zn: 5.0% to 7.0%, Mg: 2.2% to 3.0%, Cu: 0.01% to 0.10%, Zr: 0.10% or less, Cr: 0.02% or less, Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less, Ti: 0.001% or more and 0.05 %, And the balance is composed of Al and inevitable impurities, and has a chemical component having a Zn / Mg ratio of 1.7 or more and 3.1 or less. First, the reason for limiting the content range of each element will be described.

Zn: 5.0% to 7.0%,
Zn is an element that precipitates the η ′ phase by coexisting with Mg in the aluminum alloy. By containing Zn together with Mg, strength improvement by precipitation strengthening can be obtained. When the Zn content is 5.0% or less, the amount of precipitation of the η ′ phase is reduced, and the strength improvement effect is reduced. Therefore, the Zn content is preferably more than 5.0%, and more preferably 5.2% or more. On the other hand, if the Zn content exceeds 7.0%, the stress corrosion cracking resistance is lowered. Therefore, the Zn content is preferably 7.0% or less, and preferably 6.8% or less.

Mg: 2.2% to 3.0% or less,
Mg is an element that precipitates the η ′ phase by coexisting with Zn in the aluminum alloy. By containing Mg together with Zn, strength improvement by precipitation strengthening can be obtained. When the Mg content is 2.2% or less, the precipitation amount of the η ′ phase is reduced, and the strength improvement effect is reduced. On the other hand, if the Mg content exceeds 3.0%, the hot workability is lowered, the productivity is lowered, and the stress corrosion cracking resistance is lowered.

Zn / Mg ratio: 1.7 or more and 3.1 or less,
The contents of Zn and Mg are selected so that they are within the above-mentioned limited ranges, and the value of the Zn content / Mg content ratio is always within the range of 1.7 to 3.1. If the Zn / Mg ratio is less than 1.7, the strength tends to be low, whereas if it exceeds 3.1, the stress corrosion cracking resistance is lowered. In addition, Zn / Mg ratio means the value of Zn content (mass%) / Mg content (mass%).

Cu: 0.01% or more and 0.10% or less,
Cu may be mixed when a recycled material is used as a raw material for the high-strength aluminum alloy material. When the Cu content exceeds 0.10%, the surface quality deteriorates, such as a decrease in gloss after chemical polishing and a change in color tone to yellow due to anodizing treatment. If it is less than 01%, the stress corrosion cracking resistance decreases. Such deterioration of stress corrosion cracking resistance and surface quality can be avoided by controlling the Cu content to 0.01% or more and 0.10% or less.

Zr: 0.10% or less,
When the content of Zr exceeds 0.10%, generation of a recrystallized structure is suppressed, and a fibrous structure is easily generated instead. If the fibrous structure is present, the streak pattern resulting from the fibrous structure is likely to appear on the surface after the anodizing treatment, so that the surface quality may be deteriorated. Therefore, the Zr content is 0.10% or less.

Cr: 0.02% or less,
When Cr is contained in an amount of 0.02% or more, the surface after the anodizing treatment may have a yellow color tone. Such deterioration of the surface quality due to color change or the like can be suppressed by regulating the Cr content to less than 0.02%.

Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less,
Fe and Si are mixed as impurities in the aluminum ingot, and Mn is a component that may be mixed when using recycled materials. Fe, Si, and Mn have an action of suppressing recrystallization by forming an AlMn-based, AlMnFe-based, or AlMnFeSi-based intermetallic compound with Al. For this reason, when the three components are excessively mixed in the high-strength aluminum alloy material, the generation of a recrystallized structure is suppressed, and a fibrous structure is easily generated instead. When a fibrous structure is present, a streak pattern resulting from the fibrous structure is likely to appear on the surface after the anodizing treatment, so that the surface quality may be deteriorated. Such deterioration of the surface quality due to the streak pattern can be suppressed by regulating Fe to 0.30% or less, Si to 0.30% or less, and Mn to 0.02% or less. It becomes.

Ti: 0.001% or more and 0.05% or less,
Ti has the effect | action which refines | miniaturizes an ingot structure | tissue by adding to an aluminum alloy. As the ingot structure becomes finer, a more glossy surface state without spots is obtained, so that the surface quality can be improved by containing Ti. When the Ti content is less than 0.001%, the ingot structure is not sufficiently refined, and there is a possibility that spots and streaks are formed on the surface of the high-strength aluminum alloy material. In addition, when the Ti content is more than 0.05%, AlTi-based intermetallic compounds formed between the Al and the like, it is easy to generate a dot-like or streak-like defect, The surface quality may be deteriorated.

  Next, as described above, the high-strength aluminum alloy material has a metal structure composed of a granular recrystallized structure. Usually, an aluminum alloy produced by hot working has a metal structure composed of a fibrous structure, so that a streak pattern is generated on the surface, and as a result, the surface quality may be lowered. On the other hand, in the high-strength aluminum alloy, since the metal structure is composed of a recrystallized structure, no streak pattern is generated on the surface, and the surface quality is good.

  In addition, the high-strength aluminum alloy has a b * value in the L * a * b * color system defined by JIS Z8729 (ISO 7724-1) measured after anodizing using a sulfuric acid bath (blue to The chromaticity of yellow is preferably 0 or more and 0.8 or less. After the anodizing treatment, an aluminum alloy material having a b * value within the above range has an appropriate yellow density, and thus becomes an aluminum alloy material excellent in design.

  Since the high-strength aluminum alloy material has at least the specific chemical component, a color tone with a b * value of 0.8 or less can be realized. When the b * value exceeds 0.8, the color tone is yellowish after the anodizing treatment, which may reduce the designability. When anodizing is performed on an aluminum alloy material having the above chemical components, it is difficult to obtain an aluminum alloy material having a b * value that is less than 0.

  The recrystallized structure has an average grain size of 500 μm or less, and the crystal length in the direction parallel to the hot working direction is 0 with respect to the crystal length perpendicular to the hot working direction. It is preferably 5 times or more and 4 times or less.

  When the average grain size of the crystal grains exceeds 500 μm, the crystal grains become excessively coarse, so that after surface treatment such as anodic oxidation treatment, spots are likely to occur and the surface quality may be deteriorated. . Therefore, the smaller the average grain size of the crystal grains, the better.

  Further, when the aspect ratio of the crystal grains, that is, the ratio of the crystal length in the direction parallel to the hot working direction to the crystal length in the direction perpendicular to the hot working direction exceeds 4, the anodic oxidation treatment is performed. There is a risk of streak patterns appearing on the surface. On the other hand, crystal grains having an aspect ratio of less than 0.5 are difficult to obtain with substantial manufacturing equipment.

  In addition, the said metal structure can confirm whether it is a recrystallized structure, for example by performing electropolishing to the surface of an aluminum alloy material, and observing the obtained surface with a polarization microscope. That is, when the metal structure is a recrystallized structure, a uniform metal structure composed of granular crystals is observed, and solidified structures that can be formed during casting, such as coarse intermetallic compounds and suspended crystals, are observed. I can't. Similarly, in the metal structure composed of the recrystallized structure, a streak structure (so-called processed structure) formed by plastic processing such as extrusion or rolling is not observed.

  In addition, the average grain size of the crystal grains in the recrystallized structure is defined in JIS G0551 (ASTM E 112-96, ASTM E 1382-97) with respect to the metal structure image obtained by observation using the polarizing microscope. It can be calculated according to the cutting method. That is, by drawing one cutting line in each of the vertical, horizontal and diagonal directions at an arbitrary position in the metal structure image, and dividing the length of the cutting line by the number of grain boundaries crossing the cutting line. The average particle size can be calculated.

  The aspect ratio, that is, the ratio of the crystal length in the direction parallel to the hot working direction to the crystal length in the direction perpendicular to the hot working direction can be calculated according to the method described above. That is, in the same manner as described above, in the metal structure image, a cutting line in a direction parallel to the hot working direction and a perpendicular direction is drawn to an arbitrary position, and a direction parallel to the hot working direction from each cutting line. And the average particle size in the perpendicular direction is calculated. Then, the aspect ratio can be calculated by dividing the average particle size in the direction parallel to the hot working direction by the average particle size in the direction perpendicular to the hot working direction.

  Moreover, it is preferable that the said recrystallized structure was produced | generated at the time of hot processing. The recrystallized structure can be classified into a dynamic recrystallized structure and a static recrystallized structure depending on the manufacturing process. It is called crystal structure. On the other hand, a static recrystallized structure refers to a structure generated by adding a heat treatment step such as solution treatment or annealing treatment after hot working or cold working. The above-described problems to be solved by the present invention can be solved by any recrystallization structure. However, in the case of a dynamic recrystallization structure, the production process is simplified, so that it can be easily manufactured. .

  Next, in the method for producing the high-strength aluminum alloy material, a homogenization treatment is performed in which the ingot having the chemical component is heated at a temperature exceeding 540 ° C. and not more than 580 ° C. for 1 hour to 24 hours. Do. When the heating temperature for the homogenization treatment is 540 ° C. or less, the ingot segregation layer is not sufficiently homogenized. As a result, coarsening of crystal grains, formation of a non-uniform crystal structure, and the like occur, so that the surface quality of the finally obtained alloy material is deteriorated. On the other hand, when the heating temperature is higher than 580 ° C., the ingot is likely to be locally melted, which makes it difficult to manufacture. Accordingly, the temperature of the homogenization treatment is preferably more than 540 ° C. and not more than 580 ° C.

  Further, when the heating time for the homogenization treatment is less than 1 hour, the homogenization of the ingot segregation layer is insufficient, and the final surface quality is reduced as described above. On the other hand, if the heating time exceeds 24 hours, the ingot segregation layer is sufficiently homogenized, so that no further effect can be expected. Therefore, the homogenization time is preferably 1 hour or more and 24 hours or less.

  The ingot that has been subjected to the homogenization treatment is subjected to hot working to obtain a wrought material. The temperature of the ingot at the start of hot working is 440 ° C. or higher and 560 ° C. or lower. When the heating temperature of the ingot before hot working is lower than 440 ° C., deformation resistance is high, and it becomes difficult to work with substantial manufacturing equipment. On the other hand, when hot working is performed after heating the ingot to a temperature exceeding 560 ° C., the ingot is locally melted due to heat generated during the processing, and as a result, hot cracking may occur. is there. Therefore, the temperature of the ingot before hot working is preferably 440 ° C. or higher and 560 ° C. or lower. In addition, as said hot processing, an extrusion process, a rolling process, etc. are employable.

  Moreover, after the said hot process, cooling is started while the temperature of the said extending | stretching material is 400 degreeC or more, and the rapid cooling process which cools until the temperature of the said extending | stretching material becomes 150 degrees C or less is performed. When the temperature of the wrought material before the quenching treatment is less than 400 ° C., the quenching effect becomes insufficient, and the resulting wrought material may have a yield strength of less than 350 MPa. Further, even when the temperature of the wrought material after the rapid cooling treatment exceeds 150 ° C., the quenching effect becomes insufficient, and the proof stress of the resulting wrought material may be less than 350 MPa.

  In addition, the said rapid cooling process means the process which cools the said wrought material by a forced means. As the rapid cooling treatment, for example, forced rapid cooling with a fan, shower cooling, or water cooling can be employed.

  The rapid cooling treatment is performed by controlling the average cooling rate between 1 ° C./second and 300 ° C./second while the temperature of the wrought material is in the range of 400 ° C. to 150 ° C. When the average cooling rate exceeds 300 ° C./second, the equipment becomes excessive and an effect commensurate with it cannot be obtained. On the other hand, when the average cooling rate is less than 1 ° C./second, the quenching effect becomes insufficient, and the yield strength of the obtained wrought material may be less than 350 MPa. Accordingly, the average cooling rate should be fast, preferably 1 ° C./second or more and 300 ° C./second or less, preferably 3 ° C./second or more and 300 ° C./second or less.

  In addition, after the rapid cooling treatment, the temperature of the wrought material is allowed to reach room temperature. This may reach room temperature by the quenching process, or may be reached by performing an additional cooling process after the quenching process. By causing the temperature of the wrought material to reach room temperature, an effect of room temperature aging appears, so that the strength of the wrought material is improved. For the additional cooling process, a method such as fan air cooling, mist cooling, shower cooling, or water cooling can be employed.

  Here, when the wrought material is stored in a state where the room temperature is maintained, the strength of the wrought material is further improved by the aging effect at room temperature. At room temperature aging time, the strength is improved as the time is long in the initial stage, but when the room temperature aging time is 24 hours or more, the effect of room temperature aging becomes saturated.

Next, artificial aging treatment is performed in which the wrought material that has been cooled to room temperature as described above is heated. By performing artificial aging treatment, MgZn ₂ precipitates finely and uniformly in the wrought material, so that the proof stress of the wrought material can be easily increased to 350 MPa or more. As specific conditions for the artificial aging treatment, any of the following embodiments can be applied.

  First, as the artificial aging treatment, a first artificial aging treatment is performed in which the wrought material is heated at a temperature of 80 to 120 ° C. for 1 to 5 hours. A second artificial aging treatment in which the material is heated at a temperature of 145 to 200 ° C. for 2 to 15 hours can be performed.

  Here, the first artificial aging treatment and the second artificial aging treatment are performed continuously, after the first artificial aging treatment is completed, the second artificial aging treatment is performed while maintaining the temperature of the wrought material. It means that. That is, it is sufficient that the wrought material is not cooled between the first artificial aging treatment and the second artificial aging treatment. As a specific method, after the first artificial aging treatment, the first aging treatment is not taken out from the heat treatment furnace. 2 There is a method of performing artificial aging treatment.

  Thus, the artificial aging treatment time can be shortened by continuously performing the first artificial aging treatment and the second artificial aging treatment. The treatment temperature in the second artificial aging treatment is preferably 145 to 200 ° C. In the second artificial aging treatment, when heating is performed in the range of 170 to 200 ° C., the ductility of the wrought material is increased, so that the workability can be further improved. In the second artificial aging treatment, if there is a condition outside the above temperature range or time range, stress corrosion cracking of the obtained wrought material is likely to occur or the proof stress may be less than 350 MPa. .

  Moreover, as the artificial aging treatment, the wrought material can be heated at a temperature of 145 to 170 ° C. for 1 to 24 hours. In this case, since the manufacturing process becomes simple, it can be manufactured easily. If the above artificial aging treatment is out of the above temperature range or time range, the resulting wrought material may be susceptible to stress corrosion cracking, and the proof stress may be less than 350 MPa. It becomes difficult to obtain a drawn material.

Example 1
Examples relating to the high-strength aluminum alloy material will be described with reference to Tables 1 to 3. In this example, as shown in Table 1, samples (No. 1 to No. 30) in which the chemical components of the aluminum alloy material were changed were produced under the same manufacturing conditions, and the strength measurement and metal structure observation of each sample were performed. went. Furthermore, after surface-treating each sample, the surface quality was evaluated.
The manufacturing conditions, strength measurement method, metal structure observation method, surface treatment method, and surface quality evaluation method for each sample will be described below.

<Sample manufacturing conditions>
An ingot with a diameter of 90 mm having the chemical components described in Table 1 and Table 2 is cast by semi-continuous casting. Then, the homogenization process which heats this ingot for 6 hours at the temperature of 550 degreeC is performed. Thereafter, in the state where the temperature of the ingot is 520 ° C., the ingot is hot-extruded to form a stretched material having a width of 35 mm and a thickness of 7 mm. Thereafter, in the state where the temperature of the wrought material is 505 ° C., a rapid cooling process is performed in which the wrought material is cooled to 100 ° C. at an average cooling rate of 60 ° C./second. And the said wrought material which performed the said rapid cooling process is cooled to room temperature, and room temperature aging is performed at room temperature for 24 hours. Thereafter, a first artificial aging treatment is performed in which the wrought material is heated at a temperature of 100 ° C. for 4 hours using a heat treatment furnace. Next, without removing the wrought material from the heat treatment furnace, the furnace temperature is raised to 160 ° C., and a second artificial aging treatment is performed by heating at 160 ° C. for 8 hours to obtain a sample.

<Strength measurement method>
From the sample, a test piece is collected by a method according to JIS Z2241 (ISO6992-1), and a tensile test for measuring tensile strength, proof stress and elongation is performed. What shows the yield strength of 350 Mpa or more in the result of a tensile test is determined that the strength characteristic is acceptable.

<Metallic structure observation method>
After electrolytic polishing and electrolytic etching of the sample, a microscopic image of the sample surface is obtained with a polarizing microscope having a magnification of 50 to 100 times. Image analysis is performed on the microscopic image, and as described above, the average grain size of the crystal grains constituting the metal structure of the sample is obtained according to the cutting method defined in JIS G0551. The aspect ratio (the ratio of the crystal length in the direction parallel to the hot working direction to the crystal length in the direction perpendicular to the hot working direction) is the average of the directions parallel to the hot working direction as described above. Calculated by dividing the particle size by the average particle size perpendicular to the hot working direction. As a result, an average particle diameter of 500 μm or less and an aspect ratio within the range of 0.5 to 4.0 are determined as preferable results.

<Surface treatment method>
The surface of the sample subjected to the artificial aging treatment is buffed, etched with an aqueous sodium hydroxide solution, and then desmutted. The sample subjected to the desmut treatment is subjected to chemical polishing for 2 minutes at a temperature of 90 ° C. using a phosphoric acid-nitric acid method. The chemically polished sample is anodized at a current density of 150 A / m ² in a 15% sulfuric acid bath to form a 10 μm anodic oxide film. Finally, the sample after the anodizing treatment is immersed in boiling water, and the sealing treatment of the anodized film is performed.

<Surface quality evaluation method>
The surface of the sample subjected to the surface treatment is visually observed. In visual observation, what does not appear a streak pattern, a spot-like pattern, or a point defect on the surface is determined to be acceptable.
Next, the color tone of the surface of the sample is measured by a color difference meter, and the value of each coordinate in the L * a * b * color system described in JIS Z8729 is obtained. As a result, b * value (blue to yellow chromaticity): A value in the range of 0 to 0.8 is determined to be acceptable.

<Stress corrosion cracking test method>
The test is carried out according to JIS H8711 (ISO-9591). From each sample, a C-ring-shaped test piece provided with a notch in a part of the circumference is cut out from a ring shape having an outer diameter of 20 mm, an inner diameter of 17 mm, and an axial thickness of 7 mm. The direction connecting the center of the C-ring shape and the notch is aligned with the direction of extrusion during sample preparation. A stress of 330 MPa is applied to the test piece in a direction in which the C-ring shape is contracted in a direction perpendicular to the extrusion direction. In this loaded state, in a temperature atmosphere of 25 ° C., alternate immersion in which the test piece is alternately immersed in a 3.5% NaCl aqueous solution for 10 minutes and dried for 50 minutes is performed for 720 hours. The test result is determined by the presence or absence of cracks. “No crack” means “good” (◯), and “crack” means “bad” (×).

  Table 3 shows the evaluation results of the samples shown in Tables 1 and 2. In addition, about what was not determined to be acceptable or not preferable in each evaluation result, the evaluation result in Table 3 is underlined.

  As is known from Table 3, Samples 1 to 15 passed all the evaluation items, and exhibited excellent properties in terms of strength, surface quality, and stress corrosion cracking resistance.

  As a representative example of a sample having excellent surface quality, FIG. As is known from the figure, the sample having an excellent surface quality has a metal structure composed of a granular recrystallized structure, and at the same time, no streak pattern is observed in visual confirmation, and there is no spot and high gloss.

Since the sample 16 had too low Zn content, the strength improvement effect was not fully acquired and it was determined that the proof stress was disqualified.
Since the sample 17 had too high Zn content, it was determined that the stress corrosion cracking resistance was inferior and was rejected.
Since the sample 18 had too low Mg content, the strength improvement effect was not fully obtained and it was determined that the proof stress was unacceptable.

Since the sample 19 had too high Mg content, it cracked partially at the time of extrusion, and also the resistance to stress corrosion cracking was inferior, and it was determined to be unacceptable.
Since the sample 20 had a Zn / Mg ratio that was too low, the strength was inferior and it was determined to be unacceptable.
Sample 21 was judged to be rejected because the stress corrosion cracking property was lowered because the Zn / Mg ratio was too high.

Since the sample 22 had too low Cu content, it was determined that the stress corrosion cracking resistance was inferior and it was rejected.
Since the sample 23 had too high Cu content, the surface color tone was yellowish and it was determined to be unacceptable.
In Sample 24, since the Fe content was too high, a fibrous structure was formed. As a result, a streak pattern was visually recognized on the surface, and the sample 24 was determined to be unacceptable.

Since sample 25 had too high Si content, as a result of forming a fibrous structure, the streak pattern was visually recognized on the surface and it was determined to be unacceptable.
In sample 26, since the Mn content was too high, a fibrous structure was formed. As a result, a streak pattern was visually recognized on the surface, and the sample 26 was determined to be unacceptable.
Since sample 27 had too high Cr content, the color of the surface was yellowish and it was determined to be unacceptable.

Since the sample 28 has a Zr content that is too high, as a result of forming a fibrous structure, a streak pattern is visually recognized on the surface, and the sample 28 is determined to be unacceptable.
In Sample 29, since the Ti content was too low, a streak pattern resulting from a coarse ingot structure appeared and it was determined to be unacceptable.
Since the sample 30 had an excessively high Ti content, an intermetallic compound with Al was formed. As a result, streaky and point-like defects were visually recognized on the surface, and the sample 30 was determined to be rejected.

(Example 2)
Next, the Example which concerns on the manufacturing method of the said high strength aluminum alloy is described using Table 4-Table 6. FIG.
In this example, an aluminum alloy (material No. A) containing chemical components shown in Table 4 was used, and samples (No. A1 to A29) were prepared by changing the manufacturing conditions as shown in Tables 5 and 6. The strength of each sample was measured and the metal structure was observed. Furthermore, after surface-treating each sample, the surface quality was evaluated.
Below, the manufacturing conditions of each sample are explained in detail. The strength measurement method, metal structure observation method, surface treatment method, and surface quality evaluation method for each sample were performed in the same manner as in Example 1.

<Sample manufacturing conditions>
An ingot with a diameter of 90 mm having the chemical components described in Table 4 is cast by semi-continuous casting. Thereafter, using the combination of temperature, time or average cooling rate shown in Table 5 and Table 6, the ingot is subjected to homogenization treatment, hot extrusion processing, rapid cooling treatment, first artificial aging treatment and second artificial aging treatment. Apply in this order to obtain each sample. In addition, the room temperature aging time described in Tables 5 and 6 means the time from when the wrought material reaches room temperature until the first artificial aging treatment is performed after the rapid cooling treatment.

  Table 7 shows the evaluation results of the samples prepared as described above. In addition, about the thing which was not determined with the pass in each measurement result, or the thing which was not determined with the preferable result, the said evaluation result in Table 7 was underlined and shown.

  As is known from Table 7, Samples A1 to A17 passed all the evaluation items and exhibited excellent characteristics in both strength and surface quality.

Since the heating temperature in the homogenization process was too low for sample A18, the yield strength was less than 350 MPa, and the sample A18 was determined to be rejected. At the same time, the crystal grains became coarse, and spotted patterns were also visually recognized on the surface.
Sample A19 was judged to be unacceptable because its proof stress was less than 350 MPa because the treatment time in the homogenization treatment was too short. At the same time, the crystal grains became coarse, and spotted patterns were also visually recognized on the surface.

  In sample A20, the heating temperature of the ingot before hot extrusion was too high, and as a result of partial melting at the time of extrusion, hot work cracking occurred, and processing after the rapid cooling treatment could not be performed.

In Sample A21, the average cooling rate in the rapid cooling treatment was too low, so that the quenching effect was insufficient, and the proof stress was less than 350 MPa.
Since the processing temperature in the second artificial aging treatment of Sample A22 was too low, the stress corrosion cracking resistance was insufficient and the sample A22 was determined to be rejected.

Sample A23 was over-aged because the treatment temperature in the second artificial aging treatment was too high, and the yield strength was less than 350 MPa, and the sample A23 was determined to be rejected.
Sample A24 was judged to be rejected because the treatment time in the second artificial aging treatment was too short, so that age hardening was insufficient and the proof stress was less than 350 MPa, and the stress corrosion cracking resistance was insufficient.

Sample A25 was over-aged because the treatment time in the second artificial aging treatment was too long, and the yield strength was less than 350 MPa, which was determined to be unacceptable.
Sample A26 was subjected to only one stage of artificial aging treatment. However, since the treatment temperature in the artificial aging treatment was too low, the stress corrosion cracking resistance was insufficient, and the sample A26 was determined to be rejected.

Sample A27 was subjected to only one stage of artificial aging treatment, but because the treatment temperature in the artificial aging treatment was too high, it was overaged and the yield strength was less than 350 MPa, and it was determined to be unacceptable.
In Sample A28, the treatment time in the first artificial aging treatment was too short, so that age hardening was insufficient and the proof stress was less than 350 MPa, and the sample A28 was determined to be unacceptable.
Test A29 was over-aged because the treatment time in the first artificial aging treatment was too long, and the yield strength was less than 350 MPa, and it was determined to be unacceptable.

  FIG. 2 shows a metal structure observation result of sample A19 as a representative example of the sample in which the streak pattern is visually recognized among the samples whose surface quality is not acceptable. The sample in which the streak pattern was visually recognized has a metal structure composed of a fibrous structure, as is known from FIG.

Claims (5)

In high-strength aluminum alloy that is anodized,
In mass%, Zn: 5.0% to 7.0%, Mg: 2.2% to 3.0%, Cu: 0.01% to 0.10%, Zr: 0.10% or less Cr: 0.02% or less, Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less, Ti: 0.001% or more and 0.05% or less, and the balance Having a chemical component having a Zn / Mg ratio of 1.7 or more and 3.1 or less, and consisting of Al and inevitable impurities,
Yield strength is 350 MPa or more,
A high-strength aluminum alloy characterized in that the metal structure is a recrystallized structure.   The recrystallized structure has an average grain size of 500 μm or less, and the crystal grain length in the direction parallel to the hot working direction is 0 with respect to the crystal grain length perpendicular to the hot working direction. The high-strength aluminum alloy according to claim 1, wherein the strength is 5 to 4 times. A method for producing the high-strength aluminum alloy according to claim 1 or 2,
In mass%, Zn: 5.0% to 7.0%, Mg: 2.2% to 3.0%, Cu: 0.01% to 0.10%, Zr: 0.10% or less Cr: 0.02% or less, Fe: 0.30% or less, Si: 0.30% or less, Mn: 0.02% or less, Ti: 0.001% or more and 0.05% or less, and the balance Is made of Al and inevitable impurities, and ingot having a chemical component having a Zn / Mg ratio of 1.7 or more and 3.1 or less,
A homogenization treatment is performed in which the ingot is heated at a temperature of 540 ° C. to 580 ° C. for 1 to 24 hours,
In the state where the temperature of the ingot at the start of processing is 440 ° C. to 560 ° C., the ingot is hot-worked to obtain a wrought material
After starting the cooling while the temperature of the wrought material is 400 ° C. or higher, the average cooling rate while the temperature of the wrought material is in the range of 400 ° C. to 150 ° C. is 1 ° C./second to 300 ° C./second. Performs a rapid cooling process to cool by controlling to less than a second,
Cooling the temperature of the wrought material to room temperature by the rapid cooling treatment or subsequent cooling;
Then, the manufacturing method of the high strength aluminum alloy characterized by performing artificial aging treatment with respect to this wrought material.   As the artificial aging treatment, a first artificial aging treatment is performed in which the wrought material is heated at a temperature of 80 to 120 ° C. for 1 to 5 hours, and then the wrought material is 145 continuously with the first artificial aging treatment. The method for producing a high-strength aluminum alloy according to claim 3, wherein a second artificial aging treatment is performed by heating at a temperature of ~ 200 ° C for 2 to 15 hours.   The method for producing a high-strength aluminum alloy according to claim 3, wherein the wrought material is heated at a temperature of 145 to 170 ° C for 1 to 24 hours as the artificial aging treatment.