JP5023233B1 - High strength aluminum alloy material and manufacturing method thereof - Google Patents

Abstract

A high-strength aluminum alloy excellent in both strength and surface quality is provided.
Zn: 5.0% (mass%, the same applies below) to 6.5%, Mg: 0.50% to less than 1.0%, Cu: less than 0.20%, Fe: 0.30 %: Si: 0.30% or less, Mn: less than 0.05%, Cr: less than 0.05%, Zr: 0.05% or more and less than 0.20%, Ti: 0.001% or more and 0.05 % Or less and the balance has chemical components composed of Al and inevitable impurities. It consists of a fibrous structure having a proof stress of 300 MPa or more and an average width of each fibrous crystal grain of 30 μm or more.
[Selection figure] None

Description

  The present invention relates to a high-strength aluminum alloy material used for parts where both strength characteristics and appearance characteristics are important, such as transportation equipment, sports equipment, and machine parts.

  Increasing use of high-strength and lightweight aluminum alloys as materials used in applications where both strength and appearance characteristics are important, such as transportation equipment, sports equipment, and machine parts. Since durability is required for these applications, an aluminum alloy having a proof stress of 300 MPa or more is desired.

  As an aluminum alloy exhibiting such high strength, a 7000 series aluminum alloy in which Zn and Mg are added to aluminum is known. The 7000 series aluminum alloy shows high strength because Al-Mg-Zn series precipitates age. Further, among 7000 series aluminum alloys, those in which Cu is added in addition to Zn and Mg exhibit the highest strength among the aluminum alloys.

  The 7000 series aluminum alloy is manufactured by, for example, hot extrusion or the like, and is used for transportation equipment such as aircraft and vehicles, sports parts, machine parts, and the like that require high strength. Properties required for use in these applications include stress corrosion cracking resistance, impact absorption, and extensibility in addition to strength. As an example of an aluminum alloy that satisfies the above characteristics, for example, an aluminum alloy extruded material described in Patent Document 1 has been proposed.

JP 2007-119904 A

However, in an aluminum alloy having a high strength of 7000 series manufactured by the conventional component range and the conventional manufacturing method, for example, when anodizing is performed for the purpose of preventing surface scratches, a streak pattern is formed on the surface. There was an appearance problem that it would appear.
In addition, the aluminum alloy is desired to have a silver color in order to bring out a high-class feeling after performing surface treatment such as anodizing treatment. However, when the conventional 7000 series aluminum alloy is anodized, there is a problem in appearance that the surface is strongly yellowish.
As described above, the conventional 7000 series aluminum alloy is difficult to adopt because the streak pattern and the color tone change appearing after the surface treatment cause problems in the surface quality.

  The present invention has been made in view of such a background, and intends to provide a high-strength aluminum alloy material excellent in surface quality and a method for producing the same.

In one embodiment of the present invention, Zn: 5.0% (mass%, the same applies below) to 6.5%, Mg: 0.50% to less than 1.0%, Cu: less than 0.20%, Fe: 0.30% or less, Si: 0.30% or less, Mn: less than 0.05%, Cr: less than 0.05%, Zr: 0.05% or more and less than 0.20%, Ti: 0.001% or more Containing 0.05% or less, the remainder having a chemical component consisting of Al and inevitable impurities,
Yield strength is 300 MPa or more,
The metal structure observed on the surface consists of a fibrous structure,
The fibrous structure is in a high-strength aluminum alloy material characterized in that the average value of the width of each fibrous crystal grain in the direction perpendicular to the hot working direction on the surface is 30 μm or more (Claim 1).

Another aspect of the present invention is Zn: 5.0% (mass%, the same applies hereinafter) to 6.5% or less, Mg: 0.50% to less than 1.0%, Cu: less than 0.20%, Fe : 0.30% or less, Si: 0.30% or less, Mn: less than 0.05%, Cr: less than 0.05%, Zr: 0.05% or more and less than 0.20%, Ti: 0.001% An ingot containing 0.05% or less and the balance having a chemical component consisting of Al and inevitable impurities,
A homogenization treatment is performed in which the ingot is heated at a temperature exceeding 400 ° C and not more than 530 ° C for 1 to 24 hours,
Thereafter, the ingot is hot-worked at a temperature of 440 ° C. to 560 ° C. to obtain a wrought material,
While the temperature of the wrought material is 400 ° C. or higher, a rapid cooling treatment is performed to cool to a temperature of 150 ° C. or lower at a cooling rate of 5 to 1000 ° C./second ,
Cooling the temperature of the wrought material to room temperature by the rapid cooling treatment or subsequent cooling;
Then, it is in the manufacturing method of the high intensity | strength aluminum alloy material characterized by performing the artificial aging treatment which heats for 5 to 30 hours at the temperature of 100 to 170 degreeC (Claim 2).

The high-strength aluminum alloy material has the specific chemical component. Therefore, it has a yield strength equivalent to that of the conventional 7000 series aluminum alloy material, and can suppress a change in color tone that occurs after the surface treatment, thereby obtaining a good surface quality.
The high-strength aluminum alloy material has a yield strength of 300 MPa or more. Therefore, it is possible to satisfy the requirements in terms of strength as a material used for applications in which both strength characteristics and appearance characteristics are regarded as important.
The metal structure of the high-strength aluminum alloy material has a fibrous structure made of wide fibrous crystal grains having a specific width dimension or more as described above. For this reason, it is possible to suppress the occurrence of a streak pattern on the surface after the anodizing treatment and obtain a good surface quality.
Therefore, the high-strength aluminum alloy material is excellent in both strength and surface quality.

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

  The high-strength aluminum alloy material contains 5.0% or more and 6.5% or less of Zn and 0.50% or more and less than 1.0% of Mg. Zn and Mg coexist in the aluminum alloy to precipitate the η 'phase. Therefore, the strength of the high-strength aluminum alloy material containing both of them is improved by precipitation strengthening.

  When the Zn content is less than 5.0%, the precipitation amount of the η ′ phase is reduced, so that the strength improvement effect is lowered. On the other hand, when the Zn content exceeds 6.5%, the hot workability is lowered, and thus the productivity is lowered.

  On the other hand, when the Mg content is less than 0.50%, the precipitation amount of the η ′ phase is reduced, and the strength improvement effect is lowered. On the other hand, when the Mg content is 1.0% or more, the hot workability is lowered, and thus the productivity is lowered.

  The high-strength aluminum alloy material contains 0.05% or more and less than 0.20% Zr. Zr has an action of suppressing recrystallization by forming an AlZr-based intermetallic compound with Al. Therefore, when Zr is present in the aluminum alloy, the formation of a recrystallized structure is suppressed, and a fibrous structure composed of fibrous crystal grains is formed instead.

  When the content of Zr is less than 0.05%, the effect of suppressing recrystallization is low, resulting in a non-uniform metal structure in which a recrystallized structure and a fibrous structure are mixed. Therefore, the surface quality may be deteriorated, for example, a spotted pattern is visually recognized after the surface treatment. On the other hand, when the amount of Zr added is 0.20% or more, the width of the fibrous crystal grains becomes excessively small, so that a streak pattern is generated on the surface after the surface treatment, and the surface quality may be deteriorated. is there.

  Of the chemical components, the Cu content is restricted to less than 0.20%. Cu may be mixed when a recycled material is used as a raw material for the high-strength aluminum alloy material. When Cu is contained in the aluminum alloy material, the strength is increased due to the effect, but on the other hand, it causes a decrease in surface quality such as a decrease in gloss after chemical polishing and a color change to yellow due to anodization. . Such a decrease in gloss or a decrease in surface quality due to a change in color tone can be suppressed by regulating the Cu content to less than 0.20%.

  Of the above chemical components, Fe is regulated to 0.30% or less, Si to 0.30% or less, Mn to less than 0.05%, and Cr to less than 0.05%. Fe and Si are mixed as impurities in the aluminum metal, and Mn and Cr are components that may be mixed when using recycled materials.

  Among the above four components, Fe, Si and Mn have an action of suppressing recrystallization by forming an AlMn-based, AlMnFe-based or AlMnFeSi-based intermetallic compound with Al. Further, Cr has an action of suppressing recrystallization by forming an AlCr-based intermetallic compound with Al. Therefore, when the four components are mixed in the high-strength aluminum alloy material, formation of a recrystallized structure is suppressed, and a fibrous structure is formed instead.

However, when the above four components are excessively contained, the width of the fibrous crystal grains becomes excessively small. As a result, a streak pattern is generated on the surface after the surface treatment such as anodizing treatment, and the surface quality may be deteriorated.
Such deterioration in surface quality is suppressed by regulating Fe to 0.30% or less, Si to 0.30% or less, Mn to less than 0.05%, and Cr to less than 0.05%. It becomes possible to do.

  The high-strength aluminum alloy material contains 0.001% or more and 0.05% or less of Ti. Ti has the effect | action which refines | miniaturizes an ingot structure | tissue by adding to an aluminum alloy material. As the ingot structure becomes finer, the surface quality can be improved by containing Ti, because there is no unevenness and high gloss is obtained.

  When the Ti content is less than 0.001%, the ingot structure is not sufficiently refined, and the high-strength aluminum alloy material may have uneven gloss. In addition, when the Ti content is more than 0.05%, the surface quality deteriorates due to AlTi intermetallic compounds formed with Al and the like, which easily causes point-like defects. There is a risk.

  Further, the high-strength aluminum alloy material has a proof stress defined by JIS Z2241 (ISO 6892-1) of 300 MPa or more. As a result, it is possible to relatively easily obtain strength characteristics that can cope with the reduction in thickness for weight reduction.

Furthermore, the metal structure constituting the high-strength aluminum alloy material is a fibrous structure composed of fibrous crystal grains having an average width in the direction perpendicular to the hot working direction on the surface of 30 μm or more. When the average value of the crystal grain width is less than 30 μm, the crystal grain boundaries in the width direction of the fibrous crystal grains are densely arranged. For this reason, for example, after performing surface treatment such as anodizing treatment, streak patterns due to crystal grain boundaries appear, and the surface quality may be deteriorated. Therefore, the average value of the width of the fibrous crystal grains is preferably 30 μm or more, and preferably 100 μm or more.
<Metallic structure observation method>
After the sample is electropolished, a microscope 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 an average value of crystal grain widths in a direction perpendicular to the hot working direction is obtained. As a result, those having an average width value of 30 μm or more are determined as preferable results.

  In addition, although the width | variety of the said fibrous crystal grain is so good that it is large, it is substantially difficult to obtain the fibrous structure where the average value of the width of a crystal grain exceeds 400 micrometers. Moreover, the said metal structure can be confirmed by, for example, performing electrolytic polishing on the surface of an aluminum alloy material and observing the obtained surface with a polarizing microscope.

  Next, in the method for producing the high-strength aluminum alloy material, the ingot having the chemical component is subjected to a homogenization treatment in which heating is performed at a temperature exceeding 400 ° C. and not exceeding 530 ° C. for 1 hour to 24 hours. Do.

  When the heating temperature for the homogenization treatment is 400 ° C. or less, the crystallized product of Zn and Mg is hardly dissolved, and the final amount of precipitates may be reduced. As a result, the strength improvement effect by precipitation strengthening is reduced, and the yield strength is reduced. On the other hand, when the heating temperature is higher than 530 ° C., an ArZr-based coarse intermetallic compound is precipitated, and thus the yield strength of the finally obtained stretched material may be less than 300 MPa. Therefore, it is preferable that the temperature of the said homogenization process exceeds 400 degreeC and is 530 degrees C or less.

  Further, when the heating time for the homogenization treatment is less than 1 hour, the crystallization of Zn and Mg is difficult to be dissolved in the same manner as described above, so that the proof stress may be reduced. On the other hand, when the heating time exceeds 24 hours, the crystallized product of Zn and Mg is in a sufficiently solid solution state, 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 processing 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, the rapid cooling process which cools to the temperature of 150 degrees C or less from the state where the temperature of the said extending | stretching material is 400 degreeC or more is performed.
When the temperature of the wrought material before the quenching treatment is less than 400 ° C., quenching becomes insufficient, and the resultant wrought material may have a yield strength of less than 300 MPa. Moreover, when the temperature of the wrought material after the rapid cooling treatment exceeds 150 ° C., quenching becomes insufficient, and the proof stress of the resulting wrought material may be less than 300 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, methods such as fan air cooling, mist cooling, shower cooling or water cooling can be employed.

Further, the cooling rate of the rapid cooling treatment is set to 5 ° C./second or more and 1000 ° C./second or less .
When the cooling rate exceeds 1000 ° C./second, the equipment becomes excessive and an effect commensurate with it cannot be obtained. On the other hand, when the cooling rate is less than 5 ° C./second, quenching becomes insufficient, and thus the yield strength of the obtained wrought material may be less than 300 MPa. Accordingly, the cooling rate should be fast, and is 5 ° C./second or more and 1000 ° C./second or less, preferably 100 ° C./second or more and 1000 ° 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, for example, a method such as fan air cooling, mist cooling, shower cooling, or water cooling can be adopted as in the rapid cooling process.

  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 cooled to room temperature as described above is heated at a temperature of 100 ° C. to 170 ° C. for 5 hours to 30 hours. If the artificial aging treatment is out of the above temperature range or time range, the yield strength of the obtained stretched material may be less than 300 MPa, and it becomes difficult to obtain a stretched material having sufficient strength characteristics.

Example 1
Examples relating to the high-strength aluminum alloy material will be described with reference to Tables 1 and 2.
In this example, as shown in Table 1, samples (No. 1 to No. 25) 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 having a diameter of 90 mm having the chemical components described in Table 1 is cast by semi-continuous casting. Then, the ingot is heated for 12 hours at a temperature of 450 ° C. Thereafter, in the state where the temperature of the ingot is 510 ° 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 490 ° C., a rapid cooling process is performed in which the wrought material is cooled to 100 ° C. at a cooling rate of 100 ° C./second. Then, the temperature of the wrought material subjected to the rapid cooling treatment is cooled to room temperature, stored at room temperature for 24 hours, and then subjected to artificial aging treatment in which heating is performed at a temperature of 150 ° C. for 12 hours to obtain a sample. .

<Strength measurement method>
A test piece is collected from the sample by a method in accordance with JIS Z2241 (ISO6992-1), and the tensile strength, proof stress, and elongation are measured. As a result, those showing a yield strength of 300 MPa or more are determined to be acceptable.

<Metallic structure observation method>
After the sample is electropolished, a microscope 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 an average value of crystal grain widths in a direction perpendicular to the hot working direction is obtained. As a result, those having an average width value of 30 μm or more 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 1 minute 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 with a color difference meter, and the value of each coordinate in the L ^* a ^* b ^* color system described in JIS Z8729 (ISO 7724-1) is obtained. As a result, L ^* value (lightness): 87 to 97, a ^* value (green to red chromaticity): -1.5 to 0.5, b ^* value (blue to yellow chromaticity): -1 to The thing in the range of 1.5 is determined to be a pass. In addition, what each value falls in the said range is judged to be silver visually, and it is tinged with a color so strong that it remove | deviates from the said range.

  Table 2 shows the evaluation results of the samples prepared as described above. In addition, about what was not determined to be acceptable or not preferable in each evaluation result, the evaluation result in Table 2 is underlined.

  As known from Table 2, sample no. 1-No. No. 13 passed all the evaluation items and showed excellent properties in both strength and surface quality.

Sample No. In No. 14, since the Zn content was too low, the effect of improving the strength was not sufficiently obtained, and the proof stress was determined to be unacceptable.
Sample No. In No. 15, since the Zn content was too high, the hot workability was poor, and hot extrusion was impossible with substantial equipment.

Sample No. In No. 16, since the Mg content was too low, a sufficient strength improvement effect was not obtained, and the proof stress was determined to be unacceptable.
Sample No. In No. 17, since the Mg content was too high, the hot workability was poor, and hot extrusion was impossible with substantial equipment.

  Sample No. In No. 18, since the Cu content was too high, the surface color tone was yellowish and judged to be unacceptable.

Sample No. In No. 19, since the Fe content was too high, a fine fibrous structure was formed. As a result, a streak pattern was visually recognized on the surface, and it was determined to be unacceptable.
Sample No. In No. 20, since the Si content was too high, a fine fibrous structure was formed.

Sample No. In No. 21, since the Mn content was too high, a fine fibrous structure was formed.
Sample No. In No. 22, since the Cr content was too high, a fine fibrous structure was formed.

  Sample No. In No. 23, since the Zr content was too high, a fine fibrous structure was formed.

Sample No. In No. 24, since the Ti content was too low, a metal structure in which a recrystallized structure and a fibrous structure were mixed was formed.
Sample No. In No. 25, since the Ti content was too high, an intermetallic compound with Al was formed.

(Example 2)
Next, the Example which concerns on the manufacturing method of the said high intensity | strength aluminum alloy is demonstrated using Table 3-Table 5. FIG.
In this example, samples (No. A to No. Y) were prepared by changing the production conditions of aluminum alloy materials containing chemical components shown in Table 3 as shown in Table 4, and the strength of each sample was measured. Tissue observation was performed. 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 3 is cast by semi-continuous casting. Thereafter, using a combination of processing temperature, processing time or cooling time shown in Table 4, the ingot is subjected to homogenization processing, hot extrusion processing, rapid cooling processing and artificial aging processing in this order to obtain a sample. In addition, the room temperature aging time described in Table 4 means the time from when the wrought material reaches room temperature until the artificial aging treatment is performed after the rapid cooling treatment.

  Table 5 shows the evaluation results of the samples prepared as described above. In addition, about the thing which was not determined to be pass in each measurement result, or the thing which was not determined to be a preferable result, the said evaluation result in Table 5 was shown with an underline.

  As known from Table 5, sample no. A-No. O passed all the evaluation items and showed excellent properties in both strength and surface quality.

Since the heating temperature in the homogenization process was too low for the sample P, the yield strength was less than 300 MPa, and it was determined to be unacceptable.
Since the heating temperature in the homogenization process was too high for the sample Q, the yield strength was less than 300 MPa and it was determined to be rejected.
Since the processing time in the homogenization process was too short for the sample R, the yield strength was less than 300 MPa and it was determined to be rejected.

  Since the heating temperature of the ingot before the hot extrusion process was too high for the sample S, as a result of partial melting during the extrusion process, a hot work crack occurred and the process after the rapid cooling process could not be performed.

Since the cooling rate in the rapid cooling process was too low for the sample T, quenching was insufficient, and the proof stress was less than 300 MPa.
In Sample U, the temperature of the wrought material after the rapid cooling treatment was too high, so that quenching was insufficient and the proof stress was less than 300 MPa, and it was determined to be unacceptable.

Since the heating temperature in the artificial aging treatment was too low for the sample V, age hardening was insufficient, and the proof stress was less than 300 MPa, and it was determined to be unacceptable.
Since the heating temperature in the artificial aging treatment was too high, the sample W was over-aged and the proof stress was less than 300 MPa, and it was determined to be unacceptable.
In Sample X, the treatment time in the artificial aging treatment was too short, so that age hardening was insufficient, and the proof stress was less than 300 MPa, and it was determined to be unacceptable.
Sample Y was over-aged because the treatment time in the artificial aging treatment was too long, and the proof stress was less than 300 MPa, and it was determined to be unacceptable.

Claims (2)

Zn: 5.0% (mass%, the same applies hereinafter) to 6.5% or less, Mg: 0.50% to less than 1.0%, Cu: less than 0.20%, Fe: 0.30% or less, Si : 0.30% or less, Mn: less than 0.05%, Cr: less than 0.05%, Zr: 0.05% or more and less than 0.20%, Ti: 0.001% or more and 0.05% or less And the balance has a chemical component consisting of Al and inevitable impurities,
Yield strength is 300 MPa or more,
The metal structure observed on the surface consists of a fibrous structure,
The fibrous structure is a high-strength aluminum alloy material characterized in that the average value of the width of each fibrous crystal grain in the direction perpendicular to the hot working direction on the surface is 30 μm or more. Zn: 5.0% (mass%, the same applies hereinafter) to 6.5% or less, Mg: 0.50% to less than 1.0%, Cu: less than 0.20%, Fe: 0.30% or less, Si : 0.30% or less, Mn: less than 0.05%, Cr: less than 0.05%, Zr: 0.05% or more and less than 0.20%, Ti: 0.001% or more and 0.05% or less And producing an ingot having a chemical component consisting of Al and inevitable impurities in the balance,
A homogenization treatment is performed in which the ingot is heated at a temperature exceeding 400 ° C and not more than 530 ° C for 1 to 24 hours,
Thereafter, the ingot is hot-worked at a temperature of 440 ° C. to 560 ° C. to obtain a wrought material,
While the temperature of the wrought material is 400 ° C. or higher, a rapid cooling treatment is performed to cool to a temperature of 150 ° C. or lower at a cooling rate of 5 to 1000 ° C./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 material characterized by performing the artificial aging treatment which heats for 5 to 30 hours at the temperature of 100 to 170 degreeC.