JP2023146104A - Aluminum alloy sheet and method for producing the same - Google Patents

Abstract

To provide an aluminum alloy sheet with inhibited formation of MgO on its surface layer, ensuring good surface quality, and a method for producing the aluminum alloy sheet.SOLUTION: An aluminum alloy sheet according to the present invention contains Mg in an amount of 0.05 mass% or more and 2.5 mass% or less. The area percentage of spinel formed on the surface is 10% or less within a 2500 μm2 region observed in the surface layer direction. The surface Mg level is 20 mass% or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to an aluminum alloy plate and a method for manufacturing the same.

In recent years, aluminum alloys have been used in a variety of applications, such as transportation equipment and beverage cans, due to their light weight and advantages in terms of recycling. Aluminum alloys containing Mg are often used for these applications, but by adding Mg, crystalline oxides such as MgO and MgAl ₂ O ₄ are generated on the surface during material manufacturing. This causes problems such as a decrease in surface treatment properties and bondability.
Conventionally, a technique has been employed to suppress the influence of Mg by removing the entire oxide film of a material made of aluminum with Mg added, by performing alkaline cleaning and cleaning with sulfuric acid.

For example, in Patent Document 1 below, as a pretreatment method for chemical conversion treatment of an aluminum alloy, after performing solvent cleaning or alkaline cleaning, the surface is treated with a treatment liquid consisting of a sulfuric acid acidic solution or a sulfuric acid acidic solution containing fluorine ions. The technology has been disclosed.

Japanese Unexamined Patent Publication No. 60-096772

In aluminum alloys containing Mg, MgO is generated on the surface during the material manufacturing process, so for example, during drawing processing, scratches occur on the surface, during surface treatment, processing unevenness occurs in areas where MgO grows, and during bonding. This causes various problems such as poor bonding.
Methods for removing crystalline oxides such as MgO that are generated on the surface during material preparation have existed for a long time, but in the first place, it is not possible to prevent the generation of these crystalline oxides or to control the amount of generation. For example, it can be expected to simplify the processing process and improve the surface quality of the product.

The present invention was made in view of the above-mentioned circumstances, and clarifies the mechanism by which MgO is formed on the surface of an aluminum alloy containing Mg, thereby suppressing the formation of MgO, which was one of the problems in conventional manufacturing. By finding a method to do so, the present invention was achieved.
In consideration of the reason why MgO is formed on the surface of an aluminum alloy, the present invention adjusts the amount of Mg from the Al base material that diffuses into the initial natural oxide film mainly composed of Al ₂ O ₃ during material production. Furthermore, it is an object of the present invention to provide an aluminum alloy plate in which the formation of MgO on the surface is suppressed by controlling the temperature at which an oxide film containing diffused Mg crystallizes, and a method for manufacturing the same.

(1) The aluminum alloy plate of the present invention is an aluminum alloy plate containing 0.05% by mass or more and 2.5% by mass or less of Mg, and the area ratio of spinel formed on the surface is The Mg concentration on the surface is within 10% in an area of 2500 μm ² and is 20% by mass or less.
(2) In the aluminum alloy plate of the present invention, the thickness of the oxide film on the surface is preferably 40 nm or less.

(3) In the aluminum alloy plate of the present invention, the average crystal grain size at the outermost surface is 50 μm or more in equivalent circle diameter, and the average aspect ratio of the crystal grains in a cross section perpendicular to the plate width direction is 1.5 or more on average. It is preferable that there be.
(4) In the aluminum alloy plate of the present invention, it is preferable that the number of coarse aggregates of oxide formed on the surface is 10 or less in an area of 100 μm ² .
(5) In the aluminum alloy plate of the present invention, it is preferable that an element that forms an oxide having a specific crystal structure together with Al, Mg, and O is contained in an amount of 0.05% by mass or more and 1.5% by mass or less.

(6) The method for producing an aluminum alloy plate according to the present invention contains Mg of 0.05% by mass or more and 2.5% by mass or less, is processed into a plate shape by hot rolling and cold rolling, and is subjected to homogenization heat treatment. A method for manufacturing an aluminum alloy plate that is manufactured by subjecting it to annealing treatment, in which the heating conditions of homogenization heat treatment and annealing treatment and the conditions of hot rolling are controlled, and the area ratio of spinel formed on the surface is expressed. In observation in the layer surface direction, the Mg concentration on the surface is adjusted to within 10% in an area of 2500 μm ² and to 20% by mass or less.
(7) In the method for manufacturing an aluminum alloy plate according to the present invention, it is preferable to adjust the thickness of the oxide film on the surface to 40 nm or less.

(8) In the method for manufacturing an aluminum alloy plate according to the present invention, the average crystal grain size at the outermost surface is set to 50 μm or more in equivalent circle diameter, and the average aspect ratio of the crystal grains in a cross section perpendicular to the plate width direction is set to 1. It is preferable to set it to 5 or more.
(9) In the method for manufacturing an aluminum alloy plate according to the present invention, it is preferable that the number of coarse aggregates of oxide formed on the surface be 10 or less in an area of 100 μm ² .
(10) In the method for producing an aluminum alloy plate according to the present invention, it is preferable that an element that forms an oxide having a specific crystal structure together with Al, Mg, and O is contained in an amount of 0.05% by mass or more and 1.5% by mass or less .

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide an aluminum alloy plate with suppressed MgO formation in the surface layer and with excellent surface quality.

FIG. 2 is a conceptual diagram showing crystal grains of an aluminum alloy plate according to the present invention. FIG. 2 is a partial cross-sectional view showing an example of an oxide film formed on the outermost surface of an aluminum alloy plate. FIG. 2 is an enlarged cross-sectional view showing a state in which MgO is generated on the surface of an aluminum alloy plate. 2 is a microstructure photograph showing an example of the surface structure of an aluminum alloy plate according to an example, in which (A) is a microstructure photograph showing the surface of an aluminum alloy plate on which spinel has been formed, and (B) is a part of the surface shown in (A). This is an enlarged photo. Examples of samples used for surface treatment evaluation in Examples are shown, in which (A) is a surface photograph of a sample showing good surface properties, and (B) is a surface photo of a sample showing abnormal surface properties. It is a graph which shows the surface analysis result of the aluminum alloy plate after 400 degreeC heat treatment. It is a graph which shows the surface analysis result of the aluminum alloy plate after 450 degreeC heat treatment. It is a microstructure photograph showing MgO formed on the surface of an aluminum alloy plate. It is a photograph showing a cross section of a portion where MgAl ₂ O ₄ and MgO are generated on the surface of an aluminum alloy plate. A graph showing the analysis results of the portion where MgAl ₂ O ₄ and MgO shown in FIG. 9 are generated. It is a cross-sectional photograph showing an analysis position separated from a portion where MgAl ₂ O ₄ and MgO are generated on the surface of an aluminum alloy plate. 12 is a graph showing the analysis results of the analysis positions shown in FIG. 11.

Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings. Note that in the drawings used in the following description, characteristic portions may be shown enlarged for convenience in order to make the characteristics easier to understand.

The aluminum alloy plate 11 according to the first embodiment is, for example, made of an aluminum alloy containing 0.05% by mass or more and 2.5% by mass or less of Mg, with the remainder being Al and inevitable impurities. The aluminum alloy used here is not particularly limited in composition other than Mg, and may further contain necessary additive elements.
Therefore, for example, referring to general aluminum alloys specified by JIS, it is widely applied to aluminum alloys containing Mg in the above range, regardless of the composition system from 1000 series aluminum alloys to 8000 series aluminum alloys. be able to.

FIG. 1 is a partially enlarged view showing an example of the metallographic structure of the aluminum alloy plate of the first embodiment, and the aluminum alloy plate 11 of this form is produced by hot rolling and cold rolling from an aluminum alloy ingot having the above-mentioned composition. This is a strip-shaped plate material obtained through inter-rolling.
FIG. 1 shows a partially enlarged cross section of a strip-shaped aluminum alloy plate 11 perpendicular to the width direction of the plate. In FIG. 1, the thickness direction of the aluminum alloy plate 11 is parallel to the Z direction (vertical direction), and the longitudinal direction of the aluminum alloy plate 11 is parallel to the Y direction (horizontal direction). The width direction of 11 is a direction parallel to the X direction (a direction perpendicular to the paper surface of FIG. 1).

The aluminum alloy plate 11 is a polycrystalline body, and the plurality of crystal grains 11a constituting the aluminum alloy plate 11 have an average length in the plate thickness direction of a, and an average length in the longitudinal direction (rolling direction) of b. In this case, the aspect ratio b/a is 1.5 or more.
That is, as shown in FIG. 1, the plurality of crystal grains 11a have a shape that is slightly longer in the length direction than in the thickness direction.
Furthermore, by increasing the aspect ratio of the crystal grains inside the aluminum alloy plate 11, the diffusion path of Mg becomes longer and diffusion of Mg to the outermost surface can be suppressed.
On the other hand, if the aspect ratio is excessively large, surface defects will occur during material processing.
Therefore, the aspect ratio is preferably about 1.5 or more and 4.0 or less, more preferably about 1.7 or more and 3.7 or less.

In the aluminum alloy constituting the aluminum alloy plate 11, elements that form an oxide having a specific crystal structure together with Al, Mg, and O are concentrated into an oxide film by heat treatment, similar to Mg. These elements enter the oxide film where Mg may exist, thereby suppressing the diffusion of excessive Mg and reducing the formation of MgO. Examples of these elements include Cr, Fe, Co, Ni, Cu, Zn, and Mn, which form a MgAl ₂ O ₄ type structure.
Therefore, the aluminum alloy constituting the aluminum alloy plate 11 contains one or more elements selected from Cr, Fe, Co, Ni, Cu, Zn, Mn, etc. as other additive elements within a desired range. It may be contained.
Among these elements, one or more of Cr, Ni, and Co can be contained in an amount of about 0.05 to 0.5% by mass, and Fe can be contained in an amount of 0.5 to 1.0% by mass. Cu can be contained in an amount of about 0.05 to 1.0% by mass, and one or both of Zn and Mn can be contained in an amount of about 0.05 to 1.5% by mass. Since the upper limit that can be added to Al differs for each element, the upper limit value differs for each element as described above.

As shown in FIG. 2, the above-mentioned aluminum alloy plate 11 has an oxide film 11A on the surface, for example, the upper surface. Further, when the aluminum alloy plate ₁₁ is heated to a temperature higher than the spinel crystallization temperature, such as 400° C. or higher, as illustrated in _FIG . generated. When Mg is supplied from the inside of the aluminum alloy plate 11 to the spinel 11B generation region, a precipitated portion 11D of MgO is generated above the spinel 11B region and on the surface side of the oxide film 11A. Therefore, controlling the production of spinel leads to suppressing the production of MgO.
In the aluminum alloy plate 11 of this embodiment, when subjected to heat treatment at 300 to 500°C for one to several hours, the area where MgAl ₂ O ₄ is generated on the surface of the aluminum alloy plate 11 is 2500 μm ² . It is desirable that it is 10% or less.

The oxide film 11A generated on the surface of the aluminum alloy plate 11 is amorphous mainly composed of Al and O, and although it does not have a specific crystal structure, it is bonded with a certain degree of order, and other elements can enter. There are many pores. Therefore, if the oxide film is thermodynamically stable, other elements will form a solid solution in the oxide film. Therefore, during the heat treatment performed to manufacture the aluminum alloy plate 11, other elements may diffuse into the oxide film 11A and become concentrated in the oxide film. At this time, when Mg is excessively concentrated, the oxide film 11A crystallizes to generate spinel 11B, and then MgO precipitates 11D are generated, deteriorating the surface quality.
Therefore, it is desirable that the Mg concentration on the aluminum surface after annealing is 20 wt% or less, and it is further desirable that the number of precipitates 11D present on the aluminum surface be 10 or less in a 100 μm ² area.

The oxide film (Al ₂ O ₃ ) grows by heat treatment during the material manufacturing process, and as described above, the oxide film 11A crystallizes, thereby degrading the surface quality. As the thickness of the oxide film 11A increases, crystallization of the film occurs, so by controlling the thickness of the oxide film 11A, a material with good surface quality can be obtained. It is desirable that the thickness of the oxide film 11A be 40 nm or less.

In the aluminum alloy plate 11, the diffusion of Mg through the grain boundaries is faster than the diffusion through the inside of the grains, so if the grain size is too small, the supply of Mg to the oxide film 11A increases, causing oxidation. Crystallization of the film 11A is promoted. Therefore, the larger the grain size is, the less MgO on the surface of the aluminum alloy plate 11 can be obtained.

Figure 4 (A) shows that an aluminum alloy plate made of an aluminum alloy with a composition of Al-10Si-0.5Mg is heat-treated by gradually increasing the temperature of the sample to 600°C using an ESEM (environmentally controlled scanning electron microscope). It is a structure photograph showing a part of the result of sequentially observing the surface while applying.
When an aluminum alloy plate containing Mg has excessive Mg in its oxide film and is heated above the temperature at which the oxide film crystallizes, the surface of the aluminum alloy plate as shown in FIG. Many spinels that can be observed as fine white dots are generated. When the surface of this aluminum alloy plate is further magnified and observed, the existence of an agglomerated part in which a plurality of crystallized parts are aggregated is observed as shown in the microstructure photograph shown in FIG. 4(B).

The agglomerated portion is a region where a large amount of crystallized MgAl ₂ O ₄ , MgO, etc. are present. These crystallized MgAl ₂ O ₄ and MgO cause non-uniform etching when performing surface treatment on an aluminum alloy plate. In addition, when processing an aluminum alloy plate, there is a risk that the produced hard crystals will rub against each other, causing scratches on the surface, which may reduce the surface quality of the processed aluminum alloy plate.

When obtaining the above-mentioned aluminum alloy plate 11, it is preferable to perform a homogenization treatment on an ingot obtained by casting from a molten aluminum alloy having the above-mentioned target composition.
A typical homogenization process during the production of aluminum alloys is carried out at a temperature range of 300°C to 600°C. When an aluminum alloy is heat-treated at a high temperature, MgO is concentrated in the oxide film and the oxide film is crystallized, promoting the formation of MgO. Furthermore, when heat treatment is performed at a low temperature, compounds are finely precipitated inside the aluminum alloy, recrystallized grains become fine, and as a result, diffusion of Mg to the surface via grain boundaries is promoted. Therefore, in this embodiment, the homogenization treatment of the aluminum alloy is preferably carried out at a temperature range of 400°C to 500°C.

The ingot after the homogenization treatment is subjected to a soaking treatment and then hot rolled at a high temperature to a predetermined thickness, for example, about 5 mm. During hot rolling, if the rolling time at a temperature of 400° C. or more is prolonged, MgO will be concentrated in the oxide film and the oxide film will be crystallized, promoting the production of MgO. Therefore, it is desirable that the rolling time at a temperature of 400° C. or higher be short during hot rolling. Therefore, in this embodiment, it is desirable that the time for hot rolling performed at 400° C. or higher is 20 minutes or less. Moreover, when the finish temperature of hot rolling is low, recrystallized grains become fine, and as a result, diffusion of Mg to the surface via grain boundaries is promoted. Therefore, it is desirable that the finishing temperature of hot rolling is 250°C or higher. The aluminum plate material after hot rolling is cold rolled and then annealed. The aluminum alloy plate 11 can be obtained by cold rolling to a desired plate thickness, for example, a plate thickness of about 1.0 mm.
In annealing, as in the homogenization process, Mg diffuses into the oxide film, and the oxide film crystallizes, thereby promoting the production of MgO. Therefore, it is desirable that the heating conditions during annealing be below the crystallization temperature of the oxide film while suppressing the diffusion of Mg. Therefore, the annealing conditions can be selected from the range of 200 to 450° C. for 1 to 12 hours, but it is desirable to select the annealing conditions at the lowest possible temperature and for the shortest time.
However, if heat treatment is performed at a temperature exceeding 400° C. and a large amount of Mg is added, MgO will be generated, so from the viewpoint of MgO formation, it is advantageous not to perform heat treatment at a temperature of 400° C. or higher. However, if the homogenization heat treatment is performed at a low temperature, the recrystallization temperature increases, and the annealing temperature needs to be 400° C. or higher.

The aluminum alloy plate 11 obtained by the manufacturing method described above is an aluminum alloy plate containing 0.05% by mass or more and 2.5% by mass or less of Mg, and the area ratio of spinel formed on the surface is When observed in the layer surface direction, the Mg concentration on the surface was within 10% in a 2500 μm ² area, and was 20% by mass or less.
In this aluminum alloy plate 11, it is preferable that the thickness of the oxide film 11A is 40 nm or less. In this aluminum alloy plate 11, it is preferable that the average crystal grain size at the outermost surface is 50 μm or more in equivalent circle diameter, and the average aspect ratio of the crystal grains in a cross section perpendicular to the plate width direction is 1.5 or more on average. . Further, in the aluminum alloy plate 11, an element that forms an oxide having a specific crystal structure together with Al, Mg, and O can be included in an amount of 0.05% by mass or more and 1.5% by mass or less.

With the above aluminum alloy plate 11, the area ratio of spinel present on the surface is kept low and the Mg concentration on the surface is kept low, so it is possible to provide an aluminum alloy plate with good surface quality and suppressed MgO in the surface layer. .
Aluminum alloy plates with good surface quality have excellent bondability when bonded by means such as brazing. Furthermore, it is possible to provide an aluminum alloy plate that is less likely to cause surface roughness or scratches during processing when used as can material. Moreover, when performing surface treatment such as etching, it is possible to provide an aluminum alloy plate with excellent surface treatment properties that does not cause uneven etching.

Al-Mg-based aluminum alloys containing 0.05 to 2.5% by mass of Mg, with the remainder consisting of Al and unavoidable impurities, as shown in Tables 1 and 2 below, and containing Mg and further containing Zn. Each composition shown in Tables 1 and 2 below contains 0.05 to 1.5 wt% of an element selected from , Mn, Cu, Cr, Fe, Co, and Ni, with the balance consisting of Al and inevitable impurities. An Al-Mg aluminum alloy was cast.

The obtained cast material was subjected to homogenization treatment, and the homogenization treatment was carried out at 250° C. to 500° C. for each sample as shown in Table 3 below.
After rolling to a thickness of 1.0 mm by hot rolling and cold rolling, annealing was performed. In annealing, as in the homogenization process, Mg diffuses into the oxide film, and the oxide film crystallizes, thereby promoting the production of MgO. Therefore, it is desirable that the heat treatment be performed at a temperature below the crystallization temperature of the film while suppressing the diffusion of Mg. Therefore, in this example, the annealing conditions were set at 350 to 500° C. for 1 to 5 hours as shown in Table 3. The temperature increase rate for annealing was set to 1°C/min or 100°C/min as shown in Table 3.

Tables 1 and 2 below show the sample numbers, manufacturing method types (manufacturing conditions A to I shown in Table 3), and alloy compositions of Examples and Comparative Examples, as well as the area ratio of spinel (%), Measurement results or evaluation results are shown for surface Mg concentration (mass %), oxide film thickness (nm), crystal grain size (μm), aspect ratio, number of coarse agglomerated parts (pieces), and surface treatability.

The evaluation criteria for the area ratio of spinel and the number of coarse agglomerated parts of each sample shown in Tables 1 and 2 were as follows.
[Area ratio of spinel, number of agglomerated parts]
The plate material after final annealing was observed from the surface direction using a field emission scanning electron microscope (FE-SEM), and the area ratio of spinelization was measured. An example of a measurement image is shown in FIG. 4(A), and areas where a large amount of crystallized spinel and MgO exist on the surface are white areas. The area ratio of this white region was evaluated as the area ratio of spinel. Note that when measuring the area ratio of spinel, it may be difficult to measure depending on the material. In this case, the area of the spinel can be accurately measured by cutting the surface of the plate by several micrometers using a microtome's diamond knife to create a mirror surface before annealing.
In addition, particles in which crystallized MgAl ₂ O ₄ , MgO, etc. that are present in the white region are aggregated to a diameter of 0.05 μm or more in equivalent circle diameter are determined to be coarse aggregates and measured. Evaluation was made based on the number of coarse aggregates in an area of 100 μm ² (10 μm×10 μm) in an image observed with an electron microscope.

The measurements of crystal grain size and aspect ratio shown in Tables 1 and 2 were performed as follows.
[Measurement of grain size and aspect ratio]
After mirror-polishing the cross section of each sample parallel to the rolling direction, it was anodized with Barker's solution, crystal grains were observed with an optical microscope, and the crystal grain size of the cross section was determined by a cutting method. By determining the average grain length in the rolling direction (b) and the average grain length in the plate thickness direction (a) using the method described above, and dividing the average grain length in the rolling direction by the average grain length in the plate thickness direction, The aspect ratio of crystal grains was determined.

The surface Mg concentration and oxide film thickness shown in Tables 1 and 2 were measured under the following conditions.
[Measurement of surface Mg concentration and oxide film thickness]
The annealed material was subjected to elemental analysis using X-ray photoelectric spectroscopy (XPS) while sputtering from the material surface in the depth direction, and a depth profile was obtained. The measurement interval in the depth direction was 4.7 nm in terms of SiO ₂ , and measurements were made to a depth of 300 nm. The surface Mg concentration was the Mg concentration of the first layer, that is, the outermost surface, immediately after the start of the measurement. The oxide film thickness was defined as the depth at which the detected amount of oxygen became half of the value at the outermost surface.

The evaluation criteria for surface treatment properties were as follows.
[Surface treatment evaluation]
The annealed aluminum alloy plate was immersed in a 10% by mass NaOH aqueous solution for 15 seconds to perform surface etching. The surface of the aluminum alloy plate after etching was observed with an optical microscope. Samples with good surface quality without any uneven etching on the surface layer were selected as ◎, and samples with good surface quality overall were selected with minimal etching unevenness. 〇, Those with obvious etching unevenness were evaluated as ×.

As shown in Tables 1 and 2, it is an aluminum alloy plate containing 0.05% by mass or more and 2.5% by mass or less of Mg, homogenized at 400 to 500°C, and heated to 400°C or more during hot rolling. In Examples 1 to 30, in which the rolling time was 20 minutes or less, the hot finishing temperature was 250°C, and the annealing temperature was in the range of 350 to 450°C, the area ratio of spinel was 10% or less, and the surface Mg The aluminum alloy plate had a concentration of 20% by mass or less. Further, among Examples 1 to 30, Examples 9, 10, 11, 14, 16, 17, 19, 21, 23 to 30, in which the oxide film thickness exceeds 40 nm, have surface treatment properties. It was ○. Among Examples 1 to 30, the aluminum alloy plates of Examples 1 to 6 and 8 to 30 except Example 7 had large crystal grains with an average grain size of 50 μm or more and an aspect ratio of 1.5 or more. Ta. Furthermore, Examples 1 to 7, 9, 10, 12 to 15, and 17 to 22 had a small number of agglomerated parts.
Examples 16 to 30 are samples containing Zn, Mn, Cu, Fe, Ni, Cr, or Co in addition to Mg, and these samples have a spinel area ratio of 2 to 10%. The aluminum alloy plate had a surface Mg concentration of 7 to 18% by mass and an aspect ratio of 2.4 to 4.0.

Among the examples, Example 7 has a slightly smaller crystal grain size and a smaller aspect ratio, Example 8 has a large number of agglomerated parts, and Examples 9, 10, 14, 17, 19, and 21 have an oxide film. Since the thickness was slightly thick, the surface treatment property was rated as ○.
In Examples 11, 16, 23 to 30, the oxide film thickness was slightly thicker and the number of agglomerated parts was also slightly larger, so the surface treatability was rated as ○.
Comparative Example 1 is a sample in which the homogenization treatment temperature was low and the time of rolling at 400°C or higher during hot rolling was extended, but the area ratio of spinel was larger than in the example, and the surface Mg concentration was The temperature was high and the oxide film became thick.
Comparative Example 2 is a sample in which the time of rolling at 400°C or higher during hot rolling was increased and the annealing temperature was high, but the area ratio of spinel was large, the surface Mg concentration was high, and the oxide film was thick. , the surface treatment properties were poor due to the large number of coarse agglomerated parts.
In Comparative Example 3, the time of rolling at 400° C. or higher during hot rolling was long, the area ratio of spinel was large, and the surface Mg concentration was high, resulting in poor surface treatment properties.
Comparative Examples 4, 5, and 6 are samples with a high Mg content, but the area ratio of spinel is large, the surface Mg concentration is high, the oxide film is thick, and the number of coarse aggregates is large, so the surface treatment property is poor. The result was inferior.
In Comparative Example 7, the annealing temperature was high, the area ratio of spinel was large, the surface Mg concentration was high, the oxide film was thick, and the number of coarse agglomerated parts was large, resulting in poor surface treatment properties.

Next, the reason why the present inventor estimated that MgO is generated due to excessive supply of Mg to spinel will be explained.
Elemental analysis by X-ray photoelectron spectroscopy (XPS) of the surface parts of aluminum alloy plates containing 0.5 wt% Mg heat-treated at 400°C for 3 hours and at 450°C for 3 hours. The results are shown in FIGS. 6 and 7.
As shown in the analysis results shown in Figure 6, no particular concentration of elements is observed in the surface region of the 400°C heat-treated sample, but in the analysis results shown in Figure 7, Mg is concentrated on the surface and oxygen concentration is high on the surface. I understand that. From the analysis results shown in FIG. 7, it is considered that a large amount of Mg and O are present on the surface of the 450° C. heat-treated sample.

Next, FIG. 8 shows the position of a white spot assumed to be spinel and its surroundings when area analysis is performed on the surface of the aluminum alloy plate shown in FIG. 4.
It was found that in the region indicated by reference numeral 1 in FIG. 8, elements were present in a ratio of O: 55.0, Mg: 40.4, and Al: 4.7.
It was found that in the region indicated by reference numeral 2 in FIG. 8, elements were present in a ratio of O: 56.6, Mg: 39.2, and Al: 4.2.
It was found that in the region indicated by reference numeral 3 in FIG. 8, elements were present in a ratio of O: 58.2, Mg: 32.1, and Al: 9.7.
In the region indicated by reference numeral 4 in FIG. 8, it was found that elements were present in the ratio of O: 61.7, Mg: 12.2, and Al: 26.1.

From this result, it was found that the white spot portion contained a large amount of Mg and the Al content was low, and that the gray portion (non-white spot portion) contained Al and Mg to the same extent. In view of this result, it can be considered that the white spot portion is a region where MgO is formed.

FIG. 9 is an FE-SEM image showing a cross section of one of the white dots assumed to be spinel on the surface of the aluminum alloy plate shown in FIG. 4.
FIG. 10 shows the results of line analysis along the solid line extending vertically (in the thickness direction of the sample) in FIG.
From the line analysis results shown in FIG. 10, it can be estimated that MgO is generated on the surface portion of the spinel represented by the composition formula MgAl ₂ O ₄ .

FIG. 11 is an FE-SEM image showing the analysis position along a line extending vertically (in the thickness direction of the sample) in a portion away from a white dot portion assumed to be spinel.
FIG. 12 shows the results of line analysis along the solid line extending vertically in FIG. 11.
From the line analysis results shown in FIG. 12, only the presence of an oxide film represented by the compositional formula MgAl ₂ O was confirmed.

From the above test results, the inventors of the present application presumed that when Mg is supplied in excess by diffusion from the base material side to the spinel represented by the compositional formula MgAl ₂ O ₄ , MgO is generated on the surface of the spinel.
Based on the above considerations, the inventor of the present application considered the surface condition of the aluminum alloy plate 11 described above, and determined that it is effective for specifying the area ratio of spinel and the Mg concentration on the surface, and in the present invention, as described above. stipulated.

As shown by the results of the above-mentioned Examples and Comparative Examples, whether or not spinelization can be achieved is mainly determined by two factors: the heat treatment temperature and the amount of Mg added.
The Mg content of the material used in FIG. 6 is 0.5%, which is a small Mg content within the desired Mg content range defined in this application. When the amount of Mg added is large (for example, 3% Mg in Comparative Example 1), there is a possibility that some spinel will be formed even at a homogenization treatment temperature of 400°C. Furthermore, if the homogenization heat treatment temperature is high, a certain amount of spinel particles will be generated even before rolling, and therefore, as the homogenization temperature becomes high, coarse agglomerated parts tend to increase. This relationship can be understood from the results of Examples and Comparative Examples shown in Tables 1 and 2.

DESCRIPTION OF SYMBOLS 11... Aluminum alloy plate, 11A... Oxide film, 11a... Crystal grain, 11B... Spinel, 11D... Precipitation part.

Claims (10)

An aluminum alloy plate containing 0.05% by mass or more and 2.5% by mass or less of Mg, in which the area ratio of spinel formed on the surface after annealing is 10 in an area of 2500 μm ² when observed in the surface direction. % or less, and the Mg concentration on the surface is 20% by mass or less. The aluminum alloy plate according to claim 1, characterized in that the thickness of the oxide film on the surface is 40 nm or less. Claim 1 or 2, characterized in that the average crystal grain size at the outermost surface is 50 μm or more in equivalent circle diameter, and the average aspect ratio of the crystal grains in a cross section perpendicular to the plate width direction is 1.5 or more on average. The aluminum alloy plate according to claim 2. The aluminum alloy plate according to any one of claims 1 to 3, wherein the number of coarse aggregates of oxide formed on the surface is 10 or less in a 100 μm ² area. . Any one of claims 1 to 4, characterized in that it contains an element that forms an oxide having a specific crystal structure together with Al, Mg, and O in an amount of 0.05% by mass or more and 1.5% by mass or less. Aluminum alloy plate described. Production of an aluminum alloy plate containing 0.05% by mass or more and 2.5% by mass or less of Mg, processed into a plate shape by hot rolling and cold rolling, and subjected to homogenization heat treatment and annealing treatment. A method,
Controls the heating conditions of homogenization heat treatment and annealing treatment and hot rolling conditions,
Production of an aluminum alloy plate, characterized in that the area ratio of spinel formed on the surface is adjusted to within 10% in an area of 2500 μm ² when observed in the surface direction, and the Mg concentration on the surface is adjusted to 20% by mass or less. Method. The method for manufacturing an aluminum alloy plate according to claim 6, characterized in that the thickness of the oxide film on the surface is adjusted to 40 nm or less. Claim 6 or claim 6, characterized in that the average crystal grain size at the outermost surface is 50 μm or more in equivalent circle diameter, and the average aspect ratio of the crystal grains in a cross section perpendicular to the plate width direction is 1.5 or more on average. Item 7. The method for producing an aluminum alloy plate according to item 7. The aluminum alloy plate according to any one of claims 6 to 8, characterized in that the number of coarse aggregates of oxide formed on the surface is 10 or less in an area of 100 μm ² manufacturing method. Any one of claims 6 to 9, characterized in that it contains 0.05% by mass or more and 1.5% by mass or less of an element that forms an oxide having a specific crystal structure together with Al, Mg, and O. The method for manufacturing the aluminum alloy plate described above.

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