KR20180025955A - Aluminum alloy extruded material excellent in appearance quality having an anodized film and method of manufacturing the same - Google Patents

Abstract

An object of the present invention is to provide a 7000-series aluminum alloy extruded material having a desired strength and hardly causing streaks on the surface of an anodized film. According to the present invention, there is provided an aluminum alloy extruded material which comprises 4.0 to 7.5 mass% of Zn, 1.0 to 2.2 mass% of Mg, 0.05 to 0.20 mass% of Fe, 0.30 mass% or less of Cu, Ti: not less than 0.005 mass% and not more than 0.04 mass%, B: not less than 0.001 mass% nor more than 0.02 mass%, Si: not more than 0.15 mass%, Zr: not more than 0.05 mass%, Mn: not more than 0.05 mass% [Zr + Mn + Cr + V + Ti] < V: 0.05 mass% or less and the sum of the contents of Zr, Mn, Cr, Mass%, and the remainder is aluminum and inevitable impurities, except for the range where the content of Zn is 6.0 mass% or less and the content of Mg is 1.2 mass% or less, and the metal structure is a recrystallization structure An aluminum alloy extruded material excellent in appearance quality and a method for producing the same.

Description

Aluminum alloy extruded material excellent in appearance quality having an anodized film and method of manufacturing the same

The present invention relates to an aluminum alloy extruded material having an excellent anodic oxide film and an excellent method for producing the same, and more particularly to an aluminum alloy extruded material for an electronic device housing having an excellent anodic oxidation film property and a method for producing the same.

Portable personal computers and the like are becoming smaller, thinner and lighter each year. Accordingly, reduction of the thickness of the housing material has been demanded. In order to withstand thinning, an extruded material obtained by treating an anodic oxidation film of a 7000-series aluminum alloy having the highest strength among aluminum alloys has been used as a housing material.

However, when the 7000-series aluminum alloy extruded material is subjected to the anodic oxidation coating process, stripes parallel to the extrusion direction are revealed, and there is a problem in appearance. It was thought that the stripe pattern was formed by the anodic oxide film treatment that the cast structure expanded in the extrusion direction in the extrusion process became a fibrous structure. For example, in Patent Document 1, the metal structure of the extruded material is a recrystallized structure.

Japanese Patent Application Laid-Open No. H02-246555

However, even if the metallic structure is a recrystallized structure, the striations are reduced, but sufficient aesthetic appearance can not be obtained. The inventors of the present application investigated the cause of the striations and found that in addition to the crystal structure of the metal structure, the concentration of elements other than aluminum in the crystal and grain boundaries, the crystallization state of the compound, It was found that the tea greatly affected.

A portion where elements other than aluminum are segregated or a portion where a crystallized substance is present tends to be hard to form an anodized film as compared with other portions. It is considered that this is due to the fact that electrical properties are different due to the effect of concentration segregation. That is, the constituent elements are concentrated in the crystal grains, and the process elements are eliminated in the crystal grains, and concentration segregation occurs in the crystal grains and grain boundaries. When subjected to the extrusion processing, the concentration segregation portion extends in the extrusion direction in the same manner as the crystal grains of the cast structure, and a thin layer of concentration segregation of the main elements of Zn and Mg is formed in a stripe pattern, Resulting in the appearance of stripes on the surface of the anodic oxidation coating.

In addition, although there are other crystals, the crystal grains are elongated by the extrusion process, and the fact that the crystals are dotted in the extrusion direction also causes streaks.

By the extrusion processing, the cast structure is extended to form a fiber-like structure, but at this time, the concentration of the concentration-segregated portion and the crystallized portion are also increased. Even if the crystal structure becomes a recrystallized structure that is equiaxed from the fiber-like structure by the recrystallization, the concentration-segregated portion and the crystallized portion remain and are stretched, so that stripes appear when the anodic oxide coating treatment is carried out.

Further, also in the recrystallized structure, a portion in which crystals having a large difference in crystal grain size are mixed also appears to have a stripe shape.

As a result of intensive studies in view of the above circumstances, the inventors of the present invention have found out the range of the optimum alloy composition which suppresses the concentration gradient of the crystal grains of the concentration segregation and the excessive crystallization of the compound and the recrystallized structure while having a high strength of 380 MPa or more I got it.

It is an object of the present invention to provide a 7000-series aluminum alloy extruded material having a desired strength and hardly causing streaks on the surface of an anodized film.

According to the present invention, an aluminum alloy extruded material,

Zn: 4.0% by mass or more and 7.5% by mass or less,

Mg: 1.0 mass% or more and 2.2 mass% or less,

Fe: 0.05 mass% or more and 0.20 mass% or less,

Cu: 0.30 mass% or less,

Ti: 0.005 mass% or more and 0.04 mass% or less,

B: 0.001% by mass or more and 0.02% by mass or less,

Si: 0.15 mass% or less,

Zr: 0.05 mass% or less,

Mn: 0.05 mass% or less,

Cr: 0.05 mass% or less,

V: not more than 0.05% by mass

≪ / RTI >

[Zr + Mn + Cr + V + Ti], which is the sum of the contents of Zr, Mn, Cr, V and Ti,

[Zr + Mn + Cr + V + Ti]? 0.10 mass%

Lt; / RTI >

The content of Zn is 6.0 mass% or less and the content of Mg is 1.2 mass% or less,

The balance being aluminum and inevitable impurities,

There is provided an aluminum alloy extruded material excellent in appearance quality and having an anodic oxide film whose metal structure is a recrystallized structure.

According to one aspect of the present invention, in the aluminum alloy extruded material, in the anodized surface, a Zn high concentration phase and a Zn low concentration phase are present in layers in parallel with the extrusion direction, and in the direction orthogonal to the extrusion direction, And the Zn concentration difference is 1% or less in the range of 0.1 mm or more and 3 mm or less.

According to one aspect of the present invention, in the aluminum alloy extruded material, the grain size of the recrystallized structure of the anodized film-coated surface is 200 mu m or less in average value and the maximum grain size is 1 mm or less.

According to one aspect of the present invention, in the aluminum alloy extruded material, the area ratio of the intermetallic compound (crystallized product) in the anodized surface is less than 2%.

According to the present invention, the casting material is subjected to a homogenizing treatment at a temperature of 400 to 560 占 폚 for 1 to 24 hours, and an extrusion process is carried out in an extrusion process with an extrusion ratio exceeding 20, And the aging treatment is carried out at 100 占 폚 to 180 占 폚 for 1 hour to 30 hours.

According to the present invention, there is provided a 7000-series aluminum alloy extruded material having desired strength and excellent appearance quality in which stripes are unlikely to be generated on the surface of the anodized film, and a method for producing the extruded material.

1 is a photograph of a crystal structure of Experimental Example B taken by a polarizing microscope.
2 is a photograph of microstructure of Experimental Example B. FIG.
3 is a photograph of a crystal structure of Experimental Example L taken by a polarizing microscope.
4 is a photograph of a crystal structure of Experimental Example H taken with a polarizing microscope.
5 is a photograph of microstructure of Experimental Example K. FIG.
6 (a) is a graph showing the concentration analysis of Experiment B and FIG. 6 (b) is a mapping diagram.
7 is a graph showing the concentration analysis of Experimental Example G. Fig.
8 (a) is a graph showing concentration analysis of Experimental Example H and FIG. 8 (b) is a mapping diagram.

Hereinafter, embodiments of the present invention will be described.

[Aluminum alloy extrusion material]

The aluminum alloy extruded material having an anodized film according to the present embodiment is an aluminum alloy extruded material,

Zn: 4.0% by mass or more and 7.5% by mass or less,

Mg: 1.0 mass% or more and 2.2 mass% or less,

Fe: 0.05 mass% or more and 0.20 mass% or less,

Cu: 0.30 mass% or less,

Ti: 0.005 mass% or more and 0.04 mass% or less,

B: 0.001% by mass or more and 0.02% by mass or less,

Si: 0.15 mass% or less,

Zr: 0.05 mass% or less,

Mn: 0.05 mass% or less,

Cr: 0.05 mass% or less,

V: 0.05 mass% or less,

≪ / RTI >

[Zr + Mn + Cr + V + Ti], which is the sum of the contents of Zr, Mn, Cr, V and Ti,

[Zr + Mn + Cr + V + Ti]? 0.10 mass%

Lt; / RTI >

The content of Zn is 6.0 mass% or less and the content of Mg is 1.2 mass% or less,

The balance being aluminum and inevitable impurities,

And the metal structure is a recrystallized structure.

The aluminum alloy extruded material having the above-described constitution has an effect that stripes do not appear on the surface of the anodized film with desired strength.

Hereinafter, each element relating to the aluminum alloy extruded material of the present embodiment will be described.

(Zn: zinc)

Zn and Mg precipitate as a Zn-Mg phase, which contributes to the enhancement of the strength of the alloy. When the content of Zn is 4.0 mass% or more, sufficient strength can be obtained. When the content of Zn is 7.5 mass% or less, good corrosion resistance is obtained.

The aluminum alloy extruded material according to the present embodiment has a Zn content of 4.0 mass% or more and 7.5 mass% or less, more preferably 4.0 mass% or more and 7.0 mass% or less, and further preferably 4.0 mass% or more and 6.0 mass% , Still more preferably 4.0 mass% or more and less than 5.5 mass%, and most preferably 4.0 mass% or more and 5.0 mass% or less.

(Mg: magnesium)

When the content of Mg is 1.0 mass% or more, sufficient strength can be obtained. When the content of Mg is 2.2 mass% or less, good extrusion processability can be obtained.

The aluminum alloy extruded material according to the present embodiment has a Mg content of 1.0 to 2.2% by mass, more preferably 1.2 to 2.2% by mass, still more preferably 1.3 to 2.2% by mass, By mass, still more preferably 1.4% by mass or more and 2.2% by mass or less, and most preferably 1.5% by mass or more and 2.2% by mass or less.

However, when the Zn content is 6.0% by mass or less, when the Mg content is 1.2% by mass or more and the Zn content is less than 5.5% by mass, the Mg content is preferably 1.6% by mass or more.

(Fe: iron)

The aluminum alloy extruded material according to the present embodiment has a Fe content of 0.05 mass% or more and 0.20 mass% or less.

When the content of Fe is 0.05 mass% or more, coarse recrystallization of the cast structure can be suppressed during the homogenization treatment. If there is a coarse crystal structure in the ingot, uneven deformation tends to occur at the time of extrusion processing, and it becomes difficult to accommodate the dimensions of the extruded material at a predetermined size (precision, twist and warpage). Further, if there is a coarse crystal structure in the billet, recrystallized grains having different sizes are liable to coexist even in recrystallization after extrusion, even in equiaxed recrystallized structure. Such a structure is arranged in layers, which causes a color tone difference in a stripe shape. If the content of Fe is 0.20 mass% or less, Fe forms a compound with another element to form an excessive precipitate, and streaking can be suppressed. The content of Fe is more preferably 0.15 mass% or less, and the effect is further enhanced in this range.

(Cu: copper)

The aluminum alloy extruded material according to the present embodiment has a Cu content of 0.30 mass% or less. When the content of Cu exceeds 0.30 mass%, the anodic oxide film tends to have a yellowish color and the corrosion resistance tends to deteriorate.

When the Cu content is more than 0.15 mass%, the mechanical strength and the stress corrosion cracking resistance (SCC) are improved.

(Ti: titanium, B: boron)

The aluminum alloy extruded material according to the present embodiment has a Ti content of 0.005 mass% or more and 0.04 mass% or less. The aluminum alloy extruded material according to the present embodiment has a B content of 0.001 mass% or more and 0.02 mass% or less.

Ti and B are added as fine grain refining agents at the time of casting because ununiform deformation tends to occur at the time of extrusion molding and coarsening of the grain size of the grain segregation and recrystallization texture tends to occur when the crystal of the casting structure in the alloy is coarse.

When only Ti is added, it is dissolved in the mother phase, and the action as a microfine agent is weakened. Further, since concentration segregation easily occurs in the crystal, it is preferable to add the rod hardner as a TiB ₂ compound by using as a fineizing agent. On the other hand, if Ti or B is excessively added, it is excessively crystallized as a compound, which causes streaks, so that the upper limit of the addition amount becomes necessary.

(Si: silicon)

The aluminum alloy extruded material according to the present embodiment has a Si content of 0.15 mass% or less. Si forms a factor of stripes due to the formation of Mg and Mg-Si based compounds, so it is preferable to regulate Si to 0.15% or less.

It is more preferable that the content of Si is 0.1 mass% or less. If the content of Si is within this range, the above effect is further enhanced.

(Zr: zirconium, Mn: manganese, Cr: chromium, V: vanadium)

Zr, Mn, Cr, and V each have an effect of suppressing recrystallization during extrusion processing, and therefore, the content thereof is preferably 0.05 mass% or less, and more preferably 0.02 mass% or less. These elements also have an effect of suppressing the diffusion of Zn.

Further, since the element is difficult to diffuse by heat treatment (heating of the ingot upon extrusion of HO or extrusion), concentration segregation tends to easily occur, and if it exceeds the regulation range, it forms a stripe at the time of the anodic oxidation coating .

[Zr + Mn + Cr + V + Ti], which is the sum of the contents of Zr, Mn, Cr, V and Ti, satisfies the relation of [Zr + Mn + Cr + V + Ti]? 0.10 mass% desirable.

When added in an amount exceeding the above specified range, recrystallization is suppressed to form a non-recrystallized structure, crystal grain growth is caused, and furthermore, coarse excess crystals are caused. More preferably 0.09 mass% or less, still more preferably 0.08 mass% or less, still more preferably 0.07 mass% or less, and most preferably 0.05 mass% or less.

(Recrystallization organization)

When the anodic oxide film treatment is performed on the fiber-like structure, the surface of the anodized film is likely to be streaky. Therefore, it is preferable that the crystal structure is a recrystallized structure in which the crystal grain size is aligned. In order to form such a fine recrystallized structure, an alloy component, a casting HO condition, and an extrusion condition are controlled. The morphology of the crystal structure can be confirmed by the same method as that observed with a polarizing microscope after coating with a borofluoric acid aqueous solution.

In addition, since the striped shape is a problem on the anodic oxidation coating surface, only the surface thereof needs to be recrystallized.

(Concentration difference between the high-concentration portion of Zn and the low-concentration portion)

When the widths of the Zn high concentration layer and the Zn low concentration layer existing in layers in parallel with the extrusion direction on the anodized surface exceed 1% in the range of more than 0.1 mm and 3 mm or less, When the treatment is carried out, there is a difference in the film form of the high-density portion and the low-density portion, and the difference is likely to appear as a stripe shape. The concentration segregation in the range of 0.1 mm width is too narrow to be recognized as stripe. Also, gentle concentration segregation exceeding 3 mm is hardly recognized as stripe.

(Average recrystallized texture size 200 μm or less, maximum grain size 1 mm or less)

When the crystal grain size of the recrystallized structure on the anodized film-coated surface is not uniform, concentration segregation occurs and appears to have a stripe shape.

(Area ratio of the distillate is less than 2%)

If the area ratio of the intermetallic compound (crystallized product) in the anodized surface is 2% or more, the intermetallic compound (crystallized product) moved so as to be dotted in parallel to the extrusion direction when the crystal grains are expanded during the extrusion process is in a stripe shape .

The aluminum alloy extruded material according to the present embodiment has excellent anodic oxidation film property and is preferably used as a material for housing of electronic equipment.

[Manufacturing method of aluminum alloy extruded material]

Further, according to the present invention, a method of manufacturing an aluminum alloy extruded material is provided. The following embodiments are basically the same as the above embodiment.

A method for producing an aluminum alloy extruded material according to another embodiment of the present invention is an aluminum alloy extruded material and comprises 4.0 to 7.5% by mass of Zn, 1.0 to 2.2% by mass of Mg, and 0.05 to 0.20% 0.001 mass% to 0.04 mass%, B: 0.001 mass% to 0.02 mass%, Si: 0.15 mass% or less, Zr: 0.05 mass% or less, Mn: 0.05 mass% or less, Cu: 0.30 mass% or less, Mn, Cr, V and Ti contained in an amount of not more than 0.05% by mass, not more than 0.05% by mass of Cr and not more than 0.05% by mass of V and having a content of [Zr + Mn + Cr + V + Ti]

[Zr + Mn + Cr + V + Ti]? 0.10 mass%

, The remainder being composed of aluminum and inevitable impurities, except that the content of Zn is 6.0 mass% or less and the content of Mg is 1.2 mass% or less, the metal structure is a recrystallized structure, A method for producing an aluminum alloy extruded material,

The casting material is subjected to a homogenization treatment at 400 to 560 占 폚 for 1 to 24 hours,

Extrusion processing is performed so that the extrusion ratio is more than 20 in the extrusion process and the temperature of the shape material during extrusion processing is 420 캜 or more,

And the aging treatment is carried out at 100 to 180 DEG C for 1 to 30 hours.

(casting)

In the casting step, a molten aluminum alloy having the above alloy composition is prepared, and a known molten metal treatment such as debris treatment, degassing treatment and filtering is performed. Then, in the DC casting method or the like, an ingot cast billet (billet) is obtained.

During the casting, before the molten metal enters the mold, it is preferable to add a finizing agent (rod hardener) made of Al-Ti-B alloy into the molten metal. It is preferable that the fine refining agent to be added to the molten metal does not exceed Ti and B in the alloy composition in the above range. In order to make the casting structure as homogeneous as possible, it is preferable that the molten metal is poured homogeneously in the mold so that the casting temperature becomes uniform in the mold. For example, HOT TOP (hot top) casting is preferably used.

The billet diameter is preferably small, preferably 14 inches or less in diameter. If the diameter of the billet is large, cooling of the center of the billet is slowed, and the structure of the center of the billet is likely to be coarsened. If the cast structure is coarse, it is difficult to solve the concentration segregation in the homogenization treatment, and the crystal structure in the extrusion process tends to become insufficient.

(Homogenization treatment)

A homogenization treatment (HO treatment) is performed on the billet obtained in the above casting step. By the homogenization treatment, the concentration segregation of the elements is eliminated, and the crystallization is reduced.

The homogenization treatment temperature is preferably 400 to 560 占 폚, preferably within 1 hour to 24 hours. If the homogenization treatment conditions are within this range, homogenization is sufficiently performed. When the homogenization treatment temperature for 24 hours exceeds 560 DEG C, the crystal of the ingot grows, the extrusion processability is lowered, the crystal grains of the extruded material are coarsened, and the recrystallized structure locally coarsens and the grain size difference Thereby generating a pattern at the time of anodic oxidation coating.

The homogenization treatment temperature is more preferably 540 DEG C or less. Even if the homogenization treatment is performed for more than 24 hours, no further effect can be expected, and only the production cost is incurred.

In order to dissolve the concentration segregation and accelerate the employment of the crystallized product, it is preferable to carry out the homogenization treatment at 470 DEG C or higher, and more preferably to perform the homogenization treatment at 500 deg. If the cooling rate after the homogenization treatment is low, the dissolved element tends to precipitate, so that the average cooling rate from the HO temperature to 150 DEG C is preferably cooled at 100 DEG C / h or more.

(Extrusion processing)

In the extrusion step, the billet subjected to the homogenization treatment is subjected to extrusion processing to obtain a predetermined processing material.

The extrusion ratio of the extrusion process is preferably 20 or more. The extrusion ratio of the extrusion processing is more preferably 40 or more. This is because as the crystal is elongated, the concentration change is gentle (density segregation is easily improved when the interval between the high-concentration portions or the low-concentration portion is increased), and streaks are less likely to occur in the outer appearance after the anodic oxide coating.

Further, in the recrystallized structure which varies depending on the extrusion processing conditions, formation of streaks due to the crystal structure difference can be suppressed by setting the average grain size to 200 mu m or less and the maximum grain size to be 1 mm or less. Since the crystal size of the extruded material becomes finer as the billet temperature is extruded at a lower temperature, the billet temperature is preferably set in consideration of the extrusion pressure and the shape temperature, and is preferably 480 DEG C or less.

It is preferable to determine the extrusion conditions (billet temperature, die temperature, container temperature, extrusion pressure, extrusion speed, etc.) so that the temperature of the die outlet is 400 ° C or higher. If the temperature of the extruded material at the die outlet is low, there is a fear that high strength can not be obtained.

The extruded material after the extrusion from the die is cooled so that the cooling rate in the temperature range from 200 ° C to 0.3 ° C to 20 ° C / s after extrusion. When the cooling rate satisfies this condition, a high strength is obtained and a good stress corrosion cracking resistance can be obtained.

(Aging treatment)

The extruded workpiece is aged. The holding temperature in the aging treatment process is 1 to 30 hours under the condition of 100 to 180 占 폚. In the aging treatment, two stages of aging treatment may be performed in order to obtain higher strength and stress corrosion cracking resistance.

(Anodic oxidation treatment)

The extruded material obtained by sequentially passing through the casting step, the homogenizing treatment step, the extrusion step and the aging treatment step is cut into a predetermined shape and then subjected to anodizing treatment. The anodizing treatment is carried out under known conditions.

In another embodiment of the present invention, in the above-described method for producing an aluminum alloy extruded material, the homogenization treatment step is carried out at a holding temperature of 400 ° C to 560 ° C, the extrusion step has an extrusion ratio of 20 or more, Or more of the aluminum alloy extruded material having an anodic oxide coating is subjected to the aging treatment at a holding temperature of 100 ° C to 180 ° C after the extrusion and at a cooling rate of from -20 ° C to 0.3 ° C / Is provided.

Example

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples.

(Manufacture of aluminum alloy test material)

Billets of the components of Experimental Examples A to N of the following [Table 1] were obtained. The diameter of the billet was 325 mm. These billets were subjected to HO treatment under the conditions of [Table 2], and extrusion processing was carried out under the conditions of [Table 2]. The extrusion processing was carried out under the conditions of a billet temperature of 400 ° C, (a) a flat bar having a width of 100 mm and a thickness of 10 mm, (b) a flat bar having a width of 120 mm and a thickness of 25 mm, and two extruded profiles.

Then, heat treatment was carried out under the conditions shown in Table 2. After the heat treatment, the A to J and L to N were tempered under the conditions of T5 (artificial aging after extrusion) and K6 (artificially aging after solubilization).

In Table 1, the grain sizes after the casting and after the HO were measured by the crossover method, and those having crystal grains exceeding 1 mm in size were evaluated as x. In the crossing method, when a straight line is drawn in an arbitrary direction with respect to an image photographed by an optical microscope and the crystal grain crossing the straight line is n, the length of the straight line is divided by (n-1) .

The various measurement results and observation results of Experimental Examples A to N are shown in [Table 2] and [Table 3].

(Tensile test)

The extruded material was processed into a JIS 14B test piece and subjected to a tensile test. In the tensile test, 0.2% proof stress ≥380 MPa was considered acceptable.

(Observation of hue and stripes)

The surface of the aluminum alloy test piece was subjected to an abrasive polishing treatment (buff polishing) in an amount corresponding to 20% of the thickness, and the surface treatment was anodized. The treatment conditions for the anodic oxidation coating treatment were 1.5 A / dm 2 in an aqueous solution of 15% sulfuric acid at 20 캜, and a coating thickness of about 5 탆.

The color tone was judged based on that the retention ratio of glossiness before and after the treatment was 40% or more and that an L value of 78 or more and a b value of 1 or less was obtained. &Quot; satisfying " and " not satisfying " In addition, the presence or absence of streaks was evaluated. In " o ", almost no striations occurred, and in " DELTA ", thin lines were observed at a limited region. In " x ", dark stripes were formed. The color tone is based on the value of JIS Z8730.

(Observation of structure of extruded material)

The surface of the aluminum alloy test piece was coated with an amount corresponding to 20% of the thickness of the test piece, and the aluminum alloy test piece was polished in a mirror-finished surface and film-treated in an aqueous solution of borohydrofluoric acid. The observation plane is the L-LT plane (the plane parallel to the extrusion direction, the plane wide).

A to G and L to N, recrystallized structure was observed, and the aspect ratio (average crystal diameter in the extrusion long-side direction and average crystal diameter in the direction perpendicular to the extrusion) was equal to or less than 2. H to K, it was a fiber-like crystal structure. However, A to E and G, M, and N observed in the recrystallized structure had homogeneous fine crystals having an average grain size of not more than 200 mu m as measured by the cross-line method. However, in the case of F and L, There was. F, and L of the ingot after HO.

(Percentage of occupied area)

The surface of the aluminum alloy test piece was subjected to an amount corresponding to 20% of the thickness of the test piece, and after polishing with a mirror surface, the occupied area of the crystallized product was measured by an image analyzer and an optical microscope. The observation plane is the L-LT plane (the plane parallel to the extrusion direction, the plane wide).

(Stress corrosion cracking test)

A to E, M, and N were subjected to a stress corrosion cracking test in accordance with JIS H8711. In the stress corrosion cracking test, the stress corresponding to 50% of the 0.2% proof stress was applied to the direction perpendicular to the extrusion direction. The corrosion solution was immersed in 3.5% NaCl at 25 DEG C for 10 minutes and then dried for 50 minutes to obtain one cycle. The test was conducted for 30 days, and the material free from cracks was evaluated as "? &Quot;. A, M, and N show that the results of the SCC test are lowered, but it is considered that this is because the Cu content is small.

(Analysis of element concentration)

The surface of the aluminum alloy test material was subjected to elemental analysis under the following conditions by using a surface of 3 mm surface, polishing, and EPMA-1610 manufactured by Shimadzu Corporation. In order to measure the concentration of Zn, another standard sample of the Zn content was used for the measurement, and a calibration curve of Zn was prepared in advance and quantified by the calibration curve method. The difference between the maximum value and the minimum value of the element concentration values measured on the line was defined as the concentration segregation value.

(Measuring conditions)

Acceleration voltage: 15kV

Irradiation current: 200nA

Beam diameter: 1 탆 (minimum)

sweep condition: LINE × 3000

(Electron beam scanning condition: measured while scanning electron beams in a line in the range of 3000 times (about 100 占 퐉) perpendicular to the traveling direction)

Number of data: 300points

Step size: 10㎛

Length: 3000 탆 (3 mm)

Measurement time: 2 seconds / point

1 (a) and 1 (b) show the crystal structure of Experimental Example B (Inventive Example) observed with a polarizing microscope. Homogeneous recrystallized structure is observed.

2 is a view of microstructure of Experimental Example B (Inventive Example). It can be seen that the distillate is diffused and the continuity of the extreme compound is not seen.

Figs. 3 (a) and 3 (b) show a crystal structure of a sample section of Experimental Example L (Comparative Example) observed with a polarizing microscope. It was found that the size of the crystal grains was different by the observation point, and the crystal grains were partially formed. This is because, depending on the temperature condition of the HO treatment, the recrystallized structure locally coarsened.

4 shows the crystal structure of Experimental Example H (Comparative Example). It can be seen that the crystal structure is fiber-structured.

5 shows the microstructure of Experimental Example K (Comparative Example) observed. The portions where the contents of Fe, Cu, Mg, and Cr are large and where the crystallized products are segregated are extended by extrusion processing to show continuity of the compound in a stripe shape.

6 to 8, (a) the concentration analysis on the anodized film-coated surface per 3 mm of the length in the direction orthogonal to the extrusion direction of the extrusion process is performed. (b) are mapping diagrams of Zn elements at the same positions.

6 is a graph showing the Zn concentration analysis and the mapping diagram of Experimental Example B (Inventive Example). The Zn concentration segregation at a width of 3 mm is 1.0 mass% or less. 7 is a graph showing the Zn concentration distribution of Experimental Example G (Comparative Example), and FIG. 8 is a graph showing a Zn concentration distribution and mapping diagram of Experimental Example H (Comparative Example). In Experimental Examples G and H, which are comparative examples, it was found that there was a portion where concentration of Zn exceeding 1.0 mass% occurred between 3 mm width. It can also be seen that the concentration is more layered than the mapping.

From the above experimental results, it is understood that A to E, M, and N have desired strength and stripe hardly appears on the surface of the anodized film. Therefore, the aluminum alloy extruded material satisfying such conditions can be preferably used for a housing of an electronic device such as a portable personal computer, a cellular phone, and a smart phone.

In addition, since the extrusion ratios of A to D, M and N are larger than E, i.e., the degree of processing is high, the uniformity of the surface is higher.

Since F is small in Fe, crystal grains are coarsened in a part of the ingot by HO, and in the extruded material, crystal grains exceeding 1 mm are present in a part, and an uneven crystal structure is formed. Streaks occurred after treatment.

G, Ti and B, which are the crystallizing fine agents in casting, were insufficient, and the ingot after casting was coarsened. With this effect, concentration segregation of Zn is not sufficiently solved even when the homogenization treatment is performed, and concentration segregation occurs in which the Zn concentration difference exceeds 1% in the range of more than 0.1 mm and less than 3 mm, and the anodic oxidation coating Streaks occurred after treatment.

H and I indicate that the amount of added Zr exceeds the upper limit value and the crystal structure of the extruded material is maintained in the fiber structure by the pinning effect and the diffusion of Zn is also inhibited by Zr, It was not sufficiently solved, and streaking occurred after the anodic oxide coating treatment of the extruded material. Further, although the content of Zn is high, I has a low content of Mg, so that the mechanical strength is low even in a fiber structure.

J also shows that the Zr addition amount, the Cr addition amount, and the Mn addition amount exceed the upper limit value, and the crystal structure of the extruded material is retained in the fiber structure by the pinning effect and the diffusion of Zn is also inhibited by Zr, Concentration segregation was not sufficiently solved and concentration segregation occurred in which the Zn concentration difference exceeded 1% in the range of more than 0.1 mm and 3 mm or less, and streaks occurred after the anodic oxidation treatment of the extruded material.

J has a high Mg content but a low Zn content, so that the mechanical strength is low even in a fiber structure. In addition, since the Mn content is large and the crystal structure of the extruded material is maintained in the fiber structure by the pinning effect and the diffusion of Zn is also inhibited by Mn, even if the homogenization treatment is performed, Zn concentration saturation can not be sufficiently solved, Concentration segregation occurred in which the difference in Zn concentration exceeded 1% in the range of more than 3 mm and more than 3 mm, and streaks occurred after the anodic oxidation treatment of the extruded material.

K, Fe, Cu, Mg, and Cr exceeded the ranges specified in the present invention, and a large amount of crystallized material was generated, and streaking occurred after the anodic oxide coating treatment of the extruded material. Further, due to the pinning effect of Cr, the crystal structure of the extruded material is maintained in the fiber structure and the diffusion of Zn is also inhibited by Cr, and even when the homogenization treatment is performed, Zn concentration saturation can not be sufficiently solved, , Concentration segregation occurred in which the difference in Zn concentration exceeded 1% in the range of 3 mm or less, and streaking occurred after the extrusion material was subjected to anodizing treatment. Further, Cu exceeded the range specified in the present invention, and the values of L and b were other than the standard value.

Since the HO temperature exceeds the upper limit temperature, the crystal structure of the ingot grows and the grain size of the extruded material becomes uneven in the crystal structure of the extruded material, Streaks occurred after the anodic oxidation treatment.

Claims (7)

Aluminum alloy extruded material,
Zn: 4.0% by mass or more and 7.5% by mass or less,
Mg: 1.0 mass% or more and 2.2 mass% or less,
Fe: 0.05 mass% or more and 0.20 mass% or less,
Cu: 0.30 mass% or less,
Ti: 0.005 mass% or more and 0.04 mass% or less,
B: 0.001% by mass or more and 0.02% by mass or less,
Si: 0.15 mass% or less,
Zr: 0.05 mass% or less,
Mn: 0.05 mass% or less,
Cr: 0.05 mass% or less,
V: 0.05 mass% or less,
≪ / RTI >
[Zr + Mn + Cr + V + Ti], which is the sum of the contents of Zr, Mn, Cr, V and Ti,
[Zr + Mn + Cr + V + Ti]? 0.10 mass%
Lt; / RTI >
The content of Zn is 6.0 mass% or less and the content of Mg is 1.2 mass% or less,
The balance being aluminum and inevitable impurities,
An aluminum alloy extruded material having an excellent anodizing quality and having an anodic oxide film whose metal structure is a recrystallized structure. The aluminum alloy extrusion material according to claim 1, wherein the content of Zn is 4.0% by mass or more and less than 5.5% by mass, and the anodic oxide coating film is excellent in appearance quality. The aluminum alloy extruded material according to any one of claims 1 to 3, wherein the content of Mg is 1.0% by mass or more and 1.6% by mass or less. 4. The method according to any one of claims 1 to 3, wherein in the anodized surface, a Zn high-concentration phase and a Zn low-concentration phase are present in layers in parallel with the extrusion direction, and in a direction orthogonal to the extrusion direction, Wherein the difference in Zn concentration is 1% or less in the range of 3 mm or less to 3 mm or less. 5. The anodic oxide coating according to any one of claims 1 to 4, characterized in that the grain size of the recrystallized structure of the anodized film-coated surface is 200 mu m or less in average value and the maximum grain size is 1 mm or less. High quality aluminum alloy extruded material. The aluminum alloy extruded material according to any one of claims 1 to 5, wherein the area ratio of the crystallized product in the anodized surface is less than 2%. The casting material is subjected to homogenization treatment at 400 to 560 占 폚 for 1 to 24 hours,
Extrusion processing is performed so that the extrusion ratio is more than 20 in the extrusion process and the temperature of the extrusion process is 420 ° C or more during the extrusion process,
A process for producing an aluminum alloy extruded material having an excellent anodizing quality and having an anodized coating film according to any one of claims 1 to 6, characterized in that the aging treatment is carried out at 100 to 180 ° C for 1 to 30 hours.

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