JP6249435B2 - Aluminum-zinc alloy extruded material and method for producing the same - Google Patents

Description

The present invention is lightweight and high-strength, and by applying a surface treatment such as anodizing treatment, it exhibits excellent corrosion resistance even in an environment where water vapor is present, and the surface has a beautiful color tone. The present invention relates to an extruded material of an aluminum-zinc based alloy and a method for producing the same.
However, in view of the fact that the aluminum-zinc alloy according to the present invention is a heat treatment type alloy, in the present invention, the extruded material is a material that has been subjected to heat treatment for solution treatment and heat treatment for age hardening after extrusion processing. It shall be said.

The aluminum-zinc alloy is a so-called high-strength aluminum alloy characterized by being lightweight and having high strength. Under the feature, since the invention of this alloy according to Patent Document 1, It is used for parts.
However, the addition of Mg and Cu together with Zn to the alloy element can improve the strength further, and the addition of Zr can improve toughness and stress corrosion cracking resistance. In the literature.

  That is, in Patent Document 1, in the aluminum-zinc-based alloy, the component composition having the highest strength is Zn: 8.0 to 12.0% by mass, Cu: 2.0 to 3.0% by mass, Mg: 1 0.0 to 2.0 mass%, Mn: about 0.5 mass%, but such an alloy is susceptible to cracking, and 0.1 to 2.0 mass to prevent the cracking. % Addition of Cr is disclosed to be effective.

Further, for example, in Patent Document 2 and Patent Document 3, as an aluminum alloy used for aircraft wings and fuselage stiffeners, Zn: 8.3 to 14.0 mass%, Mg: 0.5 to 4.5 mass %, Cu: 0.3 to 4.0 mass%, Zr: 0.03 to 0.15 mass%, the sum of Fe and Si is 0.25 mass% or less, and Sc, Hf, La, Ti, Ce, Nd , Eu, Gd, Tb, Dy, Ho, Er, Y, Yb containing 0.02 to 0.7% by mass, and the component composition consisting of the balance Al and unavoidable impurities, Zn, Mg , chemical composition _C Zn in _Cu, C _Mg, is _{C Cu, C Mg / C Cu} > 2.4, (7.9-0.4C Zn)> (C Cu + C Mg)> (6.4-0. both tensile test properties and moldability by adjusting to satisfy the 4C _Zn) Cell technology, and _{C Mg / C Cu <2.4,} (7.7-0.4C Zn)> (C Cu + C Mg)> be adjusted to satisfy (6.4-0.4C _Zn) Discloses a technique for achieving both tensile test characteristics and toughness.

On the other hand, aluminum is chemically less basic than hydrogen, so aluminum alloys including aluminum-zinc alloys are easily corroded in an environment where water vapor is present.
Therefore, it is desirable to use an aluminum alloy that is used in a corrosive environment after being subjected to a surface treatment such as an anodizing treatment. If such a surface treatment is used, the corrosion resistance can be simply improved. It is also possible to obtain a beautiful surface with good color tone.

  For example, in Patent Document 4, Zn: 8.5 to 12.0 mass%, Mg: 1.5 to 3.0 mass%, Cu: 2.1 to 3.0 mass%, and Zr: 0.05 -0.3 mass%, Mn: 0.1-0.8 mass%, Cr: 0.12-0.30 mass%, and V: 0.01-0.15 mass%, Ti: 0.1% by mass or less and B: 0.08% by mass or less selectively, consisting of the balance Al and inevitable impurities, and Si and Fe as impurities are 0.15% by mass or less and 0.08 respectively. For alloys with a mass% or less, a cast billet was extruded, and solution treatment, quenching, and aging treatment were performed to obtain a high-strength aluminum alloy extruded tube excellent in tensile strength and fatigue strength. Anodized leather for high strength aluminum alloy extruded tube By forming, stress corrosion cracking resistance, improved resistance to exfoliation corrosion resistance, utilized as the front fork of the motorcycle is the preferred technique related high-strength aluminum alloy extruded tube have been proposed.

  Further, for example, in Patent Document 5, Zn: 1.0 to 5.5% by mass, Mg: 0.5 to 2.0% by mass, and Mn: 0.5 to 2.0% by mass, and crystal grain fineness Ti: 0.003 to 0.15% by mass as an agent, alone or in combination with B: 1 to 100 ppm by mass, consisting of the balance Al and unavoidable impurities, and a texture with a calm color after anodizing A technology for obtaining a high-strength aluminum-zinc alloy wrought material having an achromatic gray color is disclosed.

Japanese Patent No. 135036 JP 2005-530032 A JP 2005-528521 A JP-A-8-295977 JP-A-4-45241

When the present inventors performed anodizing treatment on the aluminum-zinc alloy extruded material disclosed in Patent Document 2 and Patent Document 3, the anodized film after the anodizing treatment has a non-uniform color tone, It was found that there was a spotted pattern and the corrosion resistance was insufficient.
Furthermore, according to the present inventors' microscopic observation of the surface of the extruded material, there are many pit-shaped voids having a diameter of 10 to 100 μm on the surface, and the presence of the pit-shaped voids is as described above. It has been found that this is a cause of uneven spot pattern and insufficient corrosion resistance of the anodized film after anodizing.
Therefore, the present inventors tried to remove the pit-shaped gap as described above by grinding the surface of the extruded material, but the pit-shaped gap has a depth of 0.5 to 100 mm. In order to obtain an aluminum-zinc alloy extruded material with a uniform color tone that is not easy to remove by grinding and has sufficient corrosion resistance after surface treatment such as anodizing treatment, and has no spots, It has become necessary to obtain an ingot without any in advance.

  In other words, the present invention has no pit-like voids, is light and high in strength, and further exhibits surface resistance such as anodizing to exhibit excellent corrosion resistance even in an environment where water vapor is present, and the surface thereof. It is an object of the present invention to provide an extruded material of an aluminum-zinc alloy that can be made beautiful in color and a manufacturing method thereof.

The first invention of the present invention, which solves the above-mentioned problems, has a component composition of Zn: 7 to 12 mass%, Mg: 1.0 to 3.0 mass%, Cu: 0.5 to 3.0 mass% %, Cr: 0.03 to 0.30 mass%, Zr: 0.05 to 0.20 mass%, the balance is Al and inevitable impurities, and the content of hydrogen gas is 0.2 cc / 100 g or less, The number of inclusions that are oxide films is 0.005 pieces / mm ² or less at the fracture surface of the fracture surface observation method, and there is no pit-like void having a diameter of 10 to 100 μm and a depth of 0.5 to 100 mm in the surface layer portion. Is an extruded material of an aluminum-zinc based alloy.

In the second invention of the present invention, the component composition is Zn: 7-12% by mass, Mg: 1.0-3.0% by mass, Cu: 0.5-3.0% by mass, Cr: 0.03- 0.30% by mass, Zr: 0.05-0.20% by mass, and when the ingot of the above-mentioned composition is cast from an aluminum-zinc alloy molten metal whose balance is made of Al and inevitable impurities, It is an oxide film contained in the ingot by subjecting it to degassing treatment so that the hydrogen gas content contained in the ingot is 0.2 cc / 100 g or less, and the molten metal is subjected to inclusion removal treatment. Inclusion content is 0.005 / mm ² or less in the number of inclusions in the fracture surface of the fracture surface observation method, and the solidification rate when casting the ingot is 55 to 170 mm / min throughout the casting. Casting so that the resulting ingot is extruded This is a method for producing an extruded material of an aluminum-zinc alloy.

  In the extruded material of the aluminum-zinc alloy according to the present invention, no pit-shaped voids are observed, and according to the method for producing the extruded material of the aluminum-zinc-based alloy according to the present invention, there are no pit-shaped voids. Therefore, after the anodizing treatment, an aluminum-zinc alloy extruded material having a sufficient corrosion resistance and having an anodized film having a uniform color without spots can be obtained.

  That is, the extruded material of the aluminum-zinc-based alloy of the present invention is lightweight and high in strength, and has excellent corrosion resistance even in an environment where water vapor exists by being subjected to a surface treatment such as anodizing treatment. It exhibits the effect of making the surface beautiful and having a beautiful color tone.

It is a figure which shows the external appearance after the anodizing process of the aluminum- zinc type alloy extrusion material which concerns on this invention. It is a figure which shows the external appearance after the anodizing process of the extrusion material of the conventional aluminum-zinc type alloy. It is a longitudinal cross-sectional view of the pit-shaped space | gap which exists in the extrusion material of the conventional aluminum-zinc type alloy. It is a longitudinal cross-sectional view of the pit-shaped space | gap which exists in the extrusion material of the conventional aluminum-zinc type alloy. It is a schematic diagram which shows the shape of the test piece for inclusion number measurement which is an oxide film, (a1) is a front view, (a2) is a top view, (b) is an enlarged view which shows a notch part. It is a figure which shows the example of the inclusion which appeared on the fracture surface.

  The inventors of the present invention intend to use the extruded material of the aluminum-zinc alloy disclosed in Patent Document 2 and Patent Document 3 in an environment where water vapor exists. Oxidation treatment was performed. However, the appearance after the anodizing treatment obtained as a result was uneven in color as shown in FIG. 2, had a patch pattern and insufficient corrosion resistance.

Therefore, the present inventors conducted detailed observation and investigation of the surface in order to elucidate the cause.
According to the result of the magnified observation with a microscope, the surface of the extruded material has many pit-shaped voids having a diameter of 10 to 100 μm as shown in FIGS. According to the results, it was confirmed that the presence of the pit-like voids was the cause of the uneven spot pattern and insufficient corrosion resistance of the anodized film after the anodizing treatment as described above.

  Therefore, the present inventors tried to remove the pit-shaped voids by grinding the surface of the extruded material, but the pit-shaped voids had a depth of 0.5 to 100 mm (the state of the longitudinal section was 3), the removal by grinding is not easy, and the aluminum-zinc-based alloy having a uniform color without a mottled pattern having sufficient corrosion resistance after surface treatment such as anodizing treatment. It has been found that in order to obtain an extruded material, it is necessary to obtain a material having no pit-like voids in advance.

Furthermore, according to a detailed investigation by the present inventors, the pit-like voids are generated during the heat treatment for solution treatment after the extrusion of the aluminum-zinc alloy, and the inner surface of the pit-like voids. It was clarified that there was an inclusion that was an oxide film at one end of the film.
Specifically, the pit-shaped voids are formed after the hydrogen atoms dissolved in the molten aluminum-zinc alloy are supersaturated in the solidified aluminum-zinc alloy during the casting of the aluminum-zinc alloy, and then extruded. Peeling occurs at the interface with inclusions that are oxide film due to stress applied during processing, and it is supersaturated at the interface with inclusions that are peeling oxide film during the subsequent heat treatment for solution treatment. It was presumed that the hydrogen atoms that had been deposited as hydrogen gas generated bubbles, resulting in the formation of pit-like voids and remaining in the heat treatment for age hardening.

  Therefore, the present inventors have conceived to prevent the formation of pit-shaped voids as described above by performing degassing treatment and inclusion removal processing when casting the molten aluminum-zinc alloy. In this way, hydrogen atoms are not supersaturated in the solidified aluminum-zinc alloy, and peeling does not occur at the interface with the inclusions that are oxide films due to the stress applied during extrusion. Therefore, bubbles of hydrogen gas are not generated, and as a result, no pit-shaped gap is formed.

As a result, the component composition of the aluminum-zinc alloy was changed to Zn: 7 to 12% by mass, Mg: 1.0 to 3.0% by mass, Cu: 0.5 to 3.0% by mass, Cr: 0.03. -0.30% by mass, Zr: 0.05-0.20% by mass, the balance being Al and inevitable impurities, the hydrogen gas content in the ingot being 0.2 cc by degassing during casting / 100 g or less, the inclusion content in the ingot in the ingot by the inclusion removal treatment, the number of inclusions in the fracture surface in the fracture surface observation method is 0.005 pieces / mm ² or less, The present invention has been completed by finding that the above-described pit-like voids are not formed if the solidification rate is 20 to 300 mm / min over the entire ingot.

  That is, the appearance after the anodizing treatment of the product of the present invention was a uniform color with no spots as shown in FIG. 1, and the corrosion resistance was sufficient. FIG. 1 is a view showing an appearance after an anodizing treatment of an aluminum-zinc alloy extruded material according to the present invention.

  Furthermore, the amount of inevitable impurities is 0.2% by mass or less for Fe and Si, and 0.05% by mass or less per element for other elements than the component composition of the aluminum-zinc alloy of the present invention. However, the total amount is limited to 0.2% by mass or less, depending on the required surface color tone, to the aluminum-zinc based alloy of the present invention, a specific element selected in addition to the inevitable impurities, It is also possible to perform surface treatment such as anodizing treatment.

Usually, an aluminum-zinc alloy having the same composition as that of the present invention has an oxide film in the aluminum-zinc alloy because the density of the molten aluminum-zinc alloy and the density of inclusions, which are oxide films, are substantially equal. The inclusions are easy to disperse.Therefore, there are many exfoliation points at the interface with the inclusions generated by the stress caused by the extrusion process, and pit-like voids are formed by heat treatment for solution treatment in the subsequent process. However, as shown in FIG. 2, the appearance becomes uneven after the anodizing process, and the amount of corrosion increases.
The present invention is described in detail below.

[Degassing method]
As a degassing treatment method, methods such as a chlorine gas treatment method, an inert gas treatment method, and a flux treatment method are known, and any of these treatment methods can be suitably used in the present invention.
The effect of degassing by each of these degassing treatment methods can be measured by a known hydrogen determination method such as the Lansley method or the LECO method.

  In addition, when the content of hydrogen gas in all raw materials is 0.2 cc / 100 g or less and the raw materials are dissolved, melted and cast in an inert gas, etc., during melting, melting and casting When no hydrogen is contained in the molten metal and it is clear that the hydrogen gas content in the ingot can be reduced to 0.2 cc / 100 g or less without performing degassing treatment, Needless to say, the gas treatment can be omitted.

[Inclusion removal processing method]
As an inclusion treatment method, a filtration method using a filter such as a ceramic foam filter or a porous tube filter is known. In the present invention, a filtration method using these filters can be suitably used.
The effect of removing inclusions that are oxide films by the inclusion removal treatment method can be measured by a method such as a fracture surface observation method.

In this fracture surface observation method, a test piece 1 having the shape shown in FIG. 5 (a1, a2) is prepared, and the notch portion 2 is gripped on both sides with pliers and bent repeatedly, or one side of the notch portion 2 is a vise ( (Not shown), and the other side is broken by a method of hitting and bending the other side with a hammer. FIG. 5B is an enlarged view of the notch portion 2, and the effective observation area per fracture surface is 80 mm ² .
5A1 is a front view of the test piece 1, and FIG. 5A2 is a plan view.

In such a rupture mode, a rupture crack easily propagates along the interface with a thin film-like inclusion such as an oxide film. Therefore, if there is an inclusion that is an oxide film in the vicinity of the break, Inclusions that are oxide films appear on the fracture surface. An example of inclusions appearing on the fracture surface is shown in FIG.
Therefore, the specimen is broken as described above at five or more locations per sample, the number of inclusions appearing on those fracture surfaces is counted, the count value is divided by the sum of the effective observation areas, and the unit in the fracture surface observation method Inclusions that are oxide films are quantified as the number of inclusions per fracture surface area.

In addition, the content of inclusions which are oxide films in all raw materials is 0.005 pieces / mm ² or less of inclusions measured by the fracture surface observation method, and in the inert gas, In the case of melting, melting and casting, there is no formation of inclusions that are oxide films in the molten metal during melting, melting and casting, and oxidation in the ingot can be performed without inclusion removal treatment. When it is clear that the number of inclusions in the measurement using the fractured surface observation method can be 0.005 / mm ² or less, the inclusion removal treatment can be omitted. Not too long.

  The oxide film constituting the inclusion in the present invention is mainly composed of molten metal residue, which is an oxide of the alloy component generated when the aluminum-zinc alloy of the present invention is melted. In addition to oxides of alloy components, sulfides, carbides, nitrides and the like of alloy components may be included.

[Casting method]
In the present invention, the casting method is not limited, and a widely used casting method can be used. However, the DC casting method is preferable as a method for casting an ingot for extrusion. Here, the DC casting method refers to pouring a molten metal introduced into a quenching mold whose inner wall surface is water-cooled and cooling and solidifying the molten metal on the inner wall surface of the quenching mold, and the ingot immediately after solidification is directed downward or laterally. This is a casting method that draws out sequentially and injects cooling water into the ingot to quench it, and is a known aluminum alloy casting method with excellent productivity.

  Also, hot top DC casting is also known as a casting method of aluminum alloy, in which a heat insulating hot water reservoir is provided at the upper part of the quenching mold, and the molten metal is introduced into the heat insulating hot water reservoir by boiling and casting. Such a casting method is also a category of DC casting, and can be suitably used in the practice of the present invention.

  In this casting, casting is performed so that the solidification rate is 20 to 300 mm / min throughout the entire casting for producing the ingot. If the solidification rate is 20 to 300 mm / min over the entire casting, the shape and dimensions of the ingot are not limited. However, the ingot for extrusion has a cylindrical shape and a diameter of 50 to 500 mm. It is preferable. The cooling rate when casting a cylindrical ingot having a diameter of 50 to 500 mm at a solidification rate of 20 to 300 mm / min is about 1 to 50 ° C./s.

  However, even if the above-described degassing treatment method is used, hydrogen dissolved in the molten aluminum-zinc alloy cannot be completely eliminated, and even if the above-described inclusion removal treatment method is used, the aluminum-zinc system The inclusion content, which is an oxide film in the molten alloy, cannot be completely eliminated.

That is, even when the hydrogen gas content in the molten aluminum-zinc alloy is 0.2 cc / 100 g or less, if there is a portion whose solidification rate is less than 20 mm / min, the ingot portion cast at the solidification rate In this case, the reaction between the molten aluminum-zinc alloy and water vapor in the atmosphere causes the supersaturation degree of hydrogen atoms to be excessive, and the amount of inclusions that are oxide films increases, thereby forming pit-shaped voids. Sometimes.
On the other hand, even when the content of hydrogen gas in the molten aluminum-zinc alloy is 0.2 cc / 100 g or less, if there is a portion where the solidification rate exceeds 300 mm / min, the ingot cast at the solidification rate In the portion, the release of hydrogen gas from the molten metal surface is hindered, the degree of supersaturation of hydrogen atoms becomes excessive, and the inclusion of inclusions, which are oxide films, into the ingot increases, thereby forming pit-like voids. Sometimes formed.

[Extrusion and heat treatment]
In this invention, there is no restriction | limiting in the extrusion method of the ingot after casting, The extrusion method currently used widely can be utilized. Extrusion methods include a direct extrusion method and an indirect extrusion method, any of which can be used. There are no restrictions on the extrusion processing conditions such as extrusion ratio, extrusion temperature, and extrusion speed, but the extrusion ratio is preferably 5.0 to 200 and the extrusion temperature is preferably 300 to 500 ° C.

In addition, heat treatment for solution treatment and heat treatment for age hardening are performed following extrusion, but there are no restrictions on the conditions for these heat treatments, and well-known conditions for aluminum-zinc alloys should be adopted. Can do.
For example, as a heat treatment for solution treatment, a heat treatment condition in which the solution is rapidly cooled after heating at a temperature of 420 ° C. to 500 ° C. for 1 hour to 25 hours can be employed. For the rapid cooling, a known method such as water quenching can be employed.
As heat treatment for age hardening, the conditions of 90 ° C. to 180 ° C. and 1 hour to 50 hours can be adopted, and the temperature is changed within the above temperature range during the heat treatment for age hardening. A so-called two-stage aging heat treatment may be employed.

  By applying surface treatment such as anodizing, an aluminum-zinc alloy that exhibits excellent corrosion resistance even in an environment where water vapor is present, and can make the surface beautiful and well-colored. Extruded material and method for producing the same are applicable to other uses that require light weight and high strength and that do not require pit-like voids. is there.

Aluminum, zinc, and other alloy elements were dissolved and mixed to prepare a molten aluminum-zinc alloy having the composition shown in Table 1. For the produced molten aluminum-zinc alloy, an inert gas rotary blowing method is used as a degassing treatment method, and a filtration method using a # 30 ceramic foam filter is used as an inclusion treatment method. Carried out.
A portion of the molten aluminum-zinc alloy that was subjected to degassing treatment and inclusion treatment was collected, and the effects of degassing treatment and inclusion treatment were measured by the LECO method and the fracture surface observation method, respectively.

The observed fracture surface per sample in the fracture surface observation method is 22 to 40 locations. The measurement results are shown in Table 2.
In addition, the comparative example in which content of hydrogen gas exceeds 0.2 cc / 100g was produced by not performing a degassing process or shortening implementation time.
Moreover, the comparative example in which the number of inclusions exceeds 0.005 / mm ² was produced by not performing the inclusion treatment or shortening the implementation time.

Subsequently, the molten aluminum-zinc alloy subjected to degassing treatment and inclusion treatment was cast by a DC casting method, and then extruded by an indirect extrusion method to produce an extruded material.
Table 3 shows casting conditions and Table 4 shows extrusion conditions.
Then, a heat treatment for solution treatment and a heat treatment for age hardening were performed to prepare a test material, and the number of voids on the pit and the number of inclusions were measured.
Table 5 shows the heat treatment conditions for solution heat treatment and the heat treatment conditions for age hardening.

Table 6 shows the number of pit-like voids per unit surface area of the obtained specimen (extruded material [age-cured]).
According to Table 6, in Table 2, Invention Example 1 to Invention Example 5 in which the hydrogen gas content was 0.2 cc / 100 g or less and the number of inclusions was 0.005 pieces / mm ² or less. From the comparative examples 1 to 4 in which the content of hydrogen gas or the number of inclusions exceeds the above-mentioned values, while no pit-like voids are observed in the specimens prepared above It can be seen that there are pit-like voids in the specimen.

  According to the present invention, it is light and high-strength, and by applying surface treatment such as anodizing treatment, it exhibits excellent corrosion resistance even in an environment where water vapor is present, and beautiful aluminum whose surface is well-colored -A zinc-based alloy extruded material can be obtained.

Claims (2)

Component composition is Zn: 7-12 mass%, Mg: 1.0-3.0 mass%, Cu: 0.5-3.0 mass%, Cr: 0.03-0.30 mass%, Zr: 0.05 to 0.20 mass%, the balance is Al and inevitable impurities, the hydrogen gas content is 0.2 cc / 100 g or less, and the number of inclusions that are oxide films is the fracture surface in the fracture surface observation method An extruded material of an aluminum-zinc-based alloy, which is 0.005 pieces / mm ² or less and has no pit-like voids having a diameter of 10 to 100 μm and a depth of 0.5 to 100 mm in the surface layer portion. Component composition is Zn: 7-12 mass%, Mg: 1.0-3.0 mass%, Cu: 0.5-3.0 mass%, Cr: 0.03-0.30 mass%, Zr: When casting an ingot of the above component composition from a molten aluminum-zinc alloy containing 0.05 to 0.20% by mass with the balance being Al and inevitable impurities,
Degassing the molten metal, the hydrogen gas content contained in the ingot is 0.2 cc / 100 g or less,
Inclusion removal treatment is performed on the molten metal, and the inclusion content, which is an oxide film contained in the ingot, is 0.005 pieces / mm ² or less in the number of inclusions in the fracture surface of the fracture surface observation method. ,
Furthermore, casting is performed so that the solidification rate when casting the ingot is 55 to 170 mm / min throughout the casting,
A method for producing an extruded material of an aluminum-zinc alloy, wherein the obtained ingot is extruded.