JP2008231518A - Aluminum alloy with excellent bendability and brightness after anodizing treatment, and its extruded shape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy in which the occurrence of cracks and orange peel can be suppressed at bending and which has excellent brightness after anodizing treatment and also to provide its extruded shape. <P>SOLUTION: The aluminum alloy has a composition, by mass, containing 0.10 to 0.50% Mg<SB>2</SB>Si as a stoichiometric composition of Mg<SB>2</SB>Si and 0.50 to 0.90% excess Si, also containing 0.10 to 0.60% Cu, 0.10 to 0.40% Mn, 0.005 to 0.1% Ti, ≤0.05% Fe, ≤0.10% Cr and ≤0.10% Zr and having the balance aluminum with inevitable impurities. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aluminum-based alloy suitable for fields requiring bending workability and appearance design and an extruded shape thereof.

Aluminum alloys are widely used as lightweight alloys such as home building materials and automobile parts.
In recent years, with the diversification of designs in the residential field and automobile field, strong bending processing according to the required product shape is required when producing products using extruded profiles, and the appearance is required to have high glitter. ing.
When extrusion molding is performed using a JIS 6000 series aluminum alloy, the extruded portion generally has a granular recrystallized surface.
If the crystal grain size of this recrystallized structure is large, a rough orange peel like orange peel is likely to occur on the metal surface during bending, and the surface quality is different from that of the straight part that has not been bent and the appearance quality deteriorates. .
Therefore, mechanical buffing is often performed to remove the orange peel, which increases the manufacturing cost.
In addition, if the bending process is strong, there is a problem that cracks and cracks are likely to occur in the outer periphery of the bending R.
In particular, when anodizing is performed as a rust-preventing treatment, the oxide film tends to cloud due to the added components in the aluminum alloy, and there is a limitation on the addition of recrystallized grain refining elements.
Patent Document 1 discloses an aluminum alloy excellent in glitter after anodizing treatment and surface properties of the bent portion, but in the case of strong bending, the material may be cracked.

Japanese Patent No. 3690623

  An object of the present invention is to provide an aluminum alloy that suppresses generation of cracks and orange peel during bending and is excellent in glitter after anodizing, and an extruded shape thereof.

Glitter excellent aluminum alloy after bending according to claim 1, wherein processability and anodic oxidation treatment, excess and 0.10 to 0.50 wt% _Mg 2 Si component as stoichiometry of _Mg 2 Si Si While containing 0.50-0.90 mass%, Cu component 0.10-0.60 mass%, Mn component 0.10-0.40 mass%, Ti component 0.005-0.1 mass %, Fe component 0.05 mass% or less, Cr component 0.10 mass% or less, Zr component 0.10 mass% or less, the balance being aluminum and inevitable impurities.

  An extruded profile excellent in bending workability and brightness after anodizing according to claim 2 is an extruded profile manufactured using the aluminum alloy according to claim 1, wherein the recrystallized grains have an average grain size. Is 100 μm or less.

A manufacturing process that uses aluminum alloy extruded shapes to bend to the required product shape, then performs brightening treatments such as chemical polishing and electrolytic polishing, and then anodizes for rust prevention purposes First, a material that does not easily cause cracks or cracks on the outside of the bend during bending is required.
Secondly, an extruded profile with excellent surface properties that can suppress the occurrence of orange peel that tends to occur on the surface of the material by bending is desirable.
If the orange peel is large, mechanical polishing such as buffing is required, which increases the manufacturing cost.
Thirdly, when glitter is required as an appearance design, an oxide film formed by anodizing treatment is required to be a material with little fogging and less gloss reduction.
However, as the anodic oxide film has more additive components in the aluminum alloy, the added components are more likely to remain in the oxide film and clouding tends to occur. On the other hand, in order to suppress orange peel during bending, Since a finer component is required and a precipitation component is required to ensure strength, the strength, bending workability, surface quality during bending, and glitter after anodization are in a reciprocal relationship.
The present invention has been completed as a result of extensive studies to achieve both of these qualities.

Next, the reason for setting the component range of the aluminum alloy will be described.
(Mg and Si components)
The Si component in the aluminum alloy is a factor that decreases the brightness after the anodizing treatment. However, in the 6000 series alloy, the strength is improved by precipitation of the Mg ₂ Si intermetallic compound. It is a necessary component, and the stoichiometric composition of Mg ₂ Si is preferably in the range of 0.1 to 0.5% by mass (hereinafter simply referred to as “%”).
The strength is improved by the appearance of Mg ₂ Si precipitates, but the size of the precipitates becomes finer and dispersed, and the bending workability is improved.
Relative Therefore _Mg 2 Si stoichiometric composition, the excessive amount of Si than balance Si amount in the range of from 0.50 to 0.90%, tried to fine dispersion of the _Mg 2 Si precipitate.
Excess Si remains in the structure as metallic silicon without forming an intermetallic workpiece with Mg, but this metallic silicon has the effect of reducing the size of the Mg ₂ Si precipitate.
Here, if the excess silicon is less than 0.50%, the effect of miniaturizing and dispersing Mg ₂ Si precipitates is small, and if it exceeds 0.90%, the glitter after anodizing treatment is lowered.
As described above, the Mg component is a component necessary for the precipitation of the intermetallic compound Mg ₂ Si necessary for securing the strength, but in the present invention, an excess amount of Si is 0.50 to 0.90 more than stoichiometric Si. Therefore, it is preferable that the Mg content is as small as possible within the range required for the strength required for the product, and Mg alone is preferably in the range of 0.10 to 0.50%.
When the Mg component is added in a large amount, the extrudability is lowered. Therefore, the content is preferably 0.45% or less, and more preferably 0.3% or less.

(Cu component)
The Cu component is useful for improving the glossiness during the chemical polishing process and the electrolytic polishing process, and contributes to the improvement of the strength of the material. However, if the added amount is large, the corrosion resistance is lowered and the extrudability is also inhibited. The amount is preferably in the range of 0.10 to 0.60%, and from the viewpoint that gloss is likely to appear during chemical and electrochemical polishing, the range is preferably 0.25 to 0.60% and ideally 0.40. It is in the range of ˜0.60%.

(Fe component)
Fe component is a factor that lowers the transparency of the anodized film, and it is preferable that the Fe component is small in order to maintain the glitter after the anodizing treatment.
Moreover, since Fe component forms an intermetallic compound with Si and takes in metallic silicon as a crystallized substance, 0.05% or less is good.

(Mn, Cr and Zr components)
All of the Mn, Cr and Zr components suppress the recrystallization coarsening and are effective in refining the crystal grains. To control the average grain size of the crystal grains to 100 μm or less, at least a Mn component of 0.10 to 0. 40% is required.
However, when these components are added in an increased amount, the sensitivity to quenching becomes sharp, which causes a decrease in strength and a decrease in glitter after anodization.
Therefore, when the Mn component is in the range of 0.10 to 0.40%, the Cr component is preferably 0.10% or less and the Zr component is 0.10% or less.

(Ti component)
The Ti component is effective in refining crystal grains when casting a billet for extrusion molding, and the Ti component is preferably in the range of 0.005 to 0.10% as a range where the effect is recognized.

  In the present invention, the amount of unavoidable impurities other than those described above is preferably 0.05% or less as a single substance, and is suppressed to 0.15% or less in total.

In the first aspect of the present invention, since the alloy was designed so as to contain 0.50 to 0.90% of the Si amount in excess of the stoichiometric Mg ₂ Si balance composition, the Mg ₂ Si precipitate was finely formed. By controlling the range of Mn, Cr and Zr components, which are crystal grain refining components, and suppressing Cu components to 0.10 to 0.60% and Fe components to 0.05% or less, Even when a strong bending process exceeding 30% is not generated, cracks do not occur, the orange peel on the surface of the material is smaller than before, and the number of mechanical buffing processes can be reduced. Excellent aluminum alloy can be obtained.

  In the second aspect of the invention, the billet is cast using the aluminum alloy of the first aspect, and the average grain size of the recrystallized grains of the extruded shape is controlled to 100 μm or less by extrusion molding. It is possible to obtain an extruded profile that is excellent in both the surface properties and the glitter of the part.

An example of an aluminum alloy according to the present invention was prototyped and compared with a conventional alloy, which will be described below.
The present invention is not limited to the prototype aluminum alloy.

A cylindrical billet was cast by a conventional method using a melt adjusted to the alloy components shown in the table of FIG.
Alloy No. 1 to 7 are aluminum alloys corresponding to examples of the present invention. 8 to 11 are trial manufactures of conventional alloys for glittering treatment as comparative examples.
In the table of FIG. 1, Si, Fe, Cu, Mn, Mg, Cr, Zn, Zr, and Ti are components confirmed by analysis, and the balance is Al and inevitable impurities.
The amount of Mg ₂ Si component obtained by calculation from the analysis results of the Si component and the Mg component, and the amount of Si excess from the balance Si amount are expressed as exSi, and are shown in the table.
The cast cylindrical billet was homogenized under the conditions of 565 to 595 ° C. × 4 hours or more, and then the billet was preheated to 470 to 510 ° C., and an extruded shape for test evaluation was extruded according to a conventional method.
When the homogenization temperature of the billet is less than 565 ° C., dispersion of the crystallized product during casting becomes insufficient.
Moreover, if the preheating temperature of the billet during extrusion molding is less than 470 ° C., quenching after extrusion becomes insufficient.
The extruded shape for test evaluation is a plate having a width of 80 mm and a thickness of 1.2 mm. Immediately after extrusion, the extruded shape is cooled by a fan air cooling at a cooling rate of 70 ° C./min or more, and then 175 to 195 ° C. for 1 to 24 hours. The artificial aging treatment was applied.

The result of evaluating each quality characteristic using the extruded profile prototyped above is shown in the table of FIG. 2, and the evaluation method will be described below.
In addition, the determination “◯” was made when all the quality items in the table reached the target.
(Mechanical properties of T1 and T5 materials)
Tensile strength, yield strength, and elongation at break were examined by a tensile test.
A JIS No. 5 tensile test piece was produced from the extruded profile, and obtained based on JIS-Z2241 with a tensile tester compliant with JIS standards.
Here, the T1 material means a material after extrusion and air cooling, and the elongation (δ) was set to 20% or more from the viewpoint of bending workability.
T5 material refers to a material subjected to artificial aging treatment, and the target was 0.2% proof stress (σ _0.2 ) of 150 MPa or more from the viewpoint of ensuring product strength.
(Brightness)
The test material was pickled with 20% nitric acid after chemical polishing for 90 seconds at 95-100 ° C. using an aqueous solution of 70-85% phosphoric acid and 3-3.5% nitric acid, and an electrolytic solution containing 20% sulfuric acid was used. Anodized at 100 to 120 A / m ² for 30 minutes, and an anodized film having a film thickness of about 10 μm was formed and evaluated.
The L value of the color tone of the surface of the aluminum alloy was measured by a color difference meter (Murakami Color Research Laboratory, specular color difference meter SCD-1) using a Lab color system (CIE standard).
Aiming for a luster close to metallic luster, an L value of 80 or more was targeted.
(Recrystallized grains)
The sample material was mirror-polished and then etched, and the metal structure was observed with a 400 × bright microscope, and the average crystal grain size was measured.
(Surface properties)
A 20 mm × 150 mm plate was cut out from the test material and evaluated by bending it to a U shape with a radius of 1.5 mm.
The orange peel below the extent that mechanical buffing is not required was evaluated as good.
(Bendability)
As shown in FIG. 5A, a 20 × 150 mm test piece is cut out from the specimen, fixed with a jig, and a load is applied from the top with a punch with a predetermined radius R, and the displacement-load line at that time The figure was determined as shown in FIG.
When bending is performed in this manner, the U-shaped tip needs to be stretched by 30 to 40% or more.
The comparative example aluminum alloy (conventional alloy) showed a displacement-load line like a.
On the other hand, when the aluminum alloy according to the present invention is used, a displacement-load line as shown in b is obtained.
This is because conventional aluminum alloys cannot withstand a local elongation of 30% or more, and if a crack occurs in the material near the maximum load, it grows quickly and cracks, and the load drops rapidly. In the case of the alloy of the present invention, cracks are unlikely to occur, so-called stickiness occurs, and the load gradually drops.
The state of occurrence of cracks is shown in the photograph of FIG.
For reference, the elongation at the outer periphery was estimated using the schematic diagram shown in FIG.
To predict the limit bending R, consider a simple model with a bending angle of 90 degrees as shown in FIG.
Since the difference between the length of the outer circumference and the inner circumference of the bending thickness of this part is the material elongation, assuming that there is no elongation of the inner circumference, the elongation rate from the relationship between the outer circumference length and elongation is
Assuming that the neutral axis is the center of the plate thickness, it can be estimated that elongation / 2/2 = 40%.

Example No. Alloys 1 to 7 and Comparative Example No. 1 Extruded shapes using alloys 10 and 11 have an excess Si (exSi) value in the range of 0.50 to 0.90% in excess of balance silicon, and as shown in FIG. In contrast, no cracking occurred even when bent to extend 30% or more. As for 8 and 9, the crack generate | occur | produced as shown in FIG.6 (b).
Comparative Example No. No cracks occurred in the bending evaluation of No. 10, but Comparative Example No. As shown in FIG. 3B, the average grain size of the recrystallized grains as well as 8 and 9 is 200 μm and exceeds 100 μm, so that a large orange peel as shown in FIG. .
On the other hand, Example No. The extruded shapes using the alloys 1 to 7 had an average grain size of recrystallized grains of 100 μm or less as shown in FIG. 3A and a small orange peel as shown in FIG.
When the mirror surface L values of the anodized surface having a thickness of 10 μm were compared, Example No. Comparative Examples No. 1 to 8 were 80 or more. Nos. 10 and 11 had low glitter.

  As described above, the extruded shape member using the aluminum alloy according to the present invention does not generate cracks even in local bending with an elongation of 30% or more, and obtains a glitter of 80 or more with an L value after anodizing treatment. be able to.

The component table | surface of the aluminum alloy used for test evaluation is shown. The evaluation result of each characteristic of an extrusion shape material is shown. The micrograph of a recrystallized grain is shown. The photograph of the surface property of a bending part is shown. A bending evaluation method and a displacement-load diagram are shown. An appearance photograph after the bending test is shown. It is a schematic diagram which shows the relationship between bending R and elongation.

Claims (2)

The _Mg 2 Si component 0.10-0.50 wt% and an excess amount of Si as a stoichiometric composition of Mg ₂ Si with containing 0.50 to 0.90 mass%, Cu component from 0.10 to 0. 60% by mass, Mn component 0.10 to 0.40% by mass, Ti component 0.005 to 0.1% by mass, Fe component 0.05% by mass or less, Cr component 0.10% by mass or less, Zr An aluminum alloy excellent in bending workability and brightness after anodizing treatment, wherein the component is 0.10% by mass or less and the balance is aluminum and inevitable impurities. An extruded profile produced using the aluminum alloy according to claim 1,
An extruded shape excellent in bendability and brightness after anodization, wherein the recrystallized grains have an average grain size of 100 μm or less.