JPH09249929A - Aluminum alloy sheet excellent in bendability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet excellent in bendability, in which the cracks occurring in a hard film on the surface are restricted to fine and insignificant ones at the time of bending an aluminum alloy sheet having a hard film such as anodic oxidation coating. SOLUTION: This sheet is an aluminum alloy sheet having a film of <=5μm on the surface and has a composition consisting of, by weight, 1.0-2.0% Mn, 0.005-0.2% Ti, Si and Fe limited to <=0.10% and <=0.15%, respectively, and the balance Al with inevitable impurities, or further, 0.3-1.5% Mg is added to this composition. Moreover, crystalline grains are composed of equiaxed crystals and crystalline grain size at the sheet surface and elongation at the tensile test are regulated to <=50μm and >=20%, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention suppresses the expansion of cracks generated in the hard coating on the surface during bending of an aluminum alloy plate having a hard coating having a thickness of 50 μm or less on the surface, such as anodizing treatment, and suppresses cracking. The present invention relates to an aluminum alloy plate that has no or very small and minute size.

[0002]

2. Description of the Related Art An Al--Mn alloy plate is disclosed in Japanese Patent Laid-Open No. 4-110.
As disclosed in Japanese Patent No. 493 (Mn-Al-based compound is precipitated in Mn-containing aluminum alloy and an alumite layer is provided, an aluminum plate having excellent far-infrared radiation characteristics can be provided). Since the far infrared radiation characteristics can be given, the radiation surface of the heater,
Utilization for the inner wall of a heating furnace is under consideration. At that time, from the viewpoint of efficiency, the manufacturing process is planned such that the surface treatment is performed and then the sheet is formed by sheet metal working or the like.

[0003]

However, since the coating film formed by the alumite treatment is hard, cracks are formed in the bent portion during the molding process. Since the part where such a crack is generated is local, the above-mentioned negative effect on the far-infrared radiation characteristic is not so great and the radiation characteristic is not extremely deteriorated, but it becomes a problem in appearance and corrosion resistance is also deteriorated. The characteristics of the product, such as deterioration, are regarded as problems.
In particular, if the film is dark-colored, the surface of the bent portion is discolored whitish due to the concentration of cracks, which is very conspicuous and causes a problem in appearance. For this reason, repair work such as painting is required as post-treatment.

In the present invention, in order to eliminate the defect that the appearance of coating and the corrosion resistance are deteriorated by cracking in the coating of the bent portion in the bending process of the aluminum alloy plate having the above-mentioned hard coating, first of all, A chemistry that can clarify the desirable characteristics of the aluminum material for eliminating or minimizing the occurrence of cracks in the bending process of the hard coating, and secondly, in the Al-Mn alloy having excellent far-infrared radiation characteristics, that can realize the above characteristics. This is a study of the ingredients.

[0005]

As a result of various studies on alloy components, microstructures, mechanical properties, etc., in order to solve the above problems, the inventor has arrived at the invention of the present invention. That is, the first aspect of the present invention is an aluminum alloy plate material having a film with a thickness of 50 μm or less on the surface, the crystal grains are equiaxed grains, the crystal grain size of the plate surface is 50 μm or less, and the elongation percentage in a tensile test. Is 20% or more, and the aluminum alloy plate is excellent in bending workability. The second aspect of the present invention is an aluminum alloy plate material having a coating film with a thickness of 50 μm or less on the surface, in which the component composition is Mn 1.0 to 2.0 wt%, Ti
Contains 0.005 to 0.2 wt% and Si 0.10
wt% or less, Fe 0.15 wt% or less, the balance consisting of Al and unavoidable impurities, the crystal grains are equiaxed grains, the crystal grain size of the plate surface is 50 μm or less, and the elongation rate in a tensile test. Is 20% or more, and the aluminum alloy plate is excellent in bending workability. The third aspect of the present invention is an aluminum alloy sheet material having a surface coated with a film having a thickness of 50 μm or less, and having a composition of Mn of 1.0 to 2.
0 wt%, Mg 0.3 to 1.5 wt%, Ti 0.005
.About.0.2 wt%, and regulated to Si 0.10 wt% or less and Fe 0.15 wt% or less, the balance consisting of Al and inevitable impurities, and the crystal grains are equiaxed grains, and the crystal grain size on the plate surface is It is an aluminum alloy plate excellent in bending workability, characterized in that it has an elongation of 50% or less and an elongation rate of 20% or more in a tensile test.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of each constituent element of the present invention will be described below.

First, the reasons for limiting the organization will be described. In order to suppress or minimize the expansion of cracks that occur during bending of the hard coating on the surface, the underlying aluminum material must be capable of relaxing the concentration of strain due to the notch effect of cracks in the hard coating. . That is, it is required that the strain distribution of deformation can be uniformly dispersed without locally concentrating, and the ductility of the material itself is high. When the inventor paid attention to the structure, if the crystal grain structure is coarse, the aluminum material itself, the deformation of the bending process is likely to be locally concentrated, and unevenness of skin roughness and fine cracks are likely to occur. Cannot be relaxed. Therefore, by making the crystal grain structure a fine equiaxed grain structure, it is possible to evenly disperse the strain distribution during bending, avoiding localized localization at one point, and avoiding the expansion of cracks. I found it. Specifically, in order to alleviate the cracks generated in the hard coating on the surface during bending and to reduce the cracks, the crystal grain size on the surface of the aluminum plate is 50 μm or less and the ductility of the aluminum material itself is small. It was found that the elongation percentage in the tensile test should be 20% or more. If the crystal grain size exceeds 50 μm, roughening occurs during molding, and cracks occur starting from this. Therefore, the crystal grain size is 50 μm or less.
If the elongation is less than 20%, the plate will be cracked and bending cannot be performed. Therefore, the elongation rate is 20% or more.

The thickness of the film provided on the surface is 50 μm.
If it is below, cracks can be prevented by the present invention in any coating such as anodized coating, thermal spray coating and coating coating, but if it exceeds 50 μm, cracking cannot be completely prevented only by the present invention. In some cases, the film thickness is limited.

Next, the effect of the alloy components will be described.

[Mn]: Mn forms an Al-Mn-based intermetallic compound, is a component essential for improving the far-infrared radiation characteristics by blackening the color tone after alumite treatment, and contributes to the refinement of crystal grains. To do. Normal Mn when Mn exceeds 2.0%
In casting, the range of formation of coarse primary crystals falls, which impairs the uniformity of the material and also reduces the bendability. Further, it becomes difficult to make the crystal grain shape of the final plate product into an equiaxed grain, which is not preferable.
On the other hand, if the Mn is less than 1%, the blackening of the color tone after the alumite treatment and the far infrared radiation characteristics are insufficient.

[Mg]: Mg is an additive component that contributes to the improvement of the strength of the Al material, and is a preferable element for addition to a material such as a radiation plate that requires particularly high strength. Also, Mg is Al
M tends to lower the stacking fault energy of the material, and M
Since the recrystallization of the g-added material is likely to occur in the heating step, the structure of the final plate product can be made equiaxed. If the Mg content is less than 0.3%, this effect is insufficient in the Al-Mn system. If the Mg content exceeds 1.5%, the strength becomes too high and the bending process becomes difficult.

[Fe]: The presence of Fe is limited to 0.15% or less in a high Mn-containing alloy because it tends to generate coarse Al-Fe-Mn crystallization compounds and deteriorates bendability.

[Si]: Si affects the precipitation of Al-Mn-based intermetallic compounds and weakens the grain refining action of Mn. Also, αAlMn (Fe) Si compound is generated,
Since it inhibits the blackening of the color tone after anodizing, it is 0.1
0% or less.

[Ti]: Ti refines the crystal grains of the ingot, and if it is less than 0.005%, the effect cannot be obtained.
If it exceeds 0%, a coarse compound is formed.
The range was 0.2%. When Ti is added in combination with B, the effect of refining is further promoted. Therefore, when B is added, 0.001 to 0.005% is preferable.

The other alloy elements are Cu ≦≦ as impurities.
0.5%, Zn ≦ 0.5%, Cr ≦ 0.5%, Na · K
If ≦ 5 ppm, the characteristics of the present invention are not adversely affected.

[0016]

Embodiments of the present invention will be described below.

From alloy materials having various compositions shown in Table 1, materials with a plate thickness of 1.0 mm having different metallographic structures and mechanical properties were manufactured. Inventive Examples Nos. 1, 2, and 3 are DC ingots (thickness 500 mm, width 1400 mm) of a real machine scale, 560 ° C. × 10
After soaking for about an hour, heat to 460 ° C and plate thickness 3.5m
After hot rolling to m, cold rolling to 1.0 mm thickness, 5
Continuous annealing at 00 ° C was performed. Invention Example No. 4 has no soaking 5
After heating at 00 ° C., hot rolling was performed to a plate thickness of 3.5 mm, cold rolling was performed to a plate thickness of 1.0 mm, and then box annealing was performed at 390 ° C. for 2 hours. In Comparative Examples Nos. 5 and 6, the continuously cast rolled material having a plate thickness of 7 mm was heat-treated at 450 ° C. for 2 hours, and then the plate thickness was 1.
It was cold-rolled to 0 mm and subjected to box annealing at 405 ° C. for 2 hours. Comparative examples 7 and 8 are DCs similar to Nos. 1 to 4.
After soaking at 560 ℃, the thickness of the ingot is 3.5 after heating at 460 ℃.
After hot-rolling to mm, Comparative Example No. 7 was cold-rolled to a plate thickness of 1.0 mm and then box-annealed at 390 ° C. for 2 hours. Comparative Example No. 8 was cold-rolled to a plate thickness of 1.5 mm,
After that, continuous annealing was performed at 500 ° C., and further cold rolling was performed to a plate thickness of 1.0 mm. After caustic etching of this plate material at 50 ° C. in a 5% NaOH aqueous solution for 10 μm, a film thickness of 20 μm was obtained in a 15 Vol% sulfuric acid bath at 20 ° C. under the conditions of 1.5 A / dm ^2.
Of the anodic oxide film.

[0018]

[Table 1]

Strip-shaped test pieces parallel to and perpendicular to the rolling direction were sampled from this material and bent at 90 ° (pushing punch tip radius 0.5R), and the appearance of cracks on the outer surface of the bent portion was visually observed. It was judged. Table 2 shows the results. Here, ∘ indicates that no cracks are generated or is a minor crack that can be ignored, Δ indicates that a microscopic crack that cannot be ignored is observed, and x indicates that a remarkable crack is observed. In addition, a tensile test was performed to measure tensile strength, proof stress, and elongation, and whether or not the crystal grains were equiaxed grains and the size of the crystal grains were observed and measured by microscopic observation.

[0020]

[Table 2]

As shown in Table 2, in the invention examples in which the elongation was 20% or more, the crystal grains were equiaxed, and the crystal grain size was 50 μm or less, the occurrence of cracks in the surface coating at the bend was negligible. . Nos. 1 to 4 are inventive examples, and in all of them, the occurrence of film cracking at the bent portion was not recognized, and they had good bendability. In No. 5, since the amount of Mn was too large and the crystal grain structure was layered, remarkable cracking occurred in the bent portion.
No. In Nos. 6 and 7, since Mg is not added in the annealing treatment, recrystallization is hard to occur and the equiaxed grain formation is delayed, and the structure is a mixture of equiaxed grains and layers, or softening is delayed, and There are cracks. No. No. 8 has an equiaxed grain structure, but the elongation is lower than 20%, so that the formability is inferior and cracking occurs.

[0022]

As described above, according to the present invention, in an aluminum plate material having a hard coating with a coating thickness of 50 μm or less on the surface to be bent, the texture and elongation of the aluminum alloy sheet can be adjusted to specific values. The strain distribution due to the deformation of the bent part is made fine and uniform. As a result, good bending can be performed, and there are almost no cracks on the surface of the bent part. Therefore, it has a good appearance quality and does not deteriorate the corrosion resistance. An aluminum alloy plate can be provided. Further, by specifying the component composition range, Al having excellent far infrared radiation characteristics having the above characteristics
An -Mn-based alloy plate and an Al-Mn-Mg-based alloy plate can be provided.

Claims (3)

[Claims] 1. An aluminum alloy plate material having a film having a thickness of 50 μm or less on the surface, wherein the crystal grains are equiaxed grains, the crystal grain size of the plate surface is 50 μm or less, and the elongation percentage in a tensile test is 20. % Or more, an aluminum alloy plate having excellent bending workability. 2. An aluminum alloy sheet material having a surface coated with a film having a thickness of 50 μm or less, wherein the component composition is Mn1.0.
~ 2.0 wt%, Ti 0.005-0.2 wt%, Si 0.10 wt% or less, Fe 0.15 wt%
Restricted below, the balance consists of Al and unavoidable impurities,
An aluminum alloy plate excellent in bending workability, characterized in that the crystal grains are equiaxed grains, the crystal grain size on the plate surface is 50 μm or less, and the elongation percentage in a tensile test is 20% or more. 3. An aluminum alloy plate material having a surface coated with a film having a thickness of 50 μm or less, wherein the component composition is Mn1.0.
.About.2.0 wt%, Mg 0.3 to 1.5 wt%, Ti0.
005 to 0.2 wt% and Si 0.10 wt
% Or less and Fe 0.15 wt% or less, with the balance being Al
And bending resistance, which is characterized by being inevitable impurities, having equiaxed crystal grains, having a crystal grain size of 50 μm or less on the plate surface, and having an elongation percentage of 20% or more in a tensile test. Aluminum alloy plate.