JPH11140609A - Production of aluminum alloy for building material excellent in surface treatment property and workability by using continuously cast coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the bendability as well as the uniformity of external appearance after anodic oxidation treatment of an aluminum alloy sheet for building materials obtained by continuous casting. SOLUTION: A molten aluminum alloy, having a composition consisting of, by weight, <=0.8% Fe, <=0.8% Si, <=0.2% Cu, and the balance Al with inevitable impurities, is continuously cast and rolled to directly form a strip-like cast sheet of <=10 mm sheet thickness. After cold rolling at >=10% is applied to the cast sheet, the resultant rolled sheet is heat treated at >=450 deg.C and then subjected to cold rolling at >=30% and to heat treatment at >=400>=C at >=100 deg.C/min temp. rise rate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum alloy sheet which is suitably used as an aluminum alloy sheet for a building material subjected to an anodizing treatment. More specifically, the present invention relates to a method for producing an aluminum alloy sheet for building materials having excellent surface quality after anodizing treatment and excellent bending workability by using a continuously cast and rolled coil.

[0002]

2. Description of the Related Art Generally, a method of manufacturing an aluminum alloy sheet is to perform a hot rolling after homogenizing a slab obtained by casting a molten aluminum alloy by a semi-continuous casting method, or directly form a molten aluminum alloy by a continuous casting and rolling method. Cast to a thickness of 10mm or less, and then cold roll (if necessary, before, during,
In some cases, annealing is performed later) to obtain a plate having a desired size and performance.

[0003] However, in general, an aluminum alloy plate subjected to a surface treatment is subjected to surface treatment such as chemical etching, electrochemical etching and anodic oxidation in a post-processing step after forming into a plate by the above steps. The homogeneity of the metal structure greatly affects the surface quality. That is, if there is a variation in the metallographic structure, the appearance of the sheet material after the surface treatment becomes non-uniform in the form of a band or a patch, resulting in poor appearance.

[0004] One of the causes of the variation of the metallographic structure is the unevenness of the cast structure. For example, the structure of a slab cast by a semi-continuous casting method generally changes its structure from a chill layer, a coarse cell layer, and a fine cell layer as it moves from the casting surface to the inside. Here, the portion combining the chill layer and the coarse cell layer is generally called a "frame" and becomes an unstable metal structure, which has a bad influence on the surface quality. In addition, the continuous casting and rolling method omits the soaking and hot rolling steps, is a very effective method for improving the yield and energy efficiency, etc., and can increase the cooling rate of the molten metal. Since the second phase particles are easily formed into a solid solution and the second phase particles are easily made fine, an aluminum plate excellent in impact resistance, moldability and fatigue strength is generally obtained.

However, this continuous casting and rolling apparatus is:
Since the mold continuously moves with respect to the molten metal supplied from the basic structure, contact between the molten metal and the mold during casting is unstable. For this reason, there is a problem that the cooling rate of the molten metal tends to vary, which causes a non-uniform casting structure.

[0006] As in the semi-continuous casting method, it is difficult to remove the non-uniform portion of the cast structure by face milling, since the sheet thickness is as thin as about 10 mm, and it is difficult to process. Since this affects the depth of several mm or even the center of the sheet thickness in some cases, it is not a realistic method in consideration of the yield. As described above, the continuous casting and rolling method is an attractive method in terms of production efficiency and characteristics as compared with the semi-continuous casting method, but it is difficult to remove this part because the casting structure is uneven and it is difficult to remove this part. It has been a general opinion that it is not appropriate to apply a surface treatment typified by a metal plate, a printing plate, or the like to an aluminum plate that requires strict uniformity in appearance after the treatment.

Also, an aluminum alloy plate using a continuous cast plate has a problem that a roughened portion or a crack is apt to be generated in a worked portion during bending due to a large crystal grain size. Had the disadvantage that it could not be used.

[0008]

SUMMARY OF THE INVENTION The present invention solves the problems of the prior art in the above-mentioned continuous cast sheet, and provides a method for producing an aluminum alloy sheet for building materials having an excellent appearance after anodizing and excellent bending workability. The purpose is to provide.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to overcome the above-mentioned drawbacks of the conventional production method, and as a result, have developed the following method for producing an aluminum alloy for building materials. is there.

That is, in the present invention, Fe: 0.8% by weight
(Hereinafter, the weight% is simply referred to as%.) In the following, an aluminum alloy melt containing Si: 0.8% or less, Cu: 0.2% or less, and the balance consisting of Al and inevitable impurities is continuously cast and rolled and directly. A strip-shaped cast plate having a plate thickness of 10 mm or less is obtained. After cold rolling of 10% or more is applied to the cast plate, a heat treatment is performed at a temperature of 450 ° C. or more.
A method for producing an aluminum alloy for building materials having excellent surface treatment properties and workability, characterized by performing a heat treatment at 400 ° C. or more at a rate of temperature increase of not less than ° C./min.

Next, the present invention will be described in detail. In the alloy composition, Fe is set to 0.8% or less. Fe
Has the function of making the anodized surface uniform. Fe is an element that forms an Al-Fe-based and Al-Fe-Si-based intermetallic compound by being combined with other elements in an aluminum alloy, and among these intermetallic compounds, an intermetallic compound having a size of 1 to 20 μm. Has the effect of refining recrystallized grains and the effect of forming a uniform and fine anodized surface.
However, if the content exceeds 0.8%, the anodized surface becomes non-uniform due to the formation of coarse compounds exceeding 20 μm.

The content of Si is set to 0.8% or less. Preferably it is 0.5% or less, more preferably 0.2% or less. S
i is usually contained as an impurity, and if it exceeds 0.8%, it is not preferable because defects tend to occur in which microscopically insufficient spots are scattered on the anodized surface.

The reason why Cu is limited to 0.2% or less is that if Cu exceeds 0.2% as an impurity, the corrosion resistance is reduced.

Other impurities include Mn, Mg, Cr, Ni, V, and the like contained in ordinary aluminum ingots.
There are Zn and the like, but there is no particular problem when each of them is less than 0.05%. Further, the content of Ti and B of 0.1% or less as an optional additive element is effective for refining the solidification structure at the time of casting, similarly to DC casting.

In the present invention, in casting an aluminum alloy, a "continuous casting and rolling method" is used in which a molten metal is directly cast to a thickness of 10 mm or less. Here, the reason for setting the plate thickness to 10 mm or less is that, as described above, in the continuous casting and rolling method, the cooling rate of the molten metal can be increased, so that the alloy component is easily forcibly solid-dissolved, and This is because various advantages can be obtained as material properties because
If the plate thickness is 10 mm or more, a cooling rate sufficient for forced solid solution cannot be obtained, and the intermetallic compound becomes coarse, which is not preferable. The continuous casting and rolling method to be used here includes a hunter method using twin rolls, a 3C method, a Hezley method using twin belts, and the like. However, the present invention is not limited to any particular method among them. It is not something to be done.

Next, in the present invention, the continuous cast plate obtained by the continuous cast rolling is subjected to a cold rolling of 10% or more and then to a heat treatment at a temperature of 450 ° C. or more. The cold rolling before the heat treatment has an effect of promoting the destruction of the cast structure during the heat treatment performed thereafter. If the cold rolling reduction is less than 10%, the fracture of the cast structure does not proceed sufficiently, so that a streak pattern is likely to be generated during the anodizing treatment, which is a problem in appearance. Therefore, cold rolling before heat treatment needs to be 10% or more.

The heat treatment following the cold rolling must be performed at a temperature of 450 ° C. or higher. This heat treatment has an effect of dividing and spheroidizing the crystallized product in the continuous cast plate, and has an effect of breaking an uneven casting structure and changing it to a uniform structure. The combination of the cold rolling and the high temperature annealing has succeeded in greatly improving the surface quality during the anodizing treatment of a continuous cast plate, which was impossible in the past. If the temperature is lower than 450 ° C., this effect is not sufficient, and the recrystallized grain size at the time of subsequent annealing becomes coarse, streak is likely to occur at the time of surface treatment, and appearance is impaired.

In the cold rolling following the heat treatment, a rolling reduction of 30
% Or more is required. This cold rolling reduction is for introducing a strain amount necessary for refining the crystal grains in the heat treatment of the next step. When the cold rolling ratio is less than 30%, the strain amount is insufficient and the crystal grains in the heat treatment of the next step are finely divided. Can not be converted.

The heat treatment following the above cold rolling is performed at 100 ° C.
An annealing temperature of 400 ° C. or more at a heating rate of not less than / min is required. If the temperature is less than 100 ° C./min, the second phase particles precipitate during annealing, and the crystal grains become coarse due to competition between recrystallization and precipitation, and the surface becomes rough during bending. At an annealing temperature of less than 400 ° C., a crack is generated during bending since the processed structure remains without a complete recrystallized structure.

The aluminum alloy sheet as described above is then cold-rolled, if necessary, to adjust its strength, and further subjected to anodizing treatment to be a building material.

[0021]

EXAMPLES Cast aluminum alloy melts having the chemical compositions shown in Tables 1 and 2 were formed into cast coils having a thickness of 7 mm and a thickness of 10 mm, respectively, by a hunter caster using twin rolls.
The cast coil was subjected to cold rolling and annealing in the manufacturing steps shown in Tables 1 and 2 to obtain a rolled plate having a thickness of 2 mm.
The rolled plate was subjected to sulfuric acid alumite treatment under the following treatment conditions to form an anodized film having a thickness of 15 μm. The samples thus obtained were evaluated for uniformity of appearance and bending workability by the following methods.

<Anodizing treatment conditions> Pretreatment: After immersing in a 5% NaOH solution at 50 ° C. for 1 minute, immersing in a 30% HNO ₃ solution at room temperature for 1 minute and washing with water ↓ Anodizing: 15% at 20 ° C. Processing is performed at a current density of 1.3 A / dm ² in an H ₂ SO ₄ solution to form a 15 μm film. ↓ Rinse: tap water for 15 minutes ↓ Sealed hole: immersed in boiling pure water for 15 minutes ↓ Drying: hot air drying ↓ Bending test: 90 ° bending at inner radius 0

<Evaluation method> The appearance was visually observed, and ◎ indicates that the uniformity of the appearance after the surface treatment was excellent, を indicates that it was good, Δ indicates that it was slightly inferior, and ×
The judgment was made as follows. Further, by visually observing the bent portion after the bending test, ◎ indicates that the workability is excellent without roughness and cracks, を indicates that it is good, and △ indicates that it is slightly inferior.
An inferior thing was evaluated as x.

[0024]

[Table 1]

[0025]

[Table 2]

As is clear from Tables 1 and 2, the building materials manufactured using the aluminum alloy plates cast under the conditions of the present invention have excellent appearance uniformity and bending workability.

[0027]

As described above, according to the present invention, the surface quality and bending workability of the aluminum alloy sheet for building material obtained by continuous casting and rolling are improved, and the aluminum alloy sheet for building material having excellent quality characteristics at low cost is manufactured. It has become possible.

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI // C22F 1/00 613 C22F 1/00 613 673 673 681 681 685 685Z 686 686B 691 691B 691A 694 694A

Claims (1)

[Claims] 1. Fe: 0.8% by weight or less, Si: 0.8% by weight
% By weight, Cu: 0.2% by weight or less, with the balance A
and an aluminum alloy melt comprising unavoidable impurities are continuously cast and rolled to directly obtain a strip-shaped cast plate having a plate thickness of 10 mm or less, and the cast plate is subjected to cold rolling of 10% or more.
Heat treatment at a temperature of 0 ° C. or more, followed by cold rolling of 30% or more and heat treatment at a temperature rising rate of 100 ° C./min or more at a temperature of 400 ° C. or more. Manufacturing method of aluminum alloy for building materials.