JPH06136496A - Production of aluminum alloy sheet with high formability - Google Patents

Abstract

PURPOSE:To prevent the occurrence of lueders' line and surface roughing by hot-rolling the ingot of Al alloy of specific composition and performing precipitate coarsening treatment in the course of successive cold rolling. CONSTITUTION:The Al alloy has a composition consisting of, by weight, 5-10% Mg, 0.0001-0.01% Be, 0.01-0.2%, in total, of one or more elements among Mn, Cr, Zr, and V, further 0.005-0.1% Ti or 0.005-0.1% Ti and 0.00001-0.05% B, and the balance Al with usual impurities. Further, the maximum crystalline grain size is regulated to <1000mum. An ingot of this Al alloy is subjected to homogenizing treatment at 450-540 deg.C for <=24hr. The ingot is hot-rolled and, in the course of cold rolling, the resulting sheet is subjected to precipitate coarsening treatment at 360-550 deg.C for 1-100hr one or more times. After cold rolling, annealing is done at 450-550 deg.C for <=120sec, by which average crystalline grain size is regulated to 20-120mum. The formed parts prepared by using this Al alloy sheet have excellent working embrittlement characteristic.

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 a highly formable aluminum alloy sheet for use in a molded product requiring strength and formability such as an automobile body panel, an air cleaner and an oil tank. .

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been widely used as a sheet material for forming automobile body panels and the like, but recently, in order to reduce the weight of an automobile body and improve its fuel consumption,
The demand for using aluminum alloy plates is increasing. As an aluminum alloy plate used for such an application, an Al-Mg-based 5052 alloy (Al-2.5 wt%
Mg-0.25 wt% Cr alloy) O material and 5182 alloy (Al-4.5 wt% Mg-0.35 wt% Mn alloy)
O material or Al-Cu type 2036 alloy (Al-
2.6 wt% Cu-0.25 Wt% Mn-0.45 wt
% Mg) T4 material. Of these, the Al—Mg alloy plate is excellent in both formability and strength, and is often used for members that undergo severe forming.

This Al--Mg alloy sheet is usually manufactured by the steps of casting → homogenization treatment → hot rolling → annealing, and if necessary, intermediate annealing may be performed during cold rolling.
When flatness of the plate is particularly required, straightening may be performed by means such as a tension leveler, a roller leveler, and a skin pass rolling after annealing.

[0004]

The above conventional Al-Mg
The aluminum alloy sheet has excellent ductility as an aluminum alloy, but its elongation is at most about 30%, which is inferior to the elongation of the cold rolled steel sheet of 40% or more. For this reason, the formability of which elongation is a dominant factor, such as overhanging, bending, and stretch-flanging, is inferior to that of cold-rolled steel sheets.

In the Al-Mg alloy plate, M
It is known that the higher the g content, the higher the elongation. Therefore, in order to improve the elongation, an Al-high Mg alloy plate having a higher Mg content than that of the prior art (2.5 to 5 wt%) has been studied. However, when the Mg content is high, there is a problem that hot rolling property is deteriorated and rolling becomes impossible. In addition, according to the study by the inventors, Al-high M
The g-alloy plate has a large elongation, and in order to prevent the occurrence of Luder Sumark (stretcher strain mark) and rough skin at the time of forming, it is necessary to adjust the average crystal grain size to 20 to 120 μm, preferably 30 to 80 μm. (Japanese Patent Application No. 4-102456). However, as a result of further study thereafter, it was found that when the Mg content was extremely high, the crystal grain size tended to become finer, and it was difficult to adjust the average crystal grain size to the above size.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and improves the elongation of a conventional Al-Mg alloy sheet to about 40% of that of a cold rolled steel sheet, and The present invention provides an aluminum alloy sheet for forming, which has excellent rollability and is free of Luders marks and rough skin. That is, in the present invention, Mg is 5 to 10 wt% and Be is 0.000.
1 to 0.01 wt% and contains Mn, Cr, Zr,
0.01 to 0.2 in total of one or more of V
wt% and further contains Ti 0.005 to 0.1 wt% or Ti 0.005 to 0.1 wt% and B 0.0000.
1 to 0.05 wt%, the rest is normal impurities and A
aluminum alloy ingot having a maximum crystal grain size of less than 1000 μm is homogenized at 450 to 540 ° C. for 24 hours or less, then hot-rolled, and immediately or continuously after hot-rolling. 360-550 during hot rolling
The extruded product coarsening treatment at 1 ° C for 1 to 100 hours is performed once or more, final cold rolling is performed to a predetermined plate thickness, and then 450 to 5
The method for producing a highly formable aluminum alloy sheet is characterized in that the average crystal grain size is set to 20 to 120 µm by annealing at 50 ° C for 120 seconds or less. Is F as an impurity
The method for producing a highly formable aluminum alloy plate according to claim 1 is characterized in that each of e, Si and Cu is regulated to less than 0.2 wt%.

[0007]

First, the reason for limiting the alloy components to which the present invention is applied will be described. Mg is added to give strength and elongation. However, if the Mg content is less than 5 wt%, the present alloy sheet will not be able to obtain an elongation of about 40%, while if it exceeds 10 wt%, the rolling property will drop sharply, making it difficult to manufacture. Be is added in order to prevent molten metal oxidation during melt casting, and to prevent loss of Mg and surface discoloration due to oxidation of the ingot during homogenization treatment. However, if it is less than 0.0001 wt%, its effect is insufficient, and if it exceeds 0.01%, toxicity becomes a problem.

Mn, Cr, V, and Zr are added to improve hot rolling property. The present inventors, as a result of various studies,
It has been found that the hot rolling property of the Al-high Mg alloy is very deteriorated before the hot rolling, that is, when the crystal grains of the ingot after the homogenization treatment are coarse and the maximum crystal grain size is 1000 μm or more. Further, it was found that the addition of Mn, Cr, V, and Zr suppresses the generation of coarse crystal grains during the homogenization treatment, and the hot rolling property is remarkably improved. Mn, Cr, V, and Zr were extruded into the aluminum matrix as extremely fine protrusions during the temperature raising process of the homogenization treatment, and these fine protrusions were coarse crystal grains (secondary recrystallization during the homogenization treatment). ) Has the effect of suppressing the growth. These elements are one kind or two or more kinds in total, and are 0.01 to 0.2 wt.
%, The effect is insufficient if it is less than 0.01 wt%, and if it exceeds 0.2 wt%, a coarse intermetallic compound is formed and elongation is reduced.

[0009] Ti, or Ti and B, is added in order to make the structure of the ingot uniform and fine, and to make the maximum crystal grain less than 1000 µm. However, if Ti is less than 0.005 wt%, the effect is small, and if it exceeds 0.1 wt%, a coarse intermetallic compound is formed and elongation is reduced. On the other hand, B coexists with Ti to further enhance the effect of refining the ingot structure.
It is desirable to add 0001 to 0.05 wt%. However, if B is less than 0.00001 wt%, its effect is small, and if it exceeds 0.05 wt%, coarse TiB ₂ particles are formed and elongation is reduced.

Fe, Si, and Cu are impurities in the present alloy, and are limited to less than 0.2 wt% each. When the content of each of these is 0.2 wt% or less, Fe and Si form an intermetallic compound to reduce the elongation, and Cu segregates to the grain boundaries during hot rolling to reduce the grain boundary strength. Cracks are likely to occur during hot rolling.
In particular, in the Al-high Mg alloy as in the present invention, the regulation of Cu is important in manufacturing, and it is desirable to set it to less than 0.1 wt%. If the total amount of other impurities (Zn, Pb, etc.) is 0.3 wt% or less, there is no particular problem in achieving the effect of the present invention.

Next, the manufacturing conditions of the present invention will be described.
First, the maximum crystal grain size of the above component composition is 100
For an aluminum alloy ingot having a size of less than 0 μm, the maximum crystal grain size should not exceed 1000 μm.
A homogenization treatment is performed at 550 ° C. for 24 hours or less. When the maximum crystal grain size is 1000 μm or more, stress concentration becomes remarkable at the crystal grain boundaries in the subsequent hot rolling, which induces grain boundary rupture and rolling cracks become prominent, making manufacturing impossible. The finer the crystal grains, the better the hot rolling property, and it is desirable that the maximum grain size is 200 μm or less. The homogenization treatment is performed to homogenize the distribution of solute atoms, improve strength and elongation, and homogenize the structure after annealing. If the temperature is less than 450 ° C, the effect is insufficient, and if the temperature exceeds 540 ° C or the time exceeds 24 hours, the crystal grains grow coarsely (secondary recrystallization) and the maximum crystal grain size is 1000
If it is more than μm, the hot rolling property deteriorates. If the microstructure before this homogenization treatment, that is, after casting, is coarse, the crystal grains can no longer become finer even if the homogenization treatment is performed, and therefore, by the addition of Ti or Ti and B, It is necessary to refine the ingot structure.

Next, the aluminum alloy ingot having the maximum crystal grain size of less than 1000 μm, which has been subjected to such homogenization treatment, is hot-rolled. In hot rolling, it is desirable to reduce the rolling reduction in at least the first three passes (desirably 3% or less) in order to prevent hot rolling cracks. Further, the hot rolling start temperature is preferably 320 to 470 ° C. to prevent hot rolling cracks.

Then, immediately after the hot rolling or during the subsequent cold rolling, the coarsening treatment for extrudates is carried out once or more at 360 to 550 ° C. for 1 to 100 hours. This extruded product coarsening treatment was carried out by adding Mn, Cr, added in order to improve the hot rolling property.
This is carried out in order to coarsely grow the metal compound of V and Zr and to make the recrystallized grains after the final annealing be 20 μm or more. Mn,
As described above, Cr, V, and Zr are extruded into the aluminum matrix as extremely fine protrusions during the temperature raising process of the homogenization treatment, and suppress the growth of coarse crystal grains (secondary recrystallization) during the homogenization treatment. Has the effect of However, this fine extrudate has an effect of suppressing crystal grain growth even during the final annealing, making recrystallized grains after the final annealing extremely fine, resulting in a decrease in elongation and the generation of Luder's marks. By subjecting the protrusion coarsening treatment to the fine precipitates of Mn, Cr, V, and Zr to grow by Ostwald and coarsen to a size (generally 0.2 μm or more) that does not hinder the crystal grain growth,
The recrystallized diameter after the final annealing can be optimized.
If the temperature of the coarsening treatment of extruded products is less than 360 ° C. and the time is less than 1 hour, the above effect is insufficient. If it exceeds 550 ° C., burning (local melting) occurs, and if it exceeds 100 hours, the effect is saturated. In addition to being uneconomical, surface oxidation becomes significant.

After that, high temperature short time annealing at 450 to 550 ° C. for 120 seconds or less is carried out in a continuous annealing furnace (CAL) or the like to obtain an average crystal grain size of 20 to 120 μm. Here, the reason why the average crystal grain size is limited as described above will be described. If the average crystal grain size is less than 20 μm, A
In the 1-high Mg alloy plate, the Luders marks are significantly generated and the elongation is reduced. On the other hand, when the average crystal grain size exceeds 120 μm, the surface roughness of the molded product becomes remarkable and the elongation also decreases.

For this reason, the average crystal grain size is 20 to 1
It is necessary to set the thickness to 20 μm, and high temperature short time annealing for 120 seconds or less at 450 to 550 ° C. is performed by a continuous annealing furnace (CAL) or the like. If the annealing temperature is less than 450 ° C, recrystallization is insufficient, or even if recrystallization is performed, the average crystal grain size is less than 20 µm. On the other hand, if the annealing temperature exceeds 550 ° C, burning (local melting) occurs, and if it exceeds 120 seconds, it partially becomes 1
Crystal grains exceeding 20 μm are generated, and productivity is reduced. Further, when annealing is performed in a stationary patch furnace, even if the crystal grain size is 20 to 120 μm, the elongation is small and anisotropic. The occurrence of Luders marks is remarkable.

After such final annealing, if necessary, straightening correction may be performed by means such as a tension leveler, a roller leveler, and a skin pass rolling. If necessary, the surface may be washed with acid or alkali.

[0017]

EXAMPLES The present invention will now be described in more detail based on examples. (Example 1) No. 1 shown in Table 1 1-No. DC casting of aluminum alloy of composition 12 (thickness 400 m
m, width 1650 mm, length 4500 mm), 500 ° C
After homogenizing for 1 hour, the rolling start temperature is 460 ° C., the rolling reduction in the first three rolling passes is 2%, and the rolling reduction in the final pass (28 passes) after the fourth pass is in the range of 3 to 4%. It was gradually increased and hot rolled to a plate thickness of 5 mm. Next, this hot-rolled sheet was subjected to a coarsening treatment for extrudates at 520 ° C. for 20 hours, and further cold-rolled to a sheet thickness of 1 mm. Then, it is recrystallized by heating at 520 ° C. for 10 seconds in a continuous annealing furnace, and O
It was made of wood. The average crystal grain size of the aluminum alloy plate thus obtained is measured, and the tensile strength, yield strength, elongation, and the state of occurrence of Luders marks are examined by a tensile test, and the results are shown in Table 2.

[0018]

[Table 1]

[0019]

[Table 2]

As is clear from Tables 1 and 2, the composition Nos. 1-No. 5 has good hot rolling property,
The growth is also high at 40% or more. On the other hand, N containing less Mg
o. No. 6, in which the total amount of Mn, Cr, Zr, and V exceeds 0.2 wt%. No. 9 containing a large amount of Si and Fe. 10 has low elongation. In addition, No. No. 7 with large crystal grains after casting, No. Mn, Cr, Zr, and V not added. No. 8 had large crystal grains after the homogenization treatment, and in all of them, cracking occurred during hot rolling. A large amount of Cu and Mg No. 11, N
o. No. 12 was also unmanufacturable because cracking occurred during hot rolling.

(Embodiment 2) No. 1 of the first embodiment. After homogenizing the DC ingot of the alloy No. 4 under various conditions shown in Table 3, the rolling start temperature was 390 ° C., the pass schedule was the same as in Example 1, and hot rolling was performed to a plate thickness of 5 mm, followed by hot rolling. Sex was compared. The results are also shown in Table 3.

[0022]

[Table 3]

As is apparent from Table 3, No. 1 according to the manufacturing method of the present invention was used. 13-No. No. 17 has good hot rolling property. On the other hand, in the case where the homogenization temperature is high or the time is long, 18-No. No. 20 had a maximum crystal grain of 1000 μm or more after homogenization treatment, cracks occurred during hot rolling, and it was impossible to continue rolling. Even if the homogenization conditions are within the range of the present invention, when the maximum crystal grain size after homogenization exceeds 1000 μm (No. 21, 2).
In 2), cracks still occurred during hot rolling.

(Embodiment 3) No. 2 of Embodiment 2. The hot-rolled sheet (sheet thickness 5 mm) obtained in No. 14 was sequentially subjected to cold rolling, extruded product coarsening treatment, cold rolling and annealing under the conditions shown in Table 4 to obtain an aluminum alloy sheet having a sheet thickness of 1 mm. did. The average crystal grain size of the aluminum alloy plate thus obtained is measured, and the tensile strength, yield strength, elongation, and generation of Luders marks are investigated by a tensile test, and the results are shown in Table 5.

[0025]

[Table 4]

[0026]

[Table 5]

As is clear from Tables 4 and 5, the hot rolling condition No. 23-No. The aluminum alloy plate of No. 27 has a high elongation of 40% or more and does not generate Luders marks. On the other hand, No. 28-No. In No. 31, the average crystal grain size after annealing is too fine and the elongation is low, and Luders marks also occur.

[0028]

As described above, according to the present invention, there can be obtained an aluminum alloy sheet for forming which has a large elongation, is excellent in formability, has good hot rolling property, is excellent in productivity, and is free from the generation of Luders marks. It has a remarkable industrial effect.

[Procedure amendment]

[Submission date] November 18, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

After such final annealing, if necessary, straightening correction may be performed by means such as a tension leveler, a roller leveler, and a skin pass rolling. If necessary, the surface may be washed with acid or alkali. Aluminum according to the present invention manufactured as described above
Alloy sheets are excellent in strength and deep drawability,
Suitable for molding parts such as fuel tanks, air cleaners and oil tanks
It In addition, these molded products have a wide temperature environment (for example,
Excellent work embrittlement resistance at -100 ° C to room temperature)
Show.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0028

[Correction method] Change

[Correction content]

[0028]

As described above, according to the present invention, there can be obtained an aluminum alloy sheet for forming which has a large elongation, is excellent in formability, has good hot rolling property, is excellent in productivity, and is free from the generation of Luders marks. In addition, the molded parts have resistance to work brittleness
Is also excellent and has a remarkable industrial effect.

Claims (2)

[Claims] 1. Mg5-10 wt%, Be0.0001
~ 0.01 wt%, and Mn, Cr, Zr, V
0.01 to 0.2w in total of 1 or 2 or more of them
t 0.005%, Ti 0.005 to 0.1 wt% or Ti 0.005 to 0.1 wt% and B0.00001
~ 0.05wt%, the rest is normal impurities and Al
Aluminum alloy ingot having a maximum crystal grain size of less than 1000 μm is subjected to homogenization treatment at 450 to 540 ° C. for 24 hours or less, and then hot-rolled, followed immediately or by cold rolling. 360-550 ° C during rolling
1 to 100 hours for the coarsening treatment of the extrudate once or more,
Final cold rolling to a specified plate thickness, then 450-550
A method for producing a highly formable aluminum alloy sheet, characterized in that the average crystal grain size is set to 20 to 120 µm by annealing at 120 ° C for 120 seconds or less. 2. The method for producing a highly formable aluminum alloy sheet according to claim 1, wherein Fe and SiCu as impurities are regulated to less than 0.2 wt% in the aluminum alloy ingot, respectively. .