JPH0959736A - Aluminum alloy sheet excellent in high speed superplastic formability and its formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet capable of high temp. forming at high speed and excellent in high speed superplastic formability and to shorten forming time and improve prcductivity by using the aluminum alloy sheet. SOLUTION: An alloy, having a composition which consists of, by weight, 3.0-8.0% Mg, 0.001-0.1% Ti, and the balance Al with inevitable impurities and in which Fe and Si as impurities are regulated to <=0.06% and <=0.06%, respectively, is used. Moreover, the number of Al-Fe-Si compounds of >=1μm grain size is <=2000pieces/mm<2> and average crystalline grain size is 25-200μm, and further, the elongation in the case where forming is done at 350-550 deg.C at (10<-2> to 10<0> )/s strain rate is regulated to >=350%. Small amounts of Cu, Mn, and Cr can be added, and forming is performed at 350-550 deg.C at (10<-3> to 10<0> )/s strain rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy plate excellent in high-speed superplastic forming, and particularly to a strain rate of 10 ^-2 to 10 ⁰ /
Al-Mg alloy plate that enables high-speed superplastic forming of s,
And a molding method thereof.

[0002]

2. Description of the Related Art In an Al--Mg alloy, a superplastic alloy has been developed in which recrystallization is suppressed and the crystal grains are made finer, and for example, elongation of several hundreds% is produced in a high temperature region of 500 to 550.degree. It is used for various purposes, but it is the conventional Al-M
The g-type superplastic alloy has a forming rate (strain rate) of 10 ^-4 to 10 ^-3 / s.
The optimum elongation can be obtained by molding at this temperature.When such a molding speed is applied, it takes about 30 to 100 minutes to mold a general container, for example. In production, there is a demand for a superplastic alloy that has poor productivity and can be formed at a higher forming rate.

For example, Mg: 2.0 to 6.0%, Be: 0.0001
.About.0.01%, Ti: 0.001 to 0.15%, Fe and Si as impurities are both limited to 0.2% or less, and the maximum grain size of the intermetallic compound based on the impurities is limited to 10 μm or less. (Japanese Patent Laid-Open No. 4-72030), this alloy plate is
When the strain rate is 10 ^-3 / s, the elongation is 350% or more, but the elongation decreases as the molding rate increases, and at a strain rate of 10 ^-2 / s or more, sufficient elongation cannot be obtained.

Further, Mg: 2-5%, Cu: 0.04-0.10%
And a small amount of a transition element, Cr, as a selective component.
Containing Zr and Mn, 0.10% or less of Si as an impurity, Fe
Is limited to 0.15% or less, a crystal grain size of 20 μm or less, a superplastic aluminum alloy plate in which the grain size and volume ratio of the transition element intermetallic compound are controlled within a specific range is also proposed (Japanese Patent Laid-Open No. 4-318145). However, this alloy sheet is also suitable for forming at a strain rate of about 10 ⁻⁴ / s, and there is a problem in high-speed superplastic forming.

[0005]

SUMMARY OF THE INVENTION The present invention provides an Al-Mg
In order to solve the above-mentioned conventional problems in superplastic aluminum alloys of the system, alloy components and their quantitative combinations, the amount of impurities and the distribution mode and crystal grain size of intermetallic compounds based on impurities, and superplastic forming It was made as a result of repeated experiments and studies on the relevance, and its purpose is to obtain a specific distribution and crystal grain size of an Al-Fe-Si compound based on the limitation of Fe and Si as impurities. The high molding speed, for example 10 ^-2 to 10
An object of the present invention is to provide an aluminum alloy sheet excellent in high-speed superplastic forming capable of obtaining sufficient elongation in forming at a strain rate of ⁰ / s, and a method for forming the aluminum alloy sheet.

[0006]

The aluminum alloy sheet excellent in high-speed superplastic forming according to the present invention for achieving the above object contains Mg: 3.0 to 8.0%, Ti: 0.001 to 0.1%, and contains impurities. Fe as 0.06% or less, Si as 0.06%
The grain size is limited to the following and consists of an alloy consisting of the balance Al and unavoidable impurities, and the grain size present in the matrix of the alloy.
1 [mu] m or more Al-Fe-Si based compounds are 2,000 / mm ² or less, the average crystal grain size is 25 to 200 [mu] m, molding at a strain rate of 10 ^-2 ~10 ⁰ / s in a temperature range of 350 to 550 ° C. If you do, the growth is 35
The basic characteristic of the composition is 0% or more.

In addition to Mg and Ti, Cu: 0.05-0.50
%, And Mn in addition to Mg and Ti: 0.10
In the following, one or two of Cr: 0.10% or less is contained, or in addition to Mg, Ti, Cu, one or two of Mn: 0.10% or less and Cr: 0.10% or less is contained. These are the second and third characteristics of the invention structure.

[0008] molding method of an aluminum alloy sheet with excellent high-speed superplastic forming according to the present invention, the above aluminum alloy plate at a temperature of 350 to 550 ° C., is molded at a strain rate of 10 ^-3 ~10 ⁰ / s It is characterized by

Explaining the meaning and limiting reason of the contained components in the present invention, Mg has a function of recrystallizing the alloy during high temperature deformation. The preferred content range is 3.0-
If it is less than 3.0%, the effect of promoting recrystallization is small.
If the content exceeds 8.0%, hot workability deteriorates. Cu
Is an element that improves the superplastic elongation of the Al-Mg alloy. A preferred content range is 0.05 to 0.50%, and if it is less than 0.05%, its effect is not sufficient, and if it exceeds 0.50%, the hot workability is deteriorated.

Ti serves to refine the crystal grains of the ingot and improve the superplastic properties of the alloy. The preferred content range is 0.001 to
0.1%, the effect is small when it is less than 0.001%.
If the content exceeds 1%, a coarse compound is formed and processability,
Ductility is impaired. Mn and Cr have a function of refining recrystallized grains during recrystallization of the alloy during high-temperature deformation. The preferred contents are each in the range of 0.10% or less, and 0.10% or less.
%, The Al-Fe-Si-based compound having a grain size of 1 µm or more tends to increase, and the high-speed superplastic deformability of the alloy tends to decrease.

In the present invention, Fe as an impurity,
It is important to limit each of Si to 0.06% or less. The impurities Fe and Si generate an insoluble Al-Fe-Si-based compound, which precipitates at crystal grain boundaries to increase the cavity and reduce superplastic elongation. Preferably, Fe: 0.05% or less and Si: 0.05% or less are restricted. Also, Be can be added in a range of 50 ppm or less in order to prevent oxidation of the molten metal, similarly to a normal Al-Mg alloy.

Explaining the alloy structure of the present invention, the Al--Fe--Si compound present in the matrix of the alloy causes the above-mentioned adverse effects, and particularly the grain size is
The smaller the number of compounds of 1 μm or more, the better. The limit is 2000 Al / Fe-Si diameter compounds with a grain size of 1 μm or more / mm ²
When the distribution is more than 2000 pieces / mm ² , the number of cavities increases in the grain boundaries and the superplastic elongation decreases.

Regarding the crystal grain size, it is necessary to control the initial average crystal grain size of the aluminum alloy plate to 25 to 200 μm. If the initial average crystal grain size is less than 25 μm, the original crystal grains will appear when recrystallized during high-temperature deformation, and the grain boundaries where the insoluble compounds have precipitated will disappear, resulting in cleanliness resulting from recrystallization. It is difficult to obtain a recrystallized structure composed of fine crystal grains. If the initial average crystal grain size exceeds 200 μm, the shear deformation within the crystal grains becomes remarkable as the deformation rate increases, and the crystal grains are easily broken, so that the superplastic elongation tends to decrease.

The forming process of the aluminum alloy sheet of the present invention is preferably carried out at a temperature of 350 to 550 ° C. If the temperature is lower than 350 ° C., the Al—Mg-based compound and the Al—Mg—Cu-based compound are likely to precipitate at the crystal grain boundaries, and the elongation is reduced. If the molding temperature exceeds 550 ° C, the crystal grains become coarse and the elongation becomes poor. The strain rate during molding is preferably in the range of 10 ^-3 to 10 ⁰ / s, and at a strain rate of less than 10 ^-3 / s, the crystal grains become coarse during deformation, leading to a decrease in elongation and 10 ⁰ / s. If the strain rate exceeds, shear deformation occurs in the crystal grains to cause cracking, or precipitation occurs at the crystal grain boundaries to reduce elongation.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing an aluminum alloy sheet according to the present invention will be described. According to a conventional method, the aluminum alloy having the above composition is melted and cast, and the obtained ingot is homogenized. The homogenization treatment is preferably performed at a temperature of 450 to 550 ° C. If the temperature is lower than 450 ° C., Mg and Cu segregated at the crystal grain interface and the cell boundary of the ingot are not sufficiently re-dissolved to cause hot rolling cracks. At temperatures exceeding 550 ° C, Al-Mg based materials with low melting points or Al-Mg-Cu
Eutectic melting occurs in the system crystallized material, which causes cracking during hot rolling.

After the homogenization treatment, hot rolling is performed to make the ingot structure a wrought material structure. Hot rolling start temperature is 250 ~ 500
° C, but preferably less than 400 ° C. twenty five
If the hot rolling is started at a temperature lower than 0 ° C., the deformation resistance of the material is high and the hot rolling becomes difficult. When the hot rolling temperature increases,
A change in the distribution of precipitates may make it difficult to obtain a predetermined crystal grain structure and distribution of the precipitated compound.

Cold rolling is performed subsequent to hot rolling. If necessary, intermediate annealing may be performed during cold rolling. The final annealing of the cold-rolled material is performed at a temperature of 350 to 550 ° C. 350
If the annealing is performed at a temperature lower than ℃, the anisotropy of the structure formed by the hot rolling may not be sufficiently eliminated. If the temperature exceeds 550 ℃, local melting may occur at the recrystallized grain boundaries. The final annealing is
It is preferable to use rapid annealing such as continuous annealing.

In the present invention, Fe and Si, which are impurities in the Al-Mg-based alloy, are limited, and the combination of the above manufacturing conditions is adjusted according to the combination of the alloy compositions, so that they are present in the matrix. The Al-Fe-Si-based compound is controlled to have a specific distribution, the crystal grain size is controlled to a specific range, and the compound in the crystal grain boundary is reduced by this texture property to form a cavity as a clean grain boundary. The average of recrystallized grains of 20 μm or less is formed during high-temperature deformation, and strain rate of 10
^-2 to 10 ⁰ / s at high speed molding of 350% or more, preferably 38
It is possible to obtain sufficient ductility of 0% or more.

[0019]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1, Comparative Example 1 An Al-Mg-based aluminum alloy having the composition shown in Table 1 was melted and ingot was formed by DC casting. The obtained ingot is 530 ℃
After homogenizing for 10 hours, the thickness was reduced to 30 mm, hot rolling was started at a temperature of 390 ° C, and hot rolling was performed to a thickness of 4 mm.
Then, cold rolling was performed to a plate thickness of 2 mm, and a rapid annealing treatment was performed in which the plate was rapidly heated to a temperature of 480 ° C and held for 5 minutes.
Using these plates as test materials, the temperature was 480 ° C and the strain rate was 10 ^-2.
A tensile test was performed at / s. Average crystal grain size of each test material (average crystal grain size on the plate surface), Al-Fe-S with grain size of 1 μm or more
Table 1 shows the number of i-type compounds per 1 mm ² and the elongation percentage measured by the tensile test. The amount of compound was determined by image processing. Further, in Table 1, those which do not satisfy the conditions of the present invention are underlined.

[0020]

[Table 1]

As shown in Table 1, test material N according to the present invention
All of o.1 to 5 showed an excellent elongation rate of more than 400%. On the other hand, since the test material No. 6 contained too much Cu, and the test material No. 7 contained too much Mg, cracking occurred during hot rolling and no test piece could be formed. Since the test material No. 8 contains a large amount of impurities Fe and Si, it has a large amount of large-diameter compounds and inferior elongation. Test material No. 9
Since the amount of Mg is small, recrystallization is insufficient during tensile deformation and the elongation is low.

Example 2, Comparative Example 2 An Al-Mg-based aluminum alloy having the composition shown in Table 2 was melted and cast in the same manner as in Example 1, and the same steps as in Example 1 were carried out.
A test material having a thickness of 2 mm was prepared under the same conditions, and a tensile test was performed on each test material under the same conditions as in Example 1.
Al-Fe with average crystal grain size of each test material and grain size of 1 μm or more
Table 2 shows the amount of the -Si compound and the elongation percentage measured by the tensile test. In addition, in Table 2, the values out of the conditions of the present invention are underlined.

[0023]

[Table 2]

As shown in Table 2, all of the test materials No. 10 to 12 according to the present invention showed an excellent elongation ratio exceeding 380%, but the test materials No. 13 to 14 had a Mn content. Many,
Since the test material No. 15 has a large amount of Cr, the grain size is 1 μm in both cases.
Since the Al-Fe-Si-based compound has a large distribution as described above, high temperature elongation cannot be obtained.

Example 3, Comparative Example 3 An aluminum alloy having the same composition as the test material No. 5 of Example 1 was melted and cast in the same manner as in Example 1, and the obtained ingot was heated at 520 ° C. for 8 hours. After homogenizing for a period of time, the ingot was made to have a thickness of 30 mm, hot rolling was started at a temperature of 390 ° C., and hot rolling was performed to a thickness of 4 mm. Then, it was cold-rolled into a sheet material with a thickness of 2 mm, which was rapidly annealed by rapidly heating it to a temperature of 480 ° C and holding it for 5 minutes. Using the produced plate material as a test material, as shown in Table 3, a tensile test was conducted by changing the molding temperature and the strain rate. Table 3 shows the elongation percentage of each test material. In Table 3, those out of the conditions of the present invention are underlined. The average crystal grain size (average crystal grain size on the plate surface) of each test material was in the range of 50 to 60 μm, and the grain size was 1 μm or more.
The number of Fe-Si compounds per 1 mm ² is 2000
Or less.

[0026]

[Table 3]

As shown in Table 3, test material N according to the present invention
All of o.16 to 20 showed an excellent elongation rate of 380% or more, but the test material No. 21 had a high tensile test temperature, so that the crystal grains became coarse and the elongation rate decreased. Since the test material No. 22 had a low strain rate, coarsening of crystal grains occurred during the deformation and the elongation rate decreased. Since the strain rate of test material No. 23 was too high, the elongation decreased.

[0028]

As evident from the foregoing description, according to the present invention, at high temperature, strain rate 10 ^-2 ~10 ⁰ / s fast enough superplastic elongation can be obtained even in the forming Al-Mg series aluminum alloys such as A plate is provided, and by performing superplastic forming using the aluminum alloy plate, forming time is shortened and productivity is improved.

Claims (4)

[Claims] 1. Mg: 3.0 to 8.0% (weight%, the same applies hereinafter) and Ti: 0.001 to 0.1%, and F as an impurity.
Limit e to 0.06% or less and Si to 0.06% or less, and balance Al
And an Al-Fe alloy having an inevitable impurity and having a grain size of 1 μm or more present in the matrix of the alloy.
-2000 compounds / mm ² or less of Si-based compound, average crystal grain size of 25-
200 [mu] m, 350 to 550 strain rate of 10 ^-2 to 10 in a temperature range of ° C. ⁰ / s
An aluminum alloy sheet excellent in high-speed superplastic forming characterized by an elongation of 350% or more when formed by. 2. The aluminum alloy sheet excellent in high-speed superplastic forming according to claim 1, which contains Cu: 0.05 to 0.50%. 3. An aluminum alloy sheet excellent in high-speed superplastic forming according to claim 1, which contains one or two of Mn: 0.10% or less and Cr: 0.10% or less. The 4. The aluminum alloy sheet of claim 1, wherein, at a temperature of 350 to 550 ° C., excellent high-speed superplastic forming, which comprises molding a strain rate 10 ^-3 ~10 ⁰ / s Method for forming aluminum alloy sheet.