JPH06240395A - Aluminum alloy sheet for superplastic forming, its production and superplastic formed body using it - Google Patents

Abstract

PURPOSE:To provide an Al base alloy sheet for superplastic forming having good superplastic properties and also excellent in corrosion resistance and weldability, to provide its producing method and to provide an superplastic formed body using it. CONSTITUTION:An Al alloy sheet for superplastic forming contg. 4.0 to 7.0% Mg, >1.5 to 2.5% Mn and 0.00005 to 0.01% Be and furthermore contg., at need, one or more kinds among Cr, V and Zr, and the balance substantially A1 with impurities of <0.2% Fe is produced. Or, at the time of subjecting the alloy having the same componental compsn. to DC casting, in the process of adding an Al-Ti or Al-Ti-B alloy as a refining agent, heating the cast ingot at 450 to 560 deg.C for 0.5 to 24hr and executing hot rolling-cold rolling, the final cold rolling ratio is regulated to >=30%. Or, after that, recrystallizing treatment of holding it at 280 to 560 deg.C for 0 to 5hr at >=10 deg.C/min may be executed. Furthermore, the superplastic formed body having the same componental compsn. and also contg. crystalline grains of <=50mum after superplastic forming is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy sheet for superplastic forming, that is, an aluminum alloy sheet for use after being subjected to forming processing (superplastic forming) in a temperature range of 350 to 560 ° C, and the alloy sheet. And a superplastic molded body using the alloy plate.

[0002]

2. Description of the Related Art In recent years, various superplastic materials have been developed which exhibit remarkably large elongation without causing local deformation (neck) when tensile is applied at an appropriate strain rate at high temperature. . As for aluminum alloy materials, various studies have been conducted on superplastic materials that exhibit an elongation of 150% or more at a high temperature of 350 ° C or more.

As conventional aluminum-based superplastic materials, Al-78% Zn alloy, Al-33% Cu alloy, A
1-6% Cu-0.4% Zr alloy ("SUPRAL
L "), Al-Zn-Mg-Cu alloy (AA standard 74
75 alloy, 7075 alloy, etc.), Al-2.5 to 6.0%
Mg-0.05-0.6% Zr alloy and the like are known.
If such a superplastic material is used, it becomes possible to easily perform a forming process into a complicated shape.

[0004]

Since superplastic materials can obtain excellent formability at high temperatures, they are expected to be applied to many fields. On the other hand, in general, in the case of aluminum alloy materials, sufficient consideration must be given to corrosion resistance in order to use them for interior or exterior building panels or containers such as bags. When it is used as a structural member, it is required to have not only excellent mechanical properties after molding but also excellent weldability because it is often used by welding.

However, the conventional aluminum alloys for superplastic forming require a large amount of alloying elements such as Cu in order to pursue superplasticity, and as a result, they have the drawbacks of poor corrosion resistance and poor weldability. Therefore, even if the moldability is good, it has been a serious obstacle to the practical application. On the contrary, if it is attempted to improve the corrosion resistance and the weldability, the essential superplasticity property is deteriorated, and the excellent formability cannot be expected.

The present invention has been made in view of the above circumstances, and provides an aluminum alloy plate for superplastic forming, which has excellent superplastic properties, and at the same time, has excellent corrosion resistance and weldability, and a method for producing the same. At the same time, the basic object is to provide a superplastic molded product using the aluminum alloy plate.

[0007]

[Means for Solving the Problems] In order to solve the above problems, the inventors of the present invention have conducted diligent experiments and research, and as a result, have properly set the chemical composition of the alloy, and manufacture of the rolled plate. By setting the conditions appropriately and adjusting the crystal grain size after superplastic forming to be within a predetermined range, an aluminum alloy with excellent superplastic properties as well as corrosion resistance and weldability The inventors have found that a plate can be obtained and have completed the present invention.

Specifically, the aluminum alloy sheet for superplastic forming according to the first aspect of the present invention has Mg of 4.0 to 7.0% and Mn.
More than 1.5% and 2.5% or less, Be0.00005-
Fe as an impurity is 0.2
%, And the balance consists of Al and other unavoidable impurities.

The aluminum alloy sheet for superplastic forming according to the second aspect of the present invention is Mg 4.0-7.0%, Mn 1.5%.
Over 2.5%, Be0.00005-0.01%
In addition to containing Cr of 0.05 to 0.3%, V0.
05-0.3%, Zr 0.05-0.3%, one or more of them are contained, Fe as an impurity is regulated to less than 0.2%, and the balance is Al and other unavoidable. It is characterized in that it is made up of specific impurities.

On the other hand, the invention of claim 3 relates to a method for producing an aluminum alloy plate for superplastic forming as described above, wherein Mg exceeds 4.0% to 7.0% and Mn exceeds 1.5% to 2.5. % Or less, Be0.00005-0.01%, and if necessary, Cr0.05-0.3%, V
Fe as an impurity, containing one or more of 0.05 to 0.3% and Zr 0.05 to 0.3%.
Is controlled to be less than 0.2% and the balance is Al and other unavoidable impurities. When casting an aluminum alloy, before or during casting, as a grain refiner, an Al-Ti mother alloy or Al- The Ti-B mother alloy was added in an amount of Ti of 0.15% or less, and the ingot was cast at a temperature of 450 to 560 ° C for 0.5 to 24 after casting by a DC casting method.
The final cold rolling rate is 30% when heating for a period of time and then performing hot rolling and cold rolling to obtain the required plate thickness.
The above is characterized.

According to a fourth aspect of the present invention, there is provided a method for producing an aluminum alloy sheet for superplastic forming, wherein after the final cold rolling through the same process as the method of the third aspect of the invention, further 10 ° C. is applied.
Heating to 280 to 560 ° C. at a temperature rising rate of at least min / min
It is characterized in that a recrystallization treatment (final annealing) of holding for up to 5 hours is performed.

Further, the invention of claim 5 relates to a superplastic compact using the aluminum alloy plate for superplastic compacting defined in the invention of claim 1, Mg 4.0 to 7.0.
%, Mn more than 1.5% and 2.5% or less, Be 0.000
Fe as an impurity is regulated to less than 0.2%, the balance consists of Al and other unavoidable impurities, and the size of crystal grains after superplastic forming is 50 μm. It is characterized by the following.

Further, the invention of claim 6 relates to a superplastic forming product using the aluminum alloy plate for superplastic forming specified in the invention of claim 2, wherein Mg4.0 to Mg4.0
7.0%, Mn more than 1.5% and 2.5% or less, Be0.
0.0005 to 0.01%, Cr0.
05-0.3%, V0.05-0.3%, Zr0.05
Of 0.3% to 0.3%, Fe as an impurity is regulated to less than 0.2%, the balance is Al and other unavoidable impurities, and after superplastic forming The size of the crystal grains is 50 μm or less.

[0014]

First, the reasons for limiting the component composition of the aluminum alloy rolled sheet for superplastic forming of the present invention will be explained.

Mg: Mg is: a: Recrystallized grains are refined to improve superplastic formability, b: Strength and superplastic formability are improved without impairing the corrosion resistance and weldability of the material, etc. Have an effect. Here, if the amount of Mg is less than 4.0%, the superplastic formability becomes insufficient, and if it exceeds 7.0%, the hot-rollability and cold-rollability deteriorate and the production becomes difficult. Therefore, the amount of Mg was made into the range of 4.0-7.0%.

Mn: Mn refines the crystal grains, and
It is an element effective for stabilizing the crystal structure during superplastic forming at a temperature of 50 to 560 ° C. and thereby exhibiting excellent superplastic properties. Even if the Mn content is 1.5% or less, it is possible to refine the crystal grains of the plate before superplastic forming, but the crystal grains become coarse during superplastic forming and the superplastic properties become insufficient, In addition, cavitation also grows easily. Here, cavitation causes not only a decrease in superplastic elongation but also a deterioration in mechanical properties and corrosion resistance of the product after superplastic forming. On the other hand, Mn
If the amount exceeds 2.5%, a primary crystal coarse intermetallic compound is generated during DC casting, and this coarse intermetallic compound serves as a nucleation site for cavitation, and in this case also, cavitation easily occurs. Therefore, Mn is 1.5%
Over the range of 2.5% or less.

Be: Be is generally added to prevent the oxidation of Mg in the molten metal. In the case of the present invention, however, since Be forms a dense oxide film on the surface of the molten metal, the inclusion of hydrogen. It has been found that this also helps prevent the occurrence of cavitation in the rolled plate. Also Be
Suppresses the oxidation of Mg on the surface of the rolled plate and stabilizes the surface. That is, since superplastic forming is performed at a high temperature of 350 to 560 ° C., when the amount of Mg is large as in the alloy of the present invention, surface oxidation during superplastic forming becomes severe,
The surface tends to turn black, but the addition of Be suppresses the oxidation of the plate surface during superplastic forming and stabilizes the product surface.
If the amount of Be is less than 0.00005% (0.5 ppm), the above effects are not exhibited, and if it exceeds 0.01% (100 ppm), not only the effect is saturated, but also toxicity and economical problems occur. Therefore, Be amount is 0.00005-0.01%
Within the range of.

Cr, V, Zr: In the aluminum alloy plate for superplastic forming according to the second aspect of the present invention, one or more of Cr, V and Zr are added in addition to the above alloy elements. These elements have the effect of making the recrystallized grains fine and stable and preventing abnormal coarsening of the crystal grains during superplastic forming. If Cr, V, and Zr are all less than 0.05%, the above effect cannot be sufficiently obtained, while if over 0.3%, a coarse intermetallic compound is formed, which is not preferable.
All of r, V, and Zr were within the range of 0.05 to 0.3%.

Further, in general Al alloys, Fe, Si, Cu, Zn, etc. are contained as impurities. Of these, especially Fe has a significant effect on the alloy of the present invention, so the following restrictions are imposed. There is a need to.

Fe: Fe is Al-Fe, Al-Fe-
Crystallizing an intermetallic compound such as Mn or Al-Fe-Si,
These cause cavitation during superplastic forming, cause a decrease in superplastic elongation, and the presence of cavitation deteriorates the mechanical properties, fatigue properties and corrosion resistance of the product as described above. Therefore, the smaller the Fe content, the more preferable. Further, Fe slightly affects the precipitation of Mn, and if the amount of Fe is large, it promotes the crystallization of coarse intermetallic compounds. In order to avoid these adverse effects of Fe,
It is necessary to regulate the Fe content to less than 0.2%.

The balance of each of the above elements is basically Al.
However, if the amount of Si as an impurity is large, coarse αAl-Mn (F
e) Since intermetallic compounds such as -Si phase and Mg ₂ Si phase are easily crystallized and cavitation is increased to adversely affect superplastic properties, Si is an impurity.
It is preferable to regulate to less than 5%. Further, if there is a large amount of Cu, hot rolling becomes difficult, so it is preferable to regulate the Cu content to less than 0.3%. In addition, Zn as an impurity
Is 0.5% or less, the characteristics of the aluminum alloy sheet of the present invention are not particularly impaired, and therefore Zn is allowed to be about 0.5% or less.

Further, in manufacturing the aluminum alloy sheet for superplastic forming of the present invention, Ti alone or Ti is used for refining the ingot structure before or during casting.
Is usually added in combination with B. In this case, T
i, or Ti and B are usually added in the form of an Al-Ti master alloy or an Al-Ti-B master alloy. In this case, if the Ti content exceeds 0.15%, Ti
Since coarse primary crystal grains of Al ₃ crystallize out, which is not preferable, T
The i amount is preferably within the range of 0.15% or less.
Further, B is added in coexistence with Ti to further promote the refinement and homogenization of crystal grains, but if the B content exceeds 0.05%, TiB ₂ particles are generated, which is not preferable. It is preferably within the range of 0.05%.

The aluminum alloy sheet for superplastic forming of the present invention may satisfy the above-mentioned conditions as a chemical composition, but the crystal grain size has a great influence on the superplastic properties, and the crystal grain is generally The finer the diameter, the better the superplastic properties. Here, it is of course important that the crystal grain size in the state of the rolled plate before the start of superplastic forming is fine, but if the crystal grains become large during superplastic forming performed at a temperature of 350 to 560 ° C, The plastic properties deteriorate, and eventually a large superplastic elongation cannot be obtained. Therefore, a fine crystal grain size after superplastic forming is a condition necessary for exhibiting excellent superplastic properties. Therefore, in the inventions of claims 5 and 6, the size of the crystal grain after superplastic forming is defined as 50 μm or less as the superplastic forming product. If the crystal grain size of the superplastic molded product has a large diameter exceeding 50 μm, good superplastic properties cannot be obtained. In addition, the forming process means in the superplasticity temperature range (360 to 560 ° C.) for forming the superplastically formed product is not particularly limited, and any known means can be used.

Next, a method for producing the aluminum alloy plate for superplastic forming of the present invention will be described.

First, a molten alloy having the above-described composition is melted and cast. As the casting method, semi-continuous casting (DC casting) is generally used. Before casting, or during casting, an Al-Ti master alloy or an Al-Ti-B master alloy is added to the molten metal as a refining agent in order to refine the ingot structure. The amount of addition is 0.15% or less in terms of Ti amount as described above. As the adding means, either a method of adding with a waffle prior to casting or a method of continuously adding with a rod during casting may be applied.

If necessary, the obtained ingot is faced, and then ingot is heated (homogenized) at 450 to 580 ° C.
For 0.5 to 24 hours. This ingot heating (homogenization treatment)
Is performed in a single stage for both soaking and preheating before hot rolling,
Alternatively, it may be divided into two stages. When the ingot heating is performed in two stages, the conditions in the higher temperature stage may satisfy the above.

If the ingot heating temperature is lower than 450 ° C., not only is the homogenization insufficient, but the precipitation of Mn is insufficient, and the crystal grain size after superplastic forming does not become 50 μm or less. , Adversely affect superplastic formability. On the other hand, if the ingot heating temperature exceeds 580 ° C., eutectic melting is likely to occur, and the intermetallic compound becomes coarse, which adversely affects superplastic properties. On the other hand, if the ingot heating time is less than 0.5 hours, the heating becomes uneven, and if it exceeds 24 hours, the effect is saturated and the economical efficiency is deteriorated.

Then, hot rolling and cold rolling are performed according to a conventional method to obtain a required plate thickness. At this time, intermediate annealing may be performed between the hot rolling and the cold rolling or during the cold rolling. Here, if the final cold reduction is low, the recrystallized grains become coarse, and the crystal grain size after superplastic forming is 50 μm.
It does not become m or less, and good superplastic properties cannot be obtained. Therefore, the final cold rolling reduction needs to be 30% or more.

Superplastic forming is carried out at 350 to 560 ° C. Recrystallization occurs even during the temperature rise to the superplastic forming temperature, and superplasticity develops. Therefore, the rolled plate obtained as described above is On the other hand, it is not always necessary to perform the final annealing for recrystallization during the plate manufacturing process. However, in general, the final annealing often results in a recrystallized structure. In this case, either continuous annealing or batch annealing may be used, but continuous annealing is slightly superior in superplasticity. As the final annealing (recrystallization treatment), basically, heating to 280 to 560 ° C. at a temperature rising rate of 10 ° C./min or more and no holding (holding for 0 hour) or holding for 5 hours or less may be performed. However, especially in the case of batch annealing, holding at 280 to 400 ° C. for 0.5 hour or more is general, while in the case of continuous annealing, it is 350.
Generally, the temperature is kept at ˜560 ° C., or at most 180 seconds.

[0030]

EXAMPLES Alloys 1 to 6 shown in Table 1 were melted and semi-continuously cast (DC casting) on a slab having a cross section of 350 mm × 1000 mm. During casting, Al is used as a refiner.
A rod of -5% Ti-1% B master alloy was added. After cutting each ingot by 12 mm on each side, Table 2
Ingot heating (homogenization treatment) was performed under the conditions shown in.

Next, after hot rolling to a sheet thickness of 6 mm, cold rolling to a sheet thickness of 2 mm, and then final annealing (recrystallization treatment) using a continuous annealing furnace without holding at 550 ° C.
Was done.

AA7475 alloy (alloy No. 7), which has been widely known as a superplastic material, and SUPRAL
An alloy (Al-6% Cu-0.5% Zr alloy; alloy number 8) was also used as a test material. The conventional 7475 alloy uses a plate with a thickness of 2 mm manufactured by the ordinary method by applying the DC casting method,
In addition, SUPRAL alloy is 30mm × 150mm × in a laboratory.
After die casting to 200 mm and heating at 500 ° C for 2 hours, plate thickness 6
A plate hot-rolled to mm and cold-rolled to a plate thickness of 2 mm was used.

[0033]

[Table 1]

[0034]

[Table 2]

A width of 4 mm and a parallel portion length of 1
A 5 mm test piece was cut out and examined for superplastic properties. Table 3 shows the superplastic property measurement conditions and the superplastic property measurement results for these test materials.

[0036]

[Table 3]

If the elongation is 300% or more, the superplastic property is judged to be good, but as shown in Table 3, when the component composition is within the range of the present invention (alloy Nos. 1 and 2), Except when the ingot heating is insufficient and the crystal grain size after superplastic forming exceeds 50 μm (Production code G for Alloy No. 1),
It is clear that all of them have a large elongation of 300% or more, and show superior superplasticity characteristics as compared with the comparative materials, although they are not as good as the conventional superplasticity materials (alloy numbers 7 and 8).

Next, the alloy No. 1 plate within the composition range of the present invention manufactured by the manufacturing code A, and the manufacturing code B
Alloy No. 2 within the composition range of the present invention manufactured by
Plate and conventional 7475 alloy (alloy number 7), SU
A welding crack test was performed on the PRAL alloy (alloy number 8). In this test, the fishbone crack test piece shown in FIG.
A, traveling 25 cm / min, electrode tungsten 2.4 mmφ,
TIG welding was performed under the conditions of Ar air flow and arc length of 3 mm, and the crack rate was examined. The results are shown in Table 4. The crack rate was defined by the following formula. Crack rate = ([bead length with crack] / [total weld bead length]) x 100 (%)

[0039]

[Table 4]

From the results shown in Table 4, it can be seen that the alloy of the present invention has significantly less cracking than the conventional alloy, that is, the weldability is extremely excellent.

Further, the corrosion resistance of the same material as the material used in the above-mentioned welding crack test was examined as follows.
That is, a 70 mm × 150 mm size test piece is cut out and washed with 10% NaOH aqueous solution at 50 ° C. for 1 minute → washing with pure water → dismuting with 15% HNO ₃ → washing with pure water, and then JI
A salt spray test according to SZ2371 was performed for 1000 hours to evaluate corrosion resistance (SST evaluation). The results are shown in Table 5.

[0042]

[Table 5]

It is clear from Table 5 that all the alloys of the present invention have extremely good corrosion resistance as compared with the conventional alloys.

[0044]

As is apparent from the above examples, the aluminum alloy sheet for superplastic forming of the present invention has good superplastic properties and, at the same time, has the same corrosion resistance and weldability as those of conventional superplastic forming aluminum sheets. It is remarkably superior to the alloy plate, and therefore can sufficiently satisfy the performance required for various building materials, bags and other containers, and various structural materials.

Further, in particular, according to the manufacturing method of the inventions of claims 3 and 4, the aluminum alloy plate for superplastic forming having excellent performance as described above can be reliably and stably produced on a mass production scale. Obtainable.

Further, the superplastic molded body of the inventions of claims 5 and 6 is remarkably excellent in corrosion resistance and weldability as a superplastically molded product accompanied by good superplasticity characteristics. Suitable for various applications.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing a fishbone crack test piece for determining weldability in an example.

Claims (6)

[Claims] 1. Mg 4.0 to 7.0% (weight%, the same applies hereinafter), Mn exceeding 1.5% and 2.5% or less, Be 0.00.
Fe as an impurity containing 005 to 0.01%
Is regulated to less than 0.2%, and the balance comprises Al and other unavoidable impurities, an aluminum alloy plate for superplastic forming. 2. Mg of 4.0 to 7.0%, Mn of more than 1.5% and 2.5% or less, Be of 0.00005 to 0.01%, Cr of 0.05 to 0.3%, V0. 0
5 to 0.3%, Zr 0.05 to 0.3%, and one or more of them are contained, and Fe as an impurity is 0.
An aluminum alloy plate for superplastic forming, which is regulated to less than 2% and the balance is Al and other unavoidable impurities. 3. Mg of 4.0 to 7.0%, Mn of more than 1.5% and 2.5% or less, Be of 0.00005 to 0.01%, and if necessary, Cr of 0.05 to 0.3. %,
V as an impurity, containing one or more of V0.05-0.3% and Zr0.05-0.3%
When casting an aluminum alloy in which e is restricted to less than 0.2% and the balance is Al and other unavoidable impurities, an Al-Ti mother alloy or Al is used as a grain refiner before or during casting. -Ti-B mother alloy was added in a Ti amount of 0.15% or less, and after casting by a DC casting method, the ingot was cast at 450 to 560 ° C for 0.5 to 2
The final cold rolling rate was 30 when heating for 4 hours and further performing hot rolling and cold rolling to obtain the required plate thickness.
% Or more, a method for producing an aluminum alloy sheet for superplastic forming. 4. Mg of 4.0 to 7.0%, Mn of more than 1.5% to 2.5% or less, Be of 0.00005 to 0.01%, and if necessary, Cr of 0.05 to 0.3. %,
V as an impurity, containing one or more of V0.05-0.3% and Zr0.05-0.3%
When casting an aluminum alloy in which e is restricted to less than 0.2% and the balance is Al and other unavoidable impurities, an Al-Ti mother alloy or Al is used as a grain refiner before or during casting. -Ti-B mother alloy was added in a Ti amount of 0.15% or less, and after casting by a DC casting method, the ingot was cast at 450 to 560 ° C for 0.5 to 2
The final cold rolling rate was 30 when heating for 4 hours and further performing hot rolling and cold rolling to obtain the required plate thickness.
%, And after the final cold rolling, the aluminum for superplastic forming is characterized by performing recrystallization treatment of heating at 280 to 560 ° C. at a temperature rising rate of 10 ° C./min or more and holding for 0 to 5 hours. Method for manufacturing alloy plate. 5. The composition contains Mg of 4.0 to 7.0%, Mn of more than 1.5% and 2.5% or less, Be of 0.00005 to 0.01%, and Fe as an impurity of less than 0.2%. A superplastic compact, characterized in that the balance is regulated, the balance being Al and other unavoidable impurities, and the crystal grain size after superplastic compacting is 50 μm or less. 6. Mg of 4.0 to 7.0%, Mn of more than 1.5% and 2.5% or less, Be of 0.00005 to 0.01%, Cr of 0.05 to 0.3%, V0. 0
5 to 0.3%, Zr 0.05 to 0.3%, and one or more of them are contained, and Fe as an impurity is 0.
A superplastic compact, characterized in that the content is regulated to less than 2%, the balance being Al and other unavoidable impurities, and the crystal grain size after superplastic compacting is 50 μm or less.