JPH02285046A - Aluminum alloy rolled sheet for superplastic working and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the Al alloy sheet for superplastic working having excellent corrosion resistance and strength by subjecting an alloy having specified compsn. constituted of Mg, Mn, Cr, Zr, V and Al to continuous casting into a specified plate thickness and thereafter executing specified homogenizing treatment and cold rolling. CONSTITUTION:The molten metal of an Al alloy contg., by weight, 0.5 to 3.8% Mg, furthermore contg. one or more kinds among 0.8 to 3.5% Mn, 0.1 to 0.5% Cr, 0.1 to 0.4% Zr and 0.1 to 0.4% V and the balance substantial Al with inevitable impurities is subjected to continuous casting into a plate having 3 to 15mm thickness. The continuously cast plate is immediately, or after cold-rolled, subjected to homogenizing treatment of holding under heating at 450 to 630 deg.C for 30min 20hr. The alloy plate is thereafter subjected to cold rolling at >=30% rolling reduction. If required, the cold rolled sheet is furthermore subjected to final annealing of heating to 400 to 600 deg.C at >=1 deg.C/sec temp. rising rate. In this way, the Al alloy rolled sheet for superplastic working contg. <=7mum maximum size of intermetallic compounds in the matrix, having excellent corrosion resistance obtainable of high strength without being subjected to heat treatment after plastic working and shownable of excellent superplastic characteristics can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing rolled aluminum alloy plates used for superplastic working.

BACKGROUND OF THE INVENTION In recent years, technology for performing superplastic working by utilizing the superplastic phenomenon of metal materials having fine crystal grains has been attracting attention.

Superplasticity is a phenomenon in which when a mechanical tensile force is applied to a material from the outside, a large elongation of several hundred percent or more can be obtained without causing local deformation (neck). By applying superplastic working that utilizes superplasticity, complex molding can be easily performed and mold costs can be reduced.

As a conventional aluminum-based superplastic material, Al-Z
n-MQ-Cu alloy, such as 7475 alloy of AA standard, or Al-Cu-Zr alloy, such as 2004 alloy of AA standard, and even Aj7-Mg-Cu-L 1-
Zr-based alloys, such as 8090 alloy, are known. On the other hand, aluminum-based superplastic materials can be broadly classified from the viewpoint of recrystallization behavior: those that utilize static recrystallization, which already have a fine recrystallized structure before superplastic processing, and those that utilize static recrystallization, which already have a fine recrystallized structure before superplastic processing, and The Al-Zn-Mg-Cu alloy mentioned above belongs to the static recrystallization type, and the β-Qu-7r alloy and the Afl-
The MQ-Cu-L 1-Zr alloy belongs to the dynamic recrystallization type.

Problems to be Solved by the Invention The two conventional superplastic processing materials mentioned above both contain large amounts of various additive elements, including CU, in order to enhance their superplastic properties. Therefore, there is a problem of poor corrosion resistance. In addition, all conventional materials are heat-treated materials, and in order to obtain high strength, they require another heat treatment of solution quenching after superplastic processing, which not only increases costs but also causes distortion due to quenching. Therefore, there is a problem in that the advantage of good shape fixability, which is one of the characteristics of superplastic working, is lost.

In addition, to the conventional as mentioned above! Among the basic materials for superplastic processing, those that utilize dynamic recrystallization have a strain rate (optimal strain rate) at which the largest superplastic elongation can be obtained, on the order of 10°3/s; In the type that utilizes recrystallization, the optimum strain rate is slow, on the order of 10-'/sec, resulting in a problem of low processing efficiency. On the other hand, the dynamic recrystallization type has the problem that performance varies depending on the preheating conditions during superplastic processing.

This invention was made against the background of the above-mentioned circumstances. It has excellent corrosion resistance, high strength can be obtained without heat treatment after superplastic working, and is a type that utilizes static recrystallization. At the same time, the optimum strain rate is 10 −3/sec,
The object of the present invention is to provide an aluminum alloy rolled plate for superplastic processing that can exhibit excellent superplastic properties, and a method for manufacturing the same.

Means for Solving the Problems The aluminum alloy rolled sheet for superplastic working of the present invention basically solves the problem of navigation by appropriately determining the composition of the Al-based alloy and regulating the size of the intermetallic compound. Furthermore, the present invention provides a method for obtaining an aluminum alloy rolled sheet for superplastic working, which solves the above-mentioned problems by appropriately setting the manufacturing process.

Specifically, the rolled aluminum alloy plate for superplastic working according to claim 1 contains 0.5 to 3.8 wt% of Mg;
) Mn 0.8-3.5wt%, Qr 0.1-0.
5wt%, Z r 0.1-0.4wt%, V 0.1
Contains one or more selected from ~0.4wt%, the remainder substantially consists of Al and unavoidable impurities, and the maximum diameter of the intermetallic compound in the matrix is 7 or less. It is characterized by this.

Further, the method for manufacturing an aluminum alloy rolled plate for superplastic working according to the invention of claim 2 contains MC20.5 to 3.8 wt%, Mn 0.8 to 3.5 wt%, and Cr001 to 0.
．． 5wt%, Z r 0.1-0.4wt%, V 0
．． An aluminum alloy bath temperature containing one or more selected from 1 to 0.4 wt%, with the remainder substantially consisting of Al and inevitable impurities, was continuously applied to a 3 to 15 mm thick plate. Immediately or after cold working, the continuous cast plate obtained is subjected to homogenization treatment by heating and holding at a temperature in the range of 450 to 630°C for 30 minutes to 24 hours, and the rapid rolling rate is 30. % or more of cold rolling.

Furthermore, the method for manufacturing an aluminum alloy rolled sheet for superplastic working according to the invention of claim 3 contains Mq 0.5 to 3.8 wt%, Mn 0.8 to 3.5 wt%, and Cr 0.1 to 0.
．． swt%, zr 0.1~0.4wt%, V0.1~
Continuously casting an aluminum alloy containing one or more selected from 0.4 wt%, the remainder consisting essentially of All and unavoidable impurities, into a plate with a thickness of 3 to 15 ag, Immediately or after cold working, the resulting continuous vI plate is subjected to homogenization treatment by heating and holding at a temperature within the range of 450 to 630°C for 30 minutes to 24 hours, and then subjected to a rolling reduction of 30% or more. It is characterized by performing cold rolling and further performing final annealing by heating to a temperature in the range of 400 to 600°C at a temperature increase rate of 1°C/sec or more.

Function First, the reason for limiting the components of the rolled aluminum alloy plate for superplastic working of the present invention will be explained.

MQ: MQ is a basic element in the aluminum alloy targeted by this invention, and is an element necessary to impart strength and at the same time exhibit superplastic properties, and promotes the proliferation of dislocations during cold working. The recrystallized grains are made finer, thereby effectively exhibiting superplastic properties. Mg is 0.5
These effects cannot be obtained when Mg is less than 3 wt%.
．． If it exceeds 8 wt%, casting becomes difficult. Therefore, M(II was set within the range of 0.5 to 3.8 wt%.

Mn, Cr, Zr, V: These are all transition elements, and are important elements for imparting superplastic properties. All of these must be in solid solution in the Al matrix at the time of I-forming, and by combining them with the homogenization treatment after casting, it is possible to refine the static recrystallized grains and improve the crystal grain size during superplastic deformation. Contributes to stabilization.

Any one or two or more of these may be added, but the above-mentioned effects are not sufficient when Mn is less than 0.8 wt%, Qr is less than 0.1 wt%, zr is less than 0.1 W''%, and less than 70.1 wt%. On the other hand, Mn 3.5wt%, c
r0. swt%, zr0.4wt%, V 0.4wt%
If it exceeds this, coarse primary crystal intermetallic compounds will not be sufficiently dissolved during casting, which will not only make casting difficult, but also cause vitiation during superplastic processing, reducing formability. However, sufficient superplastic properties cannot be obtained, and problems such as a decrease in elongation and a decrease in fatigue properties occur in the properties of the product during superplastic processing.

Therefore, Mn is 0.8 to 3.5 wt%, Cr is 0.1
~0. swt%, zr is 0.1 to 0.4wt%, and V is 0. It was set within the range of i to 0.4 wt%. Among these, it is particularly desirable to add 1.6 wt % or more of Mn alone or in combination with others. Also, Qr is 0.
Even within the range of 1 to 0.5 wt%, it is preferably less than 0.35 wt%.

The remainder of each of the above components may basically be All and unavoidable impurities.

Note that in normal aluminum alloys, Fe and 5i are mixed as unavoidable impurities, but if Fe exceeds 0.5 wt% or 5i exceeds 0.5 wt%, the gold-R compound becomes coarse and impairs superplastic properties. , Fe is 0. s
less than wt%, S: is 0. It is preferable to regulate it to less than swt%.

In addition, Qu and/or Zn are sometimes added to improve strength, but if Qu exceeds 10 wt%, corrosion resistance will decrease, and if Zn exceeds 2.5 wt%, corrosion resistance will similarly decrease. , CLI is 1.0wt% or less, Zn
is preferably 2.5 wt% or less.

Furthermore, in ordinary aluminum alloys, Ti % or a trace amount of Ti and B may be added to refine the ingot crystal grains, and in the case of the present invention, a trace amount of Ti s is also added.
Alternatively, it may contain Ti and B. However, T
If the amount of i added exceeds 0.20 wt%, primary TiAla
crystallizes and impairs formability, and the amount of B added is 0.01 w
If it exceeds t%, coarse particles of TiB2 will be generated and the moldability will be impaired, so Ti is 0.20wt% or less and B is 0.01wt%.
It is preferable to make it below wt%. In addition, 3e may be added in a range of 200 ppi or less to prevent wI tide oxidation during casting.

In the aluminum alloy rolled sheet for superplastic working of the present invention, not only the component composition is determined as described above, but also the maximum size of the intermetallic compound crystallized in the hema matrix is 7 m or less. There is a need. In other words, if large crystallized intermetallic compounds exist, the crystallized substances will become a starting point during superplastic processing, creating cavities called cavitation, and eventually the material will break. In order to obtain a large superplastic elongation, it is necessary that large intermetallic compound crystallizes do not exist. According to experiments conducted by the present inventors, it has been found that a superplastic elongation of several hundred percent or more can be obtained if the size of crystallized intermetallic compounds contained in a rolled sheet is 7 or less. Therefore, the size of the crystallized material was set to 7 or less.

Furthermore, as a necessary condition to obtain superplastic properties, it is necessary that the recrystallized grains be fine and stable, and specifically, the recrystallized grain size must be 10 or less, preferably 5IJa or less. is desired. Good superplastic elongation is exhibited when the recrystallized grains are 10 tIIn or less, and even more excellent superplasticity is exhibited especially when the recrystallized grains are 5 or less. However, as will be described later, such a fine recrystallized grain structure only needs to be formed just before superplastic working is started, and therefore, when the rolled sheet of the present invention is actually used, it is necessary to After the final annealing for recrystallization is performed as an independent process on the rolled sheet after inter-rolling to form the fine recrystallized grain structure as described above, the sheet is heated again to the superplastic processing temperature to perform superplastic processing. In some cases, final annealing for recrystallization is not particularly performed on the rolled sheet after cold rolling, and fine recrystallization occurs during preheating before superplastic processing or during the heating process until the superplastic processing temperature is reached. There are cases where a grain structure is generated, so in the rolled sheet of claim 1, the recrystallized grain size is not particularly defined.

As mentioned above, the maximum intermetallic compound size is 7# or less and the crystal grain size is 10IJa or less and has a fine recrystallized structure, or such a fine recrystallized structure is preheated or superplasticized before superplastic processing. A rolled plate that can be produced in the process of raising the temperature to the processing temperature can be obtained by the process defined in the invention of claim 2 or claim 3. The process will be explained below.

First, an aluminum alloy reservoir groove having the above-mentioned composition is melted in accordance with a conventional method and continuously cast into a thin plate having a thickness of 3 to 15 m. Here, in order to make the maximum intermetallic compound size 7 or less, it is necessary to increase the cooling rate during casting by applying the above-mentioned temporary continuous casting method (continuous casting and rolling method). . It is actually difficult to cast an ultra-thin plate of less than 3u, while when casting a plate of more than 15a, the cooling rate becomes so low that a maximum intermetallic compound size of 7M or less cannot be achieved. Therefore, the plate thickness during continuous casting is 3 to 15 mm. Closed.

The obtained continuously cast plate is immediately subjected to a homogenization treatment (soaking treatment) or cold worked to a required intermediate plate thickness, and then subjected to a homogenization treatment. This homogenization treatment is a necessary step to homogenize the structure and finally obtain a fine recrystallized structure. The heating temperature for homogenization treatment is 4
If the temperature is below 50°C, the homogenization effect will not be sufficient, making it difficult to obtain a sufficiently refined recrystallized structure.On the other hand, if the temperature exceeds 630°C, there is a risk of eutectic melting, and therefore the homogenization process The temperature must be within the range of 450-630°C. In addition, the homogenization treatment time requires 0.5 hours or more to uniformly heat the entire coil, and on the other hand, exceeding 24 hours will only increase the cost economically, so the homogenization treatment time was within the range of 0.5 hours to 24 hours.

This homogenization process is continuous! Generally, the homogenization treatment is performed immediately after the coil is formed, but as described above, the homogenization treatment may be performed after cold working the continuous cast plate. In the latter case, the process is complicated, but since cold working strain is introduced before the homogenization treatment, the homogenization effect is even better and the recrystallized grain refinement effect is also greater.

After the homogenization treatment, cold rolling is performed to obtain the required final thickness. This cold rolling is essential to obtain a fine recrystallized structure, and the larger the cold rolling rate, the finer the recrystallized grains. If the rolling ratio is less than 30%, it will be difficult to obtain recrystallized grains with 10 or less grains, so cold rolling was performed at a rolling ratio of 30% or more. In this cold rolling step, cold rolling may be performed two or more times with intermediate annealing in between; in this case, intermediate annealing t! It is sufficient if the rolling ratio is set to 30% or more in the final cold rolling. Moreover, the intermediate annealing in this case may be performed at about 250 to 450° C. for about 1 hour to 10 Bi.

The rolled sheet for superplastic working obtained as described above is characterized in that the recrystallized grain size and recrystallized grain shape after recrystallization annealing do not depend so much on the heating rate during recrystallization annealing. Therefore, as an independent process, the cold-rolled product is subjected to the superplastic working process without aX annealing for recrystallization, and preheating before superplastic working and heating until the superplastic working temperature is reached. Even when recrystallization occurs during the hot process, the crystal grains become sufficiently fine and exhibit good ffi plasticity. Therefore, in the manufacturing method according to the second aspect of the invention, the steps up to the cold rolling step are specified, and a case where the rolled plate after cold rolling is directly subjected to the superplastic working step is included.

However, as mentioned above, although the recrystallized grain size and recrystallized grain shape do not greatly depend on the heating rate during recrystallization,
Of course, it is affected to some extent by the heating rate,
The faster the heating rate, the more isotropic and fine the recrystallized grains become. In addition, the material is more stable if it is supplied to the superplastic processing process in the state after recrystallization, and the preheating conditions for superplastic processing and the temperature increase conditions up to 8 degrees superplastic processing, etc. Not easily affected. Therefore, it is preferable to perform I# final annealing with relatively rapid heating for recrystallization as an independent step before the superplastic working step, and the invention of claim 3 stipulates this. It is.

In this case, the final annealing has a heating rate (temperature increase rate) of 1℃/
If it is less than sec, the above-mentioned effects obtained by performing the final annealing as an independent process cannot be sufficiently obtained. Further, if the final annealing temperature is less than 400°C, recrystallization will not occur, while if it exceeds 600°C, recrystallized grains may become large or local remelting may occur. Therefore, the final annealing is 1℃/se
It is necessary to heat within the range of 400 to 600°C at a heating rate of c or more.

Example Alloy A within the composition range of the present invention shown in Table 1.

For B, C, and alloys outside the composition range of the present invention, processes within the present Komei process conditions as shown in condition numbers 1 to 4 in Table 2 were applied. That is, 31! The continuously cast plate was subjected to homogenization treatment at 550°C for 12 hours, and then the plate thickness was 1
．． It was cold rolled to a temperature of 5 (73% of the cold rolling process).

Further, for alloy B' within the composition range of the present invention, which has a composition close to that of the alloy, a process as shown in condition number 5 in Table 2 was applied as a comparative process. That is, Alloy B' was DC cast into a cross-sectional dimension of 400 x Booty, and the cast ingot was soaked at 550°C for 12 hours, and then hot rolled at SOO°C to a plate thickness of 5.5mm.
It was further cold rolled to a thickness of 1.5M.

On the other hand, for alloy B within the composition range of the present invention, a process as shown in condition number 6 in Table 2 was applied as a comparative process. In other words, except for the homogenization process, condition number 1~
4, and the homogenization treatment was performed at a temperature of 40°C at a temperature lower than the range of the present invention.
The test was carried out at 0°C for 12 hours.

Furthermore, for alloy B within the composition range of the present invention, a manufacturing method within the process condition range of the present invention as shown in condition number 7 in Table 2 was applied. In other words, condition number 1 until cold rolling
The final annealing for recrystallization was carried out at 450° C. for 45 seconds using the same procedure as in Step 4. Note that the temperature increase rate at this time is 10° C./rich or more.

Table 3 shows the results of examining the maximum crystallized product size and recrystallized grain size after recrystallization for each sample obtained as described above. Note that the recrystallized grain sizes shown in Table 3 are values determined from bonds subjected to superplastic working as described below.

Therefore, it is considered that the recrystallized grain size was actually smaller than the values shown in Table 3 in the state immediately before superplastic deformation started.

Table 3 shows the results of elongation of each of the above samples when tensile tests were conducted at various tensile rates (strain rates) after being placed in a furnace maintained at 450°C for 15 minutes. Shown below. Furthermore, for each sample, strain rate 3x10-3
The results of investigating the cavitation occurrence rate (area % in cross section) under the condition of 100% elongation at 100% elongation at
Shown in the table.

As shown in Table 3, in the case of the samples according to the examples of the present invention,
In both cases, the size of intermetallic compound crystallization is extremely small, and the recrystallized grains are extremely small at maximum of 6 yen even after superplastic deformation, so as shown in the same Table 3, cavitation occurs during superplastic processing. The occurrence of
It can be seen that the material exhibits large superplastic properties exceeding SOO%. In addition, in the samples according to the examples of the present invention, the strain rate at which the maximum elongation occurs (optimum strain rate) is on the order of 1 G-3/sec, and the optimum strain rate of the conventional superplastic material using static recrystallization is 10 Considering that the molding speed was on the order of 4/sec, it is clear that molding can be performed at an order of magnitude faster than conventional molding speeds.

Furthermore, for alloy B, a sample according to an embodiment of the present invention to which the process of condition number 2 in Table 2 was applied, and a sample of 7475 alloy of AA standard, which is known as a conventional All super superplastic processing material (X, An experiment was conducted to compare strength and corrosion resistance as follows.In other words, in order to evaluate the strength and corrosion resistance in a state corresponding to the state after superplastic working, 50s
After conducting a superplastic processing thermal H history simulation of a 5Gag plate by holding at 450°C for 30 minutes and cooling at 1so°C/hr, which corresponds to the thermal II history in superplastic processing, the hardness was investigated and further A time salt spray test was conducted to evaluate corrosion resistance. The results are shown in Table 4.

Table 4 If the conventional 7475 alloy is subjected to re-solution quenching treatment after superplastic working, the hardness will be significantly increased to about Hv 180, but as shown in Table 4, if the hardness is left as it is after superplastic working, It was confirmed that the hardness was Hv61 and low strength, whereas the material of the present invention showed high strength of Hv91 even after superplastic working. Further, as a result of the salt spray test, almost no change was observed in the material of the present invention, but the surface of the 7475 alloy had severe discoloration, and its corrosion resistance was clearly inferior.

Effects of the Invention As is clear from the above examples, the aluminum alloy rolled sheet for superplastic working according to the present invention has a fast optimum strain rate showing maximum superplastic elongation of the order of 10-3/sec.
Moreover, it can exhibit excellent superplastic properties, such as less risk of cavitation occurring during superplastic deformation.
In addition, it can exhibit high strength without undergoing heat treatment after superplastic processing, and it also has extremely excellent corrosion resistance, so it can be used as a material for superplastic processing. It is meaningful in terms of doing so.

Applicant Sky Aluminum Co., Ltd. Agent Patent Attorney Yutaka 1) Hisashi Take (and 1 other person)

Claims (3)

[Claims] (1) Contains Mg0.5-3.8wt% and Mn0
．． 8-3.5wt%, Cr0.1-0.5wt%, Zr
0.1 to 0.4 wt%, V0.1 to 0.4 wt%, and the remainder consists essentially of Al and unavoidable impurities; An aluminum alloy rolled sheet for superplastic working, characterized in that the maximum diameter of intermetallic compounds is 7 μm or less. (2) Contains Mg0.5-3.8wt% and Mn0
．． 8-3.5wt%, Cr0.1-0.5wt%, Zr
A molten aluminum alloy containing one or more selected from 0.1 to 0.4 wt%, V0.1 to 0.4 wt%, and the remainder substantially consisting of Al and inevitable impurities, Homogenization by continuous casting into plates with a thickness of 3 to 15 mm, immediately or after cold working, and heating and holding at a temperature within the range of 450 to 630°C for 30 minutes to 24 hours. treatment, and then the rolling rate was 30.
1. A method for producing an aluminum alloy rolled sheet for superplastic working, characterized by subjecting it to cold rolling of % or more. (3) Contains Mg0.5-3.8wt% and Mn0
．． 8-3.5wt%, Cr0.1-0.5wt%, Zr
A molten aluminum alloy containing one or more selected from 0.1 to 0.4 wt%, V0.1 to 0.4 wt%, and the remainder substantially consisting of Al and inevitable impurities, Homogenization by continuous casting into plates with a thickness of 3 to 15 mm, immediately or after cold working, and heating and holding at a temperature within the range of 450 to 630°C for 30 minutes to 24 hours. treatment, and then the rolling rate was 30.
An aluminum alloy rolled sheet for superplastic working, characterized in that it is cold-rolled to a temperature of 400 to 600°C at a heating rate of 1°C/sec or more, and then subjected to final annealing at a temperature in the range of 400 to 600°C. Production method.