JPH0610087A - High strength superplastic aluminum alloy excellent in corrosion resistance and its manufacture - Google Patents

Abstract

PURPOSE:To develop a clad material made of a high strength superplastic Al alloy excellent in corrosion resistance by cladding the core material made of an Al-Zn-Mg-Cu alloy having a specified compsn. with the surface material of an Al-Zn alloy under specified temp. conditions. CONSTITUTION:The ingot of the Al alloy contg., as essential components, by weight, 3 to 8% Zn, 1 to 3% Mg and 1 to 3% Cu and furthermore contg. one or >= two kinds among 0.05 to 1.0% Mn, 0.05 to 0.5% Cr, 0.05 to 0.5% Zr and <0.10% Ti is subjected to homogenizing heat treatment at 400 to 550 deg.C and is thereafter subjected to hot rolling into the lamellar core material having <=25mum grain size, and the sheet material of the Al-Zn alloy contg., as essential components, 0.8 to 1.3% Zn is formed into the surface material, and they are formed into a clad material in which the cladding ratio is regulated to 2 to 4% per single face, which is subjected to hot cladding rolling at 300 to 500 deg.C into the clad material. This clad material is subjected to annealing by holding under heating of two stages at 350 to 550 deg.C, is cooled at >=100 deg.C/hr cooling rate, is thereafter subjected to cold rolling of at least >=50% and is heated to 400 to 550 deg.C at >=500 deg.C/hr temp. raising rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superplastic aluminum alloy and a method for producing the same, and more particularly to a high strength superplastic aluminum alloy laminated plate having excellent corrosion resistance and a method for producing the same.

In the present invention, the term "superplasticity" means that the material is several hundreds without constriction or breakage under appropriate temperature and deformation conditions.
It means a phenomenon showing a large elongation of not less than%.

[0003]

2. Description of the Related Art Generally, it is necessary to make crystal grains fine, for example, 25 μm or less, in order to cause fine crystal grain superplasticity.
The present inventors have conducted extensive research based on ultra-super duralumin (7075 aluminum alloy) that is mainly used in aircraft, and as a result, Patent No. 1,388,413 (Japanese Patent Publication No. Sho 6).
No. 1-57383) "Method for producing superplastic aluminum alloy", a superplastic material having an elongation of 500% was developed and proposed.

However, in this material, after superplastic working, the material is subjected to solution treatment at 475 ° C., and usually has a maximum strength of about 570.
T6 is aged to obtain ~ 580 N / mm ^2, but if overageing treatment (T76 or T73) is performed to impart corrosion resistance, the strength is increased to about 500-510 N / mm ² to 10-1.
There was a drawback that it decreased by 5%.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-strength fine-grain superplastic aluminum alloy excellent in corrosion resistance and a method for producing the same by solving the above-mentioned drawbacks of the prior art. .

[0006]

Means for Solving the Problems As a result of intensive studies on new measures for solving the above-mentioned problems, the present inventors have hitherto carried out as one of improvement of corrosion resistance of aluminum alloys for aircraft. It was found that high strength can be maintained under the application of a clad material, and the present invention has been completed here.

That is, according to the present invention, Zn: 3 to 8%, Mg:
1 to 3% and Cu: 1 to 3% are contained as essential elements, and Mn: 0.05 to 1.0%, Cr: 0.05 to 0.5.
%, Zr: 0.05 to 0.5% and Ti: 0.10% or less, and a composition having a balance Al and impurities and having a crystal grain size of 25 μm or less. Aluminum alloy is used as core material, Zn: 0.8-1.3% is contained as an essential element, and aluminum alloy skin material of the composition consisting of balance Al and impurities is combined at a clad ratio of 2-4% on one side. The gist is a high-strength superplastic aluminum alloy excellent in corrosion resistance, which is characterized by being a plate.

The manufacturing method is as follows: Zn: 3-8%, M
g: 1 to 3% and Cu: 1 to 3% or less are contained as essential elements, and Mn: 0.05 to 1.0%, Cr: 0.05 to 0.5.
%, Zr: 0.05 to 0.5%, and Ti: 0.10% or less, and an aluminum alloy having a composition of Al and impurities, which is 400 to 550.
Homogenizing heat treatment at a temperature of ℃ and hot rolling to make a core, Zn:
An aluminum alloy containing 0.8 to 1.3% as an essential element with the balance Al and impurities as a skin material,
After hot-rolling at a temperature of 300 to 500 ° C. into a clad material on one side or both sides, 350 to 550
Two-step heating and holding annealing is performed at a temperature of ℃,
After cooling at a cooling rate of ℃ / hr or more, at least 50%
After performing the above cold rolling, it is characterized by heating to a temperature of 400 to 550 ° C. at a rate of 500 ° C./hr or more.

The present invention will be described in more detail below.

[0010]

[Action]

First, the reasons for limiting the component composition of the core material in the superplastic aluminum alloy according to the present invention will be described.

Zn: Zn is an element that imparts strength, and 3
If it is less than%, sufficient strength cannot be obtained, and 8%
If the content exceeds 1, the corrosion resistance will be impaired. Therefore, Zn
The content is 3-8%.

Mg: Mg is an element that imparts strength, and 1
If less than%, sufficient strength cannot be obtained, and 3%
If the content exceeds 1, the cold rollability is impaired. Therefore,
The Mg content is 1-3%.

Cu: Cu is an element that imparts strength, and 1
If less than%, sufficient strength cannot be obtained, and 3%
If the content exceeds the range, cold rolling property and ductility are impaired. Therefore, the Cu content is 1-3%.

In addition to containing these components as essential elements, it is necessary to add one or more of the following Mn, Cr, Zr and Ti in appropriate amounts.

Mn, Cr, Zr: If Mn, Cr, and Zr are less than 0.05%, fine crystal grains as described later cannot be obtained, and Mn is 1.0% and Cr is 0%. .5%,
If the Zr content exceeds 0.5%, a huge compound is produced during casting and sufficient superplastic elongation cannot be obtained. Therefore, the Mn content is 0.05 to 1.0% and the Cr content is 0.0.
The content of Zr is 5 to 0.5%, and the Zr content is 0.05 to 0.5%.

Ti: Ti is usually added in order to make the ingot have a fine structure, and when added in excess of 0.10%,
Enormous superplastic elongation cannot be obtained because of the formation of huge compounds during casting. Therefore, the Ti content is set to 0.10% or less.

Fe and Si which may be contained as impurities
When it is contained in a large amount, it causes the formation of insoluble intermetallic compounds (crystallized substances) such as Cu ₂ FeAl ₇ , Mg ₂ Si, etc., which leads to a decrease in the superplastic elongation. Therefore, Fe: 0.15% or less, Si: 0 It is desirable to suppress it to 0.15% or less.

Next, the reasons for limiting the component composition of the skin material in the superplastic aluminum alloy according to the present invention will be described.

Zn: Zn is such that the skin material has a sacrificial anode action with respect to the Al-Zn-Mg-Cu-based core material, and
It is an element added so that the electric potential becomes baser than that of the core material, but if it is less than 0.8%, a sufficient sacrificial anode action cannot be imparted, and if it exceeds 1.3%, the skin material itself Corrosion resistance and the potential difference between the core material are reduced, and the sacrificial anode action is reduced. Therefore, the Zn content is 0.8 to 1.3%.

Fe and Si which may be contained as impurities
As in the case of the core material, if a large amount is contained, Cu ₂ FeA
Fe: 0.15% because it causes the formation of insoluble intermetallic compounds (crystallized substances) such as l ₇ and Mg ₂ Si, which leads to a decrease in superplastic elongation.
Hereinafter, it is desirable to suppress Si: 0.15% or less.

A method of manufacturing a superplastic aluminum alloy composed of the above core material and skin material will be described.

First, an Al alloy ingot as a core material is
The mixture is heated to 550 ° C. to homogenize the microsegregation inside the ingot, and is hot-rolled to a predetermined plate thickness to obtain a core material. The hot rolling temperature is preferably 300 to 500 ° C.

Next, a skin material having the above composition is laminated on one side or both sides of this core material, and preferably 400 to 5
It is reheated to a temperature of 50 ° C., hot-rolled at a temperature of 300 to 500 ° C., and processed to a predetermined plate thickness. As a result, the core material and the skin material have a hot fiber structure, and at the same time, a part of the transition elements of Mn, Cr and Zr are partially precipitated. Here, the clad rate is preferably 2 to 4% on one side. If it is less than 2%, the sacrificial anode action of the skin material is not sufficient and good corrosion resistance cannot be obtained, and if it exceeds 4%, the strength of the skin material is smaller than that of the core material, so that the strength of the entire material becomes small, which is preferable. Absent.

After this hot rolling, two-step heating and holding annealing is performed at a temperature of 350 to 550.degree. In particular,
In this temperature range, it is preferable that the first heating and holding is performed at a high temperature and then the second heating and holding is performed at a low temperature. For example, first, at a temperature of 450 to 550 ° C, 0.5 to 0.5
The first heating and holding for 10 hours is performed, followed by cooling to the second heating and holding temperature, and the second heating and holding for 0.5 to 50 hours at a temperature of 350 to 450 ° C, and 100 ° C.
Cool at a cooling rate of / hr. In any case of heating and holding, the higher the temperature, the shorter the time.

In this heating and holding, most of the solute elements are solid-solved by the first heating and holding, and subsequently, the transition elements of Mn, Cr, and Zr are metal with Al by the second heating and holding. Intercalation compound MnAl ₆ , Cr ₂ Mg ₃ Al ₁₈ , ZrAl ₃
Etc. are deposited. Further, high temperature aging precipitates of Zn, Mg, Cu and Al are formed, the density of dislocations generated during cold rolling becomes higher, and finer crystal grains are generated, resulting in a material having a large superplastic elongation. Is obtained. If the cooling rate after the two-step heating and holding annealing is less than 100 ° C./hr, fine particles cannot be obtained.

Thereafter, cold rolling of 50% or more is performed. 5
With cold rolling of less than 0%, high strain energy is not accumulated and fine grains cannot be obtained.

Finally, at a heating rate of 500 ° C./hr or more, 4
When heated to a temperature of 00 to 550 ° C., a desired fine-grained material of 25 μm or less is obtained. If the heating rate is less than 500 ° C./hr, fine particles cannot be obtained in the temperature range of 400 ° C. or less.
Further, if the temperature exceeds 550 ° C., the material may cause burning (eutectic melting), which is not preferable.

In general, the superplastic deformation stress σ is the grain size d
And the following relationship. That is, σ∝ (1
/ D ² ) to (1 / d ³ ). Therefore, it is strongly required that the crystal grains are fine, and in the example of this material, elongation of 500% or more cannot be expected unless the crystal grain size of the core material is 25 μm or less. Therefore, the crystal grain size of the core material is controlled to 25 μm or less.

Next, examples of the present invention will be shown.

[0031]

[Example 1]

[Table 1] A core material ingot (thickness: 100 mm) of an Al—Zn—Mg—Cu alloy having the composition shown in Table 1 was homogenized and heat-treated at 480 ° C. for 12 hours, and then hot-rolled into a plate material. Then, a skin material made of Al-1 wt% Zn (7072 alloy) was superposed thereon, reheated to 480 ° C., and then hot-rolled to obtain a predetermined clad material. Clad rate is 3% of the standard for aircraft materials
And Then, under the manufacturing conditions shown in Table 2, the final plate thickness is 2.0 m.
An m laminated board was manufactured.

[Table 2]

Table 2 shows the superplastic properties of these laminated plates. The high temperature deformation is 515 ° C. and the strain rate is 2 × 10.
^-4 / sec. Also, the corrosion resistance test is ASTM
A standard EXCO test (exfoliation corrosion test) was performed.

As is clear from Table 2, in the examples of the present invention, the corrosion resistance of the conventional heat treatment material for improving corrosion resistance T76 or more was obtained,
The strength is as high as T6 material.

[0034]

Example 2 No. 2 composition (Al-5.7% Zn-) shown in Table 1
After a core ingot (thickness: 100 mm) of 2.3% Mg-1.6% Cu-0.20 Cr) was homogenized and heat-treated at 480 ° C. for 12 hours,
A core material was obtained as a plate material by hot rolling. Then, Table 3

[Table 3] The Al alloy skin material having the composition shown in (1) was piled up (impurities and the like were the same as the core material composition), reheated to 480 ° C., and hot-rolled to obtain a predetermined clad material. The clad rate was 3%, which is the standard for aircraft materials. Then, a laminated plate having a final plate thickness of 2.0 mm was manufactured under the manufacturing conditions No. 1 shown in Table 2.

Table 3 shows the super-compositional characteristics of these laminated plates. The high temperature deformation is 515 ° C. and the strain rate is 2 × 10.
^-4 / sec. Also, the corrosion resistance test is ASTM
A standard EXCO test (exfoliation corrosion test) was performed.

As is clear from Table 3, in the examples of the present invention, the corrosion resistance of the conventional heat treatment material for improving corrosion resistance T76 or more was obtained.

[0037]

As described in detail above, according to the present invention,
Since it is possible to provide a superplastic aluminum alloy that has high strength and excellent corrosion resistance, it is possible to integrally mold parts that are made by assembling parts with complicated shapes and many child parts. And is suitable for the aircraft industry and the like.

Claims (2)

[Claims] 1. By weight% (hereinafter the same), Zn: 3-8%,
It contains Mg: 1 to 3% and Cu: 1 to 3% as an essential element, and Mn: 0.05 to 1.0%, Cr: 0.05 to 0.5%.
%, Zr: 0.05 to 0.5% and Ti: 0.10% or less, and a composition having a balance Al and impurities and having a crystal grain size of 25 μm or less. Aluminum alloy is used as core material, Zn: 0.8-1.3% is contained as an essential element, and aluminum alloy skin material of the composition consisting of balance Al and impurities is combined at a clad ratio of 2-4% on one side. A high-strength superplastic aluminum alloy with excellent corrosion resistance, characterized by being a plate. 2. Zn: 3 to 8%, Mg: 1 to 3% and Cu: 1
~ 3% or less is contained as an essential element, and Mn: 0.05
~ 1.0%, Cr: 0.05-0.5%, Zr: 0.05-0.5.
1% or 2 selected from 5% and Ti: 0.10% or less
An aluminum alloy containing at least one species and having a composition consisting of the balance Al and impurities is homogenized at 400 to 550 ° C., hot-rolled into a core material, and Zn: 0.8 to 1.3% is an essential element. As a clad material on one side or both sides by hot-rolling at a temperature of 300 to 500 ° C., using an aluminum alloy having a composition of Al and impurities as a skin, and then performing two steps at a temperature of 350 to 550 ° C. After heat-holding and annealing, and cooling at a cooling rate of 100 ° C / hr or more, at least 50% or more of cold rolling is performed, and then heated to a temperature of 400 to 550 ° C at a rate of 500 ° C / hr or more. A method for producing a high-strength superplastic aluminum alloy having excellent corrosion resistance, which is characterized by the following.