JPH11131165A - Heat treated type aluminum alloy for superplastic forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to perform, under the conditions more relaxed than heretofore, practical superplastic forming of a heat treated type aluminum alloy capable of increasing strength by the application of T6 treatment, etc., after forming. SOLUTION: This aluminum alloy is a composition which consists of, by weight, 0.3-1.5% Mg, 0.4-2.0% Si, and the balance Al with inevitable impurities and the content of Fe among the inevitable impurities is regulated to <=0.15%, Further, the average crystalline grain size of this aluminum alloy is regulated to 15-120 μm. Moreover, in the region where strain rate (ε')(s<-1> ) and forming temp. T(K) satisfy ln(ε')<-65+10ln(T) [where ε'>=10<-4> s<-1> and T=673 to 853 deg.K], elongation is regulated to >=150%. Arbitrarily, one or >=2 kinds among <=0.4% Mn, <=0.1% Cr, <=0.1% Zr, <=0.1% V, <=0.1% Ti, and <=0.05% B can be incorporated, and further, <=0.8% Cu can be incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a heat-treated aluminum alloy suitable for superplastic forming.

[0002]

2. Description of the Related Art The superplastic phenomenon is characterized in that elongation is so large that it cannot be obtained under ordinary working conditions and deformation stress is small. In recent years, research and development for practical use of superplastic alloys utilizing these features have been actively conducted. In particular, aluminum alloys are being actively developed from the viewpoint of lightness, and among them, 5000 series alloys have been attracting attention because they have excellent strength and excellent corrosion resistance and surface treatment properties, and have been put to practical use. Some alloys are available.

[0003] By the way, the conditions for manifesting the superplastic phenomenon include (1) stable and fine equiaxed crystal grains (-10 to 10);
μm), (2) the heating temperature T is T> 0.5
T _m (absolute temperature of melting point), (3) low strain rate (10
And processing at ^-4 s ^-1 ~) is generally said to be suitable (e.g., Osawa, Nishimura: light metal, 39-10 (1
989), p. 765-775). So far, alloy development has been conducted based on the guidelines of refining crystal grains, making the structure thermally stable even at high temperatures, and suppressing the occurrence of cavities that impair ductility. Have been

Conventionally, in superplastic working, there are many restrictions on manufacturing conditions for making the crystal grain size fine and uniform, and processing at a low strain rate has also been required.
That is, for practical use of the superplastic phenomenon, Japanese Patent Laid-Open No.
As disclosed in JP-A-76145, a special component system as an alloy and special production conditions as disclosed in JP-A-58-81957 are essential. Was also not desirable. Regarding the processing conditions, East: Light Metal, 39-11 (1
989), p. As described in U.S. Pat. No. 751-764, there is a problem in productivity because a low strain rate is required.

However, in superplastic forming, a very large elongation such as 500% or 1000% is rarely required in practice, and it is often sufficient to achieve an elongation of about 200%. In view of the above, the inventors of the present invention disclosed an Al-Mg-based alloy sheet which is easy to manufacture without adopting special conditions and enables superplastic forming with excellent productivity, and a method for forming the same. No. 199,272.

[0006]

However, since the above-mentioned aluminum alloy is based on a non-heat-treated 5000-series alloy, it has been difficult to use a material having a tensile strength of 300 MPa or more after molding. The present invention relates to a heat treatment type 6000, which is conventionally considered to have no superplastic phenomenon.
A heat-treatable aluminum alloy that exhibits superplasticity close to that of a 5000-type alloy and performs appropriate heat treatment such as T6 treatment after superplastic forming to obtain a high tensile strength of 300 MPa or more. The purpose is to do. Here, the T6 treatment means a solution subjected to an artificial age hardening treatment after the solution treatment.

[0007]

Means for Solving the Problems The inventors have studied to increase the strength at room temperature after forming in order to secure practical superplastic formability and further reduce the weight of applicable members. As a result,
The present inventors have found that superplasticity can also be exhibited in 6000 series alloys, and have completed the present invention by limiting the components, structures, and forming methods capable of superplastic working. The gist of the present invention is as follows. It is.

(1) Mg: 0.3-1.5% by weight
%, Si: 0.4 to 2.0%, and the balance: Al and unavoidable impurities.
Is 0.15% or less, and the average crystal grain size is 15 to 120%.
μm, the strain rate ε ′ (s ⁻¹ ) and the molding temperature T
(K) and the following relationship: ln (ε ′) <− 65 + 10ln (T), where elongation is 150% or more in a range satisfying ε ′ ≧ 10 ⁻⁴ s ⁻¹ , T = 673 to 853K. A heat-treated aluminum alloy for superplastic forming, characterized in that:

(2) Further, in weight%, Mn: 0.4% or less, Cr: 0.1% or less, Zr: 0.1% or less, V:
0.1% or less, Ti: 0.1% or less, and B: 0.0
The heat-treated aluminum alloy for superplastic forming according to (1), wherein one or more of 5% or less are contained.

(3) The heat-treated aluminum alloy for superplastic forming according to (1) or (2), further comprising Cu: 0.8% by weight or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the alloy composition, superplastic working conditions and the like of the present invention will be described below. First, the reasons for limiting the alloy composition in the present invention will be described. Mg and Si
Is an essential basic alloy component that contributes to ensuring superplastic formability under the processing conditions described below and increasing the strength after performing T6 treatment and the like after forming, and Mg: 0.3 to
0.9%, Si: 0.4 to 1.5%.

Fe is generally mixed as an impurity, but when mixed, an intermetallic compound such as Al-Fe-Si is formed, which tends to generate cavities during superplastic forming and hinders superplastic forming. Therefore, the allowable mixing range is 0.15%
The following is assumed. In the alloy of the present invention, optionally Mn,
One or more of Cr, Zr, V, Ti, and B can be contained. Mn, Cr, Zr, V, Ti, and B have an effect of preventing abnormal growth of the crystal grain size during superplastic forming. When 0.4% or more of Mn is added, Al ₆ Mn or F
e, an intermetallic compound is formed with Si, and cavities are easily generated during superplastic forming. Cr, Zr, V, T
Similarly, when i is added in excess of 0.1%, cavities are likely to be generated during superplastic forming. On the other hand, B coexists with Ti and promotes homogenization of crystal grains. But,
If added in excess of 0.05%, TiB ₂ is generated, and cavities are easily formed, which hinders superplastic forming.

Therefore, the added amount of Mn is 0.4% or less, the added amount of Cr, Zr, V, and Ti is 0.1% or less, and the added amount of B is 0.05% or less. Further, the alloy of the present invention may contain Cu as necessary. Cu is effective in increasing the strength when performing T6 treatment or the like after processing. In the case of the present alloy, if Cu is contained in excess of 0.8%, cavities are liable to be segregated at crystal grain boundaries and superplastic forming is hindered. Therefore, the addition amount is set to 0.8% or less. Also, Cu impairs the corrosion resistance.
% Is preferable.

Next, the reason for defining the average crystal grain size will be described. Conventionally, it has been reported that in order to develop superplasticity, it is general to refine the crystal grain size (for example, Baba, Yoshida: Plasticity and Processing, 27-302 (198)
6), P333-338, etc.). However, as a result of intensive studies by the present inventors, it has been found that a crystal grain size larger than the conventional knowledge, that is, a range of 15 to 120 μm, is sufficient to enable superplastic forming with high productivity.

Further, the reason for defining the range of the processing conditions for enabling superplastic forming using the alloy of the present invention will be described. The elongation required for practical superplastic forming requires a minimum sheet thickness in order to secure the strength after forming. For example, a large superplastic elongation of 500% or more is not required. If the elongation is about 150% or more in the total elongation, it is often necessary and sufficient. Therefore, the inventors have intensively studied alloy plates having a practical superplastic elongation at a high strain rate enabling high productivity, mainly on heat-treated aluminum alloys.

As a result, if an aluminum alloy sheet having the above-defined alloy composition and crystal grain size is formed within the following processing conditions, a superplastic elongation of 150% or more, which is the object of the present invention, can be obtained. Was found to be. First, the strain rate ε ′ was set to ε ′ ≧ 10 ⁻⁴ s ⁻¹ from the viewpoint of productivity. If the strain rate ε ′ <10 ⁻⁴ s ⁻¹ , processing takes too much time and is not practical.

Next, the processing temperature T was set to 673 to 833K. At a temperature of 673K or lower, a practical superplastic phenomenon cannot be obtained, so the lower limit of the processing temperature was 673K. On the other hand, if the temperature is higher than 833K, the crystal grain size becomes coarse during processing, so that appropriate superplastic forming cannot be performed. In the present invention, according to the strain rate and the processing temperature, the strain rate ε '
When (s ^-1 ) and the molding temperature T (K) are set to satisfy ln (ε ′) <− 65 + 10ln (T), the deformation resistance can be reduced, and superplastic forming can be performed very advantageously. Was found.

[0018]

【Example】

(Example 1) The present invention will be specifically described based on examples. Each of the aluminum alloys shown in Table 1 was cast by a DC casting method according to a conventional method, and the obtained ingot was subjected to a homogenization treatment at 530 ° C. for 5 hours, followed by hot rolling and cold rolling. Then, after a rolled plate having a thickness of 1 mm was formed, a heat treatment was performed to adjust the average crystal grain size as shown in Table 1. The crystal grain size at this time was obtained by taking a photograph of the cross-sectional structure in the rolling direction at the center of the plate thickness at a magnification of 100, and calculating the average intercept length by the intercept method to obtain the average crystal grain size.

In order to examine the superplastic elongation of these alloy sheets, a tensile test was performed using JIS No. 5 test pieces under the conditions of temperature and strain rate shown in Table 2. T6 treatment (solution treatment at 540 ° C.)
An artificial age hardening treatment was performed at 5 ° C. for 10 hours), and a tensile test was performed to evaluate mechanical properties.

Examples Nos. 1 to 12 of the present invention in Table 2 are examples in which the alloy components and the crystal grain sizes are all within the ranges specified by the present invention and are processed under the processing conditions specified by the present invention. All of these exhibited a superplastic elongation exceeding 150%. Also, the tensile strength of T6 material is 300M
A value of Pa or more was obtained. On the other hand, Comparative Example No. 13
In Nos. To 17, the alloy components and the crystal grain size were within the ranges specified in the present invention, but the elongation of 150% or more was not obtained because the processing conditions specified in the present invention were not satisfied.

On the other hand, in Comparative Examples Nos. 18 to 21, the elongation of 150% or more was obtained even if the processing conditions specified in the present invention were satisfied because the alloy components were outside the range specified in the present invention. That was not. Alloy No. 22 had an elongation of 150 mm because the crystal grain size was larger than the value specified by the present invention in the alloy components and processing conditions.
% Did not reach. Example 2 An alloy having the composition of alloy No. A5 in Table 1 was subjected to DC casting, then hot rolling and cold rolling according to a conventional method, to obtain an alloy plate having a thickness of 2 mm. This alloy plate was subjected to a heat treatment at 793 ° C. for 10 seconds to obtain an average crystal grain size of 30 μm.
m. From the alloy plate manufactured in this way, 18
A test piece of 0 mmφ was collected and subjected to a cylindrical deep drawing test (punch diameter: 50 mmφ) using a hot press at a molding temperature of 773 K and a molding speed of 10 ^-2 s ^-1 .

As a result, good molding could be performed without breaking even if the molding height was 25 mm.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

As is apparent from the above description, according to the present invention, a heat-treated aluminum alloy having a practically sufficient superplastic formability and having a tensile strength of 300 MPa or more when subjected to an appropriate heat treatment. It is possible to provide a board. Therefore, it can be said that the present invention is an invention having extremely high industrial value.

Claims (3)

[Claims] 1. The composition according to claim 1, comprising Mg: 0.3 to 1.5%, Si: 0.4 to 2.0%, and the balance: Al and unavoidable impurities. 0.15% or less, the average crystal grain size is 15 to 120 μm, and the strain rate ε ′ (s ⁻¹ ) and the molding temperature T (K) have the following relationship: ln (ε ′) <− 65 + 10ln (T), wherein elongation is 150% or more in a range satisfying ε ′ ≧ 10 ⁻⁴ s ⁻¹ and T = 673 to 853K. 2. Mn: 0.4% or less, Cr: 0.1% or less, Zr: 0.1% or less, V: 0.1% or less, Ti: 0.1% or less by weight% And B: 0.05% or less. The heat-treatable aluminum alloy for superplastic forming according to claim 1, further comprising one or more of the following: 3. The heat-treated aluminum alloy for superplastic forming according to claim 1, further comprising Cu: 0.8% by weight or less.