JPH08199272A - Aluminum alloy sheet and forming method - Google Patents

Abstract

PURPOSE: To easily obtain an alloy sheet capable of executing practical super plastic forming without adopting special condition by specifying the temp. and strain rate at forming of the alloy sheet regulated for grain size with specified composition. CONSTITUTION: The aluminum alloy sheet contains, by weight, 3.5-8.5% Mg, <=0.5% Cu, <=0.15% Si, <=0.15% Fe, and further, one or more kinds among <=0.4 Mn, <=0.1% respective Cr, Zr, V and Ti respectively, <=0.01% B, and the balance Al, and it is constructed with an average grain size of 15-120μm. The sheet is formed at a strain rate εof >=10<-4> /sec<-1> and at a forming temp. T of 523-823K while the strain rate ε and forming temp. T are in the range of the equation: 1nε<-160+24.5lnT. By this method, an elongation of 200% or more is attained so as to make superplastic forming possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superplastic forming aluminum alloy sheet and a forming method thereof.

[0002]

2. Description of the Related Art The superplastic phenomenon is characterized in that the elongation is so large that it cannot be obtained under normal working conditions and the deformation stress is also small. Therefore, in recent years, development and research for practical use of superplastic alloys utilizing these characteristics have been actively conducted. In particular, aluminum alloy plates have been actively developed from the viewpoint of lightness, and among them, Al-Mg alloys have attracted attention because they have excellent strength as well as corrosion resistance and surface treatment properties. 5 Mg-0.6Cu-0.6M
n (Neopral) and Al-4.5Mg-0.7Mn-0.1Cr (ALNOVI-I: trade name) have been put to practical use.

By the way, the conditions for developing the superplasticity phenomenon are (1) stable and fine equiaxed crystal grains (~ 10
(2) heating temperature T> 0.5T
_m (T _m : absolute temperature of melting point), (3) low strain rate (1
It is generally said that processing at 0 ^-4 to 10 ^-2 sec ^-1 ) is appropriate (for example, Osawa and Nishimura: Light Metals, 39
-10 (1989), P.765-775, etc.). Therefore, the guidelines for alloy development up to now include making the crystal grains finer, making the structure thermally stable even at the time of processing at high temperature, or making the alloy hard to form cavities that inhibit ductility. It has been raised.

[0004]

However, there are many restrictions on the manufacturing conditions for making the grain size of the recrystallized grains fine and uniform, and the processing has also been required to be performed in the low strain rate range. . That is, the above-mentioned conditions are such that alloys have a special component system (for example, JP-A-
57-76145) or special manufacturing conditions (for example, JP-A-58-81957).
It was not desirable in terms of manufacturing cost. Also,
Processing conditions also require a low strain rate (eg East: Light Metals, 39-11 (1989), P.751-764, etc.), which has been a problem for productivity. In addition, in the case of superplastic forming, it is rare that a very large elongation such as 500% or 1000% is practically required, and it is sufficient if elongation of 200% or more and up to 300% can be achieved. There are many. In view of the above circumstances, the present invention is to provide an aluminum alloy sheet and a forming method thereof that enable superplastic forming that is easy to manufacture without adopting special conditions and has excellent productivity. .

[0005]

That is, the first aspect of the present invention
% By weight, Mg: 3.5% to 8.5% Cu: 0.5% or less Si: 0.15% or less Fe: 0.15% or less, and further 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 B: 0.01% or less One or more of the following are contained, and the balance Consists of Al and inevitable impurities, and 15
The average grain size is about 120 μm, the strain rate (ε) is 10 ⁻⁴ sec ⁻¹ or more, and the molding temperature (T) is 52.
3 to 823K, and the strain rate (ε) and the forming temperature (T) exhibit a superplastic deformation of elongation of 200% or more within the range of the following formula ln (ε) <-160 + 24.5 ln (T). And an aluminum alloy plate.

The second aspect of the present invention is to provide Mg:
3.5% to 8.5% Cu: 0.5% or less Si: 0.15% or less Fe: 0.15% or less, and further 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 B: 0.01% or less One or more of the following are contained, and the balance Is Al and inevitable impurities, and 15
Aluminium alloy sheet having an average crystal grain size of ˜120 μm has a strain rate (ε) of 10 ⁻⁴ sec ⁻¹ or more, a molding temperature (T) of 523 to 823 K, and a strain rate represented by the following equation. It is a method for forming an aluminum alloy plate, which comprises forming within a range of (ε) and a forming temperature (T). ln (ε) <-160 + 24.5 ln (T)

[0007]

[Operation] The reasons for limiting the alloy composition, superplastic working conditions and the like of the present invention will be described below. In the present invention, Mg is an essential basic alloying component that contributes to the improvement of strength at room temperature after forming and the improvement of superplastic formability, and is contained in 3.5 to 8.5%. In order to obtain high ductility, high Mg is desirable, but if it exceeds 8.5%, rolling cracking tends to occur when hot rolling is performed after casting, which is not industrially suitable. Further, if the Mg content is less than 3.5%, the strength at room temperature after molding cannot be sufficiently obtained, which is not suitable. Cu is effective in adding to secure strength after processing. However, if added over 0.5%, segregation at the grain boundaries tends to occur and cavitation tends to occur,
Inhibits superplastic forming. Therefore, the addition amount is set to 0.5% or less. Cu is also known to inhibit the corrosion resistance, and it is preferably 0.35% or less from the viewpoint of the corrosion resistance.

[0008] Fe and Si are generally mixed as impurities, but if mixed, they are Al-Mg-Si system and Al-Fe-Si.
It produces a system intermetallic compound, makes it easier to generate cavitation during molding, and hinders superplastic molding. Therefore,
The permissible mixing range is 0.15% or less. In addition,
In the alloy of the present invention, Mn, Cr, V,
At least one of Zr, Ti and B is contained. Mn and C
r, Zr, V and Ti, B may be contained for the purpose of preventing abnormal growth of the crystal grain size during superplastic forming.
In this case, if Mn is added in an amount of 0.4% or more, Al ₆ Mn, Fe, and Si are precipitated as an intermetallic compound to easily generate cavitation. Also, Cr, V, Zr, Ti
If any of the above is added in excess of 0.1%, it becomes easy to generate cavitation. On the other hand, B coexists with Ti and promotes homogenization of crystal grains. However, if added in excess of 0.05%, TiB ₂ is generated and cavitation is easily generated, and any of them impedes superplastic forming. Therefore, the addition amount of Mn is 0.4 wt% or less, Cr, V, Z
The addition amount of r and Ti is 0.1 wt% or less, and the addition amount of B is 0.05 wt% or less. There is no problem with inevitable impurities other than the above as long as the purity of Al ingot is 98% or more.

Next, the reason for defining the average crystal grain size will be described. In the past, it has been reported that the grain size is generally refined to develop superplasticity (eg, Baba, Yoshida: Plasticity and processing, 27-302 (1986), P.333.
-338). However, as a result of diligent study by the present inventors,
In order to enable highly productive superplastic forming, it has been found that it is better to set the grain size to 15 to 120 μm, which is larger than the conventional knowledge. Further, the reason for defining the range of processing conditions that can achieve superplastic forming using the alloy sheet of the present invention will be described. It has been known that when a high Mg material such as the 5182 alloy is pulled at a low speed of about 10 ⁻³ to 10 ⁻⁴ sec ^{−1, the} behavior is such that the elongation exceeds 100% at a temperature of about 250 ° C. (eg, , RAAYRES: M
(etallugical Transactions A, 10A (1979), P.849-854)
. However, such a conventional technique has a problem in high productivity because of a low strain rate, and the elongation as superplastic forming is insufficient.

Therefore, the present inventors investigated an aluminum alloy plate having superplastic elongation at a high strain rate which enables high productivity. Note that the elongation required for practical superplastic forming requires a minimum plate thickness to secure the strength after forming, and therefore, a very large elongation (for example, 500
% Or more) is not particularly required and may be 200% or more. Therefore, as a result of investigating an aluminum alloy plate showing an elongation of 200% or more as a practical elongation at the time of performing superplastic forming with good productivity, an aluminum alloy plate having alloy plasticity and grain size specified as described above was obtained. It has been found that the object of the present invention can be achieved by molding under the following processing condition range.

Further, the strain rate is set to 10 ^-4 sec ^-1 or more in consideration of productivity. And the processing temperature is 52
The range was 3 to 833K. If the processing temperature is higher than 823K, the crystal grain size becomes coarse during processing, and proper superplastic forming cannot be performed. Therefore, the upper limit of processing temperature is 82
It was set to 3K. Further, since a superplastic phenomenon cannot be obtained at a temperature of 523K or lower, the lower limit of the processing temperature was set to 523K. In the present invention, within the range of the strain rate and the processing temperature, the relationship between the two is −160 + 24.5 InT <Inε <−115 + 15.7 InT, where T: absolute temperature, ε: strain rate (sec ^−1). Within the range specified in (), superplastic forming can be advantageously performed.

[0012]

EXAMPLES Next, the present invention will be specifically described based on Examples. Example 1 Aluminum alloys (A1 to A6, B1 to B1 shown in Table 1
Regarding 6), each was cast by a DC casting method according to a usual method, the obtained ingot was subjected to a homogenizing treatment at 530 ° C. for 5 hours, and then hot rolling and cold rolling were performed,
A rolled plate having a thickness of 1 mm was used. However, the alloy of B2 could not be used for the subsequent evaluations because cracks occurred during hot rolling and the cold rolled sheet could not be obtained. The rest of the alloy plates were subsequently subjected to heat treatment to adjust the grain size as shown in Table 1. The crystal grain size at this time was taken as a crystal grain size by taking an image of a cross-section structure of the plate thickness center portion at 100 times and obtaining an average section length by a sectioning method. In order to investigate the superplastic elongation of these alloy sheets, a tensile test was conducted using JIS No. 5 pieces under the conditions of temperature and strain rate shown in Table 2. In addition, in order to investigate ordinary mechanical properties at room temperature, JIS No. 5 piece was also used, and up to YP was 1 mm / min, Y
A tensile test until breakage was performed at 10 mm / min after P. The results are also shown in Table 2.

[0013]

[Table 1]

[0014]

[Table 2]

Nos. 1 to 6 are all processed within the range defined by the present invention for alloy components, within the range defined by the present invention for grain size, and within the range defined for the present invention under processing conditions. It is an example. In these cases, the elongation is 2
It exceeded 00% and showed good superplasticity. The mechanical properties at room temperature also showed good properties. On the other hand, N
o. In Nos. 7 to 9, the alloy range and the crystal grain size range were within the ranges specified by the present invention, but the elongation did not reach the target of 200% because the superplastic working conditions specified by the present invention were not satisfied. In addition, No. No. 10 has a low amount of Mg, so that not only the superplastic elongation is low, but also the mechanical properties at room temperature are low. Furthermore, No. In Nos. 11 to 13, since the additive element exceeded the range specified by the present invention, the elongation did not reach 200% and practically effective superplasticity could not be obtained. Also, N
o. In No. 14, the elongation could not reach 200% because the crystal grain size became larger than the specified range according to the present invention.

Example 2 No. 1 in Table 1 Ordinary DC casting to hot rolling was performed using the alloy No. 3 to obtain a 3 mm alloy plate. This alloy was heat-treated at 813 K for 1 minute to adjust the average crystal grain size to about 60 μm. The alloy plate having a diameter of 180 mm thus manufactured was subjected to a cylindrical drawing test (punch diameter 50 mm) using a hot press under the conditions of a molding temperature of 723 K and a molding speed of 10 ^-2 / sec.
mm diameter). As a result, good molding could be performed without breaking even when the molding height was 30 mm.

[0017]

As is apparent from the above description, according to the present invention, an aluminum alloy plate capable of superplastic forming can be provided, and the alloy plate can be used under specific forming conditions (temperature, strain rate). With, practical high-productivity superplastic forming can be performed.

Claims (2)

[Claims] 1. By weight%, Mg: 3.5% to 8.5% Cu: 0.5% or less Si: 0.15% or less Fe: 0.15% or less, and further 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 B: 0.01% or less One or more of the following are contained, and the balance Is Al and inevitable impurities, and 15
The average grain size is about 120 μm, the strain rate (ε) is 10 ⁻⁴ sec ⁻¹ or more, and the molding temperature (T) is 52.
3 to 823K, and the strain rate (ε) and the forming temperature (T) exhibit a superplastic deformation of elongation of 200% or more within the range of the following formula ln (ε) <-160 + 24.5 ln (T). And aluminum alloy plate. 2. By weight%, Mg: 3.5% to 8.5% Cu: 0.5% or less Si: 0.15% or less Fe: 0.15% or less, and further 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 B: 0.01% or less One or more of the following are contained, and the balance Consists of Al and inevitable impurities, and 15
Aluminium alloy sheet having an average crystal grain size of ˜120 μm has a strain rate (ε) of 10 ⁻⁴ sec ⁻¹ or more, a molding temperature (T) of 523 to 823 K, and a strain rate represented by the following equation. A method for forming an aluminum alloy plate, which comprises forming within a range of (ε) and a forming temperature (T). ln (ε) <-160 + 24.5 ln (T)