JPH045736B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a superplastic aluminum alloy and a method for producing the same. Metals and alloys that can exhibit abnormal elongation of several hundred to 1,000% or more without local deformation (constriction) when external mechanical force is applied are called superplastic metals or superplastic alloys. known as. Two typical types of aluminum-based superplastic alloys are known: recrystallized fine-grained superplastic alloys and eutectic microstructured superplastic alloys. A recrystallized fine-grained superplastic alloy is one in which the recrystallized grains that are generated when a rolled plate is exposed to the temperature conditions of superplastic working are made fine, and a eutectic fine-structured superplastic alloy is one in which the recrystallized grains that are generated when a rolled plate is exposed to the temperature conditions of superplastic working are made fine. The resulting fine eutectic structure was carried over to the rolled plate as a product. In any of these superplastic alloys,
The structure consists of fine crystal grains with diameters ranging from 0.5 μm or less to around 10 μm at most, and the smooth movement or sliding of grain boundaries facilitates plastic deformation of the material. The present invention provides an aluminum-based superplastic alloy that is believed to have both recrystallized fine-grained superplasticity and eutectic microstructured superplasticity, and the production thereof. That is, the present invention uses 3.0 to 6.0% Ni, 1.0 to 3.5%
% Mg, 0.5-1.0% Mn, 0.05-0.3% Cr and 0.05-0.50% Si, with the remainder consisting essentially of impurities and Al, as well as continuous molten alloys of this composition. It is then cast and rolled into a strip with a thickness of 3 to 20 mm, annealed at a temperature of 420 to 530°C, and then cold rolled without hot rolling until a rolling reduction of 70% or more is reached. The gist of the present invention is a method for manufacturing a superplastic aluminum alloy plate, which is characterized by carrying out the following steps. To explain the present invention in more detail, the superplastic aluminum alloy according to the present invention has a content of 3.0 to 6.0%.
Ni, 1.0 to 3.5% Mg, 0.5 to 1.0% Mn, 0.05
Contains ~0.3% Cr and 0.05-0.50% Si. Ni forms a eutectic with Al, producing a fine eutectic compound (NiAl ₃ ). The eutectic composition of Al−Ni is Al−
5.5%Ni, and if the Ni content exceeds 6%,
Coarse primary crystals are formed, which deteriorates superplastic performance and also reduces rollability. Furthermore, when the Ni content is less than 3.0%, the amount of eutectic compounds produced becomes too small, resulting in a decrease in superplasticity. Mg causes dynamic recrystallization, that is, recrystallization occurs simultaneously with plastic deformation of a superplastic alloy plate, constantly regenerating the structure before deformation, reducing work hardening, and facilitating superplastic deformation. demonstrate. Mg
If the content is less than 1.0%, this effect will be small, and if it is more than 3.5%, coarse β phase (Al-Mg compound) will crystallize in the center of the strip, which will not only deteriorate the superplastic performance. Makes cold rolling difficult.
Mn and Cr have the effect of refining and stabilizing crystal grains. Mn must be 1.0% or less, that is, within a range where it is almost dissolved in solid solution during casting. If Mn is present in an amount exceeding the solid solution amount, coarse crystallized substances will be produced during casting. This crystallized material not only does not contribute to superplastic performance, but also has a negative effect on cold rolling. Cr
If it is too large, coarse compounds with Mn are likely to be formed, and the finer refinement effect of Mn and Cr is lost, so its amount must be 0.3% or less. Mn
The lower limit of Cr content is 0.5% and Cr content, respectively.
The amount is 0.05%, and if the amount is less than this, the effect will not be fully expressed. The presence of 0.50% Si suppresses the segregation of Mg that occurs in the center of the strip.
Also, Si reacts with Mg to form an intermetallic compound (Mg2Si).
However, these particles are fine particles, which themselves contribute to the development of superplasticity. The amount of Si
These effects are small below 0.15%, and below 0.50
%, more Mg reacts with Si and Mg
effect is lost. Furthermore, impurities contained in general aluminum alloys are within the allowable range in normal alloys, that is, Fe 0.40% or less,
Preferably Cu is 0.20% or less, and Cu may be present as long as it is 0.10% or less. Therefore, as a base for the superplastic aluminum alloy according to the present invention, purity
It is preferable to use an aluminum base metal of 99.70% or more (JIS Class 1). To produce the superplastic aluminum alloy according to the present invention, first, a molten aluminum alloy having the above composition is continuously cast and rolled to directly produce a strip plate with a thickness of 3 to 20 mm, preferably 4 to 15 mm. do. Continuous casting and rolling methods are well known, and several methods such as the Hunter method and the 3C method are known. According to the typical method, a nozzle is placed between a mold made up of two rotating casting rolls, and the molten alloy is introduced into the mold through this nozzle and simultaneously rolled while being cooled in the mold. This produces a strip. Cooling water flows inside the casting roll,
Since the molten metal is normally cooled at a cooling rate of 100°C/second or more, fine crystals can be generated. Furthermore, according to this method, within the composition range used in the present invention, Mn and Cr are dissolved in solid solution and are hardly crystallized as intermetallic compounds. The thus obtained strip plate can be heated to 420-530℃.
Apply annealing treatment. Through this annealing, the eutectic compound (NiAl ₃ ) crystallized during casting becomes at least partially granular, smoothing the sliding at the interface and improving superplastic performance. Furthermore, supersaturated solid solution Mn and Cr precipitate as uniform fine precipitates that are effective in inhibiting movement of recrystallized grain boundaries. When the annealing temperature is higher than 530°C, the eutectic compound (NiAl ₃ ) becomes coarse and the Mn and Cr precipitates also become coarse, resulting in deterioration of superplastic performance. Also
At temperatures below 420°C, eutectic compounds (NiAl ₃ )
is not sufficiently granulated, and precipitation of Mn and Cr is also insufficient. Suitable annealing temperature is 450-500
It is ℃. An appropriate annealing time is 6 to 24 hours. As with general heat treatment, the time is increased when the temperature is low, and the time is shortened when the temperature is high. The annealed strip is then cold rolled without hot rolling. If hot rolling is performed, the superplastic properties will be impaired. Cold rolling is carried out until a rolling reduction of 70% or more, preferably 80% or more is reached. If the rolling rate is smaller than this, sufficient superplastic performance cannot be imparted to the obtained alloy plate. Note that since work hardening progresses with cold rolling, rolling becomes progressively more difficult as the rolling rate increases. This difficulty can be overcome by performing intermediate annealing once or several times during the process. Intermediate annealing is 200-400℃, especially 250-350℃
It is preferable to do so. In other words, when a work-hardened rolled plate is annealed, it softens as the temperature rises, but
In particular, softening progresses significantly at 200 to 250°C.
Softening reaches almost saturation at 250°C, and even if heated to even higher temperatures, the improvement in softening degree is relatively small. At temperatures higher than 400°C, precipitates in the rolled sheet become coarse and inhibit superplastic performance. The time required for intermediate annealing is usually 1~
It is 4 hours. When intermediate annealing is performed, it is necessary to further cold-roll after the final intermediate annealing until the rolling reduction reaches 60% or more, particularly 65% or more. Even if the overall rolling reduction is 70% or more, if the rolling reduction after intermediate annealing is smaller than this, it is difficult to obtain a rolled sheet exhibiting excellent superplastic performance. As in the case without intermediate annealing, when there is intermediate annealing, the higher the rolling ratio after the final intermediate annealing, the better the superplastic performance of the rolled plate becomes. The superplastic aluminum alloy according to the present invention has a
It exhibits excellent superplastic performance at temperatures above ℃, especially above 400℃. Therefore, by utilizing this property, it can be formed by various processing methods applied to general superplastic materials. Typical examples are vacuum forming and bulge processing. The strain rate during processing is usually in the range of 1 x 10 ^-3 to 1 x 10 ^-1 /sec, and the uniaxial elongation is preferably in the range of 300 to 1000%. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example Molten alloy having the composition shown in Table 1 (as impurities)
(Containing 0.14% Fe, 0.01% Cu or less, and other impurities totaling 0.02% or less) was maintained at 750°C and sufficiently degassed. Using a driven mold consisting of two water-cooled rolls with a diameter of 30 cm, the above molten metal was continuously cast and rolled at a casting temperature of 700°C and a casting speed of 100 cm/min to a thickness of 6.0 to 6.0 cm.
A 6.8 mm strip was manufactured. This strip plate starts from 470
After annealing at 480°C for 12 hours, it was cold rolled into a rolled plate with a thickness of 1.0 mm. (Measurement of superplastic performance) A sample piece with a size of 150 x 150 mm was cut out from the above-mentioned rolled plate, and an expansion test was conducted using the mold shown in FIG. The pressure of the compressed air was gradually increased from 0.5 Kg/cm ² G, and the height at which the sample piece broke (bulge height) was measured. The results are shown in Table 2.

[Table] * Comparative example

【table】 [Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a bulge test mold used in an example of the present invention. A shows the state in which the test piece is attached to the mold, and B shows the state in which the test piece is swollen by compressed air. 1...Lower mold, 2...Upper mold, 3...Test piece,
4...Compressed air introduction pipe, l...Bulge height.

Claims (1)

[Claims] 1 3.0-6.0% Ni, 1.0-3.5% Mg, 0.5-1.0
% Mn, 0.05-0.3% Cr and 0.05-0.50%
A superplastic aluminum alloy that contains Si, with the remainder essentially consisting of impurities and Al. 2 3.0-6.0% Ni, 1.0-3.5% Mg, 0.5-1.0
% Mn, 0.05-0.3% Cr and 0.05-0.50%
A molten aluminum alloy containing Si, with the remainder being essentially impurities and Al, was continuously cast and rolled into a strip plate with a thickness of 3 to 20 mm, which was then annealed at a temperature of 420 to 530°C. A method for producing a superplastic aluminum alloy sheet, which is then cold rolled without hot rolling until a rolling reduction of 70% or more is reached.