JP6809693B2 - Aluminum alloy material for heat treatment and its manufacturing method - Google Patents

Description

The present invention relates to an age hardening type aluminum alloy material and a method for producing the same.

When a huge shear strain with an equivalent strain of 100 or more is applied to an aluminum alloy by, for example, a high pressure torsion process (HPT), fine crystal grains of 100 to 200 nm are obtained, and high strength and ductility are obtained. It is known that the improvement of the above can be obtained (Non-Patent Documents 1 and 2).
However, the hardness could not be expected to be improved by the subsequent aging treatment.
Further, the present inventors have reported an excess Mg-type Al-Mg-Si alloy that has been aged after HPT processing (Non-Patent Document 3), but the hardness improvement by artificial aging treatment was insufficient.
Patent Document 1 discloses an aluminum alloy conductor having a nanoparticle dispersion structure formed by performing strong processing with an equivalent strain of 100 or more on a cast aluminum body, but the alloy composition is different from that of the present invention.

Japanese Unexamined Patent Publication No. 2014-194878

Tetsuya Masuda, Wataruichi Hirosawa, Zenji Hotta, Kenji Matsuda: Journal of the Japan Institute of Metals, 57 (2011), 283-290. Daichi Akama, Noboru Lee, Zenji Hotta, Kenji Matsuda, Wataruichi Hirosawa: Light Metals, 62, (2012), 448-453. Aging behavior and microstructure observation of excess Mg-type Al-Mg-Si alloy aged after HPT processing Katsumi Watanabe, Shun Maruno, Kenji Matsuda, Noboru Lee, Zenji Hotta, Daisho Terada, Seiji Saikawa, Wataruichi Hirosawa, Light Metal, Vol. . 63 (2013) No. 11

An object of the present invention is to provide an aluminum alloy material for heat treatment and a method for producing the same, which can develop precipitation hardening by aging treatment in fine crystal grains formed by large strain processing.

The aluminum alloy material for heat treatment according to the present invention has Cu: 0.15 to 1.5 at%, Mg: 0.8 to 3.5 at%, Zn: 3.0 at% or less, Si: 0.7 at% or less, Li: 6.0 at% or less, Ge: 0.25 at% or less, Ag: 0.2 at% or less, Mn: 0.1 at% or less, Zr: 0.05 at% or less, Ti: 0.05 at% or less, and the balance is It is composed of Al and unavoidable impurities, and has a fine crystal grain structure having an average crystal grain size of 200 nm or less.

In the Al-Mg-Si (excess Mg) alloy disclosed in Non-Patent Document 3, although the hardness is improved by artificial aging treatment, it softens in a short aging time. However, in the present invention, Cu is added together with Mg. As a result, it was clarified that a precipitate of Al ₂ CuMg was expressed in the fine crystal structure, the fine crystal structure could be maintained even if the aging time was lengthened, and the aging hardening ability was high.
Although Zn is not an essential component in the present invention, when Zn is added above the solid solution range, the η'phase is precipitated and precipitation hardening is observed. Therefore, Zn is in the range of 0.5 to 3.5 at% by mass. When added in, the precipitation hardening is observed.
The present invention is characterized in that Cu and Mg-based precipitates are precipitated in a fine crystal structure having an average crystal grain size of 200 nm or less, preferably 100 to 200 nm. Therefore, Cu: 0.15 to 1.5 at%, Mg: 0.8 to 3.5 at%, Zn: 3.0 at% or less, the balance contains an aluminum alloy composed of Al and unavoidable impurities, and Cu: 0.15 to 1.5 at%, Mg: 0. Includes an aluminum alloy with a balance of 0.8-3.5 at% consisting of Al and unavoidable impurities.
Since sufficient aging hardening cannot be expected for the Cu component if it is less than 0.15 at%, the lower limit is set to 0.15 at%.
The lower limit of the Mg component was set to 0.8 at% because the Al-Cu-Mg-based precipitate would be insufficient if it was less than 0.8 at%.
Further, the total amount of Cu + Mg is important, and the value of Cu + Mg is preferably in the range of 1.0 to 3.5 at%.
Further, in the region where the amount of Zn added is 1.0 at% or less, the Cu / Mg ratio is preferably close to 1 at at%.
The value of the Cu / Mg ratio, preferably at%, is preferably in the range of 0.8 to 1.2.

Such aluminum alloy materials include Cu: 0.15 to 1.5 at%, Mg: 0.8 to 3.5 at%, Zn: 3.0 at% or less, Si: 0.7 at% or less, Li: 6. 0 at% or less, Ge: 0.25 at% or less, Ag: 0.2 at% or less, Mn: 0.1 at% or less, Zr: 0.05 at% or less, Ti: 0.05 at% or less, and the balance is unavoidable with Al. It can be produced by subjecting an aluminum alloy composed of impurities to a shear strain process having an equivalent strain of 100 or more to obtain a fine crystal grain structure having an average crystal grain size of 200 nm or less, followed by an artificial aging treatment step.
Here, various methods have been proposed as a method of applying a shear strain of equivalent strain 100 or more.
Typical examples are the twisting method (HPT), in which a material is placed between two upper and lower dies and the dies are rotated under high pressure, and the dies and push rods that are pushed along the dies. An example is the HPS (High Pressure Sliding) method in which a material is sandwiched between the dies and the push rod is pushed while a high pressure is applied to perform sliding processing.
Here, the equivalent strain (ε) is obtained by the following equation (1), where the thickness t of the material and the radius γ are used in the case of HPT and the rotation speed is N.
In the case of the HPS method, assuming that the thickness t of the material and the indentation length L, it can be obtained by the following formula (2).

In the aluminum alloy material according to the present invention, precipitates are precipitated in a fine crystal grain structure having an average crystal grain size of 200 nm or less, preferably 100 to 200 nm, formed by giant strain processing by a subsequent artificial aging treatment. By doing so, it is possible to further improve the strength (hardness).

The aluminum alloy composition used for the evaluation is shown in at%. The results of aging conditions and hardness are shown. (A) shows the hardness change curve when aging at 343K, and (b) shows the aging hardening ability (ΔHV) obtained by subtracting the hardness immediately after HPT from the hardness at each aging time. (A) shows the hardness change curve when aging at 373K, and (b) shows the aging hardening ability (ΔHV) obtained by subtracting the hardness immediately after HPT from the hardness at each aging time. (A) shows the hardness change curve of the Al-Cu-Mg-Zn-based alloy at 343K, and (b) shows the age hardening ability. (A) Hardness change curve of Al-Cu-Mg-Zn-based alloy at 373K, (b) shows age hardening ability. TEM photographs of materials (a) to (d) in which HPT-processed ex and Mg-0.7Cu alloys are aged at 373 K for each time are shown. It shows the aging time and the change in crystal grain size. Overaged ex. At 373K for 12000ks. A TEM photograph of the Mg alloy is shown. The TEM photograph of the 373K, 240ks aging treatment of the Al-Zn-Mg alloy is shown. The TEM photograph of the 373K, 240ks aging treatment which added Cu to the Al-Zn-Mg alloy is shown. A TEM photograph of an Al-Zn-Mg alloy subjected to 373K, 100 min aging treatment is shown. The presence of the S phase in the TEM image of the sample obtained by aging the Al-Cu-Mg alloy at 373 k for 100 min is shown. The relationship between peak hardness and Cu + Mg (at%) is shown. The relationship between age hardening ability and Cu + Mg (at%) is shown. Reference data in the literature is shown.

Since the evaluation was performed using the plate materials of each aluminum alloy shown in the table of FIG. 1, it will be described below.
In the table of FIG. 1, sample sample numbers are indicated by 35 to 73, and alloy abbreviations are shown in the adjacent columns.
Blanks in the table indicate that they are unavoidable impurities.
Fe is recognized as an unavoidable impurity in the range of 0.01 at% or less.
In HPT processing, a disk with a diameter of 10 mm and a thickness of 1 mm is cut out from each alloy plate, and after solution treatment, the pressure is 6 GPa, the rotation speed is 1 rpm, the rotation speed is 5 rotations (equivalent strain 100), and the processing temperature is room temperature (about 298 K). Processed under the conditions.
The evaluation results of aging conditions, solution conditions and hardness are shown in the table of FIG. In the table, temperatures (℃) indicates the aging temperature, A S _HPT represents the equivalent strain value of.

FIG. 3A shows a hardness change curve when each HPT-treated alloy gold is aged at 343K.
The hardness level of 200 HV (Vickers hardness) means that the aluminum alloy has obtained the hardness equivalent to that of steel materials.
In the graph of FIG. 3, [73C] corresponds to sample No. 73, and [73] corresponds to sample No. 71 which does not contain Cu.
Similarly, ex. Mg is sample No. 39, ex. Mg-0.2Cu is sample No. 47, ex. Mg-0.7Cu corresponds to sample No. 55, and Al-Cu-Mg corresponds to sample No. 58.
Furthermore, all of them show age hardening, and the hardness change curve of the [73C] alloy having the largest amount of added elements shows a high level.
On the other hand, [ex. The hardness of the Mg] alloy decreased sharply after showing peak aging.
FIG. 3B is a diagram showing age hardening ability (ΔHV) obtained by subtracting the hardness immediately after HPT from the hardness at each aging time.
As can be seen from this figure, focusing on the age hardening ability, Al-Mg-Si and Al-Cu-Mg alloys containing a predetermined amount of Mg and Cu have a high solute concentration even if the solute concentration is low. It has the same high age hardening ability as the −Mg alloy.
FIG. 4 is a hardness change curve when each alloy is aged at 373 K as in FIG.
At 373K, the same tendency as in FIG. 3 was observed, and ex. The Mg-0.7Cu alloy and the [73C] alloy showed high age hardening ability.
However, as previously reported, Cu-free ex. Although the Mg alloy shows a peak hardness, it has softened at an early aging time.
Figures 5 and 6 show the results of the Al-Cu-Mg-Zn-based alloy.
The sample No. is shown in the graph.
FIG. 7 shows the HPT-processed ex. It is a TEM observation result of the sample which aged Mg-0.7Cu alloy at 373K for each time.
The average crystal grain size was maintained at 160 to 170 nm even when the aging time was lengthened.
FIG. 8 shows the average crystal grain size at each aging time obtained from the images observed by TEM in this way.
Cu-free ex. The Mg alloy coarsened to 240 nm in the late aging period.
From this, it is considered that the addition of Cu is effective not only for age hardening ability but also for finer crystal grains.
FIG. 9 shows ex. Aging at 373 K for 12000 ks. It is a TEM observation result of the Mg alloy.
Granular structures considered to be precipitates were confirmed in the bright-field image of FIG. 9 (a) and the dark-field image of FIG. 6 (b).
Further, as shown by arrows and numbers in (a), in addition to precipitation on the grain boundaries, many granular precipitates are also confirmed in the crystal grains.
Conventionally, in the Al-Mg-Si alloy, needle-like precipitates parallel to the <100> direction of the matrix have been observed, but as shown this time, the HPT material was granular.
This is a fact confirmed for the first time in the present invention.
10 and 11 are TEM observation results of a sample obtained by aging an Al—Zn—Mg alloy (alloy corresponding to sample No. 71) and an alloy added with copper (alloy corresponding to sample No. 72) at 373 K and 240 ks.
As shown in the past reports, clear precipitation is confirmed in the alloy with high solute concentration in this result as well.
In particular, fine precipitates were confirmed in the Cu-added alloy of FIG. 11, and it is clear that the addition of Cu increases the aging hardening ability even in the Al-Zn-Mg-based alloy.
FIG. 12 shows TEM observation results of a sample obtained by aging an Al—Cu—Mg alloy at 373K for 100 minutes.
Fine crystals of about 270 nm have been observed.
Further, the selected area electron diffraction pattern obtained from this portion is shown in FIG.
The obtained diffraction rings 1, 2, and 3 could be analyzed as S phase (Al ₂ CuMg), respectively.
FIG. 14 shows the relationship between the amount of Cu + Mg (at%) and the peak hardness.
FIG. 15 shows the relationship between the amount of Cu + Mg (at%), with the value immediately after the HPT treatment subtracted from the maximum hardness and the hardness increased only by heat treatment as the age hardening ability.
The numbers in the graph indicate the sample No.
According to this, the total amount of Cu and Mg peaks at around 2 at%, and if it exceeds that, the age hardening ability decreases.
Further, it can be seen that the Cu / Mg ratio at at% is about 1, and the age hardening ability is particularly high in the Al—Cu—Mg-based alloy.
The high curability of the Zn-containing Al-Cu-Mg-based and 7000-based Al-Zn-Mg alloys is considered to suggest that the addition of Zn is also effective.
These are the characteristics that the S phase shown in FIG. 13 is likely to be generated on rearrangements and defects, Zn is a solid solution atom in the Al—Cu—Mg alloy, and η ′ in the 7000 Al—Zn—Mg alloy. It is presumed that it is related to the fact that the curing ability is increased as the phase precipitation.
In addition, the values of other research results obtained by the ECAP method shown in FIG. 16 are also shown in the figure.
Both values are lower than the curing ability of the present invention. The reason can be explained by the fact that the total amount of Cu and Mg is too high or the Cu / Mg ratio is lower than 1.

Claims (1)

Cu: 0.15 to 1.5 at%, Mg: 0.8 to 3.5 at%, Zn: 3.0 at% or less, Si: 0.7 at% or less, Li: 6.0 at% or less, Ge: 0. 25 at% or less, Ag: 0.2 at% or less, Mn: 0.1 at% or less, Zr: 0.05 at% or less, Ti: 0.05 at% or less, and the balance is equivalent to an aluminum alloy composed of Al and unavoidable impurities. A step of forming a fine crystal grain structure having an average crystal grain size of 200 nm or less by applying a shear strain process of 100 or more,
A method for producing an aluminum alloy material, which further comprises an artificial aging treatment step, and has a fine crystal grain structure having an average crystal grain size of 200 nm or less even after the artificial aging treatment.