JP2017210649A - Aluminum alloy sheet for structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for a structure capable of achieving both of ductility and strength at a higher level than the prior art.SOLUTION: There is provided an aluminum alloy sheet for a structure with a chemical composition consisting of Zn:2.0% (mass%, the same shall apply hereinafter) to 12.0%, Mg:1.0% to 4.5%, Cu:0.5% to 3.0% and Zr:0.01% to 0.30% with limitations to Si:0.5% or less, Fe:0.5% or less Ti:0.5% or less, Mn:0.3% or less and Cr:0.3% or less, and the balance Al with inevitable impurities. Total of η phase particles with circle equivalent diameter of 5 μm or more and S phase particles with circle equivalent diameter of 5 μm or more is 100/mmor less. Porosity with circle equivalent diameter of 5 μm or more is 50/mmor less.SELECTED DRAWING: None

Description

  The present invention relates to a structural aluminum alloy plate.

  Al-Zn-Mg-Cu (aluminum-zinc-magnesium-copper) -based aluminum alloy plates are light and high in strength, and are therefore frequently used as structural materials in the fields of aircraft, spacecrafts, vehicles, and the like. In recent years, there has been a demand for further weight reduction of structural materials used in these fields. In order to meet such demands, studies have been made to further increase the strength of aluminum alloy plates (for example, Patent Documents 1 to 3).

Japanese Patent No. 4285916 Patent No. 472159 Japanese Patent No. 5083816

Inside the Al—Zn—Mg—Cu-based aluminum alloy plate, there are crystallized substances and precipitates of η phase (MgZn ₂ ) and S phase (Al ₂ CuMg). To improve the strength of the aluminum alloy plate obtained after artificial aging treatment by decomposing these crystals and precipitates by solution treatment and dissolving Zn, Mg and Cu in the matrix. Can do.

  However, when solution treatment is performed, the strength of the finally obtained aluminum alloy plate is increased, but porosity is formed, which causes a problem of reducing ductility.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a structural aluminum alloy plate capable of achieving both ductility and strength at a higher level than before.

One embodiment of the present invention is: Zn (zinc): 2.0% (mass%, the same applies hereinafter) to 12.0% or less, Mg (magnesium): 1.0% to 4.5%, Cu (copper) : 0.5% to 3.0% and Zr (zirconium): 0.01% to 0.30%, Si (silicon): 0.5% or less, Fe (iron): 0.5 % Or less, Ti (titanium): 0.5% or less, Mn (manganese): 0.3% or less, and Cr (chromium): 0.3% or less, and the balance from Al (aluminum) and inevitable impurities Has a chemical component
The total of the η phase particles having an equivalent circle diameter of 5 μm or more and the S phase particles having an equivalent circle diameter of 5 μm or more is 100 particles / mm ² or less,
The structural aluminum alloy plate has a porosity with an equivalent circle diameter of 5 μm or more of 50 pieces / mm ² or less.

  The structural aluminum alloy plate (hereinafter simply referred to as “aluminum plate”) has chemical components in the above specific range, and has an η-phase particle having an equivalent circle diameter of 5 μm or more and an S-phase particle having an equivalent circle diameter of 5 μm or more. Is regulated within the above specific range. In the aluminum plate in which the total of the η phase particles and the S phase particles is in the specific range, the η phase and the S phase are sufficiently decomposed during the solution treatment. The amount of solid solution of Zn, Mg and Cu can be increased more than before. Therefore, the aluminum plate can easily realize high strength as compared with the conventional Al—Zn—Mg—Cu alloy plate.

  Further, the number of porosity in the aluminum plate is regulated within the specific range. Thereby, the said aluminum plate can improve ductility compared with the conventional Al-Zn-Mg-Cu type aluminum alloy, ensuring high intensity | strength.

  Thus, the aluminum plate can achieve both strength and ductility at a higher level than before. Therefore, the aluminum plate is suitable as a structural material for aircraft, spacecrafts, vehicles, and the like.

  The reason for limiting the chemical components in the aluminum plate will be described below. The aluminum plate contains Zn, Mg, Cu, and Zr as essential components.

(1) Zn (zinc): 2.0 to 12.0%
Zn has the effect | action which improves the intensity | strength of the said aluminum plate. By setting the Zn content to 2.0% or more, the strength of the aluminum plate can be improved. From the same viewpoint, the Zn content is preferably 7.0% or more, and more preferably 8.0% or more.

  When the Zn content is excessively large, Zn-Mg-based crystallized substances and precipitates may be formed in a large amount in the parent phase. These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Zn content is set to 12.0% or less. From the same viewpoint, the Zn content is preferably 11.0% or less.

(2) Mg (magnesium): 1.0 to 4.5%
Mg has the effect | action which improves the intensity | strength of the said aluminum plate. By setting the Mg content to 1.0% or more, the strength of the aluminum plate can be improved. From the same viewpoint, the Mg content is preferably 1.5% or more.

  When the Mg content is excessively large, Zn-Mg-based crystallized substances and precipitates, or Al-Mg-Cu-based crystallized substances and precipitates may be formed in a large amount in the matrix. There is. These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Mg content is set to 4.5% or less. From the same viewpoint, the Mg content is preferably 3.5% or less.

(3) Cu (copper): 0.5 to 3.0%
Cu has the effect | action which improves the intensity | strength of the said aluminum plate. By setting the Cu content to 0.5% or more, the strength of the aluminum plate can be improved. From the same viewpoint, the Cu content is preferably 1.0% or more.

  When the content of Cu is excessively large, Al-Cu-based crystallized substances and precipitates, or Al-Mg-Cu-based crystallized substances and precipitates may be formed in a large amount in the aluminum plate. There is. These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Cu content is set to 3.0% or less. From the same viewpoint, the Cu content is preferably 2.5% or less.

(4) Zr (zirconium): 0.01 to 0.30%
Zr has the effect | action which improves the intensity | strength of the said aluminum plate by suppressing the recrystallization at the time of solution treatment. By making the content of Zr 0.01% or more, the strength of the aluminum plate can be improved. From the same viewpoint, the Zr content is preferably 0.05% or more.

  When the Zr content is excessively large, Al-Zr-based crystallized substances and precipitates may be formed in a large amount in the parent phase. These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Zr content is set to 0.30% or less. From the same viewpoint, the Zr content is preferably 0.20% or less.

  The aluminum plate may contain Si, Fe, Ti, Mn and Cr as optional components. In addition, these components may be mixed when producing the said aluminum plate using a recycled material.

(5) Si (silicon): 0.5% or less When the Si content is excessively large, Al-Fe-Si-based crystallized substances and precipitates, or Si-based crystallized substances and precipitates are present. A large amount may be formed in the matrix. These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Si content is set to 0.5% or less. From the same viewpoint, the Si content is preferably regulated to 0.4% or less.

(6) Fe (iron): 0.5% or less When the content of Fe is excessively large, Al-Fe-Si-based crystallized products and precipitates, or Al-Fe-based crystallized products and precipitates There is a risk that a large amount of material is formed in the matrix. These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Fe content is set to 0.5% or less. From the same viewpoint, the Fe content is preferably regulated to 0.35% or less.

(7) Ti (titanium): 0.5% or less When the Ti content is excessively large, Al-Ti-based crystallized substances and precipitates may be formed in a large amount in the parent phase. . These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Ti content is set to 0.5% or less. From the same viewpoint, the Ti content is preferably regulated to 0.35% or less.

(8) Mn (manganese): 0.3% or less In the case where the content of Mn is excessively large, Al-Mn-based crystallized substances and precipitates, or Al-Fe-Si-Mn-based crystallized substances. And precipitates may be formed in large amounts in the matrix. These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Mn content is set to 0.3% or less. From the same viewpoint, it is preferable to regulate the Mn content to 0.2% or less.

(9) Cr (chromium): 0.3% or less When the Cr content is excessively large, Al-Cr-based crystallized substances and precipitates may be formed in a large amount in the matrix. . These precipitates and crystallized substances are not preferable because they reduce the ductility of the aluminum plate. Therefore, from the viewpoint of avoiding a decrease in ductility of the aluminum plate, the Cr content is set to 0.3% or less. From the same viewpoint, the Cr content is preferably regulated to 0.2% or less.

(10) η-phase particles and S-phase particles In the above aluminum plate, the total of η-phase particles having an equivalent circle diameter of 5 μm or more and S-phase particles having an equivalent circle diameter of 5 μm or more is 100 particles / mm ² or less. By sufficiently decomposing the crystallized or precipitated η phase or S phase during the solution treatment, the total of the η phase particles and the S phase particles can be within the specific range. In such an aluminum plate, the solid solution amount of Zn, Mg and Cu after solution treatment can be made larger than that of a conventional Al—Zn—Mg—Cu alloy. Therefore, an aluminum plate having higher strength than before can be obtained after the artificial aging treatment. From the viewpoint of increasing the strength of the aluminum plate after the artificial aging treatment, the total of the η phase particles having an equivalent circle diameter of 5 μm or more and the S phase particles having an equivalent circle diameter of 5 μm or more is 50 particles / mm ² or less. Is preferred.

When the total of η phase particles having an equivalent circle diameter of 5 μm or more and S phase particles having an equivalent circle diameter of 5 μm or more in the aluminum plate exceeds 100 particles / mm ² , Either the decomposition of precipitates may be insufficient or the content of Zn, Mg, or the like may be excessively large. In the former case, since the solid solution amounts of Zn, Mg and Cu after the solution treatment are small, the strength of the aluminum plate after the artificial aging treatment may be lowered. In the latter case, the second phase such as the η phase and the S phase is excessively formed in the matrix phase, which may reduce ductility.

(11) Porosity The porosity with an equivalent circle diameter of 5 μm or more in the aluminum plate is 50 / mm ² or less. By restricting the number of porosity within the specific range, the ductility of the aluminum plate can be improved.

When the porosity with an equivalent circle diameter of 5 μm or more exceeds 50 / mm ² , the η phase and S phase may be rapidly melted during the solution treatment, and porosity may be formed. In this case, the ductility of the aluminum plate may be reduced.

The calculation of the number of η phase particles, S phase particles, and porosity described above is based on the secondary electron image of the plate cross section (L-ST plane) parallel to the rolling direction, observed using a SEM (scanning electron microscope). Do it. Specifically, secondary electron images with a magnification of 200 times are acquired at three or more measurement positions randomly selected from the L-ST plane of the aluminum plate. Simultaneously with the acquisition of the secondary electron image, the chemical components of the particles present in the secondary electron image are identified by SEM-EDS (scanning electron microscope-energy dispersive spectroscopic analysis). To extract. Next, image analysis of the secondary electron image is performed, and the equivalent-circle diameters of all η phase particles, S phase particles, and porosity existing in the secondary electron image are calculated. Then, the number of η-phase particles, S-phase particles and porosity having an equivalent circle diameter of 5 μm or more present in the secondary electron image is counted and converted to the number per 1 mm ² . From the above, the number of η-phase particles, S-phase particles, and porosity having a circle-equivalent diameter of 5 μm or more can be calculated.

  The aluminum plate has the specific chemical component and can easily achieve a breaking elongation of 10% or more by regulating the number of porosity within the specific range.

  Moreover, the said aluminum plate has high intensity | strength, so that there is much content of Zn. For example, in an aluminum plate having a Zn content of 7.0% or more and 12.0% or less, the sum of the number of η phase particles and the number of S phase particles and the number of porosity are restricted to the specific range. By this, while ensuring the outstanding ductility, the tensile strength of 680 MPa or more and 0.2% yield strength of 620 MPa or more can be easily realized.

  Also, in an Al-Zn-Mg-Cu-based alloy plate having a chemical component in a general range, the sum of the number of η phase particles and the number of S phase particles and the number of porosity are defined as the specific range. By doing this, the strength can be further improved while ensuring excellent ductility. For example, in an aluminum plate having a Zn content of 2.0% or more and less than 7.0%, the sum of the number of η phase particles and the number of S phase particles and the number of porosity are within the specific range. Accordingly, it is possible to ensure excellent ductility and easily realize a tensile strength of 600 MPa or more and a 0.2% proof stress of 550 MPa or more.

  The said aluminum plate can be produced with the following manufacturing methods, for example. First, after preparing the ingot which has the said specific chemical component, a homogenization process and hot rolling are sequentially performed to this ingot, and a hot-rolled sheet is produced. The conditions for the homogenization treatment and hot rolling can be appropriately selected from known conditions. Next, in order to perform the solution treatment, the hot rolled plate is heated to raise the temperature. At this time, the temperature may be increased under any conditions until the temperature of the hot-rolled sheet reaches 300 ° C.

  After the temperature of the hot-rolled sheet reaches 300 ° C., heating is performed so that the average rate of temperature rise is within the range of 5 to 20 ° C./h until the solution treatment temperature is reached. Thereby, the η phase and the S phase can be gradually decomposed during the temperature rise of the hot rolled sheet. As a result, the formation of porosity due to the rapid melting of the η phase or the S phase can be suppressed.

  When the average heating rate is less than 5 ° C./h, coarse crystal grains are likely to be generated. This coarse crystal grain is not preferable because it causes a decrease in strength of the aluminum plate. In this case, the time until the solution treatment temperature is reached becomes excessively long, which leads to a decrease in productivity. From the viewpoint of avoiding these problems, the average heating rate is set to 5 ° C./h or more.

  On the other hand, when the average temperature increase rate exceeds 20 ° C./h, the η phase and the S phase are rapidly melted during the temperature increase of the hot-rolled sheet. And since it becomes easy to form a porosity in the location which the (eta) phase and S phase lose | disappeared by melting | fusing, there exists a possibility of causing the fall of the ductility of the said aluminum plate.

  The solution treatment temperature is preferably near the melting point of the η phase and the S phase. The melting point of the η phase is usually about 470 to 480 ° C., and the melting point of the S phase is usually about 485 to 500 ° C. Therefore, by selecting the solution treatment temperature within the range of 475 to 500 ° C., it is possible to decompose both the η phase and the S phase and increase the amount of Zn, Mg and Cu in the matrix phase. it can.

  When the solution treatment temperature is less than 475 ° C., the decomposition of the η phase and the S phase becomes insufficient, which may lead to a decrease in the amount of solid solution in the matrix phase of Zn, Mg, and Cu. As a result, the strength of the aluminum plate may be reduced. Therefore, from the viewpoint of sufficiently decomposing the η phase and the S phase and increasing the amount of solid solution such as Zn, the solution treatment temperature is set to 475 ° C. or higher. From the same viewpoint, the solution treatment temperature is more preferably 480 ° C. or higher.

  When the solution treatment temperature exceeds 500 ° C., the solution treatment temperature exceeds the solidus temperature of the mother phase, so that the mother phase may partially dissolve. In order to avoid this problem, the solution treatment temperature is set to 500 ° C. or lower. From the same viewpoint, the solution treatment temperature is more preferably 495 ° C. or lower.

  The solution treatment is performed by holding the temperature for 0.5 to 10 hours after the temperature of the hot-rolled sheet reaches the solution treatment temperature. By setting the retention time in the solution treatment to the above specific range, both the η phase and the S phase can be sufficiently decomposed to increase the amount of solid solution of Zn, Mg, and Cu in the parent phase.

  When the holding time is less than 0.5 hour, the decomposition of the η phase and the S phase becomes insufficient, which may cause a decrease in the amount of solid solution such as Zn. As a result, the strength of the aluminum plate may be reduced. Therefore, from the viewpoint of sufficiently decomposing the η phase and the S phase, the holding time is 0.5 hours or more. From the same viewpoint, the holding time is preferably set to 1 hour or longer.

  When the holding time exceeds 10 hours, coarse crystal grains are likely to be generated. Further, in this case, the time required for the solution treatment becomes excessively long, resulting in a decrease in productivity. From the viewpoint of avoiding these problems, the holding time is 10 hours or less. From the same viewpoint, the holding time is preferably 8 hours or less.

  After the solution treatment, the aluminum plate can be produced by sequentially performing water quenching and artificial aging treatment. Conditions for water quenching and artificial aging treatment can be appropriately selected from known conditions.

Examples of the aluminum plate will be described below. The following examples show one embodiment of the present invention. The aspect of the aluminum plate according to the present invention is not limited to the following examples, and the configuration can be changed as appropriate within a range that does not impair the gist thereof.
Example 1
This example is an example of an aluminum plate produced by changing various chemical components. In this example, first, various aluminum alloys AK having chemical components shown in Table 1 were ingoted by DC casting to obtain an ingot having a thickness of 500 mm and a width of 500 mm. In Table 1, “Bal.” Indicates a residual component (Balance).

These ingots were heated at a temperature of 470 ° C. for 10 hours for homogenization. Subsequently, the ingot after the homogenization treatment was hot-rolled to obtain a hot-rolled plate having a thickness of 20 mm. Hot rolling was started with the temperature of the ingot being 400 ° C. The strain rate in hot rolling was 0.3 s ⁻¹ and the total rolling reduction was 96%.

  Next, the hot rolled plate was heated to 480 ° C. The hot-rolled sheet was heated so that the average rate of temperature increase from the temperature of the hot-rolled sheet to 300 ° C. until it reached 480 ° C. was 10 ° C./h.

  After the temperature of the hot-rolled sheet reached 480 ° C., the temperature was maintained for 1 hour to perform solution treatment. Thereafter, the hot-rolled sheet was water-quenched and cooled to 75 ° C. or lower in 50 seconds. After water quenching, the hot-rolled sheet was heated again, and an artificial aging treatment was performed while maintaining a temperature of 120 ° C. for 24 hours. Thus, test materials 1 to 11 shown in Table 2 were obtained.

About the test materials 1-11 obtained by the above, the number of (eta) phase particle | grains, S phase particle | grains, and porosity of 5 micrometers or more in equivalent circle diameters was computed with the following method. First, secondary electron images at a magnification of 200 times were obtained at three locations randomly selected from the plate cross section (L-ST plane) parallel to the rolling direction of each test material. Simultaneously with the acquisition of the secondary electron image, the chemical components of the particles present in the secondary electron image were identified by SEM-EDS, and the η phase particles and S phase particles were extracted. Next, image analysis of the secondary electron image was performed, and the equivalent-circle diameters of all η phase particles, S phase particles, and porosity existing in the secondary electron image were calculated. Then, the number of η-phase particles, S-phase particles and porosity having an equivalent circle diameter of 5 μm or more present in the secondary electron image was counted and converted to the number per 1 mm ² .

  The total number of η-phase particles with an equivalent circle diameter of 5 μm or more and the number of S-phase particles with an equivalent circle diameter of 5 μm or more and the number of porosity with an equivalent circle diameter of 5 μm or more in each test material are as shown in Table 2. there were.

  Moreover, about the test materials 1-11, the tension test was done according to the method prescribed | regulated to JISZ2241. The specimen used for the tensile test was collected from each test material so that the tensile direction was parallel to the rolling direction. Table 2 shows the values of tensile strength, 0.2% proof stress and elongation at break obtained by a tensile test.

  As shown in Table 1 and Table 2, the test materials 1 to 4, 7, 9, and 11 have the chemical components in the specific range, and the number of η phase particles having a circle equivalent diameter of 5 μm or more and the circle equivalent diameter. The total of the number of S phase particles of 5 μm or more and the number of porosities having an equivalent circle diameter of 5 μm or more were within the specific range. Therefore, these test materials were able to achieve both strength and ductility at a high level.

  Among these test materials, Zn: 7.0% or more, Mg: 1.5% or more, Cu: 1.0% or more, and Zr: 0.05% or more of the test materials 1 to 4 are 680 MPa or more. The tensile strength, 0.2% proof stress of 620 MPa or more, and breaking elongation of 10% or more were exhibited, and higher strength could be achieved while ensuring excellent ductility.

Since the test materials 5, 6 and 8 had a content of any one of Zn, Mg or Cu in excess of the above specific range, the solid solution amounts of Zn, Mg and Cu were increased and high strength was exhibited. However, as a result of excessive Zn and the like, a large number of η-phase particles and S-phase particles that could not be decomposed in the solution treatment remain in the matrix, and the total of η-phase particles and S-phase particles is the above-mentioned specific amount. More than the range. As a result, the elongation at break was below the specific range, and the ductility was insufficient.
Since the test material 10 had a Zr content higher than the specific range, a large amount of Al-Zr crystallized substances and precipitates were formed in the matrix. As a result, the elongation at break was below the specific range, and the ductility was insufficient.

(Example 2)
This example is an example of an Al—Zn—Mg—Cu-based aluminum alloy plate having a Zn content of less than 7.0%. In this example, after producing ingots of aluminum alloys L to V having the chemical components shown in Table 3, homogenization treatment, hot rolling, solution treatment, water quenching and artificial quenching were performed under the same conditions as in Example 1. An aging treatment was performed. Thus, test materials 12 to 22 shown in Table 4 were produced. The number of η phase particles and the like were calculated and a tensile test was performed in the same manner as in Example 1. Table 4 shows these results. In Table 3, “Bal.” Indicates a residual component (Balance).

  The test materials 12 to 16 have the chemical components in the specific range, and the total number of η phase particles having an equivalent circle diameter of 5 μm or more and the number of S phase particles having an equivalent circle diameter of 5 μm or more, and an equivalent circle diameter of 5 μm or more. The number of porosity was within the specific range. Therefore, these test materials exhibited a tensile strength of 600 MPa or more, a 0.2% proof stress of 550 MPa or more, and a breaking elongation of 10% or more, and were able to achieve both strength and ductility at a high level.

The test material 17 had a Zn content less than the specific range. Therefore, the tensile strength of 600 MPa or more and the 0.2% proof stress of 550 MPa or more could not be achieved, and the strength became insufficient.
Since the test materials 18 to 22 had a high content of any one element of Si, Fe, Ti, Mn, and Cr, a large amount of crystallized substances and precipitates containing the element were formed in the matrix. . As a result, the elongation at break was below the specific range, and the ductility was insufficient.

(Example 3)
In this example, the production conditions of the aluminum plate are variously changed. In this example, Zn: 9.8%, Mg: 2.4%, Cu: 1.4%, Zr: 0.13%, Si: 0.25%, Fe: 0.12%, Ti: 0 An aluminum alloy containing 0.03%, Mn: 0.02% and Cr: 0.01%, the balance of which is an inevitable impurity and a chemical component made of Al, is ingoted by DC casting, thickness 500 mm, width 500 mm An ingot was prepared.

  The obtained ingot was homogenized and hot-rolled under the same conditions as in Example 1 to produce a hot-rolled plate having a thickness of 200 mm. Next, this hot-rolled sheet was heated to perform a solution treatment. Table 5 shows the average heating rate, solution treatment temperature, and holding time from reaching 300 ° C. to reaching the solution treatment temperature.

  Thereafter, the hot-rolled sheet was subjected to water quenching and artificial aging treatment under the same conditions as in Example 1. Thus, test materials 23 to 27 shown in Table 5 were produced. With respect to these test materials, the number of η phase particles and the like were calculated and a tensile test was performed in the same manner as in Example 1. Table 5 shows these results.

  As can be understood from Table 5, the test materials 23 to 26 have the chemical components in the above specific range, the number of η phase particles having an equivalent circle diameter of 5 μm or more, and the number of S phase particles having an equivalent circle diameter of 5 μm or more. And the number of porosities having an equivalent circle diameter of 5 μm or more were within the specific range. Therefore, these test materials showed a tensile strength of 680 MPa or more, a 0.2% proof stress of 620 MPa or more, and a breaking elongation of 10% or more, and both strength and ductility could be achieved at a high level.

  Since the average temperature increase rate until the test material 27 reached the solution treatment temperature was excessively large, the η phase and the S phase were rapidly melted. As a result, the number of porosity having an equivalent circle diameter of 5 μm or more was larger than the specific range, and the ductility was insufficient.

Example 4
In this example, as in Example 3, the manufacturing conditions for the aluminum plate were variously changed. In this example, Zn: 9.9%, Mg: 2.3%, Cu: 1.5%, Zr: 0.14%, Si: 0.06%, Fe: 0.05%, Ti: 0 An aluminum alloy containing 0.03%, Mn: 0.01% and Cr: 0.01%, the balance of which is an inevitable impurity and a chemical component consisting of Al, is ingoted by DC casting, and is 150 mm thick and 150 mm wide. An ingot was prepared.

These ingots were heated at a temperature of 470 ° C. for 10 hours for homogenization. Subsequently, the ingot after the homogenization treatment was hot-rolled to obtain a hot-rolled plate having a thickness of 5 mm. Hot rolling was started with the temperature of the ingot being 400 ° C. The strain rate in hot rolling was 0.3 s ⁻¹ and the total rolling reduction was 96.7%.

  Next, this hot-rolled sheet was heated to perform a solution treatment. Table 6 shows the average heating rate, solution treatment temperature, and holding time from reaching 300 ° C. to reaching the solution treatment temperature.

  Thereafter, the hot-rolled sheet was subjected to water quenching and artificial aging treatment under the same conditions as in Example 1. Thus, test materials 28 to 32 shown in Table 6 were produced. With respect to these test materials, the number of η phase particles and the like were calculated and a tensile test was performed in the same manner as in Example 1. Table 6 shows these results.

  As can be understood from Table 6, the test materials 28 to 31 have the chemical components in the above specific range, the number of η phase particles having an equivalent circle diameter of 5 μm or more, and the number of S phase particles having an equivalent circle diameter of 5 μm or more. And the number of porosities having an equivalent circle diameter of 5 μm or more were within the specific range. Therefore, these test materials showed a tensile strength of 680 MPa or more, a 0.2% proof stress of 620 MPa or more, and a breaking elongation of 10% or more, and both strength and ductility could be achieved at a high level.

  In the test material 32, the average rate of temperature increase until reaching the solution treatment temperature was excessively high, which caused rapid melting of the η phase and the S phase. As a result, the number of porosity having an equivalent circle diameter of 5 μm or more was larger than the specific range, and the ductility was insufficient.

Claims (6)

Zn: 2.0% (mass%, the same shall apply hereinafter) to 12.0%, Mg: 1.0% to 4.5%, Cu: 0.5% to 3.0%, and Zr: 0. Containing from 01% to 0.30%, Si: 0.5% or less, Fe: 0.5% or less, Ti: 0.5% or less, Mn: 0.3% or less, and Cr: 0.3% Regulated below, with the remainder having chemical components consisting of Al and inevitable impurities,
The total of the η phase particles having an equivalent circle diameter of 5 μm or more and the S phase particles having an equivalent circle diameter of 5 μm or more is 100 particles / mm ² or less,
A structural aluminum alloy plate having a porosity equivalent to a circle equivalent diameter of 5 μm or more and 50 pieces / mm ² or less.   Zn: 7.0% (mass%, the same applies hereinafter) to 12.0% or less, Mg: 1.5% to 4.5%, Cu: 1.0% to 3.0%, and Zr: 0.00%. The structural aluminum alloy plate according to claim 1, wherein the structural aluminum alloy plate is in the range of 05% to 0.30%.   The structural aluminum alloy sheet according to claim 2, wherein the tensile strength is 680 MPa or more and the 0.2% proof stress is 620 MPa or more.   Zn: 2.0% (mass%, the same applies hereinafter) to less than 7.0%, Mg: 1.5% to 4.5%, Cu: 1.0% to 3.0%, and Zr: 0.00%. The structural aluminum alloy plate according to claim 1, wherein the structural aluminum alloy plate is in the range of 05% to 0.30%.   The structural aluminum alloy plate according to claim 4, wherein the tensile strength is 600 MPa or more and the 0.2% proof stress is 550 MPa or more.   The structural aluminum alloy plate according to any one of claims 1 to 5, wherein the elongation at break is 10% or more.