JP4498180B2 - Al-Zn-Mg-Cu-based aluminum alloy containing Zr and method for producing the same - Google Patents

Description

  The present invention relates to an Al—Zn—Mg—Cu based aluminum alloy containing Zr, which is mainly used for aircraft materials and is also known as an AA7050 alloy, and a method for producing the same.

  Inclusions, defects, scratches, joints, and the like are unavoidably present in the members constituting the structure, and stress concentrates on the defects and the like, and tends to be the starting point of crack generation. A material in which the cracks generated in this way suddenly rapidly progress to break, that is, a material in which a slight stress concentration becomes the starting point of rapid fracture, is a structure that requires a high level of safety. Not used. An index for quantitatively displaying such characteristics is fracture inertia.

When paying particular attention to this fracture toughness, an Al—Zn—Mg—Cu-based alloy known as an AA7075 alloy is one of aluminum alloys having high fracture toughness and the highest strength.
In this Al-Zn-Mg-Cu alloy known as AA7075 alloy, a transition phase such as Cr and Mn is added to form a dispersed phase in the homogenization process of the aluminum alloy ingot, thereby recrystallization. By suppressing and maintaining the subgrain structure, high strength and excellent toughness can be obtained.

  However, in the Al-Zn-Mg-Cu alloy known as AA7075 alloy, the interface between the dispersed phase and the parent phase becomes inconsistent due to the addition of Cr and Mn, and non-uniform precipitation occurs at the interface, resulting in high quenching sensitivity. It has been known. That is, in the case of an aluminum alloy to which Mn or Cr is added, if the quenching speed is slow after the alloy solution treatment, a coarse precipitation phase preferentially precipitates on the Mn-based insoluble compound or Cr-based insoluble compound during quenching. Therefore, there is a problem that the distribution of the precipitated phase eventually becomes non-uniform and the high strength of the alloy cannot be obtained. Furthermore, this AA7075 alloy is not only limited in material dimensions due to its high quenching sensitivity, but also has a problem in that it is inferior in corrosion resistance, particularly in stress stress cracking resistance (SCC resistance). ing.

There is an Al—Zn—Mg—Cu-based alloy known as AA7050 alloy that improves the problem of high quenching sensitivity in this AA7075 alloy and is particularly excellent in stress corrosion cracking resistance. The AA7050 alloy is used as a material for aircraft structural members and high-speed rotating bodies. In this Al-Zn-Mg-Cu alloy known as the AA7050 alloy, a dispersed phase is formed during homogenization by adding Zr instead of Cr and Mn as a transition element as in the case of adding Cr and Mn. Thus, recrystallization is suppressed and high strength, excellent toughness and ductility are obtained, and stress corrosion cracking resistance (SCC resistance) is improved unlike the case of adding Cr and Mn.
This is because, when Zr is added, the interface between Al ₃ Zr and the parent phase maintains consistency, the interface does not act as a precipitation site of η phase, that is, Mg ₂ Zn, and the dispersion density of η phase is high and quenching sensitivity is low. Due to that.
Special Table 2000-504068 JP-A-6-41704

Currently, by further improving the strength characteristics, especially fracture toughness, of aluminum alloys, its application fields are expanded, contributing to resource saving by realizing further weight reduction of particularly large and thick structural members. As a result, social demands to improve environmental aptitude are urgent.
In this regard, in the conventional method for producing an Al—Zn—Mg—Cu-based alloy containing Zr, solidification segregation occurs during casting of the alloy, resulting in nonuniform Zr distribution and insufficient precipitation of Al ₃ Zr. In part, the effect of suppressing recrystallization is limited, and when recrystallization occurs, the consistency of Al ₃ Zr is lost, and the fracture toughness is caused by non-uniform precipitation of η phase with Al ₃ Zr as the nucleus. There was a problem of lowering. Accordingly, there remains room for further improving the fracture toughness value by improving the manufacturing method.

When focusing on the thick plate of the Al—Zn—Mg—Cu-based aluminum alloy containing Zr in terms of improving the fracture toughness, the crystal grains have a shape extending in the rolling direction, and therefore cracks in the rolling direction. There is a tendency that the fracture toughness value at the time of propagating decreases, and it is an important condition to improve the fracture toughness value in the TL (1/4 thickness) direction.
Regarding the improvement of the fracture toughness value, for example, in Patent Document 1, the S-L or LT direction of a thick product made of an Al-Zn-Mg-Cu alloy whose characteristics have been improved by examining the chemical composition or aging treatment conditions is disclosed. With regard to KIc.
However, Patent Document 1 only examines the chemical composition or the aging treatment conditions, and does not examine the detailed structure, particularly the structure caused by the Al ₃ Zr distribution state.

  In addition, Patent Document 2 discusses a manufacturing method that can improve ductility and SCC resistance while maintaining the strength of an alloy using an industrial manufacturing method for age-hardening aluminum alloys. After melting and casting, the temperature is increased to a temperature of 200 to 400 ° C. at a rate of temperature increase of 100 ° C./min or less, held at a temperature of 200 to 400 ° C. for 48 hours or less, and then to a soaking temperature of 100 ° C./min or less. A method for producing an age-hardening aluminum alloy, characterized in that the temperature is raised at a rate of temperature rise, is disclosed.

  However, the method for producing an age-hardening aluminum alloy of Patent Document 2 deals with Al-Cu-Mg-based and Al-Zn-Mg-Cu-based age-hardening aluminum alloys in which Mn and Cr are added, In particular, it does not focus directly on Al—Zn—Mg—Cu-based alloys containing Zr, but there is a problem that the processing conditions are complicated and it is difficult to meet the current demand for improvement in productivity. It was.

  The present invention has been made in view of the above problems in the prior art, and provides an Al-Zn-Mg-Cu-based aluminum alloy containing Zr that can be efficiently manufactured with improved fracture toughness and a method for manufacturing the same. With the goal.

The inventors of the present invention have studied various production methods for improving the toughness of an Al—Zn—Mg—Cu based alloy containing Zr based on an industrial production method. As a result, it is necessary to suppress recrystallization in order to prevent deterioration of characteristics, and for this purpose, it is recognized that it is necessary to disperse Al ₃ Zr finely and with high density. The inventors have found that the subgrain structure can be controlled by studying the conditions, and that the fracture toughness value can be improved thereby, leading to the present invention.

That is, the production method of the Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention is Cu: 2.0 to 2.6%, Mg: 1.9 to 2.6%, Zn: 5.7 to 6 .7, Zr: 0.08 to 0.15%, and the alloy ingot composed of the balance Al and inevitable impurities was kept at a temperature of 150 ° C. or higher and lower than 200 ° C. for 24 hours or more as the first stage heat treatment. After that, as the second stage heat treatment, a homogenization treatment is performed at a temperature of 450 ° C. or higher and 485 ° C. or lower for 4 hours or more, followed by hot working, solution hardening and cold working for removing residual stress, An aging treatment is performed.

The Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention has Cu: 2.0 to 2.6%, Mg: 1.9 to 2.6%, Zn: 5.7 to 6.7, Zr: 0.08 to 0.15%, the balance being Al and inevitable impurities, the area ratio of the subgrain structure in the L-ST plane at the center of the plate thickness after aging treatment being 60% or more, T The plane strain fracture toughness value in the -L direction satisfies the following formula.
KIc (T-L) MPa · m 1/2 ≧ 28.67MPa · m 1/2 - 0.028MPa · m 1/2 / mm × t (t thickness of mm units)

Furthermore, the Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention has Cu: 2.0 to 2.6%, Mg: 1.9 to 2.6%, Zn: 5.7 to 6.7, Zr: The alloy ingot containing 0.08 to 0.15% and comprising the balance Al and inevitable impurities, as a first stage heat treatment, after being held at a temperature of 150 ° C. or more and less than 200 ° C. for 24 hours or more, As a two-stage heat treatment, a homogenization treatment is performed at a temperature of 450 ° C. or more and 485 ° C. or less for 4 hours or more, followed by hot working, solution hardening, cold working for removing residual stress, and aging treatment. The area ratio of the subgrain structure in the L-ST plane at the center of the plate thickness after aging treatment is 60% or more, and the plane strain fracture toughness value in the TL direction satisfies the following formula: It is characterized by.
KIc (T-L) MPa · m 1/2 ≧ 28.67MPa · m 1/2 - 0.028MPa · m 1/2 / mm × t (t thickness of mm units)

[Action]
In order to leave the subgrain structure at an optimal volume ratio, it is necessary to deposit Al ₃ Zr which is a dispersed phase finely and densely by controlling the homogenization heat treatment to a specific condition. In the method for producing an Al—Zn—Mg—Cu-based aluminum alloy containing Zr according to the present invention, the first stage heat treatment is performed at a temperature of 150 ° C. or more and less than 200 ° C. for 24 hours in the homogenization treatment after melt casting. As described above, preferably after holding within 48 hours, as the second stage heat treatment, hold at a temperature of 450 ° C. or more and 485 ° C. or less for 4 hours or more, preferably within 48 hours, hot rolling, solution hardening, aging treatment As a result, Al ₃ Zr is finely and densely dispersed, and an Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention in which the toughness is improved while maintaining the strength of the alloy is obtained.

Moreover, the Al-Zn-Mg-Cu-based aluminum alloy containing Zr of the present invention has an area ratio occupied by the subgrain structure of 60% or more, and the plane strain fracture toughness value in the TL direction is KIc (TL). ^{MPa · m 1/2 ≧ 28.67MPa · m} 1/2 - 0.028MPa · m 1/2 / mm × t (t is the thickness in mm) from the fact that was set to become, even to satisfy AMS4050 standard The fracture toughness value can be provided, and it can be applied not only to a thin wall but also to a structural part having a wall thickness of 50 mm or more.

According to the Al-Zn-Mg-Cu-based aluminum alloy containing Zr of the present invention, it has excellent fracture toughness, and in particular can be applied to thick parts. In particular, it greatly contributes to the safety of materials required as aircraft materials.
Further, according to the method for producing an Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention, the Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention has high productivity in an efficient process. Can be realized and produced.

The reason for limiting the composition of the present invention and the reason for limiting the manufacturing method will be described below.
The Al—Zn—Mg—Cu-based aluminum alloy containing Zr of this invention has Cu: 2.0 to 2.6 mass% (hereinafter referred to as “%”), Mg: 1.9 to 2.6%, Zn: 5.7 to 6.7, Zr: 0.08 to 0.15%, and the balance is Al and inevitable impurities.
Zn combines with Mg to form an η phase, and precipitates finely in Al to improve the strength. If the effect is less than 5.7%, it is not sufficient, and if it exceeds 6.7%, the corrosion resistance decreases.
Mg forms a solid solution in Al and forms a η phase in the same manner as Zn to improve the strength. The effect is not sufficient if it is less than 1.9%, and cannot be lowered to less than 1.7% in order to maintain sufficient mechanical properties. On the other hand, if it exceeds 2.6%, stress corrosion cracking tends to occur.
Cu increases the precipitation amount and density during the aging treatment, and is effective in increasing the strength. If the effect is less than 2.0%, it is not sufficient, and if it exceeds 2.6%, the crystallized material becomes coarse and the fracture toughness is lowered.
Zr contributes to strength and toughness by forming Al ₃ Zr during the homogenization treatment, suppressing recrystallization, and leaving a subgrain structure. If the effect is less than 0.08%, it is not sufficient. If it exceeds 0.15%, a coarse crystallized product is formed, and the ductility and toughness are lowered.

In the method for producing an Al—Zn—Mg—Cu-based aluminum alloy containing Zr according to the present invention, the first stage heat treatment is carried out at the temperature of 150 ° C. or higher and lower than 200 ° C. for 24 hours or more, and then the second stage. As the heat treatment, a homogenization treatment is performed by holding at a temperature of 450 ° C. or more and 485 ° C. or less for 4 hours or more. The reason for limiting the homogenization processing conditions in the homogenization processing will be described next.
As shown in FIG. 1, the reason why the holding temperature of the first stage is set to 150 ° C. or higher and lower than 200 ° C. is to sufficiently distribute the nucleation of Al ₃ Zr and finally distribute uniform Al ₃ Zr. This is because Al ₃ Zr which is a dispersed phase may be coarsened during homogenization at a high temperature that continues at 200 ° C. or higher. The reason why the holding time at 150 ° C. or more and less than 200 ° C. is set to 24 hours or more is that if it is less than 24 hours , Al ₃ Zr may not be sufficiently generated. If it exceeds 48 hours, the nucleation of Al ₃ Zr is saturated, which is economically disadvantageous.

The reason why the holding temperature of the second stage is set to 450 ° C. or more and 485 ° C. or less is that there is a possibility that the material is not sufficiently homogenized if it is less than 450 ° C., and there is a risk of forming a melt if it exceeds 485 ° C. The reason why the holding time is set to 4 hours or longer is that if it is less than 4 hours, it may not be sufficiently homogenized. If it exceeds 48 hours, the effect of the homogenization treatment is saturated and at the same time coarsening of finely precipitated Al ₃ Zr occurs, which is economically disadvantageous.
In order to uniformly heat the inside of the ingot, the rate of temperature increase from 150 ° C. to less than 200 ° C., which is the first stage holding temperature, and the rate of temperature increase, from 450 ° C. to 485 ° C., which is the second stage holding temperature. It is preferable that the temperature is not more than ° C / min.

In the Al—Zn—Mg—Cu based aluminum alloy containing Zr of the present invention, the area ratio of the subgrain structure in the L-ST plane at the center of the plate thickness after aging treatment is defined as 60% or more.
Here, the L-ST plane is the rolling direction-thickness cross section, and the area ratio occupied by the subgrain structure in the rolling direction-thickness cross section is defined as 60% or more. This is because the area ratio is recognized as a dominant factor affecting the fracture toughness value of the Al—Zn—Mg—Cu-based aluminum alloy containing Zr.
If the area ratio of the subgrain structure on the L-ST plane is less than 60%, the effect of improving the fracture toughness value is insufficient, which is not preferable.
The area ratio of the subgrain structure on the L-ST plane is more preferably 65% or more, and most preferably 70% or more.

In the present invention, the Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention is defined as having a characteristic satisfying the following formula.
KIc (T-L) MPa · m 1/2 ≧ 28.67MPa · m 1/2 - 0.028MPa · m 1/2 / mm × t (t thickness of mm units)
KIc (TL): Plane strain fracture toughness value in the TL direction When stress (σ) is obtained from the equation showing the elastic stress distribution near the crack tip on the assumption that a sharp crack already exists in the material. When only the factor of the crack length (α) is extracted and set as K (K = ασ√πa), such K is called a stress intensity factor. Here, α is a constant depending on the shape of the test piece and the crack. K is a parameter indicating the magnitude of the stress at the crack tip. When a certain K value is reached, the crack continues to grow unstablely without increasing the external force, and the test piece breaks. The critical value of K is fracture toughness (Kc). Therefore, the fracture toughness value is a measure of resistance when a crack progresses, and the higher this value, the better the characteristics. Further, the fracture toughness (Kc) decreases as the plate thickness increases, and becomes a constant value above a certain plate thickness. In particular, since the Kc value takes the smallest value under the plane strain condition (mode I), the KIc value is most important at the time of design. Further, the KIc value is dependent on the plate thickness, and decreases as the plate thickness increases, and becomes a constant value above a certain plate thickness. Therefore, increasing the fracture toughness value is very important not only for thin plates but also for thick plates.

As for this plane strain fracture toughness (KIc), as a result of investigating the relationship between the thickness of the plate material of Al-Zn-Mg-Cu-based aluminum alloy containing Zr and the fracture toughness value in the TL direction, On the other hand, a decrease of 0.028 MPa · m ^1/2 / mm was observed. Based on this investigation, the formula for the plane strain fracture toughness value KIc (TL) in the TL direction of the Al—Zn—Mg—Cu based aluminum alloy containing Zr of the present invention was obtained.

In this plane strain fracture toughness (KIc) value, in particular, the plane strain fracture toughness value KIc (TL) in the TL direction is KIc (TL) MPa · m ^1/2 ≧ 28.67 MPa · m ^{1 / The} Al—Zn—Mg—Cu-based aluminum alloy containing Zr according to the present invention is sufficient by satisfying the relationship of 2−0.028 MPa · m ^1/2 / mm × t (t is the plate thickness in mm). It can be said that the fracture toughness value is provided, and specifically, the AMS 4050 standard can also be satisfied.

In this AMS 4050 standard, the fracture toughness value is determined for each range of sheet thickness. In this respect, the Al—Zn—Mg—Cu-based aluminum alloy containing Zr of this invention has a fracture toughness value of KIc (TL ^{) MPa · m 1/2 ≧ 28.67MPa ·} m 1/2 - by satisfying the relationship of ^{0.028MPa · m 1/2 / mm × t} (t thickness of mm units), plenty this standard Satisfied with.

Further, KIc (T-L) MPa · m 1/2 ≧ 28.67MPa · m 1/2 - 0.028MPa · m 1/2 / mm × t (t is a plate thickness in mm) composed Zr of the invention 28.67 MPa · m ^1/2 −0.028 MPa · m ^1/2 / mm × t in the formula for defining the fracture toughness value of an Al—Zn—Mg—Cu-based aluminum alloy containing is an alloy plate having a thickness of 100 mm, This stipulates that a KIc (TL) of 25.87 or more should be obtained.

In this regard, even in Al-Zn-Mg-Cu series aluminum alloy containing Zr KIc (T-L) MPa · m 1/2 ≧ 28.67MPa · m 1/2 - 0.028MPa · m 1/2 If the relationship of / mm × t (t is the plate thickness in mm) is not satisfied, it is not recognized that a sufficient fracture toughness value is provided, and the AMS 4050 standard cannot be satisfied.

  In the method for producing an Al—Zn—Mg—Cu-based aluminum alloy containing Zr according to the present invention, after performing the above-mentioned homogenization treatment, it is subsequently subjected to hot working and solution hardening by ordinary methods, and further, residual stress removal Cold working and aging treatment are performed.

  Although not particularly limited in the present invention, hot rolling or hot forging is started at 400 to 450 ° C., and processing is performed up to a predetermined plate thickness or shape. The subsequent solution treatment is performed at 471 to 482 ° C., and the holding time is maintained for several tens of minutes to several hours although the time varies depending on the thickness in order to obtain a uniform solid solution.

  The purpose of quenching treatment is to obtain a supersaturated solid solution by rapid cooling after solution treatment. Generally, in the case of plate materials, it is carried out by water cooling, and in the case of forging materials, it is quenched in an aqueous solution such as warm water or polyethylene glycol. In some cases.

  In the cold working for removing the residual stress, a permanent deformation of 1.5 to 3% is applied to remove the residual stress as necessary by tensile correction in the case of a plate material and compression processing in the case of a forged material.

  In the aging treatment, artificial aging is performed at about 120 ° C. following natural aging. In particular, this alloy is often over-aged to improve stress corrosion cracking resistance and exfoliation corrosion resistance. In this case, the first stage is artificially aged at about 120 ° C and then the second stage. As an aging condition, an artificial aging of 160 to 180 ° C. is performed.

Examples of the present invention will be described below.
As an example of the present invention, an Al—Zn—Mg—Cu-based aluminum alloy plate containing Zr is manufactured, and the results of comparing the characteristics of the comparative example and the conventional example will be described.
AA7050 alloy as an Al—Zn—Mg—Cu-based aluminum alloy containing Zr composed of chemical components (mass%) shown in Table 1 was melt cast and chamfered to a thickness of 350 mm, each between 135 and 215 ° C. After reaching the temperature range, the temperature was maintained for 24 hours or 48 hours, the temperature was raised to 475 ° C., and the mixture was homogenized at that temperature for 3 to 50 hours. After hot rolling at 400 ° C., the plate thickness was set to 100 mm, a solution treatment was performed, 2% permanent strain was applied by stretch correction to remove residual stress, and an aging treatment was performed. The solution treatment was held at 475 ° C. for 5 hours. The aging treatment was performed at 120 ° C. for 5 hours and at 165 ° C. for 24 hours.

In the plane strain fracture toughness test, a compact type test piece was sampled from a 1/4 position of the plate thickness, and the test was conducted in accordance with ASTM E399.
The area ratio of subgrains was measured by preparing a thin film sample from the central part of the plate thickness in the rolling direction-plate thickness cross section (L-ST plane), and observing 20 fields of view using a transmission electron microscope at a magnification of 3000 times. The area ratio was determined.
The test results are shown in Table 2.

From Table 2, the alloy produced by the conventional one-stage homogenization method at 475 ° C. × 24 h has a subgrain content of about 40%, whereas the homogenization process was performed in two stages. In each embodiment of the invention, all are 60% or more, and the proportion of subgrains is increasing.
Further, in the alloy manufactured by the conventional homogenization method, the plane strain fracture toughness value KIc (TL) in the TL direction is 25.1 MPa · m ^1/2 <28.67 MPa · when the plate thickness is 100 mm. m ^1/2 - whereas a ^{0.028MPa · m 1/2 /mm×100mm=25.87MPa · m 1/2} , in the present invention each embodiment, in any thickness 100 mm 25.87MPa · ^m is ^1/2 greater than 26.5MPa · ^{m 1/2} or more, it can be seen that the fracture toughness is improved from this result.

Further, in the alloy manufactured by the two-stage homogenization method of 135 ° C. × 25 h + 475 ° C. × 25 h of Comparative Example 1, the first stage holding temperature is less than 150 ° C. not reached, Al 3 _Zr nucleation can not be distributed uniform Al 3 _Zr becomes insufficient result of the proportion of sub-grains are on the order of 48%, the plate thickness center after aging However, the condition of the Al—Zn—Mg—Cu based aluminum alloy containing Zr of the present invention that the area ratio of the subgrain structure on the L-ST plane is 60% or more is not satisfied.
Consequently 25.3MPa · ^{m 1/2} plane T-L direction in the alloy of Comparative Example 1 strain fracture toughness value KIc (T-L) are in plate thickness ^{100mm <28.67MPa · m 1/2 - 0} . 028 MPa · m ^1/2 / mm × 100 mm = 28.57 MPa · m ^1/2 , and a sufficient fracture toughness value is not obtained.

Further, in the alloy manufactured by the two-stage homogenization method of Comparative Example 2 at 155 ° C. × 22h + 475 ° C. × 25 h, the retention time of the first stage homogenization treatment is 22 hours, and this invention The condition of holding for 24 hours or more is not reached, and nucleation of Al ₃ Zr is insufficient and uniform Al ₃ Zr cannot be distributed. As a result, the proportion of subgrains is about 55%. The condition of the Al—Zn—Mg—Cu based aluminum alloy containing Zr of the present invention that the area ratio of the subgrain structure in the L-ST plane at the center of the plate thickness after aging treatment is 60% or more is satisfied. It has not been.
Consequently 25.3MPa · ^{m 1/2} plane T-L direction in the alloy of Comparative Example 2 strain fracture toughness value KIc (T-L) are in plate thickness ^{100mm <28.67MPa · m 1/2 - 0} . 028 MPa · m ^1/2 / mm × 100 mm = 28.57 MPa · m ^1/2 , and a sufficient fracture toughness value is not obtained.

Further, in the alloy manufactured by the two-stage homogenization method of Comparative Example 3 at 155 ° C. × 25 h + 475 ° C. × 3 h, the holding time of the second stage homogenization treatment is 3 hours and 4 hours. The condition of the present invention of holding the above is not reached, the effect of refining by precipitation of Al ₃ Zr becomes insufficient, the proportion of subgrains is about 54%, and L− The condition of the Al—Zn—Mg—Cu based aluminum alloy containing Zr of the present invention that the area ratio of the subgrain structure on the ST plane is 60% or more is not satisfied.
Consequently 25.6MPa · ^{m 1/2} plane T-L direction in the alloy of Comparative Example 3 strain fracture toughness value KIc (T-L) are in plate thickness ^{100mm <28.67MPa · m 1/2 - 0} . 028 MPa · m ^1/2 / mm × 100 mm = 28.57 MPa · m ^1/2 , and a sufficient fracture toughness value is not obtained.

Further, in the alloy manufactured by the two-stage homogenization method of 195 ° C. × 22 h + 475 ° C. × 25 h of Comparative Example 4, the holding time of the first stage homogenization treatment is 22 hours and 24 hours. The condition of the present invention for maintaining the above is not reached, and the nucleation of Al ₃ Zr is insufficient and uniform Al ₃ Zr cannot be distributed. As a result, the proportion of subgrains is about 56%. The condition of the Al—Zn—Mg—Cu-based aluminum alloy containing Zr of the present invention that the area ratio of the subgrain structure in the L-ST plane at the center of the plate thickness after aging treatment is 60% or more is satisfied. It has not been.
Consequently 25.7MPa · ^{m 1/2} plane T-L direction in the alloy of Comparative Example 4 strain fracture toughness value KIc (T-L) are in plate thickness ^{100mm <28.67MPa · m 1/2 - 0} . 028 MPa · m ^1/2 / mm × 100 mm = 28.57 MPa · m ^1/2 , and a sufficient fracture toughness value is not obtained.

Further, in the alloy manufactured by the two-stage homogenization method of Comparative Example 5 of 195 ° C. × 25 h + 475 ° C. × 3 h, the holding time of the second stage homogenization treatment is 3 hours and 4 hours. The condition of the present invention of holding the above is not reached, the effect of refining by precipitation of Al ₃ Zr becomes insufficient, the proportion of subgrains is about 57%, and L− The condition of the Al—Zn—Mg—Cu based aluminum alloy containing Zr of the present invention that the area ratio of the subgrain structure on the ST plane is 60% or more is not satisfied.
Consequently 25.8MPa · ^{m 1/2} plane T-L direction in the alloy of Comparative Example 5 strain fracture toughness value KIc (T-L) are in plate thickness ^{100mm <28.67MPa · m 1/2 - 0} . 028 MPa · m ^1/2 / mm × 100 mm = 28.57 MPa · m ^1/2 , and a sufficient fracture toughness value has not yet been obtained.

Further, in the alloy manufactured by the two-stage homogenization method of 215 ° C. × 25 h + 475 ° C. × 25 h of Comparative Example 6, the first stage holding temperature is 215 ° C. exceeding 200 ° C. Of Al ₃ Zr, which is a dispersed phase, becomes coarse during homogenization at a high temperature, and the proportion of subgrains is about 55%. The condition of the Al—Zn—Mg—Cu based aluminum alloy containing Zr according to the present invention that the area ratio of the subgrain structure on the L-ST plane is 60% or more is not satisfied.
As a result, in the alloy of Comparative Example 6, the plane strain fracture toughness value KIc (TL) in the TL direction was 25.6 MPa · m ^1/2 <28.67 MPa · m ^1/2 −0 at a plate thickness of 100 mm. 0.028 MPa · m ^1/2 / mm × 100 mm = 28.57 MPa · m ^1/2 , and a sufficient fracture toughness value is not obtained.

  The Al—Zn—Mg—Cu-based aluminum alloy containing Zr and the manufacturing method thereof according to the present invention are preferably used mainly for aircraft structural members and various high-speed rotating bodies.

It is explanatory drawing which shows the homogeneous heat processing conditions of this invention.

Claims (3)

Cu: 2.0 to 2.6% by mass (%), Mg: 1.9 to 2.6%, Zn: 5.7 to 6.7, Zr: 0.08 to 0.15% Then, the alloy ingot composed of the remaining Al and inevitable impurities is held as a first stage heat treatment at a temperature of 150 ° C. or higher and lower than 200 ° C. for 24 hours or more, and then as a second stage heat treatment as 450 ° C. or higher and 485 ° C. or lower. Al-Zn-containing Zr, characterized in that it is subjected to a homogenization treatment at a temperature of 4 hours or more, followed by hot working, solution hardening, cold working for residual stress removal, and aging treatment Manufacturing method of Mg-Cu type aluminum alloy. It contains Cu: 2.0-2.6%, Mg: 1.9-2.6%, Zn: 5.7-6.7, Zr: 0.08-0.15%, and the balance is inevitable with Al. It consists of impurities, and the area ratio of the subgrain structure in the L-ST plane at the center of the plate thickness is 60% or more, and the plane strain fracture toughness value in the TL direction satisfies the following formula: An Al—Zn—Mg—Cu-based aluminum alloy containing Zr.
KIc (T-L) MPa · m 1/2 ≧ 28.67MPa · m 1/2 - 0.028MPa · m 1/2 / mm × t (t thickness of mm units) Cu: 2.0 to 2.6%, Mg: 1.9 to 2.6%, Zn: 5.7 to 6.7, Zr: 0.08 to 0.15%, and Si: 0 0.12% or less, Mn: 0.1% or less, Ti: 0.06% or less, and the alloy ingot composed of the balance Al and inevitable impurities is heated to 150 ° C. or more and less than 200 ° C. as the first stage heat treatment. After holding at temperature for 24 hours or more, as the second stage heat treatment, homogenization treatment is performed at 450 ° C. or more and 485 ° C. or less for 4 hours or more, followed by hot working, solution hardening and residual stress removal Is produced by performing cold working and aging treatment, and the area ratio of the subgrain structure in the L-ST plane is 60% or more at the center of the plate thickness after aging treatment, and the plane strain in the TL direction Al-Zn-Mg-Cu-based aluminum alloy containing Zr characterized by fracture toughness value satisfying the following formula .
KIc (T-L) MPa · m 1/2 ≧ 28.67MPa · m 1/2 - 0.028MPa · m 1/2 / mm × t (t thickness of mm units)

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