JP2003277868A - Aluminum alloy forging having excellent stress corrosion cracking resistance and stock for the forging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al alloy forging in which stress corrosion cracking does not occur in the part of the cut face between a product and a flash or the vicinity thereof even in severe use environments or corrosive environments, and which has high strength and high toughness, and to provide a stock for the forging. <P>SOLUTION: The aluminum alloy forging comprises 0.6 to 1.8% Mg and 0.4 to 1.8% Si, and further containing one or more kinds of metals selected from 0.01 to 0.6% Mn, 0.1 to 0.2% Cr and 0.1 to 0.2% Zr, and the balance Al with inevitable impurities. In the aluminum alloy forging after artificial aging treatment, 0.2% proof stress is ≥300 MPa, and Charpy impact value is ≥10 J/cm<SP>2</SP>. Further, the maximum in the crystal grain size in a direction vertical to a die parting plane 4 in the structure of a cut face 5a between a product 2 and a flash 3 is ≤400 μm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an Al having excellent corrosion resistance such as stress corrosion cracking resistance, which is suitable for structural material parts of transport aircraft.
-Mg-Si based high strength and high toughness aluminum alloy forgings (hereinafter,
Aluminum is simply referred to as Al) and forging material.

[0002]

2. Description of the Related Art As is well known, JIS 6000 series (Al-Mg-Si series) and other Al alloys are used for structural materials and parts of vehicles such as vehicles, ships, aircraft, motorcycles and automobiles. There is. This JIS 6000 series Al alloy is relatively excellent in corrosion resistance, and is also excellent in terms of recyclability in which scrap can be reused as a JIS 6000 series Al alloy melting raw material.

Taking the structural material of the transportation machine as an example, an Al alloy cast material or an Al alloy forged material is used from the viewpoints of reduction of manufacturing cost and processing into parts having complicated shapes. Of these, Al is used for parts requiring higher strength and mechanical properties such as high toughness.
Alloy forgings are mainly used. These Al alloy forged materials are manufactured by homogenizing heat treatment of the Al alloy cast material, hot forging such as mechanical forging, hydraulic forging, and the like, and then subjected to heat treatment such as T6. The extruded material obtained by extruding the cast material may be used as the forging material.

In recent years, even in the structural materials of these transport aircraft,
There is a demand for higher strength and higher toughness after being made thinner. However, the JI currently used for these applications
In the S 6000 series Al alloy forged material, strength and toughness inevitably occur.

For this reason, the Al alloy material side has been conventionally improved. For example, in Japanese Patent Laid-Open No. 06-256880, JIS 6000 series (A
(l-Mg-Si system) The components such as Mg and Si of the cast material are specified, the average grain size of crystal precipitates (crystallized substances and precipitates) is reduced to 8 μm or less, and the dendrite secondary arm interval is set. (DAS)
It has been proposed to make the Al alloy forging material finer with a fineness of 40 μm or less to have higher strength and toughness.

However, although the strength and toughness of the Al alloy forged material obtained by this conventional technique are higher than those of Al alloys such as JIS 6061 and 6151, the strength and toughness of the forged material are further reduced after being made thinner. There is still a shortage of the required level of toughness.

On the other hand, the inventors of the present invention have proposed Japanese Patent Application No. 10-238564 and Japanese Patent Application No. 11-238564 in order to increase the strength and toughness of the forged Al alloy material after making it thinner. According to No. 224024, Mg: 0.6 to 1.6% (mass%, the same hereinafter), Si: 0.4 to 0.
6 to 1.8%, Cu: 0.01 to 0.1 to 1.0%, and Fe
Is controlled to 0.25% to 0.30% or less, and Mn: 0.15 to 0.6
%, Cr: 0.1 to 0.2%, Zr: 0.1 to 0.2% selectively or indispensably containing one or more kinds, an aluminum alloy forging material consisting of the balance Al and unavoidable impurities, Mg ₂ Si
And the total area ratio of crystal precipitates such as Al-Fe-Si- (Mn, Cr, Zr) series is 1.5% or less per unit area, and the average value of proof stress (σ _0.2 ) is 350 N / mm ² or more and We proposed a high-strength and high-toughness Al alloy forged material that can achieve an average Charpy impact value of 30 J / cm ² or more.

In these inventions, the amount of excess Si is increased, or a strengthening element such as Cu is added to enhance the strength of the forged material, and the forged material is a crystal precipitate of the cast material. Mg ₂ S, a specific crystal precipitate that causes the fracture of the Al alloy structure
i and Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates such as Al-Fe-Si-Mn, Al-Fe-Si-Cr, Al-Fe-Si-Zr, etc. High toughness is ensured by opening and dispersing (defined by the total area ratio of crystal precipitates).

However, as described above, when the amount of excess Si is increased or when a strengthening element such as Cu is included, the structure of the Al alloy forged material is susceptible to intergranular corrosion and stress corrosion cracking. Is significantly increased, and corrosion resistance is reduced, which causes another problem. The problem of deterioration in corrosion resistance becomes serious as a problem relating to durability and reliability, which are basic required characteristics as a structural material.

For example, structural materials such as transportation machines are basically used unpainted (bare), and even in the running or use environment of transportation machines such as automobiles, they contain seawater or salt water, and have low temperatures below freezing. It is exposed to severe salt water corrosive environment from to high temperature in midsummer. Then, these structural materials are used in a state in which a load, a stress, or an impact is applied under these salt water corrosive environments. All of these conditions are factors that significantly promote intergranular corrosion and further stress corrosion cracking.

Further, in structural materials such as transport aircraft, the structure is Al
In addition to alloy forgings, it is often used by combining or joining with other metal materials such as steel, which is more precious than Al alloy. And, in this way, when the Al alloy forged material is joined to another metal material which is more noble than the Al alloy, and is used in a corrosive environment, under load or stress, or with a shock applied, Intergranular corrosion and even stress corrosion cracking,
The usage environment is very likely to occur.

Against this stress corrosion cracking, the present inventors have further described the invention of the present inventors according to Japanese Patent Application No. 11-285372, in which Cu: 0.25% or less and Mn: 0.05% or less. , Fe:
Restricted to 0.30% or less, hydrogen: 0.25 cc / 100g Al or less,
In addition, Mg ₂ Si and Al-Fe-Si- (Mn, Cr, Zr) existing on grain boundaries
The average particle size of the system crystal deposits (crystallized substances and precipitates) is 1.2 μm.
In addition to the following, the average distance between these crystal precipitates was 3.0 μm or more, and high strength and high toughness Al with excellent corrosion resistance
An alloy forging was proposed.

This Japanese Patent Application No. 11-285372 discloses the above-mentioned Japanese Patent Application Laid-Open No.
In addition to reducing the average grain size of the crystalline precipitates in the ingot as in JP-A No. 06-256880, by controlling the morphology to disperse the crystalline precipitates at intervals, improvement of toughness and intergranular corrosion and Improves stress corrosion cracking.

[0014]

However, even with these proposed high strength and high toughness Al alloy forgings excellent in corrosion resistance,
The present inventors have found that under the severe corrosive environment, stress corrosion cracking is particularly likely to occur at a specific portion of the forged material in use.

The specific portion of the forged material is shown in FIG.
Product 2 and flash 3 of Al alloy forging 1 after aging treatment
This is a part of the cut surface 5a.

As shown in FIG. 2, the Al alloy forged material 1 is usually manufactured by the upper die 7 and the lower die 8 in die forging.
Die split surface 4 (also called parting line), which is the boundary surface (divided surface) that can be the boundary between both molds, upper mold 7 and lower mold
It is forged with a gutter 9 which is a space for discharging excess Al alloy from the gap between the die 8 and the die during forging, and a fixed gap 10 called a flash stand. In the Al alloy forged material 1 forged in this way, burrs 3 called flash are inevitably formed in the gutter 9. This flash 3 is forged and then trim line (flash cutting line) 5
At, separated from product 2.

Therefore, the inventors of the present invention have found that on the flash cutting line 5 the (molding surface 4
The cut surface 5a and its vicinity are the outer surface of the Al alloy forged product 2 in use, and the direction perpendicular to the split surface 4 during use (the direction of the cut surface 5a). It was found that stress corrosion cracking is particularly likely to occur when a tensile stress is applied to ().

As shown in FIG. 1, a product of Al alloy forging 1
In each metal flow (grain flow line) 6 of 2, the space between the metal flows 6 is narrowed and flows into the flash 3 as it is. However, in the forging process, depending on the conditions such as homogenizing heat treatment and hot forging of the casting material that is the forging material,
The crystal grains in the cut surface 5a between the product and the flash or in the vicinity thereof may become coarse. And this cut surface 5a
In the case where crystal grain coarsening occurs in a portion in the vicinity thereof or in the vicinity thereof, or the cutting surface 5a or the vicinity thereof becomes an outer surface during use, or when the tensile stress is added, the severe corrosion described above is performed. Due to the synergistic effect with the environment, there is a high possibility that stress corrosion cracking will occur in this part.

In view of such circumstances, an object of the present invention is to cause stress corrosion cracking at or near the cut surface between the product and the flash even under the severe operating environment or corrosive environment. The present invention is intended to provide an Al alloy forged material and a material for forged material which are high in strength and toughness.

[0020]

In order to achieve this object, the gist of the Al alloy forged material of the present invention is Mg: 0.6 to 1.8%, Si:
0.4-1.8%, Mn: 0.01-0.6%, Cr: 0.1-0.2
% And Zr: 0.1-0.2% of one or more, an aluminum alloy forged material consisting of the balance Al and unavoidable impurities, the aluminum alloy forged material after artificial aging treatment, 0.2% proof stress is 300 MPa or more And Charpy impact value
10 J / cm ² or more, and the crystal grain size in the direction perpendicular to the parting plane in the structure of the cut surface between the product and the flash, and the maximum grain size is 400 μm or less. It will be.

The microstructure of the Al alloy forged material of the present invention is all about the microstructure of the Al alloy forged material after the artificial aging treatment except for the microstructure specification such as the dendrite secondary arm interval of the cast material.

As described above, the cut surface of the product of the Al alloy forged material and the flash referred to in the present invention is as shown in FIG.
A cut surface portion 5a of the Al alloy forged material 1 shown in 4 along a cutting line 5 between the product 2 and the flash 3. The crystal grain size in the direction perpendicular to the parting plane (ST direction) in the structure of the cut surface 5a is the crystal grain size in the direction perpendicular to the parting plane, and is along the direction of the vertical cutting line 5. The vertical grain size. Further, in the structure of the cut surface 5a, among the crystal grain sizes having various sizes, the crystal grain having the maximum grain size is 400 μm or less, preferably 200 μm or less in the present invention.

In the texture of the cut surface 5a, the crystal grain size in the direction perpendicular to the mold splitting surface, the grain boundary of the crystal becomes clear by the etching of the cut surface 5a. It is possible to measure and evaluate the diameter.

The inventors of the present invention have found that the crystal grain size of the cut surface 5a in the direction perpendicular to the parting plane governs the stress corrosion cracking resistance of the cut surface 5a in the severe corrosive environment or use environment. It was found to be a major factor that Therefore, in the present invention, the crystal grain coarsening that causes the stress corrosion cracking described above is evaluated by the crystal grain size in the direction perpendicular to the parting plane of the cut surface 5a portion, and the crystal grain size is refined. By doing so, stress corrosion cracking in the severe corrosive environment or use environment is prevented.

The present inventors have also found that the crystal grain size of the cut surface 5a in the direction perpendicular to the parting plane easily exceeds the limit of stress corrosion cracking resistance during the forging (manufacturing) process, and coarsens easily. It was also found that the maximum crystal grain size, which is the limit for stress corrosion cracking resistance, is 400 μm.

In the present invention, in order to secure the strength and toughness basically required for the use of forged materials such as the above-mentioned transport machines, the 0.2% proof stress (σ) of the aluminum alloy forged material after the artificial aging treatment is _0.2 ) to 300 MPa or more and Charpy impact value to 10 J / cm ² or more.

During the forging step, coarsening of the crystal grain size (hereinafter, simply referred to as the crystal grain size of the cut surface) of the cut surface 5a in the direction perpendicular to the mold splitting surface is prevented, and the crystal grain size is fine within the above range. In order to achieve this, the state of existence of dispersed particles, which will be described later, in the crystal grains, which occurs in the homogenizing heat treatment before hot forging, is also important. That is, in order to prevent coarsening of the crystal grain size of the cut surface and to refine the maximum crystal grain size to a range of 400 μm or less, a relatively large number of fine dispersed particles are present in the crystal grains. Is preferred.

More specifically, as in claim 4,
In the forged material structure, Al-Fe-Si- (M
n, Cr, Zr) and other crystal precipitates have an average particle size of 1.2 μm or less, and the average spacing between these crystal precipitates is 3.
0 μm or more, further, the average size of the dispersed particles in the crystal grains is 1100 angstroms (Å) or less,
10 dispersed particles of size 50 angstroms or more / μ
It is preferable that m ³ or more is present.

Then, in order to obtain the finely dispersed state of the dispersed particles as in claim 4, as described in claim 2, the homogenizing heat treatment temperature of the Al alloy ingot as a forging material is set.
The temperature is preferably 500 to 550 ° C.

Similarly, as described in claim 3, the hot forging start temperature of the Al alloy ingot after the homogenizing heat treatment is set to
The temperature is preferably 350 to 450 ° C.

On the other hand, in order to increase the toughness of the Al alloy forged material of the present invention, as described in claim 5, an ingot cast so that the dendrite secondary arm interval (DAS) is 30 μm or less is used. Is preferred. Similarly, in order to increase the toughness of the Al alloy forged material, as described in claim 6, it is also preferable that the ingot is extruded or rolled and then forged.

In the Al alloy forged material of the present invention as described above, the stress corrosion cracking resistance is particularly likely to be lowered, and tensile stress is applied to the cut surface 5a portion in the ST direction as described in claim 7. It is suitable for an Al alloy forged material used as described above and an Al alloy forged material for a structural material of a transportation machine as described in claim 10.

In addition, the toughness is liable to be lowered, and there is a portion where the processing rate from the ingot is less than 75%, as described in the above claim 8, or the cutting as described in the above claim 9. Face 5a
It is suitable for an Al alloy forged material whose thickness in the ST direction is 30 mm or more.

Furthermore, the gist of claim 11 of the present invention as a material for forging according to any one of claims 1 to 10 is as follows:
Made of aluminum alloy ingot, Mg: 0.6 ~ 1.8
%, Si: 0.4 to 1.8%, Mn: 0.1 to 0.6%, Cr: 0.1
.About.0.2% and Zr: 0.1 to 0.2%, one or more of them, and the balance Al and unavoidable impurities, and the dendrite secondary arm spacing in the ingot structure is 30 .mu.m or less.

In order to increase the toughness of the Al alloy forged material, as described in claim 12, the ingot may be further processed by hot extrusion or hot rolling to obtain a material for forging material. preferable.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, high strength and high toughness are obtained.
Al forged material, even when used in the corrosive environment,
In order to suppress the intergranular corrosion susceptibility to a low level, at the same time as defining the Al alloy composition, it is the grain size of the Al alloy forged material structure in the direction perpendicular to the mold splitting surface in the structure of the cut surface between the product and the flash. Then, the maximum size of these crystal grain sizes is restricted to 400 μm or less, preferably 200 μm or less.

(Crystal grain size in the direction perpendicular to the parting plane in the cut surface structure of the product and the flash) First, in the Al alloy forged material of the present invention, perpendicular to the parting surface in the structure of the cut surface of the product and the flash. The crystal grain size in different directions and the distribution state of dispersed particles within the crystal grain that is preferable for finely controlling the crystal grain size will be described below.

Among the forged parts, the maximum crystal grain size in the direction perpendicular to the parting plane in the structure of the cut surface between the product and the flash (hereinafter,
(Simply referred to as the maximum crystal grain size of the cut surface) is 400 μm or less, preferably 200 μm or less specified in the present invention, and other parts of the forged material are necessarily specified in the present invention. It becomes the range to do. On the contrary, even if the maximum grain size of the other part of the forged material in the direction perpendicular to the parting plane is 400 μm or less, there is no guarantee that the maximum grain size of the cut surface will be 400 μm or less. Rather, from the above-mentioned problems of the prior art, even if other parts of the forged material are within the range of the present invention, the maximum crystal grain size of the cut surface is likely to deviate from the range of the present invention.

In the present invention, the maximum crystal grain size of the cut surface of the Al alloy forged material is 400 μm or less. If the maximum crystal grain size of this cut surface exceeds 400 μm, or more strictly exceeds 200 μm, the stress corrosion cracking resistance of the cut surface of the forged material is markedly reduced.

As described above, the maximum crystal grain size of the cut surface is to clarify the grain boundaries of the crystal by the chemical etching of the cut surface, and the variation of the material is taken into consideration by the projector of 5 to 400 times and the optical microscope. In order to do so, 1 field of view for each Al alloy forging, and 20 fields of view of the Al alloy forging of 20 rods. The evaluation is performed by the maximum value of the observation results of the cut surface of each of these forged products. If it is difficult to identify the crystal grain boundaries, after electrolytically etching the cut surface,
Measure with a 400x polarizing microscope.

(Dispersed particles in crystal grains) Then, the coarsening of the maximum crystal grain size of the cut surface during the forging process is prevented, and
In order to reduce the size to less than μm, the dispersed particles generated in the homogenizing heat treatment before hot forging are finely distributed in the crystal grains. The compound name will be described later.Since these dispersed particles have an effect of hindering grain boundary movement after subcrystallization and recrystallization (pinning), the microstructure of the Al alloy forged material, especially the crystal grains on the cut surface, is made fine. It can be a crystal grain or a sub-crystal grain.

In order to exert the effect of preventing the coarsening of the crystal grains on the cut surface by the dispersed particles, the average size of the dispersed particles in the crystal grains is 1100 angstroms (Å) or less and the dispersed particles having a size of 50 angstroms or more. 10 pieces
It is preferable that the particles are present at a density of / μm ³ or more. The dispersed particles themselves become coarse, or the number of dispersed particles themselves is insufficient,
If the above requirements are not satisfied, the effect of refining the crystal grains may not be obtained, and the crystal grains on the cut surface may become coarse. The size (size) of the dispersed particles is the maximum length of one dispersed particle, and the average size of the dispersed particles is also the average size of dispersed particles having a size of 50 angstroms or more.

The size and density of the dispersed particles in the crystal grains are measured by observing the structure of the cut surface with a transmission electron microscope (TEM) of about 5,000 to 20,000 times, and considering variations in materials, Two visual fields for each Al alloy forging, and 20 visual fields for observing the Al alloy forging of 10 rods. Here, the size of the dispersed particles in the crystal grains referred to in the present invention is the maximum length of the dispersed particles. The density means the distribution in the total volume of the 20 fields of view as a unit volume (1 μm ³ )
It is converted into per hit.

6 and 7 show the distribution of dispersed particles in the crystal grains in the texture of the cut surface 5a of the Al alloy forged material. Figures 6 (a) and 6 (b) show 20,000 times the texture of the cut surface.
Fig. 3 is a TEM micrograph (photographed from a photograph) showing the distribution of dispersed particles represented by black dots in crystal grains.

FIG. 6 (a) is an Al alloy forged material of an example described later.
(Fig. 3) and the structure of the cut surface 5a of Comparative Example 9 in Table 2,
The average size of dispersed particles is relatively large, and the number of dispersed particles is relatively small. On the other hand, the structure of the cut surface 5a of the Al alloy forged material of FIG. 6 (b) is Invention Example 6 of Example Table 2 described later, in which the average size of the dispersed particles is relatively small and the number thereof is relatively small. Many (high density).

(Crystal Deposits on Grain Boundaries) Next, the average grain size and the average interval of the crystal deposits on the grain boundaries of the Al alloy forged material structure of the present invention will be described below. In the present invention, Al after artificial aging treatment
Improves the toughness of alloy forgings and has a 0.2% proof stress (σ _0.2 ) of 300M.
In order to secure Pa or more and Charpy impact value of 10 J / cm ² or more, and to improve stress corrosion cracking resistance, Al
A preferable range is defined for the average grain size and the average spacing of the crystal precipitates on the grain boundaries of the alloy forging material. That is, the average grain size of crystal precipitates (crystallized substances or precipitates) such as Mg ₂ Si, Al-Fe-Si-based intermetallic compounds and simple substance Si existing on the grain boundaries of the Al alloy forged material is 1.2 μm. In addition to the following, it is preferable that the average distance between these crystal precipitates is 3.0 μm or more.

The average spacing between the crystal precipitates on these grain boundaries is
When it is less than 3.0 μm, for example, in the morphology control such as the above-mentioned JP-A-06-256880, which only reduces the average particle size of the crystal precipitate, the average particle size of the crystal precipitate is as small as 1.2 μm or less. However, since the distance between them is small and they are in a dense state or a connected state, the toughness, fatigue characteristics and stress corrosion cracking resistance cannot be improved.

Even if the distance between the crystal precipitates is 3.0 μm or more, when the average particle size of the crystal precipitates exceeds 1.2 μm, as a result, the crystal precipitates are in a dense state or a connected state, and the toughness is And fatigue characteristics and stress corrosion cracking resistance cannot be improved.

That is, if the crystal precipitates are densely present on the grain boundaries, mechanical properties such as toughness and fatigue properties are deteriorated. Further, since these crystal precipitates themselves and their surroundings are eluted under the corrosive environment during use of the forged material, stress corrosion cracking is likely to occur. On the other hand, even if the average particle size of the crystal precipitate is large,
It is spaced and dispersed (sparsely present)
If so, the connection of cracks originating from the crystal precipitates is less likely to occur, contributes to the improvement of toughness and fatigue properties, and further, the connection of the corrosion surface due to the dissolution of each crystal precipitate itself and the surroundings under the corrosive environment. Less likely to occur.

In an actual Al alloy forged material, the working ratio may be lowered even by hot forging such as mechanical forging, depending on the size, shape and thickness of the forged material part or the part part. For example, in the case of arms such as suspension parts for automobiles, the machining rate may be as low as about 50%. In addition, since the cast structure remains in the portion having a low processing rate even if it is forged, the toughness and fatigue characteristics tend to be inevitably lower than those in other portions having a high processing rate.

In particular, there is a portion where the workability from the ingot is less than 75%, in which the toughness and fatigue characteristics are likely to decrease,
In the case of an Al alloy forged material such that the thickness of the cut surface in the ST direction is 30 mm or more, in particular, the average grain size of the crystal precipitates and the average spacing between the crystal precipitates present on the grain boundaries of the present invention. Control is
It is suitable for achieving high toughness and high fatigue characteristics.

Then, the size control of the crystal precipitates and the situation in which the crystal precipitates are distributed with an interval between each other (the intervals between the crystal precipitates are small and not close to each other or not connected to each other) As an index that corresponds well, in the present invention,
The average particle size of the crystal precipitates and the average spacing between the crystal precipitates are selected. The above-mentioned part for controlling crystal precipitates is described in Japanese Patent Application No. 11-285372.
It has the same content as the issue.

The average grain size of these crystal precipitates and the average spacing between the crystal precipitates were measured by observing the structure of the Al alloy forged material with an optical microscope of about 400 times or a scanning electron microscope (S) of about 500 times.
EM), in order to take into account variations in material, one for each of the Al alloy forgings, one place on the cut surface, 20 Al alloy forgings
(20 fields of view) is measured by visual observation or average of image analysis results.

Here, the average grain size of the crystal precipitates on the grain boundaries referred to in the present invention means the average length of the crystal deposit particles existing on the grain boundaries, which can be measured on the grain boundaries of the respective visual fields. That is, the average length measured in each of the visual fields is averaged in the 20 visual fields.

The interval between crystal precipitates in the present invention is the length of the grain boundary measured in each visual field divided by the number of crystal precipitate particles observed on the grain boundary in each visual field. The values are averaged in the 20 fields of view.

The stress corrosion cracking resistance of the Al alloy forged material in the above corrosive environment uniquely corresponds to the intergranular corrosion resistance, and the stress corrosion cracking resistance of the Al alloy forged material should be evaluated. Also leads to the evaluation of intergranular corrosion susceptibility.

(Al alloy ingot structure) Next, the Al alloy ingot structure as a material for the Al alloy forged material of the present invention will be described below. The ingot structure for a forged material in the present invention preferably has a dendrite secondary arm spacing (DAS) of the ingot of 30 μm or less in order to ensure high toughness and high fatigue characteristics of the Al alloy forged material. This refines the crystal grains of the Al alloy ingot and the Al alloy forged material, and particularly lowers the total area ratio of the crystallized substances, and improves the toughness of the Al alloy forged material. The dendrite secondary arm spacing (DAS) of this ingot is 30
When the size exceeds μm, the processing rate from the ingot (the overall processing rate when the ingot is only forged, or when the ingot is extruded or rolled and then forged) is 70% or less. If there is a portion of low Al content, crystallized substances cannot be refined, and there is a risk that the fatigue characteristics and toughness of the entire Al alloy forged material cannot be improved.

The material for the forging material of the present invention includes an ingot, an ingot which is homogenized and heat treated, and an ingot which is once extruded or rolled. . Further, the shape of the ingot or the material for forging material is an ingot such as a round bar, a slab shape, or a near net shape close to the shape of a product, and is not particularly limited.

Next, the chemical composition of the Al alloy forged material of the present invention or the material for the forged material will be described. The Al alloy of the present invention is required to ensure high strength, high toughness, and high durability such as stress corrosion cracking resistance for transportation equipment such as automobiles and ships, structural materials or parts.

Therefore, the chemical composition of the Al alloy forged material of the present invention is the composition standard of the Al-Mg-Si based JIS 6000 series Al alloy.
(JIS 6101, 6111, 6003, 6151, 6061, 6N01, 6063, etc.)
Basically, Mg: 0.6-1.6%, Si:
Including 0.4-1.8%, Mn: 0.1-0.6%, Cr: 0.1-0.2% and Z
r: Contains 0.1 to 0.2% of one or more kinds. In addition, all percentages in each element amount mean% by mass.

However, other elements for improving the characteristics or adding other characteristics are provided within the range not impairing the characteristics of the present invention, even if they do not conform to the respective component specifications of JIS 6000 series Al alloy. It is permissible to appropriately change the composition of components such as containing. Further, impurities that are inevitably mixed in from melted raw material scraps and the like are also permitted within a range that does not impair the quality of the forged material of the present invention.

Next, the critical meaning and preferable range of the content of each element in the Al alloy forged material of the present invention will be described.

Mg: 0.6-1.8%. Due to artificial aging treatment, Mg precipitates as β '' and β'phases with Si, resulting in high strength (proof stress) when the final product is used.
Is an essential element for imparting. If the content of Mg is less than 0.6%, the amount of age hardening during the artificial aging treatment decreases. On the other hand, when the content exceeds 1.8%, the strength (proof stress) becomes too high, which hinders the forgeability. In addition, a large amount of Mg ₂ Si and simple substance Si are likely to precipitate during the quenching after the solution treatment, and the average grain size of the crystal precipitates existing on the grain boundaries is set to 1.2 μm or less, and these crystal precipitates are It is impossible to set the average interval of over 3.0 μm. Therefore, the content of Mg is 0.
The range is 6 to 1.8%.

Si: 0.4 to 1.8%. Si, together with Mg, is an essential element for precipitating as β ″ phase and β ′ phase by artificial aging treatment and imparting high strength (proof stress) when the final product is used. If the Si content is less than 0.4%, sufficient strength cannot be obtained by artificial aging treatment. On the other hand, if the content exceeds 1.8%, coarse single Si particles crystallize and precipitate during casting and during quenching after solution treatment, and as described above, the corrosion resistance and toughness deteriorate.
In addition, the excess Si increases, the average grain size of the crystal precipitates existing on the grain boundaries is 1.2 μm or less, and the average spacing between these crystal precipitates cannot be 3.0 μm or more. Corrosion resistance, high toughness, and high fatigue properties cannot be obtained. Workability is also hindered, for example, elongation is reduced. Therefore, the Si content is set in the range of 0.4 to 1.8%, and in this range, it is preferable to reduce the excess Si as much as possible in relation to the Mg content.

Mn: 0.01-0.6%, Cr: 0.1-0.2% and Zr:
0.1 to 0.2% of one or more kinds. Fe, Mn, Cr, Zr, Si, Al, etc. are selectively combined according to their contents during homogenizing heat treatment and subsequent hot forging.Al-Mn system, Al-Cr system, Al-Zr-based intermetallic compound, (Fe, Mn, Cr) ₃ SiAl ₁₂ , Al ₃ Zr, (AlS
i) Generate dispersed particles (dispersed phase) represented by ₃ Zr.

Since these dispersed particles have an effect of hindering the movement of grain boundaries after recrystallization, they prevent coarsening of the crystal grains in the ST direction of the cut surface and, at the same time, over the entire Al alloy forged material of the present invention, It is possible to obtain fine crystal grains and sub-crystal grains.
As a result, the maximum crystal grain in the ST direction of the cut surface is 400
The size can be reduced to less than or equal to μm, preferably less than or equal to 200 μm. Further, Mn, Cr, and Zr can be expected to increase strength and Young's modulus due to solid solution.

If the contents of Mn, Cr, and Zr are too small, these effects cannot be expected. On the other hand, if the contents of these elements are excessively large, coarse intermetallic compounds and crystallized substances are formed during melting and casting. It easily becomes a starting point of fracture and causes deterioration of toughness and fatigue properties. Therefore, each of these elements is Mn:
One kind or two or more kinds are contained in the range of 0.01 to 0.6%, Cr: 0.1 to 0.2% and Zr: 0.1 to 0.2%.

However, among these elements, Zr is Al-Mn system or Al-Cr having a size of tens to hundreds of angstroms.
Finer Al-Zr-based dispersed particles are precipitated than the dispersed particles of the system. Therefore, especially Zr has a large effect of blocking the movement of the crystal grain boundaries and the sub-crystal grain boundaries, refining the crystal grains, and sub-graining, and has a great effect of improving the fracture toughness and fatigue characteristics.

On the other hand, since Mn produces crystallized substances, when Mn is contained, the average particle size of the crystal precipitates existing on the grain boundaries and the average spacing between the crystal precipitates are varied depending on the production conditions. However, there is a high possibility that the preferred range defined by the present invention cannot be achieved. Therefore, it is difficult to control when Mn is contained, and from the viewpoint of ensuring high stress corrosion cracking resistance of the Al alloy forged material, it is preferable to regulate the Mn content to 0.05% or less. Therefore, among the elements of Mn, Cr, and Zr, it is preferable to selectively contain Zr alone or Zr and Cr.

Cu: 0.50% or less. Cu remarkably increases the susceptibility of the Al alloy forged material to stress corrosion cracking and intergranular corrosion, and reduces the corrosion resistance and durability of the Al alloy forged material. Therefore, in the present invention, from this viewpoint, Cu
Control the content as low as possible. But on the other hand,
Cu contributes to the improvement of strength by solid solution strengthening, and also has the effect of significantly promoting the age hardening of the final product during the aging treatment. If the Cu content is reduced, it is necessary to use a high-purity metal ingot, which causes a problem of high casting cost. Therefore, Cu is allowed up to a content of 0.50% or less.

Fe: 0.40% or less. Fe contained as an impurity in the Al alloy forms a coarse crystallized substance, which is a problem in the present invention. As described above, these crystallized substances deteriorate the fracture toughness and fatigue properties. In particular, when the Fe content exceeds 0.40%, more strictly 0.35%, the average grain size of Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates present on the grain boundaries There is a high possibility that the average distance between the objects cannot be set within the preferable range specified in the present invention. Therefore, the Fe content is preferably 0.40% or less, more preferably 0.35% or less.

Hydrogen: 0.25 cc / 100g Al or less. Hydrogen (H _2), particularly when working ratio forging is reduced,
Since bubbles caused by hydrogen do not press-bond during forging and the like and become the starting point of fracture, the toughness and fatigue properties are significantly reduced. In addition, hydrogen has a large influence particularly on the structural material of the transportation machine having high strength. Therefore, hydrogen is 0.25 c
c / 100g Al Content should be as low as possible.

Zn, Ti, B, Be, V and the like. Zn, Ti, B 2, Be, V 3 and the like are elements selectively contained according to the purpose. Zn: 0.005-1.0%. Zn precipitates MgZn ₂ finely and densely during artificial aging to realize high strength. Further, solid-solubilized Zn can be expected to have the effect of lowering the potential inside the grains and reducing the intergranular corrosion and stress corrosion cracking as a result of the corrosion morphology being not the grain boundaries but the overall corrosion. However, if the content of Zn is less than 0.005%, sufficient strength cannot be obtained by artificial aging, and there is no effect of improving the corrosion resistance. On the other hand, if the content exceeds 1.0%, the corrosion resistance is significantly reduced. Therefore, when the Zn is selectively contained, the Zn content is preferably in the range of 0.005 to 1.0%.

Ti: 0.001 to 0.1%. Ti is an element added for refining the crystal grains of the ingot and improving workability during extrusion, rolling and forging. But,
If the content of Ti is less than 0.001%, the effect of improving the workability cannot be obtained. On the other hand, if the content of Ti exceeds 0.1%, coarse crystal precipitates are formed and the workability is deteriorated. Therefore, when selectively contained, the Ti content is preferably in the range of 0.001 to 0.1%.

B: 1 to 300 ppm. B is similar to Ti in that the crystal grains of the ingot are refined, extruded, rolled,
It is an element added to improve workability during forging. However, if the content of B 2 is less than 1 ppm, this effect cannot be obtained. On the other hand, if the content of B exceeds 300 ppm, coarse crystal precipitates are formed and the workability is deteriorated. Therefore, the content of B when selectively contained is 1 to 300p.
It is preferably in the range of pm.

Be: 0.1 to 100 ppm. Be is an element contained to prevent reoxidation of the molten Al in the air. However, if the content is less than 0.1 ppm,
This effect cannot be obtained. On the other hand, if the content exceeds 100 ppm, the material hardness increases and the workability decreases. Therefore, the content of Be when selectively contained is 0.1 to
It is preferably in the range of 100 ppm.

V: 0.15% or less. V, similar to Mn, Cr, and Zr, produces dispersed particles (dispersed phase) during homogenizing heat treatment and subsequent hot forging. Since these dispersed particles have an effect of preventing grain boundary movement after recrystallization, fine crystal grains can be obtained. However, excessive content easily forms coarse Al-Fe-Si-V-based intermetallic compounds and crystal precipitates during melting and casting, becomes a starting point of fracture, and causes deterioration of toughness and fatigue properties. Therefore, V content is allowed up to 0.15%.

Next, a preferred method for manufacturing the Al alloy forged material in the present invention will be described. The Al alloy forged material according to the present invention can be manufactured by an ordinary method. For example, when casting a melted Al alloy melt adjusted within the Al alloy component range, for example, ordinary melt casting such as continuous casting and rolling method, semi-continuous casting method (DC casting method), and hot top casting method. The method is appropriately selected and casting is performed.

However, the crystal grains of the Al alloy ingot are refined,
And, in order to make the average particle size of the crystal precipitates existing on the grain boundaries, the average interval between the crystal precipitates within the range defined in the present invention, the Al alloy molten metal is cooled at 10 ° C / sec or more. It is preferable to cast into a ingot. In addition, the cooling rate of the ingot is 10
By setting the temperature to be at least ° C / sec, the dendrite secondary arm spacing (DAS) of the ingot can be set to 30 µm or less. On the other hand, if the cooling rate is slower than this, the average grain size of the crystal precipitates existing on the grain boundary, the average interval between the crystal precipitates, it cannot be within the range specified in the present invention, and the crystal grains become coarse, It may not be possible to reduce the dendrite secondary arm spacing (DAS) of the ingot to 30 μm or less.

Next, the homogenizing heat treatment temperature of this Al alloy ingot (cast material) is preferably in the temperature range of 500 to 550 ° C. If the homogenizing heat treatment temperature exceeds 550 ° C and is too high, burning occurs and causes forging cracks. It also reduces mechanical properties such as toughness and fatigue properties of the product. In addition, the dispersed particles become coarse and the number of dispersed particles themselves becomes insufficient. As a result, the average size of the dispersed particles within the crystal grains cannot be reduced to 1100 angstroms or less, and
A relatively large number of finely dispersed particles of 10 particles / μm ³ or more cannot be distributed. For this reason, the crystallized substances in the product portion in the vicinity of the flash portion cannot be solid-solved and refined, and the crystal grains cannot be refined.

On the other hand, if the homogenizing heat treatment temperature is too low, less than 500 ° C., Mg ₂ Si or Al-Fe-Si- existing on the grain boundaries of the product is
The average grain size of (Mn, Cr, Zr) -based crystal precipitates should be 1.2 μm or less, and the average spacing between these crystal precipitates should be 3.0 μm.
It becomes difficult to set it to m or more.

After this homogenizing heat treatment, hot forging is performed by mechanical forging, hydraulic forging, etc. to form an Al alloy forged material having a final product shape (near net shape). On this occasion,
The hot forging start temperature of the Al alloy ingot after the homogenizing heat treatment is set to 350
It is preferable to set the temperature to 450 ° C. Hot forging start temperature is 45
If the temperature exceeds 0 ° C., the deformation resistance becomes small, and the crystal grains are likely to become coarse at the end of forging or at the time of temperature rise in the heat treatment, so that the grain refinement cannot be obtained particularly in the product portion near the flash portion. On the other hand, if the hot forging start temperature is less than 350 ° C, the forging process itself becomes difficult.

After forging, the required strength and toughness,
T6 (artificial age hardening treatment to obtain maximum strength after solution treatment) to obtain corrosion resistance, T7 (excess aging treatment beyond artificial age hardening treatment condition to obtain maximum strength after solution treatment), T8
After the solution treatment, cold working is performed, and further, tempering treatment such as artificial age hardening treatment for obtaining maximum strength is appropriately performed. For the homogenization heat treatment and the solution heat treatment, an air furnace, an induction heating furnace, a glass stone furnace, etc. are appropriately used. Further, for the artificial age hardening treatment, an air furnace, an induction heating furnace, an oil bath or the like is appropriately used. Cooling after the solution treatment is preferably water cooling. When the cooling rate becomes low, Mg ₂ Si, Si, etc. are precipitated on the grain boundaries, and the grain boundary fracture easily occurs in the product after artificial aging, and the toughness and fatigue properties are lowered. In addition, stable phases Mg ₂ Si and Si are formed in the grains during cooling, and the amount of β ^′ phase and β ^″ phase that precipitate during artificial aging decreases, so the strength decreases. On the other hand, when the cooling rate is high, the amount of quenching strain is large, which necessitates a new straightening step after quenching or increases the number of steps in the straightening step. Therefore, in order to shorten the product manufacturing process and reduce the cost, quenching strain is reduced.
Quenching in warm water at ~ 85 ° C is preferred. Where the hot water quenching temperature is
If it is less than 50 ° C, the quenching strain becomes large, and if it exceeds 85 ° C, the cooling rate becomes too low, and the toughness, fatigue property and strength become low.

In the T7 material, the proportion of β ^′ phase precipitated on the grain boundaries is high. This β ^' phase is difficult to elute in a corrosive environment, reduces intergranular corrosion susceptibility, and enhances stress corrosion cracking resistance. On the other hand, the β ^″ phase, which is often precipitated in the T6 material, is likely to be eluted in a corrosive environment, which increases the intergranular corrosion susceptibility and reduces the stress corrosion cracking resistance. Therefore, by using the T7 material as the Al alloy forged material, the proof stress is slightly lowered, but the corrosion resistance is higher than the other temper treatments.

In order to eliminate the cast structure remaining in the Al alloy forged material and further improve the strength, toughness and fatigue characteristics, the Al alloy ingot is subjected to homogenizing heat treatment, and then extruded or rolled, and then the forging is performed. You can go.

[0086]

EXAMPLES Next, examples of the present invention will be described. The Al alloy ingots with the chemical composition shown in Table 1 (Al alloy cast materials, all of which are round bars with a diameter of φ82 mm) were
It was cast at a cooling rate of ℃ / sec. Then, the outer surface of this ingot is chamfered to a thickness of 3 mm and cut to a length of 500 mm, and
As shown in Fig. 1, two types of forgings were produced by varying the homogenizing heat treatment conditions (temperature and time) and the forging start temperature.

Of the two types, one of the forged materials was for mechanical property evaluation, and was free forged to have a thickness of 2 mm as shown in the plan view in FIG.
A disc-shaped forged material 1b of 5 mm was produced. This disc-shaped forging 1b
The processing rate from the ingot was intentionally lowered so that the processing rate was less than 75%, which is low.

The other forging material was for evaluating the microstructure and corrosion resistance, and was mechanically forged using the upper and lower molds shown in FIG.
As shown in FIG. 3, a round bar-shaped forging 1a with a flash 3 and a product diameter of 50 mm was produced. The heating time up to the homogenizing heat treatment temperature was 1 to 4 hours.

Next, these Al alloy forged materials were commonly subjected to solution treatment at 550 ° C. for 3 hours using an air furnace, followed by quenching in hot water at 60 ° C., and within 30 minutes thereafter, 180
Artificial aging treatment was performed at 5 ° C for 5 hours to obtain T6 material. In addition,
The temperature rising time to the solution heat treatment temperature was 1 to 2 hours.

From the disc-shaped forged material 1b shown in FIG. 5, tensile test pieces A (L direction) and Charpy test pieces B (L
Five samples each in the T direction) were sampled, and the average values of tensile strength (MPa), 0.2% proof stress (MPa), elongation (%), and Charpy impact value were measured. The results are shown in Table 2.

Furthermore, from the round bar-shaped forging material 1a shown in FIG.
The cut surface 5a is used for observing the structure such as the crystal grain size in the direction perpendicular to the parting surface in the structure of the cut surface 5a between the product and the flash.
A test piece D (L direction) was taken from a nearby product section as shown in FIG. 4, which is an enlarged view of FIG. In addition, as shown in Fig. 3, for the stress corrosion cracking test, from the product part near the cut surface 5a.
C-ring test pieces were collected.

Then, the maximum crystal grain size of the texture of the cut surface 5a in a direction perpendicular to the mold splitting surface, the average size of the dispersed particles of 50 Å or more in the crystal grains of the texture of the cut surface 5a, and the dispersed particle of 50 Å or more The density and the form of precipitates existing on the grain boundaries of the texture of the cut surface 5a (average grain size μm and average interval μm) were measured. Each of these measurement conditions was as described above. These results are also shown in Table 2, and the Al alloy numbers in Table 2 correspond to those in Table 1. Among the examples of evaluation of the mechanical properties, those having low mechanical properties were not subjected to the structure observation or the stress corrosion cracking test.

A stress corrosion cracking test was conducted using the C ring test piece. The stress corrosion cracking test conditions are as described above.
C-ring specimens were tested according to the ASTM G47 Alternate Dipping Method. However, the test conditions further simulate that the forged material is used with tensile stress applied to the cut surface 5a in the ST direction, and the mechanical properties are tested in the ST direction of the C ring test piece. A stress of 75% of the yield strength of the piece in the L direction was applied. In this state, the C-ring test piece was repeatedly immersed in salt water and pulled up for 90 days to confirm whether or not stress corrosion cracking occurred in the test piece. These results are × when stress corrosion cracking occurs, but not stress corrosion cracking,
△ indicates that intergranular corrosion that is likely to lead to stress corrosion cracking has occurred, and that no stress corrosion cracking or intergranular corrosion has occurred (including cases where surface general corrosion has occurred). Table 2 shows as ○.

As is clear from Table 2, the chemical composition of No. 1 to No. 7 in Table 1 is within the scope of the present invention, and the cut surface of the T6 material is
Inventive Examples Nos. 1 to 7 in which the maximum crystal grain size in the direction perpendicular to the parting plane in the structure of 5a is 400 μm or less are all excellent in stress corrosion cracking resistance.

Inventive Examples Nos. 1 to 7 have small dendrite secondary arm intervals (DAS) of the ingot of 30 μm or less, the average size and density of the dispersed particles in the crystal grains of the cut surface 5a, and the cutting Satisfying the preferred conditions of the average grain size and average spacing of the precipitates present on the grain boundaries of the structure of the surface 5a, even if the processing rate from the ingot is low, the average value of the proof stress (σ _0.2 ) is 300 MPa.
Above, and the average value of Charpy impact value is 10 J / cm ² or more, high strength and high toughness are secured.

On the other hand, as is clear from Tables 1 and 2,
As is clear from Tables 1 and 2, even in the chemical composition within the scope of the present invention, a comparative example in which the maximum crystal grain size in the direction perpendicular to the parting plane in the structure of the cut surface 5a in the T6 material exceeds 400 μm Nos. 9, 10, and 11 are all inferior in stress corrosion cracking resistance.

In addition, Comparative Example N in which the homogenizing heat treatment temperature and the hot forging start temperature are out of the preferred ranges or have the upper and lower limits, respectively.
o.8, 9, 10, 11, 14 and Comparative Example No. in which the amount of Mg is out of the lower limit.
13, Comparative Example No. 15 in which the amount of Mn deviates from the upper limit, and Comparative Example No. 12 in which the secondary dendrite arm interval (DAS) of the ingot exceeds 30 μm, the proof stress (σ _0.2 ) or Charpy impact value, elongation, etc. The mechanical properties of are significantly inferior to the invention examples.

Therefore, from these results, the present invention Al
The critical significance of requirements for alloy forging structure and preferable manufacturing conditions can be understood.

[0099]

[Table 1]

[0100]

[Table 2]

[0101]

EFFECTS OF THE INVENTION According to the present invention, stress corrosion cracking does not occur in the portion of the structure of the cut surface between the product of the Al alloy forged material and the flash even under the severe use environment, and high strength,
It is possible to provide an Al alloy forged material having high toughness and a material for forged material. Therefore, the use of the Al-Mg-Si based Al alloy forged material for transport aircraft can be expanded, which is of great industrial value.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a macrostructure of a ST-direction cross section of a structure portion defined by an Al alloy forged material of the present invention.

FIG. 2 is a cross-sectional view showing an Al alloy forging die of the present invention.

FIG. 3 is an Al showing a test piece collection site in an example of the present invention.
It is a perspective view of an alloy forging material.

FIG. 4 is a partially enlarged view of FIG.

FIG. 5 is an Al showing a test piece sampling site in the example of the present invention.
It is a top view of an alloy forged material.

FIG. 6 is a structural diagram showing a distribution state of dispersed particles in the Al alloy forged material of the present invention.

[Explanation of symbols]

1: Al alloy forged material, 2: Product part, 3: Flash, 4: Molding surface, 5: Flash cutting line, 6: Metal flow, 7: Upper mold,
8: Lower mold, 9: Gutta, 10: Flash stand,

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 624 C22F 1/00 624 630 630A 630Z 631 631Z 682 682 691 691B (72) Inventor Hiroki Sawada Mie 1100 Umeto, Daian-cho, Oita-cho, Kenben-gun Inside the Daian Plant of Kobe Steel Co., Ltd.

Claims (12)

[Claims] Claims: 1. Contains Mg: 0.6-1.8%, Si: 0.4-1.8%, Mn: 0.01-0.6%, Cr: 0.1-0.2% and Zr: 0.1-0.2%.
The aluminum alloy forged material containing one or two or more of the above, and the balance Al and unavoidable impurities, and the 0.2% proof stress of the aluminum alloy forged material after artificial aging treatment is 300M.
Pa or more and Charpy impact value is 10 J / cm ² or more,
Further, in the structure of the cut surface between the product and the flash, the crystal grain size in the direction perpendicular to the mold splitting surface, and the maximum grain size is 400 μm or less. Aluminum alloy forged material with excellent stress corrosion cracking. 2. The forged material is an aluminum alloy ingot
The aluminum alloy forging material excellent in stress corrosion cracking resistance according to claim 1, which is obtained by hot forging after homogenizing heat treatment at a temperature of 500 to 550 ° C. 3. The stress corrosion cracking resistance according to claim 1 or 2, wherein the forged material is obtained by hot forging an aluminum alloy ingot after homogenizing heat treatment at a starting temperature of 350 to 450 ° C. Aluminum alloy forgings. 4. The average grain size of crystal precipitates existing on the crystal grain boundaries of the forged material structure is 1.2 μm or less, and
The average interval between these crystal precipitates is 3.0 μm or more, and further, the average size of dispersed particles in the crystal grains is 1100 Å or less, and there are 10 or μm ³ or more dispersed particles having a size of 50 Å or more. An aluminum alloy forged material excellent in stress corrosion cracking resistance according to any one of claims 1 to 3. 5. The stress corrosion cracking resistance according to any one of claims 1 to 4, wherein the forged material is an ingot cast such that a secondary dendrite arm interval (DAS) is 30 μm or less. Excellent aluminum alloy forging material. 6. The forged aluminum alloy material having excellent resistance to stress corrosion cracking according to claim 5, wherein the ingot is extruded or rolled and then forged. 7. The stress resistance according to claim 1, wherein the forged aluminum alloy material is used by applying tensile stress in the ST direction to the structure of the cut surface between the product and the flash. Aluminum alloy forged material with excellent corrosion cracking resistance. 8. The aluminum alloy forging material excellent in stress corrosion cracking resistance according to any one of claims 1 to 7, wherein the forging material has a portion having a hot forging rate of less than 75%. 9. The aluminum alloy forging material excellent in stress corrosion cracking resistance according to claim 1, wherein a thickness of a cut surface between the product of the aluminum alloy forging material and the flash is 30 mm or more. . 10. The aluminum alloy forged material excellent in stress corrosion cracking resistance according to claim 1, wherein the aluminum alloy forged material is used for a structural material of a transportation machine. 11. The forging material according to any one of claims 1 to 10, which is made of an aluminum alloy ingot and contains Mg: 0.6 to 1.8%, Si: 0.4 to 1.8%. ,
Furthermore, Mn: 0.1-0.6%, Cr: 0.1-0.2% and Zr: 0.1-0.2%
For aluminum alloy forgings excellent in stress corrosion cracking resistance, characterized in that the dendrite secondary arm spacing in the ingot structure is 30 μm or less, including the balance Al and unavoidable impurities. Material. 12. The material for an aluminum alloy forging material excellent in stress corrosion cracking resistance according to claim 11, wherein the aluminum alloy ingot is further processed by hot extrusion or hot rolling.