JP2002294382A - High strength and high toughness aluminum forging having excellent corrosion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al alloy forging which has high strength and high toughness, and further has excellent corrosion resistance and durability. SOLUTION: The aluminum alloy forging has a composition containing, by mass, 0.6 to 1.8% Mg and 0.6 to 1.8% Si, and further containing one or two kinds selected from 0.1 to 0.2% Cr and 0.1 to 0.2% Zr, and in which the content of Cu is controlled to <=0.25%, Mn to <=0.05%, Fe to <=0.30%, and hydrogen to 0.25 cc/100 g Al or lower, respectively, and the balance Al with inevitable impurities. The average particle size of Mg2 Si and Al-Fe-Si-(Mn, Cr, Zr) that are crystallized and precipitated products present on the grain boundaries in the aluminum alloy structure is controlled to <=1.2 μm, further, the average spacing between the crystallized and precipitated products is controlled to >=3.0 μm, and further, the lowest value of the natural potential of the aluminum alloy forging is controlled to >=-1,020 mV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al alloy 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 toughness aluminum alloy forgings (hereinafter referred to as
(Al is simply called Al).

[0002]

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

[0003] Taking the structural material of the transport machine as an example, an Al alloy cast material or an Al alloy forged material is used from the viewpoint of reduction in manufacturing cost and processing into a part having a complicated shape. Of these, components requiring higher strength and mechanical properties such as higher toughness include Al
Alloy forgings are mainly used. Then, these Al alloy forgings are manufactured by subjecting an Al alloy casting to homogenizing heat treatment, hot forging such as mechanical forging, hydraulic forging, and the like, and then performing tempering treatment such as T6. Note that an extruded material obtained by once extruding a cast material may be used as the forged material.

In recent years, the structural materials of these transport aircraft have
There is a demand for thinner walls and higher strength, and there is a need for the forged Al alloy to have higher strength and higher toughness. However, JIS 60 currently used for these applications
In the case of the 00 series Al alloy, the strength is insufficient.

For this reason, improvement of the Al alloy material has been conventionally performed. For example, in Japanese Patent Application Laid-Open No. 06-256880, JIS 6000 series (A
l-Mg-Si system) Define the components such as Mg and Si of the cast material, reduce the average particle size of crystal precipitates (crystals and precipitates) to 8 μm or less, and set the dendrite secondary arm spacing (DAS)
It has been proposed to make Al alloy forgings higher in strength and toughness by reducing the diameter to 40 μm or less.

However, as shown in the embodiment of Japanese Patent Application Laid-Open No. 06-256880, the Al
The dendrite secondary arm spacing (DAS) of the forged alloy is very large, at most about 30 μm, even if it is small.

[0007] In an actual Al alloy forged material, the working ratio may be reduced depending on the size, shape, thickness, or part of the forged material component even by hot forging such as mechanical forging. For example, in the case of a shape such as an arm as a suspension component for an automobile, the machining rate may be as low as about 50%. Then, in a portion having a low working rate, a cast structure remains even after forging, and therefore, in particular, the toughness tends to necessarily be lower than other portions having a high working ratio.

Therefore, 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, a portion with a low processing rate is formed, and this portion is formed. In particular, the toughness of the Al alloy forged material is insufficient for an Al alloy forged material having low toughness. That is, in the above-described conventional technology, a high toughness value of the whole part cannot be obtained in a forged product in which a part having a low processing rate exists.

As a result, even if the DAS is reduced, the toughness cannot be attained with a forged product even if the DAS is reduced, and it is applied to structural materials that require higher strength and higher toughness as a whole. Inability to do so hindered the expansion of applications for transport aircraft structural materials.

On the other hand, the inventors of the present invention have forged aluminum alloy
Japanese Patent Application No. 10-238564 for higher strength and higher toughness
Therefore, Mg: 0.6 to 1.6% (mass%, the same applies hereinafter), Si: 0.8 to 1.
8%, Cu: 0.1-1.0%, Fe is regulated to 0.30% or less.
Mn: 0.15-0.6%, Cr: 0.1-0.2%, Zr: 0.1-0.
Contains 1% or more of 2%, with the balance being Al and inevitable
Forged aluminum alloy made of impurities, Mg_TwoS
i and total area of Al-Fe-Si- (Mn, Cr, Zr) system crystal precipitates
Rate is 1.5% or less per unit area, and the yield strength (σ _0.2Flat)
Average value is 350N / mm^TwoAnd the average of the Charpy impact values is
30J / cm^TwoHigh strength and high toughness Al alloy forging that can achieve the above
Proposed material.

According to the invention of Japanese Patent Application No. 10-238564, specific crystal precipitates, Mg ₂ Si and Al—, which are the starting points of the fracture of the forged Al alloy structure, out of the crystal precipitates of the Al alloy casting material. Fe-Si-M
n, Al-Fe-Si-Cr, Al-Fe-Si-Zr and other Al-Fe-Si- (Mn, C
(r, Zr) system by dispersing the crystal precipitates at an interval from each other (defined by the total area ratio of the crystal precipitates),
It ensures high toughness.

As described in Japanese Patent Application No. 10-238564, in the field of aluminum alloy forging, when increasing the strength of the forged material, it is usually necessary to increase the excess Si or increase the strength of the material such as Cu. Add elements.

[0013]

However, as described above, when excess Si is increased or a high-strength element such as Cu is contained, the grain boundary corrosion of the structure of the forged Al alloy is reduced. Another problem is that the susceptibility to corrosion and stress corrosion cracking is significantly increased and the corrosion resistance is reduced. The problem of deterioration of 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 transport aircraft are basically used without painting (bare), and the running or use environment of automobiles includes seawater and salt water, and ranges from low temperatures below freezing to high temperatures in midsummer. Until severe salt water corrosion environment. These structural materials are used under a salt water corrosive environment with a load, stress, or impact applied thereto. And these conditions are all intergranular corrosion and
Further, it is a factor that remarkably promotes stress corrosion cracking.

Further, in a structural material such as a transport machine, the structure is Al.
In addition to alloy forgings, it is often used in combination with other metallic materials that are nobler than Al alloys, or joined. When the forged Al alloy is used by being joined to another metal material that is more noble than the Al alloy, the use environment in which the intergranular corrosion and further the stress corrosion cracking are very likely to occur is Has become.

Further, depending on the use condition, a tensile stress may be applied at a specific portion of the product in a direction perpendicular to the forging line (corresponding to the ST direction in the plate material). In general, the toughness and stress corrosion cracking resistance at such sites are low, and mechanical failure and fracture due to corrosion first occur at such sites.

Therefore, even in such a severe use environment, as described above, even when a large amount of excess Si is included, or when a high strength element such as Cu is included,
Al alloy forgings have strict or contradictory required characteristics and technical problems that they do not generate intergranular corrosion or stress corrosion cracking and that they have high strength and high toughness.

Focusing on such circumstances, the present inventors have proposed, as Japanese Patent Application No. 11-285372, M.
g: 0.6 to 1.8% (mass%, the same applies hereinafter), Si: 0.6 to 1.8%, Cr: 0.1 to 0.2% and Zr: 0.1 to 0.2%, and Cu: 0.25 % Or less, Mn: 0.05% or less,
Fe: 0.30% or less, hydrogen: regulated to 0.25 cc / 100g Al or less, Mg ₂ Si or Al-Fe-Si- (consisting of the balance of Al and unavoidable impurities and present on the grain boundaries of the aluminum alloy structure) Mn,
The average grain size of the (Cr, Zr) -based crystal precipitates is set to 1.2 μm or less, and the average distance between these crystal precipitates is set to 3.0 μm or more.Al, which has high strength and toughness, and has excellent corrosion resistance and durability An alloy forging was proposed.

The present invention provides high-strength and toughness, further improved, in order to more reliably improve or guarantee the intergranular corrosion resistance and stress corrosion cracking resistance of the forged Al alloy, An object of the present invention is to provide an aluminum alloy forged material having excellent corrosion resistance and durability.

[0020]

In order to achieve this object, the gist of the forged aluminum alloy of the present invention is as follows: Mg: 0.6 to 1.8% (mass
%, The same applies hereinafter), Si: 0.6 to 1.8%, and further, Cr: 0.1 to
0.2% and Zr: Including one or two of 0.1 to 0.2%, Cu: 0.25% or less, Mn: 0.05% or less, Fe: 0.30% or less, Hydrogen: 0.25 cc / 100g Al or less, respectively regulated, The average particle size of Mg ₂ Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates consisting of the balance of Al and unavoidable impurities and existing on the grain boundaries of the aluminum alloy structure is reduced to 1.2 μm or less. At the same time, the average interval between these crystal precipitates is set to 3.0 μm or more, and the aluminum alloy forged material is used as an anode, and 5% Na at 30 ° C.
The minimum value of the natural potential of the forged aluminum alloy measured after DC electrolysis at 100 μA / cm ² for 30 minutes in a Cl aqueous solution is set to −1020 mV or more.

The aluminum alloy forged material of the present invention is obtained by subjecting an aluminum alloy ingot to a homogenizing heat treatment at a temperature of 530 to 595 ° C. and then hot forging to improve corrosion resistance, as described later. Is preferable (corresponding to claim 2). And, in order to obtain the required mechanical properties, the forged material is T6, T
It is preferable to be used after being subjected to a temper treatment at T7 and T8 (corresponding to claim 3).

Further, in order to increase the toughness of the aluminum alloy forging of the present invention, as described later, the dendrite secondary arm spacing
It is preferable to use an ingot cast so that (DAS) is 30 μm or less (corresponding to claim 4). Then, in order to increase the toughness of the Al alloy forging, it is also preferable to forge the ingot after working by extrusion or rolling.
Corresponding).

Further, the Al alloy forged material of the present invention is particularly suitable for an Al alloy forged material which has a portion where the working ratio from the ingot is less than 75% and whose toughness is apt to be reduced. ). Further, more preferably, it is suitable for an Al alloy forged material or a structural material of a transport machine, which is used by applying a tensile stress in a direction perpendicular to the forging line, in which the corrosion resistance is apt to be reduced. , 8
Corresponding).

According to the present invention, the use of a toughened Al alloy forged material under the above-mentioned severe corrosive environment,
Even in cases where excess Si is increased or a high strength element such as Cu is included, the composition is specified to improve the intergranular corrosion resistance and stress corrosion cracking resistance. Mg ₂ Si and Al-Fe-Si- (Mn, Cr, Zr) crystal precipitates
The average particle size of (crystals and precipitates) is 1.2 μm or less, and the average distance between these crystal precipitates is 3.0 μm or more.

For example, morphological control of crystal precipitates as disclosed in JP-A-06-256880, that is, merely reducing the average particle size of crystal precipitates in an ingot does not contribute much to improvement in toughness. The present inventors, contrary to the idea as described in JP-A-06-256880, even if the average particle size of the crystal precipitate is large,
It is dispersed at intervals (sparsely present)
If so, it contributes to improvement in toughness. In other words, even if the average particle size of the crystal precipitates is small, mechanical properties such as toughness are deteriorated in a state where the distance between the crystal precipitates is small and dense or connected.

That is, if Mg ₂ Si or Al—Fe—Si— (Mn, Cr, Zr) -based crystal precipitates are densely present on the grain boundaries, these crystal precipitates themselves and their surroundings elute, and the Corrosion and stress corrosion cracking are more likely to occur.

For this reason, in the present invention, it exists on the grain boundary.
Controls the morphology of Mg ₂ Si and Al-Fe-Si- (Mn, Cr, Zr) crystal precipitates. However, simply reducing the average particle size of the crystal precipitates present on the grain boundaries does not contribute much to improving stress corrosion cracking resistance and intergranular corrosion resistance. What is important for improving these corrosion resistances is Mg ₂ Si or Al-F
It is indispensable that e-Si- (Mn, Cr, Zr) -based crystal precipitates are dispersed (sparsely present) at intervals from one another. On the other hand, even if the average particle size of the crystal precipitates is small, it is necessary to prevent the stress corrosion cracking and intergranular corrosion from propagating along the grain boundaries in a state in which the distance between the crystal precipitates is small and dense or long. And the toughness is also reduced.

The size control of the crystal precipitates and the state in which the crystal precipitates are dispersed at intervals from each other (not in a state where the distance between the crystal precipitates is small and dense or connected). As a well-corresponding index, in the present invention,
The average particle size of the crystal precipitate and the average interval between the crystal precipitates are selected.

The above organizational improvement is the same as in Japanese Patent Application No. 11-285372. On the other hand, in order to ensure the intergranular corrosion resistance and stress corrosion cracking resistance of the Al alloy forged material, the present inventor, in addition to the above-described structural improvement, further performed an electrochemical Prescribe specific characteristics.

According to the present invention, an aluminum alloy forged material is used as an anode, as an electrochemical property corresponding to the actual intergranular corrosion and stress corrosion cracking.
In 5% NaCl aqueous solution at 30 ° C., 30 at 100 μA / cm ²
Select the spontaneous potential of the forged Al alloy measured after DC electrolysis for one minute.

The applicant of the present invention disclosed in Japanese Patent Application No. Hei 11-281 as to the natural potential of this Al alloy forged material, including a measuring method and a simple evaluation method of intergranular corrosion and stress corrosion cracking.
No. 149 filed on October 1, 1999.

The method for measuring the spontaneous potential of this Al alloy forged material is as follows.
Simulated in a saltwater corrosion environment such as seawater for transport aircraft structural materials
First, in a NaCl aqueous solution, forcible etching of a forged Al alloy material is performed by DC electrolysis, and
The minimum value of the spontaneous potential is measured by measuring the change over time of the spontaneous potential of the forged Al alloy in a Cl aqueous solution.
The tendency of the measured self-potential (the lowest value) corresponds well to the actual tendency of intergranular corrosion resistance and stress corrosion cracking resistance.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Average grain size and average spacing of crystal precipitates on grain boundaries. Next, the definition of the average diameter and the average interval of the crystal precipitate existing on the grain boundary in the present invention will be described more specifically. As defined in the present invention, Mg ₂ Si and Al-Fe-Si-
The (Mn, Cr, Zr) -based crystal precipitate is the same as the crystal precipitate defining the area ratio. In the present invention, as described above, in order to improve the toughness and stress corrosion cracking resistance and intergranular corrosion resistance of the Al alloy forged material, the average grain size of crystal precipitates present on these grain boundaries is determined. 1.2 μm or less,
The average distance between these crystal precipitates is 3.0 μm or more.

Mg ₂ Si and Al—Fe—Si— (Mn, C
(r, Zr) When the average distance between the crystal precipitates is less than 3.0 μm, even if the average particle diameter of the crystal precipitates is as small as 1.2 μm or less, the distance between the crystal precipitates is small and dense or connected, The toughness, stress corrosion cracking resistance and intergranular corrosion resistance cannot be improved. Further, even if the distance between the crystal precipitates is 3.0 μm or more, if the average particle size of the crystal precipitates exceeds 1.2 μm, the crystal precipitates will be in a dense or connected state, resulting in the toughness and stress resistance. Corrosion cracking and intergranular corrosion resistance cannot be improved.

The average grain size of these crystal precipitates and the average interval between the crystal precipitates were measured by examining the structure of the forged Al alloy with an optical microscope of about 400 times or a scanning electron microscope (SEM) of about 500 times.
EM) in order to take account of the variation in the material, the measurement is performed by visual observation or averaging the results of image analysis in 20 visual fields at arbitrary measurement points of the forged Al alloy material. The measurement is performed at each position where the surface from the forged material to the center is equally divided into 20.

Here, the average particle size of the crystal precipitates on the grain boundaries referred to in the present invention means Mg ₂ Si and Al—Fe—Si existing on the grain boundaries, which can be measured on the grain boundaries in each of the above-mentioned fields. -(Mn, Cr, Zr)
It refers to the average length of the systemic precipitate particles, and the average length measured in each visual field is averaged in the 20 visual fields.

The term "interval between crystal precipitates" as used in the present invention is obtained by dividing the length of a grain boundary measured in each visual field by the number of crystal precipitate particles observed on the grain boundary in each visual field. The values are averaged over the 20 visual fields.

(Spontaneous potential) FIG. 1 shows that various aluminum alloy forgings were used as anodes at 30 ° C. in a 5% NaCl aqueous solution.
An example of the change over time of the natural potential a of a forged aluminum alloy measured after DC electrolysis at μA / cm ² for 30 minutes is shown. In addition,
FIG. 1 shows a 6000 series (Al-Mg-Si series) in an example described later.
3 shows an example of a temporal change of a spontaneous potential in a NaCl aqueous solution after direct current electrolysis of an Al alloy forging.

The minimum value of the spontaneous potential of the Al alloy forged material in the present invention means, for example, 5 minutes (selected from 2 to 10 minutes) of the Al alloy forged material after the electrolytic treatment under the DC electrolytic conditions in FIG. of the values of the soaked natural potential a measured by a lowest potential a ₁ ~a _5.

A specific method for measuring the natural potential of the Al alloy forging is as follows.
In an electrolytic solution of NaCl under DC electrolysis conditions described below, for example,
It can be easily measured by using a known potentiometer with Hg / HgCl 2 as a reference or standard electrode.

The temperature and concentration conditions of the NaCl aqueous solution,
The reason why the conditions of the current density and the time of DC electrolysis are specified as one condition is that the measured value of the natural potential of the forged Al alloy has reproducibility. Although the natural potential can be measured even outside the above range, the measured value tends to vary when the natural potential is out of the range as defined in the invention.

In the above NaCl aqueous solution,
Just by measuring the change over time of the natural potential of an Al alloy forged material, the value of the measured natural potential (including the lowest value) is
It does not correspond to the actual tendency of intergranular corrosion or stress corrosion cracking of Al alloy forgings.

In the above-mentioned NaCl aqueous solution, forcibly etching of the forged Al alloy by direct current electrolysis,
By promoting the intergranular corrosion of the forged alloy, the tendency of the self-potential value (including the lowest value) measured thereafter tends to be better than that of the actual intergranular corrosion resistance and stress corrosion cracking resistance. Corresponding.

On the other hand, as described in the section on the anode melting method, it is known that intergranular corrosion of an Al alloy material is promoted by DC electrolysis using an Al alloy material as an anode. However, even with this known method of promoting intergranular corrosion, the actual
The evaluation itself of the intergranular corrosion resistance of the Al alloy material is performed by evaluating the area and depth of the intergranular corrosion portion of the Al alloy material. In other words, in the conventional technology, the degree of intergranular corrosion (evaluation of intergranular corrosion resistance) of an aluminum alloy forged material is consistently evaluated directly based on the corrosion state and volume of the intergranular corrosion part. I was

On the other hand, according to the present invention, the evaluation of the intergranular corrosion resistance of the forged Al alloy material is not performed based on the corrosion state or volume of the part where the intergranular corrosion is performed as in the above-described prior art, but is performed. Al
This is performed indirectly by the natural potential after DC electrolysis using the forged alloy as an anode.

It is not clear why the natural potential after DC electrolysis using an aluminum alloy forged material as an anode and the tendency of the lowest value of the natural potential correspond well to the actual tendency of intergranular corrosion resistance. It is assumed that: That is, when the intergranular corrosion resistance of the forged Al alloy occurs, the diffusion of ions is delayed at the leading end of the corrosion, so that the pH changes to acidic. When the pH changes to acidic, a phenomenon occurs in which the natural potential of the forged Al alloy decreases. In the present invention, since the measurement conditions are well understood (reflected) for the tendency of a decrease in the spontaneous potential of the Al alloy forging due to intergranular corrosion resistance, the Al alloy forging is used as an anode. It is presumed that the natural potential after DC electrolysis corresponds well to the actual tendency of intergranular corrosion resistance.

Incidentally, the stress corrosion cracking resistance of the forged Al alloy material in the environment of use of the transport machine corresponds uniquely to the intergranular corrosion property, and the intergranular corrosion resistance of the forged Al alloy material was evaluated. This leads to an evaluation of stress corrosion cracking resistance.

(Evaluation of Intergranular Corrosion by Natural Potential) Evaluation of intergranular corrosion by natural potential is based on the difference between the initial natural potential and the natural potential after the temporal change in the temporal change of the natural potential in FIG. It can be performed by the lowest value of the spontaneous potential after aging. More specifically, in FIG. 1, as in the examples described later, the minimum value a ₁
a ₂ is relatively high Al alloy forged material excellent in intergranular corrosion resistance, minimum a _3, a _4, a ₅ are relatively low Al natural potential after aging
Alloy forgings have poor intergranular corrosion resistance. Further, those having relatively high minimum values a ₁ and a ₂ of the natural potential after aging have a small difference from the initial natural potentials, and the minimum values a ₃ , a ₄ and a of the natural potential after aging are small. Those having a relatively low value of ₅ have a large difference from the initial self potentials.

Therefore, as shown in FIG. 1, the relationship between the intergranular corrosion and the change over time in the self-potential is determined for each type of Al alloy or each manufacturing history of heat treatment and the like. The intergranular corrosion resistance of the forged Al alloy can be evaluated based on the difference between the initial natural potential and the natural potential after aging, the minimum value of the natural potential after aging, and the like.

As described above, in the natural potential of the 6000 series (Al-Mg-Si system) Al alloy forged material after the change with time, the minimum value of the natural potential is larger than -1020 mV to -1020 m, as described above.
If the above mV (negative value is small) at a _1, a _2,
The 6000 series Al alloy forged material is excellent in actual intergranular corrosion resistance and stress corrosion cracking resistance. On the other hand, the minimum value of the self potential is-
If it is less than 1020 mV or less than −1020 mV (a large negative value) a ₃ , a ₄ , a ₅ , the actual intergranular corrosion resistance and stress corrosion cracking resistance of the 6000 series Al alloy forged material are reduced. are doing. Therefore, with the lowest value of this natural potential, forged material, plate material, shape material, etc., which have better corrosion resistance than forged material
It is possible to easily evaluate the intergranular corrosion resistance and stress corrosion cracking resistance of forged aluminum alloys.

(Ingot for Al alloy forging) The ingot for forging in the present invention has a dendrite secondary arm spacing (DAS) of 30 μm in order to ensure the toughness of the Al alloy forging.
It is preferable to set the following. As a result, the crystal grains of the Al alloy ingot and the Al alloy forged material are refined, and the Mg
₂ Reduce the total area ratio of Si and Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates and improve the toughness of forged Al alloy. If the dendrite secondary arm spacing (DAS) of this ingot becomes larger than 30 μm, the aluminum ingot is disclosed in Japanese Patent Application Laid-Open No. 06-256880.
Dendrite secondary arm spacing (DAS) of alloy forging is 30μ
As in the case of about m, when there is a part with a low processing rate from the ingot (when only the ingot is forged, or when the ingot is extruded or rolled and forged after rolling), Al It may not be possible to improve the toughness of the entire alloy forging.

The forged material includes a case where the ingot is directly hot forged, and a case where the ingot is once extruded or rolled and then hot forged. Therefore, the shape of the ingot includes an ingot such as a round bar, a slab shape, and a near net shape close to a product shape, and is not particularly limited.

(Chemical component composition of Al alloy forged material) Next, the chemical component composition of the Al alloy forged material of the present invention will be described. The Al alloy of the present invention is required to guarantee high durability such as high strength, high toughness and high corrosion resistance for use in 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 same as that of JIS 6000 Al alloy of Al-Mg-Si system.
(JIS 6101, 6111, 6003, 6151, 6061, 6N01, 6063, etc.)
Basically, Mg: 0.6-1.6%, S
i: 0.6-1.8%, Cr: 0.1-0.2% and Zr: 0.1
Including one or two of 0.2% or less, Cu: 0.20% or less, Mn: 0.05% or less, Fe: 0.30% or less, more preferably hydrogen: 0.25 cc / 100g Al or less, and the remaining Al and An Al alloy composed of unavoidable impurities.

However, even if the above-mentioned various properties are satisfied, even if the above-mentioned various properties are not satisfied, other elements for further improving the properties and adding other properties are not required. A change in the composition of the components, such as appropriately including Further, impurities that are inevitably mixed in from the raw material scrap and the like are allowed as long as the quality of the forged material of the present invention is not impaired.

(Amount of Each Element) Next, the critical significance and preferred range of the content of each element in the forged aluminum alloy of the present invention will be described.

Mg: 0.6-1.8%. Mg is precipitated as Mg ₂ Si (β ′ phase) together with Si by artificial aging, and is an essential element for imparting high strength (proof stress) when the final product is used. When the content of Mg is less than 0.6%, the age hardening amount decreases. On the other hand, if it is contained in excess of 1.8%,
The strength (proof strength) becomes too high, impairing forgeability. In addition, a large amount of Mg ₂ Si tends to precipitate during quenching after the solution treatment, and Mg ₂ Si or Al-Fe-Si- (Mn, C
The average particle size of (r, Zr) -based crystal precipitates is not more than 1.2 μm, and the average distance between these crystal precipitates cannot be more than 3.0 μm. Therefore, the content of Mg is 0.6
The range is ~ 1.8%.

Si: 0.6-1.8%. Si and Mg are combined with Mg ₂ Si (β '
Phase), resulting in high strength (proof stress) when the final product is used
Is an essential element for imparting If the content of Si is less than 0.6%, sufficient strength cannot be obtained by artificial aging. Meanwhile, 1.8%
When it is contained in excess of, coarse single Si particles are crystallized and precipitated during casting and during quenching after the solution treatment, and as described above, the corrosion resistance and toughness are reduced. Also,
Excess Si increases and Mg ₂ Si or Al-Fe-
The average particle size of Si- (Mn, Cr, Zr) -based crystal precipitates is set to 1.2 μm or less, and the average distance between these crystal precipitates is set to 3.0 μm.
μm or more, and high corrosion resistance and high toughness cannot be obtained. Further, workability is impaired, such as lower elongation. Therefore, it is preferable that the Si content is in the range of 0.6 to 1.8%, and in this range, the excess Si is reduced as much as possible in relation to the Mg content.

One or two types of Cr: 0.1-0.2% and Zr: 0.1-0.2%. These elements are dispersed particles such as Al ₁₂ Mg ₂ Cr, Al-Cr-based, and Al-Zr-based during homogenization heat treatment and subsequent hot forging.
(Dispersed phase). Since these dispersed particles have an effect of hindering the movement of the grain boundary after recrystallization, fine crystal grains and subcrystal grains can be obtained. Among these elements, Zr is an aluminum alloy having a size of several tens to several hundreds of angstroms.
Finer Al-Zr than dispersed particles of -Mn or Al-Cr
System-dispersed particles precipitate. For this reason, Zr in particular has a great effect of preventing the movement of the crystal grain boundaries and sub-crystal grain boundaries, making the crystal grains finer and sub-crystallizing, and has a great effect of improving the fracture toughness and the fatigue properties. If the content is too small, these effects cannot be expected, while excessive content of these elements will dissolve,
During casting, coarse Al-Fe-Si- (Mn, Cr, Zr) -based intermetallic compounds and crystal precipitates are easily formed, which is a starting point of fracture, and causes a decrease in toughness and fatigue properties. Therefore, Al-F
The total area ratio of e-Si- (Mn, Cr, Zr) -based crystal precipitates cannot be reduced to 1.5% or less, preferably 1.0% or less per unit area, and high toughness and high fatigue properties are obtained. Can not do.
Therefore, the content of each of these elements is Cr: 0.1 to 0.2
%, Zr: 0.1 to 0.2%.

Cu: 0.25% or less. Cu significantly increases the susceptibility of the structure of the Al alloy forging to stress corrosion cracking and intergranular corrosion, and lowers the corrosion resistance and durability of the Al alloy forging. Therefore, in the present invention, from this viewpoint, Cu
Regulate the content as low as possible. But on the other hand,
Cu contributes to improvement of strength by solid solution strengthening, and also has an effect of remarkably promoting age hardening of a final product during aging treatment. If the Cu content is reduced, it is necessary to use a high-purity ingot, and there is a problem that the casting cost is high. Therefore, Cu is allowed up to 0.25% or less.

Mn: 0.05% or less. Mn forms Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates.
Therefore, when the content of Mn is large, Al-F
The average particle size of the e-Si- (Mn, Cr, Zr) -based crystal precipitates and the average distance between the crystal precipitates cannot be in the ranges specified in the present invention. Therefore, in the present invention, the Mn content is regulated as small as possible from the viewpoint of ensuring high strength, high toughness and high corrosion resistance of the forged Al alloy. But on the other hand, Mn
As in the case of Cr and Zr, Al-Mn-based dispersed particles such as Al ₂₀ Cu ₂ Mn ₃ are generated during the homogenization heat treatment and during the subsequent hot forging, and the dispersed particles are used to form the recrystallized particles. This also has the effect of hindering field movement and obtaining fine crystal grains. Further, an increase in strength and Young's modulus due to solid solution can be expected. There is also a problem that casting cost is required to reduce the content of Mn. Therefore, Mn is allowed up to a content of 0.05% or less.

Fe: 0.30% or less. Fe contained as impurities in the Al alloy is Al ₇ Cu ₂ Fe, Al ₁₂ (F
(e, Mn) ₃ Cu ₂ , (Fe, Mn) Al ₆ , or coarse Al—Fe—Si— (Mn, Cr, Zr) -based crystal precipitates of the present invention.
As described above, these crystal precipitates deteriorate the fracture toughness and the fatigue properties. In particular, the content of Fe is 0.30%,
More strictly, if it exceeds 0.25%, Al-Fe-Si- (Mn, Cr, Z
r) The total area ratio of the system crystal precipitates is 1.5% per unit area.
Below, preferably, it cannot be made 1.0% or less, and it is not possible to obtain higher strength and higher toughness required for a structural material of a transport machine or the like. Therefore, the content of Fe is preferably 0.30% or less, more preferably 0.25% or less.

Hydrogen: 0.25 cc / 100 g Al or less. Hydrogen (H ₂ ), especially when the degree of work of the forged material is reduced,
Bubbles due to hydrogen are not pressed by forging or the like but serve as starting points for destruction, so that toughness and fatigue characteristics are significantly reduced. And, in the structural material of the transport machine with the increased strength, the influence of hydrogen is particularly large. Therefore, hydrogen is 0.25 c
c / 100g Al should be as low as possible.

Zn, Ti, B, Be, V, etc. Zn, Ti, B, Be, V and the like are elements that are selectively contained depending on the purpose. Zn: 0.005 to 1.0%. Zn achieves high strength by precipitating MgZn ₂ finely and at high density during artificial aging. Further, the solid solution Zn lowers the potential in the grains, and the effect of reducing the intergranular corrosion and stress corrosion cracking as a result can be expected because the corrosion form is not the grain boundary but the entire surface 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, when the content exceeds 1.0%, the corrosion resistance is significantly reduced. Therefore, the content of Zn is 0.005
It is preferably in the range of 1.0% 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 reduced. Therefore, Ti
Is preferably in the range of 0.001 to 0.1%.

B: 1 to 300 ppm. B refines the crystal grains of the ingot, like Ti, extrudes, rolls,
It is an element added to improve workability during forging. However, if the content of B is less than 1 ppm, this effect cannot be obtained. On the other hand, if the content of B exceeds 300 ppm, coarse crystalline precipitates are also formed and the processability is reduced. Therefore, the content of B is preferably in the range of 1 to 300 ppm.

Be: 0.1 to 100 ppm. Be is an element contained to prevent re-oxidation of the Al melt in the air. However, if the content is less than 0.1 ppm,
If this effect cannot be obtained, on the other hand, if the content exceeds 100 ppm, the hardness of the material increases and the workability decreases. Therefore, the content of Be is preferably in the range of 0.1 to 100 ppm.

V: 0.15% or less. V forms dispersed particles (dispersed phase) during homogenizing heat treatment and subsequent hot forging, like Mn, Cr, and Zr. Since these dispersed particles have an effect of hindering the movement of the grain boundary after recrystallization, fine crystal grains can be obtained. However, excessive content tends to generate coarse Al-Fe-Si-V-based intermetallic compounds and crystal precipitates during melting and casting, becomes a starting point of fracture, and lowers toughness. Therefore, when V is contained, the content should be 0.15% or less.

(Method of Manufacturing Al Alloy Forging) Next, a preferred method of manufacturing an Al alloy forging according to the present invention will be described. The production of the forged Al alloy in the present invention itself can be carried out by an ordinary method. For example, when casting an Al alloy melt that has been melt-adjusted within the range of the above-mentioned Al alloy components, for example, a normal melt casting such as a continuous casting rolling method, a semi-continuous casting method (DC casting method), and a hot top casting method. Casting is performed by appropriately selecting a method.

However, the crystal grains of the Al alloy ingot were refined,
In addition, the average particle size of the Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates present on the grain boundaries, and the average interval between the crystal precipitates, in order to fall within the range specified in the present invention. , Al alloy melt at 10 ℃ / sec
It is preferable that the ingot is cast at the above cooling rate to form an ingot.
Also, by setting the cooling rate of the ingot to 10 ° C / sec or more, the dendrite secondary arm interval (DAS) of the ingot is set to 30 μm.
It can be: On the other hand, if the cooling rate is slower than this, the average particle size of the Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates present on the grain boundaries, the average interval between the crystal precipitates, according to the present invention. There is a possibility that the range cannot be specified and the crystal grains are coarsened, so that the dendrite secondary arm interval (DAS) of the ingot cannot be reduced to 30 μm or less.

Next, the homogenizing heat treatment temperature of the Al alloy ingot (cast material) is preferably in a temperature range of 530 to 595 ° C. The normal homogenizing heat treatment temperature of this type of Al alloy casting material is about 500 to 520 ° C., but in the present invention, as described above, in order to improve corrosion resistance and toughness, Al-Fe- The Si- (Mn, Cr, Zr) -based crystal precipitates are sufficiently dissolved to form a solid solution, and Mg present on the grain boundaries of the structure of the forged material after the tempering treatment.
₂ The average particle size of Si and Al-Fe-Si- (Mn, Cr, Zr)
In addition to 1.2 μm or less, the average interval between these crystal precipitates must be 3.0 μm or more.

For this purpose, the above-mentioned homogenization heat treatment at a high temperature of 530 to 595 ° C. is required, and when the homogenization heat treatment temperature is lower than 530 ° C., the Al—Fe—Si— (Mn, Cr, Zr) -based The average of Mg ₂ Si and Al-Fe-Si- (Mn, Cr, Zr) crystal precipitates on the grain boundaries of the structure of the forged material after tempering treatment, where the crystal precipitates are not sufficiently dissolved. It is difficult to reduce the particle size to 1.2 μm or less and to make the average spacing between these crystal precipitates 3.0 μm or more. On the other hand, if the homogenization heat treatment temperature exceeds 595 ° C., on the contrary, burning (melting damage) occurs in the Al alloy ingot (cast material) and cracks are likely to occur during hot working. In addition, there is a possibility that mechanical properties such as toughness and fatigue properties of the final forged material are significantly reduced.

After the homogenizing heat treatment, hot forging is performed by mechanical forging, hydraulic forging, or the like to form an Al alloy forged material having a final product shape (near net shape). Then, after forging, T6 to obtain necessary strength and toughness, corrosion resistance (artificial age hardening treatment to obtain maximum strength after solution treatment), T7
(After solution treatment, over-aging treatment beyond the artificial aging hardening conditions to obtain the maximum strength), T8 (after solution treatment, cold working, and then artificial aging hardening to further maximize the strength), etc. Temper treatment is performed appropriately. For the homogenization heat treatment and the solution treatment, an air furnace, an induction heating furnace, a nitrite furnace, or the like is appropriately used. Further, for the artificial age hardening treatment, an air furnace, an induction heating furnace, an oil bath and the like are appropriately used. In particular, in the T7 material, of the β ^′ phase and β phase (stable phase) precipitated on the grain boundaries,
The proportion of phases is higher. This β phase is easily eluted in a corrosive environment and enhances intergranular corrosion resistance and stress corrosion cracking resistance. On the other hand, the β ^' phase, which is largely precipitated in the T6 material, is easily eluted in a corrosive environment, and lowers intergranular corrosion resistance and stress corrosion cracking resistance.
Therefore, when the forged Al alloy is made of the T7 material, the proof stress is slightly lowered, but the corrosion resistance is higher than other tempering treatments.

In order to eliminate the cast structure remaining in the Al alloy forged material and to further improve the strength and toughness, the Al alloy ingot may be subjected to a homogenizing heat treatment, extruded or rolled, and then subjected to the forging. good.

[0075]

Next, an embodiment of the present invention will be described. An aluminum alloy ingot (Al alloy cast material, both round bars of φ68 mm diameter) with the chemical composition shown in Table 1 was subjected to hot-top casting at 20 ° C.
Casting was performed at a cooling rate of / sec. This ingot was subjected to a homogenizing heat treatment at a temperature of 550 ° C. for 8 hours, reheated to 400 ° C., and then spread hot forging by mechanical forging to produce a plate-shaped aluminum alloy forging material having a thickness of 20 mm. Next, the forged aluminum alloy was heated at a heating rate of 300 ° C./hr using an air furnace, and was heated to 540 ° C.
Solution cooling for 1 hour, then water cooling (water quenching)
Then leave at room temperature (20-30 ℃) for 1 hour, then 175 ℃
Aging treatment (T6 treatment) for × 8 hours was performed. Also, some
(Invention Example No. 11 in Table 2) was aged at 195 ° C for 5 hours (T7
Processing). The chemical composition of the ingot of Comparative Example No. 10 in Table 1 was the same as that of Inventive Example No. 2, but the temperature of the homogenization heat treatment was lowered to 470 ° C.

Then, test specimens were collected from each of the Al alloy forgings, and various investigations described below were conducted. The results are shown in Table 2. The numbers in Table 2 correspond to the numbers in Table 1, and are the same Al alloy forged material (Al alloy ingot). However, the table
Inventive Example No. 11 of No. 2 is not described in Table 1, but has the same chemical composition as that of Inventive Example No. 3 Al alloy ingot of Table 1. In addition, in order to clarify the direction of the test piece in each test, the most elongated longitudinal direction of the plate of the plate-shaped Al alloy forged material (test piece) is the L direction, the most compressed plate thickness direction is the ST direction, Said
The sheet width direction perpendicular to the L direction is called the LT direction.

(Crystal Precipitate on Grain Boundary) The average diameter of the crystal precipitates present on the grain boundaries of the Al alloy forged material structure and the average distance between the crystal precipitates were measured by a 400-fold optical microscope. went.
As described above, the measurement surface is subjected to a tensile stress in the thickness direction (corresponding to the ST direction) perpendicular to the forging line (L direction), and is likely to be broken due to mechanical breakage or corrosion. The central part of the LT-ST surface of the forged material (the surface that cuts through the plate). Then, at this central portion, the measurement was performed by averaging the visual observation results of the 20 visual fields at the measurement points. Table 2 shows the results.

(Grain Intergranular Corrosion Test) Next, test specimens were taken from the forged Al alloy and subjected to a grain boundary corrosion test. The corrosion test surface of the test piece was the same as the crystal precipitate measurement surface on the grain boundary, and for the same reason, the LT-ST surface (the propagation direction of corrosion was
L direction). The intergranular corrosion test was performed according to the JIS W 1103 method to evaluate intergranular corrosion. After this intergranular corrosion test,
(Cross section of test piece) was added to etching solution (2.5 ml of 70% concentrated nitric acid).
, Concentrated hydrochloric acid 1.5 ml, 48% hydrofluoric acid 1.0 ml, distilled water 95.
(Composition of 0 ml) for 10 seconds, washed with distilled water and dried, and the state of corrosion of the LT-ST surface was observed with a 200-fold metal microscope.

In the observation of intergranular corrosion, corrosion progresses along the crystal grain boundaries in the visual field of the microscope, being distinguished from other pitting corrosion, general corrosion, etc., and is typically determined to be intergranular corrosion. It was evaluated whether corrosion had occurred. These results are shown in Table 2 as x when grain boundary corrosion has occurred and as ○ when grain boundary corrosion has not occurred.

(Stress Corrosion Cracking Test) Similarly, a C-ring test piece having the LT-ST surface as the back surface was sampled from the forged Al alloy, and subjected to a stress corrosion cracking test. The stress corrosion cracking test conditions were performed in accordance with the provisions of the alternate immersion method using the ASTM G47 C ring. The test was conducted for 90 days with a stress of 75% of the proof stress in the LT direction of the test piece, and the presence or absence of stress corrosion cracking of the test piece was confirmed. The results are shown in Table 2 as x when stress corrosion cracking occurred and as ○ when stress corrosion cracking did not occur.

[0081] (Tensile Test) In addition, the tensile strength of the plurality collected specimen from Al alloy forging (sigma _B, MPa), yield strength
Mechanical properties such as (σ _0.2 , MPa), elongation (δ,%), and toughness = Charpy impact value (J / cm ² ) were measured. The longitudinal direction of the tensile test piece was the LT direction, and the tensile test was performed in the LT direction. The longitudinal direction of the Charpy impact test was the LT direction, and the L-ST plane was a fracture surface. Table 2 also shows these results.

Then, the lowest value of the spontaneous potential of the test piece taken from each of the Al alloy forgings was measured by the above-mentioned measuring method.
The measurement surface was the LT-ST surface. DC electrolysis is 5%
In the NaCl aqueous solution of the above, the test piece as an anode,
The electrolysis was performed at 30 ° C. and at 100 μA / cm ² for 30 minutes under DC electrolysis. Table 2 shows the minimum measured value of the natural potential of each of these Al alloy forgings.

As is clear from Table 2, the chemical composition within the range of the present invention from No. 1 to No. 5 in Table 1 was determined at a temperature of 550 ° C.
Invention Examples Nos. 1 to 5 and 11 after 8 hours of homogenizing heat treatment
Is Mg ₂ Si or Al-Fe-Si-
The average particle size of the (Mn, Cr, Zr) -based crystal precipitates is 1.2 μm or less, and the average distance between these crystal precipitates is 3.0 μm.
m or more. And, Al-Fe on the grain boundaries of these invention examples
Observation of the morphology of the -Si- (Mn, Cr, Zr) crystal precipitates confirmed that the crystal precipitates were small and that the crystal precipitates were finely dispersed at intervals.

Further, in each of the invention examples having such a structure, the minimum value of the spontaneous potential was commonly −1020 mV or more.

As a result, in each of the invention examples, the forging rate was 50%.
Even if it is low, the average strength (σ _0.2 ) is 300 MPa or more and the average Charpy impact value is 10 J / cm ² or more, ensuring high strength and high toughness. Incidentally, assuming that the invention examples Nos. 1 to 6 in Table 1 were the same as the other conditions, the hot forging with a forging rate of 75% was 350 MPa or more in average of the proof stress (σ _0.2 ) and the Charpy impact. An average value of 20 J / cm ² or more was obtained.

Further, it can be seen that Invention Examples Nos. 1 to 5 and 11 are also excellent in intergranular corrosion resistance and stress corrosion cracking resistance. In particular, Invention Example No.
No. 11 has a higher minimum value of the self potential than that of the invention example in which other T6 materials are used.

On the other hand, as is clear from Tables 1 and 2, Comparative Example No. 6 in which the amount of Cu deviated from the range of the present invention was relatively high (Al No. 6 in Table 1).
Alloy No.), Comparative Example No. 7 in which the amount of Fe was outside the range of the present invention.
(No. 7 Al alloy in Table 1), Comparative Example No. 8 in which the amount of Mn was outside the range of the present invention, (No. 8 Al alloy in Table 1), hydrogen amount out of the range of the present invention Comparative Example No. 9 (No. 9 Al alloy in Table 1)
Comparative Example No. 10 (No. 10 Al alloy in Table 1) in which the homogenization heat treatment temperature deviated from the preferred range of the present invention was lower than that of Mg ₂ Si or Al-Fe present on the grain boundaries. -Si- (Mn, Cr, Zr)
If the average size of the precipitates is larger than 1.2 μm,
Average spacing is small, less than 3.0 μm. Then, when the morphology of the Al-Fe-Si- (Mn, Cr, Zr) -based crystal precipitates of these comparative examples was observed in the same manner as in the invention example, the crystal precipitates were relatively large and connected long. Was doing.

In each of the comparative examples having such a structure, the lowest value of the spontaneous potential was commonly less than −1020 mV.

As a result, the average tensile properties of the whole Al alloy forged material were the same as those of the inventive example except for Comparative Example No. 10, but the average value of the Charpy impact value was Except for .6, it is less than 10 J / cm ² . These comparative examples are also significantly inferior in grain boundary corrosion resistance and stress corrosion cracking resistance, except for Comparative Example No. 9, to the invention examples. Accordingly, it can be seen that these comparative examples do not have any of the tensile properties, the Charpy impact value, and the corrosion resistance.
Therefore, it can be seen that these comparative examples cannot be used due to the problem of reliability as a structural material such as durability.

Therefore, from these results, it can be seen that the present invention Al
The critical significance of the requirements for the structure of the alloy forgings can be seen. Further, it can be seen that the minimum value of the natural potential of −1020 mV of the forged aluminum alloy of the present invention has a critical significance.

[0091]

[Table 1]

[0092]

[Table 2]

[0093]

According to the present invention, it is possible to provide an Al alloy forged material having high strength, high toughness and excellent corrosion resistance.
Therefore, the use of the Al-Mg-Si-based Al alloy forged material for a transport machine can be expanded, which is of great industrial value.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a change over time of a natural potential in a NaCl aqueous solution after direct current electrolysis of a forged Al alloy.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 C22F 1/00 630A 640 640D 682 682 691 691B 691C 692 692Z 694 694A (72) Inventor Yoshiyoshi Inagaki Ya 1100 Umedo, Oyasu-cho, Inabe-gun, Mie Prefecture Inside the Oyasu Plant of Kobe Steel, Ltd.

Claims (8)

[Claims] (1) Mg: 0.6 to 1.8% (mass%, the same applies hereinafter), S
i: 0.6-1.8%, Cr: 0.1-0.2% and Zr: 0.1
Including one or two kinds of up to 0.2%, Cu: 0.25% or less, Mn: 0.05% or less, Fe: 0.30% or less, hydrogen: 0.25 cc / 100g
Al 2 or less, Mg ₂ S which consists of Al and unavoidable impurities and exists on the grain boundaries of the aluminum alloy structure
i and Al-Fe-Si- (Mn, Cr, Zr)
2 μm or less, the average spacing between these crystal precipitates is 3.0 μm or more, and the aluminum alloy forged material is used as an anode, in a 5% NaCl aqueous solution at 30 ° C., 100 μA / cm ² at 30 μA / cm ² . A high-strength, high-toughness aluminum alloy forging with excellent corrosion resistance, characterized in that the minimum value of the natural potential of the aluminum alloy forging measured after DC electrolysis for one minute is at least −1020 mV. 2. The forging material comprises an aluminum alloy ingot.
The high-strength high-toughness aluminum alloy forged material having excellent corrosion resistance according to claim 1, which is obtained by hot forging after homogenizing heat treatment at a temperature of 530 to 595 ° C. 3. The high-strength, high-toughness aluminum alloy forged material having excellent corrosion resistance according to claim 1, wherein the forged material is used after being subjected to a tempering treatment at T6, T7, T8. 4. The high corrosion-resistant high forged material according to claim 1, wherein said forged material is an ingot cast so that a secondary dendrite arm spacing (DAS) is 30 μm or less. High strength tough aluminum alloy forging. 5. The high-strength and high-toughness aluminum alloy forged material having excellent corrosion resistance according to claim 4, wherein the ingot is processed by extrusion or rolling and then forged. 6. The high-strength, high-toughness aluminum alloy forging excellent in corrosion resistance according to claim 1, wherein the aluminum alloy forging has a portion where a working ratio from an ingot is less than 75%. Wood. 7. The high-strength and toughness excellent in corrosion resistance according to claim 1, wherein the forged aluminum alloy is used by applying a tensile stress in a direction perpendicular to the forging line. Forged aluminum alloy. 8. The high-strength, high-toughness aluminum alloy forging having excellent corrosion resistance according to claim 1, wherein the aluminum alloy forging is used for a structural material of a transport machine.