JPH07252573A - Al-zn-mg-cu alloy excellent in toughness and its production - Google Patents

Abstract

PURPOSE:To produce an Al-Zn-Mg-Cu alloy excellent in toughness, contg. specified amounts of Zn, Mg, Cu, Fe, Si, Cr or the like, by executing hot rolling or the like after continuous casting and specifying the cooling rate at the time of solidification. CONSTITUTION:An Al alloy contg., by weight, 1 to 7% Zn, 0.5 to 3.0% Mg, 0.2 to 3.0% Cu, 0<Fe<=0.8 and 0<Si<=0.8, contg. one or more kinds among 0.05 to 0.3% Cr, 0.05 to O.4% Mn, 0.05 to 0.3% Zr and 0.03 to 0.3% Ti, and the balance Al is used. This alloy is subjected to hot rolling after continuous casting or subjected to hot rolling and cold rolling and is furthermore subjected to heat treatment to regulate the maximum length of insoluble compound grains contg. Fe and Si to <=2mum and the volume fractional rate to <=2.0%. For regulation in such manner, the continuous casting is executed under the conditions in which the cooling rate R ( deg.C/sec) at the time of solidification satisfies R>=5 and R>=7.5 ([Fe]+[Si])+2, where [Fe] and [Si] denote the contents (%) of Fe and Si in the Al alloy.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to Al-Z having excellent toughness.
More specifically, the present invention relates to an n-Mg-Cu alloy and a method for producing the same, which is a high-strength Al alloy suitable for structural members that require high strength in aircraft, railway vehicles, sports equipment, etc., and has excellent toughness. The present invention relates to an Al alloy and a manufacturing method thereof.

[0002]

2. Description of the Related Art Al is a typical high strength Al alloy.
Duralumin, which is a -Cu-Mg-based alloy, may be mentioned.
The Cu-based alloy is called super duralumin, which is JIS standard 7
075 alloy, 7175 alloy, 7475 alloy, etc. have been developed. The above Al-Cu-Mg-based alloy and Al-Zn-
The high-strength characteristics of duralumin-based alloys such as Mg-Cu-based alloys are obtained by age-hardening, and in producing this, first, an ingot is cast, and if necessary, homogenization treatment is performed at high temperature. A general method is to forge sufficiently to remove the cast structure, and then perform quenching after solution treatment and then perform aging treatment.

However, the duralumin-based alloy has low toughness, and especially in the sheet thickness direction (ST
There is a problem that the toughness in the (direction) is significantly lower than that in the processing direction (L direction) and the width direction (LL direction). This is due to the fact that the insoluble compound in the alloy extends in the working direction and becomes continuous, and acts as a sharp notch. The above-mentioned insoluble compound is a compound containing impurities such as Fe and Si remaining during Al refining, and does not form a solid solution in the alloy even if the treatment temperature in the homogenization treatment or the solution treatment is increased to form particles. It is a compound that crystallizes out.

As a means for improving the toughness of such a duralumin alloy, Fe, which causes the insoluble compound, is used.
A possible method is to limit the content of impurity elements such as Si and Si as much as possible. For example, in the JIS standard, the amount of Fe in the 2014 alloy is specified to be 0.7% or less and the amount of Si is 0.5 to 1.2%. In JP-A-55-47371, Fe as an impurity is specified. A method of limiting the content to 0.15% or less and Si to 0.1% or less is disclosed. However, limiting the contents of Fe and Si, which are inevitable impurities, as much as possible requires Al ingot with extremely high purity, resulting in high cost and poor practicability.

[0005]

The present invention has been made in view of the above circumstances, and is an unavoidable impurity Fe.
Provide an Al-Zn-Mg-Cu-based alloy excellent in toughness even in the ST direction after rolling and a manufacturing method thereof by improving the manufacturing method even if the content of Al and Si is similar to the conventional one. It is what

[0006]

The Al-Zn-Mg-Cu alloy according to the present invention, which has been able to solve the above-mentioned problems, includes: Zn: 1 to 7% Mg: 0.5 to 3.0% Cu : 0.2 to 3.0% Fe: 0.8% or less (0% is not included) Si: 0.8% or less (0% is not included), and Cr, Mn, Zr and Ti are satisfied. One or more selected from the group consisting of Cr: 0.05 to 0.3% Mn: 0.05 to 0.4% Zr: 0.05 to 0.3% Ti: 0.03 to 0. In an Al alloy containing 3% by weight and the balance being Al and inevitable impurities, hot rolling is performed after continuous casting, or hot rolling and cold rolling are performed together with heat treatment,
The maximum length of insoluble compound particles containing Fe and Si is 2 μm
The gist of the invention is to control the volume fraction to 2.0% or less.

As one of the preferred means for producing the above Al-Zn-Mg-Cu alloy, the present invention has a cooling rate R during solidification R ≧ 5 (1) R ≧ 7.5 ( [Fe] + [Si]) + 2 (2) where R: cooling rate during solidification (° C./sec) [Fe], [Si]: Fe and Si content (%) in the Al alloy It is intended to provide a method of hot-rolling immediately after being continuously cast under a condition satisfying the conditions, in a state where the slab is kept at a hot-rolling temperature or higher, or after being adjusted to the hot-rolling temperature. The recommended range represented by the conditional expressions (1) and (2) is such that the value of [Fe] + [Si] is 0.4 as shown in FIG.
% Or less, according to the equation (1), [Fe] + [S
When the value of i] exceeds 0.4%, it means that it is defined by the equation (2).

[0008]

The present inventors have conducted extensive studies on the problem of improving the toughness of Al-Zn-Mg-Cu alloys, and as a result, Al-Z containing Fe and Si to some extent has been found.
Even if it is an n-Mg-Cu-based alloy, Fe is produced by continuous casting.
And Si are forced to form a solid solution in the alloy, the maximum length of the insoluble compound particles containing Fe and Si is 2 μm or less, and the volume fraction thereof is controlled to 2% or less. It was found that the toughness in the subsequent ST direction can also be improved. Furthermore, in order to control the maximum length and volume fraction of the insoluble compound particles, it is best to control the cooling rate during solidification in the continuous casting process within a certain condition to force Fe and Si to form a solid solution in the alloy. The present invention has been completed by identifying the above method. First, the reasons for limiting the component composition according to the present invention will be described below.

Zn: 1 to 7% Mg: 0.5 to 3.0% Cu: 0.2 to 3.0% Zn, Mg and Cu are fine precipitates of 1 μm or less such as MgZn ₂ and Al ₂ CuMg. Is an element that forms a large amount and greatly contributes to the improvement of strength. Even if any one element of Zn, Mg and Cu is less than the lower limit value of the above component range, sufficient strength cannot be obtained, while Zn, Mg and Cu are not obtained.
If any one of these elements exceeds the upper limit of the above component range, the maximum length of the insoluble compound particles containing Fe and Si exceeds 2 μm to form coarse crystallized substances, which lowers the toughness. Therefore, Zn, Mg, and Cu must all satisfy the above component ranges.

The lower limit of Zn is more preferably 2
% Or more, more preferably 3% or more, while the upper limit is preferably 6% or less, more preferably 5.5% or less. Mg
The lower limit is more preferably 0.8% or more, still more preferably 1% or more, while the upper limit is preferably 2.5% or less, further preferably 2% or less. The lower limit of Cu is more preferably 0.5% or more, further preferably 1% or more, while the upper limit is preferably 2.5% or less, more preferably 2% or less.

Cr: 0.05-0.3% Mn: 0.05-0.4% Zr: 0.05-0.3% Ti: 0.03-0.3% In the Al alloy of the present invention, By containing at least one of the above four metal elements within the above range, A
It is possible to refine the crystal grains of the 1-alloy and improve the toughness. Moreover, the above four kinds of metal elements are combined with Al to form 0.1
The formation of fine precipitates of about 0.5 μm also contributes to the improvement of strength. However, if the content is too small, the effect of improving toughness and strength is not sufficient, and if the content is too large, coarse crystallized substances are formed and the toughness is reduced. Therefore, the Cr content is 0.05 to 0.3% and the Mn content is 0.1%.
05-0.4%, Zr amount is 0.05-0.3%, and Ti amount is 0.03-0.3%.

The lower limit of Cr is more preferably 0.08% or more, further preferably 0.1% or more, while the upper limit is preferably 0.25% or less, more preferably 0.2.
% Or less. The lower limit of Mn is more preferably 0.1% or more, still more preferably 0.2% or more, while the upper limit is preferably 0.35% or less, further preferably 0.3%.
It is the following.

The lower limit of Zr is more preferably 0.
08% or more, more preferably 0.1% or more, while the upper limit is preferably 0.25% or less, more preferably 0.2% or less. Further, the lower limit of Ti is more preferably 0.05% or more, still more preferably 0.07% or more, while the upper limit is preferably 0.2% or less, further preferably 0.1%.
It is 5% or less.

Fe: 0.8% or less (not including 0%) Si: 0.8% or less (not including 0%) Fe and Si are inevitable impurities remaining during Al refining and form an insoluble compound. Therefore, it is generally an undesirable element for Al alloys and is usually limited as much as possible. In the present invention, both the amount of Fe and the amount of Si are 0.8
%, But if it exceeds 0.8%, coarse and large amounts of insoluble compounds are formed, and the toughness is significantly reduced.

In the Al-Zn-Mg-Cu alloy according to the present invention, it is very important to control the maximum length of insoluble compound grains containing Fe and Si and the volume fraction thereof to obtain high toughness. Is. When the maximum length of the insoluble compound particles is 2 μm or less and the volume fraction thereof is 2.0% or less, excellent toughness is exhibited also in the ST direction after rolling. The maximum length of the insoluble compound particles is preferably 1.5 μm or less in order to obtain high toughness, and more preferably 1 μm or less. On the other hand, the volume fraction of the insoluble compound is preferably 1.5% or less, more preferably 1.0% or less.

The maximum length of the insoluble compound grains is, for example, a maximum diameter when a cut surface is formed so as to give a maximum diameter in the case of spherical or disc-shaped crystals, and is a substantially cubic or rectangular parallelepiped crystal. If there is a crystal with an unspecified shape, it means the length of the longest diagonal, if any, and the length between two points on the most distant surface. When measuring the maximum length of the insoluble compound particles, it may be calculated from the microscope field using an electron microscope.

In order to control the maximum length and volume fraction of the above-mentioned insoluble compound particles, Al which satisfies the above-mentioned component composition requirements.
The alloy is used, and the cooling rate R during solidification is the following equations (1) and (2) R ≧ 5 ... (1) and R ≧ 7.5 ([Fe] + [Si]) + 2. However, R: cooling rate during solidification (° C./sec) [Fe], [Si]: It is important to carry out continuous casting under conditions satisfying Fe and Si contents (%) in the Al alloy. .

That is, in the Al alloy of the present invention, the size and amount of the insoluble compound which adversely affects the toughness are limited by rapidly cooling during solidification by the continuous casting method to forcibly dissolve inevitable impurity elements such as Fe and Si. If the above conditions are satisfied, the maximum length of insoluble compound particles containing Fe and Si can be controlled to 2 μm or less and the volume fraction can be controlled to 2% or less. On the other hand, when the cooling rate at the time of solidification does not satisfy the above conditions, the impurity elements such as Fe and Si cannot be sufficiently forced to form a solid solution, and the maximum length and volume of the insoluble compound particles containing Fe and Si are The fraction cannot be controlled within the range of the present invention, and sufficient toughness cannot be obtained.

As described above, the recommended range represented by the conditional expressions (1) and (2) is such that the value of [Fe] + [Si] is 0.4%.
In the following cases, according to equation (1), [Fe] + [S
When the value of i] exceeds 0.4%, it means that it is defined by the equation (2). Thus, when the content of unavoidable impurity elements such as Fe and Si in producing the Al alloy according to the present invention is high, the cooling rate during solidification in the continuous casting process is increased according to the content, and It is desirable to control the maximum length and volume fraction of the compound grains.

The Al alloy of the present invention is continuously cast at a cooling rate under a specific condition using the Al alloy having the above-mentioned composition, and the maximum length and volume fraction of insoluble compound particles containing Fe and Si are determined. Excellent toughness can be obtained by controlling, and other production conditions are not particularly limited, but the following production methods can be exemplified.

First, an Al alloy having the alloy composition according to the present invention is used as a melt, and this melt is continuously cast. As the continuous casting method, a water-cooled continuous casting method, a twin roll type continuous casting method, a belt type continuous casting method, a block type continuous casting method, etc. can be adopted, but the transition time from the continuous casting to the hot rolling step It is preferable to adjust the timing after the inside of the slab has fallen below the solidus temperature and has completely solidified.

In the present invention, the temperature of the moving strip obtained by continuous casting is maintained at the hot rolling temperature or higher and hot rolling is immediately performed, and subsequently or once wound, it is sent to the cold rolling process. It is advantageously applied to continuous casting and direct-feed rolling, but in addition to this method, after continuous casting, it is temporarily held and sent to hot rolling before the slab temperature drops substantially, and further cold rolling is performed. Can also be applied.

When hot rolling is performed, the starting temperature is 450.
It is preferable to finish at a finishing temperature of 300 to 350 ° C. In the continuous casting method, a moving strip having a wall thickness of about 4 to 30 mm is usually continuously manufactured, and hot rolling is performed, and if necessary, cold rolling is performed to obtain a thickness of about 0.7 to 20 mm. It is rolled into a thick Al alloy plate. The rolling reduction is preferably 30% or more.

The hot-rolled or hot-rolled and cold-rolled Al alloy sheet is subjected to solution treatment, water-quenched, and then subjected to an aging treatment. As the conditions of the solution treatment, the treatment temperature is preferably 450 to 500 ° C., and the treatment time is preferably 1 to 8 hours. As the condition of the aging treatment, an aging temperature of 100 to 150 ° C. and 8 to 24 hours are preferable.

[0025]

【Example】

Examples 1 to 15 Using an Al alloy having the composition shown in Table 1 as a melt, a moving strip having a thickness of 20 mm was prepared by a continuous casting method, and immediately hot-rolled to obtain a plate having a thickness of 5 mm. The cooling rate during continuous casting was 12 ° C./sec, the rolling start temperature of the hot rolling was 450 ° C., and the finishing temperature was 350 ° C. The plate material was subjected to solution treatment at 480 ° C. for 4 hours, water quenching, and aging treatment at 120 ° C. for 24 hours.

With respect to the Al alloy plate thus obtained, the maximum length and volume fraction of the insoluble compound particles are obtained by observing with a scanning electron microscope and performing image analysis.
A fracture toughness test in the ST direction was performed. Further, the yield strength was measured by a tensile test to evaluate the strength. The results are also shown in Table 1.

Comparative Examples 1 to 15 Using Al alloy melts having the compositions shown in Table 2, Al alloy plates were obtained in the same manner as in Examples except for the conditions described below. The maximum length and volume fraction of the insoluble compound grains were determined by observing with a scanning electron microscope and image analysis, and a fracture toughness test in the ST direction was performed. Further, the yield strength was measured by a tensile test to evaluate the strength. The results are also shown in Table 2.

The Al alloy plates of Comparative Examples 1 and 2 were obtained in the same manner as in the Example except that the cooling rate during continuous casting was 3 ° C./sec. The plate does not satisfy the conditions for at least one element of the alloy composition according to the present invention.

With respect to these Al alloy plates for comparison, the maximum length and volume fraction of the insoluble compound particles were obtained by observing with a scanning electron microscope and image analysis.
A fracture toughness test in the T direction was performed. Further, the yield strength was measured by a tensile test to evaluate the strength. The results are also shown in Table 2.

[0030]

[Table 1]

[0031]

[Table 2]

As is clear from Table 1, in the Al alloy according to the present invention, the maximum length of the insoluble compound grains is 2 μm or less and the volume fraction is 2% or less.
It can be seen that the toughness in the direction is also high and the strength is high. Further, as is clear from Table 2, the comparative examples that do not satisfy any of the conditions according to the present invention are not sufficient in toughness or strength.

In the comparative example, No. 1 and No. 2 are different in continuous casting conditions, No. 1 has a maximum length of insoluble compound particles exceeding 2 μm, and No. 2 has a volume fraction of insoluble compound of 2%.
Therefore, the fracture toughness is low. No.3 is Zn
No. 5 is a comparative example when the amount of Mg is too small, No. 5 is a comparative example when the amount of Mg is too small, and No. 7 is a comparative example when the amount of Cu is too small. No.4 is Z
No. 6 is a comparative example when the amount of n is too large, No. 6 is a comparative example when the amount of Mg is too large, and No. 8 is a comparative example when the amount of Cu is too large, and the maximum length of the insoluble compound particles is 2 μm. Beyond that, the toughness is extremely low. No. 9 is Cr, Mn,
This is a comparative example when the amounts of Zr and Ti are both too small, and the toughness is poor. No. 10 to 13 are Cr, Mn, Zr
It is a comparative example when either of Ti and Ti is too large, and the maximum length of the insoluble compound particles exceeds 2 μm and the volume fraction exceeds 2%, and the toughness is extremely low.
Nos. 14 and 15 are comparative examples when the amount of inevitable impurities Fe or Si is too large, and the toughness is poor.

[0034]

The present invention is constituted as described above, and the maximum length of the insoluble compound particles in the Al-Zn-Mg-Cu alloy is set to 2 µm or less by the continuous casting method, and the volume fraction thereof is Since it is controlled to 2% or less, Al-Z
In addition to the high strength characteristic of the n-Mg-Cu alloy, its toughness can be improved, and Al-Z excellent in toughness.
It has become possible to provide an n-Mg-Cu based alloy and a manufacturing method thereof.

[Brief description of drawings]

FIG. 1 is a graph showing a preferable cooling rate condition during continuous casting used in the manufacturing method of the present invention.

Claims (4)

[Claims] 1. Zn: 1 to 7% (meaning% by weight, the same hereinafter unless otherwise specified) Mg: 0.5 to 3.0% Cu: 0.2 to 3.0% Fe: 0.8% The following (not including 0%) Si: 0.8% or less (not including 0%), and one or more selected from the group consisting of Cr, Mn, Zr and Ti, respectively, Cr: 0 0.05 to 0.3% Mn: 0.05 to 0.4% Zr: 0.05 to 0.3% Ti: 0.03 to 0.3%, with the balance being Al and unavoidable impurities In an Al alloy consisting of, hot rolling after continuous casting, or hot rolling and cold rolling and heat treatment,
The maximum length of insoluble compound particles containing Fe and Si is 2 μm
An Al-Zn-Mg-Cu-based alloy excellent in toughness, characterized in that the volume fraction is controlled to 2.0% or less. 2. The Al-Zn-Mg-Cu according to claim 1.
In producing a system alloy, the cooling rate R during solidification is R ≧ 5 and R ≧ 7.5 ([Fe] + [Si]) + 2 where R: cooling rate during solidification (° C./sec) [Fe ], [Si]: Fe and Si in the Al alloy are continuously cast under the conditions satisfying the content ratio (%), and then the slab temperature is maintained at the hot rolling temperature or higher and hot rolling is performed. And a method for producing an Al-Zn-Mg-Cu alloy having excellent toughness. 3. The method according to claim 2, wherein the continuously cast moving strip is immediately sent to the hot rolling step. 4. The manufacturing method according to claim 2, wherein the continuously cast slab is adjusted to a hot rolling temperature and sent to a hot rolling step.