JPH07252574A - Al-cu-mg alloy excellent in toughness and its production - Google Patents

Abstract

PURPOSE:To produce an Al-Cu-Mg alloy excellent in toughness, contg. specified amounts of Cu, Mg, 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 having a compsn. contg., by weight, 2 to 7% Cu, 0.2 to 2.5% Mg, 0<Fe<=1.0% and 0<Si<=1.0%, contg. one or more kinds among 0.05 to 0.3% Cr, 0.05 to 0.8% 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 is subjected to heat treatment together with hot rolling and cold rolling to control the maximum length of insoluble compound grains contg. Fe and Si to <=2mum and the volume fractional rate to <=2.0%. For control 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]

The present invention relates to Al-C having excellent toughness.
More specifically, the present invention relates to a u-Mg 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 a manufacturing method thereof.

[0002]

2. Description of the Related Art Al is a typical high strength Al alloy.
-Cu-Mg-based alloy is known under the name of duralumin, and JIS alloy 2014 alloy, 2017 alloy, 202
4 alloys have been developed. The high-strength characteristics of the Al-Cu-Mg-based alloy are obtained by age hardening, and in producing this, first, an ingot is cast, and if necessary, homogenization treatment is carried out, and high temperature is sufficient. A general method is to forge and remove the cast structure, and then perform solution treatment, quenching, and aging treatment.

However, the Al-Cu-Mg-based alloy has low toughness, and in particular, the toughness in the sheet thickness direction (ST direction) after hot / cold working is the same in the working direction (L direction) and width direction (LL direction). ) Has a problem that it is significantly lower than 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 means F which remains during Al refining.
It is a compound containing impurities such as e and Si, and is a compound that does not form a solid solution in the alloy and crystallizes into particles even if the treatment temperature in the homogenization treatment or the solution treatment is increased.

As a means for improving the toughness of such an Al--Cu--Mg type alloy, a method of limiting the content of impurity elements such as Fe and Si, which cause the insoluble compound, as much as possible is considered. For example, according to the JIS standard, the amount of Fe in the 2014 alloy is 0.7% or less, and the amount of Si is 0.5 to 1.2%.
However, in JP-A-55-47371, Fe, which is an impurity, is 0.15% or less, and Si is 0.1%.
The methods limited below are 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.
The present invention aims to provide an Al-Cu-Mg-based alloy excellent in toughness in the ST direction after rolling and a method for producing the same by improving the production method even if the content of Si and Si is about the same as conventional ones. It is a thing.

[0006]

The Al-Cu-Mg alloy according to the present invention, which has been able to solve the above-mentioned problems, includes Cu: 2 to 7% Mg: 0.2 to 2.5% Fe: 1 0.0% or less (not including 0%) Si: 1.0% or less (not including 0%), and one or more selected from the group consisting of Cr, Mn, Zr and Ti, respectively. Cr: 0.05 to 0.3% Mn: 0.05 to 0.8% Zr: 0.05 to 0.3% Ti: 0.03 to 0.3%, with the balance being Al In an Al alloy consisting of and unavoidable 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-Cu-Mg alloy, the present invention has a cooling rate R during solidification of R ≧ 5 (1) R ≧ 7.5 ([Fe ] + [Si]) + 2 (2) However, R: cooling rate during solidification (° C / sec) [Fe], [Si]: Fe and Si contents (%) in the Al alloy are satisfied. It is intended to provide a method of hot-rolling immediately after the continuous casting under the conditions and holding the slab at a temperature higher than the hot-rolling temperature or after adjusting 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 intensive studies on the problem of improving the toughness of Al-Cu-Mg alloys, and as a result,
Al-Cu-M containing some Fe and Si
Even in the case of a g-based alloy, Fe and Si are forcibly solid-solved in the alloy by continuous casting, the maximum length of insoluble compound particles containing Fe and Si is 2 μm or less, and the volume fraction thereof is 2
It was found that when the content is controlled to be not more than%, the toughness in the ST direction after rolling can be improved without impairing the strength. 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.

Cu: 2 to 7% Mg: 0.2 to 2.5% Cu and Mg are elements that form fine precipitates of 1 μm or less called Al ₂ CuMg and greatly contribute to the improvement of strength. If the Cu content is less than 2% or the Mg content is less than 0.2%, sufficient strength cannot be obtained, while if the Cu content exceeds 7% or the Mg content exceeds 2.5%, Fe and Si are contained. The maximum length of the insoluble compound particles exceeds 2 μm to form coarse crystallized substances, which lowers the toughness. Therefore, the amount of Cu is 2
.About.7% and the amount of Mg is required to be 0.2 to 2.5%.

The lower limit of Cu is more preferably 2.5% or more, still more preferably 3.5% or more, while the upper limit is preferably 6.5% or less, more preferably 5.5% or less. Further, the lower limit of Mg is more preferably 0.5% or more, still more preferably 1.0% or more, while the upper limit is preferably 2.0% or less, more preferably 1.7% or less.

Cr: 0.05 to 0.3% Mn: 0.05 to 0.8% Zr: 0.05 to 0.3% Ti: 0.03 to 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%.
05-0.8%, 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 0.6% or less, more preferably 0.5% or less.

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: 1.0% or less (not including 0%) Si: 1.0% 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 1.0
%, But if it exceeds 1.0%, coarse and large amounts of insoluble compounds are formed, and the toughness is significantly reduced.

In the Al-Cu-Mg alloy according to the present invention, it is very important to control the maximum length of insoluble compound particles containing Fe and Si and the volume fraction thereof in order to obtain high toughness. . The maximum length of the insoluble compound particles is 2
When it is not more than μm and its volume fraction is not more than 2.0%, it exhibits excellent toughness in the ST direction after rolling. The maximum length of the insoluble compound particles is preferably 1.5 μm or less, and more preferably 1.0 μm or less in order to obtain high toughness. 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 for the solution treatment, it is desirable that the treatment temperature is 450 to 520 ° C. and the treatment time is 1 to 6 hours. As the condition of the aging treatment, an aging temperature of 160 to 200 ° 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 500 ° C. for 4 hours, water quenching, and aging treatment at 180 ° 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 sheets 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 did not satisfy the conditions in at least one element of the alloy composition according to the present invention, and Comparative Examples 14 and 15 were produced by a conventional casting method (cooling rate 1 ° C./sec) using a conventional alloy. It is a thing.

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 Cu
No. 5 is a comparative example when the amount is too small, and No. 5 is a comparative example when the amount of Mg is too small, and both have extremely low strength. No.
No. 4 is a comparative example when the amount of Cu is too large, and No. 6 is a comparative example when the amount of Mg is too large. The maximum length of the insoluble compound grains exceeds 2 μm and is coarse, and the toughness is extremely low. N
o.7 is a comparative example in which the amounts of Cr, Mn, Zr, and Ti are all too small, and the toughness is poor. Nos. 8 to 11 are comparative examples when the amount of any one of Cr, Mn, Zr and Ti is too large, and the maximum length of the insoluble compound particles exceeds 2 μm and the volume fraction exceeds 2%. The toughness is extremely low. Nos. 12 and 13 are comparative examples when the amount of inevitable impurities Fe or Si is too large, and the toughness is poor. Nos. 14 and 15 are conventional Al alloys,
The maximum length and volume fraction of the insoluble compound particles are beyond the range of the present invention, the toughness is poor, and No. 15 is also poor in strength.

[0034]

The present invention is constituted as described above, and the maximum length of the insoluble compound particles in the Al-Cu-Mg alloy is set to 2 μm or less by the continuous casting method, and the volume fraction thereof is 2%. Since it is controlled below, Al-Cu-M
In addition to the high strength property of the g-based alloy, its toughness can be improved, and an Al-Cu-Mg-based alloy excellent in toughness and a method for producing the same can be provided.

[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. Cu: 2 to 7% (meaning% by weight, the same hereinafter unless otherwise specified) Mg: 0.2 to 2.5% Fe: 1.0% or less (not including 0%) Si: One or more selected from the group consisting of Cr, Mn, Zr and Ti satisfying the requirement of 1.0% or less (not including 0%) Cr: 0.05-0.3% Mn: 0 0.05 to 0.8% Zr: 0.05 to 0.3% Ti: 0.03 to 0.3% contained in the range with the balance being Al and inevitable impurities. Hot rolling 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-Cu-Mg-based alloy excellent in toughness, characterized in that the volume fraction is controlled to 2.0% or less. 2. In producing the Al—Cu—Mg alloy according to claim 1, the cooling rate R during solidification is R ≧ 5 and R ≧ 7.5 ([Fe] + [Si]) + 2. , R: cooling rate during solidification (° C./sec) [Fe], [Si]: Fe and Si content ratio (%) in the Al alloy are continuously cast under conditions that satisfy the following conditions, A method for producing an Al-Cu-Mg-based alloy having excellent toughness, which is characterized by holding at a hot rolling temperature or higher and hot rolling. 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.