JP2001011559A - High strength aluminum alloy extruded material excellent in corrosion resistance and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an aluminum alloy extruded material excellent in corrosion resistance, having high strength, and moreover, good in extrudability and to provide a method for producing the same. SOLUTION: This is an extruded material of an aluminum alloy contg. 0.5 to 1.5% Si, 0.9 to 1.6% Mg and 0.8 to 2.5% Cu, furthermore satisfying the following conditions of (1), (2), (3) and (4) of (1): 3<=Si%+Mg%+Cu%<=4, (2): Mg%<=1.7×Si%, (3): Mg%+Si%<=2.7 and (4): Cu%/2<=Mg%<=(Cu%/2)+0.6, moreover contg. 0.5 to 1.2% Mn, and the balance aluminum with inevitable impurities, in which, in the case the minimum thickness of the extruded material is defined as (t) (mm), the extrusion ratio as R, and the thickness G (μm) of the recrystallized layer in the surface layer part of the extruded material satisfies G<=0.326t×R.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength aluminum alloy extruded material having excellent corrosion resistance, and particularly to a high-strength aluminum alloy having excellent corrosion resistance which is suitably used as a structural material for transportation equipment such as automobiles, railway vehicles and aircraft. The present invention relates to an alloy extruded material and a method for producing the same.

[0002]

2. Description of the Related Art Aluminum alloys of the 6000 series (Al-Mg-Si series) are widely used as transportation equipment members because of their good workability, easy production, and excellent corrosion resistance. There is a disadvantage that the strength is inferior to that of a 7000 series (Al-Zn-Mg) or 2000 series (Al-Cu) high-strength aluminum alloy. On the other hand, 7000
Although the system-based alloy and the 2000-type alloy are excellent in strength, there are problems in corrosion resistance and manufacturability, so there are restrictions in terms of application.

[0003] Under such circumstances, attempts have been made to improve the strength of 6000 series aluminum alloys.
56 alloy, 6082 alloy and the like have been developed. Also, Mg,
An aluminum alloy (JP-A-59-50147) in which Mn, Cr and Zr are contained in a specific range in addition to the hardening elements of Si and Cu to improve toughness has also been proposed. Mg, S for transport equipment structures
The relationship between the i and Cu contents is defined, and the impurity Mn is defined.
Al-Cu- with excellent strength and corrosion resistance with limited content of
An extruded Mg-Si alloy (Japanese Patent Application Laid-Open No. 10-306338) has also been proposed.

For transportation equipment members such as automobile members,
In recent years, regulations on exhaust gas have become stricter from the viewpoint of maintaining the global environment, and a reduction in vehicle weight has been strongly promoted in order to reduce fuel consumption and emission of harmful gas and carbon dioxide gas. As one of them, the effect has been improved by changing the conventionally used iron-based members to aluminum-based members, but with the progress of weight reduction, the demand for thinner materials has become stricter, The developed alloys such as 6013 and the proposed aluminum alloy materials are not always satisfactory in terms of strength and corrosion resistance.

[0005] The inventors of the present invention have proposed an Al-C alloy which has been proposed in order to obtain an aluminum alloy extruded material capable of satisfying the requirements relating to the weight reduction of transportation equipment, particularly automobiles.
Extruded material of u-Mg-Si alloy (JP-A-10-30633)
No. 8) as a base, and in the examination process for further improving the characteristics, even when the strength is improved by containing Mn, by controlling the crystal layer thickness of the extruded material,
It has been found that corrosion resistance can be maintained.

[0006]

The present invention has been made as a result of further experiments based on the above-mentioned findings, and its object is to provide an aluminum alloy having excellent corrosion resistance and strength and good extrudability. An object of the present invention is to provide an extruded material and a method for producing the same.

[0007]

In order to achieve the above object, a high-strength aluminum alloy extruded material having excellent corrosion resistance according to claim 1 of the present invention comprises Si: 0.5% to 1.5% and Mg: 0.9%.
% To 1.6% and Cu: 0.8% to 2.5% and satisfy the following conditional expressions (1), (2), (3) and (4): 3 ≦ Si% + Mg% + Cu% ≦ 4 --- (1) Mg% ≦ 1.7 × Si% --- (2) Mg% + Si% ≦ 2.7 --- (3) Cu% / 2 ≦ Mg% ≦ (Cu% / 2) +0 .6 --- (4) An extruded material of an aluminum alloy further containing Mn: 0.5% to 1.2%, the balance being aluminum and unavoidable impurities, wherein the minimum thickness of the extruded material is t (mm), Extrusion ratio is R
, The thickness G (μ) of the recrystallized layer on the surface of the extruded material
m) satisfies G ≦ 0.326t × R.

The high-strength aluminum alloy extruded material having excellent corrosion resistance according to claim 2 is obtained by adding Cr: 0.02% to 0.4% and Zr: 0.03% to 0.3% to the aluminum alloy according to claim 1.
2%, V: 0.03% to 0.2%, and Zn: 0.03% to 2.0%.

A method for producing a high-strength aluminum alloy extruded material having excellent corrosion resistance according to the present invention is described in claim 1 or 2.
The ingot obtained by ingoting the aluminum alloy according to
After homogenizing at a temperature of 0 ° C. or higher and lower than the melting point of the ingot,
A homogenization treatment step of cooling at an average cooling rate of 25 ° C./h or more from the homogenization treatment temperature to at least 250 ° C., and heating the homogenized aluminum alloy ingot to a temperature of 450 ° C. or more and lower than the melting point of the ingot. An extrusion step of extruding, and a press quenching step of cooling to a temperature of 100 ° C. or lower at a cooling rate of 10 ° C./second or higher while the surface temperature of the extruded material immediately after extrusion is maintained at 450 ° C. or higher. One of a quenching step of subjecting the extruded material to a solution treatment at a temperature of 450 ° C. or more and less than the melting point of the extruded material, and then cooling it to a temperature of 100 ° C. or less at a cooling rate of 10 ° C./sec or more;
A tempering step of performing a heat treatment at 0 to 200 ° C. for 2 to 24 hours.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The significance of the alloy components in the high-strength aluminum alloy excellent in corrosion resistance of the present invention and the reasons for limiting the same will be described. Si coexists with Mg and forms Mg ₂
It has the function of precipitating Si and improving the strength of the aluminum alloy. The preferable content range of Si is 0.5% to 1.5%.
If less than 0.5%, the effect is not enough, and 1.5%
If it exceeds, the corrosion resistance decreases. The more preferable content range of Si is 0.7% to 1.2%.

Mg coexists with Si to precipitate Mg ₂ Si, and coexists with Cu to finely precipitate CuMgAl ₂ , thereby improving the strength of the aluminum alloy. M
The preferred content range of g is 0.9% to 1.6%, and 0.9% to 0.9%.
If the content is less than 1.6%, the effect is not sufficient. If the content exceeds 1.6%, the corrosion resistance is reduced. The more preferable content range of Mg is
0.9% to 1.2%.

Cu, like Si and Mg, is an elemental component that contributes to strength improvement, and its preferred content is 0.8%
~ 2.5%. If it is less than 0.8%, the effect is small, and 2.
If the content exceeds 5%, the production becomes difficult and the corrosion resistance decreases. The more preferable content range of Cu is 0.9% to 2.0%.

Mn plays an important role in suppressing recrystallization during hot working to form a fibrous structure and obtaining high strength. A preferred content range of Mn is 0.5% to 1.2%,
If it is less than 0.5%, the effect of suppressing recrystallization becomes insufficient, and
%, Coarse intermetallic compounds are formed and hot workability is deteriorated. The more preferable content range of Mn is 0.6%.
~ 1.0%.

[0014] The high-strength aluminum alloy of the present invention comprises S
i, Mg, Cu, Mn as essential components, Si, Mg, C
It is necessary to satisfy conditional expressions (1) to (4) between u. As a result, the amount and distribution of the intermetallic compound are controlled, and a well-balanced high strength and corrosion resistance are imparted to the aluminum alloy. If the total content of the essential components Si, Mg and Cu is less than 3%, the desired strength cannot be obtained, and 4%
Is exceeded, the corrosion resistance decreases, and the total content of Mg and Si
If it exceeds 2.7%, the corrosion resistance decreases and the ductility deteriorates.

Cr, Zr, V, and Zn added as selective components to the aluminum alloy of the present invention have a function of reducing the crystal grain size. Cr, Zr, V, Zn
However, if the respective values are less than the lower limits, the effect is small, and if the values exceed the upper limits, coarse intermetallic compounds are formed, which adversely affects the mechanical properties of the extruded material, such as elongation and decrease in toughness. The characteristics of the present invention will not be impaired even if the aluminum alloy of the present invention contains a small amount of Ti or B which is usually added for refining the ingot structure.

In the extruded aluminum alloy material of the present invention, the thickness G (μm) of the recrystallized layer in the surface layer portion is G ≦ G.
It is important to satisfy 0.326 t × R (conditional expression (5)). In this alloy, quenching and tempering
-Si-Cu quaternary compound precipitates finely to achieve high strength, but this quaternary compound preferentially precipitates at the grain boundaries of the recrystallized layer during the press quenching step or the quenching step. To reduce strength and corrosion resistance. Therefore, it is necessary to control the recrystallized layer in order to achieve high strength while maintaining corrosion resistance. If G is greater than 0.326 t × R, intergranular corrosion is likely to occur, and strength is also reduced.

Next, a preferred method of manufacturing the extruded aluminum alloy material of the present invention will be described. First, a molten metal of the aluminum alloy material having the above-described composition is formed by, for example, semi-continuous casting, and the ingot is homogenized. In the process, 4
Homogenizing at a temperature of 50 ° C. or higher and lower than the melting point of the ingot, and 25 ° C./h from the homogenizing temperature to at least 250 ° C.
The extruded billet is cooled at the above average cooling rate.

If the homogenization treatment temperature is lower than 450 ° C., homogenization is not sufficiently performed, solute penetration of the solute element is also insufficient, and sufficient strength can be obtained by so-called press quenching in which water is cooled immediately after extrusion. Strength cannot be obtained. If the homogenization temperature is equal to or higher than the melting point of the ingot, the heat treatment furnace becomes contaminated, the aluminum alloy material is deformed, and the like, which makes industrial implementation difficult.

By cooling to 250 ° C. at an average cooling rate of 25 ° C./h or more, the solid solution state of the solute element introduced by the homogenization treatment is maintained, and high strength is achieved. If the cooling rate is less than 25 ° C./h, the solute component dissolved in the homogenization treatment precipitates and agglomerates to become coarse, and the agglomerated component is hard to re-solid-solve, so that it is difficult to obtain sufficient strength. In order to stably obtain a high strength, a more preferable cooling rate is 100 ° C./h or more.

After completion of the homogenization treatment step, the extruded billet is heated to a temperature of 450 ° C. or more and lower than the melting point of the extruded billet in the extrusion processing step to perform hot extrusion to obtain an extruded material. At this time, the temperature of the extrusion billet before extrusion was 450
If the temperature is lower than 0 ° C., the penetration of the solute element becomes insufficient, and sufficient strength cannot be obtained by press quenching. If the temperature exceeds the melting point, cracks occur during the extrusion operation.

Further, the extruded material whose surface temperature is maintained at a temperature of 450 ° C. or more immediately after extrusion is cooled to a temperature of 100 ° C. or less at a cooling rate of 10 ° C./sec or more in a press quenching step. Alternatively, the extruded material is subjected to a solution treatment at a temperature of 450 ° C. or more and less than the melting point of the extruded material in a heat treatment furnace such as an atmosphere furnace or a salt bath furnace according to a quenching process, and then 10 ° C.
Cooling to 100 ° C. or less at a cooling rate of / sec or more.

If the surface temperature of the extruded material is less than 450 ° C. in the press quenching step, so-called quenching delay occurs in which solute components are precipitated, and a desired strength cannot be obtained. The more preferable surface temperature of the extruded material is 500 ° C. or more. Further, if the cooling rate is less than 10 ° C./sec, the solute component precipitates during cooling, so that a desired strength cannot be obtained and the corrosion resistance is lowered. A more preferred cooling rate is 16 ° C./sec or more.

If the heat treatment temperature during the solution treatment during the quenching treatment step is lower than 450 ° C., the penetration of the solute element is insufficient, and the desired strength cannot be obtained, and the temperature is higher than the melting point of the extruded material. In the case of (1), there is contamination of the heat treatment furnace, deformation of the extruded material, and the like, which makes industrial implementation difficult. Further, if the cooling rate is less than 10 ° C./sec, as in the case of the press quenching step, precipitation of a solute component occurs during cooling, a desired strength is not obtained, and corrosion resistance is reduced. A more preferred cooling rate is 16 ° C./sec or more.

The quenched extruded material is subjected to a tempering process at 150 to 200 ° C. for 2 to 24 hours in a tempering process step to obtain a final product. At this time, the tempering temperature is 1
If the temperature is lower than 50 ° C., tempering must be performed for more than 24 hours to obtain sufficient strength, which is inconvenient for industrial production. If the temperature exceeds 200 ° C., the ultimate strength is low. Further, if the heat treatment time is less than 2 hours, sufficient strength cannot be obtained, and if it exceeds 24 hours, the strength decreases.

[0025]

EXAMPLE 1 An aluminum alloy having a composition shown in Table 1 was ingot-formed by semi-continuous casting to produce an ingot having a diameter of 200 mm. After homogenizing these ingots at 530 ° C. for 8 hours,
Cooling from 30 ° C. to 250 ° C. is performed at an average cooling rate of 250 ° C./h to obtain each extrusion billet. Each of these extrusion billets was extruded at 520 ° C. into a tube shape having an outer diameter of 30 mm and an inner diameter of 20 mm (extrusion ratio: 80).

Next, the obtained tubular extruded material was heated at 540 ° C.
Quenching treatment by water cooling within 10 seconds, and three days after the quenching treatment, an artificial aging treatment (tempering treatment) at 175 ° C. for 8 hours is performed, and each tubular extruded material is subjected to T6.
Tempered wood. Using these T6 materials as test materials, (1) tensile tests and (2) intergranular corrosion tests were performed to evaluate the properties according to the following methods.

(1) Tensile test The tensile strength (UTS), proof stress (YS) and elongation at break (δ) of each test piece are measured based on JIS Z2241. (2) Intergranular corrosion test 57 g of sodium chloride (NaCl), 30% H ₂ O ₂ 1
0 ml is adjusted to 1 liter with distilled water to prepare a test solution. The test solution is kept at 30 ° C., each test piece is immersed for 6 hours, and the corrosion loss is measured. Those having a corrosion weight loss of less than 1.0% were judged to have good corrosion resistance.

Table 2 shows the recrystallized layer thickness (G) of the surface layer, the value of 0.326 t × R, the tensile properties, and the results of the intergranular corrosion test for each test material. As can be seen from Table 2, all the test materials according to the present invention have excellent strength and good corrosion resistance. The thickness of the recrystallized layer (G) in the surface layer was measured by taking a photograph of the microstructure of a right-angle cross section of the coarse recrystallized grain layer in the surface layer at a magnification of 100 and measuring one straight line perpendicular to the contour line of the outer shape. 50 or more lines were drawn, and the length of these straight lines crossing the coarse recrystallized grain layer was measured, and the measured values were averaged.

[0029]

[Table 1]

[0030]

[Table 2]

Comparative Example 1 An ingot having a diameter of 200 mm was manufactured by semi-continuous casting an aluminum alloy having the composition shown in Table 3. These ingots were treated in the same manner as in Example 1 to obtain a tubular extruded material, which was further tempered into a T6 material. Using these T6 materials as test pieces,
As in Example 1, (1) tensile test and (2) intergranular corrosion test were performed to evaluate the characteristics. Table 4 shows the results. In addition,
In Table 3, those out of the conditions of the present invention are underlined.

[0032]

[Table 3] << Table Note >> For alloy M, Si + Mg + Cu is out of range. For alloy O, Mg ≦ 1.7 × Si is not satisfied. For alloy P, Mg + Si is out of range.

[0033]

[Table 4]

As shown in Table 4, the test material No. 11 is M
Due to the small amount of n, recrystallization occurred during extrusion and the strength was reduced. Test material No. In No. 12, since the amount of Mn was large, a coarse intermetallic compound was formed and elongation was reduced. Test material No. 13
Has poor corrosion resistance because the total amount of Si, Mg and Cu is out of the range of the present invention. Test material No. 14, 15 are
Since the respective amounts of Mg and Mg ≦ 1.7 × Si are out of the range of the present invention, the corrosion resistance is inferior. Test material No. 1
In Nos. 6 and 17, the total amount of Mg and Si, respectively, and Si were out of the range of the present invention, the corrosion resistance was poor, and the ductility was lowered. Test material No. No. 18 is inferior in corrosion resistance because of a large amount of Mg.

Example 2 An aluminum alloy A having a composition shown in Table 1 was ingot by semi-continuous casting to produce an ingot having a diameter of 200 mm.
The ingot was processed under the respective manufacturing conditions shown in Table 5 to produce a tubular extruded material, and the tubular extruded material was press-hardened or quenched under the conditions shown in Table 5, and further tempered under the same conditions as in Example 1. This was processed into T6 material.

Using the obtained T6 material as a test piece, the recrystallized layer thickness (G) of the surface layer was measured, and 0.326 t × R was calculated. Further, in the same manner as in Example 1, (1) a tensile test and (2) an intergranular corrosion test were performed to evaluate the characteristics. Table 6 shows the evaluation results.

Comparative Examples 30 to 34 Aluminum alloy A having the composition shown in Table 1 was semi-continuously cast to produce an ingot having a diameter of 200 mm.
The ingot was processed under the respective manufacturing conditions shown in Table 5 to produce a tubular extruded material, and the tubular extruded material was press-hardened or quenched under the conditions shown in Table 5, and further tempered under the same conditions as in Example 1. This was processed into T6 material.

Using the obtained T6 material as a test piece, the recrystallized layer thickness (G) of the surface layer was measured, and 0.326 t × R was calculated. Further, in the same manner as in Example 1, (1) a tensile test and (2) an intergranular corrosion test were performed to evaluate the characteristics. Table 6 shows the evaluation results. In Table 5, those outside the conditions of the present invention are underlined.

[0039]

[Table 5] << Table Note >> The cooling rate after homogenization is the average cooling rate from the homogenization processing temperature to 250 ° C. The cooling rate for press quenching is the average cooling rate from the material temperature before water cooling to 100 ° C. The cooling rate for quenching is the solution treatment. Average cooling rate from temperature to 100 ° C Use solution furnace for heating

[0040]

[Table 6]

As shown in Table 6, the test materials No. 19 to 29 showed excellent strength and good corrosion resistance. On the other hand, the test material No. 30
-34 are inferior in either strength or corrosion resistance. That is, the test material No. In No. 30, the cooling rate after the homogenization treatment was low, so that the strength after the artificial aging treatment was low, and the corrosion resistance was lowered. Test material No. In No. 31, since the extrusion temperature was lower than the range of the present invention, a sufficient solid solution of the solute element was not achieved, the strength was lowered, and the corrosion resistance was lowered. Test material N
o. Sample No. 32 had a low cooling rate at the time of press quenching, so that the strength was poor and the corrosion resistance was low. Test material No. No. 33 has a low cooling rate after the solution treatment, so that high strength cannot be obtained and corrosion resistance is low.

[0042]

According to the present invention, there is provided an aluminum alloy extruded material having excellent corrosion resistance, high strength and good extrudability, and a method for producing the same. The aluminum alloy can be suitably used as a structural material for transportation equipment such as automobiles, railway vehicles, and aircraft, instead of a conventional iron-based structural material.

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Claims (3)

[Claims] 1. Si: 0.5% (% by weight, hereinafter the same) to 1.5%
%, Mg: 0.9% to 1.6%, Cu: 0.8% to 2.5%, and satisfies the following conditional expressions (1), (2), (3) and (4): 3 ≦ Si% + Mg % + Cu% ≦ 4 --- (1) Mg% ≦ 1.7 × Si% --- (2) Mg% + Si% ≦ 2.7 --- (3) Cu% / 2 ≦ Mg% ≦ (Cu % / 2) +0.6 --- (4) An extruded material of an aluminum alloy further containing Mn: 0.5% to 1.2%, the balance being aluminum and unavoidable impurities. t (mm), extrusion ratio is R
, The thickness G (μ) of the recrystallized layer on the surface of the extruded material
m) satisfies G ≦ 0.326 t × R, a high-strength aluminum alloy extruded material having excellent corrosion resistance. 2. The aluminum alloy according to claim 1,
Further, Cr: 0.02% to 0.4%, Zr: 0.03% to 0.2%,
A high-strength aluminum alloy extruded material having excellent corrosion resistance, characterized by containing at least one of V: 0.03% to 0.2% and Zn: 0.03% to 2.0%. 3. An ingot obtained by ingoting the aluminum alloy according to claim 1 or 2 is subjected to a homogenization treatment at a temperature of 450 ° C. or more and less than the melting point of the ingot, and at least a temperature from the homogenization treatment temperature. A homogenization treatment step of cooling at an average cooling rate of 25 ° C./h or more up to 250 ° C., and an aluminum alloy ingot after the homogenization treatment is heated to 450 ° C. or more and lower than the melting point of the ingot to perform extrusion. An extrusion step, a press quenching step of cooling the extruded material immediately after extrusion to a temperature of 100 ° C. or less at a cooling rate of 10 ° C./sec or more while the surface temperature of the extruded material is maintained at 450 ° C. or more; One of a quenching step of performing a solution treatment at a temperature lower than the melting point of the extruded material and then cooling to a temperature of 100 ° C. or less at a cooling rate of 10 ° C./sec or more, and 150 to 200 ° C. for 2 to 24 hours Heat treatment A method for producing a high-strength aluminum alloy extruded material having excellent corrosion resistance, comprising a return treatment step.