JP4281609B2 - Aluminum alloy extruded material excellent in formability and method for producing the same - Google Patents

Description

  The present invention relates to an aluminum alloy extruded material excellent in strength and formability suitable for a member capable of forming a thin and complex member such as a motorcycle part and requiring strength after welding.

As an aluminum alloy with good formability, a so-called 6000 series aluminum alloy of Al-Mg-Si series is known. Since this type of alloy has good strength and corrosion resistance, it is widely used as various structural materials. However, since the 6000 series aluminum alloy has a problem in strength after welding, it is unsuitable for an embodiment in which it is used after being welded.
For a member that requires mechanical properties after welding, a so-called 7000 series aluminum alloy of Al—Zn—Mg series is used. Use as an extruded material is also proposed in Patent Documents 1, 2, 3, and 4, for example.

  In Patent Document 1, Zn: more than 6.00 wt% and 7.50 wt% or less, Mg: 0.10 to 0.80 wt%, Cu: 0.10 to 0.30 wt%, Zr: 0.10 to 0.30 wt %, Mn: 0.05 to 0.30 wt%, Fe + Si is 0.30 wt% or less and Fe / Si is 1.5 or more, and the balance is made of Al and unavoidable impurities. An alloy ingot having a total content of 0.05 wt% or less and a total of 0.15 wt% or less is homogenized for 2 to 24 hours at a temperature of 420 to 520 ° C, and then subjected to extrusion at a temperature of 430 to 520 ° C. An aluminum alloy having excellent bending workability after first-stage aging treatment at a temperature of 90 to 110 ° C. for 2 to 12 hours and further at the temperature of 120 to 180 ° C. for 5 to 24 hours. Extruded material is obtained.

  Patent Document 2 includes Zn: 4.0-6.5 wt%, Mg: 0.4-1.8 wt%, Cu: 0.1-0.5 wt%, Zr: 0.1-0.5 wt% Further, Mn: 0.05 to 0.20 wt%, Cr: 0.05 to 0.20 wt% of one or two of them, Fe and Si, Fe + Si is 0.6 wt% or less and Fe / Si is Al-Zn-Mg system containing an amount satisfying 1.5 or more, the balance being Al and unavoidable impurities, each of unavoidable impurities being 0.05 wt% or less, and the total being 0.15 wt% or less The alloy ingot is subjected to homogenization heat treatment at 420 to 520 ° C. for 2 to 24 hours, then extruded at 430 to 520 ° C., sprayed with fine mist at the time of extrusion, and cooled to room temperature at a cooling rate of 10 to 50 ° C./s. After cooling, as the artificial aging treatment, the first stage at 90-110 ° C. for 2-12 hours, the second stage A heat treatment is performed at 120 to 170 ° C. for 5 to 24 hours to obtain an Al—Zn—Mg based alloy hollow shape excellent in strength and formability.

  Patent Document 3 includes Zn: 8.5 to 12.0%, Mg: 1.5 to 3.0%, Cu: 1.5 to 3.0%, Zr: 0.05 to 0.3%. Further, if necessary, one of Mn: 0.1 to 0.8%, Cr: 0.12 to 0.30%, Ti: 0.1% or less, B: 0.08% or less Alternatively, there has been proposed a high-strength aluminum alloy extruded material excellent in fatigue strength, characterized by comprising two types, the balance being Al and inevitable impurities.

Furthermore, in Patent Document 4, Zn: 4.5 to 7.5%, Mg: 0.20% or more and less than 0.50%, Ti: 0.001 to 0.1%, B: 0.0001 to 0.00%. Contains 0.8%, Fe: 0.35% or less, Si: 0.30% or less, Cu: 0.2% or less, Mn: 0.1 to 0.3%, Zr: 0.1 to 0.3 %, Cr: 0.05 to 0.2% of one or more of aluminum alloy, the balance being Al and inevitable impurities, cooling the extrusion die with liquid nitrogen or cooling the extrusion die Without extruding, followed by artificial aging treatment, liquid nitrogen cooling and extrusion, surface roughness R _max 10 μm or less, when extrusion without liquid nitrogen cooling R _max 15 μm or less, and The surface recrystallized layer has a thickness of 50 μm or less, and also has excellent SCC properties, and at the same time, it is swayed in a strongly processed region. Interested ring workability and bending workability and excellent hardness recovery characteristics after welding motorcycle structural member for an aluminum alloy extruded shapes.

JP-A-6-306522 Japanese Patent Laid-Open No. 8-144031 JP-A-8-295977 JP-A-10-298691

  However, the 7000 series aluminum alloy containing a large amount of Zn and containing Mg, Mn, Cr and Cu is a class of alloy having the highest strength among aluminum alloys, but contains Mg. The extrudability is relatively poor and it is difficult to produce a thin-walled material. For example, the material containing a large amount of Mg and Cu described in Patent Document 3 has a high strength exceeding 600 MPa after aging treatment, but has a high hot deformation resistance and a thin wall thickness of 2 mm or less. It is very difficult to extrude a tubular body industrially. Moreover, although the raw materials described in Patent Documents 1 and 2 also contain Mg, Mn, Cr, and Cu, the strength is high. If it is going to be obtained, a pressing force exceeding 2200 t is required, and clogging or die damage is likely to occur. As a result, it contributes to the cost increase.

On the other hand, as can be seen in Patent Document 4, a material with a reduced Cu content has low strength, so that, for example, when it is used as a component material for a motorcycle, desired mechanical characteristics cannot be obtained.
As described above, when trying to apply the existing technology to a thin-wall extruded material to be applied to building structural materials, automobile frames, motorcycle parts, etc. that require mechanical properties after welding, the yield is poor. The production cost will be high.
The present invention has been devised to solve such problems, and provides an extruded aluminum alloy material having high strength, particularly strength after welding, and excellent formability.

In order to achieve the object, the aluminum alloy extruded material having excellent formability according to the present invention is Zn: 4.5-7 mass%, Mg: 0.2-0.38 mass%, Cu: 0.25-0. 0.4% by mass, Zr: 0.1 to 0.3% by mass, Si: 0.05 to 0.3% by mass, and Fe: 0.05 to 0.3% by mass (Fe mass% / Si (Mass%) = 1-3, and the balance is made of Al and inevitable impurities.
Furthermore, 1 type or 2 types in Ti: 0.001-0.2 mass% and B: 0.0001-0.01 mass% can also be contained.

Further, an aluminum alloy material having the above component composition is homogenized under the conditions shown in the following (1), and then extruded under the conditions shown in the following (2), thereby extruding an aluminum alloy material excellent in formability. Is obtained.
(1) Homogenization treatment conditions-Heating rate 200 ° C / h or less-Homogenization temperature x time 450-520 ° C x 1-24h
・ Cooling rate: 150 ° C./h or more (2) Extrusion conditions ・ Extrusion temperature: 450 to 540 ° C.
-Die temperature 400-500 ° C
-Shaped material outlet side temperature: 450 ° C or higher-Cooling temperature: 100 ° C / min or higher Further, a drawing step may be added after the extrusion process.

According to the present invention, in an Al—Zn—Mg-based aluminum alloy, by adjusting the content of other elements, particularly Cu, Si, and Fe, without including Mn and Cr, which are structural strengthening elements, By adjusting the homogenization conditions, extrusion conditions, etc., it is possible to easily extrude a thin tubular body having a thickness of 2 mm or less even if it is an Al—Zn—Mg based aluminum alloy, while maintaining weldability. An aluminum alloy extruded material capable of exhibiting mechanical strength could be produced.
Therefore, it is possible to produce a thin extruded material to be applied to a building structure material, an automobile frame, a motorcycle part material, or the like that requires mechanical properties after welding.

The present invention will be specifically described.
First, the effect | action and content of the component which comprises this invention Al-Zn-Mg type aluminum alloy are demonstrated.
Mn and Cr contained in a normal 7000 series alloy form precipitates and suppress recrystallization, contributing to improvement of mechanical properties and prevention of cracking during welding. However, since the hot deformation resistance value is increased and the extrudability is deteriorated, it is difficult to produce a thin material. Therefore, the alloy of the present invention does not contain Mn and Cr. However, Mn and Cr which are inevitably mixed as impurities from the raw aluminum alloy scrap during melting are not taken into consideration. If both are less than 0.05 mass%, extrusion moldability is hardly affected.

Zn: 4.5-7 mass%
Zn forms the Mg—Zn-based precipitate and is the most important component for improving the strength of the aluminum alloy, and its preferable content range is 4.5 to 7% by mass. If the Zn content is less than 4.5% by mass, the effect of improving the strength is not sufficient. Even if the content exceeds 7% by mass, no further improvement in strength can be expected, and the corrosion resistance decreases.

Mg: 0.2 to 0.38% by mass
Mg forms a Mg—Zn-based precipitate and is dispersed in the matrix phase to improve the mechanical strength of the extruded material. This effect becomes remarkable when Mg is contained in an amount of 0.2% by mass or more. On the other hand, when the content exceeds 0.38% by mass, hot deformation resistance is increased, moldability and extrusion processability are deteriorated, and productivity is lowered. Therefore, the content of Mg is set to 0.2 to 0.38% by mass. Preferably it is 0.30-0.35 mass%.

Cu: 0.25 to 0.4 mass%
Cu dissolves in the matrix and improves the mechanical strength. This effect becomes remarkable when the Cu content is 0.25% by mass or more. On the other hand, if the content exceeds 0.4% by mass, the corrosion resistance decreases. Therefore, the Cu content is set to 0.25 to 0.4 mass%. It is preferable to set it as 0.25-0.35 mass%.

Zr: 0.1 to 0.3% by mass
Zr forms an Al—Zr-based compound and is dispersed in the matrix phase, and the pinning effect suppresses the coarsening of the recrystallized grains to increase the strength, and also prevents cracking during welding. This effect becomes remarkable when the Zr content is 0.1% by mass or more. However, if the content exceeds 0.3% by mass, a coarse Al—Zr-based compound is generated and the hot workability is lowered. Further, when the precipitate is generated excessively, the hot deformation resistance is increased and the extrusion processability is hindered.

Si: 0.05-0.3 mass%
Si forms an Al—Si—Fe-based compound and is finely dispersed in the matrix to suppress the coarsening of crystal grains, thereby improving the mechanical strength. This effect becomes significant when the Si content is 0.05 mass% or more. However, when the content exceeds 0.3% by mass, an Mg—Si compound is formed, and thus the formation of the Mg—Zn compound is inhibited. For this reason, natural age hardenability falls and sufficient intensity | strength is not obtained after welding. Preferably, it is contained in the range of 0.05 to 0.15% by mass.

Fe: 0.05-0.3 mass%
Fe forms an Al—Si—Fe-based compound and is finely dispersed in the matrix to suppress the coarsening of crystal grains, thereby improving the mechanical strength. This effect becomes prominent when the Fe content is 0.05 mass% or more. However, when the content exceeds 0.3% by mass, the Al—Si—Fe-based compound is dispersed in a large amount, so that the surface properties of the extruded material are impaired. Preferably, it is contained in the range of 0.10 to 0.20% by mass.

(Fe mass% / Si mass%) = 1-3
Fe and Si are contained in order to obtain the effect of preventing grain coarsening after extrusion. In addition, although there is an effect of suppressing casting cracks, as described above, if the content of both is too large, the mechanical properties are deteriorated and the extrusion processability is inhibited. Therefore, the Fe / Si ratio is restricted to 1 to 3 in order to efficiently form the Al—Si—Fe based compound. If the Fe / Si ratio is less than 1, excess Si forms a compound with Mg, which inhibits the formation of the Mg—Zn compound and the mechanical properties deteriorate. On the other hand, when the Fe / Si ratio exceeds 3, excess Fe forms an Al—Fe-based compound, which deteriorates extrusion processability.

Ti: 0.001 to 0.2% by mass, B: 0.0001 to 0.01% by mass or less of one or two types of Ti and B are used to refine crystal grains of the cast material, It has the effect of preventing cracking and improving extrudability. For this reason, in the range of Ti: 0.001-0.2 mass% and B: 0.0001-0.01 mass%, these 1 type or 2 types can be contained in an alloy. When the content of Ti and B exceeds the upper limit, a coarse compound is formed and the surface properties of the extruded material are deteriorated.

By the way, an extruded material of an Al—Zn—Mg-based aluminum alloy is generally manufactured by a method in which a homogenized heat-treated ingot is hot-extruded and subjected to press quenching or a separate solution treatment, and then an artificial aging treatment.
The aluminum alloy extruded material of the present invention can also achieve the intended purpose by limiting the temperature conditions and processing time conditions at each stage.
Hereinafter, the manufacturing conditions and the reasons for limitation will be described.

(1) Homogenization treatment / heating rate: 200 ° C./h or less When the heating rate is high, the Al—Zr-based precipitates are coarsened, the effect of suppressing recrystallization is lowered, and the mechanical properties are lowered. Moreover, the crack sensitivity at the time of welding also becomes high. However, it is not economical if it is too late. Preferably, it is about 100 ° C./h.

-Homogenization temperature x time; 450-520 ° C x 1-24h
This is carried out in order to homogenize the segregation of Mg, Zn, etc. generated during casting, to obtain a sufficient solid solution state during extrusion, and to form an Al—Zr compound suitable for suppressing recrystallization of the extruded material. Even at a temperature of less than 450 ° C. for 24 hours, a sufficient structure cannot be obtained. On the other hand, when it exceeds 520 ° C. or exceeds 24 hours, Mg and Zn are homogenized, but the Al—Zr-based compound is coarsened and the effect of suppressing recrystallization of the extruded material cannot be sufficiently obtained. Homogenization is insufficient in the treatment for less than 1 hour. Therefore, the homogenization treatment is performed under conditions of 450 to 520 ° C. × 1 to 24 hours.

・Cooling rate: 150 ° C./h or more Mg and Zn are homogenized by maintaining the above high temperature, but when the cooling rate is slow, coarse precipitates are formed and sufficient solution cannot be formed during extrusion.
Therefore, the cooling rate after homogenization is fast and is 150 ° C./h or more.

(2) Extrusion / extrusion temperature: 450-560 ° C.
The billet heating temperature and the extrusion speed are adjusted so that the shape material temperature immediately after extrusion is 450 to 560 ° C. Thereby, Mg and Zn can be sufficiently dissolved. If it is less than 450 ° C., the solid solution state becomes insufficient, and sufficient strength cannot be obtained even by the subsequent aging treatment. On the other hand, when extruded at a temperature exceeding 560 ° C., it is easy to recrystallize and not only the strength is lowered, but also cracking sensitivity at the time of welding is increased. For this reason, in the manufacture of thin hollow materials, it is preferable to extrude at an extrusion speed of 3 to 20 m / min with a billet temperature of 450 to 540 ° C. and a die temperature of 400 to 500 ° C.

And cooling temperature; rigidity of the cross-section is high at 100 ° C. / min or more on <br/> thickness 2mm or more standard tubular body and a thick material, hard to deform even at a high temperature immediately after extrusion, but in the present invention Since a thin extruded material having a thickness of 2 mm or less, which is the target, is easily deformed at high temperatures and in the cooling process, the shape is actively cooled immediately after extrusion for the purpose of preventing deformation. Deformation can be suppressed by cooling to an average cooling rate of 100 ° C./min or higher to 150 ° C. or lower. The cooling rate is preferably 200 ° C./min or more.
As a cooling method, air cooling or liquid nitrogen spray cooling is preferable. In the case of water cooling, the cooling is too strong and variations in cooling tend to occur, and deformation due to variations in cooling tends to occur. Therefore, water cooling is not preferable in the case of a thin extruded material.

(3) Drawing processing When high dimensional accuracy is required, drawing processing is performed. However, if the deformation resistance is high, an annealing treatment may be performed before drawing. The annealing treatment is preferably 200 to 270 ° C. × 1 to 6 hours.
The drawing rate is preferably 5 to 25%. If it is less than 5%, the effect of improving the dimensional accuracy in the drawing process cannot be obtained. On the other hand, if it exceeds 25%, the material breaks. In addition, since this material is an alloy which age-hardens in a room temperature environment, it is preferable to carry out within 10 days when drawing after extrusion.
In addition, the material may be subjected to artificial aging in order to promote age hardening. As artificial aging, it is preferable to perform two-stage aging of 80 to 110 ° C. × 4 to 12 hours + 120 to 170 ° C. × 4 to 24 hours.

A 203 mmφ billet having various compositions shown in Table 1 was cast, and the billet was subjected to a homogenization treatment at a heating rate of 100 ° C./h, a holding temperature of 480 ° C. × 4 h, and a cooling rate of 300 ° C./h.
Subsequently, a thin elliptical tube having a cross-sectional dimension of 120 mm in major axis, 85 mm in minor axis and 1.3 mm in thickness as shown in FIG. 1 was extruded. At this time, the billet temperature was 500 ° C., the die temperature was 470 ° C., and the extrusion speed was 6 m / min. The cooling conditions are as shown in Table 1. The cooling was performed by air cooling.
For test No. 4, after extrusion, annealing was performed at 200 ° C. for 4 hours, and then drawing was performed to evaluate whether it was possible. The drawing rate is shown by the cross-sectional reduction rate.

About the extruded material, the test piece of JIS5 was cut out and the tension test was done. A similar tensile test was performed after welding. In addition, the tensile test after welding was extract | collected so that a welding part might be located in the center of the parallel part of a test piece.
The results are shown in Table 2.
In Table 2, the extrudability of extrudability is ◯ when the hollow body having the dimensions shown in FIG. 1 is extruded at 2200 t or less, the pushing force exceeds 2200 t, and the extruded material is obtained due to clogging or the like. Those that did not appear were marked with x. Similarly, the dimensional accuracy is indicated by ○ for those satisfying the outer dimensions JIS special class (height ± 0.86 mm, width ± 1.12 mm), and x outside the JIS special class.
In addition, whether or not pulling is possible is indicated by ○.
Furthermore, regarding the strength evaluation, those having a tensile strength of 220 MPa or more and a 0.2% proof stress of 170 MPa or more were rated as ◯, and those less than that were rated as x. Regarding the tensile strength after welding, those with a pressure of 250 MPa or more were marked with ◯, and those with less than that were marked with x.
Considering the above, we made a comprehensive evaluation.

As can be seen from the results shown in Table 2, Test Nos. 1 to 5 as examples of the present invention are excellent in extrusion processability and high in strength. However, for test No. 5 where the cooling rate after extrusion was slow, the deformation was large during cooling and the dimensional accuracy was poor.
On the other hand, test No. 6 with a low Cu content has low proof stress, although it can be extruded. In Test No. 7 with a high Mn content and Test No. 8 with a high Mg content, hot deformation resistance increased, and when the extrusion process was attempted, the pushing force exceeded 2200 t, and clogging or the like occurred. Occurred and could not be extruded.

Diagram illustrating the shape of an extruded thin-walled elliptical tube

Claims (4)

  Zn: 4.5-7 mass%, Mg: 0.2-0.38 mass%, Cu: 0.25-0.4 mass%, Zr: 0.1-0.3 mass%, and further Si : 0.05-0.3 mass% and Fe: 0.05-0.3 mass% in the range of (Fe mass% / Si mass%) = 1-3, with the balance being Al and inevitable impurities An aluminum alloy extruded material excellent in formability characterized by   The aluminum alloy extrusion excellent in formability according to claim 1, further comprising one or two of Ti: 0.001-0.2 mass% and B: 0.0001-0.01 mass%. Wood. A formability characterized by homogenizing the aluminum alloy material having the component composition according to claim 1 or 2 under the conditions shown in the following (1) and then extruding it under the conditions shown in the following (2). The manufacturing method of the aluminum alloy extrusion material excellent in.
(1) Homogenization treatment conditions-Heating rate 200 ° C / h or less-Homogenization temperature x time 450-520 ° C x 1-24h
・ Cooling rate: 150 ° C./h or more (2) Extrusion conditions ・ Extrusion temperature: 450 to 540 ° C.
-Die temperature 400-500 ° C
・ Shape outlet temperature 450 ℃ or more ・ Cooling temperature 100 ℃ / min or more   The manufacturing method of the aluminum alloy extrusion material excellent in the moldability of Claim 3 which adds a drawing process after an extrusion process.

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