JP2006316295A - Aluminum alloy extruded material for high temperature forming, and high temperature formed product thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy extruded material which is excellent in formability and the anxiety about the reduction of material strength is reduced because cavitation hardly occurs in a forming stage even if forming is performed at high temperature, so as to obtain high productivity and high formability, and to provide a high temperature forming method therefor. <P>SOLUTION: The aluminum alloy extruded material for high temperature forming has a composition containing 0.5 to 2.0% Mg, 4.0 to 7.0% Zn, ≤0.35% Cu, ≤0.20% Zr, ≤0.25% Cr, ≤0.5% Mn and ≤0.1% Ti, and the balance Al with inevitable impurities. The extruded material is cold-worked, thereafter subjected to heat treatment, and is molded at 400 to 520°C at a strain rate of 10<SP>-2</SP>/s to 10<SP>0</SP>/s, so as to obtain a formed product. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an Al—Zn—Mg-based aluminum alloy extruded material having good high temperature formability, low cavitation, excellent strength, and good productivity.

For Al-Mg alloys, for example, superplastic alloys have been developed that achieve high formability by producing a high elongation of several hundred percent in a high temperature range of 460 ° C to 550 ° C. Is the molding speed at 10 ⁻⁴ to 10 ⁻³ / s. At such a molding speed, it takes 30 to 100 minutes even for molding of general equipment, so that the productivity was poor in production on an industrial scale. On the other hand, high-speed superplastic forming alloys that can be formed at a higher strain rate than conventional superplastic alloys at a strain rate of 10 ⁻² to 10 ⁰ / s have been proposed and developed (see, for example, Patent Document 1). This has the risk of reducing the strength due to the coarsening of the crystal grains, and there is room for further improvement from the viewpoint of the occurrence of cavitation.

On the other hand, Al—Zn—Mg alloys are used for motorcycle frames and bumper beams because of their high strength, but there are few examples of hot working of extruded materials at a high strain rate of 10 ⁻² to 10 ⁰ / s. So far, cold work has been the main. As an example of cold working, there is an example in which an aluminum alloy extruded tube is formed into a complicated shape by performing pipe expansion processing, hydroforming processing (hydraulic bulge processing), or the like (see, for example, Patent Document 2). However, due to the cold working, there is a problem that when trying to process into a complicated shape, the elongation is insufficient and the material cannot be formed to be sufficiently satisfactory and the material is broken.
Japanese Patent Laid-Open No. 10-259441 Japanese Patent Laid-Open No. 11-104751

  The present invention has been made paying attention to such circumstances, and its purpose is excellent in moldability, and even if molding is performed at a high temperature, cavitation is unlikely to occur in the molding process, so there is little risk of a decrease in material strength. An object of the present invention is to provide an aluminum alloy extruded material that can be produced with high productivity and high formability, and a high-temperature molded product thereof.

As a result of intensive studies in view of the above problems, the present inventors set the contents of Mg and Zn, which are basic components of an Al—Zn—Mg-based aluminum alloy, within a specific range, and high-temperature forming of an aluminum alloy extruded material. As a result of repeated research, the inventors have found that by adjusting the alloy composition and molding conditions, it is possible to suppress the coarsening of crystal grains generated during high-temperature molding and to reduce the amount of cavitation that occurs.
That is, the present invention
(1) Mg 0.5% (mass%, the same shall apply hereinafter) to 2.0%, Zn 4.0% to 7.0%, Cu 0.35% or less, Zr 0.20% For high temperature forming, characterized in that it is an aluminum alloy composition containing Cr and 0.25% or less, Mn and 0.5% or less, and Ti and 0.1% or less, the balance being Al and inevitable impurities. Aluminum alloy extrusions,
(2) Mg is 0.5% to 2.0%, Zn is 4.0% to 7.0%, Cu is 0.35% or less, Zr is 0.20% or less, and Cr is 0.25. %, Mn 0.5% or less, Ti 0.1% or less, aluminum alloy extruded material of the alloy composition consisting of Al and inevitable impurities in the balance, after cold working, heat treatment for strain removal High temperature forming aluminum alloy extruded material,
(3) Mg is 0.5% to 2.0%, Zn is 4.0% to 7.0%, Cu is 0.35% or less, Zr is 0.20% or less, and Cr is 0.25. %, Mn is 0.5% or less, Ti is 0.1% or less, and after the aluminum alloy extruded material with the alloy composition consisting of Al and inevitable impurities is cold worked, strain is removed immediately before high temperature forming. High temperature forming aluminum alloy extruded material, characterized by being heat treated for, and
(4) After cold-working the aluminum alloy extruded material for high-temperature forming according to claim 1, heat treatment for strain removal is performed, and then 400 to 520 ° C. and a strain rate of 10 ⁻² / s to 10 Molded product characterized by being molded at ⁰ / s,
Is to provide.

  The extruded aluminum alloy material of the present invention can ensure strength without coarsening of crystal grains during high-temperature molding, and cavitation hardly occurs even when molding at high temperature, so the material strength does not decrease and is high for high-temperature molding. Formability can be obtained and high productivity can be obtained.

A preferred embodiment of the high temperature forming aluminum alloy extruded material of the present invention will be described in detail. The aluminum alloy extruded material referred to in the present invention refers to aluminum alloy rods, flat bars or hollow materials such as pipes and profiles.
First, for each component element of the alloy composition of the aluminum (Al) alloy, the reason for selecting the element and the reason for defining the content will be described.
In the present invention, Zn and Mg are added in order to ensure the strength of the material necessary for the extruded material and the high-temperature molded product. Further, Zr, Cr, Mn, and Ti are added in order to suppress the coarsening of crystal grains generated during high temperature forming. Further, Cu is added to improve stress corrosion cracking resistance.

  Other alloy elements such as Fe, Si and Ni other than the above alloy elements are basically impurities. However, from the viewpoint of recycling, not only high-purity Al ingots but also A1-Zn-Mg alloys, other Al alloy scrap materials, low-purity Al ingots, etc. are used as melting materials. When manufacturing what has the Al alloy composition of invention, these other alloy elements are necessarily contained. Therefore, in the present invention, it is allowed that other alloy elements such as Fe are contained within a range not impairing the effect of the intended invention.

The preferable content range and significance of each element of the alloy composition of the aluminum alloy, or the allowable amount will be described.
Magnesium (Mg) and zinc (Zn) affect strength and extrudability. In the alloy of the present invention, the Mg content is 0.5% (mass%, the same applies hereinafter) to 2.0%, preferably 0.5% to 1.5%, and the Zn content is 4.0. % To 7.0%, preferably 4.4% to 6.0%. When Mg is less than the specified value or Zn is less than the specified value, the extrudability is good but high strength cannot be obtained. On the other hand, when Mg is contained in excess of the prescribed value or Zn is contained in excess of the prescribed value, the extrudability is inferior, the required shape cannot be extruded, and the productivity is also inferior.
Therefore, the Mg content is 0.5% to 2.0%, and the Zn content is 4.0% to 7.0%.

Copper (Cu) improves the strength and stress corrosion cracking resistance of the aluminum alloy of the present invention, so 0.35% or less, preferably 0.01% to 0.2% is added. If the Cu content is too high, the corrosion resistance deteriorates. Therefore, Cu is 0.35% or less.
Zirconium (Zr) is an element that suppresses the coarsening of crystal grains generated during high-temperature forming, and is therefore added in an amount of 0.2% or less, preferably 0.03% to 0.17%. However, if Zr is added in excess of the specified value, a huge compound is produced during casting, and the toughness is reduced. Therefore, the Zr content is 0.2% or less.

Chromium (Cr) is also an element that suppresses the coarsening of crystal grains generated during high-temperature forming, and is therefore added at 0.25% or less, preferably 0.01% to 0.2%. If Cr is added in excess of the specified value, a huge compound is produced during casting and the toughness is reduced. Accordingly, the Cr content is 0.25% or less.
Manganese (Mn) is an element that suppresses the coarsening of crystal grains generated during high-temperature forming, and is added in an amount of 0.5% or less, preferably 0.01% to 0.4%. When there is too much Mn, extrudability will deteriorate and it will become difficult to quench. Therefore, the content is 0.5% or less.

Titanium (Ti) is an element that is generally added during the casting of industrial billets because it has the effect of refining the cast structure and has advantages such as prevention of ingot cracking. Also in the present invention, 0.1% or less, preferably 0.001% to 0.03% is added. If there is too much Ti, coarse intermetallic compounds will crystallize, and the toughness and fatigue characteristics of the material will be greatly reduced. If it is too little, the effect of miniaturization will be insufficient. It is desirable to limit the addition amount to 0.001% or more and 0.1% or less.
If boron (B) is added at the same time as Ti, the effect of refinement of the cast structure is further enhanced. Therefore, if desired, B is added together with Ti, but the content is preferably 0.02% or less.

In addition to the above-mentioned additive components, elements such as silicon (Si) and iron (Fe) are impurity elements mainly entering from raw materials such as aluminum bullion and scrap. These elements form Al-Fe-based, Al-Fe-Si-based, Al-Fe-Si-Mn-based intermetallic compounds and crystallized substances, Mg-Si-based intermetallic compounds, and the like during high-temperature molding. It is an element that makes the origin of cavitation generation. Therefore, when the Si content is limited to 0.25% or less and the Fe content is limited to 0.35% or less, the size of the intermetallic compound and its distribution density are reduced, and cavitation occurs during high temperature forming. Since it can suppress, it is preferable.
In addition, 0.05% or less of other impurity elements are allowed as impurities mixed from raw materials such as aluminum ingots and scraps other than Si and Fe. In the present invention, the total amount of inevitable impurities is preferably 0.1% or less.

Next, a method for forming the aluminum alloy extruded material for high temperature forming according to the present invention will be described.
As in the past, when cold working after extruding an Al-Zn-Mg-based aluminum alloy extrudate, strain remains in the material, but Al-Zn-Mg-based alloys contain many transition elements such as Zr and Cr. Therefore, when high-temperature forming is performed without sufficient recovery, Al-Fe-based and Al-Fe-Si-based intermetallic compounds may be the origin of cavitation, which may reduce the material strength.
Therefore, in the present invention, residual distortion of the material is removed by heat treatment before high temperature forming, and cavitation is greatly reduced by performing high temperature forming thereafter. Moreover, it turned out that it may carry out forced air cooling after the extrusion process at high temperature, and may perform high temperature shaping | molding in the state which has almost no distortion.

  The ingot of the aluminum alloy having the component composition as described above is subjected to homogenization treatment (for example, 450 ° C. to 520 ° C., 3 to 24 hours) according to a conventional method, and then a predetermined shape, for example, a hollow material such as a pipe It is extruded into a bar material, a plate material, etc., and can be used as an aluminum alloy extruded material for high temperature forming according to the present invention. A conventionally used aluminum alloy extruder can be used for the extrusion process, and the temperature of the extruded billet is preferably 400 ° C to 520 ° C, more preferably 420 ° C to 500 ° C. The extrusion speed is preferably 1 m / min to 15 m / min, more preferably 2 m / min to 10 m / min. In order to improve the dimensional accuracy, this extruded material can be subjected to drawing or stretching after the extrusion. A light stretch of about 1% after extrusion does not affect cavitation during high temperature molding.

Forcible air cooling after extrusion at high temperature and high temperature molding may be performed with almost no distortion, but cold bending and crushing can also be performed as preliminary processing before high temperature molding. If high temperature molding is performed with the residual strain remaining in the cold working, the material may not be sufficiently stretched, and a desired shape may not be molded. Therefore, it is preferable to perform heat treatment such as blunting to remove strain after cold working.
In addition, the heat treatment for removing the strain may be held at a high temperature when the temperature is raised before high-temperature molding, and then high-temperature molding may be performed. The heat treatment temperature for removing the strain is preferably as high as possible and requires a short time, so that the productivity is good. However, the balance is important because coarse crystal grains can be formed when held at a high temperature for a long time. Therefore, it is also preferable to raise the temperature in two stages, such that the first stage temperature rise is a temperature for distortion removal and the second stage temperature rise is a temperature for high temperature molding. The heat treatment conditions for removing the strain may be adjusted each time depending on the amount of residual strain, temperature increase, temperature decrease conditions, etc., for example, 350 ° C. to 500 ° C., 1 minute to 180 minutes, temperature increase time 1 minute ~ 120 minutes.

The temperature of the high temperature forming for forming the aluminum alloy extruded material for high temperature forming according to the present invention is such that if the temperature is too low, the elongation is small, the forming load is high, and if the forming temperature is too high, coarse crystal grains are likely to be generated. 400 ° C. to 520 ° C., more preferably 420 ° C. to 480 ° C.
If the strain rate is too high, the strain recovery is delayed and the elongation decreases, and if it is too slow, the time required for forming becomes longer, the crystal grains become coarse, and the productivity deteriorates. strain rate at the time of molding of the extruded material is ^preferably from 10 -2 / s~10 ⁰ / ^s, further preferably carried out at 10 -2 / s~10 ^-1 / s.

Next, although this invention is demonstrated in detail based on an Example with a comparative example, this invention is not restrict | limited to this.
Example 1
Aluminum alloys A to F having the metal components and composition ratios (mass%) shown in Table 1 below as extrusion materials were melt-cast into billets each having a diameter of 220 mm, and homogenized at 470 ° C. for 18 hours. Each billet was heated to 450 ° C., extruded into a flat rectangular shape having a width of 180 mm and a plate thickness of 5.5 mm at an extrusion speed of 6 mm / min. After forced air cooling with a fan to room temperature, the extruded material was stretched by about 0.5% of the total length. .

Further, a tensile test piece was cut out from each flat angle in the direction perpendicular to the extrusion direction and processed into the shape shown in FIG. These correspond to numbers 1 to 4 in Table 2 below.
On the other hand, each extruded flat was cold-rolled at room temperature to a sheet thickness of 4 mm, heat-treated under the conditions described in Table 2 for heat-retaining conditions for strain relief, and then a tensile test piece was cut out perpendicular to the rolling direction. It was processed into the shape shown in 1. This corresponds to numbers 5 to 10 and 15 in Table 2, respectively.
Further, similarly to the above, the extruded flat was cold-rolled, a tensile test piece was cut out perpendicular to the rolling direction without performing heat treatment, and processed into the shape shown in FIG. These correspond to numbers 11 to 14 and 16 in Table 2.
In FIG. 1, the unit of the numerical value indicating the length of the tensile test piece is mm.
In accordance with JIS Z 2241, these test pieces at room temperature are held in a high-temperature air furnace, and when the test pieces reach 430 ° C., they are pulled by 10 mm at a strain rate of 0.2 / s, and the following cavitation amounts are measured. Carried out.

Measurement and evaluation of the amount of cavitation Cut out a specimen for tissue observation (5 mm x 4 mm) from the center of the parallel part of the high-temperature tensile specimen, analyze the photograph taken with an optical microscope after polishing, and create a concave part in the shape of a hole The area ratio was measured using cavitation. The results are shown in Table 2 as cavity area ratio (%). In addition, the evaluation was shown as “◯” when the cavity area ratio was less than 1%, and “x” when 1% or more was rejected.

Since the tensile test corresponds to high-temperature molding of a rectangular material, numbers 1 to 4 correspond to those obtained by directly forming a rectangular high temperature, and the amount of cavitation generated during high-temperature molding is small, which is good for high-temperature molding. It turned out to be a flat square.
Nos. 5 to 10 were heat-treated after cold rolling, and the amount of cavitation generated at the time of high-temperature forming was small, and it was found that these were flat materials for good high-temperature forming.
On the other hand, Nos. 11 to 14 were not subjected to heat treatment for strain removal after cold rolling, and it was revealed that the amount of cavitation was large.
Further, numbers 15 and 16 were found to have an alloy composition outside the range defined by the present invention, and the amount of these cavitations was further increased.

(Example 2)
The aluminum alloys A to D having the metal component compositions shown in Table 1 as in Example 1 were cast and homogenized in the same manner as described in Example 1, extruded into a flat shape, and then cold-rolled. A tensile test piece was cut out from the rolling flat and perpendicular to the rolling direction, and processed into the shape shown in FIG.
For Nos. 21 to 26, after holding the test piece at room temperature in a high-temperature air furnace under the heat treatment conditions shown in Table 3, the temperature was changed, and when the test piece temperature reached 460 ° C., the strain rate was 0.03. / S was pulled by 10 mm, and the amount of cavitation was measured in the same manner as in Example 1 for evaluation.
Nos. 27 to 30 were obtained by heating a test piece at room temperature in a high temperature air furnace, pulling 10 mm at a strain rate of 0.03 / s when the test piece temperature reached 460 ° C., and measuring the amount of cavitation. It is.
The obtained results are shown in Table 3.

Nos. 21 to 26 were heat-treated for distortion removal immediately before high-temperature molding, and the amount of cavitation generated at the time of high-temperature molding was small, and it was found to be a good flat material.
On the other hand, numbers 27 to 30 were not subjected to heat treatment for removing strain after cold rolling, and it was found that the amount of cavitation was large.

It is a top view of the tensile test piece cut out in the Example.

Claims (4)

  Mg is 0.5% (mass%, the same shall apply hereinafter) to 2.0%, Zn is 4.0% to 7.0%, Cu is 0.35% or less, Zr is 0.20% or less, Cr Of aluminum alloy for high-temperature forming, characterized in that it has an aluminum alloy composition containing 0.25% or less, Mn 0.5% or less, Ti 0.1% or less, the balance being Al and inevitable impurities Wood.   Mg is 0.5% or more and 2.0% or less, Zn is 4.0% or more and 7.0% or less, Cu is 0.35% or less, Zr is 0.20% or less, Cr is 0.25% or less, An aluminum alloy extruded material containing 0.5% or less of Mn and 0.1% or less of Ti and the balance of Al and unavoidable impurities being cold worked and then heat-treated for strain removal An aluminum alloy extruded material for high temperature forming characterized by   Mg is 0.5% or more and 2.0% or less, Zn is 4.0% or more and 7.0% or less, Cu is 0.35% or less, Zr is 0.20% or less, Cr is 0.25% or less, After cold working an aluminum alloy extruded material containing 0.5% or less of Mn and 0.1% or less of Ti and the balance being Al and inevitable impurities, the strain is removed immediately before high temperature forming. An aluminum alloy extruded material for high temperature forming characterized by heat treatment. The aluminum alloy extruded material for high temperature forming according to claim 1 is cold-worked, and then subjected to heat treatment for strain removal, and then 400 ° C to 520 ° C and a strain rate of 10 ^-2 / s to 10 ⁰ / s. Molded product characterized by being molded with

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