WO2022181307A1 - Method for manufacturing aluminum alloy extruded material - Google Patents

Abstract

The purpose of the present invention is to provide a method for manufacturing an aluminum alloy extruded material with which it is possible to widen the allowable range for Si and Fe as impurities and obtain a high strength, so as to enable use of an aluminum recycled material.　The present invention is a method for manufacturing an aluminum alloy extruded material in which is used an aluminum alloy containing 20-95 mass% of an aluminum recycled material obtained by recovering an extruded material of an aluminum alloy comprising a used scrap material or a scrap material generated during a manufacturing process and re-melting the extruded material, and containing, by mass, 6.0 to 8.0% of Zn, 1.0 to 2.0% of Mg, 0.10 to 0.50% of Cu 0.10 to 0.25% of Zr, and 0.005 to 0.05% of Ti, as well as 0.30% or less of Si and 0.40% or less of Fe as impurities with the remainder made up by Al, the method for manufacturing an aluminum alloy extruded material being characterized in performing cooling from an extruded material temperature of 325-550°C immediately after the extrusion processing at a cooling speed of 50-750°C/min, and then performing a two-stage artificial aging treatment of 1-8 hours at 90-130°C and then 1-20 hours at 130-180°C.

Description

Method for manufacturing aluminum alloy extruded material

The present invention relates to a method for producing an extruded material using an Al-Zn-Mg-based aluminum alloy, and in particular can effectively utilize recycled aluminum material.

High-strength aluminum alloys used for extruded materials are roughly classified into Al--Mg--Si based 6000 series aluminum alloys and Al--Zn--Mg based 7000 series aluminum alloys.
The aluminum alloy used for extruded materials is continuously cast into long billets by injecting molten metal with an alloy composition adjusted to a predetermined range from the top of the mold and cooling and solidifying from the bottom or bottom of the mold. Used.
In this manufacturing process, Si and Fe components are likely to be mixed as impurities.
Therefore, when used products that have been produced as extruded materials using aluminum alloy billets or scrap materials such as mill ends generated in the manufacturing process of products are remelted and used as recycled aluminum materials, this Inclusion of Si and Fe poses a problem.
Al--Si--Mg-based aluminum alloys originally have a large Si content, and the allowable range of Fe content is relatively large, so this is not a big problem. If there is, the contamination of Si and Fe causes a decrease in strength and bending formability, which is a serious problem.

For example, in Patent Document 1, Zn: 5.0 to 7.0 wt%, Mg: 1.0 to 1.50 wt%, Cu: 0.1 to 0.3 wt%, Zr: 0.05 to 0.20 wt% , Cr: 0.03 to 0.2 wt%, Mn: 0.3 wt% or less, Ti: 0.001 to 0.05 wt%, and the balance being Al and unavoidable impurities. .
In the extruded aluminum alloy material disclosed in the same publication, Si and Fe are also treated as impurities, and in the examples, Si is suppressed to a level of 0.1 wt% or less and Fe is suppressed to a level of 0.21 wt% or less.
This is because 0.03 to 0.2 wt% of Cr is added to suppress the size and depth of the recrystallized layer formed on the surface of the extruded material. ) properties [stress corrosion cracking resistance], it was necessary to suppress the amounts of impurities such as Si and Fe.

Japanese Patent No. 2928445

The purpose of the present invention is to provide a method for manufacturing an aluminum alloy extruded material that can widen the allowable range of impurities Si and Fe and obtain high strength so that recycled aluminum can be used.

In the method for producing an aluminum alloy extruded material according to the present invention, an aluminum alloy extruded material made of used or scrap material generated in the manufacturing process is recovered, and 20 to 95% by mass of remelted aluminum recycled material is contained. All in mass %, Zn: 6.0 to 8.0%, Mg: 1.0 to 2.0%, Cu: 0.10 to 0.50%, Zr: 0.10 to 0.25%, Ti A method for producing an aluminum alloy extruded material using an aluminum alloy containing: 0.005 to 0.05%, Si: 0.30% or less, Fe: 0.40% or less as impurities, and the balance being Al There, the extruded material is cooled from 325 to 550 ° C. immediately after extrusion at a cooling rate of 50 to 750 ° C./min, and then at 90 to 130 ° C. for 1 to 8 hours and 130 to 180 ° C. for 1 to 20 It is characterized by two-stage artificial aging treatment of time.
In the present invention, the composition of the molten metal is adjusted by remelting the recycled aluminum material and adding the virgin material to it.
Here, Mn may be contained at 0.35% or less, and Sr may be contained at 0.25% or less.
As a result, an extruded material having a tensile strength of 400 MPa or more and a 0.2% yield strength of 380 MPa or more is obtained.

In the present invention, in order to improve the usage ratio of recycled aluminum materials, the amount of Si and Fe mixed as impurities is expanded to the following mass%, Si: 0.30% or less, Fe: 0.40% or less. The composition of the aluminum alloy is set so that it can be quenched at a cooling rate equivalent to that of air cooling immediately after extrusion, has high strength, and is resistant to SCC.
<Zn component>
In the 7000 series aluminum alloys, the Zn component has the highest content, because even at a relatively high concentration, there is little decrease in extrudability.
However, excessive addition of Zn lowers the resistance to stress corrosion cracking.
<Mg component>
The Mg component is an important additive component along with Zn because high strength is obtained by the precipitates of the Zn component and _MgZn2 . , Mg: in the range of 1.0 to 2.0%.
<Cu component>
The Cu component improves the strength by dissolution, and when it exists together with MgZn ₂ at the grain boundary of the metal structure, it has the effect of lowering the potential difference with the PF zone, thereby improving the SCC resistance.
Here, the PF zone refers to a region where precipitates do not exist (Precipitate-Free-Zone) observed on both sides of the grain boundary.
However, if added excessively, extrudability deteriorates and general corrosion resistance deteriorates.
<Zr, Mn, Cr components>
Zr, Mn, and Cr components are all transition elements, and have the effect of suppressing the depth of the recrystallized layer formed on the surface of the extruded material during extrusion, the effect of refining crystal grains, and the SCC resistance. improves.
However, there is a difference in the effect on quenching immediately after extrusion. The Cr component has the sharpest quenching sensitivity, and the required high strength cannot be obtained without high-speed water cooling in die end quenching.
Next, it is the Mn component that sharpens the quenching sensitivity, and the Zr component has the least quenching sensitivity.
Therefore, Zr: 0.10 to 0.25%, Mn: 0.35% or less, it is preferable not to add Cr, and when it is added, it is preferable to suppress the level of unavoidable impurities to less than 0.05%. .
<Sr component>
The Sr component has a great effect on the crystal structure during billet casting, and the addition of a small amount of Sr component suppresses coarsening of crystal grains and suppresses recrystallization on the surface of the extruded material during extrusion.
Although it is not an essential component in the present invention, Sr is preferably added at 0.25% or less.
However, if it is added excessively, coarse crystallized substances appear and the strength decreases, so it is necessary to adjust the amount of transition elements added, and the total of [Mn + Zr + Sr] is 0.25 to 0.50%. range.
<Ti component>
The Ti component is effective for refining crystal grains during billet casting, and the Ti content is preferably in the range of 0.05 to 0.05%.
In addition, a very small amount of B is often contained.

Next, billet casting and homogenization processing will be described.
A billet for extrusion processing is generally continuously cast as a cylindrical long billet.
There are various casting methods such as hot top casting and float type casting. Cast into a cylindrical billet.
The billet used in the present invention preferably has a fine structure composed of fine crystal grains, and is cooled and solidified and cast to the lower side of the mold at a casting speed of 50 mm / min or more. As a result, the microstructure of the billet preferably has a casting structure with an average grain size of 250 µm or less, preferably 200 µm or less.

The extrusion processing conditions will be explained.
The extruder has a container with an extrusion die attached on the front side, and a cylindrical billet is loaded into this container and hot-extruded from the rear using a stem or the like.
Here, the billet is preheated to 400° C. or higher, preferably 430 to 510° C., loaded into a container, and extruded.
The extruded material extruded by hot working becomes hot due to the heat of processing, but it is preferable to secure a temperature of 440 ° C. or higher in order to sufficiently perform the subsequent quenching, and at least 325 ° C. or higher is required at the start of cooling by air cooling. do.
Further, if the temperature of the extruded material immediately after extrusion exceeds 550° C., it is not preferable because the appearance tends to be distorted.

The extruded material extruded as described above is subjected to die end quenching by air cooling.
Ensure a cooling rate in the range of 50 to 750°C/min by fan air cooling or the like.
In conventional water cooling, the extruded material is often locally quenched, and strain deformation such as cross-sectional deformation is likely to occur in the extruded material. It can also prevent deformation.

The artificial aging treatment after extrusion will be described.
An extruded material made of a 7000 series aluminum alloy contains G.I. in the crystal structure of the extruded material. P. High strength is obtained by precipitating zones and intermediate phases, and two-stage artificial aging treatment is performed at 90 to 130°C for 1 to 8 hours in the first stage and at 130 to 180°C for 1 to 20 hours in the second stage. done.

By adopting the aluminum alloy composition and manufacturing conditions as described above, the present invention can increase the amount of recycled material used, and obtains an extruded material with high strength and excellent SCC resistance.

The composition of the aluminum alloy used for evaluation is shown. Billet casting and extrusion conditions are shown. The evaluation results of extruded materials are shown.

By adjusting the composition of various aluminum alloys, cylindrical billets with a diameter of 8 inches were experimentally produced and evaluated while examining the extrusion conditions, which will be described below.
Using molten aluminum alloys of various alloy compositions shown in the table of FIG. 1, 8-inch long billets were cast at the casting speeds shown in the table of FIG.
In this case, to adjust the composition shown in the table of FIG. 1, recycled aluminum material was used in the ratio shown in the table of FIG.
Next, immediately after performing homogenization treatment under the homogenization treatment conditions indicated as "HOMO" in the table of FIG. 2, cooling was performed under the conditions of "cooling rate after HOMO" in the table of FIG.
Each condition shown in the table indicates conditions suitable for the present invention.
In the table, "billet crystal grain size" refers to the value of the average crystal grain size measured with an optical microscope after cutting out a test piece of the casting cross section from the billet, polishing and etching the piece.
In the table, "BLT temperature" indicates the preheat temperature when the billet is loaded into the container of the extruder, "post-extrusion shape temperature" is the surface temperature of the extruded material immediately after extrusion, "cooling start shape temperature" and ""Post-extrusion cooling rate" indicates the surface temperature of the extruded material at the start of die end insertion and the cooling rate by fan air cooling.
"Heat treatment condition" in the table indicates the condition and treatment time of the artificial aging treatment.
The evaluation results are shown in the table of FIG.
"T5 tensile strength", "T5 yield strength", and "T5 elongation" in the table are JIS-Z2241, JIS-5 test pieces cut out in the extrusion direction from the two-stage artificially processed extruded material, and tensile tests according to JIS standards. Measured by machine.
In the table, "SCC property" is obtained by cutting out a test piece from the extruded material in the extrusion direction, applying a stress of 80% of the 0.2% yield strength value shown in "T5 yield strength" in the table in the bending direction, and under the following conditions. 720 cycles were carried out and the presence or absence of cracks was evaluated.
"○" in the table indicates that no crack occurred.
SCC resistance test <1 cycle>
After being immersed in a 3.5% NaCl aqueous solution at 25° C. for 10 minutes, it was held in an atmosphere of 25° C. and humidity of 40% for 50 minutes, then taken out from the test furnace and air-dried.
"Microstructure, surface recrystallization depth" in the table was obtained by polishing and etching the extruded cross section of the extruded material and measuring the depth of the recrystallized layer formed on the surface side of the extruded material with an optical microscope.

From the evaluation results in FIG. 3, the following can be said.
In Examples 1 to 8, the composition of the aluminum alloy, the casting conditions of the aluminum billet, and the extrusion processing conditions were set within the set ranges, so that the usage rate of the recycled aluminum material could be set high within the range of 20 to 95%.
On the other hand, in Comparative Example 1, since the recycled aluminum material was 100%, Si: 0.30% or less and Fe: 0.40% or less could not be suppressed, and the SCC resistance did not reach the target. rice field.
In Comparative Example 2, although the amount of recycled aluminum material used was suppressed to 25%, the target SCC resistance was not achieved because the alloy composition was outside the set range.
In Comparative Example 3, 100% recycled aluminum material was used, but in this case the target strength was also not achieved.

According to the present invention, aluminum alloy extruded materials with high strength and excellent SCC resistance can be obtained while effectively using recycled aluminum materials, which can be used for structural members of vehicles and various machines.

Claims (3)

1. It contains 20 to 95% by mass of aluminum alloy extruded material that is used or made of scrap material generated in the manufacturing process and is remelted. 0%, Mg: 1.0 to 2.0%, Cu: 0.10 to 0.50%, Zr: 0.10 to 0.25%, Ti: 0.005 to 0.05%,
   A method for producing an aluminum alloy extruded material using an aluminum alloy containing as impurities Si: 0.30% or less, Fe: 0.40% or less, and the balance being Al,
   Cooling at a cooling rate of 50 to 750 ° C./min from the extruded material temperature of 325 to 550 ° C. immediately after extrusion processing,
   A method for producing an aluminum alloy extruded material, characterized in that it is then subjected to a two-stage artificial aging treatment at 90 to 130° C. for 1 to 8 hours and at 130 to 180° C. for 1 to 20 hours.
2. The method for producing an aluminum alloy extruded material according to claim 1, wherein an aluminum alloy containing 0.35% or less of Mn and 0.25% or less of Sr is used.
3. The method for producing an aluminum alloy extruded material according to claim 1 or 2, characterized in that the tensile strength is 400 MPa or more and the 0.2% yield strength is 380 MPa or more.

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