Patent Application
20250065385
This application is based upon and claims the benefit of priority to Japanese Patent Application No. 2023-137035 filed on Aug. 25, 2023, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a recycled material-containing 7000 series aluminum alloy, a billet and an extruded material using the same, and particularly relates to an extruded material excellent in stress corrosion cracking resistance (SCC resistance) and high strength while increasing the use rate of recycled materials (scrap materials), and a method of manufacturing the extruded material.
Al—Zn—Mg series and Al—Zn—Mg—Cu series aluminum alloys that are 7000 series aluminum alloys are known as aluminum alloys excellent in high strength.
In these 7000 series aluminum alloys, Fe and Si are alloy components belonging to impurities, and influence thereof is large in expanded materials.
If these impurity components increase in the process of recycling scrap materials, it causes stress corrosion cracking resistance to decrease and prevents high strength from being obtained.
JP-A-2023-17976 discloses the technique that allows use of scrap materials by forming the shapes of intermetallic particles into a circular or spherical shape with an aspect ratio of 4 or less, but sufficient strength and SCC resistance cannot be obtained.
The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. These are, of course, merely examples and are not intended to be limiting. In addition, the disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, when a first element is described as being “connected” or “coupled” to a second element, such description incudes embodiments in which the first and second elements are directly connected or coupled to each other, and also includes embodiments in which the first and second elements are indirectly connected or coupled to each other with one or more other intervening elements in between.
The present disclosure has an object to provide an extruded material excellent in SCC resistance with high strength while increasing a use rate of recycled materials (scrap materials) in a 7000 series aluminum alloy, and a method of manufacturing the extruded material.
In accordance with one of some aspect, there is provided a recycled material-containing 7000 series aluminum alloy comprising, by mass %, 6.0 to 8.0% of Zn, 1.0 to 2.0% of Mg, 0.10 to 1.0% of Cu, 0.004 to 0.40% of Mn, 0.10 to 0.25% of Zr, 0.005 to 0.05% of Ti, and 0.05% or less of Cr, wherein 30% or more of recycled material is contained with content ranges of Si and Fe set as ranges of 0.01 to 0.25% of Si, 0.10 to 0.40% of Fe, and 0.20 to 1.05% of [Fe+Mn+Zr].
The recycled materials include remnants and chips generated during the manufacturing process of aluminum products, and scrap materials and the like collected from the city.
In order to use recycled materials during extrusion, the recycled materials are melted, and are adjusted as a component in a molten aluminum alloy, thereafter are cast into a columnar billet and subjected to extrusion processing.
Accordingly, Fe and Si are easily included from impurity elements contained in the city scrap material, and from furnaces and dies contacting the aluminum alloy in the processes of remelting and casting.
Expanded materials are more affected by impurities as compared with cast materials, and in particular in 7000 series alloys, Fe has been usually kept at 0.1% or less, and at most to a 0.2% level.
Further, Si has been also preferably 0.1% or less.
This limits the use rate of the recycled materials.
Thus, the present disclosure is characterized in that the content ratio of the recycled materials can be increased by controlling the length and ratio of crystallized substances that appear in the metal texture.
In the present disclosure, the extrusion processing billets are billets for extrusion processing that are cast by using a 7000 series aluminum alloy according to claim 1, and it is preferable that in the billets, an average length of the crystallized substances in the metal texture is 100 μm or less, and a crystalized substance ratio is 6% or less.
The billets formed from the metal texture like this are obtained by making a casting rate 45 mm/min or more and making a solidification rate a high rate of 5° C./sec or more, for example in a billet diameter of 174 mm or more, for example, 204 mm.
The billets for extrusion processing are produced by pouring a molten aluminum alloy into a casting die from above and casting it downward continuously or semi-continuously while cooling and solidifying it.
At this time, by rapidly cooling the billets so that the solidification rate is 5° C./sec or more, the average length of the crystallized substances such as the needle-like crystallized substances made of intermetallic compounds in the metal texture can be 100 μm or less, and the ratio of the crystallized substances can be 6% or less.
As a result, even if the amount of impurities such as Fe and Si increases, it is possible to maintain excellent SCC resistance and high strength of the extruded material in the next extrusion processing.
In accordance with one of some aspect, there is provided an aluminum alloy extruded material obtained by using the extrusion processing billet, wherein in the extruded material, an average length of crystallized substances in a metal texture is 20 □m or less, and a crystallized substance ratio is 6% or less.
The extruded material like this is obtained by setting the sectional area of the extruded material with respect to the billet diameter so that the extrusion ratio that should increase processibility during the extrusion processing is 12 or more.
As a result, even if 30% or more of recycled materials are contained, it is possible to obtain an extruded material excellent in SCC resistance and having high strength with tensile strength of 400 MPa or more, 0.2% yield strength of 380 MPa or more by die end hardening immediately after extrusion processing and two-stage artificial aging treatment.
Exemplary embodiments are described below. Note that the following exemplary embodiments do not in any way limit the scope of the content defined by the claims laid out herein. Note also that all of the elements described in the present embodiment should not necessarily be taken as essential elements.
Molten aluminum alloys having the aluminum alloy compositions of Examples 1 to 14 and the aluminum alloy compositions of Comparative Examples 1 to 3 illustrated in
In
An in-process scrap and a city scrap represent the breakdown of the total amount of recycled materials.
The in-process scrap refers to remnants and the like generated in the manufacturing process of aluminum products within the company, while the city scrap refers to sash scraps, chips, and remnants obtained from outside the company.
In the present disclosure, the target of the use rate of the recycled materials was 30% or more.
For evaluation, the columnar billets having a diameter D=174 mm or more, for example, 204 mm were produced and used as illustrated in
The content of hydrogen gas in the molten metal was set to 0.2 cc/100 g Al or less, and the targets were a casting rate of 45 mm/min or more and a solidification rate of 5° C./sec or more using a water-cooled vertical continuous casting machine.
The cast billets were subjected to homogenization treatment (HOMO) at 470 to 540° C. for 2 to 8 hours and then, cooled to 100° C. or less at a cooling rate of 50° C./hr or more.
The measurement results of average crystal grain sizes, crystallized substance lengths, and crystallized substance rates in the metal textures of the billets obtained by this are illustrated in
The measurement method is as follows.
From the billet cast materials, the respective samples of a center portion (C), a radius ½ portion (R/2), and a surface layer portion (R) illustrated in
The metal textures were observed by optical microscope observation, the crystallized substance lengths inside the billets were measured by using 500× images, and the average values were calculated.
The crystallized substances in the 500× images were measured as area ratios by image analysis.
Note that the targets were an average crystallized substance length of 100 μm or less, and a crystallized substance rate of 6% or less.
Extrusion processing is performed under the conditions illustrated in
The sectional areas of the extruded materials used in the evaluation are of two types that are 981 mm2 and 1307 mm2, and the extrusion ratios are 33 and 25 respectively.
The billets were preheated so that the billet temperatures (BLT temperatures) reach to the temperatures illustrated in Table 3, and then subjected to extrusion processing so that the temperatures of the extruded profiles immediately after extrusion were 440° C. or higher. As the conditions of die end hardening (air cooling) immediately after extrusion, natural cooling was performed for 0.1 min or more until the extruded material temperature (cooling start temperature) after extrusion reached 400 to 550° C., and fan air cooling was started at a cooling rate of 50 to 750° C./min thereafter (cooling rate after start of cooling).
Next, two-stage artificial aging treatment was performed under the conditions illustrated in
The evaluation items and the evaluation conditions are as follows.
Based on JIS-Z2241, JIS-5 tensile test pieces were prepared from the extruded profiles, and tensile tests were conducted with a tensile tester in accordance with the JIS standard.
Samples were cut out from the extruded profiles, mirror polishing finish of the extrusion sections was performed, and then, the metal textures were observed by optical microscope observation.
The crystallized substance lengths inside the extrusions were measured from 1000× images, and calculated as the average values.
The crystallized substances in the 1000× images were measured in area rate by image analysis.
Test pieces of a thickness t3 mm×width w20 mm×length L100 mm were cut out from the extruded profiles, and the SCC resistance was evaluated by three-point bending stress load as illustrated in
The test piece is immersed in 3.5% NaCl aqueous solution at 25° C. for 10 min, after which, it is left in 40% humidity at 25° C. for 50 min, and then naturally dried.
Based on JIS-Z2242, JIS-V notch No. 4 test pieces are prepared from the extruded profiles, and a Charpy impact test is carried out by using a Charpy impact tester in accordance with the JIS standard.
Samples are cut out from the extruded profiles, mirror polishing finish of the extruded sections is performed, and then etching is carried out by a sodium hydroxide reagent (3% NaOH).
The metal textures are observed by optical microscope observation, and the thicknesses of the recrystallized textures from the extrusion surfaces are measured from 1000× images.
The surfaces of the extruded profiles after extrusion were observed for the presence of attachment of foreign matter and cracks by visual observation.
Examples 1 to 14 were able to clear all the quality targets even if the use rate of the recycled materials is 30% or more.
On the other hand, in Comparative example 1, the average length of the crystallized particles was large, the tensile strength and the yield strength did not reach the targets, because the Si amount was 0.30% which exceeded 0.25% in the present disclosure, the casting rate was also 40 mm/min which did not meet the requirement of 45 mm/min or more in the present disclosure.
In Comparative example 2, the amount of Cu components is 1.10% which is larger than 1.00% in the present disclosure. Therefore, under the cooling conditions and the artificial aging treatment conditions after extrusion processing according to the present disclosure, the strength was insufficient, and the tensile strength and the yield strength did not reach the targets.
Comparative example 3 was adopted as a comparative example as reference because it did not include recycled materials. In Comparative example 3, SCC resistance, the Charpy impact value, the average length of the crystallized substances and the surface recrystallization depth did not reach the targets.
The present disclosure can improve the SCC resistance by selecting appropriate billet casting conditions and extrusion processing conditions even if the Si and Fe component amounts increase by including the recycled materials.
Although only some embodiments of the present disclosure have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-137035 | Aug 2023 | JP | national |
