US20240247342A1

US20240247342A1 - Aluminum alloy, aluminum-alloy hot-worked material, and manufacturing method thereof

Info

Publication number: US20240247342A1
Application number: US18/561,402
Authority: US
Inventors: Yuki Aisu; Tadashi Minoda
Original assignee: UACJ Corp
Current assignee: UACJ Corp
Priority date: 2021-06-16
Filing date: 2022-05-26
Publication date: 2024-07-25
Also published as: JP7705744B2; JP2022191887A; DE112022001222T5; CN117242198A; WO2022264767A1

Abstract

An aluminum alloy has a chemical composition that contains Sc: 0.01 mass % or more and 0.40 mass % or less, Mg: 0 mass % or more and 2.5 mass % or less, and Zr: 0 mass % or more and 0.4 mass % or less, the remainder being Al and unavoidable impurities. The compressive-deformation resistance, which is calculated based on the true stress when the aluminum alloy is deformed by compressing at a temperature of 450° C. and a strain rate of 1 s⁻¹, is 62 MPa or less.

Description

TECHNICAL FIELD

The present invention relates to an aluminum alloy, an aluminum-alloy hot-worked material, and a manufacturing method thereof.

BACKGROUND ART

Aluminum materials (including pure aluminum and aluminum alloys) take capitalize on characteristics, such as high specific strength and excellent workability, and are used in a variety of fields, such as: materials for transport, such as vehicles, aircrafts, and ships; building materials; common mechanical parts; etc. Among these applications as well, there is demand for high strength with regard to, for example, materials for vehicles in order to make vehicles lightweight. In addition, for vehicle materials and the like, the materials are formed into complex cross-sectional shapes or cross-sectional shapes having a fine structure. To meet this demand, there is demand for aluminum materials used in vehicles to have both a 0.2% offset yield strength of 140 MPa or more and excellent hot workability. 6000-series alloys, which contain Al (aluminum), Mg (magnesium), and Si (silicon), and 7000-series alloys, which contain Al, Mg, and Zn (zinc), are examples of aluminum alloys that satisfy such demand.
However, because 6000-series alloys have a low weld-joint efficiency, they are not suited to applications in which welding is required. In addition, there is a problem in that the corrosion resistance of 7000-series alloys is low.
On the other hand, 1000-series aluminum and 5000-series alloys, which include Al (aluminum) and Mg (magnesium), are known (e.g., Patent Document 1) as examples of aluminum materials that excel in weld-joint efficiency and corrosion resistance.

PRIOR ART LITERATURE

Patent Documents

Patent Document 1

- Japanese Patent No. 6446124

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, because 1000-series aluminum has a low alloying element content, there is a problem in that its strength is low. In addition, to increase the strength of 5000-series alloys, a method is conceivable in which the Mg content is simply made high. However, if the Mg content becomes high, then there is a risk that deformation resistance during hot working, such as, for example, hot rolling, hot extrusion, and the like, will become large, and therefore it will become difficult to form 5000-series alloys into desired shapes.
The present invention was conceived considering this background, and an object of the present invention is to provide: an aluminum alloy that can achieve both excellent hot workability and high strength even if Mg is not included and even if the Mg content is comparatively small; an aluminum-alloy hot-worked material composed of that aluminum alloy; and a manufacturing method thereof.

Means for Solving the Problems

One aspect of the present invention is an aluminum alloy having:

- a chemical composition that contains Sc (scandium): 0.01 mass % or more and 0.40 mass % or less, Mg (magnesium): 0 mass % or more and 2.5 mass % or less, and Zr (zirconium): 0 mass % or more and 0.4 mass % or less, the remainder being Al (aluminum) and unavoidable impurities;
- wherein compressive-deformation resistance, which is calculated based on the true stress when deformed by compressing at a temperature of 450° C. and a strain rate of 1 s⁻¹, is 62 MPa or less.

Another aspect of the present invention is an aluminum-alloy hot-worked material having:

- a chemical composition that contains Sc: 0.01 mass % or more and 0.40 mass % or less, Mg: 0 mass % or more and 2.5 mass % or less, and Zr: 0 mass % or more and 0.4 mass % or less, the remainder being Al and unavoidable impurities; and
- Al—Sc-series second-phase particles, which are dispersed in the Al parent phase;
- wherein the number density of the Al—Sc-series second-phase particles is 3,000 particles/μm³or higher.

Yet another aspect of the present invention is a method of manufacturing the aluminum-alloy hot-worked material comprising:

- a hot-working process, in which hot working is performed on the aluminum alloy according to the aspects above in the state in which the temperature is within the range of 350° C. or higher and 550° C. or lower; and
- a heat-treatment process, in which the aluminum alloy is held, at least one of before the hot-working process and after the hot-working process, for a total of 30 min or more at a hold temperature of 250° C. or higher and 550° C. or lower.

Effects of the Invention

The above-mentioned aluminum alloy contains Sc as an essential component and Mg and Zr as optional components. Sc in the above-mentioned aluminum alloy exists as a solid-solution element formed as a solid solution in the Al parent phase and as Al—Sc-series second-phase particles dispersed in the Al parent phase. The effect of Sc on deformation resistance during hot working is small in either of these states. For this reason, even in the situation in which the above-mentioned aluminum alloy does not contain Mg and the situation in which the above-mentioned aluminum alloy contains Mg in the above-mentioned specific range, an increase in deformation resistance is curtailed, and therefore a degradation in hot workability can be avoided.
In addition, by performing the above-mentioned specific heat-treatment process, the Sc as a solid-solution element precipitates into the Al parent phase as Al—Sc-series second-phase particles. Owing to the precipitation strengthening of the Al—Sc-series second-phase particles, the strength of the above-mentioned aluminum alloy can be increased.
As described above, in both the situation in which the above-mentioned aluminum alloy does not contain Mg and the situation in which the Mg content is comparatively low, both excellent hot workability and high strength can be achieved.
In addition, the above-mentioned aluminum-alloy hot-worked material has the above-mentioned specific chemical composition, and the number density of the Al—Sc-series second-phase particles dispersed in the Al parent phase is within the above-mentioned specific range. By setting the number density of the Al—Sc-series second-phase particles to the above-mentioned specific range, the above-mentioned aluminum-alloy hot-worked material having high strength can be easily achieved.
In addition, the method of manufacturing the above-mentioned aluminum-alloy hot-worked material comprises the hot-working process, in which hot working is performed on the aluminum alloy according to the above-mentioned aspect, and the heat-treatment process, in which the above-mentioned aluminum alloy is heated under the above-mentioned specific conditions. In the above-mentioned heat-treatment process, by heating the above-mentioned aluminum alloy under the above-mentioned specific conditions, the Sc that has formed as a solid solution in the aluminum alloy can be caused to precipitate as Al—Sc-series second-phase particles. Thereby, the strength of the ultimately obtained aluminum-alloy hot-worked material can be increased.

MODES FOR CARRYING OUT THE INVENTION

(Aluminum Alloy)

The chemical composition of the above-mentioned aluminum alloy and reasons for restrictions thereof will now be explained.

Sc: 0.01 Mass % or More and 0.40 Mass % or Less

The above-mentioned aluminum alloy contains 0.01 mass % or more and 0.40 mass % or less of Sc as an essential component. As described above, Sc in the above-mentioned aluminum alloy exists in the state of a solid-solution element that has formed as a solid solution in the Al parent phase, Al—Sc-series second-phase particles, or the like. Sc that forms a solid solution in the Al parent phase precipitates into the Al parent phase as Al—Sc-series second-phase particles when the above-mentioned aluminum alloy is held at a hold temperature of 250° C. or higher and 550° C. or lower. Furthermore, the Al—Sc-series second-phase particles that dispersed into the Al parent phase act to increase the strength of the above-mentioned aluminum alloy owing to precipitation strengthening.
The above-mentioned aluminum alloy is constituted such that, by setting the Sc content to the above-mentioned specific range, the number density of the Al—Sc-series second-phase particles existing in the Al parent phase can be set within the above-mentioned specific range. For that reason, the strength of the above-mentioned aluminum alloy can be increased easily. In addition, as described above, the effect on the hot workability of both the Sc, which forms a solid solution in the Al parent phase, and the Al—Sc-series second-phase particles is small. For that reason, even when Al—Sc-series second-phase particles exist in the above-mentioned aluminum alloy, the increase in deformation resistance during hot working can be curtailed.
The Sc content is preferably 0.03 mass % or more, more preferably 0.05 mass % or more, and yet more preferably 0.07 mass % or more. By making the Sc content in the above-mentioned aluminum alloy large, the number density of the Al—Sc-series second-phase particles after heat treatment can be made higher. As a result, the strength of the above-mentioned aluminum alloy can be further increased. When the Sc content is less than 0.01 mass %, there is a risk that it will become difficult to make the number density of the Al—Sc-series second-phase particles high, and therefore it will become difficult to make the strength high.
On the other hand, if the Sc content becomes excessively large, then the Sc content will exceed the solid-solubility limit, and therefore it will become difficult to form a solid solution of the Sc in the above-mentioned aluminum alloy. As a result, there is a risk that the effect of increased strength due to the Al—Sc-series second-phase particles will no longer be obtained. From the viewpoint of avoiding such a problem, the Sc content is set to 0.40 mass % or less. From the same viewpoint, the Sc content is preferably 0.35 mass % or less, more preferably 0.30 mass % or less, yet more preferably 0.25 mass % or less, and particularly preferably 0.15 mass % or less.

Mg: 0 Mass % or More and 2.5 Mass % or Less

The above-mentioned aluminum alloy may contain 2.5 mass % or less of Mg as an optional component. Mg in the above-mentioned aluminum alloy exists as a solid-solution element that forms a solid solution in the Al parent phase and acts to increase the strength of the above-mentioned aluminum alloy. By setting the Mg content in the above-mentioned aluminum alloy to the above-mentioned specific range, the effect of increased strength due to Mg can be obtained while curtailing the increase in deformation resistance during hot working.
From the viewpoint of further increasing the effect of increased strength due to Mg, the Mg content is preferably 0.2 mass % or more, more preferably 0.4 mass % or more, yet more preferably 0.8 mass % or more, particularly preferably 1.0 mass % or more, and most particularly preferably 1.2 mass % or more. On the other hand, from the viewpoint of further improving hot workability, the Mg content is preferably 2.2 mass % or less, more preferably 2.0 mass % or less, and yet more preferably 1.8 mass % or less.

Zr: 0 Mass % or More and 0.40 Mass % or Less

The above-mentioned aluminum alloy may contain 0.40 mass % or less of Zr as an optional component. Zr in the above-mentioned aluminum alloy exists in the state of a solid-solution element formed as a solid solution in the Al parent phase, a Zr-based precipitate, or the like. When the above-mentioned aluminum alloy is held at a hold temperature of 250° C. or higher and 550° C. or lower, Zr formed as a solid solution in the Al parent phase precipitates so as to surround the Al—Sc-series second-phase particles. The Zr-based precipitate that has precipitated in this manner acts to curtail an increase in the coarseness of the Al—Sc-series second-phase particles. Furthermore, owing to the Zr-based precipitate curtailing an increase in the coarseness of the Al—Sc-series second-phase particles, a large number of finer Al—Sc-series second-phase particles can be precipitated into the Al parent phase. As a result of the above, the effect of increased strength due to the Al—Sc-series second-phase particles can be further increased.
From the viewpoint of further increasing the above-described functions and effects due to Zr, the Zr content is preferably 0.01 mass % or more, more preferably 0.03 mass % or more, yet more preferably 0.06 mass % or more, and particularly preferably 0.09 mass % or more.
On the other hand, if the Zr content becomes excessively large, then the Zr content will exceed the solid-solubility limit, and therefore it will become difficult to form a solid solution of the Zr in the above-mentioned aluminum alloy. As a result, there is a risk that the above-described functions and effects due to the Zr-based precipitate will no longer be obtained. From the viewpoint of avoiding this problem, the Zr content is set to 0.40 mass % or less. From the same viewpoint, the Zr content is preferably 0.35 mass % or less, more preferably 0.30 mass % or less, and yet more preferably 0.25 mass % or less.
Cu (Copper): Greater than 0 Mass % and 1.0 Mass % or Less
The above-mentioned aluminum alloy may contain greater than 0 mass % and 1.0 mass % or less of Cu as an optional component. In this situation, the strength of the above-mentioned aluminum alloy can be further increased. From the viewpoint of further increasing the effect of increased strength due to Cu, the Cu content is preferably 0.10 mass % or more, more preferably 0.20 mass % or more, and yet more preferably 0.30 mass % or more.
On the other hand, if the Cu content becomes excessively large, then there is a risk that it will lead to a decrease in corrosion resistance. From the viewpoint of obtaining the effect of increased strength due to Cu while avoiding a decrease in corrosion resistance, the Cu content is preferably 0.90 mass % or less, more preferably 0.80 mass % or less, and yet more preferably 0.70 mass % or less.
Mn (Manganese): Greater than 0 Mass % and 1.0 Mass % or Less, Cr (Chrome): Greater than 0 Mass % and 0.30 Mass % or Less
The above-mentioned aluminum alloy may contain one or two elements from among greater than 0 mass % and 1.0 mass % or less of Mn and greater than 0 mass % and 0.30 mass % or less of Cr as optional components. By setting the content of each of these elements to the corresponding above-mentioned specific range, an increase in the coarseness of the crystal-grain composition during the process of manufacturing the above-mentioned aluminum alloy can be curtailed more effectively.
Ti (Titanium): Greater than 0 Mass % and 0.10 Mass % or Less, B (Boron): Greater than 0 Mass % and 0.10 Mass % or Less
The above-mentioned aluminum alloy may contain one or two elements from among greater than 0 mass % and 0.10 mass % or less of Ti and greater than 0 mass % and 0.10 mass % or less of B as optional components. These elements act to increase the fineness of the crystal grains when the melt is solidified in the process of manufacturing the above-mentioned aluminum alloy. By setting the Ti content and the B content to the above-mentioned specific ranges, the crystal grains of the above-mentioned aluminum alloy can be made sufficiently fine, and therefore the strength of the ultimately obtained aluminum-alloy hot-worked material can be further increased.

Unavoidable Impurities

Elements such as, for example, Fe (iron), Si (silicon), etc. are examples of unavoidable impurities contained in the above-mentioned aluminum alloy. As unavoidable impurities, the Fe content is 0.50 mass % or less and the Si content is 0.50 mass % or less. In addition, unavoidable impurities other than Fe and Si are 0.05 mass % or less for each element. As long as the content of each element that serves as an unavoidable impurity is within the corresponding above-described range, impairment of the above-described functions and effects due to unavoidable impurities can be easily avoided.

Compressive-Deformation Resistance: 62 MPa or Less

The aluminum alloy having the chemical composition in the above-mentioned specific ranges has a compressive-deformation resistance of 62 MPa or less. It is noted that compressive-deformation resistance in the present specification is the compressive-deformation resistance calculated based on the true stress when deformed by compressing at a temperature of 450° C. and a strain rate of 1 s⁻¹.
By setting the compressive-deformation resistance of the above-mentioned aluminum alloy to the above-mentioned specific range, the hot workability of the aluminum alloy can be improved. In addition, aluminum alloys having compressive-deformation resistance in the above-mentioned specific range can also be applied to a forming method in which particularly high hot workability is required, such as, for example, porthole extrusion, i.e., a forming method in which an aluminum alloy is drawn from a die constituted by combining a male type and a female type.

(Aluminum-Alloy Hot-Worked Material)

By performing hot working, such as hot rolling, hot extrusion, or the like, on the above-mentioned aluminum alloy, an aluminum-alloy hot-worked material (hereinbelow, called “hot-worked material”) can be obtained. The chemical composition of the above-mentioned hot-worked material is identical to the chemical composition of the aluminum alloy used as the raw material.
Al—Sc-series second-phase particles, i.e., second-phase particles that contain Al and Sc, are dispersed in the Al parent phase of the above-mentioned hot-worked material. Specifically, the Al—Sc-series second-phase particles are constituted from intermetallic compounds having a composition of Al₃Sc, Al₃(Sc_xZr_1-x), or the like. It is noted that the value of x in Al₃(Sc_xZr_1-x) is 0<x<1. The value of x in Al₃(Sc_xZr_1-x) varies in accordance with the Zr content in the aluminum alloy and the heating conditions in the heat-treatment process.
The number density of the Al—Sc-series second-phase particles in the above-mentioned hot-worked material is preferably 3,000 particles/μm³or higher. The Al—Sc-series second-phase particles act to increase the strength of the hot-worked material due to precipitation strengthening. By setting the number density of the Al—Sc-series second-phase particles in the hot-worked material to the above-mentioned specific range, the strength of the hot-worked material can be increased.
The effect of precipitation strengthening due to the second-phase particles can be predicted to a certain degree based on equation (1) below, which is described in C. B. Fuller et al., Acta Materialia 51 (2003) 4803-4814.
$\begin{matrix} σ = 2.8 / λ (\ln λ + 5.4) + σ_{0} & (1) \end{matrix}$
It is noted that σ in the equation above is the 0.2% offset yield strength [MPa] of the aluminum alloy that has precipitation hardened due to the second-phase particles, λ is the average inter-grain distance [μm] of the second-phase particles, and σ₀is the 0.2% offset yield strength [MPa] of an aluminum alloy that does not contain second-phase particles.
Average inter-grain distance λ of the second-phase particles in equation (1) above can be expressed as equation (2) below using number density N [particles/μm³] per unit of volume of the second-phase particles.
$\begin{matrix} λ = N^{- 1 / 3} & (2) \end{matrix}$
When 35 MPa, which is the typical 0.2% offset yield strength of JIS A1100 aluminum, is used as σ₀, equation (1) above can be expressed as equation (3) below.
$\begin{matrix} σ = 2.8 N^{1 / 3} (\ln N^{- 1 / 3} + 5.4) + 3 5 & (3) \end{matrix}$
Furthermore, when N in equation (3) above is set to 3,000 particles/μm³, the 0.2% offset yield strength σ becomes approximately 145 MPa. Accordingly, by setting the number density of the Al—Sc-series second-phase particles to the above-mentioned specific range, it can be expected that the 0.2% offset yield strength of the aluminum alloy will become 140 MPa or more, even in the situation in which Mg is not contained.
From the viewpoint of further increasing the strength of the hot-worked material, the number density of the Al—Sc-series second-phase particles is more preferably 5,000 particles/μm³or higher and yet more preferably 7,000 particles/μm³or higher. It is noted that the upper limit of the number density of the Al—Sc-series second-phase particles is naturally determined in accordance with the Sc amount contained in the above-mentioned aluminum-alloy hot-worked material.
The number density of the Al—Sc-series second-phase particles in the above-mentioned hot-worked material can be calculated based on the result when the fine structure is observed using a transmission electron microscope (TEM). More specifically, first, from among measurement specimens sampled from the above-mentioned hot-worked material, the thickness of a measurement specimen is set to 0.1 μm by electrolytic polishing. The measurement specimen is observed using a TEM, and the number of Al—Sc-series second-phase particles having a circle-equivalent diameter of 0.5 nm or more and less than 10 nm existing within the visual field is counted. Furthermore, a value calculated by converting the number of the Al—Sc-series second-phase particles existing within the visual field to the number per 1 μm³of volume is used as the number density of the Al—Sc-series second-phase particles.
The shape of the above-mentioned aluminum-alloy hot-worked material is not particularly limited; for example, the material can take on a variety of shapes such as a sheet material, a bar material, a pipe material, a strip material, an extruded shape, or the like. The above-mentioned aluminum-alloy hot-worked material is preferably prepared by porthole extrusion. The hot-extrusion material prepared by porthole extrusion has a hollow part at at least one location surrounded by wall parts composed of the aluminum alloy. In addition, a welding surface at at least one location constituted by welding the above-mentioned aluminum alloys together may be formed at the above-mentioned wall part of the hot-extrusion material prepared by porthole extrusion.
As described above, the above-mentioned aluminum alloy has hot workability to the extent that porthole extrusion is possible. Accordingly, by using the above-mentioned aluminum alloy, a hot-extrusion material having a complex cross-sectional shape and a cross-sectional shape having a fine structure implementable by porthole extrusion can be easily prepared.

(Method of Manufacturing the Aluminum-Alloy Hot-Worked Material)

A method of manufacturing the above-mentioned aluminum-alloy hot-worked material comprises: a hot-working process in which hot working is performed in the state in which the temperature of the above-mentioned aluminum alloy is within the range of 350° C. or higher and 550° C. or lower; and

- a heat-treatment process in which the above-mentioned aluminum alloy is held for a total of 30 min or more at a hold temperature of 250° C. or higher and 550° C. or lower in at least one among before the above-mentioned hot-working process and after the above-mentioned hot-working process has completed.

Hot-Working Process

Objects, which have been prepared by a usual method, can be used as the aluminum alloy that will be subjected to the hot-working process. For example, the aluminum alloy may be an ingot, in which a melt having the above-mentioned specific chemical composition is cast by a method such as DC casting or CC casting, or may be a billet.
A variety of working methods, such as hot rolling, hot extrusion, hot forging, and the like, can be used as the hot working in the hot-working process. An aluminum alloy having the above-mentioned specific chemical composition and that excels in hot workability is used as the above-mentioned manufacturing method. For this reason, porthole extrusion, which serves as the hot working in the hot-working process, can be used as the above-mentioned manufacturing method. Furthermore, by performing porthole extrusion, a hot-extrusion material having a complex cross-sectional shape or a cross-sectional shape having a fine structure can be obtained easily.
The start temperature of the hot working in the hot-working process is set to 350° C. or higher and 550° C. or lower. In the situation in which the start temperature is lower than 350° C., the deformation resistance of the above-mentioned aluminum alloy becomes excessively high, and therefore it becomes difficult to perform hot working. On the other hand, in the situation in which the start temperature is higher than 550° C., there is a risk that the aluminum alloy will tend to partially melt during hot working owing to the working-induced heat generation.

Heat-Treatment Process

In the above-mentioned manufacturing method, a heat-treatment process that heats the aluminum alloy is performed. The hold temperature in the heat-treatment process is set to 250° C. or higher and 550° C. or lower. In addition, the hold time in the heat-treatment process is set to a total of 30 min or more. By setting the hold temperature and the hold time in the heat-treatment process to the above-mentioned specific ranges, fine and numerous Al—Sc-series second-phase particles are caused to precipitate into the Al parent phase, and thereby the strength of the hot-worked material can be increased.
In the situation in which the hold temperature in the heat-treatment process is lower than 250° C. and in the situation in which the total hold time is less than 30 min, the amount of the Al—Sc-series second-phase particles that precipitate becomes insufficient, and therefore there is a risk that it will lead to a decrease in the strength of the hot-worked material. In the situation in which the hold temperature in the heat-treatment process is higher than 550° C., there is a risk that it will lead to a partial melting of the aluminum alloy.
The heat-treatment process may be performed prior to performing the hot-working process or may be performed after the hot-working process has completed. In addition, the heat-treatment process may be performed both prior to performing the hot-working process and after the hot-working process has completed. As described above, the effect of the Al—Sc-series second-phase particles on hot workability is small. For this reason, even in the situation in which the heat-treatment process is performed prior to performing the hot-working process and the hot working is then performed on the aluminum alloy into which the Al—Sc-series second-phase particles have precipitated, the hot working can be performed easily.

Working Examples

Working examples of the above-mentioned aluminum alloy, the above-mentioned aluminum-alloy hot-worked material, and the manufacturing method thereof will be explained below. It is noted that the specific aspects of the aluminum alloy, the aluminum-alloy hot-worked material, and the manufacturing method thereof according to the present invention are not limited to the aspects described in the working examples, and the composition can be appropriately changed within a range that does not impair the gist of the present invention.
In the present example, first, melts of the aluminum alloys having the chemical compositions indicated in Table 1 were cast by a usual method, and billets exhibiting a circular-column shape having a diameter of 90 mm and a length of 200 mm were prepared. It is noted that the symbol “Bal.” in Table 1 is a symbol that indicates the remainder. The billets were held for 10 h at a hold temperature of 300° C. and subsequently held for 10 h at a hold temperature of 400° C. (heat-treatment process).
After the heat-treatment process was completed, hot extrusion, in which the billets were heated to 450° C., was performed (hot-working process). During the hot extrusion, the container temperature was set to 450° C., the die temperature was set to 450° C., and the extrusion rate was set to 1.0 m/min. Based on the above, Test Materials A-F could be obtained. It is noted that Test Materials A-F were strip materials having a width of 35 mm and a thickness of 2 mm.
In addition, a billet was heated to 500° C., and hot extrusion was performed under the conditions of a container temperature of 500° C., a die temperature of 500° C., and an extrusion rate of 1.4 m/min, and thereby Test Material G could be obtained. It is noted that Test Material G was a strip material having a width of 35 mm and a thickness of 2.6 mm.
In addition, Test Material H and Test Material I indicated in Table 1 were test materials for comparison with Test Materials A-G. The method of manufacturing Test Material H and Test Material I was the same as the method of manufacturing Test Materials A-F, other than the chemical compositions of the aluminum alloys being different.
Each of the test materials and the physical properties of the aluminum alloys used in the preparation of the test materials could be evaluated using the method below.

Compressive-Deformation Resistance of Aluminum Alloy

After the heat-treatment process was performed, a test piece for compression testing that exhibited a circular-column shape having a diameter of 8 mm and a length of 12 mm was sampled from a billet prior to performing hot working. Using this test piece, compression testing was performed under the conditions of a temperature of 450° C. and a strain rate of 1 s⁻¹, and a load-displacement curve was obtained. Based in this load-displacement curve, it was assumed that the deformation of the test piece during the compression test was uniform, and the true strain and true stress were calculated. Furthermore, the true stress was arithmetically averaged over the range in which the true strain was 0.3 or more and less than 0.6, and this value was used as the compressive-deformation resistance. The compressive-deformation resistance of each test material is shown in Table 2.

Number Density of Al—Sc-Series Second-Phase Particles Existing in Test Material

A test piece having a thickness of 0.1 μm was prepared by cutting the test material to an appropriate size and then performing electrolytic polishing. Observations were performed, using a TEM, at three locations randomly selected from the test piece, and a dark-field image having a visual field of 2 μm×2 μm was acquired. Furthermore, the number density of the Al—Sc-series second-phase particles was calculated by converting the number of Al—Sc-series second-phase particles having a circle-equivalent diameter of 0.5 nm or more and less than 10 nm existing in the dark-field images at these three locations to the number per 1 μm³of volume.
The number density of the Al—Sc-series second-phase particles existing in Test Material A was 10,000 particles/μm³. In addition, the number density of the Al—Sc-series second-phase particles existing in each of Test Materials B-G was assumed to be approximately the same as that of Test Material A.

Mechanical Characteristics of Test Materials

Test Piece No. 5, as stipulated in JIS Z2241:2011, was sampled from the test material. A tension test was performed using this test piece, and the tensile strength and the 0.2% offset yield strength were calculated. The tensile strength and the 0.2% offset yield strength of each of the test materials are shown in Table 2.

Extrudability

The evaluation of extrudability was performed using the method below. First, the billet after the heat-treatment process had completed was heated to 520° C. Furthermore, porthole extrusion was performed on the billet using a die configured such that a square pipe was formable having a square shape whose cross-sectional shape was 31 mm on a side and whose thickness of the wall parts that surround the hollow part was 2.5 mm. During the porthole extrusion, the container temperature was set to 450° C., the die temperature was set to 450° C., and the extrusion rate was set to 1.0 m/min.
Symbol “A” noted in the “Extrudability” column in Table 2 indicates that the square pipe could be prepared when the porthole extrusion was performed under the conditions described above, and symbol “B” indicates that a square pipe could not be prepared.

	TABLE 1

	Chemical Composition (mass %)

	Mg	Ti	Zr	Sc	Al

Test Material A	1.0	0.01	0.21	0.10	Bal.
Test Material B	1.3	0.01	0.22	0.10	Bal.
Test Material C	1.4	0.01	0.20	0.10	Bal.
Test Material D	1.6	0.01	0.19	0.10	Bal.
Test Material E	1.8	0.01	0.25	0.10	Bal.
Test Material F	1.9	0.01	0.21	0.09	Bal.
Test Material G	2.0	0.01	0.20	0.10	Bal.
Test Material H	1.1	0.01	<0.01	<0.01	Bal.
Test Material I	3.0	0.01	<0.01	<0.01	Bal.

TABLE 2

Tensile	0.2% Offset	Compressive-
Strength	Yield Strength	Deformation Resistance
(MPa)	(MPa)	(MPa)	Extrudability

Test Material A	232	179	48	A
Test Material B	246	190	47	A
Test Material C	254	191	51	A
Test Material D	258	192	53	A
Test Material E	260	198	55	A
Test Material F	272	200	56	A
Test Material G	240	159	57	A
Test Material H	101	39	40	A
Test Material I	197	72	67	B

As shown in Table 1 and Table 2, the aluminum alloys used in Test Materials A-G had the above-mentioned specific chemical compositions, and the compressive-deformation resistance of the billets was 62 MPa or less. Consequently, these test materials had excellent hot workability and it was possible to perform porthole extrusion. In addition, because each of the Test Materials A-G had the above-mentioned specific chemical compositions, the number density of the Al—Sc-series second-phase particles could be set to 3,000 particles/μm³or higher by performing the heat treatment. As a result, the 0.2% offset yield strength of each of the Test Materials A-G after the heat treatment could be set to 140 MPa or more.
On the other hand, because Test Material H was composed of an aluminum alloy that did not contain Sc, Al—Sc-series second-phase particles were not formed in the billet after the heat treatment. For this reason, the 0.2% offset yield strength of Test Material H was lower than that of Test Material A.
The aluminum alloy that constituted Test Material I contained a larger amount of Mg than that of Test Material H to make the strength of Test Material I higher than that of Test Material H. However, because the Mg content became greater, the compressive-deformation resistance of the aluminum alloy increased, and therefore hot extrudability degraded. For this reason, it was difficult to perform porthole extrusion on Test Material I. In addition, although the 0.2% offset yield strength of Test Material I was higher than that of Test Material H, it was lower than that of Test Materials A-G.

Claims

1. An aluminum alloy having:

Sc: 0.01 mass % or more and 0.40 mass % or less, Mg: 0 mass % or more and 2.5 mass % or less, and Zr: 0 mass % or more and 0.4 mass % or less;

wherein compressive-deformation resistance, which is calculated based on the true stress when deformed by compressing at a temperature of 450° C. and a strain rate of 1 s⁻¹, is 62 MPa or less.

2. The aluminum alloy according to claim 1, wherein the Mg content is 0.2 mass % or more and 2.5 mass % or less.

3. The aluminum alloy according to claim 1, wherein the Zr content is 0.01 mass % or more and 0.4 mass % or less.

4. The aluminum alloy according to claim 1, wherein the aluminum alloy further contains one or two or more elements selected from the group consisting of Cu: greater than 0 mass % and 1.0 mass % or less, Mn: greater than 0 mass % and 1.0 mass % or less, Cr: greater than 0 mass % and 0.30 mass % or less, Ti: greater than 0 mass % and 0.10 mass % or less, and B: greater than 0 mass % and 0.10 mass % or less.

5. An aluminum-alloy hot-worked material having:

wherein:

Al—Sc-series second-phase particles are dispersed in the Al parent phase; and

the number density of the Al—Sc-series second-phase particles is 3,000 particles/μm³or higher.

6. The aluminum-alloy hot-worked material according to claim 5, wherein the Mg content is 0.2 mass % or more and 2.5 mass % or less.

7. The aluminum-alloy hot-worked material according to claim 5, wherein the Zr content is 0.01 mass % or more and 0.4 mass % or less.

8. The aluminum-alloy hot-worked material according to claim 5, wherein the aluminum-alloy hot-worked material further contains one or two or more elements selected from the group consisting of Cu: greater than 0 mass % and 1.0 mass % or less, Mn: greater than 0 mass % and 1.0 mass % or less, Cr: greater than 0 mass % and 0.30 mass % or less, Ti: greater than 0 mass % and 0.10 mass % or less, and B: greater than 0 mass % and 0.10 mass % or less.

9. The aluminum-alloy hot-worked material according to claim 5, wherein:

the aluminum-alloy hot-worked material has a hollow part at at least one location surrounded by a wall part composed of aluminum alloy; and

a welding surface at at least one location, constituted by welding the aluminum alloys together, is formed on the wall part.

10. A method of manufacturing an aluminum-alloy hot-worked material, comprising:

performing hot working on the aluminum alloy according to claim 1 in a state in which the temperature is within the range of 350° C. or higher and 550° C. or lower; and

before and/or after the hot-working step, holding the aluminum alloy for a total of 30 min or more at a hold temperature of 250° C. or higher and 550° C. or lower.

11. The method according to claim 10, wherein, in the hot-working step, porthole extrusion is performed as the hot working on the aluminum alloy.