US20180347017A1 - Aluminum alloy material and production method therefor - Google Patents

Aluminum alloy material and production method therefor Download PDF

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US20180347017A1
US20180347017A1 US15/777,798 US201615777798A US2018347017A1 US 20180347017 A1 US20180347017 A1 US 20180347017A1 US 201615777798 A US201615777798 A US 201615777798A US 2018347017 A1 US2018347017 A1 US 2018347017A1
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equigranular
aluminum alloy
specimen
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Taichi Suzuki
Hidenori HATTA
Shuhei Shakudo
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UACJ Corp
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/10—Alloys based on aluminium with zinc as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
    • C22F1/053—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with zinc as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon

Definitions

  • the present disclosure relates to an aluminum alloy material and a production method therefor.
  • Conventional 7000-series aluminum alloys with Zn and Mg added to Al have been known as aluminum alloys exhibiting a high strength. Such 7000-series aluminum alloys exhibit a high strength due to age precipitation of Al—Mg—Zn-based fine precipitates. 7000-series aluminum alloys to which Cu has been added in addition to Zn and Mg exhibit the highest strength among aluminum alloys.
  • 7000-series aluminum alloys are produced by, for example, hot extrusion or other process, and are used in applications requiring a high strength, including transportation equipment, such as aircraft and vehicles, and machine parts, as well as sporting goods and so on.
  • Properties that 7000-series aluminum alloys are required to have when used in such applications include impact absorbability (toughness), resistance to stress corrosion cracking (hereinafter referred to as resistance to SCC, which is an abbreviation of Stress Corrosion Cracking), and so on, in addition to strength.
  • 7000-series aluminum alloys is, for example, an aluminum alloy extruded material disclosed in Patent Document 1.
  • Patent Document 1 Japanese Unexamined Patent Application Publication No. 2007-119904
  • Means for solving the above-described problems in surface quality, such as generation of the streak patterns include to make the metallographic structure to be a recrystallized structure, which is not fibrous but equigranular. With such a recrystallized structure, a situation can be inhibited in which the compounds precipitated on the grain boundary are arranged linearly, whereby generation of streak patterns can be reduced.
  • a 7000-series aluminum alloy has the recrystallized structure, its strength is lowered and its toughness and resistance to SCC are also decreased in some cases, as compared with the case of having the fibrous structure.
  • scale-like patterns are conspicuous although generation of the streak patterns can be reduced. In this way, conventional 7000-series aluminum alloys have been difficult to use in the applications requiring properties such as resistance to SCC and surface quality as well, in addition to a high strength and a high toughness.
  • An aluminum alloy material as one aspect of the present disclosure has a chemical composition comprising: Zn: more than 6.5% (mass %, same applies hereafter) and 8.5% or less; Mg: 0.5% or more and 1.5% or less; Cu: 0.10% or less; Fe: 0.30% or less; Si: 0.30% or less; Mn: less than 0.05%; Cr: less than 0.05%; Zr: 0.05% or more and 0.10% or less; and Ti: 0.001% or more and 0.05% or less, a balance comprising Al and inevitable impurities.
  • a mass ratio of Zn to Mg (Zn/Mg) is 5 or more and 16 or less, and a metallographic structure comprises an equigranular recrystallized structure.
  • the above-described aluminum alloy material has the above-specified chemical composition, and its metallographic structure comprises the equigranular recrystallized structure. This makes it possible to inhibit poor surface quality after surface treatment such as anodization, as compared with a case in which its metallographic structure is a fibrous structure.
  • regulation of the upper limit of the Mg content makes it possible to inhibit precipitation of the compounds on the grain boundary while ensuring a high strength, thereby inhibiting generation of scale-like patterns on the surface caused by the recrystallized structure after surface treatment such as anodization.
  • regulation of the upper limit of the Cu content makes it possible to inhibit the surface from becoming yellowish in color tone by surface treatment. As a result, a good surface quality can be obtained.
  • the mass ratio of Zn to Mg (Zn/Mg) to the above-specified range, toughness and resistance to SCC can be improved while ensuring a high strength.
  • a production method for an aluminum alloy material as another aspect of the present disclosure is a method for producing an aluminum alloy material, a metallographic structure of which comprises an equigranular recrystallized structure.
  • the method comprises: preparing an ingot having a chemical composition comprising: Zn: more than 6.5% (mass %, same applies hereafter) and 8.5% or less; Mg: 0.5% or more and 1.5% or less; Cu: 0.10% or less; Fe: 0.30% or less; Si: 0.30% or less; Mn: less than 0.05%; Cr: less than 0.05%; Zr: 0.05% or more and 0.10% or less; and Ti: 0.001% or more and 0.05% or less, a balance comprising Al and inevitable impurities, wherein a mass ratio of Zn to Mg (Zn/Mg) is 5 or more and 16 or less; and performing a homogenizing treatment in which the ingot is heated at a temperature higher than 540° C. and 580° C. or lower for 1 hour or longer and
  • the ingot having the above-specified chemical component and having the mass ratio of Zn to Mg (Zn/Mg) set to the above-specified range is prepared in the production process. Then, the ingot is subjected to the homogenizing treatment under the above-specified conditions.
  • the heating temperature in the homogenizing treatment to a high temperature, which is higher than 540° C. and 580° C. or lower, it becomes possible to easily obtain the above-described aluminum alloy material, that is, a high-strength aluminum alloy material, a metallographic structure of which comprises an equigranular recrystallized structure and which is excellent in surface quality, toughness, and resistance to SCC.
  • FIG. 1 is an explanatory diagram showing a bending test method.
  • FIG. 2 is an explanatory diagram showing a method for observing metallographic structures.
  • Zn coexists with Mg to precipitate a ⁇ ′ phase, and provides an effect of improving strength.
  • the range of Zn content is more than 6.5% and 8.5% or less. If the Zn content is 6.5% or less, a precipitation amount of the ⁇ ′ phase is reduced, thus decreasing the strength improving effect. In contrast, if the Zn content is more than 8.5%, hot workability is reduced to thereby decrease productivity.
  • a preferred range of the Zn content is 7.0% or more and 8.0% or less.
  • Mg coexists with Zn to precipitate a ⁇ ′ phase, and provides the effect of improving strength.
  • the range of Mg content is 0.5% or more and 1.5% or less.
  • the upper limit of the Mg content it is possible to inhibit precipitation of compounds on a grain boundary (a crystal grain boundary, a sub-grain boundary, or the like), while obtaining the strength improving effect. This makes it possible to reduce, at the time of surface treatment such as anodization, an amount of the compounds that have precipitated on the grain boundary to be etched at pretreatment, to thereby inhibit generation of scale-like patterns on the surface-treated surface.
  • the Mg content is less than 0.5%, a precipitation amount of the ⁇ ′ phase is reduced, thus decreasing the strength improving effect.
  • the Mg content is more than 1.5%, coarse compounds are likely to be generated on the grain boundary, thus increasing an amount of the compounds to be etched at pretreatment of surface treatment such as anodization. Therefore, scale-like patterns are generated on the surface-treated surface, resulting in poor surface quality.
  • the Mg content is preferably 1.0% or more and 1.3% or less.
  • Cu may get mixed in when a recycled material is used as a raw material for an aluminum alloy material.
  • inclusion of Cu contributes to improvement in strength, whereas change in color tone or the like occurs, such as yellowing of the color tone of the surface caused by surface treatment such as anodization. Such change in color tone may cause poor surface quality.
  • the upper limit of Cu content needs to be regulated. Regulation of the upper limit of the Cu content to 0.10% or less makes it possible to reduce the above-described poor surface quality.
  • the Cu content is preferably 0.08% or less.
  • Fe and Si may get mixed in as impurities of aluminum metal.
  • Mn and Cr may get mixed in when a recycled material is used as a raw material for an aluminum alloy material.
  • Fe, Si, and Mn have an effect of inhibiting recrystallization by forming Al—Mn-based, Al—Mn—Fe-based, and/or Al—Mn—Fe—Si-based intermetallic compounds in combination with Al.
  • Cr has an effect of inhibiting recrystallization by forming Al—Cr-based intermetallic compounds in combination with Al.
  • Zr is added to obtain a fine and uniform recrystallized structure.
  • the range of Zr content is 0.05% or more and 0.10% or less.
  • Zr forms fine Al—Zr-based compounds in combination with Al.
  • the crystal structure of the Al—Zr-based compounds changes depending on the temperature at which the ingot is subjected to homogenizing treatment. If the temperature in the homogenizing treatment is 540° C. or lower, a metastable phase is formed which has an L1 2 structure commensurate with the matrix, thus inhibiting recrystallization in the structure subjected to hot working and readily leading to formation of a fibrous structure. In contrast, if the homogenizing treatment is performed at a temperature higher than 540° C. and 580° C.
  • the Al—Zr-based compounds change into an equilibrium phase having a D0 23 structure. This results in formation of an equigranular recrystallized structure, not a fibrous structure, after hot working, and also inhibits recrystallized grains from coarsening by blocking movement of the crystal grain boundary.
  • the Zr content is less than 0.05%, the effect of inhibiting the recrystallized grains from coarsening is less likely to be obtained, resulting in formation of a nonuniform metallographic structure in which the recrystallized grains have partially coarsened. This causes a problem that mottled patterns are visually confirmed on the surface subjected to surface treatment such as anodization, or other problem, and results in poor surface quality.
  • the Zr content is more than 0.10%, the Al—Zr-based compounds are distributed more densely; thus, recrystallization is inhibited to form a fibrous structure. This causes generation of streak patterns on the surface-treated surface, and results in poor surface quality.
  • Ti is added to seek micronization of crystal grains in the ingot.
  • the range of Ti content is 0.001% or more and 0.05% or less. If the Ti content is less than 0.001%, an effect of micronizing the crystal grains is reduced. Thus, mottled patterns are likely to be generated on the surface subjected to surface treatment such as anodization, resulting in poor surface quality.
  • the Ti content is more than 0.05%, a point defect is likely to occur on the surface-treated surface due to Al—Ti-based intermetallic compounds formed in combination with Al or other cause, resulting in poor surface quality.
  • Contained other than the above-listed elements may be basically Al and inevitable impurities. Elements to be generally added to the aluminum alloy other than the above-listed elements are allowed to be present as inevitable impurities, within a range not greatly affecting the properties of the aluminum alloy.
  • the mass ratio of Zn to Mg is 5 or more and 16 or less.
  • 7000-series aluminum alloys can generally obtain higher strength by addition of Zn and Mg.
  • addition of a large amount of Zn reduces hot workability, and addition of a large amount of Mg facilitates generation of coarse compounds to thereby reduce surface treatmentability and toughness.
  • general 7000-series alloys are known as having a decreased resistance to SCC when the metallographic structure thereof is a recrystallized structure.
  • upper limits of the Zn content and the Mg content are regulated and, further, the mass ratio (Zn/Mg) is set to be within the above-specified range. As a result, the following properties can be obtained.
  • the absolute value of the generation amount of MgZn 2 compounds is made smaller. Further, by setting the mass ratio (Zn/Mg) to 16 or less, that is, by decreasing the Mg content relatively and also by regulating the mass ratio (Zn/Mg) to 16 or less, the MgZn 2 compounds are inhibited from growing coarse. As a result, fine compounds are obtained and toughness can be improved.
  • the resistance to SCC will be discussed below.
  • an electric potential of the matrix in the vicinity of the grain boundary is nobler than that of the MgZn 2 compounds precipitated on the grain boundary.
  • Such an electric potential difference causes a local anodic dissolution under a stress corrosion environment, thus generating a crack in the vicinity of the grain boundary. This is considered to cause stress concentration and, thus, generation and progress of cracking.
  • the mass ratio (Zn/Mg) is set to 5 or more, that is, an amount of Zn that is solid-solved in the matrix is made to be relatively large and also the mass ratio (Zn/Mg) is regulated to 5 or more. This makes it possible to alleviate the electric potential difference from the MgZn 2 compounds present on the grain boundary, thus improving the resistance to SCC even in the recrystallized structure.
  • a high-strength aluminum alloy material which has a good surface quality and is excellent in toughness and resistance to SCC can be obtained by regulating the upper limits of the Zn content and the Mg content and also by setting the mass ratio (Zn/Mg) to 5 or more and 16 or less.
  • the mass ratio (Zn/Mg) is less than 5, the effect of reducing and micronizing the compounds composed of Zn and Mg is decreased, and the effect of improving toughness cannot be sufficiently obtained.
  • the mass ratio (Zn/Mg) is more than 16, the Zn content becomes larger to thereby cause anodic dissolution in the vicinity of the grain boundary more likely, resulting in decrease in resistance to SCC.
  • a preferable range of the mass ratio (Zn/Mg) is 7 or more and 16 or less.
  • the metallographic structure of the above-described aluminum alloy material comprises an equigranular recrystallized structure.
  • the recrystallized structure means a metallographic structure comprising equigranular recrystallized grains.
  • the metallographic structure can be confirmed by, for example, observing a surface or a cross-section of the aluminum alloy material with a polarizing microscope.
  • the recrystallized structure be such that: an average grain diameter of the crystal grains in a cross-section parallel to a direction orthogonal to a working direction of the aluminum alloy material (e.g., a direction of extrusion in the case of an extruded material) is 500 ⁇ m or less; and also such that a difference between the maximum value and the minimum value of the grain diameters of the crystal grains is less than 300 ⁇ m. In this case, the grain diameters of the crystal grains in the recrystallized structure are more uniform, and a good surface quality is thereby obtained.
  • “Working” as in the “working direction” means extruding, rolling, or other processing.
  • the “cross-section parallel to a direction orthogonal to a working direction” means, for example, a cross-section parallel to a width direction (a cross-section orthogonal to a thickness direction) when the working direction is assumed to be a length direction.
  • the crystal grains in the recrystallized structure are more than 500 ⁇ m, the crystal grains are excessively coarse, resulting in a risk that mottled patterns caused by the coarse crystal grains may be generated on the surface subjected to surface treatment such as anodization. If the difference between the maximum value and the minimum value of the grain diameters of the crystal grains is 300 ⁇ m or more, the metallographic structure is nonuniform, resulting in a risk that a light reflection state may be nonuniform on the surface subjected to surface treatment.
  • the yield strength, as defined in JIS Z2241 (ISO 6892-1), of the above-described aluminum alloy material is preferably 300 MPa or more, and more preferably 350 MPa or more. This makes it possible to relatively easily obtain strength properties applicable to a lesser wall thickness for weight reduction.
  • an ingot which comprises the above-described chemical components and in which the mass ratio of Zn to Mg (Zn/Mg) is 5 or more and 16 or less, and then a homogenizing treatment is performed in which the ingot is heated at a temperature of higher than 540° C. and 580° C. or lower for 1 hour or longer and 24 hours or shorter.
  • the heating temperature in the above-described homogenizing treatment is 540° C. or lower, the Al—Zr-based compounds present in the ingot form a metastable phase having an L1 2 structure commensurate with the matrix, thus inhibiting recrystallization in the structure subjected to hot working and readily leading to formation of a fibrous structure.
  • This causes generation of streak patterns on the surface subjected to surface treatment such as anodization, and results in poor surface quality.
  • a segregated layer in the ingot is not homogenized, and the structure subjected to hot working becomes a nonuniform recrystallized structure. As a result, a final surface quality becomes similarly poor.
  • the heating temperature in the above-described homogenizing treatment is higher than 580° C., the ingot may be melt locally, resulting in difficulty in practical production.
  • the heating temperature in the above-described homogenizing treatment is set to be higher than 540° C. and 580° C. or lower, whereby the Al—Zr-based compounds present in the ingot change to an equilibrium phase having a D0 23 structure.
  • the heating time for the above-described homogenizing treatment is shorter than 1 hour, the segregated layer in the ingot is not homogenized, and the structure subjected to hot working becomes a nonuniform recrystallized structure. As a result, a final surface quality becomes poor similarly to the above.
  • the heating time for the above-described homogenizing treatment exceeds 24 hours, the segregated layer in the ingot is sufficiently homogenized; thus, no further effect can be expected. Accordingly, the heating time for the above-described homogenizing treatment is set to 1 hour or longer and 24 hours or shorter.
  • the above-described aluminum alloy material includes, for example, an extruded material, a plate material, and so on made of aluminum alloy.
  • the present disclosure can be applied to various aluminum alloy materials and production methods therefor.
  • a cylindrical ingot (billet) having a diameter of 90 mm containing chemical components shown in Table 1 is forged by semicontinuous casting. Then, a homogenizing treatment is performed in which the ingot is heated at 560° C. for 12 hours. The heating temperature in the homogenizing treatment may be higher than 540° C. and 580° C. or lower. Subsequently, the ingot is subjected to hot extrusion with the temperature of the ingot maintained at 520° C. In this way, an extruded material having a width of 150 mm and a thickness of 10 mm is obtained.
  • a quenching treatment is performed in which the extruded material subjected to hot extrusion is cooled to 100° C. at a cooling rate of 1500° C./min. Then, after the quenched extruded material is cooled to room temperature, an artificial aging treatment is performed in which the extruded material is heated at 140° C. for 12 hours. In this way, a specimen of the aluminum alloy material (extruded material) is obtained.
  • test piece is prepared from the specimen by a method based on JIS Z2241 (ISO 6892-1), and a tensile strength, a yield strength, and an elongation of the test piece are measured.
  • the test piece having a yield strength of 300 MPa or more is determined to be acceptable.
  • the criterion for determining the yield strength is just an example.
  • a test piece 10 having a thickness of 10 mm, a width of 10 mm, and a length of 120 mm is prepared from a width-direction central portion of the specimen, and an amount ⁇ of bending deformation of the test piece 10 is measured by a three-point bending test.
  • a jig comprising a base 11 and two supporting portions 12 is prepared, and the test piece 10 is left at rest on the two supporting portions 12 .
  • the two supporting portions 12 each support the test piece 10 at a position 10 mm from the corresponding end of the test piece 10 , so that a distance between supporting points becomes 100 mm.
  • a downward load in a direction orthogonal to the width direction of the specimen is applied to the specimen by an indenter 13 , the dimension of which at a leading end surface is 10 mm ⁇ 10 mm.
  • the test piece 10 is determined to be unacceptable “X”; if more than 2 mm and 4 mm or less, the test piece 10 is determined to be acceptable “ ⁇ ”; and if 2 mm or less, the test piece 10 is determined to be desirable “ ⁇ ”.
  • a Charpy impact test is performed by a method based on JIS Z2242. Specifically, a test piece having a thickness of 7.5 mm, a width of 10 mm, and a length of 55 mm is prepared. A longitudinal direction of the test piece is parallel to a direction of extrusion, and the test piece has a U-shaped notch having a depth of 2 mm, formed so as to be orthogonal to the direction of extrusion. The Charpy impact test is performed on the test piece, and an impact value is measured. If the impact value is 15 J/cm 2 or more, the test piece is determined to be acceptable, and if less than 15 J/cm 2 , the test piece is determined to be unacceptable. The criteria for determining the impact value is just an example.
  • An SCC test is performed by a method based on JIS Z8711. Specifically, a test piece having a C-ring shape (outside diameter: 19 mm, inside diameter: 16 mm, thickness: 8 mm) is prepared. Then, a stress of 90% of the yield strength is applied to the test piece such that a direction of application of a tensile stress at a stress-concentrated part corresponds to a direction of extrusion of the test piece. In such a state and under a temperature environment of 25° C., the test piece is immersed in salt water with the concentration of 3.5% for 10 minutes and then dried for 50 minutes. Such steps as one cycle are repeatedly performed. Thirty days later, whether a cracking is generated in the test piece is visually confirmed. If no cracking is generated, the test piece is determined to be acceptable, and if a cracking is generated, the test piece is determined to be unacceptable.
  • a texture observation of the specimen is performed at a cross-section parallel to a width direction when the working direction (the direction of extrusion here) is assumed to be a length direction. In particular, a portion in the vicinity of a width-direction center of the cross-section is observed.
  • an extruded material 20 as the specimen is cut, and three cross-sections in total, that is, a cross-section at a thickness-direction central position of the extruded material 20 and cross-sections at 1 ⁇ 4 positions from the top and the bottom in the thickness directions of the extruded material 20 , are electrolytically polished. Then, a microscopic image (e.g., a photograph shown in a lower part of FIG.
  • the obtained microscopic image thereof is subjected to image analysis.
  • Equivalent circle diameters of the crystal grains on the respective cross-sections are found, and an average grain diameter of the crystal grains on each cross-section is calculated.
  • the greatest diameters and the smallest diameters of the crystal grains on the respective cross-sections are found, and the greatest one of the greatest diameters and the smallest one of the smallest diameters are respectively referred to as a maximum value and a minimum value. Then, a difference between the maximum value and the minimum value of the grain diameters of the crystal grains (a grain diameter difference) is calculated.
  • the specimen is determined to be desirable.
  • the specimen After a surface of the specimen is mechanically polished (buffed), the specimen is etched with an aqueous sodium hydroxide and is further desmutted. Then, the desmutted specimen is chemically polished by a phosphoric acid-nitric acid method for 1 minute at a temperature of 90° C.
  • the chemically polished specimen is anodized at a current concentration of 150 A/m 2 in a 15% sulfuric acid bath to form an anodized coating having a thickness of 10 ⁇ m.
  • the anodized specimen is immersed in boiling water to perform a sealing treatment on the anodized coating. In this way, the specimen is subjected to a surface treatment (anodization).
  • the surface-treated (anodized) surface of the specimen is visually observed.
  • the specimen is observed from a viewpoint vertical to a surface thereof, and the specimen having no surface defect, such as a scale-like pattern, a streak pattern, a mottled pattern, or a point defect, generated on its surface is determined to be acceptable. Further, the specimen is observed from a viewpoint at an angle of 30° with respect to its surface, and the specimen whose light reflection state on its surface is uniform is determined to be desirable.
  • the scale-like pattern is a pattern looking like scales along a grain boundary (a pattern in which crystal grains are seen more conspicuously) generated as a result of etching the compounds precipitated on the grain boundary at pretreatment of the surface treatment, in a case where the metallographic structure is an equigranular recrystallized structure.
  • the streak pattern is a pattern looking like a streak along a grain boundary generated as a result of etching the compounds precipitated on the grain boundary at pretreatment of the surface treatment, in a case where the metallographic structure is a fibrous structure.
  • the mottled pattern is a pattern generated because differences in the crystal grain size make the crystal grains partially coarse or fine and such larger and smaller crystal grains look like mottles after the surface treatment.
  • the point defect is caused when, for example, coarse compounds come off by being etched. Concave pits are formed in a position where the compounds were present, and such concave pits look like points after the surface treatment.
  • Evaluation results of the respective specimen are shown in Table 2. As for the specimens that were not determined to be acceptable (that were determined to be unacceptable), evaluation results or the like thereof are indicated with underlines applied thereto in Table 2.
  • Specimens 1 to 23 whose metallographic structures were equigranular recrystallized structures, were determined to be acceptable or to be acceptable and also desirable in all evaluation items, that is, in terms of the mechanical properties (the yield strength and the bending test), the toughness (the impact value), the resistance to SCC (the stress corrosion cracking), the metallographic structure observation (the metallographic structure, the average grain diameter, and the grain diameter difference), and the surface quality (the defect after surface treatment, and the light reflection state).
  • the mechanical properties the yield strength and the bending test
  • the toughness the impact value
  • the resistance to SCC the stress corrosion cracking
  • the metallographic structure observation the metallographic structure, the average grain diameter, and the grain diameter difference
  • the surface quality the defect after surface treatment, and the light reflection state
  • Specimen 23 Although no defect after surface treatment was observed, the light reflection state was partially nonuniform because the grain diameter difference among the crystal grains (the difference between the maximum value and the minimum value) was slightly large. However, such partial nonuniformity was not bad enough to be a problem in the surface quality. Specimen 23 was determined to be acceptable or to be acceptable and also desirable in all of the evaluation items other than the light reflection state. In sum, Specimen 23 exhibited excellent properties in terms of the strength, the toughness, and the surface quality, and also exhibited excellent properties in terms of the resistance to SCC.
  • Specimen 26 whose Mg content was too low, was determined to be unacceptable in terms of the yield strength because the strength improving effect was not sufficiently obtained.
  • Specimen 28 whose Cu content was too high, was determined to be unacceptable due to appearance of the defect after surface treatment because its anodized surface was yellowish in color tone.
  • Specimen 29 whose Zr content was too low, was determined to be unacceptable due to appearance of the defect after surface treatment because a coarse and nonuniform recrystallized structure was formed to generate mottled patterns on the anodized surface.
  • Specimen 30 whose Zr content was too high, was determined to be unacceptable due to appearance of the defect after surface treatment because a fibrous structure was formed to generate streak patterns on the anodized surface.
  • Specimen 31 whose Si content was too high, was determined to be unacceptable due to appearance of the defect after surface treatment because a fibrous structure was formed to generate streak patterns on the anodized surface.
  • Specimen 32 whose Fe content was too high, was determined to be unacceptable due to appearance of the defect after surface treatment because a fibrous structure was formed to generate streak patterns on the anodized surface.
  • Specimen 33 whose Mn content was too high, was determined to be unacceptable due to appearance of the defect after surface treatment because a fibrous structure was formed to generate streak patterns on the anodized surface.
  • Specimen 34 whose Cr content was too high, was determined to be unacceptable due to appearance of the defect after surface treatment because a fibrous structure was formed to generate streak patterns on the anodized surface.
  • Specimen 35 whose Ti content was too low, was determined to be unacceptable due to appearance of the defect after surface treatment because the structure of the ingot was coarse and the metallographic structure subjected to hot extrusion was nonuniform to generate mottled patterns on the anodized surface.
  • Specimen 36 whose Ti content was too high, was determined to be unacceptable due to appearance of the defect after surface treatment because coarse intermetallic compounds were generated to cause a point defect on the anodized surface.
  • Specimens 27 and 29 to 36 which were determined to be unacceptable in terms of the defect after surface treatment, were nonuniform in the light reflection state.
  • Specimen 37 whose mass ratio (Zn/Mg) was too low, was determined to be unacceptable in terms of the impact value (toughness) because the impact value was less than 15.
  • Specimen 38 whose mass ratio (Zn/Mg) was too high, was determined to be unacceptable in terms of the stress corrosion cracking (resistance to SCC) because a stress corrosion cracking was generated in the test of resistance to SCC.
  • Example 3 a plurality of specimens (examples: Specimens A to H, comparative examples: Specimens I to N) of the aluminum alloy material were prepared under different production conditions, and various evaluations were conducted on each specimen.
  • the chemical components of the aluminum alloy material were similar to those of Specimen 10 or Specimen 11 (see Table 1) of Example 1 described above.
  • a preparation method for the specimens will be described below.
  • Various evaluation methods were similar to those in the above-described Example 1.
  • a cylindrical ingot (billet) having a diameter of 90 mm containing chemical components similar to those of Specimen 10 or Specimen 11 (see Table 1) of the above-described Example 1 is forged by semicontinuous casting. Then, a homogenizing treatment is performed in which the ingot is heated at a temperature and for a period of time shown in Table 3. Subsequently, the ingot is subjected to hot extrusion with the temperature of the ingot maintained at 520° C. In this way, an extruded material having a width of 150 mm and a thickness of 10 mm is obtained.
  • a quenching treatment is performed in which the extruded material subjected to hot extrusion is cooled to 100° C. at a cooling rate of 1500° C./min. Then, the quenched extruded material is cooled to room temperature, and an artificial aging treatment is performed in which the extruded material is heated at a temperature of 140° C. for 12 hours. In this way, the specimen of the aluminum alloy material (extruded material) is obtained.
  • Specimens A to H whose metallographic structures were equigranular recrystallized structures, were determined to be acceptable or to be desirable in all evaluation items, that is, in terms of the mechanical properties (the yield strength and the bending test), the toughness (the impact value), the resistance to SCC (the stress corrosion cracking), the metallographic structure observation (the metallographic structure, the average grain diameter, and the grain diameter difference), and the surface quality (the defect after surface treatment, and the light reflection state).
  • the mechanical properties the yield strength and the bending test
  • the toughness the impact value
  • the resistance to SCC the stress corrosion cracking
  • the metallographic structure observation the metallographic structure, the average grain diameter, and the grain diameter difference
  • the surface quality the defect after surface treatment, and the light reflection state
  • Specimens I and J which were each homogenized at too low a temperature, Al—Zr-based compounds having an L1 2 structure were present and fibrous structures were formed. Thus, Specimens I and J were determined to be unacceptable due to appearance of the defect after surface treatment because streak patterns were generated on the anodized surface.
  • Specimens M and N which were each homogenized for too short a time, were determined to be unacceptable due to appearance of the defect after surface treatment because their metallographic structures after hot extrusion were nonuniform to generate mottled patterns on the anodized surface.

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