JP2009024219A - High strength and formable aluminum alloy cold-rolled sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-Mg based alloy cold-rolled sheet of high Mg which can provide a total elongation of ≥10% in spite of having high strength satisfying a tensile strength of ≥500 MPa, can be formed in spite of its high strength, and has an excellent balance of the strength and ductility, and excellent formability. <P>SOLUTION: The crystal grain diameter in the sheet thickness direction of an Al-Mg based aluminum alloy cold-rolled sheet having a high Mg content are finely elongated to a rolling direction, also, Mg based precipitates in the crystal grains are finely suppressed so as to have a fixed numerical density or below, thus the total elongation when tensile strength is 500 to <600 MPa is controlled to ≥10%. In this way, the characteristics of the Al-Mg based aluminum alloy cold-rolled sheet where it can be formed in spite of its high strength are improved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an Al-Mg based aluminum alloy cold-rolled sheet having high formability, and particularly to an aluminum alloy cold-rolled sheet that has an excellent balance of strength and ductility and can be formed with high strength. The present invention relates to an aluminum alloy plate manufactured as a plate by cold rolling, and relates to an aluminum alloy cold rolled plate before being used as a member or component described later.

  As is well known, various aluminum alloy plates (hereinafter referred to as aluminum as Al) have been conventionally used for transportation equipment such as automobiles, ships, aircraft or vehicles, machines, electrical products, architecture, structures, optical equipment, and members and parts of equipment. Is also widely used depending on the characteristics of each alloy.

  In many cases, these aluminum alloy plates are formed by press molding or the like, and are used as members and parts for the above-described applications. In this respect, from the viewpoint of high formability, among the Al alloys, an Al—Mg alloy having an excellent balance between strength and ductility is advantageous.

  For this reason, conventionally, regarding the Al—Mg-based Al alloy plate, examination of component systems and optimization of manufacturing conditions have been performed. As this Al—Mg-based Al alloy, for example, JIS A 5052, 5182 and the like are typical alloy component systems. However, even this Al—Mg-based Al alloy is inferior in ductility and inferior in formability as compared with a cold-rolled steel sheet.

  On the other hand, when the Al-Mg-based Al alloy is made to have a high Mg content of 6%, preferably 8%, if the Mg content is increased, the strength ductility balance is improved. However, Al-Mg-based Al alloy with high Mg content is easily cracked during hot rolling in a normal manufacturing method in which an ingot cast by DC casting or the like is hot-rolled after soaking. Become.

  For this reason, it has hitherto been known that an Al—Mg-based Al alloy plate having a high Mg content exceeding 8% is manufactured by twin-roll continuous casting. In this twin-roll continuous casting method, molten aluminum alloy is poured from a refractory hot-water supply nozzle between a pair of rotating water-cooled copper molds (twist rolls) and solidified. In this method, the aluminum alloy sheet is solidified, moderately reduced, and rapidly cooled. As this twin roll type continuous casting method, the Hunter method, the 3C method and the like are known.

An example in which the structure is defined for the purpose of improving the formability of a high Mg Al—Mg alloy plate manufactured using such a twin-roll continuous casting method has also been proposed. For example, an aluminum alloy plate for automobiles having excellent mechanical properties, in which the average size of an Al—Mg based intermetallic compound of an Al—Mg based alloy plate having a high Mg content of 6 to 10% is 10 μm or less has been proposed. (See Patent Document 1). Also proposed is an aluminum alloy plate for automobile body sheets in which the number of Al—Mg intermetallic compounds of 10 μm or more is 300 pieces / mm 2 or less and the average crystal grain size is 10 to 70 μm (see Patent Document 2). )
JP-A-7-252571 JP-A-8-165538

  However, even if such an Al-Mg alloy plate having a high Mg content exceeding 8% is manufactured by the continuous casting method such as the twin roll type, other alloy systems such as 5000 series and 6000 series are used. Similarly, as the tensile strength increases, the elongation decreases rapidly. For this reason, in the balance between strength and ductility, it has been impossible to obtain a total elongation of 10% or more when the tensile strength is 500 MPa or more.

  Usually, as described above, many Al alloy plates are formed by press molding or the like, and are used as members or parts for the above-mentioned applications. Therefore, no matter how high the strength of the Al-Mg-based Al alloy plate made high in Mg, if the elongation can only be press-molded, it cannot be formed into members and parts for each of the above applications. After all, practical use (actual use) is not possible.

  The present invention has been made in order to solve such a problem, and the purpose thereof is, for example, high tensile strength of 500 MPa or more, even with a high strength capable of obtaining a total elongation of 10% or more. An object of the present invention is to provide a high Mg Al-Mg alloy cold-rolled sheet that can be formed.

In order to achieve this object, the gist of the aluminum alloy cold-rolled sheet of the present invention, which can be formed even with high strength, is Mg: 6.0 to 15.0% by mass, the balance being Al—Mg composed of Al and impurities. Aluminum alloy cold-rolled sheet, the average crystal grain size in the plate thickness direction of this cold-rolled plate is 30 μm or less, and the ratio of the average crystal grain size in the rolling direction to the average crystal grain size in the plate thickness direction A certain aspect ratio is 3.0 or more on average, and the average particle diameter of Mg-based precipitates in crystal grains is 100 nm or less in terms of the equivalent sphere diameter of each precipitate, and the average of these Mg-based precipitates The number density is 4 × 10 ⁴ pieces / μm ³ or less.

  Here, it is preferable that the aluminum alloy cold-rolled sheet has a characteristic that the total elongation is 10% or more when the tensile strength is 500 MPa or more. The aluminum alloy cold-rolled sheet is preferably a cold-rolled sheet obtained by cold rolling and tempering an Al—Mg-based aluminum alloy sheet having an equiaxed recrystallized structure. Further, the aluminum alloy cold-rolled sheet is further in mass%, Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.3% or less, V: 0.3% or less, or It is preferable that 2 or more types are included. More preferably, the aluminum alloy cold-rolled sheet is, by mass%, Cu: 1.0% or less, Fe: 1.0% or less, Si: 0.5% or less, Ti: 0.1% or less, Zn : It is allowed to contain 1.0% or less.

  The present invention defines the average crystal grain size, average aspect ratio, and Mg-based precipitates in the crystal grains of the Al—Mg-based Al alloy sheet having a high Mg content. For example, the tensile strength is 500 MPa or more and less than 600 MPa. In this case, the total elongation is 10% or more, and a characteristic that enables press molding is provided.

  In order to satisfy the specifications of the average crystal grain size, average aspect ratio, and Mg-based precipitates in the crystal grains of the present invention, an Al—Mg-based Al alloy preferably having an equiaxed recrystallized structure It is essential to cold-roll the plate to obtain a cold-rolled plate as in the present invention. In other words, unless cold rolling is performed, the average crystal grain size, the average aspect ratio, and the Mg-based precipitates in the crystal grains cannot be satisfied as in the present invention. Therefore, for example, when the tensile strength is 500 MPa or more and less than 600 MPa, the total elongation is 10% or more, and it is not possible to provide such a characteristic that press molding is possible.

  Here, the production method to the Al—Mg-based Al alloy plate that is cold-rolled (having an equiaxed recrystallized structure) is not particularly limited. The Al—Mg-based Al alloy having a high Mg content that is cold-rolled may be manufactured by a normal manufacturing method in which an ingot cast by DC casting or the like is hot-rolled after soaking. Or you may manufacture by the above-mentioned twin roll type continuous casting.

(Chemical composition)
The significance of each alloy element and the reason for its limitation in the chemical composition of the Al alloy cold-rolled sheet of the present invention will be described below. In the present invention, as an Al alloy cold-rolled sheet, for example, the tensile strength is 500 MPa or more and less than 600 MPa. In order to obtain such a high strength and a desired strength-elongation balance, it is assumed that the cold-rolled sheet contains Mg: 6.0 to 15.0 mass%, and the balance is made of Al and impurities. It is set as the Al-Mg type aluminum alloy composition which becomes. In addition,% display of content of each element means the mass% altogether.

  Further, the Al alloy cold-rolled sheet of the present invention is further a mass%, Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.3% or less, V: 0.3% or less Or it is preferable that 2 or more types are included.

  Here, the Al alloy cold-rolled sheet of the present invention preferably has Cu: 1.0% or less, Fe: 1.0% or less, Si: 0.5% or less, Ti: 0.1 as other elements. % Or less and Zn: 1.0% or less are allowed. These elements are basically impurities, but are inevitably mixed as a melting raw material when the Al alloy of the present invention is melted. For this reason, excessive reduction of these elements is uneconomical in production, and therefore, the inclusion in the above range that does not impair the above properties of the Al alloy cold rolled sheet of the present invention is allowed.

(Mg: 6.0 to 15.0%)
Mg is an important alloy element that increases the strength and ductility of the Al alloy sheet. If the Mg content is too small, the high strength and press-molding characteristics of the present invention will not be obtained, and the strength, ductility (elongation) and formability will be insufficient. On the other hand, when there is too much Mg content, even if it controls a manufacturing method and conditions, the crystal precipitation of an Al-Mg type compound will increase. As a result, ductility (elongation) and formability are significantly reduced. In addition, the work hardening amount is increased and the cold rollability is also lowered. Therefore, Mg is in the range of 6.0 to 15.0%, preferably more than 8% and 14% or less.

(Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.3% or less, V: 0.3% or less)
Transition elements such as Mn, Cr, Zr, and V are preferable elements for precipitating a β phase in crystal grains and satisfying the provisions of the present invention for Mg-based precipitates in crystal grains. That is, in the β-phase precipitation environment, transition element-based precipitates of transition elements in the crystal grains become β-phase nucleation sites (driving force) in the crystal grains, and the β-phase is also formed in the crystal grains. Precipitate fine. As a result, the properties that enable press molding with high strength are exhibited. For this reason, one or two or more of Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.3% or less, and V: 0.3% or less are selectively contained.

  The effects of these transition elements can be exhibited even in a small amount. In other words, even if the amount is small, transition element-based precipitates are formed in the crystal grains. It becomes. Therefore, the lower limit of the content of these transition elements is not defined. However, in order to efficiently exhibit these effects under normal plate manufacturing conditions, the lower limit value of the content of each of these elements is preferably 0.05% or more.

(Grain structure)
The crystal grain structure of the Al-Mg-based Al alloy cold-rolled sheet of the present invention has, for example, a total elongation of 10% or more when the tensile strength is 500 MPa or more and less than 600 MPa, and can be press-molded with high strength. It is important to have such characteristics. Therefore, the crystal grain structure of the present invention has an average crystal grain size in the plate thickness direction of 30 μm or less, and an aspect ratio that is a ratio of the average crystal grain size in the rolling direction to the average crystal grain size in the plate thickness direction. The average value is 3.0 or more.

(Aspect ratio of crystal grains)
The crystal grain of the aluminum alloy cold rolled sheet is not a regular equiaxed grain, but the average aspect ratio, which is the ratio of the average crystal grain size in the average rolling direction and the average crystal grain size in the plate thickness direction, is 3.0 or more on average. By making it elongated in the rolling direction, it is possible to have the above-described characteristics that allow high-strength press molding.

  If this aspect ratio is less than 3.0 on average, there will be no significant difference from normal equiaxed grains, and the above-mentioned effects of elongated crystal grains will be insufficient, so that the above-described properties capable of press forming with high strength cannot be provided. In this respect, the elongation of the crystal grains in the rolling direction is better, and the aspect ratio of the crystal grains is preferably 4.0 or more, more preferably 6.0 or more.

  The aspect ratio of the crystal grains is determined by the crystal grain structure of the hot-rolled sheet, the cold rolling rate, and the cold rolling temperature in the process in which intermediate annealing is not performed. In this respect, the upper limit of the average aspect ratio of the crystal grains is determined from the capability limit of the manufacturing process for forming elongated grains such as hot rolling and cold rolling, but the level is about 20.

(Average aspect ratio measurement method)
The aspect ratio of the crystal grains is measured by observing the upper surface (polarized light observation) at the center in the thickness direction. After cold rolling, the central portion in the thickness direction of the cold-rolled sheet after the tempering treatment such as final annealing and the upper surface of the rolled surface are performed by polarization observation after mechanical polishing, electrolytic polishing, and anodizing treatment with Barker liquid.

  When the central portion of the plate in the thickness direction is observed from the upper surface and the crystal grain structure is observed with polarized light using an optical microscope of × 100 magnification, a difference in black and white appears due to a difference in crystal orientation. In this observation, for the crystal grains in the field of view where the outline can be clearly observed, the maximum length in the rolling direction of each crystal grain and the maximum length in the plate thickness direction are measured respectively, and the rolling of the crystal grains is measured. The average maximum length in the direction (average crystal grain size in the rolling direction) and the average maximum length in the plate thickness direction (average crystal grain size in the plate thickness direction) are determined. Then, (average crystal grain size in rolling direction: average maximum length) / (average crystal grain size in plate thickness direction: average maximum length) of these crystal grains is calculated as an aspect ratio. Note that the number of crystal grains to be measured is 100.

(Average crystal grain size)
Here, in the above-described measurement, the average value of the maximum lengths of the individual crystal grains in the plate thickness direction is defined as the average crystal grain size in the plate thickness direction. When the average crystal grain size in the plate thickness direction is larger than 30 μm, it is impossible to give the above-described characteristics that enable high-strength press molding.

(Intracrystalline precipitate)
In the Al-Mg-based Al alloy cold-rolled sheet of the present invention, Mg-based precipitates (Al-Mg-based compounds) in crystal grains are finely precipitated at the nano level to improve the strength-elongation balance. The precipitation state of Mg-based precipitates in the crystal grains has a great influence on the plastic deformation behavior. Like the other requirements described so far, the Al-Mg-based Al alloy cold-rolled sheet of the present invention has the above-described high strength. This is important in order to provide such characteristics that press molding is possible. Therefore, more specifically, in the intragranular precipitate structure of the present invention, the average particle diameter of Mg-based precipitates in the crystal grains is 100 nm or less in terms of the equivalent sphere diameter of each precipitate, and these Mg It is assumed that the average number density of the system precipitates is 4 × 10 ⁴ pieces / μm ³ or less.

  When the Mg-based precipitates in the crystal grains become coarser than the above average grain size specification, or when the number density exceeds the above specification, it becomes a starting point of fracture and also precipitates at the grain boundaries. Therefore, the formability of the Al—Mg-based Al alloy cold-rolled sheet is significantly deteriorated.

(Measurement method of precipitates in crystal grains)
A sample was taken from the center of the thickness of the Al-Mg-based Al alloy cold-rolled sheet, the sample surface was mechanically polished by 0.05 to 0.1 mm, and then electroetched (either in the thickness direction or in the longitudinal direction of the plate) May be observed with a 20,000-fold FE-TEM (transmission electron microscope). The structure observation by the FE-TEM at the center of the plate thickness was performed so that the total area of the observation field was 4 μm ² or more per one center of the plate thickness, and this was appropriately spaced in the longitudinal direction of the plate. Observe the location. In addition, the film thickness at each observation position is obtained by equal thickness interference fringes. Then, the particle size converted by the equivalent sphere diameter and the number density per unit volume of each Mg-based precipitate in each observed crystal grain are obtained and averaged.

  The Mg-based precipitate referred to in the present invention is a precipitate (Al-Mg-based compound) that has been confirmed to contain Mg by analyzing the visual field observed by the FE-TEM with an X-ray spectrometer (EDX). ) And is distinguished from other precipitates not containing Mg. The amount containing Mg may be an amount (a trace amount) that can be detected by EDX.

(Production method)
Below, the manufacturing method of the Al-Mg type Al alloy cold-rolled sheet in this invention is demonstrated. In order to satisfy the above-described specifications of the average crystal grain size, average aspect ratio, and Mg-based precipitates in the crystal grains, the Al—Mg-based Al having an equiaxed recrystallized structure is preferable. It is essential to cold-roll the alloy plate to form a cold-rolled plate. In other words, unless cold rolling is performed, the average crystal grain size, the average aspect ratio, and the Mg-based precipitates in the crystal grains cannot be satisfied as in the present invention.

  However, the manufacturing method of the Al—Mg-based Al alloy plate having a high Mg content until cold rolling is not particularly limited. The Al alloy sheet to be cold-rolled may be manufactured by a normal manufacturing method in which an ingot cast by DC casting or the like is hot-rolled after soaking, or by the above-described twin-roll continuous casting. It may be manufactured.

(Cold rolling)
However, in order to obtain the cold-rolled plate structure of the present invention, whether it is a normal manufacturing method or a twin roll type, the plate before cold rolling is preliminarily equiaxial recrystallized structure. It is preferable to have. On the other hand, if the plate before cold rolling has a processed structure, the plate is likely to crack due to the β phase being Mg-based precipitate during the cold rolling. As a result, there is a high possibility that the average crystal grain size, the average aspect ratio, and the Mg-based precipitates in the crystal grain cannot be satisfied.

  In order to make the plate before cold rolling into such an equiaxed recrystallized structure in advance, the plate is recrystallized and solution effect can be obtained before cold rolling. It is preferable to roughen (anneal) at a relatively high temperature. In the case where the roughening is performed by continuous annealing, the temperature rise rate is preferably 1 ° C./s or more, the holding time is 0 second or more and 5 minutes or less, and the cooling rate is 1 ° C./s or more. Moreover, when performing this roughing by batch annealing, it is preferable that the temperature rising rate is 200 ° C./hr or less, the holding time is 4 hours or less, and the cooling rate is 200 ° C./hr or less. The temperature increase rate and the cooling rate are defined because if these rates are slow, a large amount of β phase may be precipitated at the grain boundary during this temperature increase-cooling process. This is because there is a high possibility that the regulation of system precipitates cannot be satisfied.

  In cold rolling, a reverse or tandem pass cold rolling mill may be used, and intermediate annealing may be performed for each pass if necessary, but the cold rolling rate (working rate) is 50% or more. When the cold rolling rate is low, there is a high possibility that the average crystal grain size, the average aspect ratio, and the Mg-based precipitates in the crystal grains cannot be satisfied.

(Final annealing)
The Al alloy sheet after cold rolling is subjected to final annealing at a low temperature for a short time in order to obtain a recovery effect capable of subgraining the crystal grains and improving the elongation without producing a β phase and without reducing the strength. . This low-temperature short-time final annealing is performed at a low temperature of 250 ° C. or lower, unlike a normal final annealing at a relatively high temperature of 400 ° C. or higher where a solution effect can be obtained.

  When this final annealing is performed by continuous annealing, preferably, the annealing temperature is 400 ° C. or less, the heating rate is 1 ° C./s or more, the holding time is 0 s or more, 5 min or less, and the cooling rate is 1 ° C./s or more. Condition. Moreover, when this final annealing is performed by batch annealing, it is preferable that the annealing temperature is 200 ° C. or less, the heating rate is 200 ° C./hr or less, the holding time is 4 hours or less, and the cooling rate is 200 ° C./hr or less. Condition.

  The temperature increase rate and the cooling rate are defined because if these rates are slow, a large amount of β phase may be precipitated at the grain boundary during this temperature increase-cooling process. This is because there is a high possibility that the regulation of system precipitates cannot be satisfied. Note that at 250 ° C. or higher, there is a high possibility that the definition of Mg-based precipitates in the crystal grains cannot be satisfied, the elongation of the high Mg Al—Mg alloy plate is lowered, and the strength-ductility balance is lowered. There is a high possibility that moldability will be reduced. Furthermore, in annealing at 400 ° C. or higher where a normal solutionizing effect is obtained, solid solution is promoted to satisfy the definition of Mg-based precipitates, and the elongation is improved, but the strength is lowered.

  Examples of the present invention will be described below. Al—Mg-based Al alloy melts (Invention Examples A to G, Comparative Examples H and I) having various chemical composition compositions shown in Table 1 were cast on each ingot by the twin roll continuous casting method and the DC casting method described above. .

  In the case of the DC casting method, the pouring temperature of the Al alloy molten metal (melt temperature before casting) is set to a temperature range of 640 to 700 ° C., and each Al alloy ingot is placed in a batch heat treatment furnace under the conditions shown in Table 2. After soaking, the steel sheet was hot-rolled at a start temperature of about 300 ° C. and an end temperature of about 350 ° C. to the plate thicknesses shown in Table 2.

  In the case of the twin roll continuous casting method, the pouring temperature of the Al alloy molten metal (melting temperature before casting) is set to a temperature range of 640 to 700 ° C., and the cooling rates in the range of 200 to 400 ° C./s are shown in Table 2. A plate-thick Al alloy sheet ingot was produced. The peripheral speed of the twin roll was 70 m / min, and the twin roll surface was not lubricated.

  Both the hot rolled sheet by the DC casting method and the thin sheet ingot by the twin roll continuous casting method were subjected to roughening (annealing) and then cold rolled. Roughening was performed by continuous annealing, and heating was performed at each annealing temperature shown in Table 2 with a holding time of 60 s constant in each example. At this time, the heating rate was 50 to 100 ° C./s, and the cooling rate was 50 to 100 ° C./s. The cold rolling was performed at the processing rates and plate thicknesses shown in Table 2, and no intermediate annealing was performed during the cold rolling.

  Each of these cold-rolled sheets was subjected to final annealing under the annealing conditions shown in Table 2. At this time, in the batch annealing furnace, the heating rate is 40 ° C./hr, the cooling rate is 40 ° C./hr, and in the continuous annealing furnace indicated by * in Table 2 (Comparative Examples 17 and 23), the heating rate is 50 to 100. C./s, cooling rate: 50 to 100.degree. C./s.

(Plate structure)
From the central part of the plate thickness at 10 arbitrary measurement points at intervals of 100 mm or more over the longitudinal direction (rolling direction) of the Al—Mg-based Al alloy plate after final annealing thus obtained. Samples were taken, and the average crystal grain size (μm), aspect ratio, average grain size (μm) of Mg-based precipitates in the crystal grains, and number density (pieces / μm2) were measured by the measurement methods described above. . Table 3 shows the measurement results. Here, FE-TEM used Hitachi field emission transmission electron microscope: HF-2000.

  The structure of the board of the inventive examples and comparative examples photographed in this way (drawing substitute photos) is shown in FIGS. FIG. 1 shows the structure of Invention Example 1 of Table 3, FIG. 2 shows the structure of Invention Example 2 of Table 3, FIG. 3 shows the structure of Invention Example 3 of Table 3, and FIG.

  Further, a test piece was taken from the center of the thickness of the Al-Mg-based Al alloy plate after the final annealing, and the mechanical properties and strength ductility balance of each test piece "tensile strength (TS: MPa) x total elongation ( EL:%) ”(MPa%) was determined. These results are also shown in Table 3.

(Tensile test)
The tensile test was performed according to JIS Z 2201, and the shape of the test piece was a JIS No. 5 test piece, and the test piece was manufactured so that the longitudinal direction of the test piece coincided with the rolling direction. The crosshead speed was 5 mm / min, and the test piece was run at a constant speed until the test piece broke.

As shown in Table 1, the invention examples have compositions within the scope of the invention, and as shown in Table 2, they are produced within the preferred production conditions. For this reason, as shown in Table 3, the invention example has an average crystal grain size in the thickness direction of the cold-rolled sheet of 30 μm or less, and the ratio between the average crystal grain size in the rolling direction and the average crystal grain size in the thickness direction. The average aspect ratio is 3.0 or more. Further, the average particle diameter of the Mg-based precipitates in the crystal grains is 100 nm or less in terms of the sphere equivalent diameter of each precipitate, and the average number density of these Mg-based precipitates is 4 × 10 ⁴ pieces / μm ^3. It is as follows.

  As a result, the inventive example has a property that the total elongation is 10% or more when the tensile strength is 500 MPa or more and less than 600 MPa as an aluminum alloy cold-rolled sheet, and is excellent in strength ductility balance and formability.

  On the other hand, although Comparative Examples 15-23 have a composition within the range of invention, as shown in Table 2, it is manufactured outside the range of preferable manufacturing conditions. For this reason, as shown in Table 3, in Comparative Examples 15 to 23, the average crystal grain size and aspect ratio of the cold-rolled sheet, the average grain size of Mg-based precipitates in the crystal grains, and the average number density are outside the specified range of the invention. ing. As a result, Comparative Examples 15 to 23 have low total elongation for the tensile strength as aluminum alloy cold-rolled plates, and are inferior in strength ductility balance and formability.

  Although Comparative Examples 24-27 are manufactured outside the range of preferable manufacturing conditions, they have compositions outside the scope of the invention. For this reason, although 24-27 are the average crystal grain diameter of a cold-rolled sheet, an aspect ratio, the average grain diameter of the Mg-type precipitate in a crystal grain, and an average number density are in an invention prescription | regulation range, an aluminum alloy cold-rolled sheet As for the tensile strength, the total elongation is low, and the strength ductility balance and formability are inferior.

  1-4, the average crystal grain size in the thickness direction (vertical direction in the figure) of the cold rolled sheet is 30 μm or less and the average crystal in the rolling direction (horizontal direction in the figure). Inventive Examples 1 to 3 in FIGS. 1 to 3 in which the aspect ratio, which is the ratio of the grain size and the average crystal grain size in the plate thickness direction (vertical direction in the figure), is 3.0 or more on average, It is elongated and has a fine grain structure in the vertical direction of the figure. On the other hand, in Comparative Example 17 of FIG. 4, the average crystal grain size in the thickness direction of the cold-rolled sheet is too large exceeding 30 μm, and the aspect ratio is too small as an average of less than 3.0. A so-called equiaxed axis with no difference in length between the vertical direction in the figure and the horizontal direction in the figure has a coarse crystal grain structure.

  Therefore, from the results of these Examples, the criticality for the strength ductility balance and formability of the present invention, the composition, crystal grain size, Mg-based precipitate definition within the crystal grains, and preferable production conditions within these specifications I understand the significance.

  As described above, according to the present invention, a total elongation of 10% or more can be obtained even when the tensile strength is 500 MPa or higher, and the strength ductility balance and moldability are excellent even if the strength is high. A high Mg Al—Mg alloy cold-rolled sheet can be provided. As a result, for aluminum alloy plate applications that require strength and formability, such as transportation equipment such as automobiles, ships, aircraft, and vehicles, machines, electrical products, architecture, structures, optical equipment, and members and parts of equipment. The application of can be expanded.

It is a drawing substitute photograph which shows the structure | tissue of this invention Al-Mg type alloy cold-rolled sheet. It is a drawing substitute photograph which shows the structure | tissue of this invention Al-Mg type alloy cold-rolled sheet. It is a drawing substitute photograph which shows the structure | tissue of this invention Al-Mg type alloy cold-rolled sheet. It is a drawing substitute photograph which shows the structure | tissue of a comparative example Al-Mg type alloy cold-rolled sheet.

Claims (5)

Mg: An Al—Mg-based aluminum alloy cold-rolled sheet containing 6.0 to 15.0% by mass with the balance being Al and impurities, and the average crystal grain size in the thickness direction of the cold-rolled sheet is 30 μm or less And the average aspect ratio, which is the ratio of the average crystal grain size in the rolling direction and the average crystal grain size in the plate thickness direction, is 3.0 or more on average, and the average grain size of the Mg-based precipitates in the crystal grains is In terms of the equivalent sphere diameter of each precipitate, it is 100 nm or less, and the average number density of these Mg-based precipitates is 4 × 10 ⁴ pieces / μm ³ or less. Aluminum alloy cold rolled sheet.   The aluminum alloy cold-rolled sheet according to claim 1, wherein the aluminum alloy cold-rolled sheet has characteristics of a tensile strength of 500 MPa or more and a total elongation of 10% or more.   The said aluminum alloy cold-rolled sheet is a cold-rolled sheet obtained by cold rolling and tempering an Al-Mg-based aluminum alloy sheet having an equiaxed recrystallized structure, and is formed with high strength according to claim 1 or 2. Possible aluminum alloy cold rolled sheet.   The aluminum alloy cold-rolled sheet further comprises one or two of mass%: Mn: 1.0% or less, Cr: 0.3% or less, Zr: 0.3% or less, V: 0.3% or less. The aluminum alloy cold-rolled sheet that can be formed with high strength according to any one of claims 1 to 3, including the above.   The aluminum alloy cold-rolled sheet is further, in mass%, Cu: 1.0% or less, Fe: 1.0% or less, Si: 0.5% or less, Ti: 0.1% or less, Zn: 1.%. The aluminum alloy cold-rolled sheet according to any one of claims 1 to 4, wherein the aluminum alloy cold-rolled sheet is capable of being formed with high strength.

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