JP4328242B2 - Aluminum alloy plate with excellent ridging mark characteristics - Google Patents

Description

  The present invention is an Al-Mg-Si based aluminum alloy plate that can suppress ridging marks during molding processing and is excellent in BH properties such as baking coating curability and bendability (hereinafter, aluminum is also simply referred to as Al). It is about.

  Conventionally, Al alloy plates with excellent formability and bake hardenability have been used for transportation equipment such as automobiles, ships, aircraft or vehicles, machines, electrical products, architecture, structures, optical equipment, and components and parts of equipment. Has been.

  In particular, in the field of the body of a transport device such as an automobile, in recent years, improvement in fuel efficiency has been pursued by reducing the weight in response to global environmental problems caused by exhaust gas and the like. For this reason, the application of lighter Al alloy materials instead of steel materials conventionally used for automobile bodies is increasing.

  Among these, panels such as outer panels (outer plates) and inner panels (inner plates) of panel structures such as automobile hoods, fenders, doors, roofs, and trunk lids are thin and high-strength Al alloy plates. The use of Al-Mg-Si-based AA to JIS 6000-based (hereinafter simply referred to as 6000-based) Al alloy plates is being studied.

  The 6000 series Al alloy sheet basically contains Si and Mg as essential and has excellent age-hardening ability. BH properties (bake hardness, artificial age hardening ability) that can ensure the required strength by age hardening by heating at the time of processing, such as paint baking treatment of the subsequent panel, and heat resistance during treatment. Paint bake hardenability).

  Further, the 6000 series Al alloy plate has a relatively small amount of alloy elements as compared with other 5000 series Al alloys having a large amount of alloy such as Mg. For this reason, when the scraps of these 6000 series Al alloy sheets are reused as an Al alloy melting material (melting raw material), the original 6000 series Al alloy ingot is easily obtained and the recyclability is also excellent.

  On the other hand, as is well known, the outer panel and the like of the automobile are manufactured by performing a combination of molding processes such as press molding and bending on an Al alloy plate. For example, an outer panel such as a hood or a door is formed into a molded product shape as an outer panel mainly by strict press molding (overhang processing, deep drawing processing, etc.). Next, the outer panel is bent (turned 180 degrees) and joined to the inner panel edge by harsh hem (other name for hemming) processing such as flat hem. It is said.

  For this reason, 6000 series Al alloy sheets for outer panel applications such as automobiles are required to have not only press formability but also bend formability (bend formability). In addition, automobile outer panels and the like tend to be made thinner for weight reduction, and 6000 series Al alloy plates have high BH (high strength) that is thin and excellent in dent resistance. )) Is also required.

  On the other hand, in order to improve these required characteristics of the 6000 series Al alloy plate, various measures have been conventionally taken by precisely controlling the components, structure, or manufacturing method.

  Here, in the 6000 series Al alloy plate which is the object of the present invention, there is a surface defect called a ridging mark as a peculiar defect caused by the press forming. When this ridging mark is generated remarkably, the outer panel, which is required to have a particularly beautiful surface, has a problem in appearance and cannot be used.

  This ridging mark is a surface irregularity such as a streak-like structure unevenness generated on the surface of the Al alloy panel or a long streak defect generated in the rolling direction of the plate after the press working or drawing.

  This ridging mark is generated due to the fact that when crystal grains having close crystallographic orientation are clustered, the deformation behavior differs greatly at the boundary between the crystal grain groups. For this reason, even if the crystal grains of the Al alloy plate are fine enough not to cause rough skin, the point caused by press molding is troublesome. This ridging mark is particularly likely to occur when the press molding conditions become severe due to an increase in the size, complexity, or thickness of the panel structure. In addition, there is a problem that it becomes relatively inconspicuous immediately after press molding and becomes conspicuous only after proceeding to the painting process as it is as a panel structure.

  To solve this ridging mark problem, the 6000 series Al alloy ingot was conventionally cooled after homogenization heat treatment at a temperature of 500 ° C or higher, and hot rolling was started at a relatively low temperature of 350 to 450 ° C. It is known to prevent the formation of precipitates and to prevent ridging marks (see, for example, Patent Documents 1 and 2).

  Various methods for improving the ridging mark from the viewpoint of texture control and the like have been proposed by paying attention to the crystal orientation component of the {110} plane of the 6000 series Al alloy plate. For example, it has been proposed to make the degree of integration of the Cube orientation in the surface portion of the plate 2-5 and the crystal grain size of the surface portion of the plate to 45 μm or less (see Patent Document 3). Further, it has been proposed that the Goss orientation distribution density of the plate is 3 or less, the PP orientation distribution density is 3 or less, and the Brass orientation distribution density is 3 or less (see Patent Document 4). Furthermore, it has been proposed that the proportion of crystal grain boundaries whose adjacent crystal orientation difference is 15 ° or less is 20% or more (see Patent Document 5).

  It has also been proposed that the ear rate in a 6000 series Al alloy plate is 4% or more and the crystal grain size is 45 μm or less (see Patent Document 6).

Japanese Patent No. 2823797 (Claims, pages 1 to 5) JP-A-8-232052 (Claims, pages 1-5) Japanese Patent Laid-Open No. 11-189836 (Claims, pages 1 to 5) Japanese Patent Laid-Open No. 11-236639 (Claims, pages 1 to 5) JP 2003-171726 (Claims, pages 1 to 5) Japanese Unexamined Patent Publication No. 2000-96175 (Claims, pages 1 to 5)

However, as described in Patent Documents 1 and 2, when cooling to a low hot rolling start temperature after homogenization heat treatment at a temperature of 500 ° C. or higher, if the cooling rate during this cooling is slow, the Mg ₂ Si-based compound Aggregation occurs and precipitates and becomes coarse. For this reason, it is necessary to carry out the solution treatment and quenching treatment at a high temperature and for a long time in the subsequent steps, so that productivity is remarkably lowered and there is a problem in reproducibility.

  In recent years, ingots have been increased in size to, for example, 500 mmt or more from the viewpoint of production efficiency. The larger the ingot, the more quickly it is cooled to the hot rolling start temperature after the homogenization heat treatment, the stable control of the cooling rate and the hot rolling start temperature is not limited to actual manufacturing equipment or manufacturing processes. It will be very difficult. Therefore, in an actual manufacturing process, when cooling to a low hot rolling start temperature after the homogenization heat treatment, the cooling rate is inevitably low. Therefore, in reality, only the means for initiating hot rolling at the relatively low temperature may cause the material properties of the final product to become unstable, or may cause a decrease in productivity during solution treatment and quenching, thereby preventing ridging marks. It is hard to say that it is an effective method.

  These problems are the same in Documents 3 to 5, and controlling these textures and characteristics has a certain effect on ridging mark suppression. However, in order to control the texture, it is necessary to make control of hot rolling conditions and heat treatment conditions including processing temperature, processing rate and finishing temperature according to the required characteristics and thickness. In addition, it is very difficult to combine the surface properties with ridging marks suppressed and the various required properties. For this reason, the productivity of the plate is significantly reduced, and there is a problem in the reproducibility of characteristics.

  Furthermore, the refinement of crystal grains common to these conventional techniques also has a certain effect on suppressing ridging marks. However, as described above, even if the crystal grain size is refined or the same average crystal grain size, a difference may occur in the generation degree of ridging marks, which is not a fundamental solution.

  In addition, these problems tend to be severe in recent press forming conditions, and tend to use a lot of return materials (scrap materials) containing many impurity elements including Mn and Fe instead of high purity Al ingots. Is more conducive. For example, with the adoption of Al alloy plates for automobile panels, etc., the shape is more complicated, the panel shape is becoming larger and more complicated, and the application to difficult-to-form panels is increasing. Molding defects such as cracks and rough skin are more likely to occur. Therefore, in these tendencies, the limit of the ridging mark suppression effect of the above-described prior art becomes larger.

  The present invention has been made paying attention to such circumstances, and its purpose is to prevent ridging marks during press molding with good reproducibility, and Al-Mg-Si excellent in bending workability and BH properties. An aluminum alloy plate is to be provided.

In order to achieve this object, the gist of the aluminum alloy plate excellent in ridging mark characteristics of the present invention is mass%, Mg: 0.2 to 3.0%, Si: 0.5 to 2.5%, Mn: 0.02 to 0.5% , Fe : In an Al-Mg-Si-based aluminum alloy plate containing 1.5% or less (excluding 0%), the balance being Al and inevitable impurities , the average particle size of the compound having a particle size of 0.2 μm or more is The elemental amount A of Mn existing as an Mn compound having a particle size of 3 μm or less and a particle size of 0.2 μm or more is a ratio A (mass%) / B (mass) with the Mn content B in the aluminum alloy sheet. %) In the range 0.3 to 0.9, and the Mg elemental amount C present as the Mg compound having a particle size of 0.2 μm or more is a ratio C (mass%) to the Mg content D in the aluminum alloy sheet. / D (mass%) is in the range of 0.03 to 0.5 .

  The Al alloy plate referred to in the present invention is an Al alloy plate that has been subjected to a tempering treatment after cold rolling, and is an Al alloy plate before being subjected to press forming or bending. Moreover, the compound said by this invention is the intermetallic compound thru | or precipitate which exist in the Al alloy board structure | tissue observed by FE-SEM mentioned later. Furthermore, the Mn compound referred to in the present invention is an Al—Mn based intermetallic compound or Al—Mn based precipitate separated and extracted by the extraction residue method described later.

  The present inventors have found that, in a 6000 series Al alloy plate containing a substantial amount of Mn, the amount of Mn compound having a particle size of 0.2 μm or more, together with its component composition and coarse compound, greatly affects the ridging mark characteristics. did.

  That is, on the premise of the definition of the component composition of the 6000 series Al alloy sheet containing a substantial amount of Mn and the suppression of coarse compounds, among the Mn series intermetallic compounds or Mn series precipitates present in the Al alloy sheet structure, 0.2% When the amount of Mn compound (Mn-based precipitate) having a particle size of μm or more is large, the Al alloy sheet structure after tempering treatment tends to form recrystallized orientation with random orientation, and ridging marks are suppressed. It is inferred that

  As described above, ridging marks are likely to be generated when crystal grains having close crystallographic orientation are clustered, because the deformation behavior is greatly different at the boundary between the crystal grain groups. On the other hand, when the amount of relatively large Mn compound is large, these particles have a particle size of 0.2 μm or more in the recrystallization process in the temperature raising process of the final solution condition in the tempering treatment of 6000 series Al alloy sheet. Mn compounds work in a random orientation. As a result, it is presumed that in the Al alloy plate structure, crystal grains having close crystallographic orientations do not form a cluster, and recrystallized orientations having random orientations are generated, and ridging marks are suppressed.

  However, the effect of this Mn compound is greatly influenced by the relationship between the size of the Mn compound itself and the amount of dissolved Mn, as will be described later. For this reason, in the present invention, the particle size of the relatively large Mn compound that affects the ridging mark is defined, and the amount of the Mn element in the Mn compound is not directly defined, but the amount of the Mn element in the Mn compound is not directly defined. It is specified in relation to the content.

  The embodiment of the Al alloy plate of the present invention will be specifically described below. First, the structure of the Al alloy plate of the present invention will be described.

(Mn compound)
Mn is selectively bonded with Al and other Si, Fe, Cr, etc. according to its content during homogenization heat treatment and subsequent hot rolling, in the structure of 6000 series Al alloy plate, Al-Mn compounds such as Al ₆ Mn, Al ₆ [Fe, Mn], Al ₁₂ [Fe, Mn] Si (Mn compounds referred to in the present invention: hereinafter, between Al-Mn precipitates and Al-Mn metals) Compound, also called Mn-based precipitate).

  Among these Mn compounds, relatively large Mn compounds having a particle size of 0.2 μm or more are recrystallized with random orientation as recrystallization nuclei for suppressing ridging marks in the final solution conditions as described above. Works as orientation formation.

  However, in the present invention, the amount of the Mn compound having a particle diameter of 0.2 μm or more is not directly defined, but the amount of the Mn element existing as the Mn compound having a particle diameter of 0.2 μm or more is determined by the Mn content ( It is specified in relation to the total Mn content in the Al alloy sheet. This is because the effect of forming a recrystallized orientation with a random orientation of an Mn compound having a grain size of 0.2 μm or more is exhibited in relation to the amount of Mn that dissolves in the Al alloy sheet structure. That is, even if there are many Mn compounds having a grain size of 0.2 μm or more, if the amount of Mn to be dissolved is insufficient, the effect of forming a recrystallization orientation with random orientations of Mn compounds having a grain size of 0.2 μm or more is also achieved. This is because it is halved.

  For this reason, in the Al alloy sheet of the present invention, the elemental amount A of Mn existing as the Mn compound having a particle diameter of 0.2 μm or more is set to a ratio A (mass) of the Mn content B contained in the Al alloy sheet. %) / B (mass%) in the range of 0.3 to 0.9. The Mn content B of the Al alloy sheet is defined as Mn: 0.02 to 0.5% in the compositional composition of the Al alloy sheet of the present invention, and is the total amount of Mn in the Al alloy sheet. .

  If this A (mass%) / B (mass%) is less than 0.3, it is no different from the conventional 6000 series Al alloy plate, and there is too little Mn compound having a particle size of 0.2 μm or more, and the random orientation of the Al alloy plate structure The effect of promoting the formation of recrystallized orientation is lost, and ridging marks are not suppressed.

  The conventional 6000 series Al alloy sheet has less Mn compound itself having a particle size of 0.2 μm or more, or the elemental amount A of Mn present as this Mn compound, due to differences in production methods such as soaking conditions described later. . For this reason, even if the Mn content B 1 of the Al alloy plate is satisfied, the A (mass%) / B (mass%) inevitably falls below the lower limit of 0.3. As a result, the conventional 6000 series Al alloy plate lacks recrystallization orientation formation with random orientation, and ridging marks are not suppressed.

  On the other hand, when A (mass%) / B (mass%) exceeds 0.9, the solid solution Mn content of the Al alloy sheet is insufficient in the range of the Mn content of 0.02 to 0.5%. For this reason, even if the abundance of the Mn compound having a particle diameter of 0.2 μm or more is sufficient, the effect of promoting recrystallization orientation formation with random orientation of the Al alloy sheet structure is lost, and the ridging mark is not suppressed. Therefore, A (mass%) / B (mass%) is in the range of 0.3 to 0.9, preferably 0.4 to 0.85.

  These relatively large Mn compounds having a particle size of 0.2 μm or more can be separated and extracted by the extraction residue method. That is, by using an extraction residue method using, for example, hot phenol as a solvent, a filter having a pore size of 0.2 μm is separated and extracted as a residue on the filter. At this time, other Mn compounds having a relatively small particle size of less than 0.2 μm and solid Mn existing in the structure of the 6000 series Al alloy plate pass through the filter having a pore size of 0.2 μm (permeation). Therefore, it is not separated and extracted.

  Then, the residue containing Mn compound having a particle size of 0.2 μm or more on the filter was analyzed by ICP emission analysis, and the elemental amount of Mn present as Mn compound having a particle size of 0.2 μm or more (mass%) ) Can be measured.

  Further, the so-called total Mn content B existing in the Al alloy plate as Mn compound or dissolved Mn can be analyzed by ordinary X-ray analysis or ICP emission analysis in the same manner as other contained elements.

(Mg compound)
Mg forms a compound phase with Si. Among these Mg compounds, a relatively large Mg compound having a particle size of 0.2 μm or more is a ridging mark in the same way as the above-mentioned Mn compound. There is an effect to suppress. Furthermore, there is an effect of increasing local uniform deformability of the plate and alleviating the occurrence of surface irregularities. It is also effective in securing strength.

  Therefore, in order to exert these effects, the elemental amount C of Mg present as an Mg compound having a particle size of 0.2 μm or more is a ratio C (mass%) to the Mg content D contained in the Al alloy plate. ) / D (mass%) in the range of 0.03 to 0.5, preferably in the range of 0.04 to 0.4, more preferably in the range of 0.05 to 0.3, and still more preferably in the range of 0.05 to 0.2. Incidentally, the Mg content D of the Al alloy plate is defined as Mg: 0.2 to 3.0% in the component composition rule of the Al alloy plate of the present invention, similarly to the Mn content B. This is the total amount of Mg in the alloy sheet.

  The reason why the amount of the Mg compound having a particle size of 0.2 μm or more is not directly defined but is defined in relation to the Mg content is the same as that of the above-described Mn compound having a particle size of 0.2 μm or more. That is, the recrystallization orientation forming effect with random orientation of the Mg compound is exhibited in relation to the amount of Mg dissolved in the Al alloy plate structure, and even if there are many Mg compounds having a particle size of 0.2 μm or more, This is because when the amount of Mg to be dissolved is insufficient, the effect of forming a recrystallized orientation with random orientation of an Mg compound having a particle size of 0.2 μm or more is also halved.

  If this C (mass%) / D (mass%) is less than 0.03, or more preferably less than the lower limit of 0.04, 0.05, etc., there are too few Mg compounds having a particle size of 0.2 μm or more, and these effects cannot be exhibited. On the other hand, when the C (mass%) / D (mass%) exceeds the upper limit of 0.5, or more preferably exceeds the upper limit of 0.4, 0.3, 0.2, etc., the above Mg content of 0.2 to 3.0% On the contrary, these effects are not exerted.

  However, the ridging mark suppression effect of the Mg compound is considerably smaller than the ridging mark suppression effect of the Mg compound. This is because most of the Mg compound re-dissolves during the temperature rising process such as the final solution treatment of the plate, so the Mg compound that works in the recrystallization process during the temperature rising process of the solution treatment described above is absolute. This is because the number is reduced and it is inevitably smaller than the effect of the Mn compound. Therefore, when the ridging mark suppression effect of these Mg compounds is used, it is used only as a complement to the above Mn compounds.

  These relatively large Mg compounds having a particle size of 0.2 μm or more can be separated and extracted by the same extraction residue method as the above-described Mg compounds having a particle size of 0.2 μm or more. Further, the amount of Mg element (% by mass) existing as an Mg compound having a particle size of 0.2 μm or more is the same ICP as the amount of Mg element existing as an Mn compound having a particle size of 0.2 μm or more. It can be measured by residue analysis on a measurement filter by luminescence analysis.

(Compound rules)
Here, including the above-mentioned Mn compound and Mg compound, and also including all other compounds, among the compounds (intermetallic compounds or precipitates) present in the Al alloy sheet structure, the coarse compound is: Similar to the above-described Mn compound and Mg compound having a particle size of 0.2 μm or more, it becomes a nucleus of random orientation, promotes formation of recrystallized orientation having random orientation, and has an effect of suppressing ridging marks.

  However, importantly, on the other hand, these coarse compounds have a risk of greatly hindering the formability of the plate itself, and may make the ridging mark suppression effect of the above-described Mn compounds and Mg compounds themselves meaningless. There is.

  Therefore, in the present invention, for all compounds present in the Al alloy plate structure, from the viewpoint of suppressing ridging marks and ensuring the formability of the plate that is the premise, the average particle size of these coarse compounds, It is specified as a precondition for the above-mentioned definition of Mn compounds and Mg compounds. If the average particle size (size) of these coarse compounds exceeds 3 μm, the formability of the plate itself, such as press formability and bending workability, is greatly hindered. For this reason, in this invention, the average particle diameter of the compound which has a particle size of 0.2 micrometer or more is controlled to 3 micrometers or less.

  These compounds can be identified (identified) by visual field observation of about 100 μm × 100 μm using a 1000 × FE-SEM (Field Emission Scanning Electron Microscopy). In this case, observation with reflected electrons is preferable because each compound can be observed more clearly.

  And the measurement of the average particle diameter of these compounds can perform image analysis using the image observed by the said method. That is, as image analysis software, MEDIA CYBERNETICS manufactured by Image-Pro Plus, the particle diameter of each compound having a particle diameter of 0.2 μm or more that can be observed in the field of view is measured and averaged by the centroid diameter, Furthermore, observation (number of fields of view) is performed at 200 or more locations of the test material, and the average value of these is the average particle size of compounds having a particle size of 0.2 μm or more.

(Component composition of Al alloy sheet)
Next, the chemical component composition of the Al alloy sheet of the present invention will be described below. The basic composition of the Al alloy sheet of the present invention is the structure specified as described above, and also required for panel materials such as automobile outer panels, press formability, bendability, BH property (strength), or even weldability. Stipulated to ensure various properties such as corrosion resistance.

For this purpose, the basic composition of the Al alloy sheet of the present invention is Mg: 0.2 to 3.0%, Si: 0.5 to 2.5%, Mn: 0.02 to 0.5% , Fe: 1.5% or less (but not including 0%). It is set as Al alloy composition which contains and remainder consists of Al and an impurity. In the present invention, “%” for the chemical component composition means “% by mass”, including “%” in claims.

However, in the present invention, in order to improve various properties necessary for the above-mentioned application, the above-mentioned basic composition of the 6000 series Al alloy is further added with other alloy elements, or in accordance with AA or JIS standards. An impurity level content may be included. The other alloying elements, specifically, Cu: 0.01 to 2.0% or, alternatively, Cr: 0.5% or less, Zr: 0.5% or less under, Ti: 0 .005~0.20%, B : 0.0001~0.05% 1 type or 2 types or more may be selectively included. In addition to these, or instead of these, the further, Zn: may selectively comprise 1.0% or less.

  Other alloy elements and gas components other than the above alloy elements are impurities. However, from the viewpoint of recycling, not only high-purity Al ingots but also 6000 series alloys and other Al alloy scrap materials, low-purity Al ingots, etc. are used as melting raw materials as melting materials. In the case of melting, these other alloy elements are necessarily included. Therefore, in the present invention, these impurity elements are allowed to be contained within a range that does not hinder the intended effect of the present invention.

The content range and significance of each element in the 6000 series Al alloy, the preferable content range or the allowable amount will be described below.
(Si: 0.5-2.5%)
When Si is solid-solution strengthened and maintained at an appropriate temperature after solution treatment, an aggregate of Mg-Si atoms called the GP zone and an intermediate phase in which this aggregate is further developed generate artificial age hardening. To do. That is, during artificial aging treatment at a relatively low temperature and short time, such as paint baking after molding, the compound phase (β ") is formed with Mg to exhibit age hardening ability and obtain the required strength as a plate. Therefore, it is the most important element for combining necessary properties as a panel such as press formability.

  If the Si content is less than 0.5%, the age-hardening ability and further various properties such as press formability required for each application cannot be obtained. On the other hand, if Si exceeds 2.5%, press formability and bending workability are significantly impaired. Furthermore, weldability is significantly impaired. Therefore, Si is in the range of 0.5 to 2.5%.

  In order to improve BH properties at relatively low temperatures, such as low-temperature artificial aging treatment, an excess Si-type 6000-based Al alloy composition with Si / Mg at a mass ratio of 1.0 or more and containing Si in excess of Mg It is preferable that

(Mg: 0.2-3.0%)
As described above, Mg forms an Mg compound having a particle size of 0.2 μm or more, and suppresses ridging marks by setting the Al alloy plate structure after the tempering treatment as a recrystallization orientation having a random orientation. In addition, it is an essential element for forming a compound phase with Si during the above-mentioned artificial aging treatment such as solid solution strengthening and paint baking treatment to exhibit the age hardening ability and obtain the necessary strength as the panel.

  If the Mg content is less than 0.2%, the absolute amount of the Mg compound having a particle diameter of 0.2 μm or more is insufficient. Moreover, the said compound phase cannot be formed at the time of artificial aging treatment, and age-hardening ability cannot be exhibited. For this reason, the said required intensity | strength required as a board cannot be obtained. On the other hand, if the Mg content exceeds 3.0%, the formability itself such as press formability and bending workability is significantly inhibited. Therefore, the Mg content is in the range of 0.2 to 3.0%.

(Mn: 0.02-0.5%)
As described above, Mn forms an Mn compound having a particle size of 0.2 μm or more, and suppresses ridging marks by using the Al alloy plate structure after the tempering treatment as a recrystallization orientation having a random orientation. Further, solute Mn has an effect of alleviating the occurrence of surface irregularities due to uniform deformability. If the Mn content is less than 0.02%, the Mn compound having a particle size of 0.2 μm or more is insufficient, and these effects cannot be obtained. On the other hand, if the Mn content exceeds 0.5%, the amount of crystallized substances increases and the bending workability of heme and the like deteriorates. Therefore, the Mn content is in the range of 0.02 to 0.5%, preferably in the range of 0.03 to 0.45%.

(Cu: 0.01-2.0%)
Cu is useful for improving the age hardening rate in a 6000 series Al alloy. That is, it has the effect of promoting the precipitation of a compound phase such as a GP zone into the crystal grains of the Al alloy material structure under the conditions of artificial aging (hardening) treatment such as a paint baking process. Moreover, Cu dissolved in the artificial aging treatment state also has an effect of improving formability. If the Cu content is less than 0.01%, these effects are insufficient.

  However, if the Cu content exceeds 2.0% and is too large, there is a high possibility that a coarse compound is formed and the moldability is deteriorated. In addition, there is a high possibility that the corrosion resistance such as yarn rust resistance required for an automobile outer panel will deteriorate. Therefore, the upper limit of the content when Cu is selectively contained is preferably 2.0% or less.

(One or more of Fe, Cr, Zr, Ti and B)
All of these elements contribute to the refinement of crystal grains. It also contributes to the improvement of mechanical properties (strength, ductility, toughness, hardening, etc.). For example, Cr, etc. Zr generates dispersed particles (dispersion phase) at homogenization heat treatment, these dispersed particles have the effect of hindering grain boundary migration after recrystallization. Moreover, since Fe, Ti, etc. generate crystallized substances and serve as nuclei for recrystallized grains and prevent coarsening of the crystal grains, fine crystal grains can be obtained. However, if each content is too large, a coarse compound is formed, which becomes a starting point of destruction, and the moldability deteriorates instead. Therefore, when Fe is contained or when each of the above elements is selectively contained, the content is set to the upper limit value or the content range described below. Fe: 1.5% or less, Cr: 0.5% or less, Zr: 0.5% or less , Ti : 0.005 to 0.20 %, B: 0.0001 to 0.05%.

(Zn: 1.0% or less)
Zn is useful for improving the age hardening rate. That is, at a relatively low temperature short time conditions of artificial aging, the effect there to promote the precipitation of the compound phase, such as GP zones into grains of the Al alloy material structure Ru. However, when containing organic content is too high, the formability is deteriorated to form a coarse compound. Therefore, when the elements are selectively contained, the content is made Zn : 1.0% or less.

(Average crystal grain size)
In defining these structures, it is preferable to refine the average grain size of the Al alloy plate to 50 μm or less. By making the crystal grain size fine or small within this range, bending workability and press formability can be ensured or improved. When the crystal grain size becomes larger than 50 μm, the press formability such as bending workability and overhang is remarkably deteriorated, and defects such as cracking and rough skin are easily generated.

  The crystal grain size referred to here is the maximum diameter of crystal grains in the longitudinal (L) direction of the plate. The crystal grain size is measured by a line intercept method in the L direction by observing the surface of the Al alloy plate that has been mechanically polished by 0.05 to 0.1 mm and then electrolytically etched using an optical microscope. 1 The measurement line length is 0.95mm, and the total measurement line length is 0.95 x 15mm by observing a total of 5 fields with 3 lines per field.

(Production method)
The method for producing the Al alloy plate of the present invention will be described below.
First, in order to make the 6000 series Al alloy plate excellent in ridging mark characteristics, preferable production conditions in which the above specific compound exists and the specific Mn compound exist will be described.

For this purpose, first, when soaking (homogenizing heat treatment) a 6000 series Al alloy ingot of the composition range of the present invention, as shown in the heat pattern in FIG. It is preferable to hold | maintain for 1 h or more and 10 h or less in the temperature range of 450-500 degreeC shown by. This temperature range is the temperature range in which this temperature range is most likely to precipitate, and the size distribution and amount of the Mn compound can be controlled within the scope of the present invention by the holding process 2 in this temperature range. When the holding temperature is less than 450 ° C., Mg ₂ Si is likely to precipitate, and the Mn compound does not precipitate. For this reason, in order to make Mg ₂ Si form a solid solution and to precipitate the Mn compound, the holding temperature is set to 450 ° C. or higher. On the other hand, even when the holding temperature exceeds 500 ° C., the precipitation of the Mn compound is reduced.

  Therefore, holding out of this temperature range eliminates the meaning of holding in the temperature rising process itself, which is the same as the conventional soaking temperature rising process that does not hold in temperature rising process 1 as shown in Fig. 2, There is a high possibility that the size distribution and amount of the Mn compound cannot be controlled within the scope of the present invention. Since the conventional 6000 series Al alloy sheet is not retained in this temperature rising process, the elemental amount A of Mn existing as an Mn compound having a particle size of 0.2 μm or more is reduced. Therefore, even if the Mn content B of the Al alloy plate is satisfied, the A (mass%) / B (mass%) inevitably falls below the lower limit of 0.3, and recrystallization orientation formation having a random orientation Is insufficient and ridging marks are not suppressed.

As other soaking conditions for the ingot, the maximum holding temperature indicated by 3 in FIG. 1 is 500 ° C. to 560 ° C. for re-solidification of Mg ₂ Si present as the ingot crystallized product. It is preferable to be in the range. In addition, the rate of temperature increase in the soaking temperature increasing process 1a, 1b is preferably 20 ° C. to 50 ° C./h in order to ensure precipitation of the Mn compound in the above temperature range.

  It is an advantage of the present invention that the Al alloy sheet of the present invention can be manufactured basically by a conventional method other than the soaking condition of the ingot, and can be manufactured without greatly changing the process.

  First, in the melting and casting process of the Al alloy, a normal melting and casting method such as a continuous casting rolling method and a semi-continuous casting method (DC casting method) is appropriately used for the molten Al alloy melt adjusted within the specification range of the present invention. Select and cast. Next, the Al alloy ingot is subjected to homogenization heat treatment under the above conditions. Thereafter, the Al alloy ingot is hot-rolled by a conventional method to obtain a hot-rolled product such as a coil or plate, or is further subjected to intermediate annealing as necessary to perform cold rolling, and then the coil. Processed into a cold-rolled product.

  Al alloy plates such as hot-rolled plates or cold-rolled plates after these processing are tempered by the following solution treatment and quenching treatment as a tempering treatment, and are made into product plates such as coils and plates. . Of course, it is also possible to add tempering treatment such as aging treatment, stabilization treatment, or recovery treatment according to the application and necessary characteristics.

(Solution and quenching)
Utilizing Mn compounds controlled to the size distribution and amount within the scope of the present invention by soaking of the above ingot, random orientation as recrystallization nuclei to suppress ridging marks in the final solution treatment and quenching treatment In order to obtain a recrystallized orientation having the above, it is preferable to set the heating rate of the final solution treatment to 50 ° C./min or more. In the final temperature increasing process of 50 ° C./min or more in the solution treatment, the Mn compound serves as a nucleus for formation of recrystallized crystal orientation.

  The solution treatment conditions are preferably 500 ° C. or higher and 560 ° C. in order to sufficiently precipitate Mg / Si clusters and β ”phases in the grains by artificial aging treatment such as paint baking hardening after press molding of the plate. Perform in the temperature range up to ℃.

  Next, in the quenching treatment from the solution treatment temperature, if the cooling rate is slow, Si, MgSi, etc. are likely to precipitate on the grain boundary, which tends to be the starting point of cracks during press molding and bending, and these formability decreases. To do. In order to ensure this cooling rate, it is preferable to use the quenching process by selecting water cooling means and conditions such as air cooling such as a fan, mist, spray, and immersion, respectively.

  In the present invention, in order to further improve the age-hardening property in the artificial age-hardening treatment such as the paint baking process of the molded panel, in order to suppress the formation of clusters and promote the precipitation of the GP zone after the quenching treatment, the pre-aging treatment You may do it. This preliminary aging treatment is preferably held in a temperature range of 50 to 100 ° C., preferably 60 to 90 ° C., for a required time of 1 to 24 hours. The cooling rate after the pre-aging treatment is preferably 1 ° C./hr or less. As this preliminary aging treatment, after the cooling end temperature of the quenching treatment is increased to 50 to 100 ° C., it is immediately reheated or kept as it is. Alternatively, it is immediately reheated to 50 to 100 ° C. after quenching to room temperature after solution treatment.

  Furthermore, in order to suppress aging at room temperature, a GP zone may be further generated by performing a heat treatment (artificial aging treatment) at a relatively low temperature without time delay after the preliminary aging treatment. When the time delay is present, room temperature aging (natural aging) occurs with time even after the preliminary aging treatment, and after the room temperature aging occurs, the effect of the heat treatment at the relatively low temperature is exhibited. It becomes difficult.

  Next, examples of the present invention will be described. Each of the Al alloy plates having the chemical composition of A to H shown in Table 1 was manufactured by changing various holding conditions during temperature rising during soaking as shown in Table 2, and Mn as shown in Table 3. The size and amount of the compound and Mg compound were changed, and as shown in Table 4, BH property, bending workability, ridging mark property and the like were evaluated.

  The production of the Al alloy sheet is the same except for the tempering treatment conditions. After a 500 mm thick large ingot of each composition shown in Table 1 is melted by the DC casting method, it is homogenized at 500-550 ° C shown in Table 2. Heat treatment was performed, followed by hot rolling at an end temperature of 300 ° C. This hot-rolled sheet was cold-rolled at a cold rolling rate of 60% without being subjected to intermediate annealing to obtain a sheet having a thickness of 1.0 mm.

  These cold-rolled sheets were subjected to a solution treatment at a temperature of 550 ° C. for 5 seconds in a continuous heat treatment facility, and were subsequently quenched from the temperature at a cooling rate of 100 ° C./second or more. The quenching end temperature (quenching temperature) was set to room temperature, and after 5 minutes of quenching, reheating treatment at 70 ° C for 2 hours (slow cooling at a cooling rate of 0.6 ° C / hr after maintaining the temperature) gave a T4 material. It was.

  A plurality of test pieces each having a predetermined size were cut out from the tempered Al alloy plate after standing at room temperature for 15 days after the tempering treatment, and various measurements and evaluations described below were performed.

(Dispersed state of compound)
For sample preparation, the Al alloy plate obtained as described above is polished to about 0.05 to 0.1 mm with emery paper, and then buffed with a roughness of 3 μm and 1 μm. Here, OPU was used as the buffing polishing liquid. Using the thus prepared plate sample, the dispersion state of the following compounds was observed and evaluated.

(Dispersion degree of intermetallic compound)
Using an S4500 type FE-SEM manufactured by Hitachi, Ltd., observation with reflected electrons is performed in a field of about 100 μm × 100 μm by observation at × 1000 magnification, and image analysis is performed by the above-described method using the observed image. The average particle size of an intermetallic compound having a particle size of 0.2 μm or more was measured.

(Mn compound, Mg compound)
Mn compounds and Mg compounds having a particle size of 0.2 μm or more are separated and extracted by the above-described extraction residue method, and Mn compounds existing as Mn compounds and Mg compounds are analyzed by residue analysis on the measurement filter by ICP emission analysis. The element amount (mass%) of Mg and Mg was measured, and the ratio between the content of Mn and Mg was calculated.

  In both the inventive examples and the comparative examples, the crystal grain sizes of the Al alloy plates after aging at room temperature by the measurement method were all 50 μm or less.

(Riding mark)
The ridging mark was evaluated by observing the occurrence of surface irregularities by a tensile test and the surface roughness of the molded product after drawing.

  Specifically, No. 5 test piece (25 mm × 50 mmGL × plate thickness) of JIS Z 2201 was collected from the Al alloy plate obtained as described above, and a room temperature tensile test was performed. The room temperature tensile test was performed at room temperature of 20 ° C. based on JIS Z 2241 (1980) (metal material tensile test method). At this time, the specimens were sampled in a direction perpendicular to the rolling direction and a direction perpendicular to the rolling direction. The tensile speed was 5 mm / min up to 0.2% proof stress, and 20 mm / min after proof stress.

  By this tensile test, 15% and 20% tensile deformation was given to the plate, and the unevenness of the plate surface was measured with a roughness meter. As shown in FIG. Was measured, and the difference h between the maximum height crest a and the maximum depth trough b was measured, and the average value of the three measurement points of the Al alloy plate was obtained. Since the actual measured value is a fine fluctuation profile as shown in Fig. 4, the profile of the plate surface unevenness averaged at each surface position is obtained as shown in Fig. 3, and is obtained with this profile. Further, the height h of the unevenness was evaluated.

  The surface properties (skin roughness) after drawing were evaluated by visually checking the surface of the drawn product. That is, the evaluation was made in four stages: ◎: no occurrence of skin roughness, ○: slight occurrence of skin roughness, △: occurrence of skin roughness, ×: strong occurrence of skin roughness. The drawing conditions at that time are shown below. A blank was prepared by blank cutting and a test piece was collected. Lubricating oil: Castrol No.700 diluted to 50%. Molding tester: Molded into cup shape by Eriksen tester. Blank diameter: 100 mm. Punch diameter: φ50mm. R at the shoulder of the punch: 4.5 mm. Die diameter: φ65.1mm. R on the die side shoulder: 14 mm. Wrinkle holding pressure: 500kgf. Aperture ratio: 2 (aperture ratio = 50%).

(As proof stress)
A JIS Z 2201 No. 5 test piece (25 mm × 50 mmGL × plate thickness) was taken from the original Al alloy plate of the test plate immediately after the tempering treatment, and a room temperature tensile test was performed. The room temperature tensile test was performed at room temperature of 20 ° C. based on JIS Z 2241 (1980) (metal material tensile test method). At this time, the specimen was collected in the direction parallel to the rolling direction. The crosshead speed was 5 mm / min, and the test was performed at a constant speed until the test piece broke. By this method, 0.2% proof stress was evaluated, and AS proof strength was set (N number = average value of 5).

(Yield strength after BH)
In order to investigate the artificial aging treatment ability, after simulating that these Al alloy plates were press-molded as panels, the JIS No. 5 test piece was preliminarily given a strain of 2%, and then 170 ° C. for 20 minutes. Artificial age hardening treatment was performed, and the yield strength (MPa) of each test plate after treatment was measured as the post-BH yield strength (MPa) under the tensile test conditions described above.

(Hem bending workability)
A bending test piece having a length of 180 mm and a width of 30 mm was collected from the aluminum alloy plate and evaluated for flat hemming workability. In the flat hemming process, a strain of 10% was applied in advance, and then bending at an angle of 180 ° (inner bending radius R = about 0.25 mm) was performed. The flat hemming workability was evaluated based on the following criteria by visually confirming the degree of cracking at the edge of the bending. In addition, 0 to 2 steps are acceptable and 3 to 5 steps are unacceptable.
0: Rough skin and no fine cracking 1: Slight roughening occurs 2: Rough skin occurs but there are no cracks including minute parts 3: Small cracks occur 4: Large cracks occur Occurrence 5: Multiple or many large cracks occur

As shown in Tables 1 and 2, Invention Examples 1 to 12 are manufactured within the composition range of the Al alloy of the present invention and within the above-mentioned preferable ranges of soaking and solution treatment conditions. As a result, as is apparent from Table 3, the Al alloy sheet of the present invention has an average particle size of a compound having a particle size of 0.2 μm or more of 3 μm or less and exists as an Mn compound having a particle size of 0.2 μm or more. The elemental amount A of Mn is in the range of 0.3 to 0.9 in the ratio A (mass%) / B (mass%) with the Mn content B. Furthermore, the elemental amount C of Mg present as an Mg compound having a particle size of 0.2 μm or more is in the range of 0.03 to 0.5 in the ratio C (mass%) / D (mass%) with the Mg content D. is there. However, Invention Example 4 in Tables 2, 3, and 4 has a ratio C (mass%) / D (mass%) to the Mg content D of 0.01 as shown in Table 3, which is within the scope of the present invention. This is a reference example that deviates from the range.

  As a result, as is apparent from Table 4, the Al alloy plate of the present invention has a smaller surface irregularity when subjected to 15% and 20% tensile deformation than the comparative example, and the surface after drawing. Excellent properties (skin texture). These results mean that rigging mark properties and press formability are excellent even after actual severe press forming.

  In addition, the Al alloy plate of the present invention has a low proof stress of about 115 to 130 MPa for As, and a high proof strength for BH after BH of about 190 to 230 MPa while ensuring formability such as press molding. The difference between the post-proof strength and the As-proof strength is large, and the baking finish hardening property (BH property) is also excellent. As for the evaluation of formability, the evaluation of flat hem workability is 2 at the lowest level and 1 at the higher level, and the bending workability is also excellent. Therefore, it can be seen that the Al alloy sheet of the present invention can guarantee the ridging mark property with good reproducibility, and also has press formability, bending workability and BH property.

  In comparison between Invention Examples 8 and 9 and Invention Examples 4 to 7, Invention Examples 8 and 9 have a relatively small average particle diameter of a compound having a particle diameter of 0.2 μm or more, or A (mass%) / B (mass%) or C (mass%) / D (mass%) is not close to the upper and lower limits. Therefore, Invention Examples 8 and 9 are more excellent in ridging marks than Invention Examples 4 to 7. These results support the critical significance of the specific conditions for compound dispersion of the present invention.

  On the other hand, Comparative Example 10 uses Al alloy of A within the composition range of the present invention, but in the temperature rising process when soaking the Al alloy ingot, it is 1 h or more and 10 h in the temperature range of 450 to 500 ° C. Not held below. The same applies to Comparative Example 11 in which the Mn content exceeds the upper limit and is too high. Therefore, as is clear from Table 3, Comparative Examples 10 and 11 lack the element amount A of Mn present as an Mn compound having a particle size of 0.2 μm or more, and A (mass%) / B (mass%) is The average particle size of a compound having a particle size of less than the lower limit or having a particle size of 0.2 μm or more exceeds the upper limit of 3 μm.

  As a result, as is apparent from Table 4, in Comparative Examples 10 and 11, the surface roughness (skin roughness) after 15% and 20% tensile deformation, or the surface property (skin roughness) after drawing was the above-mentioned invention. It is significantly inferior to the examples. That is, Comparative Examples 10 and 11 mean that the rigging mark property and press formability are inferior even when actual severe press forming is applied.

  Incidentally, Comparative Example 10 in which the elemental amount A of Mn existing as an Mn compound having a particle diameter of 0.2 μm or more is insufficient and A (mass%) / B (mass%) is below the lower limit is the conventional 6000 series. It can be said that it corresponds to an Al alloy plate, and is superior in BH property and bending workability as compared with Comparative Example 11 and similar to the inventive example. However, it is proved that it does not have only ridging mark property.

  ADVANTAGE OF THE INVENTION According to this invention, the ridging mark at the time of press molding can be prevented with sufficient reproducibility, and the Al-Mg-Si type aluminum alloy plate excellent in bending workability and BH property can be provided. As a result, for transportation equipment such as automobiles, ships, aircraft or vehicles, machines, electrical products, architecture, structures, optical equipment, equipment parts and parts, and in particular, body panels of transportation equipment such as automobiles, The application of Al alloy sheets can be expanded.

It is explanatory drawing which shows the temperature rising process of the soaking | uniform-heating of this invention Al alloy plate. It is explanatory drawing which shows the temperature rising process of the soaking | uniform-heating of the conventional Al alloy plate. It is explanatory drawing which shows the measurement profile of the surface roughness of Al alloy plate. It is explanatory drawing which shows the measurement profile of the surface roughness of Al alloy plate.

Explanation of symbols

1a, 1b: heating process, 2: holding process, 3: maximum soaking temperature,

Claims (4)

Mass: Mg: 0.2-3.0%, Si: 0.5-2.5%, Mn: 0.02-0.5%, Fe: 1.5% or less (excluding 0%), the balance being Al and inevitable impurities In the Al-Mg-Si-based aluminum alloy plate, an element of Mn existing as an Mn compound having an average particle size of 3 μm or less and a particle size of 0.2 μm or more in a compound having a particle size of 0.2 μm or more The amount A is in the range of 0.3 to 0.9 in terms of the ratio A (mass%) / B (mass%) to the Mn content B in the aluminum alloy sheet, and exists as an Mg compound having a particle size of 0.2 μm or more. An aluminum alloy sheet excellent in ridging mark characteristics in which the elemental amount C of Mg is in the range of 0.03 to 0.5 in the ratio C (mass%) / D (mass%) to the Mg content D in the aluminum alloy sheet. The aluminum alloy plate excellent in ridging mark characteristics according to claim 1, wherein the aluminum alloy plate further contains Cu: 0.01 to 2.0% by mass%. The aluminum alloy plate is further mass%, Cr: 0.5% or less (excluding 0%), Zr: 0.5% or less (excluding 0%), Ti: 0.005 to 0.20%, B: 0.0001 The aluminum alloy plate excellent in ridging mark characteristics according to claim 1 or 2, wherein the aluminum alloy plate contains at least one of -0.05%. 4. The ridging mark property according to claim 1, wherein the aluminum alloy sheet further contains, by mass%, Zn: 1.0% or less (excluding 0%). 5. Aluminum alloy plate.