WO2016031937A1

WO2016031937A1 - Aluminum alloy sheet for forming

Info

Publication number: WO2016031937A1
Application number: PCT/JP2015/074297
Authority: WO
Inventors: 有賀　康博; 久郎宍戸; 松本　克史
Original assignee: 株式会社神戸製鋼所
Priority date: 2014-08-27
Filing date: 2015-08-27
Publication date: 2016-03-03
Also published as: JP2016047949A; JP6224550B2; US20170233853A1; KR20170029633A; KR20180095117A; CN106574327A

Abstract

　The present invention pertains to an Al-Mg-Si based aluminum alloy sheet for forming, that contains 0.2-2.0% of Mg, 0.3-2.0% of Si, and 0.005-0.3% of Si (all amounts given with respect to mass), the balance comprising Al and unavoidable impurities, wherein the aluminum alloy sheet for forming is characterized in that the structure of the aluminum alloy sheet is such that the average number density of compounds having a circle-equivalent diameter within a range of 0.3-20 μm as measured by SEM at 500 times magnification is more than 0/mm² but not more than 5,000/mm², and of the compounds measured by SEM, the average count ratio of compounds that contain 0.5% by mass or more of Sn as identified using an X-ray spectrograph, is 0% or more but less than 50%. This aluminum alloy sheet for forming exhibits high BH properties and good workability.

Description

Aluminum alloy sheet for forming

The present invention relates to an Al—Mg—Si based aluminum alloy sheet for forming. The aluminum alloy sheet referred to in the present invention is a rolled sheet such as a hot-rolled sheet or a cold-rolled sheet, and is subjected to tempering such as solution treatment and quenching process, and is baked and coated and cured. Says aluminum alloy plate before being done. In the following description, aluminum is also referred to as aluminum or Al.

In recent years, due to consideration for the global environment, social demands for weight reduction of vehicles such as automobiles are increasing. In order to meet such demands, as a material for large-sized body panels (outer panels, inner panels) such as automobile panels, especially hoods, doors, roofs, etc., instead of steel materials such as steel plates, it was excellent in formability and bake coating curability. The application of lighter aluminum alloy materials 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 aluminum alloy plates. The use of Al—Mg—Si based AA to JISＪ6000 (hereinafter also simply referred to as 6000) aluminum alloy plates is being studied.

This 6000 series aluminum alloy plate contains Si and Mg as essential components. Particularly, the excess Si type 6000 series aluminum alloy has a composition in which these Si / Mg is 1 or more in mass ratio, and has excellent age hardening ability. Have. For this reason, formability is ensured by reducing the yield strength during press molding and bending, and age-hardening is achieved by heating during relatively low-temperature artificial aging (curing) treatment such as paint baking treatment of panels after molding. And has a baking coating curability (hereinafter also referred to as bake hard property = BH property, bake curability) that can secure the required strength as a panel.

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

On the other hand, as is well known, an outer panel of an automobile is manufactured by combining an aluminum alloy plate with a forming process such as press forming and bending forming. For example, in a large outer panel such as a hood or a door, it is formed into a molded product shape as an outer panel by press molding such as overhanging, and then the inner panel is formed by hem (hemming) processing such as flat hem on the outer peripheral edge of the outer panel. Are joined to form a panel structure.

Here, the 6000 series aluminum alloy has an advantage of having excellent BH property, but has aging property at room temperature, and after the solution quenching treatment, it is age-hardened by holding at room temperature for several months to increase the strength. As a result, there is a problem that the formability to the panel, particularly the bending workability, is lowered. For example, when a 6000 series aluminum alloy plate is used for an automotive panel, it usually takes about 1 to 4 months after it is solution-quenched by an aluminum maker (after manufacture) and then molded into a panel by an automotive maker. It is left at room temperature (and left at room temperature), and during this time, it is considerably age-hardened (room temperature aging). In particular, in the outer panel that undergoes severe bending, there was a problem that cracking occurred at the time of hem processing after three months even though it could be molded without any problem after one month after manufacture. Therefore, it is necessary to suppress room temperature aging over a relatively long period of about 1 to 4 months in a 6000 series aluminum alloy plate for automobile panels, particularly for outer panels.

Further, when such room temperature aging is large, the BH property is lowered, and depending on the heating at the relatively low temperature artificial aging (curing) treatment such as paint baking treatment of the panel after molding, There is also a problem that the yield strength is not improved to the required strength.

Conventionally, from the viewpoint of the structure of a 6000 series aluminum alloy sheet, particularly the compound (crystallized product, precipitate) formed by the contained elements, improvement of properties such as improvement of formability and BH property, or suppression of room temperature aging Various proposals have been made. Recently, in particular, attempts have been made to directly measure and control clusters (aggregates of atoms) that affect the BH properties and room temperature aging properties of 6000 series aluminum alloy plates.

Also, as a prior patent related to the addition of Sn in the present invention, a number of methods have been proposed in which Sn is positively added to a 6000 series aluminum alloy plate to suppress room temperature aging and improve baking coating hardening. For example, in Patent Document 1, there is a method that combines room temperature aging suppression and baking coating curing by adding an appropriate amount of Sn having a temporal change suppressing effect and applying pre-aging after solution treatment. Patent Document 2 proposes a method for improving formability, baking paintability, and corrosion resistance by adding Sn having a temporal change suppressing effect and Cu for improving formability.

Japanese Unexamined Patent Publication No. 09-249950 Japanese Unexamined Patent Publication No. 10-226894

However, even Al-Mg-Si based aluminum alloy sheets to which Sn is positively added still have room for improvement in order to have both good formability after long-term aging at room temperature and high BH properties. there were.

In view of such problems, an object of the present invention is to form Sn-containing Al—Mg, which can exhibit high BH properties and good workability even in a car body paint baking process after long-term aging at room temperature. -To provide a Si-based aluminum alloy sheet.

In order to achieve this object, the gist of the forming aluminum alloy plate of the present invention is, in mass%, Mg: 0.2 to 2.0%, Si: 0.3 to 2.0%, and Sn: 0.00. When an Al—Mg—Si-based aluminum alloy plate containing 005 to 0.3% and the balance being Al and inevitable impurities is measured using a 500-fold SEM as the structure of the aluminum alloy plate The average number density of the compound having an equivalent circle diameter of 0.3 to 20 μm is 0 / mm ^{2 and} 5000 / mm ² or less, and among the compounds measured by the SEM, The average number ratio of the compound containing 0.5 mass% or more of Sn to be identified is 0% or more and less than 50%.

Sn, in the structure of Al-Mg-Si aluminum alloy plate, traps atomic vacancies at room temperature, thereby suppressing the diffusion of Mg and Si at room temperature and increasing the strength at room temperature. Has the effect of improving press formability such as hem workability, drawing and overhanging (hereinafter also referred to as hem workability as a representative of this press formability) when forming plates into panels. . And since the vacancies captured during the artificial aging treatment such as the paint baking treatment of the panel are released, the diffusion of Mg and Si can be promoted and the BH property can be increased.

However, according to the knowledge of the present inventors, such addition of Sn has a great restriction due to the characteristics peculiar to Sn. The effect of capturing and releasing Sn atomic vacancies is exhibited only when Sn is dissolved in the matrix. However, the amount of Sn dissolved in the matrix is very small (low), and in the ordinary plate manufacturing method, even if the addition amount of Sn is kept below the theoretical solid solution amount, most of it does not dissolve, Crystallized or precipitated as a compound. Thus, Sn crystallized or precipitated as a compound has no effect of trapping or releasing atomic vacancies.

For this reason, in this invention, after deliberately reviewing the manufacturing method of the plate, as described later, the manufacturing conditions such as intermediate annealing are devised, and the presence state of the contained Sn is controlled to precipitate Sn as a compound. It suppresses and promotes the solid solution of Sn in the matrix, and ensures the solid solution amount of Sn. As a result, the effect of improving heme workability and BH property is sufficiently exhibited by the trapping of Sn atomic vacancies and the suppression of aging by the release effect.

As a result, it is possible to provide an Sn-containing Al—Mg—Si based aluminum alloy plate that can exhibit higher formability and BH properties even when it is aged at room temperature for a long time, for example, for 100 days after the plate is manufactured.

Incidentally, the conventional Sn-containing Al—Mg—Si based aluminum alloy plate could not sufficiently exhibit such effects of Sn.

The reason for this is that in the past, the solid solution and precipitation of Sn, which was only one of the selective additive elements, while always paying attention to the solid solution and precipitation of the main elements Mg and Si. This is probably due to the fact that they did not pay much attention. Further, the Sn present form of the plate produced by a conventional method is crystallization or precipitation (hereinafter, also simply referred to as precipitation) as a compound. In contrast to this, it is difficult to solidify Sn itself, and since the solid solution state of Sn is a very rare form, it is difficult to know the effects exhibited by the solid solution of Sn. Inferred.

Hereinafter, the embodiment of the present invention will be specifically described for each requirement.

(Chemical composition)
First, the chemical composition of the Al—Mg—Si (hereinafter also referred to as 6000) aluminum alloy sheet of the present invention will be described below. The 6000 series aluminum alloy plate targeted by the present invention is required to have excellent properties such as formability, BH property, strength, weldability, and corrosion resistance as a plate for an automobile panel. That is, even for a plate that has been aged at room temperature for a long period of 100 days after the tempering treatment, the As proof stress is 110 MPa or less, the BH (bake hard) property is proof stress difference of 100 MPa or more, and the hem workability is described later in the examples. It is required that it is excellent in press formability and hem workability to automobile panels, etc., and BH properties are excellent, such as 2 or more on the basis.

In order to satisfy such a requirement, the composition of the aluminum alloy sheet as a premise is Mg: 0.2-2.0%, Si: 0.3-2.0%, and Sn: 0.0. 005 to 0.3% is included, and the balance is made of Al and inevitable impurities. In addition,% display of content of each element means the mass% altogether. Moreover, in this specification, the percentage (mass%) based on mass is the same as the percentage (wt%) based on weight. In addition, the content of each chemical component may be expressed as “X% or less (excluding 0%)” as “over 0% and X% or less”.

The 6000 series aluminum alloy plate targeted by the present invention is an excess Si type 6000 series aluminum alloy plate having a better BH property and a Si / Mg mass ratio of Si / Mg of 1 or more. Is preferred. The 6000 series aluminum alloy sheet secures formability by reducing the yield strength during press molding and bending, and is age-hardened by heating during relatively low temperature artificial aging treatment such as paint baking treatment of the panel after molding. Yield strength is improved, and it has excellent age-hardening ability (BH property) that can secure the required strength. Among these, the excess Si type 6000 series aluminum alloy plate is more excellent in this BH property than the 6000 series aluminum alloy plate having a mass ratio Si / Mg of less than 1.

In the present invention, these other elements other than Mg and Si are impurities or elements that may be contained, and the content (allowable amount) at each element level in accordance with AA or JIS standards.

That is, from the viewpoint of resource recycling, in the present invention, not only high-purity Al ingots but also 6000 series alloys containing many other elements other than Mg and Si as additive elements (alloy elements) are used as melting raw materials for alloys. When a large amount of aluminum alloy scrap material, low-purity Al metal, etc. is used, the following other elements are necessarily mixed in substantial amounts. And refining itself that dares to reduce these elements increases the cost, and it is necessary to allow a certain amount of inclusion. Moreover, even if these elements are contained in substantial amounts, there is a useful content range that does not impair the object and effects of the present invention.

Therefore, in the present invention, the following elements are allowed to be contained in the range below the upper limit amount in accordance with the AA to JIS standards specified below.

Specifically, Mn: 1.0% or less (excluding 0%), Cu: 1.0% or less (excluding 0%), Fe: 1.0% or less (excluding 0%) %), Cr: 0.3% or less (excluding 0%), Zr: 0.3% or less (excluding 0%), V: 0.3% or less (provided that 0%), Ti: 0.05% or less (excluding 0%), Zn: 1.0% or less (excluding 0%), and Ag: 0.2% or less (provided that In addition to the basic composition described above, it may further include one or more selected from the group consisting of:

In addition, when these elements are contained, since Cu tends to deteriorate the corrosion resistance when the content is large, the Cu content is preferably 0.7% or less, more preferably 0.3% or less. Further, when Mn, Fe, Cr, Zr, and V are contained in a large amount, a relatively coarse compound is likely to be generated, and the hem workability (hem bendability) that is a subject of the present invention is likely to be deteriorated. Therefore, the Mn content is preferably 0.6% or less, more preferably 0.3% or less, and the Cr, Zr, and V contents are each preferably 0.2% or less, more preferably 0.1%. % Or less.

The content range and significance of each element in the 6000 series aluminum alloy, or the allowable amount will be described in order below.

Si: 0.3-2.0%
Si is a major element, and forms Mg-Si-based precipitates that contribute to strength improvement during solid solution strengthening and artificial aging treatment such as paint baking treatment, and exhibits age-hardening ability, which is necessary for automobile outer panels It is an indispensable element for obtaining a sufficient strength (yield strength). In addition, in order to exhibit the excellent age-hardening ability in the paint baking process after forming on the panel, Si / Mg is set to 1.0 or more in mass ratio, and Si is further Mg than the excessive Si type generally called. It is preferable to make the composition of 6000 series aluminum alloy excessively contained. If the Si content is too small, the amount of Mg—Si based precipitates is insufficient, and the BH property is significantly reduced. On the other hand, when there is too much Si content, a coarse crystallized substance and a precipitate will be formed and bending workability will fall remarkably. Therefore, Si is set in the range of 0.3 to 2.0%. A more preferred lower limit is 0.6%, and a more preferred upper limit is 1.4%.

Mg: 0.2-2.0%
Mg is also a major element, forming solid solution strengthening and forming an Mg-Si-based precipitate that contributes to strength improvement during artificial aging treatment such as paint baking treatment, and exhibits age-hardening ability and the required proof strength as a panel It is an essential element for obtaining. If the Mg content is too small, the amount of Mg—Si-based precipitates is insufficient, and the BH property is significantly reduced. For this reason, the proof stress required as a panel cannot be obtained. On the other hand, when there is too much Mg content, a coarse crystallized substance and a precipitate will be formed and bending workability will fall remarkably. Therefore, the Mg content is in the range of 0.2 to 2.0%. A more preferred lower limit is 0.3%, and a more preferred upper limit is 1.0%.

Sn: 0.005 to 0.3%
Sn is an essential element. By capturing atomic vacancies at room temperature, the diffusion of Mg and Si at room temperature is suppressed, and the increase in strength at room temperature (room temperature aging) is suppressed over a long period of time. There is an effect of improving press formability, particularly hemmability, at the time of press-molding a subsequent plate to a panel. And on the other hand, the trapped pores are released during the artificial aging treatment such as the paint baking treatment of the molded panel. On the contrary, the diffusion of Mg and Si can be promoted and the BH property can be increased. .

If the Sn content is too small, the increase in strength at room temperature cannot be suppressed, the yield strength becomes high, the hemmability deteriorates, and the amount of Mg-Si precipitates produced during BH treatment also decreases. Therefore, the BH property tends to be low. Therefore, the Sn content is in the range of 0.005 to 0.3%. A more preferred lower limit is 0.01%, and a more preferred upper limit is 0.2%.

However, these effects of Sn are exhibited only after Sn is dissolved. Therefore, in the present invention, as will be described later, among the compounds having a specific range of sizes, the ratio of the number of compounds containing a certain amount or more of Sn is specified to ensure the necessary solid solution amount of Sn.

Therefore, the Sn—Al—Mg—Si based aluminum alloy sheet of the present invention is an Al—Mg—Si based aluminum alloy sheet that does not contain Sn in terms of its solid solution in terms of structure and characteristics. It is very different compared to Similarly, even in the case of Al—Mg—Si-based aluminum alloy plates containing Sn (the same amount), if the production conditions such as intermediate annealing are different, the solid solution amount of Sn is different, Under manufacturing conditions (ordinary method), Sn is likely to precipitate as a compound, and the amount of solid solution is remarkably reduced (decreased). For this reason, even if it contains Sn (the same amount) in the same manner, it is possible to obtain a structure having an effect of suppressing room temperature aging at a high level as in the present invention and improving BH properties and hemmability. Not necessarily.

(Organization)
The structure of the 6000 series aluminum alloy plate of the present invention will be described below.

Average number density of compounds:
First, the average number density of a compound having a circle equivalent diameter in the range of 0.3 to 20 μm when measured using a 500-fold SEM as the structure of the plate is 5000 pieces / mm ² or less (including 0 pieces / mm ²⁾ . In other words, more than 0 pieces / mm ^{2 and} 5000 pieces / mm ² or less, preferably 4500 pieces / mm ² or less (excluding 0 pieces / mm ² ), more preferably 4000 pieces / mm ² or less (0 pieces / mm). ² is not included).

When the number density of the compound having an equivalent circle diameter of 0.3 μm or more is reduced to 5000 / mm ² or less, the starting point of breakage in the structure of the plate at the time of molding is reduced, and hem workability is improved. Furthermore, since the amount of solid solution Mg and the amount of solid solution Si are increased and the amount of Mg—Si based precipitates generated during the BH treatment and contributing to the increase in strength is increased, the BH property is also improved. On the other hand, if the number density of the compound having an equivalent circle diameter of 0.3 μm or more exceeds 5000 / mm ² , the starting point of breakage in the structure of the plate at the time of molding increases, and hemming workability, drawing and tensioning are increased. The press formability such as protrusion decreases. Furthermore, the amount of solid solution Mg and the amount of solid solution Si decrease, and the amount of Mg—Si-based precipitates that are generated during the BH treatment and contribute to increasing the strength is insufficient, and the BH property is also lowered.

Whether or not it can be the starting point of breakage during hemming depends on the size (size) of the compound, and the larger the equivalent circle diameter is, the more likely it is to be the starting point of breakage and not depending on the composition. . However, a coarse compound having a circle-equivalent diameter exceeding 20 μm, which is the upper limit to be defined, remarkably hinders the basic mechanical properties and quality of the plate. For this reason, in the manufacturing method and quality control of a normal board, it manufactures so that such a coarse compound may not exist as much as possible, and it is meaningless as a measurement range by SEM. Therefore, the equivalent circle diameter of the compound defined in the present invention is in the range of 0.3 to 20 μm, and the composition of the compound is not limited. Incidentally, the equivalent circle diameter of the compound defined in the present invention is the diameter of a circle having the same area as the compound that is indefinite, and as a method for measuring or defining the size of the compound accurately and with good reproducibility, It has been widely used.

The average number density of compounds having an equivalent circle diameter in the range of 0.3 to 20 μm is preferably as small as possible from the viewpoint of reducing the starting point of fracture during heme processing and securing the solid solution amount of Sn. From the production limit of the efficient production method of the plate, it cannot be completely 0 pieces / mm ² . Therefore, the lower limit in the present invention of the average number density of compounds having an equivalent circle diameter in the range of 0.3 to 20 μm does not include 0 pieces / mm ^2. The lower limit is about 100 pieces / mm ² .

The compounds observed in the plate structure by SEM of 500 times are observed as white particles scattered in the structure when observed in a black and white image. It is a variety of compounds (precipitates, crystallization products) containing Sn such as Mn, Al—Fe—Mn—Si, Al—Si—Sn, and the like. In addition, Mg—Si compounds may also be found in small numbers as black particles scattered in the structure. As described above, the composition of the compound varies widely depending on the composition of the aluminum alloy plate, and it is difficult to limit the composition to a specific composition.

Standard of Sn solid solution amount:
The present invention is characterized by securing the solid solution amount of Sn necessary for exhibiting the effect of Sn. As a guideline (standard) for securing the solid solution amount of Sn, 0.5 mass, which is identified by an X-ray spectrometer among compounds having a circle equivalent diameter measured by the SEM in the range of 0.3 to 20 μm. % Or more of the compounds containing Sn in an amount of less than 50% (including 0%), that is, not less than 0% but less than 50%, preferably less than 40% (including 0%), more preferably less than 30% (0 % Included). In addition, a compound having a Sn content of less than 0.5% is not a measurement target of a compound containing Sn as a measure of the Sn solid solution amount. By the way, when a compound containing Sn with a very small amount of Sn having a Sn content of less than 0.5% by mass is also measured, a compound containing Sn smaller than the measurement error of the X-ray spectrometer is detected, and the size described above. There is a possibility that all the compounds in the range will be measured. In this case, it cannot be said that the solid solution amount of Sn is accurately reflected. Therefore, from the viewpoint of correlation and reproducibility, a lower limit value of 0.5% by mass or more is provided for the Sn content of the compound.

The ratio of the number of compounds containing 0.5 mass% or more of Sn (average number) out of the total number of compounds measured by SEM having an equivalent circle diameter of 0.3 to 20 μm is less than 50%. Indicates that the amount of Sn that precipitates is small and the solid solution amount of Sn is sufficient to exhibit the effect of the added Sn. On the other hand, when the ratio of the number of compounds containing 0.5 mass% or more of Sn (average number) is 50% or more, the amount of precipitated Sn increases, and the solid solution amount of Sn contributes to the effect of the added Sn. The amount is so small that it does not show.

In the present invention, indirect measurement of the amount of Sn solid solution, that is, the ratio of the number of compounds containing Sn in a specific amount or more in a compound of a specific size, allows easy evaluation of the solid solution amount of Sn with good reproducibility. is there.

Further, the evaluation of the Sn solid solution amount by the number ratio of the Sn-containing compound is an indirect measurement method, but includes 0.5 mass% or more of Sn having an equivalent circle diameter in the range of 0.3 to 20 μm. If the compound is the object of measurement, it correlates well with the effect exhibited by solid solution Sn. That is, the effect exhibited by solid solution Sn correlates well with the ratio of the number of compounds containing Sn (average number), which is identified by the X-ray spectrometer whether or not Sn is contained by 0.5 mass% or more. To do. This point is supported by the examples described later.

As stated above, the ratio of the average number of compounds containing Sn of 0.5% by mass or more is less than 50%, and only after securing the solid solution amount of Sn, the capture of atomic vacancies at room temperature is not possible. The effect of suppressing the diffusion of Mg and Si and the increase in strength at room temperature (room temperature aging) are exhibited over a long period of time. As a result, the press formability, particularly the hem workability, is improved at the time of press forming the panel after aging at room temperature onto the panel. In addition, during the artificial aging treatment such as paint baking treatment of the molded panel, the effect of releasing the trapped holes is also exhibited, and the diffusion of Mg and Si can be promoted to increase the BH property. .

The lower limit of the ratio (average number) of compounds containing 0.5 mass% or more of Sn is theoretically 0% when the number of compounds containing Sn is 0 when all Sn is dissolved. This is the case. However, as in the plate manufacturing method described later, Sn is likely to precipitate in the conventional method, and it is difficult to re-dissolve Sn once precipitated. Therefore, if the production efficiency is ignored, the number ratio of compounds containing Sn can be reduced to 0%, but the number of compounds containing Sn (average number) coming from an efficient (industrial) production limit. The lower limit of the ratio is about 0.1%.

Compound measurement:
Measurement by SEM, which is 500 times the number density of the compound having an equivalent circle diameter of 0.3 to 20 μm, is performed at 10 points at an arbitrary point of 1/4 part in the plate thickness direction from the surface of the test plate (samples Ten samples are collected), and the number density of each sample is averaged to obtain an average number density (pieces / mm ² ). The measurement of the number ratio of the compound containing 0.5 mass% or more of Sn, which will be described later, is also performed along with this SEM, and similarly, the average number ratio (%) is obtained by averaging the number ratio of each sample. . Specifically, with respect to a cross section perpendicular to the plate thickness direction of the test plate immediately after the tempering treatment, an SEM of 500 times the surface parallel to the plate surface passes through an arbitrary point from the surface in a 1/4 part of the plate thickness direction. Measure using (Scanning Electron Microscope). A sample is prepared by mechanically polishing a plate cross-section sample surface sampled 10 pieces from the above-mentioned site, cutting off about 0.25 mm from the plate surface by mechanical polishing, and further performing buffing to adjust the surface. Next, using the backscattered electron image, the number of compounds in the equivalent circle diameter range is measured by an automatic analyzer to calculate the number density. The measurement site is the sample polishing surface, and the measurement area per sample is 240 μm × 180 μm.

Further, an X-ray spectrometer used for measuring the number ratio of compounds containing Sn is well known as an analyzer using energy dispersive X-ray spectroscopy (Energy Dispersive X-ray Spectroscopy), and is usually called EDX. This X-ray spectrometer is generally attached to the SEM used in the present invention and is widely used for quantitative analysis of the composition of the observed compound. Using this X-ray spectrometer, the number of compounds identified as containing Sn out of the total number of compounds having an equivalent circle diameter of 0.3 to 20 μm measured by the SEM was measured. The sample measurement results are averaged and calculated as an average number ratio.

(Production method)
Next, a method for producing the aluminum alloy plate of the present invention will be described below.
The aluminum alloy sheet of the present invention is a conventional process or a known process, and the aluminum alloy ingot having the above-mentioned 6000 series component composition is subjected to homogenization heat treatment after casting, and then subjected to hot rolling and cold rolling to obtain a predetermined process. It is manufactured by being subjected to a tempering treatment such as solution hardening and quenching.

However, in these manufacturing processes, in order to make Sn a solid solution and to make the ratio of the number of compounds containing Sn to be defined (average number), as described later, in addition to controlling the average cooling rate during casting, It is set as the preferable conditions which prescribe | regulate the intermediate annealing in the middle of cold rolling. Unless such intermediate annealing conditions are used, it is difficult to make Sn a solid solution and to obtain the ratio of the number of compounds containing Sn (average number).

(Dissolution, casting cooling rate)
First, in the melting and casting process, an ordinary molten casting method such as a continuous casting method and a semi-continuous casting method (DC casting method) is appropriately selected for the molten aluminum alloy adjusted to be dissolved within the above-mentioned 6000 series component composition range. Cast. Here, in order to obtain the number density of compounds having an equivalent circle diameter of 0.3 μm or more as defined in the present invention and the ratio of the number of compounds containing Sn (average number), the average cooling rate during casting is as follows: It is preferable that the liquidus temperature to the solidus temperature be as large (fast) as possible at 30 ° C./min or more.

If such temperature (cooling rate) control in the high temperature region during casting is not performed, the cooling rate in this high temperature region is inevitably slow. In this way, when the average cooling rate in the high temperature region becomes slow, the amount of crystallized material generated coarsely in the temperature range in this high temperature region increases, and in the plate width direction and thickness direction of the ingot. Variations in the size and amount of crystallized material also increase. As a result, there is a high possibility that the number density of compounds having an equivalent circle diameter of 0.3 μm or more and the ratio of the number of compounds containing Sn (average number) cannot be controlled within the specified range of the present invention.

(Homogenization heat treatment)
Next, the cast aluminum alloy ingot is subjected to a homogenization heat treatment prior to hot rolling. The purpose of this homogenization heat treatment (soaking) is to homogenize the structure, that is, eliminate segregation in crystal grains in the ingot structure. The conditions are not particularly limited as long as the object is achieved, and normal one-stage or one-stage processing may be performed.

The homogenization heat treatment temperature is appropriately selected from the range of 500 ° C. or more and less than the melting point, and the homogenization time is 4 hours or more. When this homogenization temperature is low, segregation within the crystal grains cannot be sufficiently eliminated, and this acts as a starting point of fracture, so that stretch flangeability and bending workability are deteriorated. Thereafter, the hot rolling may be started immediately, or the hot rolling may be started after cooling to an appropriate temperature.

After performing this homogenization heat treatment, it is cooled to room temperature at an average cooling rate of 20 to 100 ° C./h between 300 ° C. and 500 ° C., and then 350 ° C. to 450 ° C. at an average heating rate of 20 to 100 ° C./h. It is possible to reheat up to this temperature and start hot rolling in this temperature range.

When the average cooling rate after the homogenization heat treatment and the subsequent reheating rate are not satisfied, there is a high possibility that a coarse Mg—Si compound will be formed. Basic mechanical properties such as strength and elongation of the 6000 series aluminum alloy plate are lowered.

(Hot rolling)
Hot rolling is composed of an ingot (slab) rough rolling process and a finish rolling process according to the thickness of the rolled sheet. In these rough rolling process and finish rolling process, a reverse or tandem rolling mill is appropriately used.

At this time, under conditions where the hot rolling (rough rolling) start temperature exceeds the solidus temperature, burning occurs, making hot rolling itself difficult. On the other hand, when the hot rolling start temperature is less than 350 ° C., the load during hot rolling becomes too high, and the hot rolling itself becomes difficult. Therefore, the hot rolling start temperature is preferably 350 ° C. to the solidus temperature, more preferably 400 ° C. to the solidus temperature.

(Hot rolled sheet annealing)
Annealing (roughening) before cold rolling of this hot-rolled sheet is not always necessary, but it can be performed to further improve properties such as formability by refining crystal grains and optimizing the texture. good.

(Cold rolling)
In cold rolling, the hot-rolled sheet is rolled to produce a cold-rolled sheet (including a coil) having a desired final thickness. However, in order to further refine the crystal grains, the total cold rolling rate is desirably 60% or more regardless of the number of passes.

(Intermediate annealing)
Before this cold rolling (after hot rolling) or in the middle of cold rolling (between passes), the plate is held at a high temperature of 480 ° C or higher and below the melting point for 0.1 to 10 seconds, and then 3 ° C / second or higher It is preferable to repeat the intermediate annealing forcibly cooling (rapid cooling) to room temperature at an average cooling rate of 2 times or more, so that Sn produced as a compound in the hot rolling step or the like is dissolved. In the usual method, Sn is likely to precipitate, and it is difficult to re-dissolve once precipitated Sn, and the ratio of the average number of compounds containing Sn is less than 50% of the number of compounds of the specific size described above. In order to achieve this, it is necessary to perform such short-time heat treatment at a high temperature a plurality of times. However, as long as it is within this condition range, a plurality of heat treatment conditions may not be the same, but may be changed.

For this intermediate annealing condition, if the temperature of the plate is less than 480 ° C., the amount of Sn solid solution is insufficient even if the intermediate annealing is performed twice or more. This is the same even if the number of intermediate annealings in which the annealing temperature and the rapid cooling conditions are within the range is only one. Further, the holding time may be a short time including momentary such as 0.1 seconds, but if it exceeds 10 seconds, the mechanical properties of the plate are remarkably deteriorated. In addition, if the cooling after annealing is not the forced cooling (rapid cooling) to room temperature by air cooling, mist, water cooling or the like with an average cooling rate of 3 ° C./second or more, that is, the average cooling rate is less than 3 ° C./second. Then, Sn once dissolved is reprecipitated and compounded.

Annealing under such conditions is impossible in a batch furnace, including rapid cooling, and requires a continuous heat treatment furnace that winds the sheet through the furnace while unwinding it. Thus, even when continuous annealing capable of rapid cooling is used, according to the knowledge of the present inventors, the solid solution amount of Sn is inevitably insufficient by only one continuous annealing. For this reason, the intermediate annealing by continuous annealing shall be repeated twice or more. However, the number of repetitions of continuous annealing is preferably about 2 because the efficiency of the manufacturing process is greatly reduced as the number of repetitions increases.

(Solution and quenching)
After cold rolling, a solution hardening treatment is performed. The solution treatment and quenching treatment may be heating and cooling using a normal continuous heat treatment line, and is not particularly limited. However, since it is desirable to obtain a sufficient solid solution amount of each element and that the crystal grains of the plate structure are finer, the solution treatment temperature is 520 ° C. or higher and the melting temperature or lower. It is preferable that the heating be performed for at least 2 seconds, and the conditions are maintained for 0 to 10 seconds.

The average cooling rate from the solution temperature to the quenching stop temperature is preferably 3 ° C./second or more. When the cooling rate is low, Mg—Si compounds and the like are likely to be precipitated during cooling, which tends to be the starting point of cracks during press molding and bending, and these formability is reduced. In order to ensure this cooling rate, the quenching treatment is performed by selecting water cooling means and conditions such as air cooling such as a fan, mist, spray, and immersion, respectively.

(Reheating treatment)
Subsequently, a pre-aging treatment (reheating treatment) is performed after the solution quenching treatment in order to form an aggregate (cluster) of atoms serving as nuclei of the Mg—Si-based compound generated during the BH treatment. The ultimate temperature (substance temperature) of the plate is preferably in the temperature range of 80 to 150 ° C., and the holding time is preferably in the range of 3 to 50 hours. The cooling to room temperature after the reheating treatment may be allowed to cool or may be forcibly quenched using the cooling means at the time of quenching in order to increase production efficiency.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

Embodiments of the present invention will be described. 6000 series aluminum alloy plates having different Sn solid solution amounts defined in the present invention were prepared according to the intermediate annealing conditions, and the number density of the compounds and the Sn solid solution amount based thereon were investigated. And BH property (coating bake hardenability) after holding this board at room temperature for 100 days and hem workability were also evaluated. The results are shown in Table 2.

The specific production conditions for these aluminum alloy plates were as follows. Aluminum alloy ingots having respective compositions shown in Table 1 were commonly melted by DC casting. At this time, in common with each example, the average cooling rate during casting was set to 50 ° C./min from the liquidus temperature to the solidus temperature. In the display of the content of each element in Table 1 showing the composition of the 6000 series aluminum alloy plate of each example, the display in which the numerical value in each element is blank, the content is below the detection limit and includes these elements No 0%.

Subsequently, the ingot was subjected to soaking treatment at 540 ° C. for 4 hours in common with each example, and then hot rough rolling was started. And in each example, it was hot rolled to a thickness of 2.5 mm in the subsequent finish rolling to obtain a hot rolled sheet. As shown in Table 2, the aluminum alloy plate after hot rolling was subjected to rough annealing at 500 ° C. for 1 minute in common with each example, and then during the cold rolling pass (between passes) as shown in Table 2. Intermediate annealing with an annealing furnace was performed under various conditions with different numbers, temperatures, average cooling rates, and the like, and finally a cold-rolled sheet (product sheet) having a thickness of 1.0 mm was obtained.

Furthermore, these cold-rolled sheets were subjected to a solution treatment in a 560 ° C. glass stone furnace in common with each example, held for 10 seconds after reaching the target temperature, and quenched by water cooling. Immediately after this quenching, a preliminary aging treatment was carried out by holding at 100 ° C. for 5 hours (after holding, slow cooling at a cooling rate of 0.6 ° C./hour).

A test plate (blank) was cut out from each plate immediately after the tempering treatment, and the structure (number density of compounds, number ratio of compounds containing Sn) of each test plate was measured. Moreover, the test plate (blank) was cut out from each plate after being left at room temperature for 100 days after the tempering treatment, and the strength (AS proof stress) and BH property of each test plate were examined. These results are shown in Table 2.

(Test plate structure)
As the structure of each test plate immediately after the tempering treatment, the average number density (pieces / mm ² ) of the compound having a circle equivalent diameter in the range of 0.3 to 20 μm was measured with the SEM of 500 times by the measurement method described above. The average number ratio (%) of compounds containing 0.5% or more of Sn identified by the X-ray spectroscopic apparatus among the measured compounds was investigated.

(Tensile test)
In the tensile test, JISZ2201 No. 5 test pieces (25 mm × 50 mmGL × plate thickness) were sampled from each test plate after being left at room temperature for 100 days after the tempering treatment, and a tensile test was performed at room temperature. It was. The tensile direction of the test piece at this time was the 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. The N number for the measurement of mechanical properties was 5, and each was calculated as an average value. The test piece for measuring the yield strength after the BH was subjected to the BH treatment after giving a pre-strain of 2% simulating press forming of the plate to the test piece by the tensile tester.

(BH property)
Each test plate was commonly aged at room temperature for 100 days and then subjected to an artificial age-hardening treatment at 185 ° C. for 20 minutes (after BH). Yield strength) was determined by the tensile test. And the BH property of each test plate was evaluated from the difference between these 0.2% proof stresses (increased proof stress), and the case where the increased amount of 0.2% proof stress was 100 MPa or more was regarded as acceptable.

(Heme workability)
Hem workability was measured for each test plate after standing at room temperature for 100 days. In the test, a strip-shaped test piece with a width of 30 mm was used, and after bending 90 ° with an internal bend R of 1.0 mm by a down flange, a 1.0 mm thick inner was sandwiched, and the bent portion was further bent inwardly to about 130 degrees. Pre-hem processing was performed, and flat hem processing was performed in which the end was closely attached to the inner by bending 180 degrees.

The flat hem bend (edge bend) is visually observed for surface conditions such as rough skin, minute cracks, and large cracks, and visually evaluated according to the following criteria. .
0: No cracking, rough skin, 1: Mild rough skin, 2; Deep rough skin, 3: Small surface crack, 4; Continuous surface crack, 5: Break

Each of the inventive examples shown in the numbers 1 to 4 and 12 to 23 in Table 2 is within the composition range of the present invention (alloy numbers 1 to 13 in Table 1) and within the above-mentioned preferable condition range including the intermediate annealing. Manufacture. For this reason, as shown in Table 2, each of these inventive examples satisfies the average number density of the compound defined in the present invention and the average number ratio of the compound containing 0.5 mass% or more of Sn, and precipitates Sn contained. Is suppressed, and the solid solution amount of Sn is high.

As a result, as shown in Table 2, each of the above-mentioned invention examples has a BH (baked hard) even after the long-term room temperature aging for 100 days after the tempering treatment, or even when the As proof strength is 90 to 110 MPa. ) The yield strength is 190 MPa and the difference in yield strength is 100 MPa or more. Further, even after long-term aging after the tempering treatment, the As yield strength is relatively low, so that it is excellent in press formability to automobile panels and the like, and is excellent in hem workability.

Further, as can be seen from Table 2, even when alloy number 1 in Table 1 is used, the average number density of compounds and the solid solution state of Sn (average number ratio of compounds containing Sn) are large due to the difference in intermediate annealing conditions. The characteristics are very different. That is, among Invention Examples 1 to 4, the intermediate annealing temperature is relatively low and the average cooling rate is relatively small, compared to Invention Examples 1 and 2, the intermediate annealing temperature is relatively high and the average cooling rate is also relatively large. In Invention Examples 3 and 4, while the average number density of the compounds is small, the average number ratio of the compounds containing Sn is low, the precipitation of the contained Sn is suppressed, and the solid solution amount of Sn is high. As a result, compared to Invention Examples 1 and 2, Invention Examples 3 and 4 have a higher yield strength difference after BH and a higher BH property even after 100 days after room temperature aging. Better.

On the other hand, Comparative Examples 5 to 11 in Table 2 using the same alloy number 1 in Table 1 as those of the invention examples are examples in which the intermediate annealing conditions deviate from the preferred range. For this reason, these comparative examples have too many compounds prescribed | regulated by this invention, and the average number density remove | deviates beyond an upper limit. Moreover, even if the average number density of the compound is within the specified range of the present invention, the average number ratio of the compound containing 0.5 mass% or more of Sn is higher than 50%, and precipitation of contained Sn is suppressed. It is not made, and the solid solution amount of Sn is low. For this reason, compared with the said invention example which is the same alloy composition, it is inferior to the press moldability and hem workability to a motor vehicle panel etc., and a yield strength difference is less than 100 Mpa, and BH property is also inferior.

Comparative Example 5 is not subjected to intermediate annealing.
Although the comparative example 6 satisfy | fills the conditions of temperature, holding time, and average cooling rate, it is an intermediate annealing only once.
In Comparative Example 7, the second intermediate annealing satisfies the conditions of temperature, holding time, and average cooling rate, but the temperature of the first intermediate annealing is too low at 480 ° C.
In Comparative Example 8, the first intermediate annealing satisfies the conditions of temperature, holding time, and average cooling rate, but the temperature of the second intermediate annealing is too low at 480 ° C.
In Comparative Example 9, the temperatures of the first and second intermediate annealings are both less than 480 ° C. and too low.
In Comparative Examples 10 and 11, the temperature and holding time of the first and second intermediate annealing satisfy the conditions, but the average cooling rate of the first or second time is too slow.

Further, although Comparative Examples 24 to 29 in Table 2 are manufactured within a preferable range including intermediate annealing conditions, Alloy Nos. 14 to 19 in Table 1 are used, and inclusion of essential elements Mg, Si, and Sn Each amount is outside the scope of the present invention. For this reason, as shown in Table 2, these Comparative Examples 24 to 29 have a relatively high As yield strength after holding at room temperature for 100 days, as compared with each invention example. It is inferior in workability or BH property. In Comparative Example 27, Sn was too much, and cracking occurred during hot rolling, so that the hot rolled sheet itself could not be manufactured.

The comparative example 24 is the alloy 14 of Table 1, and there is too little Si.
The comparative example 25 is the alloy 15 of Table 1, and there is too much Si.
The comparative example 26 is the alloy 16 of Table 1, and there is too little Sn The comparative example 27 is the alloy 17 of Table 1, and there is too much Sn.
The comparative example 28 is the alloy 18 of Table 1, and there is too little Mg.
The comparative example 29 is the alloy 19 of Table 1, and there is too much Mg.

From the results of the above examples, the composition and compound structure defined in the present invention and intermediate annealing conditions for the improvement of heme workability and BH property after long-term aging of a 6000 series aluminum alloy plate containing Sn The critical significance or effect of preferable manufacturing conditions such as the above is supported.

Although the invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on August 27, 2014 (Japanese Patent Application No. 2014-173278), which is incorporated by reference in its entirety.

According to the present invention, it is possible to provide a 6000 series aluminum alloy plate having both BH properties and formability after long-term room temperature aging. As a result, the application of the 6000 series aluminum alloy plate can be expanded as a member for a transport device such as an automobile, a ship or a vehicle, a home appliance, a building or a structure, and particularly as a member for a transport device such as an automobile.

Claims

In mass%, Mg: 0.2 to 2.0%, Si: 0.3 to 2.0% and Sn: 0.005 to 0.3%, respectively, with the balance being Al and inevitable impurities Al -Mg-Si based aluminum alloy plate, wherein the average number density of the compound having an equivalent circle diameter in the range of 0.3 to 20 μm when measured using an SEM of 500 times is 0 as the structure of the aluminum alloy plate pieces / mm 2 ultra-5000 / mm 2 or less, of the compound measured by the SEM, is identified by the X-ray spectrometer, the average number ratio of the compound containing 0.5% by mass or more of Sn An aluminum alloy sheet for forming, characterized by being from 0% to less than 50%.
Further, by mass%, Mn: more than 0% and 1.0% or less, Cu: more than 0% and 1.0% or less, Fe: more than 0% and 1.0% or less, Cr: more than 0% and 0.3% or less, Zr: more than 0% and 0.3% or less, V: more than 0% and 0.3% or less, Ti: more than 0% and 0.05% or less, Zn: more than 0% and 1.0% or less, and Ag: more than 0% and 0% The aluminum alloy sheet for forming according to claim 1, comprising one or more selected from the group consisting of 2% or less.