JP5918209B2 - Aluminum alloy sheet for forming - Google Patents

Description

  The present invention relates to an Al—Mg—Si 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 and the like, 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. Al-Mg-Si-based AA to JIS 6000-series (hereinafter also simply referred to as 6000-series) aluminum alloy plates have been 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 bake coating curability (hereinafter also referred to as bake hard property = BH property, bake curability) that can secure the required strength as a panel.

  Further, 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 these aluminum alloy sheet scraps 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 an extension forming in a press forming or a bending forming. For example, a large outer panel such as a hood or door is formed into a molded product shape as an outer panel by press molding such as overhanging, and then the inner panel and 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 application, it is usually about 1 to 4 months after being solution-quenched by an aluminum maker (after manufacture) and before being molded into a panel by an automobile 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.

  Furthermore, when such room temperature aging is large, the BH property decreases, and depending on the heating during 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.

  In addition, 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 sheet to suppress room temperature aging and improve bake 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.

JP 09-249950 A JP-A-10-226894 JP 2000-144294 A JP 2003-221737 A JP 2003-268472 A

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

  In view of such problems, the object of the present invention is to form Sn-containing Al-Mg that can exhibit high BH properties and good workability even in the case of car body paint baking 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 sheet of the present invention is, in mass%, Mg: 0.3-1.3%, Si: 0.5-1.5%, Sn: 0.5. An Al—Mg—Si aluminum alloy plate containing 005 to 0.2% each, the balance being Al and unavoidable impurities, separated from the Sn content of this plate by a residue extraction method using hot phenol The amount of Sn obtained by subtracting the Sn content contained in the residual compound having a particle size exceeding 0.1 μm is 0.005% by mass or more.

  Sn, in the structure of Al-Mg-Si based aluminum alloy sheet, captures atomic vacancies at room temperature (capture, trap), 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.

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

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

(Chemical composition)
First, the chemical component 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.

  In order to satisfy such requirements, the composition of the aluminum alloy plate is, by mass, Mg: 0.3 to 1.3%, Si: 0.5 to 1.5%, Sn: 0.005 to 0. 2% each, and the balance consisting of Al and inevitable impurities. In addition,% display of content of each element means the mass% altogether.

  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 is in accordance with AA to 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.

  Accordingly, in the present invention, the following elements are allowed to be contained in the range of the upper limit amount or less in accordance with AA to JIS standards defined 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% not included), Ti: 0.05% or less (excluding 0%), Zn: 1.0% or less (excluding 0%), Ag: 0.2% or less (excluding In addition to the basic composition described above, one or more of the above may be further contained within this range.

  In addition, when these elements are contained, since Cu tends to deteriorate 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, V content is preferably 0.2% or less, more preferably 0.1% or less. And each.

  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: 0.5 to 1.5%
Si is a major element that forms Mg-Si precipitates that contribute to strength improvement during solid solution strengthening and artificial aging treatments such as paint baking treatment, and exhibits age-hardening ability and is required as an outer panel for automobiles It is an indispensable element for obtaining a sufficient strength (yield strength). In addition, in order to exhibit excellent age-hardening ability in the paint baking process after forming on the panel, Si / Mg is set to a mass ratio of 1.0 or more, and Si is further added to Mg rather than the excessive Si type generally referred to. 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 made 0.5 to 1.5% in range. A more preferred lower limit is 0.6%, and a more preferred upper limit is 1.4%.

Mg: 0.3 to 1.3%
Mg is also a major element, forming solid solution strengthening and Mg-Si-based precipitates that contribute to strength improvement during artificial aging treatment such as paint baking treatment, exhibiting age-hardening ability, and necessary 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, so that the BH property is significantly lowered. 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 0.3 to 1.3%. A more preferred lower limit is 0.4%, and a more preferred upper limit is 1.2%.

Sn: 0.005-0.2%
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-based precipitates generated 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 0.2%. A more preferred lower limit is 0.01%, and a more preferred upper limit is 0.18%.

  However, these effects of Sn are exhibited only when Sn is dissolved. Therefore, in the present invention, as will be described later, the necessary solid solution amount of Sn measured by the residue extraction method is ensured.

  Therefore, the Al—Mg—Si based aluminum alloy sheet containing Sn of the present invention is an Al—Mg—Si based aluminum alloy sheet that does not contain Sn in terms of structure and characteristics in terms of solid solution of Sn. It is very different compared to Similarly, even if it is an Al—Mg—Si-based aluminum alloy plate containing Sn (the same amount), if the production conditions such as intermediate annealing are different, the solid solution amount of Sn is different, and the production of a normal plate Under conditions (ordinary method), Sn is likely to precipitate as a compound, and the amount of solid solution is remarkably low (small). For this reason, even if it contains Sn in the same manner (the same amount), 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. Is not limited.

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

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 described above. As a guideline (standard) for securing the solid solution amount of Sn, the Sn content contained in the residual compound having a particle size of more than 0.1 μm separated by the residue extraction method using hot phenol is subtracted from the Sn content of the plate. The amount of Sn is 0.005 mass% or more. The insoluble residue compound having a particle size of more than 0.1 μm separated by the residue extraction method using hot phenol is a precipitate, and the Sn content contained in this is the Sn contained in the alloy composition of the plate The solid Sn content is excluded, and the amount of Sn deposited as a precipitate is shown. Therefore, the amount of Sn obtained by subtracting the Sn content contained in the residual compound having a particle size of more than 0.1 μm separated by the residue extraction method using hot phenol from the Sn content as the alloy composition of this plate is In the invention, it means the solid solution amount of Sn.

  If the amount of the subtracted Sn is 0.005% by mass or more, the amount of precipitated Sn is small, and the solid solution amount of Sn is an amount sufficient to exhibit the effect of the added Sn. On the other hand, when the amount of Sn subtracted is less than 0.005% by mass, the solid solution amount of Sn is a small amount that does not exhibit the effect of the added Sn.

  In addition, the upper limit of the subtracted amount of Sn (the solid solution amount of Sn) is the Sn content (amount of Sn deposited) contained in the residue compound having a particle size of more than 0.1 μm separated by the residue extraction method. This is a case of 0. That is, this is the case where the Sn contained in the plate is in solid solution in the matrix, and the case where the Sn content of the plate is the same as the subtracted amount of Sn. However, when Sn is added or contained in a certain amount or more, Sn is likely to precipitate in the usual method, and it is difficult to dissolve all Sn from the efficient (industrial) production limit. Therefore, the actual upper limit of the subtracted Sn amount (Sn solid solution amount) is smaller than the Sn content as the alloy composition of the plate. It becomes about 15 mass%.

  In the present invention, the amount of Sn deposited as a residue compound (precipitate) with a particle size exceeding 0.1 μm can be accurately measured with good reproducibility using the method of residue extraction method described later, and at the same time, as the alloy composition It was found that the solid solution amount of Sn can be measured alternatively (indirectly) by subtracting the precipitated Sn amount from the Sn content. It was also found that the evaluation of the Sn solid solution amount using the residue amount by this residue extraction method correlates well with the effect exhibited by actual Sn (solid solution Sn).

  In a commonly used residue extraction method, the filter is usually separated and classified by setting the filter mesh for separating and separating solid liquid to 0.1 μm, and setting the boundary of the size of particles (solid) separated from the liquid to 0.1 μm. Then, residual compounds exceeding 0.1 μm are regarded (handled) as precipitates, while those having a size of 0.1 μm or less are regarded (handled) as a solution (solid solution state) in which the alloy elements are dissolved. Here, as the residue compound to be separated becomes finer than 0.1 μm or less, it approaches a nano-level solid solution state, and it is difficult to determine whether it is a solid solution or a precipitate. There is no correlation with the effect. The same applies to the case where the element content on the filtrate side is measured and used as the solid solution amount of the element. Therefore, in the widely used residue extraction method, the content of the element as the alloy composition is obtained by subtracting the content of the element contained in the residual compound whose separated particle size exceeds 0.1 μm. This is often regarded as the solid solution amount of the element.

  Accordingly, in the present invention, this is followed, and the particle size is separated and classified by 0.1 μm, and those exceeding 0.1 μm are regarded as residual compounds (to be precise) as Sn precipitates. A value obtained by subtracting the amount of precipitated Sn (presumed to be precipitated) from the Sn content as a composition is defined as a solid solution amount of Sn (to be exact).

  As stated above, it is not until the solid solution amount of Sn is secured that the diffusion of Mg and Si at room temperature and the increase in strength at room temperature (room temperature aging) are captured over a long period of time by trapping atomic vacancies at room temperature. The suppression effect is exhibited. 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. .

Extraction residue method:
The extraction residue method for measuring the solid solution amount of Sn is performed as follows. First, after putting phenol into a decomposition flask and heating, each sample plate sample to be measured is transferred to this decomposition flask and thermally decomposed. Next, after adding benzyl alcohol, suction filtration was performed to collect undissolved residue on the filter. The collected residue is washed with benzyl alcohol and methanol, and the Sn content is quantitatively analyzed. For this quantitative analysis, atomic absorption spectrometry (AAS), inductively coupled plasma optical emission spectrometry (ICP-OES), or the like is appropriately used. As described above, a membrane filter having a mesh (collected particle diameter) of 0.1 μm and a diameter of 47 mm is used for the suction filtration. Then, the Sn content contained in the residual compound having a particle size exceeding 0.1 μm is subtracted from the Sn content as the alloy composition, and calculated as the solid solution amount (mass%) of Sn. This measurement and calculation are performed at any 10 locations on the test plate (10 samples are collected), and the solid solution amount (mass%) of Sn in each sample is averaged.

(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 order to dissolve Sn in these manufacturing steps, as described later, in addition to the average cooling rate control during casting, a preferable condition for defining intermediate annealing during cold rolling is set. Unless such intermediate annealing conditions are used, it is difficult to make Sn dissolve.

(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 dissolve Sn as defined in the present invention, the average cooling rate during casting is as large as possible (fast) from the liquidus temperature to the solidus temperature of 30 ° C./min or more. It is preferable to do.

  When 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. Thus, 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 Sn cannot be dissolved in the prescribed 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 20-100 ° C / h between 300 ° C and 500 ° C, and then 350 ° C-450 ° C at an average heating rate of 20-100 ° 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 is 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 and thus the hot rolling itself becomes 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 set to 350 ° C. to the solidus temperature, more preferably 400 ° C. to the solidus temperature.

(Hot rolled sheet annealing)
Annealing (roughening) of the hot-rolled sheet before cold rolling 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 ordinary methods, Sn is likely to precipitate, and it is difficult to re-dissolve Sn once precipitated. In order to dissolve Sn as defined in the present invention, a short heat treatment at such a high temperature is required. Must be done multiple 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.

  With regard to the intermediate annealing conditions, if the plate temperature is lower than 480 ° C., even if the intermediate annealing is performed twice or more, the Sn solid solution amount is insufficient. 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 an instantaneous time such as 0.1 second, 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 passes the sheet through the furnace and winds it up. 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 by 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. The heating is performed for at least 2 seconds, and the condition is maintained for 0 to 10 seconds. And the average cooling rate from solution temperature to quenching stop temperature shall be 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 moldability 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.

  Incidentally, the solution annealing treatment and the roughing conditions after the hot rolling are also similar in temperature and the like to the intermediate annealing conditions, but the intermediate annealing does not exist or is performed at a temperature of 520 ° C. or higher. If the various conditions such as the above are not satisfied, Sn cannot be dissolved in the required amount or the specified amount only by performing the solution quenching process or the roughening after the hot rolling.

(Reheating treatment)
Subsequently, a pre-aging treatment (reheating treatment) is performed after the solution hardening treatment in order to form an aggregate (cluster) of atoms serving as nuclei of the Mg—Si compound generated during the BH treatment. The ultimate temperature (substance temperature) of the plate is desirably in the temperature range of 80 to 150 ° C., and the holding time is desirably 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.

  Next, examples of the present invention will be described. 6000 series aluminum alloy plates having different Sn solid solution amounts were prepared according to the intermediate annealing conditions, and the Sn solid solution amount defined in the present invention was 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 addition, 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 of each element is blank is the content below the detection limit. It shows 0% not containing any elements.

  Subsequently, the ingot was subjected to soaking 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.

  Further, these cold-rolled sheets were subjected to 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 (solid solution amount of Sn) of each test plate was measured. Further, a 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 solid solution amount of Sn in each test plate immediately after the tempering treatment, a residue having a particle size of more than 0.1 μm separated from the Sn content of this plate by the residue extraction method using hot phenol by the measurement method described above. The amount (mass%) of Sn after subtracting the Sn content contained in the compound was investigated.

(Tensile test)
In the tensile test, JISZ2201 No. 5 test pieces (25 mm × 50 mmGL × plate thickness) were collected 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. Then, 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 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 surface state of the flat hem bent portion (edge curved portion) such as rough skin, minute cracks, and large cracks was visually observed, visually evaluated according to the following criteria, and criteria 0 to 2 were accepted. .
0: No cracking, rough skin, 1: Mild rough skin, 2; Deep rough skin, 3: Small surface crack, 4; Continuous surface crack, 5: Break

  Each invention example shown in 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 preferable condition range described above including intermediate annealing. Manufacture. For this reason, as shown in Table 2, each of these invention examples is the Sn content obtained by subtracting the Sn content contained in the residue compound separated by the residue extraction method from the Sn content of the plate as defined in the present invention. (Mass%) is satisfied, precipitation of contained Sn 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 is BH (baked hard) even after a long-term room temperature aging for 100 days after the tempering treatment or even when the As proof strength is at a level of 90 to 110 MPa. ) The yield strength is 190 MPa and the yield strength difference 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 the same alloy number 1 in Table 1 is used, the solid solution state of Sn is greatly different and the characteristics are greatly different depending on the difference in intermediate processing conditions. 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. Invention Examples 3 and 4 have a large amount of Sn (% by mass) obtained by subtracting the Sn content contained in the residue compound separated by the residue extraction method from the Sn content of the plate, and suppress the precipitation of the contained Sn. The amount of Sn dissolved 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 5-11 of Table 2 which uses the same alloy number 1 of Table 1 as these invention examples are examples in which intermediate annealing conditions deviate from a preferable range. For this reason, in these comparative examples, the Sn content (% by mass) obtained by subtracting the Sn content contained in the residue compound separated by the residue extraction method from the Sn content of the plate defined in the present invention is too small. Thus, precipitation of contained Sn cannot be suppressed, 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 400 ° C. and less than 480 ° C., which is too low.
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 400 ° C. and less than 480 ° C., which is too low.
In Comparative Example 9, the temperature of the first and second intermediate annealings is 460 ° C., which is 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.

  Moreover, although the comparative examples 24-29 of Table 2 are manufactured in the preferable range including intermediate annealing conditions, they use the alloy numbers 14-19 of Table 1, and contain Mg, Si, Sn of an essential element 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 Sn is too little. The comparative example 27 is the alloy 17 of Table 1, and there is too much Sn.
Comparative example 28 is 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, for the heme workability and BH improvement after long-term aging of the Sn-containing 6000 series aluminum alloy plate, the composition defined in the present invention and the Sn solid solution amount, The critical significance or effect of preferable manufacturing conditions such as intermediate annealing conditions is supported.

  ADVANTAGE OF THE INVENTION According to this invention, the 6000 series aluminum alloy plate which has BH property and formability after long-term room temperature aging can be provided. 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 (2)

  In mass%, Mg: 0.3 to 1.3%, Si: 0.5 to 1.5%, Sn: 0.005 to 0.2%, respectively, with the balance being Al and inevitable impurities Al -Mg-Si-based aluminum alloy plate, which is obtained by subtracting the Sn content contained in the residual compound having a particle size of more than 0.1 μm separated by the residue extraction method using hot phenol from the Sn content of this plate An aluminum alloy sheet for forming, characterized in that the amount of is 0.005 mass% or more.   The aluminum alloy plate further comprises Mn: 1.0% or less (excluding 0%), Cu: 1.0% or less (excluding 0%), Fe: 1.0% or less ( However, 0% is not included), Cr: 0.3% or less (however, 0% is not included), Zr: 0.3% or less (however, 0% is not included), V: 0.3% or less (However, 0% is not included), Ti: 0.05% or less (However, 0% is not included), Zn: 1.0% or less (However, 0% is not included), Ag: 0.2% The forming aluminum alloy sheet according to claim 1, comprising one or more of the following (excluding 0%).