KR20160040653A - Aluminum alloy plate having excellent bake hardening properties - Google Patents

Abstract

It is an object of the present invention to provide a 6000-series aluminum alloy plate having BH properties after aging at a room temperature for a long period of time and molding properties after aging at a long-term room temperature. In one embodiment of the present invention, a specific cluster of a 6000-series aluminum alloy plate containing Sn, which is measured by a three-dimensional atom probe electric field ion microscope and has a large BH effect, is contained at a constant number of densities or more, The average radius of the circle-equivalent diameter is set to a constant range and the standard deviation of the radius of the circle-equivalent diameter is reduced to further improve the BH property after the long-term room temperature aging.

Description

[0001] ALUMINUM ALLOY PLATE HAVING EXCELLENT BAKE HARDENING PROPERTIES [0002]

The present invention relates to an Al-Mg-Si based aluminum alloy plate. 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 shattering treatment and is subjected to artificial age hardening treatment such as baking paint hardening treatment Is an aluminum alloy plate before it is used. In the following description, aluminum is also referred to as aluminum or Al.

In recent years, due to consideration of the global environment, the social demand for lightening of vehicles such as automobiles is increasing. In order to meet such demands, it is desirable to provide a material for a large-sized body panel (outer panel, inner panel) such as a car panel, particularly a hood, a door, The application of lightweight aluminum alloys is increasing.

Among these, a panel such as an outer panel (outer plate) and an inner panel (inner plate) of a panel structure such as a hood of a car, a fender, a door, a roof, a trunk lid and the like includes a thin aluminum- (Hereinafter simply referred to as " 6000 system ") aluminum alloy sheet has been studied.

The 6000-series aluminum alloy plate contains Si and Mg as essential components. In particular, the excess Si-type 6000-series aluminum alloy has a composition of Si / Mg of 1 or more in mass ratio and has excellent age hardenability. As a result, during press forming or bending, the moldability is ensured by lowering the yield stress, and the age hardening is performed by heating during the artificial aging (curing) treatment at a relatively low temperature such as paint baking treatment of the molded panel (Hereinafter, referred to as baking hardness = BH property or baking hardenability) that can secure the required strength as a panel.

In addition, the 6000-series aluminum alloy plate has a relatively small amount of the alloy element, compared with other 5000-series aluminum alloys having a large amount of alloy such as Mg amount. Therefore, when scraps of these 6000-series aluminum alloy plates are reused as an aluminum alloy dissolution material (dissolution raw material), the original 6000-system aluminum alloy ingot is easy to obtain and the recyclability is also excellent.

On the other hand, as is well known, an outer panel of an automobile is manufactured by performing extrusion molding or press forming such as bending molding on the aluminum alloy plate in a press molding. For example, in a large outer panel such as a hood or a door, it is formed in the form of a molded product as an outer panel by press molding such as extrusion. Subsequently, in a hemeing process such as flat hem of the outer panel periphery Thereby joining with the inner panel, thereby forming a panel structure.

Here, the 6000-series aluminum alloy has an advantage of having excellent BH properties, but has an aging property at room temperature and is aged by maintaining the room temperature for several months after the solution treatment, There is a problem that the moldability, particularly the bending workability, is lowered. For example, when a 6000-series aluminum alloy plate is used for an automobile panel, it is usually used for about 1 to 4 months after the aluminum alloy maker is subjected to solution casting treatment (after manufacturing) (Left at room temperature) at room temperature, and during this time, it becomes considerably age-hardening (room temperature aging). Particularly, in the outer panel in which rigid bending is performed, there is a problem that after 1 month from the production, cracks are generated at the time of heme processing after 3 months even if it can be molded without any problem. Therefore, it is necessary to suppress the aging at room temperature over a relatively long period of time of about 1 to 4 months in a 6000-series aluminum alloy plate for automobile panels, particularly for an outer panel.

When the room temperature aging is large, the BH property is lowered. Depending on the heating at the relatively low temperature artificial aging (curing) treatment such as the paint baking treatment of the panel after the molding as described above, There is a problem that the improvement is not achieved.

Conventionally, various proposals have been made for improving the BH property and suppressing the room temperature aging from the viewpoint of the structure of the 6000-series aluminum alloy plate, especially the clusters (aggregates of atoms). However, most of them are merely indirectly predicting the behavior of clusters (aggregates of atoms) that directly affect the BH properties or room temperature aging properties of the 6000-series aluminum alloy plates.

On the other hand, attempts have been made to directly measure clusters (aggregates of atoms) affecting BH properties and room temperature aging properties of 6000 aluminum alloy sheets.

In Patent Document 1, the average number density (number of clusters) of clusters in the range of circle-equivalent diameter of 1 to 5 nm among the clusters (aggregates of atoms) observed when the structure of the 6000-system aluminum alloy plate is analyzed by a transmission electron microscope Is defined in the range of 4000 to 30,000 / 탆 ² , and the BH property is excellent and the room temperature aging is suppressed.

Furthermore, in Patent Documents 2 and 3, it is possible to control a cluster of specific atoms (clusters) directly measured by a three-dimensional atom probe electric field ion microscope to control 6000 (cluster) which can exhibit high BH property even in the case of body- Based aluminum alloy sheet has been proposed. These patent documents disclose that a total of 10 or more or 30 or more of the Mg atoms and / or the Si atoms as a cluster of these atoms are contained in total, and even if any one of the Mg atoms and Si atoms contained in these atoms , And the distance between the reference atom and any other atom adjacent to the other atom is 0.75 nm or less.

Under such premise, in Patent Document 2, it is supposed that the aggregate of atoms satisfying these conditions is included at an average number density of 1.0 × 10 ⁵ / μm ³ or more.

Patent Document 3 discloses that an aggregate of atoms satisfying these conditions is contained at an average number density of 5.0 x 10 < ²³ > / m < 3 > or more and, at the same time, The average number density of the atomic aggregates having a size smaller than 1.5 nm is regulated to not more than 10.0 x 10 ²³ atoms / m 3, and the average number density a of the atomic aggregates having a radius of the circle- And the ratio a / b of the average number density b of the atomic aggregates having a diameter of the circle having the largest diameter of 1.5 nm or more to the maximum is 3.5 or less, the radius of the circle- As shown in FIG.

On the other hand, as a prior art related to the addition of Sn in the present invention, a method of positively adding Sn to a 6000-series aluminum alloy plate to improve the room temperature aging and to improve baking paint hardening is disclosed in Patent Documents 4 and 5 Has been proposed. For example, Patent Document 4 discloses that the compositional relationship between Mg and Si is limited to -2.0 > 4Mg-7Si, an appropriate amount of Sn having an aging change inhibiting effect is added, and preliminary aging is performed after solution treatment, The method combines both inhibition and baking paint curing. Patent Document 5 discloses that the compositional relationship between Mg and Si is limited to -2.0? 4 Mg-7 Si? 1.0, Sn having an aging change suppressing effect and Cu improving moldability are added, and zinc plating is performed A method of improving moldability, baking paintability and corrosion resistance has been proposed.

Japanese Patent Application Laid-Open No. 2009-242904 Japanese Patent Laid-Open Publication No. 193399/1995 Japanese Patent Application Laid-Open No. 2013-60627 Japanese Patent Application Laid-Open No. 09-249950 Japanese Patent Application Laid-Open No. 10-226894

However, the demand for improving the fuel efficiency of the automobile is still high, and the weight reduction of the automobile is promoted. As a result, thinning of the aluminum alloy sheet tends to be required. On the other hand, in the prior art in which the behavior of the aggregates of atoms (clusters) is deduced by indirect measurement, or in the patent literature which is controlling the size and number density of aggregates of relatively large atoms evaluated by TEM observation 1, the aggregate of atoms is not evaluated accurately or in detail. As a result, precise control of the atomic aggregate could not be achieved, and the BH property after room temperature aging was insufficient. Also, Patent Documents 2 and 3, which control a cluster of specific atoms directly measured by a transmission electron microscope of a million-fold magnification or a three-dimensional atom probe electric field ion microscope, show high BH performance after prolonged room temperature aging, There is still room for improvement in combining the workability. This also applies to Patent Documents 4 and 5 in which Sn is positively added to a 6000-series aluminum alloy plate.

In view of the above problems, it is an object of the present invention to provide an Al-Si-Mg system capable of exhibiting high BH performance and good processability even after a long time of room temperature aging, To provide an aluminum alloy plate.

In order to achieve this object, an essential point of an aluminum alloy plate excellent in baking painting curability according to one embodiment of the present invention (hereinafter also referred to as the first embodiment of the present invention) , Si: 0.3 to 2.0%, and Sn: 0.005 to 0.3%, with the balance being Al and an inevitable impurity, and is measured by a three-dimensional atom probe electric field ion microscope And the cluster of the atoms contains at least one of Mg atom and Si atom in a total of 10 or more, and even if any one of the Mg atom and the Si atom contained in these atom atoms is referred to, is the distance of each other and any of the other atoms one atom adjacent to the atom that is not more than 0.75㎚, an aggregate of atoms that meet these conditions 2.5 × 10 ²³ gae / ㎥ or more, 20.0 × 10 ²³ gae / ㎥ below Average number density of And the average radius of the circle equivalent diameter of the atom aggregate satisfying these conditions is 1.15 nm or more and 1.45 nm or less and the standard deviation of the radius of the circle equivalent diameter is 0.45 nm or less.

In order to achieve this object, an essential point of an aluminum alloy plate excellent in baking painting hardenability with respect to another embodiment of the present invention (hereinafter also referred to as a second embodiment of the present invention) is Mg: 0.2 Mg-Si based aluminum alloy plate containing Al in an amount of 0.05 to 2.0%, Si in an amount of 0.3 to 2.0% and Sn in an amount of 0.005 to 0.3%, and the balance being Al and inevitable impurities, The sum of the number of Mg atoms and the number of Si atoms measured by the three-dimensional atom probe ion microscope is N _total , and either one or both of the Mg atom and the Si atom as the aggregate of atoms measured by the three- And the distance between the reference atom and any other atom adjacent to the reference atom is 0.75 nm or less even if any one of these Mg atoms and Si atoms is used as a reference city The ratio (N _cluster / N _total ) × 100 of the N _cluster to the N _total is 1% when the sum of all Mg atoms and Si atoms contained in all of the atomic assemblies is taken as N _cluster , Or more and 15% or less, and the average radius of the circle equivalent diameter of the atom aggregate is 1.20 nm or more and 1.50 nm or less.

In order to achieve this object, an essential point of an aluminum alloy plate excellent in baking painting curability according to another embodiment of the present invention (hereinafter also referred to as a third embodiment of the present invention) is Mg: 0.2 Mg-Si based aluminum alloy plate containing Al in an amount of 0.05 to 2.0%, Si in an amount of 0.3 to 2.0% and Sn in an amount of 0.005 to 0.3%, and the balance being Al and inevitable impurities, , It is preferable that at least 10 or more of the Mg atoms and / or the Si atoms are contained in total, and even if any one of the Mg atoms and Si atoms contained in these atoms is used as a reference, The average number density of the atomic assemblies satisfying the condition that the distance between the atom to be atomized and any one of atoms adjacent to the atom is not more than 0.75 nm is not less than 3.0 x 10 ²³ atoms / m 3 and not more than 25.0 x 10 ²³ atoms / m 3 , And these conditions Of the aggregate of meeting atom, the ratio to be greater than or equal to (Mg / Si) is not less than 1/2 of the average ratio of the atomic aggregate can Mg atoms and the number of Si atoms is 0.70.

In the first embodiment of the present invention, Mg atoms and Si atoms are added to the Al-Mg-Si aluminum alloy plate containing Sn in total (cluster) of atoms measured by 3DAP It was found that the average number density of specific clusters such as those containing a specific abnormality and the distance between adjacent atoms contained in them is not more than a specific value greatly correlates with BH.

However, not only that but also the distribution of the aggregate size of the specific atom satisfying these conditions is important, and the average radius of the circle-equivalent diameter and the standard deviation of the radius of the circle-equivalent diameter greatly affect the BH property. The shape was known.

That is, in order to improve the BH property of the Al-Mg-Si aluminum alloy sheet containing Sn, the average radius of the circle equivalent diameter of the specific atomic aggregate is 1.15 nm or more and 1.45 nm or less, which is a specific range, Of 0.45 nm or less is necessary for improving the BH property. According to the present embodiment, it is possible to provide an Al-Si-Mg aluminum alloy plate capable of exhibiting a higher BH property even when aging is effected at room temperature for a long period of time of 100 days.

Further, in the second embodiment of the present invention, in the Al-Mg-Si aluminum alloy plate containing Sn, the distance between the atoms in the cluster of atoms (clusters) measured by 3DAP is 0.75 nm or less It is premised that a large number of fine clusters are present. The total amount (total amount) of Mg and Si present in these clusters is balanced with the total amount of Mg and Si in the matrix, and the distribution state of the cluster size is also controlled as the average radius of the circle- To increase the BH property.

When the total amount of Mg atoms and Si atoms present in the cluster defined above is balanced with the total amount of Mg and Si dissolved in the matrix, the BH property can be increased. Further, Mg and Si contained in the 6000-series aluminum alloy sheet are contained in coarse clusters as well as coarse precipitates or intermetallic compounds in a form other than the employment of the clusters and the matrix specified in the present embodiment There is a possibility that it exists. On the other hand, if the total amount of Mg and Si in the cluster is controlled in terms of balance with the total amount of Mg and Si dissolved in the matrix, a coarse cluster attributable to Mg and Si or a coarse precipitate or intermetallic Leading to reduction of the compound itself.

The distribution of the cluster size also greatly affects the BH property. For improving the BH property of the Al-Mg-Si aluminum alloy plate containing Sn, the average radius of the circle equivalent diameter of the atomic aggregate is 1.20 nm or more , And 1.50 nm or less. By controlling the total amount of Mg atoms and Si atoms present in the clusters and the distribution of the cluster size, it is possible to obtain Al-Si- A Mg-based aluminum alloy plate can be provided.

In the third embodiment of the present invention, an Al-Mg-Si aluminum alloy plate containing Sn is used in which the distance between atoms of the cluster of atoms (clusters) measured by 3DAP is 0.75 nm or less It is premised that a large number of fine clusters are present. Furthermore, among the elements constituting these fine clusters, the ratio of clusters having a large number of atoms of Mg is increased to increase the BH property.

The inventors of the present invention have found that clusters rich in Si atoms adversely affect BH properties, while clusters rich in Mg accelerate BH properties, even though the same clusters have different influences on BH properties depending on their composition. Therefore, in the present embodiment, it is controlled so that the number of clusters having a small distance between the atoms among the clusters measured by the 3DAP is increased, and control is performed so that the ratio of clusters having a large number of atoms of Mg is increased , And BH.

Thus, in the present embodiment, it is possible to provide an Al-Si-Mg-based aluminum alloy plate capable of exhibiting a higher BH property even at room temperature aging.

Hereinafter, the embodiments of the present invention will be described in detail for each of the requirements.

Cluster (cluster of atoms):

First, what the cluster means in the present invention means. The clusters referred to in the present invention refer to clusters of atoms (clusters) of atoms measured by 3DAP, which will be described later, similarly to the above Patent Documents 2 and 3, and in the following description, they are mainly referred to as clusters. In the 6000-series aluminum alloy, it is known that Mg and Si form aggregates of atoms called clusters after solution treatment and shining treatment, at room temperature, or during heat treatment at 50 to 150 캜. However, the clusters generated during the holding at room temperature and the heat treatment at 50 to 150 占 폚 completely differ in their behavior.

The clusters formed in the room temperature holding suppress precipitation of the GP zone or the beta 'phase to increase the strength in the subsequent artificial aging or baking painting treatment. On the other hand, clusters (or Mg / Si clusters) formed at 50 to 150 ° C, on the contrary, have been disclosed to promote precipitation of the GP zone or β 'phase (see, for example, Yamada et al. materials).

Incidentally, in Patent Document 1, it is stated that, throughout the paragraphs 0021 to 0025, these clusters are conventionally analyzed by specific heat measurement or 3DAP (three-dimensional atom probe) or the like. At the same time, in the analysis of clusters by 3DAP, it has been observed that even if the presence of the clusters themselves is supported, the size and number density of the clusters specified in the present invention can be unclear or limited.

Obviously, in the 6000-series aluminum alloy, an attempt has been made to interpret the cluster by a 3DAP (3D atom probe). However, as described in Patent Document 1, even if the existence of the cluster itself is supported, the size and number density of the clusters are unclear. This is unclear as to which clusters and BH properties are highly correlated among the cluster of atoms (clusters) measured by 3DAP, and it is unclear which cluster of atoms largely involved in BH properties is unclear.

On the other hand, the present inventors have clarified clusters greatly influencing the BH property in the above Patent Document 2. That is, in the clusters measured by 3DAP, a specific cluster containing a specific amount of Mg atoms or Si atoms in total and having a certain distance from each other among adjacent atoms contained therein and a specific cluster such as BH Which is the most important factor. By increasing the number density of the atomic assemblies satisfying these conditions, it was found that high BH property can be exhibited even in the case of the body paint baking treatment at a low temperature and shortened time after room temperature aging.

According to this Patent Document 2, the presence of a cluster containing at least one of Mg atoms and Si atoms in a total of 30 or more, and the distance between atoms adjacent to each other is 0.75 nm or less improves the BH property. By allowing these clusters to exist in a certain amount or more, the Al-Si-Mg aluminum alloy plate aged at room temperature can exhibit a higher BH property even in the case of low temperature and short time baking of the body coating at 150 ° C for 20 minutes .

On the other hand, the present inventors have further studied and found that among the clusters measured by 3DAP, the presence of a large number of clusters surely improves the BH property, but it has been found that the improvement effect is not sufficient yet. In other words, although it is a prerequisite (necessary condition) for improving the BH property, it is not necessarily sufficient to provide the cluster in a large number.

Therefore, the present inventors also filed the patent document 3. This is because clusters containing either one or both of the Mg atom and Si atom have a difference (size) in their size (distribution), and a large difference in the effect on the BH property due to the cluster size is known. That is, there is a diametrically opposite difference in the effect on the BH property due to the size of the cluster, in which a cluster of relatively small size inhibits BH property while a cluster of relatively large size promotes BH property. On the basis of this, it is possible to improve the BH property by reducing the number of clusters of a relatively small size and increasing the number of clusters of a relatively large size among the specific clusters. Clusters of a relatively small size are extinguished at the time of BH treatment (artificial age hardening treatment), but it is presumed that the BH property is lowered by inhibiting the precipitation of large clusters which are highly effective in improving the strength at the time of BH. On the other hand, it is presumed that the cluster of a relatively large size grows at the time of BH treatment, promotes the precipitation of the precipitate at the time of BH treatment, and increases the BH property.

However, it has also been found that an excessively large cluster grows too large at the time of the BH treatment, the size becomes too large, conversely the BH property is lowered, the strength before the BH treatment becomes too high, and the workability is deteriorated. That is, in order to increase the BH property without deteriorating workability, there is a cluster of the optimum size. It is also known that the average radius of the circle equivalent diameter which is the average size of the specific atom aggregates and the standard deviation of the radius of the circle equivalent diameter greatly affect the BH property. The present inventors have also filed this application as Japanese Patent Application No. 2012-051821 (filed on Mar. 8, 2012). This Japanese Patent Application No. 2012-051821 discloses that the average radius of the circle equivalent diameter of the clusters is 1.2 nm or more and 1.5 nm or less and the standard deviation of the radius of the circle equivalent diameter is 0.35 nm or less, Only clusters are generated.

According to the subsequent studies, it has been found that, in the Al-Mg-Si-based aluminum alloy sheet containing Sn, in the first embodiment of the present invention, the Al-Mg-Si-based aluminum alloy containing no Sn It was found that the optimum range for improving the BH property is different from the average radius of the circle equivalent diameter which is the average size of the cluster of the specific atoms and the standard deviation of the radius of the circle equivalent diameter. That is, in order to improve the BH property of the Al-Mg-Si aluminum alloy sheet containing Sn, the average radius of the circle-equivalent diameter of the specific atomic aggregate is 1.15 nm or more and 1.45 nm or less, which is a specific range, The standard deviation of the radius of the equivalent diameter was small and 0.45 nm or less was found to be necessary for improving the BH property. In order to improve the BH property, the aggregate size of the specific atom is widely present from a small size to a large size, and the size distribution is not largely varied, and it is better that only the cluster of the optimum size is generated. Means that the average radius of the circle equivalent diameter defined in the first embodiment of the present invention is 1.15 nm or more and 1.45 nm or less and the standard deviation of the radius of the circle equivalent diameter is 0.45 nm or less. Thus, in the first embodiment of the present invention, the BH property of the Al-Mg-Si aluminum alloy plate can be further improved even when the body painting baking treatment is maintained at room temperature for a long period of time of 100 days.

In the second embodiment of the present invention, in the Al-Mg-Si-based aluminum alloy sheet containing Sn, the balance between the amount of Mg and Si contained in the aggregate (cluster) And the strength after the BH treatment. That is, the second embodiment of the present invention is characterized in that the ratio of Mg and Si atoms present in the matrix to the Mg and Si atoms contained in the aggregate of atoms satisfying the above-mentioned prescribed conditions is controlled to increase the strength before baking, Based on the knowledge that the BH property can be increased.

At the same time, in an Al-Mg-Si based aluminum alloy plate containing Sn, too large clusters become too large in size when grown at the time of BH treatment, and conversely decrease the BH property, Is too high, and the workability is deteriorated. That is, in order to increase the BH property without deteriorating workability, it is also known that clusters having an optimum size exist. It is also known that the distribution of the aggregate size of the specific atom is important, but the average radius of the circle-equivalent diameter, which is the average size of the specific atom aggregates, also greatly affects the BH property. That is, in order to improve the BH property of the Al-Mg-Si aluminum alloy plate containing Sn, it is necessary that the average radius of the circle equivalent diameter of the specific atomic aggregate is 1.20 nm or more and 1.50 nm or less, Do.

Further, regarding the third embodiment of the present invention, in the Al-Mg-Si based aluminum alloy plate containing Sn, even in the same cluster as described above, the influence on the BH property differs depending on the composition thereof, Si - rich clusters adversely affect BH properties, whereas Mg - rich clusters promote BH. This is the thinking mode of the present embodiment. Therefore, in this embodiment, it is controlled so that the number of clusters having a small distance between the atoms among the clusters measured by the 3DAP is increased, and the number of atoms of Mg The ratio of large clusters is controlled to increase the BH property.

<Cluster in the First Embodiment of the Present Invention>

Hereinafter, a cluster according to the first embodiment of the present invention will be described.

(Cluster specification of this embodiment)

Hereinafter, the cluster specification of the present embodiment will be described in detail.

As described above, the aluminum alloy plate defining the clusters of the present embodiment is a plate after a series of tempering such as solution solidification and quenching treatment and reheating treatment is performed after rolling, and is formed into a panel by press molding or the like (Plate before artificial age hardening treatment such as baking paint hardening treatment). However, in order to press-mold such an automobile panel or the like, it is often left at room temperature over a relatively long period of about one to four months after production of the plate. For this reason, it is preferable that the structure of the plate after being left at room temperature over the long term is a structure specified in the present embodiment. In this respect, when the characteristic after the long-term room temperature is taken as a problem, it is expected that the characteristic is not changed and the structure is not changed after about 100 days at room temperature. Therefore, It is more preferable to investigate and evaluate the structure and properties of the plate after 100 days or more have passed.

(Definition of cluster in this embodiment)

The structure at an arbitrary plate thickness central portion of the Al-Mg-Si-based aluminum alloy plate after the tempering such as solution treatment and shimming treatment before being left at room temperature is measured by a three-dimensional atom probe ion microscope . As a cluster existing in the measured tissue, in the present embodiment, it is assumed that the cluster contains at least 10 or more of Mg atoms and / or Si atoms in total. The upper limit of the number of Mg atoms and Si atoms contained in this cluster of aggregates is preferably as high as possible. The upper limit of the number of Mg atoms and Si atoms contained in this cluster is not particularly specified, Respectively.

In Patent Document 2, it is supposed that the clusters contain at least 30 or more of Mg atoms and Si atoms in total. However, in the present embodiment, as described above, clusters of a relatively small size inhibit the BH property, so that it is regulated to be smaller. For this reason, in order to control the comparatively small-sized cluster to be regulated in such a measurable range, it is defined that at least 10 or more of the Mg atoms and / or the Si atoms are contained in the same manner as in Patent Document 3.

In this embodiment, similar to the above Patent Documents 2 and 3, even when any one of the Mg atom and the Si atom contained in these clusters is used as a reference, any one of atoms adjacent to the reference atom (Clusters) of atoms (satisfying the requirements of the present embodiment) defined in the present embodiment are set to be 0.75 nm or less. The distance of 0.75 nm between them ensures that the distance between the atoms of Mg and Si is close to each other and the number density of clusters of large size having the effect of improving the BH property in a short time at a low temperature after long-term room temperature aging is ensured, It is a numerical value determined to regulate the cluster and to control the number density. The inventors of the present invention have studied in detail the aggregate relationship at an atomic level with an aluminum alloy plate capable of exhibiting high BH property even in the body paint baking treatment under the conditions of a short time at low temperature until now. As a result, It has been found experimentally that a large density is a tissue form exhibiting high BH properties. Therefore, although the technical reason for the distance between atoms of 0.75 nm is not fully understood, it is necessary for strictly ensuring the density of the atomic aggregates exhibiting high BH properties, and is a numerical value determined for that.

The clusters specified in this embodiment most often contain Mg atoms and Si atoms, but the cluster contains Mg atoms but does not contain Si atoms, or contains Si atoms but does not contain Mg atoms . In addition, it is not limited to Mg atoms and Si atoms only, and Al atoms are contained at a very high probability.

Further, depending on the composition of the Al-Mg-Si-based aluminum alloy sheet containing Sn, which is the object of the present embodiment, Sn, Fe, Mn, Cu, Cr, Zr, V, Ti, Zn, Ag, or the like is contained in clusters and these other atoms are counted by 3DAP analysis inevitably occurs. However, even if these atoms (derived from alloying elements or impurities) are contained in the cluster, they are at a lower level than the total number of Mg atoms and Si atoms. Therefore, even when these other atoms are contained in the clusters, the clusters of the present embodiment that fulfill the above-mentioned conditions (conditions) function in the same manner as clusters composed only of Mg atoms or Si atoms. Therefore, the clusters defined in the present embodiment may contain any atoms other than those described above.

It is to be noted that, even in the case where any one of the Mg atom and the Si atom contained in these elements is used as a reference, the distance between the reference atom and any atom adjacent to the other atom is 0.75 mm or less Means that all the Mg atoms and Si atoms present in the cluster have at least one Mg atom or Si atom whose distance therebetween is 0.75 nm or less.

In the clusters of the present embodiment, the distances between atoms of atoms in the clusters are such that even if any one of the Mg atom and the Si atom contained in these atoms is used as a reference, They may not all be 0.75 nm or less, or they may all be 0.75 nm or less. In other words, other Mg atoms or Si atoms having a distance exceeding 0.75 nm may be adjacent to each other, and other Mg atoms or Si (atoms) which satisfy the specified distance (interval) At least one atom is required.

When there is one adjacent Mg atom or Si atom satisfying the specified distance, the number of Mg atoms and Si atoms to be counted, which satisfy the distance condition, It becomes two including atoms. When there are two adjacent Mg atoms or two Si atoms satisfying the specified distance, the number of Mg atoms and Si atoms to be counted, which satisfy the distance condition, 3 atoms including Si atoms.

The clusters described above are clusters produced by the above-described processes and, more specifically, by solution treatment in the tempering after rolling and temperature holding treatment after quenching at high temperature, which will be described later in detail. That is, the clusters in this embodiment are aggregates of atoms generated by solution treatment and temperature holding treatment after quenching at high temperature, and contain at least 10 or more of Mg atoms and Si atoms in total, Even when any one of the Mg atom and the Si atom contained in these atoms is used as a reference, the distance between the reference atom and any atom adjacent to the atom is 0.75 nm or less.

Up to now, clusters promoting precipitation in the GP zone or on the beta 'phase which increase the strength in the artificial aging or baking coating process are Mg / Si clusters as described above, and this clusters are 50 to 150 Lt; 0 &gt; C. On the contrary, in the artificial aging treatment or the baking painting treatment, it is reported that the cluster inhibiting the deposition of the GP zone or β 'phase is a Si-rich cluster, which is formed at room temperature (room temperature aging) after solution polymerization (For example, Sato: Light Metals vol. 56, page 595).

However, the inventors of the present invention have analyzed in detail the relationship between the strength and the cluster at the time of artificial aging treatment or baking painting, and as a result, the tissue factor contributing to the strength at the time of artificial aging treatment or baking painting treatment, ), But the cluster size distribution state generated by the plate tempering process. In addition, the distribution of the cluster size was interpreted by the above-described definition, and the correspondence with the strength at the time of artificial aging treatment or baking painting heat treatment became clear.

On the contrary, the clusters formed at room temperature (room temperature aging) by the above-mentioned three-dimensional atom probe electric field ion microscope can measure the number of atoms or clusters Density. Therefore, the definition of the clusters (atomic assemblies) of the present embodiment distinguishes clusters formed at room temperature (room temperature aging) from the clusters formed at room temperature and prevents Mg and Si (added) It is also a regulation.

(Density of cluster)

It is assumed that the clusters satisfying the clusters and the precondition conditions defined in the present embodiment described above have an average number density of not less than 2.5 × 10 ²³ / m 3 and not more than 20.0 × 10 ²³ / m 3. If the average number density of the clusters is less than 2.5 x 10 &lt; ²³ &gt; / m &lt; 3 &gt;, an excessively small cluster is generated during a prolonged room temperature decrease, resulting in deterioration of BH property and deterioration of workability. On the other hand, if it is more than 20.0 x 10 &lt; ²³ &gt; / m &lt; 3 &gt;, the strength before the BH treatment becomes too high, and as a result, the workability is deteriorated.

When the average number density of the clusters defined in the present embodiment is small, the formation amount of the clusters themselves becomes insufficient, and most of Mg and Si added (contained) is consumed in the cluster formed by the room temperature aging it means. Thus, even if the effect of enhancing the precipitation of the GP zone or the β 'phase and improving the BH property is obtained, the improvement of the BH property after an elongation at room temperature (room temperature aging) over a long period is about 30 to 40 MPa . Therefore, under such conditions, a higher desired BH property can not be obtained.

(Specification of size distribution of clusters of this embodiment)

In order to improve the BH property on the premise that the cluster defined in the present embodiment exists in the predetermined amount (the average number density or more), the present embodiment is characterized in that, as described above, Is 1.15 nm or more and 1.45 nm or less, and the standard deviation of the radius of the circle-equivalent diameter is 0.45 nm or less.

Average radius of the circle equivalent diameter of the atomic assembly E (r):

The average radius E (r) (nm) of the circle equivalent diameter of the atomic assemblies satisfying the above conditions is expressed by E (r) = (1 / n)? R. Here, n is the number of aggregates of atoms satisfying the above-mentioned precondition. and r is the radius (nm) of the circle equivalent diameter of each of the atomic assemblies satisfying the above conditions.

The size of the aggregate of atoms which satisfy the above-mentioned preconditioning condition itself becomes important for improving the BH property first. (Clusters) in which the average radius E (r) of the circle-equivalent diameter is excessively small disappear at the time of BH treatment (artificial age hardening treatment), and at this BH, β "or β (Clusters) of atoms having an average radius E (r) of a circle-equivalent diameter that is excessively large are also inhibited from being precipitated before (right before or before) BH treatment Quot; or &lt; [beta] '&gt; by precipitation at room temperature at the time of BH, so that the pre-BH strength is excessively increased and the press formability and bending workability are inhibited. Further, if it is already an intermediate precipitate such as? "Or? 'At the point of time before the BH treatment and is precipitated out, it suppresses precipitation of intermediate precipitates such as a new?"Or?' At the time of BH, It inhibits. In addition, since both of the above-mentioned β "and β 'are intermediate precipitated phases and at the same time are Mg ₂ Si, the crystal structure (arrangement of atoms) is different and it is difficult to express differently. 'Is called β prime, and β' is called β double prime.

On the other hand, when the aggregate of atoms satisfying the above-mentioned preconditioning conditions has a size in the range of 1.15 nm or more and 1.45 nm or less in the average radius E (r) of the circle equivalent diameter, (Which contributes to strength improvement), and precipitates out at a stage of press forming or bending. Thus, it is possible to have a property that the strength is low and the workability is good and the strength is increased only after BH Therefore, the size of the above-mentioned atomic aggregate is 1.15 nm or more and 1.45 nm or less in the average radius E (r) of the circle-equivalent diameter.

Standard deviation of circle equivalent diameter of atomic assembly σ:

Further, the standard deviation σ of circle-equivalent diameter of the atomic aggregate meeting the above prerequisites, from the average radius E (r) of the circle-equivalent ^{diameter, σ 2 = (1 / n} ) Σ [rE (r)] 2 Lt; / RTI &gt;

The average radius E (r) of the circle-equivalent diameter, which is the average size of the specific atomic assemblies satisfying the above-mentioned conditions, is also important, although the size of the atomic aggregate satisfying the above- ) Is also a distribution state of the size of the atom aggregate, which greatly affects the BH property. That is, in order to improve the BH property, the average radius of the circle-equivalent diameter of the specific atomic assembly is in a specific range of 1.15 nm or more and 1.45 nm or less and the standard deviation of the radius of the circle- It is necessary for BH improvement.

In order to improve the BH property, the cluster size of the specific atom is not greatly changed from small to large, and it is better that only the cluster of the optimum size is generated. When the average radius of the circle-equivalent diameter is 1.15 nm or more and 1.45 nm or less and the standard deviation of the radius of the circle-equivalent diameter is 0.45 nm or less, this means that only clusters having the optimum size are generated. Thus, in the present embodiment, the BH property of the Al-Mg-Si-based aluminum alloy plate can be further improved even when the body paint bake processing is performed after maintaining the room temperature for a long time.

In the present embodiment, the size distribution of the specified atom aggregate is defined by both the average radius of the circle equivalent diameter and the standard deviation of the radius of the circle equivalent diameter of the specified atom aggregate, (Clusters) of atoms of similar size among the atomic groups. This further improves the BH property of the Al-Mg-Si-based aluminum alloy plate even when the body coating baking treatment is performed after maintaining the room temperature for a long time.

Even in the case of the above-described cluster, if there are many clusters having a small size which hinders the BH property, the average radius of circle equivalent diameter becomes smaller than 1.15 nm in the above rule. Further, the standard deviation of the radius of the circle equivalent diameter becomes larger than 0.45 nm.

On the other hand, even in a cluster defined in the present embodiment, among clusters having a large size, which inhibits the BH property, the average radius of circle equivalent diameter becomes larger than 1.45 nm. Further, the standard deviation of the radius of the circle equivalent diameter becomes larger than 0.45 nm.

(Clusters) of atoms having an extremely small average radius of circle equivalent diameter disappear during the BH treatment (artificial age hardening treatment), and at the time of BH, the effect of enhancing the strength (Clusters) of atoms having an average radius of the circle-equivalent diameter of too large are also observed at the time before the BH treatment by the aging at room temperature, Already precipitates in the form of intermediate precipitates such as "beta &quot; or beta ', and the strength before BH is excessively increased to inhibit the bending workability. Further, if it is already an intermediate precipitate such as? "Or? 'At the point of time before the BH treatment and is precipitated out, it suppresses precipitation of intermediate precipitates such as a new?" Or?' At the time of BH, It inhibits.

&Lt; Cluster in the Second Embodiment of the Present Invention >

Next, a cluster in the second embodiment of the present invention will be described.

(Cluster specification of this embodiment)

Hereinafter, the cluster specification of the present embodiment will be described in detail.

As described above, the aluminum alloy plate that defines the clusters of the present embodiment is a rolled plate such as a hot rolled plate or a cold rolled plate, and after the tempering such as solution treatment and shimming treatment is performed, (Plate before artificial age hardening treatment such as baking painting hardening treatment) before it is molded into a panel. However, in order to be molded as the automobile member or the like, it is often left at room temperature over a relatively long period of about 0.5 to 4 months after the production of the plate. For this reason, it is preferable that the structure of the plate after being left at room temperature over the long term is a structure specified in the present embodiment. In this regard, it is expected that when the characteristic after the elapse of the room temperature is taken as a problem, the characteristic is not changed and the structure is not changed after about 100 days at room temperature. Therefore, It is more preferable to investigate and evaluate the structure and properties of the plate after 100 days or more have passed since the tempering.

(Cluster definition in this embodiment)

The structure at the center of an arbitrary plate thickness of such an aluminum alloy plate is measured by a three-dimensional atom probe ion microscope. As a cluster existing in the measured tissue, in the present embodiment, it is assumed that the cluster contains at least 10 or more of Mg atoms and / or Si atoms in total. The upper limit of the number of Mg atoms and Si atoms contained in this cluster of aggregates is preferably as high as possible. The upper limit of the number of Mg atoms and Si atoms contained in this cluster is not particularly specified, Respectively.

In Patent Document 2, it is supposed that the cluster contains at least 30 or more of Mg atoms and Si atoms in total. However, in the present embodiment, as described above, a cluster of a relatively small size inhibits the BH property, so that it is restricted. For this reason, in order to control the comparatively small-sized cluster to be regulated in such a measurable range, it is defined that at least 10 or more of the Mg atoms and / or the Si atoms are contained in the same manner as in Patent Document 3.

In this embodiment, similar to the above Patent Documents 2 and 3, even when any one of the Mg atom and the Si atom contained in these clusters is used as a reference, any one of atoms adjacent to the reference atom (Clusters) of atoms (satisfying the requirements of the present embodiment) defined in the present embodiment are set to be 0.75 nm or less. The distance of 0.75 nm between them ensures that the distances between atoms of Mg and Si are close to each other and that the number of large-sized clusters having BH property improving effect after room temperature aging is guaranteed, conversely, This is a numerical value determined to control the density of water. The inventors of the present invention have studied in detail the relationship between an aluminum alloy plate capable of exhibiting high BH property by body painting baking treatment and an aggregate at an atomic level. As a result, it has been found that a large number of atom aggregates, It is experimentally found that the tissue form exhibits high BH. Therefore, although the technical reason for the distance between atoms of 0.75 nm is not fully understood, it is necessary for strictly ensuring the density of the atomic aggregates exhibiting high BH properties, and is a numerical value determined for that.

The clusters specified in this embodiment most often contain Mg atoms and Si atoms, but the cluster contains Mg atoms but does not contain Si atoms, or contains Si atoms but does not contain Mg atoms . In addition, it is not limited to Mg atoms or Si atoms alone, and Al atoms are contained in a very high probability.

Further, depending on the composition of the Al-Mg-Si-based aluminum alloy sheet containing Sn, which is the object of the present embodiment, Sn, Fe, Mn, Cu, Cr, Zr, V, Ti, Zn, Ag, or the like is included in the cluster, and other atoms are counted by 3DAP analysis inevitably occurs. However, even if these atoms (derived from alloying elements or impurities) are contained in the cluster, they are at a lower level than the total number of Mg atoms and Si atoms. Therefore, even when these other atoms are contained in the clusters, the clusters of the present embodiment that fulfill the above-mentioned conditions (conditions) function in the same manner as clusters composed only of Mg atoms or Si atoms. Therefore, the clusters defined in the present embodiment may contain any atoms other than those described above.

It is to be noted that, even in the case where any one of the Mg atom and the Si atom contained in these elements is used as a reference, the distance between the reference atom and any atom adjacent to the other atom is 0.75 mm or less Means that all the Mg atoms and Si atoms present in the cluster have at least one Mg atom or Si atom whose distance therebetween is 0.75 nm or less.

The distance between atoms in the clusters of this embodiment is defined by the distance between all the atoms of atoms other than the reference atom and the atom May not all be 0.75 nm or less, and conversely, they may all be 0.75 nm or less. In other words, other Mg atoms or Si atoms having a distance exceeding 0.75 nm may be adjacent to each other, and other Mg atoms or Si (atoms) which satisfy the specified distance (interval) At least one atom is required.

When there is one adjacent Mg atom or Si atom satisfying the specified distance, the number of Mg atoms and Si atoms to be counted, which satisfy the distance condition, It becomes two including atoms. When there are two adjacent Mg atoms or two Si atoms satisfying the specified distance, the number of Mg atoms and Si atoms to be counted, which satisfy the distance condition, And three Si atoms are contained.

The clusters described above are clusters produced by the above-described processes and, more specifically, by solution treatment in the tempering after rolling and temperature holding treatment after quenching at high temperature, which will be described later in detail. That is, the clusters in this embodiment are aggregates of atoms generated by solution treatment and temperature holding treatment after quenching at high temperature, and contain at least 10 or more of Mg atoms and Si atoms in total, Even when any one of the Mg atom and the Si atom contained in these atoms is used as a reference, the distance between the reference atom and any atom adjacent to the atom is 0.75 nm or less.

(Amount of Mg and Si in the cluster)

In the present embodiment, the total amount of atoms of Mg and Si contained in the entire cluster, which is contained in the entire Al-Mg-Si aluminum alloy plate containing Sn and which is defined as above (satisfying the precondition) Is controlled by the relationship between the total amount of Mg and Si contained in the aluminum alloy sheet as a whole. This properly controls the balance between the total amount of Mg and Si atoms present in the cluster defined above and the total amount of atoms of Mg and Si dissolved in the matrix of the aluminum alloy plate. As a result, the BH property can be increased.

For this balance control, in the present embodiment, it is assumed that the sum (total amount) of Mg and Si atoms contained in the specific cluster (atomic assembly) measured is N _cluster is set at a constant ratio with respect to N _total , which is the sum (total amount) of all the Mg and Si atoms measured.

That is, the ratio (N _cluster / N _total ) × 100 of N _cluster to N _total is set in a range of 1% to 15%. Here, the ratio of the N _cluster of N _clusters calculated from (N _cluster / N _total ) x 100 to the _total of N measurements of the _cluster thickness of the central portion of the plate thickness of the test plate The average (average ratio) in the place is assumed.

With this balanced structure, it is possible to realize a strength of 200 MPa or more and a BH property (difference in strength before and after baking treatment) exceeding 90 MPa after baking after 100 days of holding at room temperature (room temperature) after the production of the plate.

However, the correlation between these tissues and BH was found experimentally and the mechanism can not be fully explained yet. However, the weaker the average ratio _{(N cluster / N total) ×} 100 is less than 1% for the N _total of the above N _cluster, the results are Mg and Si, which employ the aluminum alloy sheet to be increased, precipitation strengthening by the cluster, Due to the limit of strengthening employment, the strength before baking becomes lower. As a result, the strength after baking tends to be lowered inevitably.

On the other hand, when the average ratio for the N _total of the above _{N cluster (N cluster / N total} ) × 100 is more than 15%, and too large amount of Mg and Si included in the cluster, Mg and Si to employ the aluminum alloy plate . As a result, the number of reinforcing phases (β ") produced in the artificial aging hardening treatment is reduced, the BH property is likely to be lowered, and the strength after baking is likely to be lowered.

(Density of cluster)

In order to control within the average ratio (N _cluster / N _total) range of a × 100 1% to 15% for the N _total of the above N _cluster, average the cluster specified by the present embodiment more than 2.5 × 10 ²³ gae / ㎥ It is preferable that it is contained at a number density. If the average number density of these clusters is less than 2.5 x 10 &lt; ²³ &gt; / m &lt; 3 &gt;, the formation amount of the clusters themselves becomes insufficient, and most of Mg and Si added (contained) . As a result, it becomes difficult to make the total amount of Mg and Si present in the cluster equal to or more than 1%, and the effect of improving the BH property is deteriorated after leaving at room temperature for a long period of time (room temperature aging). By the way, the preferred range as 2.5 × 10 ²³ gae / ㎥ average number density range of at least, less than 20.0 × 10 ²³ gae / ㎥ the mean number density of the cluster.

(Specification of size distribution of clusters of this embodiment)

In this embodiment, in the Al-Mg-Si-based aluminum alloy plate containing Sn, the total amount of atoms of Mg and Si in the above-described clusters is controlled, and a cluster of atoms satisfying these conditions, The average radius is 1.20 nm or more and 1.50 nm or less. A cluster in which the total amount of Mg and Si atoms is controlled and whose size is in the range of 1.20 nm or more and 1.50 nm or less at the average radius E (r) of the circle equivalent diameter is effective in improving the strength at the time of BH (Contributing to the strength improvement), and precipitates out as intermediate precipitates such as "b &quot; or &apos;, etc. Therefore, it has low strength in the step of press forming or bending, and has good workability and high strength after BH.

The average radius E (r) (nm) of the circle equivalent diameter of the atom aggregate is expressed by E (r) = (1 / n)? R. Here, n is the number of aggregates of atoms satisfying the above-mentioned precondition. and r is the radius (nm) of the circle equivalent diameter of each of the atomic assemblies satisfying the above conditions.

(Clusters) in which the average radius E (r) of the circle-equivalent diameter is excessively small disappear at the time of BH treatment (artificial age hardening treatment), and at this BH, β "or β (Clusters) of atoms having an average radius E (r) of a circle-equivalent diameter that is excessively large are also inhibited from being precipitated before (right before or before) BH treatment Quot; or &lt; [beta] '&gt; by precipitation at room temperature at the time of BH, so that the pre-BH strength is excessively increased and the press formability and bending workability are inhibited. Further, if it is already an intermediate precipitate such as? "Or? 'At the point of time before the BH treatment and is precipitated out, it suppresses precipitation of intermediate precipitates such as a new?"Or?' At the time of BH, It inhibits. In addition, since both of the above-mentioned β "and β 'are intermediate precipitated phases and at the same time are Mg ₂ Si, the crystal structure (arrangement of atoms) differs and it is difficult to express another expression. Therefore, β 'is called β prime, and β "is called β double prime.

As described above, even in a cluster in which the total amount of Mg and Si atoms is controlled, the larger the number of clusters having a small size inhibiting BH, the smaller the average radius of the circle-equivalent diameter becomes smaller than 1.20 nm and the BH property is lowered. On the other hand, even in a cluster defined in this embodiment, even when there are many clusters having a large size inhibiting BH, the average radius of the circle-equivalent diameter exceeds 1.50 nm and the strength before BH becomes too high, The bendability and bendability are lowered, and the BH property is lowered.

On the other hand, the fact that the size of the aggregate of atoms satisfying the above-mentioned precondition is in the range of 1.20 nm or more and 1.50 nm or less in the average radius E (r) of the circle equivalent diameter is effective for improving the strength (Which contributes to strength improvement), and precipitates out at a stage of press forming or bending. Thus, it is possible to have a property that the strength is low and the workability is good and the strength is increased only after BH have.

&Lt; Cluster in the Third Embodiment of the Present Invention >

Next, a cluster according to a third embodiment of the present invention will be described.

(Cluster specification of this embodiment)

Hereinafter, the cluster specification of the present embodiment will be described in detail.

As described above, the aluminum alloy plate defining the clusters of the present embodiment is a plate after a series of tempering such as solution solidification and quenching treatment and reheating treatment is performed after rolling, and is formed into a panel by press molding or the like (Plate before artificial age hardening treatment such as baking paint hardening treatment).

However, in order to press-mold such an automobile panel or the like, it is often left at room temperature over a relatively long period of about one to four months after production of the plate. For this reason, it is preferable that the structure of the plate after being left at room temperature over the long term is a structure specified in the present embodiment. In this respect, when the characteristic after the long-term room temperature is taken as a problem, it is expected that the characteristic is not changed and the structure is not changed after about 100 days at room temperature. Therefore, It is more preferable to investigate and evaluate the structure and properties of the plate after 100 days or more have passed.

(Definition of cluster in this embodiment)

The structure at the center of an arbitrary plate thickness of such an aluminum alloy plate is measured by a three-dimensional atom probe ion microscope. As a cluster existing in the measured tissue, in the present embodiment, it is assumed that the cluster contains at least 10 or more of Mg atoms and / or Si atoms in total. The upper limit of the number of Mg atoms and Si atoms contained in this cluster of aggregates is preferably as high as possible. The upper limit of the number of Mg atoms and Si atoms contained in this cluster is not particularly specified, Respectively.

In Patent Document 2, it is supposed that the clusters contain at least 30 or more of Mg atoms and Si atoms in total. However, in the present embodiment, as described above, a cluster of a relatively small size inhibits the BH property, so that it is restricted. For this reason, in order to control the comparatively small-sized cluster to be regulated in such a measurable range, it is defined that at least 10 or more of the Mg atoms and / or the Si atoms are contained in the same manner as in Patent Document 3.

In this embodiment, similar to the above Patent Documents 2 and 3, even when any one of the Mg atom and the Si atom contained in these clusters is used as a reference, any one of atoms adjacent to the reference atom (Clusters) of atoms (satisfying the requirements of the present embodiment) defined in the present embodiment are set to be 0.75 nm or less. The distance of 0.75 nm between them ensures that the distance between the atoms of Mg and Si is close to each other, ensuring a large number of cluster number densities that have an effect of improving the BH property after room temperature aging. On the contrary, It is a numerical value that is set to control density less. The inventors of the present invention have studied in detail the aggregate relationship at an atomic level with an aluminum alloy plate capable of exhibiting high BH properties by the body coating baking treatment. As a result, it has been found that a high number density of the atomic aggregates defined in the above- And it was found experimentally that it is a tissue form showing sex. Therefore, although the technical reason for the distance of 0.75 nm between atoms is not fully understood, it is necessary for strictly ensuring the density of the atomic aggregates exhibiting a high BH property, and is a numerical value determined for that purpose.

The clusters specified in this embodiment most often contain Mg atoms and Si atoms, but the cluster contains Mg atoms but does not contain Si atoms, or contains Si atoms but does not contain Mg atoms . In addition, it is not limited to Mg atoms or Si atoms alone, and Al atoms are contained in a very high probability.

Further, depending on the composition of the Al-Mg-Si-based aluminum alloy sheet containing Sn, which is the object of the present embodiment, Sn, Fe, Mn, Cu, Cr, Zr, V, Ti, Zn, Ag, or the like is included in the cluster, and other atoms are counted by 3DAP analysis inevitably occurs. However, even if these atoms (derived from alloying elements or impurities) are contained in the cluster, they are at a lower level than the total number of Mg atoms and Si atoms. Therefore, even when these other atoms are contained in the clusters, the clusters of the present embodiment that fulfill the above-mentioned conditions (conditions) function in the same manner as clusters composed only of Mg atoms or Si atoms. Therefore, the clusters defined in the present embodiment may contain any atoms other than those described above.

It is to be noted that, even in the case where any one of the Mg atom and the Si atom contained in these elements is used as a reference, the distance between the reference atom and any atom adjacent to the other atom is 0.75 mm or less Means that all the Mg atoms and Si atoms present in the cluster have at least one Mg atom or Si atom whose distance therebetween is 0.75 nm or less.

In the clusters of the present embodiment, the distances between atoms of atoms in the clusters are such that even if any one of the Mg atom and the Si atom contained in these atoms is used as a reference, They may not all be 0.75 nm or less, and conversely all may be 0.75 nm or less. In other words, other Mg atoms or Si atoms having a distance exceeding 0.75 nm may be adjacent to each other, and other Mg atoms or Si (atoms) which satisfy the specified distance (interval) At least one atom is required.

When there is one adjacent Mg atom or Si atom satisfying the specified distance, the number of Mg atoms and Si atoms to be counted, which satisfy the distance condition, It becomes two including atoms. When there are two adjacent Mg atoms or two Si atoms satisfying the specified distance, the number of Mg atoms and Si atoms to be counted, which satisfy the distance condition, And three Si atoms are contained.

The clusters described above are clusters produced by the above-described processes and, more specifically, by solution treatment in the tempering after rolling and temperature holding treatment after quenching at high temperature, which will be described later in detail. That is, the clusters in this embodiment are aggregates of atoms generated by solution treatment and temperature holding treatment after quenching at high temperature, and contain at least 10 or more of Mg atoms and Si atoms in total, Even when any one of the Mg atom and the Si atom contained in these atoms is used as a reference, the distance between the reference atom and any atom adjacent to the atom is 0.75 nm or less.

Up to now, clusters promoting precipitation in the GP zone or on the beta 'phase which increase the strength in the artificial aging or baking coating process are Mg / Si clusters as described above, and this clusters are 50 to 150 Lt; 0 &gt; C. On the contrary, in the artificial aging treatment or baking painting treatment, it is reported that the cluster inhibiting the precipitation of the GP zone or β 'phase is a Si-rich cluster, which is formed at room temperature (room temperature aging) after solution polymerization (For example, Sato: Light Metals vol. 56, page 595).

However, in the general aluminum alloy manufacturing process, as described above, after the plate is manufactured, it is usually left at room temperature for about 1 to 4 months (left at room temperature) until it is molded into a panel by an automobile maker, It is difficult to form only Mg-Si clusters that promote BH properties, because Mg-Si clusters produced at the time of production of SiH 2 and Si rich clusters generated at room temperature aging coexist.

Therefore, in order to improve the BH property, it is considered important for the inventors to control the ratio of Si-rich clusters adversely affecting BH properties and Mg-Si clusters promoting BH properties. And the clustering form for improving the BH property was clarified.

(Composition of this embodiment clusters)

Clusters satisfying the cluster or the precondition defined in the present embodiment have different influences on the BH property depending on the composition thereof. Si-rich clusters adversely affect the BH properties, but the Si-rich clusters are generated at the time of baking coating, and the difference in Mg / Si composition between the strengthening phase such as? Or? Since it is relatively large, it does not promote the formation of the reinforcing phase at the time of baking, and rather suppresses the formation of reinforcing phases.

On the other hand, clusters in which Mg atoms are rich improve the BH property, but Mg-rich clusters are generated at the time of baking painting, and the strengthening phase such as? "Or? It promotes the formation of reinforcing phases at the time of baking painting.

In this embodiment, on the basis of the compositional relationship of these clusters, the ratio of clusters having a large number of atoms of Mg in the cluster is controlled so as to increase the BH property. Therefore, in the present embodiment, a total of 10 or more Mg atoms and / or Si atoms are contained in total, and any one of Mg atoms and Si atoms contained in these atoms is used as a standard (Mg / Si) ratio of the number of Mg atoms to the number of Si atoms of 1/2 or more among the aggregates of atoms satisfying the condition that the distance between the atom and any atom adjacent to the atom is 0.75 nm or less The ratio of the rich atomic aggregates is defined as 0.70 or more. When the proportion of the atomic aggregates having a Mg / Si ratio of 1/2 or more is less than 0.70, the number of clusters in which Si atoms are rich increases, and the BH property tends to be small due to the above mechanism.

Here, the upper limit of the ratio of the atomic aggregates having a Mg / Si ratio of not less than 1/2 is not particularly specified, but about 0.95 is a manufacturing limit.

(Density of cluster)

In the present embodiment, it is assumed that the clusters satisfying the cluster or the precondition described above are contained at an average number density of 3.0 x 10 ²³ / m 3 or more and 25.0 x 10 ²³ / m 3 or less. If the average number density of the clusters defined in this embodiment is less than 3.0 x 10 &lt; ²³ &gt; / m &lt; 3 &gt;, the amount of formation of the clusters themselves becomes insufficient and the clusters formed by the room- And most of Si is consumed, and after leaving at room temperature (room temperature aging), the BH property is lowered and the workability is deteriorated.

On the other hand, the upper limit of the average number density of the clusters is about 25.0 x 10 &lt; ²³ &gt; / m &lt; 3 &gt; (about 2.5 x 10 ²⁴ / m &

(Measurement principle and measurement method of 3DAP)

The measurement principle and measurement method of the 3DAP of the present invention are disclosed in Patent Documents 2 and 3 above. That is, the 3DAP (three-dimensional atom probe) is equipped with a time-of-flight mass spectrometer in a field ion microscope (FIM). With such a constitution, it is a local analyzer capable of observing individual atoms of a metal surface with an electric field ion microscope and identifying these atoms by flight time mass spectrometry. In addition, since 3DAP can simultaneously analyze the type and position of atoms emitted from a sample, it is a very effective means for analyzing the structure of an atomic assembly. As a result, as described above, it is used for analyzing a structure of a magnetic recording film, an electronic device, or a steel material. In addition, recently, as described above, it is also used for cluster identification of the structure of an aluminum alloy plate.

In this 3DAP, the ionization phenomenon of the sample atoms themselves under a high electric field called electric field evaporation is utilized. When a high voltage is applied to the sample to evaporate the sample atoms, the atoms are ionized from the surface of the sample, and the electrons escape from the probe hole and reach the detector.

This detector is a position sensitive detector that measures the time of flight up to the individual ion detectors together with the individual ion mass analysis (identification of atomic species) So that it can be decided. Therefore, 3DAP can simultaneously measure the atomic position and the atomic species at the tip of the sample, so that the atomic structure at the tip of the sample can be reconstructed and observed three-dimensionally. In addition, since the electric field evaporation occurs sequentially in the front end face of the sample, the depth direction distribution of atoms from the sample front end can be irradiated with the decomposition ability at the atomic level.

In order to use a high electric field in this 3DAP, a sample to be analyzed needs to have a high conductivity such as a metal, and furthermore, the shape of the sample is generally required to be a fine needle shape having a tip diameter of about 100 nm? have. Therefore, a sample is taken from the central portion of the plate thickness of the aluminum alloy plate to be measured, and the sample is cut and electrolytically polished by a precision cutting device to prepare a sample having a fine needle tip for analysis. As a measurement method, for example, "LEAP3000" manufactured by Imago Scientific Instruments was used, and a high pulse voltage of 1 kV order was applied to an aluminum alloy plate sample having the tip formed into a needle shape, and millions of The atoms are continuously ionized. Ions are detected by a position sensitive detector and mass analysis of ions (atomic species identification) is carried out from the flight time until a pulse voltage is applied and individual ions are ejected from the tip of the sample and reaches the detector ).

By using the property that the electric field evaporation occurs regularly in order from the tip end face of the sample, coordinates in the depth direction are suitably given to the two-dimensional map indicating the arrival position of the ions, and the analysis software "IVAS" Dimensional mapping (atomic structure in three dimensions: construction of atom map) is performed. As a result, a three-dimensional atom map at the tip of the sample is obtained.

The atomic cluster (cluster) is analyzed by using the Maximum Separation Method, which is a method of defining the atom and the atoms belonging to the precipitate or cluster. In this analysis, the number of Mg atoms or Si atoms (or a total of 10 or more), the distance (interval) between adjacent Mg atoms or Si atoms, and the specific narrow gap (0.75 nm or less) Is given as the parameter.

In the first embodiment of the present invention, even if any one or both of the Mg atom and the Si atom are contained in a total of 10 or more and any one of the Mg atom and the Si atom contained therein is used as a reference, And the distance between one atom and another atom adjacent to the atom is 0.75 nm or less. A cluster satisfying this condition is defined as an aggregate of atoms of the present embodiment. Then, the dispersion state of the atom aggregates suitable for this definition is evaluated, and the number density of the atom aggregates is averaged to three or more measurement specimens to measure and quantify the average density per cubic meter (m 3 / m 3).

That is, the radius of rotation _{g g} that is the maximum when the aggregate of the atoms to be measured is regarded as the object of measurement by the original analysis software originally possessed by the 3DAP is obtained by the following expression (1).

In the equation (1), l _g is a radius of gyration that is automatically calculated by the software of the three-dimensional atom probe electric field ion microscope. x, y and z are the x, y and z axes which do not change in the measurement layout of the three-dimensional atom probe field microscope. x _i , y _i , and z _i are the lengths of the x, y, and z axes, and are the spatial coordinates of Mg and Si atoms constituting the aggregate of atoms. "X-bar" and the like having "-" on each of "x", "y", and "z" are the lengths of the x, y, and z axes. and n is the number of Mg and Si atoms constituting the atomic assembly.

Then, this turning radius l _g is converted into the radius r _G in the guinea by the following expression: r _G = √ (5/3) · l _g .

Is considered in terms of the radius on the guinea _G r as radius of the atom aggregate and calculates each of the maximum equivalent circle diameter is r of the measurement target the atomic aggregate. In addition, the number n of atomic assemblies satisfying the above-mentioned conditions is also calculated. From this number n, the average number density (number / m 3) of the atomic assemblies satisfying the above-mentioned precondition can also be calculated.

The measurement of the clusters by these 3DAPs is performed on 10 sites in the central portion of an arbitrary plate thickness of the Al-Mg-Si aluminum alloy plate after the above tempering, and the respective measured values (calculated values) are averaged , And is set as the value of each mean specified in the present embodiment.

The average radius E (r) (nm) of the circle equivalent diameter of the atomic aggregate is calculated from the above-mentioned E (r) = (n) from the calculated equivalent maximum diameter r and the number n of atom aggregates satisfying the above- (1 / n)? R.

The standard deviation σ of the circle-equivalent diameter of the atomic assembly satisfying the above-mentioned conditions is calculated from the average radius E (r) of the circle-equivalent diameter by the above-mentioned σ ² = (1 / n) ] ² .

Further, the above-described calculation formula of the radius of the atomic assemblies, and the measurement and conversion method from the rotating radius l _g to the guinea to the radius r _G are described in MK Miller: Atom Probe Tomography, (Kluwer Academic / Plenum Publishers, New York, 184 pages. In addition, the radius calculating formulas of the atomic assemblies are described in many other documents. For example, in "(2) Three-dimensional atom probe analysis" on page 140 of "microstructure change of ion-irradiated low alloy steel" (Katsuhiko Fujii, Fukutani Koji, Okubo Daikatsu, 1, or a conversion equation for the radius r _{G in the} guinea (the symbol of the radius _g of revolution is given as r _G ).

Further, in the second embodiment of the present invention, even if a total of 10 or more Mg atoms and / or Si atoms are contained and any one of Mg atoms and Si atoms contained in these atoms is used as a reference, And the distance between the atom and any other atom adjacent to the atom is 0.75 nm or less. A cluster satisfying this condition is defined as an atomic assembly of the present embodiment. Then, the dispersion state of the atom aggregates suitable for this definition is evaluated, and the number density of the atom aggregates is averaged to three or more measurement specimens to measure and quantify the average density per cubic meter (m 3 / m 3).

Then, the number of Mg and Si atoms N _cluster contained in all the aggregates of atoms satisfying this condition is obtained. In addition, the number N _total of all the Mg and Si atoms contained in both the solid solution and the atom aggregate detected by the detector, i.e., measured by 3DAP, is obtained. And the ratio of the _total N of the _cluster N, obtained from the formula _cluster N / _total N × 100, and controls such that the average value (average rate) is 1% or more and 15% or less.

Further, the radius of rotation _g , which is the maximum when the aggregate of the atoms to be measured is regarded as the object to be measured by the inherent analysis software originally possessed by the 3DAP, is obtained by the equation (1).

Then, this turning radius l _g is converted to the radius r _G in the guinea by the relation of the formula (2), r _G = √ (5/3) · l _g .

It is considered in terms of the radius on the guinea _G r as radius of the atom aggregate and calculates the equivalent circle is the maximum of the measurement target the atomic aggregate having a diameter r. In addition, the number n of atomic assemblies satisfying the above-mentioned conditions is also calculated. From this number n, the average number density (number / m 3) of the atomic assemblies satisfying the above-mentioned precondition can also be calculated.

The measurement of the clusters by these 3DAPs is performed on 10 sites in the central portion of an arbitrary plate thickness of the Al-Mg-Si aluminum alloy plate after the above tempering, and the respective measured values (calculated values) are averaged , And is set as the value of each mean specified in the present embodiment.

The average radius E (r) (nm) of the circle equivalent diameter of the atomic aggregate is calculated from the above-mentioned E (r) = (n) from the calculated equivalent maximum diameter r and the number n of atom aggregates satisfying the above- (1 / n)? R.

Further, in the third embodiment of the present invention, even if any one or both of the Mg atom and the Si atom are contained in a total of 10 or more and any one of the Mg atom and the Si atom contained therein is used as a reference, And the distance between the atom and any other atom adjacent to the atom is 0.75 nm or less. A cluster satisfying this condition is defined as an atomic assembly of the present embodiment. Then, the dispersion state of the atom aggregates suitable for this definition is evaluated, and the number density of the atom aggregates is averaged to three or more measurement samples and measured and quantified as the average density per cubic meter (m 3 / m 3).

(Detection efficiency of atoms by 3DAP)

At present, the detection efficiency of atoms by these 3DAPs is limited to about 50% of the atomized atoms, and the remaining atoms can not be detected. If the variation of the detection efficiency of the atoms by this 3DAP is greatly changed, for example, in the future, the measurement result by the 3DAP of the average number density (number / 탆 ³ ) of clusters of each size specified by the present invention fluctuates There is a possibility. Therefore, in order to have reproducibility in this measurement, it is preferable that the detection efficiency of the atoms by 3DAP is made approximately constant at about 50%.

(Chemical composition)

Next, the chemical composition of the 6000-series aluminum alloy sheet will be described below. The 6000-series aluminum alloy plate to which the present invention is applied is required to have various properties such as excellent moldability, BH property, strength, weldability, and corrosion resistance as a plate for automobile shell plating.

In order to satisfy such a demand, the aluminum alloy plate preferably contains 0.2 to 2.0% of Mg, 0.3 to 2.0% of Si, and 0.005 to 0.3% of Sn, in terms of% by mass, And includes impurities. In addition, the percentages of the content of each element are all expressed in% by mass. Also, in the present specification, the percentage (mass%) based on mass is equal to the percentage (% by weight) based on weight. In addition, the content of each chemical component may be expressed as &quot; X% or less (however, 0% is not contained) &quot;

It is preferable that the 6000-series aluminum alloy plate to which the present invention is applied is an excess Si-type 6000-series aluminum alloy plate having a better BH property and a Si / Mg mass ratio Si / Mg of 1 or more. The 6000-series aluminum alloy sheet ensures moldability by lowering the stress at the time of press forming or bending, and at the same time, it hardens by aging due to heating at a relatively low temperature artificial aging treatment, And has an excellent age hardenability (BH property) which enables the strength to be secured and the proof strength to be improved. Among them, the excess Si-type 6000-series aluminum alloy plate is superior to the 6000-series aluminum alloy plate in which the mass ratio Si / Mg is less than 1, and this BH property is more excellent.

In the present invention, other elements other than Mg and Si are basically impurities or elements that may be contained, and the content is the content (allowable amount) of each element level according to the AA to JIS standards.

That is, from the viewpoint of recycling of resources, in the present invention, a 6000-series alloy containing a large amount of other elements other than Mg and Si as an additive element (alloying element) as well as high- Alloy scrap material, low-purity aluminum and the like are used in large quantities, the following other elements are inevitably incorporated in the raw mass. In addition, refining itself to reduce these elements drastically increases the cost, and it is necessary to allow a certain amount of refining. In addition, even when contained in a mass per unit area, there is a content range that does not impair the objects and effects of the present invention.

Therefore, in the present invention, the following elements are allowed to be contained within the upper limit amount in accordance with the AA to JIS standards stipulated below. Concretely, it is preferable that the content of Mn is not more than 1.0% (excluding 0%), the content of Cu is not more than 1.0% (excluding 0%), the content of Fe is not more than 1.0% ), Cr: not more than 0.3% (but not containing 0%), Zr: not more than 0.3% (excluding 0%), V: not more than 0.3% Ti: not more than 0.1%, preferably not more than 0.05% (but not containing 0%), Zn: not more than 1.0% (but not including 0%), Ag: not more than 0.2% ) May be contained in addition to the above basic composition in the above range. Further, when these elements are contained, the content of Cu is liable to deteriorate the corrosion resistance when the content is large, so that the content of Cu is preferably set to 0.7% or less, more preferably 0.3% or less. Further, when the content of Mn, Fe, Cr, Zr, and V is large, a relatively coarse compound is easily produced, and the heme bendability is easily deteriorated. Therefore, the Mn content is preferably 0.6% or less, more preferably 0.3% or less, and the Cr, Zr, or V content is preferably 0.2% or less, more preferably 0.1% or less. The content range, meaning or allowable amount of each element in the 6000-series aluminum alloy will be described below.

Si: 0.3 to 2.0%

Si, together with Mg, is an important element of the cluster formation defined in the present invention. In addition, an aged precipitate which contributes to the improvement of strength is formed at the time of the artificial aging treatment at the low temperature such as solid solution strengthening and paint baking treatment to exhibit the age hardening ability and to obtain the strength (proof strength) necessary for the outer panel of the automobile It is an essential element to obtain. Further, in the 6000 series aluminum alloy sheet of the present invention, it is the most important element to combine various properties such as total elongation which affects press formability. In order to exhibit excellent age hardening ability in the coating baking treatment at a lower temperature and in a short time after molding for the panel, Si / Mg is preferably set to 1.0 or more in mass ratio, and Si is more preferable than the excess Si- It is preferable to use a 6000-series aluminum alloy composition excessively contained in Mg.

If the Si content is too small, the absolute amount of Si is insufficient, so that the clusters defined by the present invention can not be formed to a predetermined density, and the coating baking hardenability is markedly reduced. Furthermore, it can not combine various properties such as total elongation required for each application. On the other hand, when the Si content is excessively large, coarse crystals and precipitates are formed, and the bending workability, the total elongation, and the like remarkably decrease. In addition, the weldability is remarkably hindered. Therefore, Si is set in the range of 0.3 to 2.0%. More preferably, the lower limit value is 0.6%, and the more preferable upper limit value is 1.4%.

Mg: 0.2 to 2.0%

Mg, together with Si, are important elements of the cluster formation specified in the present invention. It is an indispensable element for forming an aged precipitate that contributes to the improvement of strength together with Si during artificial aging treatment such as solid solution strengthening and paint baking treatment to exhibit an age hardening ability and to obtain a required strength as a panel.

If the Mg content is too small, the absolute amount of Mg is insufficient, so that the clusters specified by the present invention can not be formed at a density as high as the prescribed density, and the coating baking hardenability is markedly reduced. As a result, the required strength as a panel can not be obtained. On the other hand, when the Mg content is excessively large, coarse crystals and precipitates are formed, and the bending workability, the total elongation, and the like remarkably decrease. Therefore, the content of Mg is set in the range of 0.2 to 2.0%. More preferably, the lower limit value is 0.3%, and the more preferable upper limit value is 1.0%. It is also preferable that Si / Mg is in an amount such that Si / Mg is 1.0 or more in a mass ratio.

Sn: 0.005 to 0.3%

Sn trap diffusion at room temperature, suppressing diffusion at room temperature, and inhibiting cluster formation at room temperature. As a result, As strength at the initial stage of room temperature aging (7 days) and the room temperature aging period (100 days) is reduced, and hem forming ability is improved. In addition, when the baking paint is applied at high temperature, since the trapped holes are released, the diffusion can be promoted and the BH property can be increased. This makes it possible to increase the BH property in the case of containing Sn even at a cluster density of the same degree as compared with the case where Sn is not contained. When the content of Sn is too small, can not be suppressed cluster generated at room temperature, the number density of the cluster is too much or, the average rate for the N _total of the above _{N cluster (N cluster / N total} ) × 100 15 %. &Lt; / RTI &gt; As a result, the As proof strength after holding the room temperature for 100 days is excessively high, resulting in a decrease in the press formability and the hem forming property, and the number of the reinforcing phases (β ") generated during the artificial age hardening treatment is reduced, The lower limit value is 0.01%, and the more preferable upper limit value is 0.2%. The Al-Si-Mg-based aluminum alloy plate containing Sn is structurally Is different from that in which Sn is not contained. However, even if Sn is contained in the same manner, since the structure is different when the manufacturing conditions are different, the baking painting hardening can be suppressed It can not be said that a tissue having an effect of improving the quality is obtained.

(Manufacturing method)

Next, a method of producing the aluminum alloy sheet of the present invention will be described below. The aluminum alloy sheet of the present invention is manufactured by a conventional method or a known method. The aluminum alloy ingot having the composition of the 6000 series composition is subjected to homogenization heat treatment after casting, subjected to hot rolling and cold rolling, , And further subjected to a tempering treatment such as solution polymerization or the like.

However, in order to control the clusters of the present invention in order to improve the BH property in these manufacturing processes, as described later, it is necessary to carry out a solution treatment and a quenching treatment and a proper quenching (cooling) quenching temperature, It is necessary to control it more appropriately. In other processes, there are also preferable conditions for controlling the clusters within the scope of the present invention.

(Melting, casting cooling rate)

First, in the melting and casting steps, the molten aluminum alloy melt-adjusted within the composition range of the 6000 system component is appropriately selected and cast by a conventional melt casting method such as a continuous casting method or a semi-continuous casting method (DC casting method). Here, in order to control the clusters within the specified range of the present invention, it is preferable that the average cooling rate at the time of casting is as large as possible (as fast as possible) from the liquidus temperature to the solidus temperature at 30 DEG C / min or more.

If the temperature (cooling rate) control in the high temperature region at the time of casting is not carried out, the cooling rate in this high temperature region is inevitably slowed down. When the average cooling rate in the high temperature region is slowed, the amount of the crystals to be produced in a large temperature range in the high temperature region becomes large, and the size and the amount of deviation of the crystals in the plate width direction and the thickness direction of the ingot also become large . As a result, there is a high possibility that the regulatory clusters can not be controlled within the scope of the present invention.

(Homogenization heat treatment)

Subsequently, the cast aluminum alloy ingot is subjected to homogenizing heat treatment prior to hot rolling. This homogenizing heat treatment (cracking treatment) is intended to homogenize the structure, that is, to eliminate segregation in crystal grains in the ingot texture. And is not particularly limited as long as it is a condition for achieving this object, and it may be a usual one-time or one-stage processing.

The homogenization heat treatment temperature is suitably selected in the range of 500 DEG C or higher and lower than the melting point, and the homogenization time is 4 hours or more. If the homogenization temperature is low, segregation in the crystal grains can not be sufficiently eliminated, and this acts as a starting point of fracture, so that elongation flangeability and bending workability are deteriorated. Thereafter, even if the hot rolling is immediately started or the hot rolling is started after cooling to a suitable temperature, the number of clusters defined in the present invention can be controlled to several densities.

After the homogenization heat treatment is performed, the temperature between 300 ° C and 500 ° C is cooled to room temperature at an average cooling rate of 20 to 100 ° C / h, and then the temperature is increased to 350 ° C to 450 ° C at an average heating rate of 20 to 100 ° C / Reheating, and hot rolling may be started in this temperature range.

If the conditions of the average cooling rate after the homogenization heat treatment and the reheating rate thereafter are exceeded, the possibility of forming a coarse Mg-Si compound increases.

(Hot rolling)

Hot rolling consists of rough rolling (ingot rolling) and finish rolling in accordance with the sheet thickness to be rolled. In these rough rolling and finishing rolling processes, a rolling machine such as a reverse type or tandem type is suitably used.

At this time, under the condition that the hot rolling (rough rolling) start temperature exceeds the solidus temperature, burning occurs, so that hot rolling itself becomes difficult. When the hot rolling start temperature is less than 350 캜, the load during hot rolling becomes excessively high, and hot rolling itself becomes difficult. Therefore, the hot-rolling start temperature is in the range of 350 占 폚 to the solidus line temperature, more preferably 400 占 폚 to the solidus line temperature.

(Annealing of hot rolled sheet)

Annealing (preliminary annealing) of the hot-rolled sheet before cold rolling is not always necessary, but may be carried out in order to further improve the properties such as formability by making fine grains and optimizing aggregate structure.

(Cold rolling)

In the cold rolling, the hot-rolled sheet is rolled to produce a cold-rolled sheet (including a coil) having a desired final sheet thickness. However, in order to make the crystal grains more finer, the cold rolling rate is preferably 60% or more, and intermediate annealing may be performed between the cold rolling passes for the same purpose as the above-mentioned coarse annealing.

(Solubilization and etching treatment)

After cold rolling, solution treatment is carried out. The solution treatment treatment process may be heating and cooling by a conventional continuous heat treatment line and is not particularly limited. However, it is preferable to obtain a sufficiently large amount of each element and as described above, the crystal grains are preferably finer. Therefore, the crystal grains are heated to a solution treatment temperature of 520 DEG C or higher and a melting temperature or lower at a heating rate of 5 DEG C / To 10 seconds.

From the viewpoint of suppressing the formation of coarse grain boundary compounds which decrease the formability and the hempability, it is preferable that the average cooling rate from the solution temperature to the quenching temperature is 3 DEG C / s or more. If the cooling rate of the solution is small, coarse Mg ₂ Si and single Si are produced during cooling, and the formability is deteriorated. Further, the amount of the solution after the solution is lowered and the BH property is lowered. In order to ensure this cooling rate, the cooling process is performed by selecting the cooling means and conditions such as air cooling, mist, spray, immersion, etc., such as a fan.

(Temperature holding treatment after quenching)

Here, in the first embodiment of the present invention, the quenching treatment does not cool the solution treated plate to room temperature but stops cooling (quenching) in a temperature region T where the plate is at 80 to 130 캜, A holding process of keeping the temperature within the temperature range for a predetermined time t, and then cooling to room temperature, regardless of cooling means such as cold cooling or forced cooling. The holding (treatment) at the temperature of 80 to 130 占 폚 may be conducted by heating or by non-heating, and may be isothermal or temperature gradient. However, the holding time t at this temperature is determined so as to satisfy the following equation in relation to the above-mentioned quenching stop temperature T.

1.6 × 10 ⁴ × exp [-0.096 × T] <t <4.3 × 10 ⁵ × exp [-0.097 × T]

In the present embodiment, the relationship among various stop temperature, holding time, and the like was examined in detail for stopping conditions of the etching process for obtaining a prescribed size distribution of clusters. As a result, the size distribution of clusters during temperature holding after quenching was greatly influenced by the diffusion distances of Mg and Si, and as a result of the analysis, it was found that the diffusion distances of Mg and Si were 1.3 × 10 ^-9 m to 6.5 × 10 &lt; ^-9 &gt; m.

This diffusion distance of Mg or Si is expressed by the following expression (3). , D ₀ of the equation is the diffusion coefficient, which is represented by the formula in Equation 4, 6.2 × 10 ^- is ⁶ (㎡ / s). Q is the activation energy of diffusion and 11500 (J / mol). R is the gas constant and 8.314.

The upper limit value and the lower limit value of the temperature holding time t after the quiescent stop are set to a relationship with the quenching stop temperature T in order to obtain the range of the preferable diffusion distance of Mg or Si, Was determined as in the above formula.

By the cooling stop at a relatively high temperature and the temperature holding treatment in this etching treatment, the size distribution of a predetermined cluster defined in the present embodiment is obtained. Also, the average number density of the atomic aggregates defined in the present embodiment of not less than 2.5 × 10 ²³ atoms / m 3 and not more than 20.0 × 10 ²³ atoms / m 3 is obtained. This is because most of the atomic assemblies defined in the present embodiment are uniformly or similarly formed in the steps of cooling stop at a relatively high temperature and temperature holding treatment in this etching treatment.

In other words, even if any one or both of the Mg atom and the Si atom are contained in a total of 10 or more, and either one of the Mg atom and the Si atom contained in these atoms is used as a reference, Most of the atomic assemblies in which the distance between one atom and one of the atoms is 0.75 nm or less are formed in the process of the cooling stoppage and the temperature holding treatment at the relatively high temperature in this etching treatment. At the same time, since the sizes of most of the atomic assemblies formed during the temperature holding treatment are equal or similar, the average radius of the circle-equivalent diameter is 1.15 nm or more and 1.45 nm or less, and the standard deviation of the radius of the circle- And has a uniformity in size that satisfies the condition of 0.45 nm or less.

As a result, in the plate subjected to cooling stop and temperature holding at a relatively high temperature in this etching treatment, the number of clusters formed by room temperature aging at room temperature after the temperature holding treatment is reduced and the room temperature aging is reduced. Thus, the press formability including bending workability is improved. Even after holding for a long time at room temperature, by heating at 170 占 폚 for 20 minutes in artificial aging treatment such as panel painting baking treatment or the like, 0.2 % Strength difference of 90 MPa or more.

Even when the reheating treatment (annealing treatment) is carried out after the quenching at a high temperature and the quenching to the room temperature is carried out as in the prior art or when the quenching temperature at the time of quenching is too low to room temperature, It is possible. However, even if clusters of uniform or similar sizes defined in the present embodiment are formed, there is a possibility that the absolute number is not small or the standard deviation becomes large. This causes disadvantage that the cluster specification of the present embodiment can not be satisfactorily reproduced.

(Cooling after the temperature holding treatment)

The cooling to the room temperature after the temperature holding treatment may be forced quenching using the cooling means in the above-mentioned method in order to improve the production efficiency even when the cooling is performed. That is, since uniform or similar clusters of the sizes specified in the present embodiment are produced by the temperature holding process, it is unnecessary to perform forced quenching such as the conventional reheating process, and control of the complicated average cooling rate for various stages.

(Reheating treatment)

Further, in the second embodiment of the present invention, reheating treatment is performed after the solution coating treatment. This reheating treatment is carried out in two stages, and the first stage is carried out in a temperature range of 80 to 250 占 폚 at a reaching temperature (heating temperature) in a range of several seconds to several tens of seconds. The cooling after the reheating treatment in the first stage may be forced quenching by cooling means for cooling the solution in order to improve production efficiency even in cooling. Subsequently, after the completion of the cooling after the reheating treatment at the first stage, the reheating at the second stage is carried out at a temperature within the range of 70 to 130 占 폚 for the reheating temperature in the range of 3 to 48 hours . If the holding time at room temperature after completion of cooling after the reheating treatment in the first stage exceeds 24 hours, the room temperature aging proceeds excessively and the effect of the reheating treatment at the second stage is impaired.

When deviated from such reheating treatment conditions, it is difficult to set the average content of Mg and Si contained in the above-described aggregate of atoms to 10% or more and 30% or less of the total content of Mg and Si contained in the aluminum alloy sheet Loses. For example, if the arrival temperature of reheating in the first stage is less than 100 占 폚 or the arrival temperature of reheating in the second stage is less than 70 占 폚, Mg-Si clusters promoting BH property are not sufficiently generated. On the other hand, if the reaching temperature of the reheating is too high, some of the intermetallic compound phases such as? "And? '' That are different from the clusters are formed, so that the number of clusters is likely to be less than several densities and the BH property is too low. beta ', and the moldability tends to deteriorate.

The cooling to the room temperature after the reheating treatment at the second stage may be forced quenching using the cooling means at the time of cooling to improve the production efficiency even in the cooling. That is, since uniform or similar clusters of the sizes specified in the present embodiment are produced by the temperature holding process, it is unnecessary to perform forced quenching such as the conventional reheating process, and control of the complicated average cooling rate for various stages.

(Processing with a deformation amount of 0.1 to 5%)

In the third embodiment of the present invention, in order to further improve the BH property, the plate is subjected to a processing of 0.1 to 5% in deformation amount from the completion of the solution treatment and the quenching treatment to the reheating treatment described later . The means is appropriately selected by leveler correction, skin pass rolling, and the like. The plating is performed on the plate at a strain of 0.1 to 5% from the completion of the solution treatment and the quenching treatment until the reheating treatment is performed, whereby the Mg atoms are more rich than the clusters in which the Si atoms are rich, It becomes easy to generate one cluster, and it becomes easy to make the ratio of the atomic mass of Mg / Si ratio not less than 1/2 to 0.70 or more. On the other hand, if the amount of deformation is larger than 5%, the hem forming ability tends to deteriorate. Although this mechanism has many unclear points, it is assumed as follows. That is, after the solution treatment, the plate is subjected to the processing of 0.1 to 5% in deformation amount, whereby the freezing vacancy after the solution treatment is reduced, and as a result, the diffusion at room temperature is suppressed. As a result, Si-rich clusters produced at room temperature are hardly produced, and it is assumed that the ratio of the atomic aggregates having a Mg / Si ratio of 1/2 or more can be made to be 0.70 or more.

(Maintained at room temperature)

In order to further increase the BH property, the room temperature holding time from the end of the solution treatment and the quenching treatment to the start of the reheating treatment including the processing step of 0.1 to 5% . By shortening the room temperature holding time, the ratio of the atomic mass of Mg / Si ratio of not less than 1/2 is likely to be 0.70 or more. The room temperature holding time is preferably as short as possible, and the solution treatment and shaking treatment and the reheating treatment may be continuous so that there is little time difference, and the lower limit time is not particularly set.

(Reheating treatment)

It is preferable that the temperature reached in the reheating treatment is in the range of 80 to 160 ° C and the holding time is in the range of 3 to 100 hr. If the reaching temperature of reheating is less than 80 캜 or less than 3 hr, Mg-Si clusters promoting BH properties are not sufficiently generated, and as a result, the ratio of clusters having a Mg / Si ratio of 1/2 or more tends to be less than 0.70. On the other hand, under the condition that the reaching temperature of the reheating exceeds 160 DEG C or the holding time exceeds 100 hours, a part of the intermetallic compound phase such as? "Or?" Which is different from the cluster is formed, And the BH property becomes too low. Also, due to β "and β ', the moldability tends to deteriorate.

The cooling to the room temperature after the reheating treatment may be forced quenching by using the cooling means at the time of the above-mentioned for efficiency of production even if the cooling is performed. That is, since uniform or similar clusters of the sizes specified in the present embodiment are produced by the temperature holding process, it is unnecessary to perform forced quenching such as the conventional reheating process, and control of the complicated average cooling rate for various stages.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is of course not limited by the following Examples, and it is also possible to carry out the present invention by modifying it appropriately within a range that is suitable for the purpose , All of which are included in the technical scope of the present invention.

Example

Next, an embodiment of the present invention will be described. First, an embodiment according to the first embodiment of the present invention will be described. A 6000-series aluminum alloy plate having different cluster conditions defined in the present embodiment was separately manufactured by quenching at a relatively high temperature and holding treatment at that temperature at the time of solution treatment and quenching treatment, BH properties (coating baking hardenability) after the maintenance for the day and after the maintenance for 100 days were respectively evaluated. In addition, hem forming properties as press formability and bending workability were also evaluated.

The cluster condition according to the present embodiment is a standard deviation of the average number density of the atomic aggregates, the average radius of the circle equivalent diameter, and the radius of the circle equivalent diameter. The aggregate of these atoms means that a total of 10 or more of Mg atoms and / or Si atoms are contained in total, and even if any one of Mg atoms and Si atoms contained in these atoms is used as a reference, And the distance between the atom and any one of atoms adjacent to the other atom is 0.75 nm or less.

As shown in Table 2, the 6000-series aluminum alloy sheet having the composition shown in Table 1 was subjected to the above-described separation-producing process in such a manner that the cooling stop temperature T at a relatively high temperature in the smoothing treatment after the solution treatment, And the holding time t (h) at the stop temperature was varied. Here, in the indication of the content of each element in Table 1, the indication with the numerical value of each element as blank indicates that the content thereof is below the detection limit.

Specific manufacturing conditions of the aluminum alloy plate were as follows. Aluminum alloy ingots of the respective compositions shown in Table 1 were commonly dissolved by the DC casting method. At this time, in all of the examples, the average cooling rate at the time of casting was 50 ° C / min from the liquidus temperature to the solidus temperature. Subsequently, the ingot was subjected to a crack treatment at 540 DEG C for 4 hours in all of the examples in common, and hot rolling was started. In each of the examples, hot rolled sheets (coils) were hot rolled up to a thickness of 3.5 mm by subsequent finish rolling. The aluminum alloy sheet after hot rolling was subjected to rough annealing at 500 ° C for 1 minute in common to all of the examples and then subjected to cold rolling at a machining ratio of 70% without intermediate annealing during the cold rolling pass. 1.0 mm thick cold-rolled sheet (coil).

These cold-rolled sheets (coils) were continuously subjected to tempering treatment (T4) while being rewound and wound by a continuous heat treatment facility in common in all the examples. Concretely, the heating and quenching treatment in which the average heating rate up to 500 ° C is set at 10 ° C / sec, the temperature is raised to the solution treatment temperature shown in Table 2, and the solution is immediately cooled at the average cooling rate shown in Table 2 Respectively. At this time, in each example in which quenching (cooling) at a high temperature was stopped and the holding treatment at the temperature was carried out, cooling to a quenching temperature T shown in Table 2 And the temperature holding treatment at the holding time t (unit h) was performed at that temperature. This temperature holding treatment was carried out in a holding furnace maintained at each quenching temperature in the continuous type heat treatment equipment. Further, the temperature holding time (actual holding time) t of the actual plate (coil) is 1.6 x 10 ⁴ x exp [-0.096 x T] <t <4.3 x 10 ⁵ x exp [-0.097 x T]. In this equation, the holding time of the lower limit and the upper limit calculated from the respective holding temperatures T and the holding times (actual holding times) of the actual plates (coils) are shown in Table 2 by unit h (time). The cooling after the temperature was maintained was forcibly quenched at a cooling rate of 100 ° C / S by using the cooling means in the above-mentioned all of the examples in which the temperature was maintained.

The blank (blank) was cut out from each final product plate after leaving the room temperature for 7 days and 100 days after the tempering treatment, and the properties of each of the blank plates were measured and evaluated. In addition, tissue observation using 3DAP was performed only for samples 7 days after the tempering treatment. The results are shown in Table 3.

(cluster)

First, the structure at the center of the thickness of the plate was analyzed by the above-described 3DAP method, and the average number density (x 10 ²³ pieces / m 3) of the clusters defined in the present embodiment and the average radius Nm) and the standard deviation of the radius of the circle-equivalent diameter were respectively obtained by the above-mentioned method. The results are shown in Table 3.

In Table 2, it is described that, in the cluster conditions according to the present embodiment, at least 10 or more of Mg atoms and Si atoms are contained in a total of at least 10 atoms of Mg and Si atoms have. Also, even if any one of the Mg atom and the Si atom contained in these atoms is used as a reference, the distance between the reference atom and any one of atoms adjacent to the other atom is 0.75 nm or less, Nm or less &quot;.

(Coating baking hardenability)

The 0.2% proof stress (As proof strength) and the total elongation (As total elongation) of each of the release boards after being left at room temperature for 7 days or 100 days after the tempering treatment were determined by a tensile test. Each of these respective publicly known plates was aged at room temperature for 7 days and at room temperature for 100 days and then subjected to an artificial aging hardening treatment at 185 ° C for 20 minutes (after BH) (BH post hysteresis) was determined by a tensile test. Then, the BH properties of the respective release boards were evaluated from the difference (history increase amount) between the 0.2% proof stresses.

In the tensile test, a No. 5 test specimen (25 mm x 50 mm GL x thickness) of JISZ2201 was taken from each of the above described test plates and subjected to a tensile test at room temperature. At this time, the tensile direction of the test piece was the direction perpendicular to the rolling direction. The tensile speed was set to 5 mm / min to 0.2% proof stress and to 20 mm / min after proof stress. The number of N of the mechanical property measurement was 5, and the average value was calculated. Further, in the test piece for measuring the strength after the BH test, 2% of the prescribed deformation simulating the press forming of the plate was given to the test piece by the tensile tester, and then the BH treatment was performed.

(Hem-forming property)

The hempability was measured only for each of the publicly available plates after 7 days or 100 days of the tempering treatment. In the test, a rectangular test piece having a width of 30 mm was used. After a 90 ° bend of the inner bend R1.0 mm by the down flange, an inner plate having a thickness of 1.0 mm was inserted and the bend was again bent inward at about 130 degrees , And the flat hem was processed by bending it by 180 degrees and bringing the end portion into close contact with the inner portion.

Surface conditions such as surface roughening, minute cracking, and large cracking of the bent portion of the flat hem were visually observed and evaluated visually by the following criteria.

0; Cracks, no surface roughness, 1; Surface roughness of hardness, 2; Deep surface roughness, 3; Micro-surface cracks, 4; Continuous surface cracks in a line, 5; Fracture

As shown in the alloy numbers 0 to 12 in Table 1 and the numbers 0, 1, 7, 13 and 19 to 27 in Table 2, each embodiment can be manufactured within the composition range of the present invention, , And a tempering process is performed. As a result, each of these embodiments satisfies the cluster condition defined in the present embodiment, as shown in Table 2. As a result, each of the embodiments is excellent in BH property even after coating and curing at a low temperature in a short time after aging at a long-term room temperature after the tempering treatment. Further, as shown in Table 3, even after long-term room temperature aging after the tempering treatment, since the As proof strength is comparatively low, the press formability to automobile panels and the like is excellent and the hem workability is also excellent. That is, according to the present invention, even when the body paint baking treatment is carried out after a long-term room temperature aging for 100 days, the Al-Si-Mg system can exhibit a higher BH property with a strength difference of 100 MPa or more and press formability and bending workability It is possible to provide an aluminum alloy plate.

In Comparative Examples 2, 8 and 14 of Table 2, Inventive Alloys Examples 1, 2 and 3 of Table 1 are used. However, in each of these comparative examples, as shown in Table 2, the cooling rate of the solution treatment is too small beyond the preferable condition. As a result, since the average radius standard deviation of the clusters defined in the present embodiment is deviated, and compared with the case of the same alloy composition as in the case of the inventive example, the room temperature aging time is large and the As proof strength after maintaining the room temperature for 100 days is relatively high. The sex and the hematility are falling, and the BH sexuality is falling.

Comparative Examples 3 to 6, 9 to 12 and 15 to 18 in Table 2 use Invention Alloys 1, 2 and 3 of Table 1. However, in each of these comparative examples, as shown in Table 2, the temperature holding treatment condition after the above quenching is out of the preferable range. As a result, any of the cluster conditions specified in the present embodiment is deviated, and the As proof strength after maintaining the room temperature for 100 days is relatively high, compared with the case of the same alloy composition, and the press formability and hem forming property Or the BH castle is falling.

Comparative Examples 28 to 37 in Table 2 were prepared in a preferred range including the temperature holding treatment conditions after the quenching, but alloy Nos. 13 to 22 of Table 1 were used, and Mg, Si , The Sn content is out of the range of the present invention, or the amount of the impurity element is excessively large. As a result, as shown in Table 3, these Comparative Examples 28 to 37 show that the As proof strength after holding at room temperature for 100 days is relatively high, so that the press formability and the hem forming property of the automobile panel or the like are lowered, The BH castle is falling. Particularly, in Comparative Example 30 in which the Sn content is too small, the room temperature aging was not suppressed, and the As proof strength after holding the room temperature for 100 days was too high, resulting in a decrease in press formability and hem forming property and a BH hardness increase of less than 100 MPa not. Further, in Comparative Example 31 in which Sn was excessively large, cracks were generated during hot rolling, and the plate itself could not be produced.

Comparative Example 28 is the alloy 13 in Table 1, and Si is excessively small.

Comparative Example 29 is the alloy 14 of Table 1, and Si is excessively large.

Comparative Example 30 is the alloy 15 of Table 1, and Sn is excessively small.

Comparative Example 31 is the alloy 16 of Table 1, and Sn is excessively large.

Comparative Example 32 is the alloy 17 shown in Table 1, and Fe is excessively large.

Comparative Example 33 is the alloy 18 shown in Table 1, and Mn is excessively large.

Comparative Example 34 is the alloy 19 shown in Table 1, and Cr and Ti are excessively large.

Comparative Example 35 is the alloy 20 of Table 1, and Cu is excessively large.

Comparative Example 36 is the alloy 21 shown in Table 1, and Zn is excessively large.

Comparative Example 37 is the alloy 22 of Table 1, and Zr and V are excessively large.

From the results of the above examples, it is proved that there is a need to satisfy all the conditions of the clusters defined in the above-described embodiment for improving the BH property after long-term room temperature aging. In addition, a critical meaning or effect of each component requirement or preferable manufacturing conditions in the present embodiment for obtaining such cluster conditions, BH properties, and the like is also supported.

Next, an embodiment according to the second embodiment of the present invention will be described. A 6000-series aluminum alloy plate having different compositions and cluster conditions specified in the present embodiment was separately produced by two-step reheating treatment conditions after solution treatment and quenching treatment. The structures (clusters) and strength, BH properties (coating baking hardenability), and hem forming properties as press formability and bending workability of the respective samples were also evaluated after 100 days of storage at room temperature.

The cluster condition is the total amount of atoms of Mg and Si existing in the aggregate of atoms, the average radius of circle equivalent diameter, and the average number density. The aggregate of these atoms means that a total of 10 or more of Mg atoms and / or Si atoms are contained in total, and even if any one of Mg atoms and Si atoms contained in these atoms is used as a reference, And the distance between one atom of any of the adjacent atoms is 0.75 nm or less.

Specific manufacturing conditions of the aluminum alloy plate were as follows. Aluminum alloy ingots of the respective compositions shown in Table 4 were commonly dissolved by the DC casting method. At this time, in all of the examples, the average cooling rate at the time of casting was 50 ° C / min from the liquidus temperature to the solidus temperature. In the display of the content of each element in Table 4 showing the composition of the 6000-series aluminum alloy plate of each example, the indication in which the numerical value in each element is a blank indicates that the content thereof is below the detection limit, 0%.

Subsequently, the ingot was subjected to a crack treatment at 540 DEG C for 4 hours in all of the examples in common, and hot rolling was started. In each of the examples, hot rolled steel sheets were hot rolled up to a thickness of 3.5 mm by subsequent finish rolling. The aluminum alloy sheet after hot rolling was subjected to rough annealing at 500 ° C for 1 minute in common to all of the examples and then subjected to cold rolling at a machining ratio of 70% without intermediate annealing during the cold rolling pass. 1.0 mm thick.

These cold-rolled sheets were subjected to solution treatment in a potassium nitrate solution of 560 占 폚 in a common manner in all of the examples, followed by holding for 10 seconds after reaching the target temperature and quenching by water cooling. After the quenching treatment was finished, the first-stage pre-aging treatment at 100 to 250 ° C was carried out under the conditions shown in Table 5, and water cooling to room temperature was carried out. Thereafter, the preliminary aging treatment at the second stage was carried out at 70 to 130 ° C, and the solution was cooled to room temperature by water cooling. Here, in this embodiment, cooling is performed by water cooling after the reheating process in the first stage and the second stage, respectively, but the same structure can be obtained even if this cooling is cold.

After these tempering treatments, the plates (blank) were cut out from each plate after being left at room temperature for 100 days, and the structure and strength (AS proof stress) of each of the plates were measured. The observation of the structure using the 3DAP was performed only for the sample after 100 days after the tempering treatment. The results are shown in Table 6.

(cluster)

After the 100 days of room temperature aging, the structure in the plate thickness direction cross section of the central portion of the plate thickness of the publicly known plate was analyzed by the above-described 3DAP method, and the number of clusters (X 10 ²³ / m 3), the average radius of the circle-equivalent diameter (nm), the ratio of the _total amount of Mg and Si atoms contained in the _cluster N _{cluster to} the _total number N of the _total number of Mg and Si atoms measured Respectively.

The results are shown in Table 6. In Table 6, those containing at least one of Mg atoms and Si atoms or a total of 10 atoms or more among the cluster conditions according to the present embodiment are simply described as "at least 10 atoms of Mg and Si" have. Also, even if any one of the Mg atom and the Si atom contained in these atoms is used as a reference, the distance between the reference atom and any one of atoms adjacent to the other atom is 0.75 nm or less, Nm or less &quot;.

In the measurement by the 3DAP method, three pieces of each of the twin pillars having a length of 30 mm, a width of 1 mm, and a thickness of 1 mm were cut out from a publicly known plate having a thickness of 1 mm at intervals of 1 mm in the width direction with a precision cutting device , And then the prism was finely worked by electrolytic polishing to prepare a needle-like specimen having a radius of the tip of 50 nm. As a result, the measurement site measures the vicinity of the center of the plate thickness. The aluminum alloy plate sample having the tip portion formed into a needle shape was subjected to 3DAP measurement using "LEAP3000" manufactured by Imago Scientific Instruments. (X 10 ²³ / m 3) of the clusters, the average radius of the circle-equivalent diameter (nm), and the total amount N _cluster of the total number of Mg and Si atoms contained in the _clusters , The ratio of N _total , the number of Mg and Si atoms measured, was averaged. Therefore, each value in this embodiment is an average value of the number of measurements N = 3. In addition, the measurement volume by the 3DAP method is approximately 1.0 x 10 &lt; ^-22 &gt; to 10 &lt; ^-21 &gt;

(Coating baking hardenability)

The 0.2% proof stress (As proof strength) and the 0.2% proof strength (after BH) after artificial aging hardening treatment at 185 占 폚 for 20 minutes were the same as the mechanical properties of the respective release plates after 100 days of aging at room temperature Tensile test. Then, the BH properties of the respective release boards were evaluated from the difference (history increase amount) between the 0.2% proof stresses.

In the tensile test, a No. 5 test specimen (25 mm x 50 mm GL x thickness) of JISZ2201 was taken from each of the above described test plates and subjected to a tensile test at room temperature. At this time, the tensile direction of the test piece was set to the direction perpendicular to the rolling direction. The tensile speed was set to 5 mm / min to 0.2% proof stress and to 20 mm / min after proof stress. The number of N of the mechanical property measurement was 5, and the average value was calculated. Further, in the test piece for measuring the strength after the BH test, 2% of the prescribed deformation simulating the press forming of the plate was given to the test piece by the tensile tester, and then the BH treatment was performed.

(Hem-forming property)

The hempability was measured only for each of the publicly available plates after 7 days or 100 days of the tempering treatment. In the test, a rectangular test piece having a width of 30 mm was used. After a 90 ° bend of the inner bend R1.0 mm by the down flange, an inner portion having a thickness of 1.0 mm was inserted and the bent portion was further inwardly Preheme processing for bending, 180 degree bending, and flat hem processing for bringing the end portion into close contact with the inner portion was performed.

Surface conditions such as surface roughening, minute cracking, and large cracking of the bent portion of the flat hem were visually observed and evaluated visually by the following criteria.

0; Cracks, no surface roughness, 1; Surface roughness of hardness, 2; Deep surface roughness, 3; Micro-surface cracks, 4; Continuous surface cracks in a line, 5; Fracture

As shown in Inventive Examples, alloy numbers 23 to 32 in Table 4 and numbers 38, 39, 45, 51 and 57 to 62 in Table 5, respectively, each embodiment is within the component composition range of the present invention, Manufacturing and tempering processes are performed in the range of conditions. As a result, each of these examples satisfies the cluster condition specified in this embodiment, as shown in Table 6. [ That is, clusters, a preferred average number density (3.0 × 10 ²⁴ gae / ㎥ or more) to that following, the ratio for the N _total of N _cluster satisfy (N _cluster / N _total) satisfies the predetermined condition in the embodiment × 100 is 1% or more and 15% or less, and the average radius of circle equivalent diameter is 1.20 nm or more and 1.50 nm or less.

As a result, each example shows excellent press formability to automobile panels and the like because of excellent BH property and relatively low As proof strength even after prolonged room temperature aging such as 100 days as shown in Table 6, great. That is, according to the present invention, even when the body paint baking treatment is carried out after a long-term room temperature aging for 100 days, the Al-Si-Mg system can exhibit a higher BH property with a strength difference of 100 MPa or more and press formability and bending workability It is possible to provide an aluminum alloy plate.

Comparative Examples 39 to 44, 46 to 50, and 52 to 56 in Table 5 use alloy alloys Examples 24, 25, and 26 of Table 4. However, in each of these comparative examples, as shown in Table 5, the two-step reheating treatment condition is deviated from the preferable condition after the solution treatment and the quenching treatment.

In Comparative Examples 40, 46 and 52, the reheating process is only the second stage.

In Comparative Examples 41, 47, and 53, the reheat treatment temperature in the first stage is too low.

In Comparative Examples 42, 48, and 54, the reheat treatment temperature in the first stage is excessively high.

In Comparative Examples 43, 49, and 55, the reheat treatment temperature in the second stage is excessively high.

In Comparative Examples 44, 50, and 56, the reheat treatment temperature in the second stage is too low.

Therefore, in each of these comparative examples, as shown in Table 6, the average radius of the circle-equivalent diameter of the atomic aggregate is less than 1.20 nm, exceeds 1.50 nm, or is calculated as N _cluster / N _total × 100 , And the average ratio of Mg and Si atoms contained in the atom aggregate is less than 1% or exceeds 15%, which is outside the scope of the present embodiment. As a result, compared with Inventive Examples 39, 45, and 51 which are the same alloy compositions, the As proof strength after holding at room temperature for 100 days is relatively high, so that the press formability and hem forming property to automobile panels are lowered and the BH property is lowered.

Comparative Examples 63 to 72 in Table 5 were prepared in a preferable range including the above-mentioned tempering treatment. However, alloys Nos. 33 to 42 in Table 4 are used, and the contents of Mg, Si, and Cu, which are essential elements, It is out of the scope of the invention, or the amount of the impurity element is excessively large. As a result, in these Comparative Examples, as shown in Table 6, the BH property and the hem-forming property were respectively lower than those of the respective examples. In particular, Sn is too small Table 6. Comparative Example 65 has been increased the number density of the cluster, the average ratio _{(N cluster / N total) ×} 100 also by too high excess of 15% for the N _total of the above N _cluster . As a result, the room temperature aging is not suppressed, and the As proof strength after holding at room temperature for 100 days is too high to decrease the press formability and hempability, and the BH resistance is not as high as less than 100 MPa in the increase in the yield strength. Further, in Comparative Example 66 in which Sn was excessively large, cracks were generated during hot rolling, and the plate itself could not be produced.

Comparative Example 63 is the alloy 33 of Table 4, and Si is excessively small.

Comparative Example 64 is the alloy 34 shown in Table 4, and Si is excessively large.

Comparative Example 65 is the alloy 35 of Table 4, and Sn is excessively small.

Comparative Example 66 is the alloy 36 shown in Table 4, and Sn is excessively large.

Comparative Example 67 is the alloy 37 in Table 4, and Fe is excessively large.

Comparative Example 68 is the alloy 38 in Table 4, and Mn is excessively large.

Comparative Example 69 is the alloy 39 shown in Table 4, and Cu is excessively large.

Comparative Example 70 is the alloy 40 of Table 4, and Cr is excessively large.

Comparative Example 71 is the alloy 41 shown in Table 4, and Ti and Zn are excessively large.

Comparative Example 72 is the alloy 42 of Table 4, and Zr and V are excessively large.

From the results of the above examples, it is proved that it is necessary to satisfy the conditions of the clusters defined in the present embodiment in order to be able to exhibit higher BH properties and post-BH loadings even when the strength before baking is increased. In addition, a critical meaning or effect of each component requirement or preferable manufacturing conditions in the present embodiment for obtaining such cluster conditions, BH properties, and the like is also supported.

Next, an embodiment of the third embodiment of the present invention will be described. The 6000 aluminum alloy sheet having different composition and cluster conditions specified in the present embodiment is used for the time from the completion of the solution treatment and the quenching treatment to the start of the reheating treatment and the processing rate of the skin pass rolling after completion of the solution treatment and quenching treatment , Reheating treatment conditions, and the like. The BH properties (coating baking hardenability) after each of these examples were maintained at room temperature for 100 days were evaluated. In addition, the hem-forming property as the bending workability was also evaluated.

In the display of the content of each element in Table 7 showing the composition of the 6000-series aluminum alloy plate of each example, the indication in which the numerical value in each element is blank indicates that the content thereof is below the detection limit.

Specific manufacturing conditions of the aluminum alloy plate were as follows. Aluminum alloy ingots of the respective compositions shown in Table 7 were commonly dissolved by the DC casting method. At this time, in all of the examples, the average cooling rate at the time of casting was 50 ° C / min from the liquidus temperature to the solidus temperature. Subsequently, the ingot was subjected to a crack treatment at 540 DEG C for 4 hours in all of the examples in common, and hot rolling was started. In each of the examples, hot rolled sheets were hot rolled to a thickness of 3.5 mm by subsequent finish rolling. The aluminum alloy sheet after hot rolling was subjected to rough annealing at 500 ° C for 1 minute in common to all of the examples and then subjected to cold rolling at a machining ratio of 70% without intermediate annealing during the cold rolling pass. 1.0 mm thick.

These cold-rolled sheets were subjected to solution treatment in common in all of the examples at a temperature of 550 占 폚 with potassium nitrate, held for 10 seconds after reaching the target temperature, and subjected to heat treatment by water cooling. After completion of the smelting treatment, skin pass rolling with a deformation amount of 0 to 5% shown in Table 8 was immediately performed by a rolling mill and kept at room temperature until the start of the reheating treatment for the time shown in Table 8. Thereafter, the annealing furnace was subjected to the reheating treatment at the temperature and the holding condition shown in Table 8, and the cooling was performed after the holding for the predetermined time.

After these tempering treatments, a blank (blank) was cut out from each final product plate after being allowed to stand at room temperature for 100 days, and the properties of each blank were measured and evaluated. Tissue observation using 3DAP was performed only for samples 100 days after the tempering treatment. The results are shown in Table 9.

(cluster)

First, the structure at the center of the thickness of the plate was analyzed by the above-described 3DAP method. The average number density (x 10 ²³ pieces / m 3) of the clusters defined in this embodiment, the number of Mg atoms and the number of Si atoms (Mg / Si) of not less than 1/2 was obtained by the above-mentioned method, respectively. The results are shown in Table 9.

In Table 9, those containing at least one of Mg atoms and Si atoms or a total of 10 or more of the Mg atoms and the Si atoms in the cluster conditions according to the present embodiment are simply described as "at least 10 atoms of Mg and Si" have. Also, even if any one of the Mg atom and the Si atom contained in these atoms is used as a reference, the distance between the reference atom and any one of atoms adjacent to the other atom is 0.75 nm or less, Nm or less &quot;.

(Coating baking hardenability)

The 0.2% proof stress (As proof strength) was determined by a tensile test as the mechanical properties of each of the release boards after the tempering treatment and left at room temperature for 100 days. The 0.2% proof stress (post-BH proof strength) of the release plate after artificially aged hardening treatment at 185 ° C for 20 minutes (after BH) was evaluated as follows. Tensile test. Then, the BH properties of the respective release boards were evaluated from the difference (history increase amount) between the 0.2% proof stresses.

In the tensile test, a No. 5 test specimen (25 mm x 50 mm GL x thickness) of JISZ2201 was taken from each of the above described test plates and subjected to a tensile test at room temperature. At this time, the tensile direction of the test piece was the direction perpendicular to the rolling direction. The tensile speed was set to 5 mm / min to 0.2% proof stress and to 20 mm / min after proof stress. The number of N of the mechanical property measurement was 5, and the average value was calculated. Further, in the test piece for measuring the strength after the BH test, 2% of the prescribed deformation simulating the press forming of the plate was given to the test piece by the tensile tester, and then the BH treatment was performed.

(Hem-forming property)

The hem-forming properties were measured for each of the publicly available plates after being left for 100 days after the tempering treatment. The test was conducted by using a rectangular test piece of 30 mm in width and after bending at a bending angle of R1.0 mm by a down flange, a 1.0 mm thick inner part was inserted and the bent part was further bent inward by about 130 degrees And then flat-hem processing was carried out in which the end portion was closely contacted with the inner portion.

Surface conditions such as surface roughening, minute cracking, and large cracking of the bent portion of the flat hem were visually observed and evaluated visually by the following criteria.

0; Cracks, no surface roughness, 1; Surface roughness of hardness, 2; Deep surface roughness, 3; Micro-surface cracks, 4; Continuous surface cracks in a line, 5; Fracture

As shown in the alloy Nos. 43 to 52 of Table 7 and the Nos. 73, 74, 80, 86 and 92 to 97 of Table 8, each of the inventions can be produced within the composition range of the present invention, And a tempering process is performed. As a result, each of these embodiments satisfies the cluster condition defined in this embodiment, as shown in Table 8. Namely, the cluster satisfying the predetermined condition in this embodiment satisfies the preferable average number density (3.0 x 10 ²⁴ / m 3 or more), and then the ratio of the number of Mg atoms to the number of Si atoms (Mg / Si) is 1 / 2 &lt; / RTI &gt; is 0.70 or more.

As a result, as shown in Table 9, each example shows excellent press formability to an automobile panel or the like because the BH property is excellent and the As proof strength is comparatively low even after the long-term room temperature aging after the tempering treatment, great. That is, according to the present invention, even when the body paint baking treatment is carried out after a long-term room temperature aging for 100 days, the Al-Si-Mg system can exhibit a higher BH property with a strength difference of 100 MPa or more and press formability and bending workability It is possible to provide an aluminum alloy plate.

In Comparative Examples 75, 81, and 87 of Table 8, inventive alloys Examples 44, 45, and 46 of Table 9 are used. However, in each of these comparative examples, as shown in Table 8, the time taken from the completion of the solution treatment and the quenching treatment to the start of the reheating treatment is too long. As a result, as shown in Table 9, the average number density (x 10 ²³ / m 3) of the clusters defined in this embodiment satisfies the requirement, but the ratio of the number of Mg atoms to the number of Si atoms (Mg / Si) The average ratio of the atomic aggregates of not less than 1/2 is too small and the BH property after the room temperature is maintained for 100 days is lower than that of Examples 74, 80 and 86 which are the same alloy composition, respectively.

As Comparative Examples 76, 82, and 88 in Table 8, Invention Examples 44, 45, and 46 in Table 9 are used. However, as shown in Table 8, these comparative examples are manufactured under preferable manufacturing conditions except for the skin pass rolling after the solution casting treatment. For this reason, the average number density (x 10 ²³ pieces / m 3) of the clusters defined in the present embodiment satisfies the requirement. However, since skin pass rolling is not performed, as shown in Table 9, among the aggregates of atoms satisfying such conditions, the ratio of the number of Mg atoms to the number of Si atoms (Mg / Si) The average ratio is too small and the BH property after keeping the room temperature for 100 days is lower than that of Inventive Examples 74, 80 and 86 which are the same alloy composition.

Comparative Examples 77 to 79, 83 to 85, and 89 to 91 in Table 8 use inventive alloys Examples 44, 45, and 46 of Table 7. However, in each of these comparative examples, as shown in Table 8, the conditions for reheating treatment are out of the preferable range. As a result, the average number density of the atomic assemblies and the average ratio of the atomic aggregates in which the ratio of the number of Mg atoms to the number of Si atoms (Mg / Si) was 1/2 or more were too small, , The BH property and the hem-forming property after the holding at room temperature for 100 days are lowered.

Comparative Examples 98 to 107 in Table 9 were prepared in the preferred ranges including the above tempering treatment, but alloy numbers 53 to 62 in Table 7 were used, and the contents of Mg, Si, and Sn, which are essential elements, Or the amount of the impurity element is excessively large. As a result, as shown in Table 9, the BH properties and the hempability of these Comparative Examples are lower than those of the respective Examples, especially after maintaining the temperature at room temperature for 100 days. Particularly, in Comparative Example 100 of Table 9 in which the Sn content was too small, the room temperature aging was not suppressed, and the As proof strength after the holding at room temperature for 100 days was too high to lower the press formability and the hem forming property and the BH hardness was as high as 100 MPa not. Further, in Comparative Example 101 in which Sn was excessively large, cracks were generated during hot rolling, and the plate itself could not be produced.

Comparative Example 98 is the alloy 53 of Table 7, and Si is excessively small.

Comparative Example 99 is the alloy 54 in Table 7, and Si is excessively large.

Comparative Example 100 is the alloy 55 of Table 7, and Sn is excessively small.

Comparative Example 101 is the alloy 56 of Table 7, and Sn is excessively large.

Comparative Example 102 is the alloy 57 of Table 7, and Fe is excessively large.

Comparative Example 103 is the alloy 58 of Table 7, and Mn is excessively large.

Comparative Example 104 is the alloy 59 of Table 7, and Cr is excessively large.

Comparative Example 105 is the alloy 60 of Table 7, and Cu is excessively large.

Comparative Example 106 is the alloy 61 shown in Table 7, and Ti and Zn are excessively large.

Comparative Example 107 is the alloy 62 of Table 7, and Zr and V are excessively large.

From the results of the above examples, it is proved that there is a need to satisfy all the conditions of the clusters defined in the present embodiment with respect to the BH property improvement after room temperature aging. In addition, a critical meaning or effect of each component requirement or preferable manufacturing conditions in the present embodiment for obtaining such cluster conditions, BH properties, and the like is also supported.

Although the present invention has been described in detail with reference to specific embodiments thereof, it is apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

The present application is based on Japanese patent application (Japanese Patent Application No. 2013-185197) filed on September 6, 2013, Japanese Patent Application filed on September 6, 2013 (Japanese Patent Application No. 2013-185198 And Japanese Patent Application (Japanese Patent Application No. 2013-185199) filed on September 6, 2013, the entirety of which is hereby incorporated by reference.

According to the present invention, it is possible to provide a 6000-series aluminum alloy plate that combines BH properties at a low-temperature short-time condition after long-term room temperature aging and formability after aging at a long-term room temperature. Further, it is possible to provide a 6000-series aluminum alloy plate capable of exhibiting a higher BH property even in the case of room temperature aging at which the strength before baking is increased. As a result, it is possible to expand the application of the 6000-series aluminum alloy plate to transportation equipment such as automobiles, ships or vehicles, home appliances, structures and structures, and particularly to automotive parts such as automobiles. For example, panel members such as automobile panel members, arm members such as pillars or side arms such as a center pillar, which are structural members of automobiles, reinforcements such as bumper reinforcements and door beams, It is suitable for use as a thin plate on skeletal members and structural members.

Claims (6)

Mg-Si based aluminum alloy plate containing 0.2 to 2.0% of Mg, 0.3 to 2.0% of Si and 0.005 to 0.3% of Sn, and the balance of Al and inevitable impurities, A three-dimensional atom probe An aggregate of atoms measured by an electric field ion microscope, wherein the aggregate of the atoms contains at least 10 or more of Mg atoms and / or Si atoms in total, and Mg atoms and Si atoms Even when a single atom is regarded as a reference, the distance between the reference atom and any one of other atoms adjacent to each other is 0.75 nm or less, and the aggregate of atoms satisfying these conditions is 2.5 x 10 &lt; ²³ & Or more and 20.0 x 10 &lt; ²³ &gt; / m &lt; 3 &gt; or less and at least one of an aggregate of atoms satisfying these conditions, an average radius of the circle equivalent diameter of 1.15 nm or more and 1.45 nm or less, The standard deviation of the radius of 0.45 Lt; 2 &gt; / nm or less. 3. The steel sheet according to claim 1, wherein the aluminum alloy sheet further contains, by mass%, Mn: more than 0% and not more than 1.0%, Cu: not less than 0% but not more than 1.0%, Fe: not less than 0% , Zr: more than 0% to 0.3%, V: more than 0% to 0.3%, Ti: more than 0% to 0.1%, Zn: more than 0% to 1.0% An aluminum alloy plate excellent in baking painting hardenability. Mg-Si based aluminum alloy plate containing 0.2 to 2.0% of Mg, 0.3 to 2.0% of Si and 0.005 to 0.3% of Sn, and the balance of Al and inevitable impurities, A _total of atoms of Mg atoms and Si atoms measured by a three-dimensional atom probe electric field ion microscope is N _total and an aggregate of atoms measured by this three-dimensional atom probe electric field ion microscope is Mg atom or Si atom Or a total of 10 or more of these atoms and either or both of the Mg atom and the Si atom is used as a reference, the distance between the atoms serving as the reference and any atoms adjacent to any other atom is contained in the aggregate all of the atoms, when the number of the sum of all the Mg and Si atoms to N atoms _cluster, the ratio of the _total N of the N _cluster (N _cluster / _total N) which satisfies the condition more than 0.75㎚ × 100 is 1% or more and 15% or less And an average radius of the circle-equivalent diameter of the atomic aggregate is not less than 1.20 nm and not more than 1.50 nm. The aluminum alloy sheet according to claim 3, wherein the aluminum alloy sheet further contains, by mass%, Mn: more than 0% and not more than 1.0%, Cu: not less than 0% and not more than 1.0%, Fe: not less than 0% , Zr: more than 0% to 0.3%, V: more than 0% to 0.3%, Ti: more than 0% to 0.1%, Zn: more than 0% to 1.0% An aluminum alloy plate excellent in baking painting hardenability. Mg-Si based aluminum alloy plate containing 0.2 to 2.0% of Mg, 0.3 to 2.0% of Si and 0.005 to 0.3% of Sn, and the balance of Al and inevitable impurities, A three-dimensional atom probe An aggregate of atoms measured by an electric field ion microscope, which contains at least one of Mg atom and Si atom in a total of 10 or more, and contains at least any one of Mg atom and Si atom contained therein The average number density of the atomic assemblies satisfying the condition that the distances between the reference atom and any one of the other atoms adjacent to the reference are 0.75 nm or less is 3.0 x 10 ²³ / m 3 or more and 25.0 × 10 ²³ and more / ㎥ or less, and that the aggregate of atoms that meet these conditions, not less than non-(Mg / Si) is not less than 1/2 of the average ratio of the atomic aggregate can Mg atoms and the number of Si atoms is 0.70 , Baking paint Excellent hardenability Minyum alloy plate. 6. The steel sheet according to claim 5, wherein the aluminum alloy sheet further contains, by mass%, Mn: more than 0% and not more than 1.0%, Cu: not less than 0% and not more than 1.0%, Fe: not less than 0% , Zr: more than 0% to 0.3%, V: more than 0% to 0.3%, Ti: more than 0% to 0.1%, Zn: more than 0% to 1.0% An aluminum alloy plate excellent in baking painting hardenability.