JP2016037632A - Aluminum alloy sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a 6000 series aluminum alloy sheet excellent in coating galling curable property at low temperature.SOLUTION: There is provided an aluminum alloy sheet containing Mg:0.2 to 2.0 mass%, Si:0.3 to 2.0 mass% and Fe:0.01 to 0.5 mass% and one or both of Ni and Co of total 0.002 to 0.3 mass% and the balance Al with inevitable impurities and having total content of Ni and Co in a residual compound having over 0.1 μm of particle size separated from solution by a residual extraction method with heat phenol of 0.005 mass% or more and a solid solution Si amount with a ratio of the Si content in the solution to the Si content of the aluminum alloy sheet of 80% or more.SELECTED DRAWING: None

Description

  The present invention relates to an aluminum alloy plate. More specifically, the present invention relates to an Al—Si—Mg-based aluminum alloy plate having excellent paint bake hardening characteristics at low temperatures.

  In recent years, due to consideration for the global environment and the like, social demands for weight reduction of vehicles such as automobiles are increasing. In order to meet such demands, as a material for automobile panels, especially large body panels (outer panels, inner panels) such as hoods, doors, roofs, etc., instead of steel materials such as steel plates, it has excellent formability and paint bake hardening properties. The application of lighter aluminum alloy materials is increasing.

  As this aluminum alloy material, Al-Mg-Si-based AA to JIS6000-based (hereinafter also simply referred to as 6000-based) aluminum alloy plates are often used.

  This 6000 series (Al-Mg-Si) aluminum alloy sheet is hardened by the paint baking process of the panel after press molding to the panel, and the strength (hardness) is improved, ensuring the necessary strength as a panel. It has excellent paint bake-hardening properties. Hereinafter, this paint bake hardening property is also referred to as bake hard property or BH property.

  Conventionally, it has been important to secure solid solution Si for constituting artificial aging precipitates that contribute to strength with respect to the improvement of paint bake hardening characteristics of such 6000 series aluminum alloy plates. For example, in a 6000 series aluminum alloy, the amount of Al-Fe-Si based crystals containing iron increases as the amount of iron increases, so the amount of solid solution silicon decreases, and age hardening capacity is said to decrease. ing.

  For this reason, conventionally, the number of coarse crystallized substances is reduced or the crystallized substances are refined to ensure solid solution Si. However, in order to reduce or refine the number of such coarse crystals, the casting conditions such as increasing the cooling rate must be greatly changed during DC casting of 6000 series aluminum alloy ingots. (See Non-Patent Document 1).

  In addition, in connection with the control of the BH property of this solid solution Si, the solid solution Si is controlled by a balance with the solid solution Mg amount to suppress an increase in strength due to long-term room temperature aging, and the subsequent formability and bending It has also been proposed in Patent Document 1 that the workability and BH properties are not deteriorated. In the technique disclosed in Patent Document 1, Mg and Si atoms dissolved in an aluminum matrix are kept in Mg-Si, while maintaining at room temperature, by controlling the balance between the amount of dissolved Si and the amount of dissolved Mg. The formation of nanoclusters such as Si—Si and Mg—Mg is suppressed to suppress an increase in strength due to room temperature aging.

JP 2008-174797 A

Tokuda Kenji and Kuma Shinji, “Effects of iron content and cooling rate on solidification on mechanical properties of Al—Mg—Si alloy plates”, Kobe Steel Technical Report, Vol. 58. No. 3, December 2008, P2-P6

However, even in these conventional techniques, an Al—Si—Mg-based aluminum alloy plate that is easy to age harden at room temperature and has different conditions such as room temperature aging time, has a heating temperature of 150 ° C. or 135 ° C. There is a fact that it is quite difficult to achieve high strength (high hardness) stably by low-temperature paint baking and curing treatment.
In both Patent Document 1 and Non-Patent Document 1, the evaluation for the BH property investigation is performed by a relatively high-temperature artificial age hardening treatment at a heating temperature of 170 ° C. (× 20 minutes, etc.). BH property in low-temperature paint bake hardening treatment such as ℃ or 135 ℃ has not been evaluated.

  Therefore, in view of the above circumstances, the present invention provides high strength (high hardness) even with low-temperature paint bake-hardening treatment, and is excellent in BH property at low temperature or paint bake-hardening characteristics at low temperature. The main object is to provide a Si-Mg aluminum alloy sheet.

The present invention includes Mg: 0.2-2.0 mass%, Si: 0.3-2.0 mass%, and Fe: 0.01-0.5 mass%, and among Ni and Co One or both of them are aluminum alloy plates containing 0.002 to 0.3% by mass in total, the balance being Al and inevitable impurities, and the particle size separated from the solution by the residual extraction method using hot phenol is 0.00. The total content of Ni and Co in the residual compound exceeding 1 μm is 0.005% by mass or more, and the ratio of the Si content in the solution to the Si content of the aluminum alloy plate is 80% or more. An aluminum alloy plate having a solid solution Si amount is provided.
This aluminum alloy plate may be subjected to preliminary aging treatment.
The “aluminum alloy plate” as used in the present invention refers to an aluminum alloy plate before paint bake hardening.

  According to the present invention, an Al—Si—Mg-based aluminum alloy that has high strength (high hardness) even in low-temperature paint bake-hardening treatment and has excellent BH properties at low temperatures or excellent bake-hardening properties at low temperatures. Board can be provided.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. Note that the present invention is not limited to the embodiments described below.

  The aluminum alloy plate of the embodiment according to the present invention includes Mg: 0.2 to 2.0 mass%, Si: 0.3 to 2.0 mass%, and Fe: 0.01 to 0.5 mass%. At the same time, one or both of Ni and Co are included in a total amount of 0.002 to 0.3 mass%, and the balance is made of Al and inevitable impurities. And this aluminum alloy plate has a total content of Ni and Co in the residual compound with a particle size of more than 0.1 μm separated from the solution by the residue extraction method with hot phenol is 0.005 mass% or more The ratio of the Si content in the solution to the Si content of the aluminum alloy plate is 80% or more.

By the way, in the prior art, as described above, the number of coarse crystallized substances themselves is reduced, or Si consumed in the crystallized substances is reduced by refining the crystallized substances, so that a 6000 series aluminum alloy is obtained. An attempt was made to secure the amount of dissolved Si in the plate.
However, there is a limit to this, and in particular, in the relatively low-temperature paint bake hardening process in the range of 135 to 150 ° C., the Vickers hardness of the aluminum alloy plate after BH is more than 80 Hv, and further, high strength (high Hardness) could not be increased stably. Moreover, in order to reduce the number of coarse crystallization products themselves or to refine the crystallization products, it is necessary to change the casting conditions such as increasing the cooling rate of the ingot.

  On the other hand, in this embodiment, by adding one or both of Ni and Co to the 6000 series aluminum alloy plate, the number of Al-Fe-Si based crystallized substances is not reduced (reducedly). (Not), the composition of the crystallized product is changed so that the amount of Si decreases. That is, the Al—Fe—Si-based crystallized material contains one or both of Ni and Co instead of Si (in other words, Si is substituted with one or both of Ni and Co). Change to Si- (Ni, Co) -based crystallized material, decrease the amount of Si contained in the crystallized product, and increase the amount of dissolved Si necessary for low-temperature BH property (artificial age hardening at low temperature) Prior to the paint baking and hardening process, it is secured in advance.

  Thus, in the aluminum alloy plate of the present embodiment, the solid solution Si amount of the 6000 series aluminum alloy plate is secured in advance to improve the paint bake hardening characteristics. In the present embodiment, this is performed by a novel metallurgical viewpoint or means in which the composition of the crystallized substance is changed or replaced with a composition containing one or both of Ni and Co instead of Si. As a result, the amount of Si consumed in the crystallized matter is reduced, while the amount of solid solution Si in the aluminum matrix is increased, and the amount of solid solution Si is secured in advance to ensure BH properties at low temperatures. As a result, the Vickers hardness of the aluminum alloy plate after this BH is more than 80 Hv, even in the case of relatively low-temperature paint bake hardening treatment with a heating temperature in the range of 135 to 150 ° C. due to the increase in the amount of dissolved Si. The strength after BH can be stably increased to a high strength (high hardness).

  Therefore, in the production of an aluminum alloy plate, a method for tempering an aluminum alloy plate for adding one or both of Ni and Co and ensuring solid solution Si in an aluminum matrix (without precipitating Si) is provided. An excellent BH property is ensured only by devising. For this reason, there is also an advantage that an aluminum alloy plate can be manufactured without greatly changing the manufacturing process according to a conventional method. By performing preliminary aging treatment as the tempering method, it becomes possible to form nanoclusters by this preliminary aging treatment in addition to the increase of the solid solution Si. Thereby, the amount of fine Mg-Si based precipitates generated during the paint bake hardening process can be increased. Therefore, the aluminum alloy plate of the present embodiment is preferably an aluminum alloy plate (preliminary aging treatment material) that has been subjected to a pre-aging treatment, and as will be described later, the pre-aging treatment is performed as a tempering treatment after the rolling treatment. More preferably, it is an aluminum alloy plate (preliminary aging treatment material).

[Chemical composition of aluminum alloy sheet]
Next, the chemical component composition of the aluminum alloy plate of this embodiment will be described.

  The target 6000 series aluminum alloy plate is age-hardened by heating at a relatively low temperature artificial aging treatment such as paint baking after being molded into an automobile panel, and has an excellent ability to ensure the required strength (hardness). It is required to have age-hardening ability (BH property). In addition, various characteristics such as excellent formability, weldability, and corrosion resistance are also required for the above-described automotive outer plate.

  As a premise for satisfying such required characteristics, in the present embodiment, the composition of the aluminum alloy plate is Mg: 0.2 to 2.0 mass%, Si: 0.3 to 2.0% by mass, Fe: 0.01 to 0.5% by mass, respectively, and one or both of Ni and Co in total 0.002 to 0.3% by mass, the balance Is defined as consisting of Al and inevitable impurities.

  Other than these specified elements, other elements such as Mn, Cu, Cr, Ti, and Zn are basically inevitable impurities, and the content (allowable amount) at each element level in accordance with AA to JIS standards. And

  The content range of each of the above elements and its significance or allowable amount will be described below.

[Si: 0.3 to 2.0% by mass]
Si, together with Mg, is an indispensable element for increasing the BH property by generating aging precipitates effective for BH properties (artificial age hardening ability) during artificial aging treatment at low temperatures such as paint baking treatment in the present invention. is there. It is also an important element that has the effect of improving solid solution strengthening and total elongation that affects press formability.

  If the Si content is less than 0.3% by mass, the absolute amount of Si is insufficient, so that the amount of aging precipitates generated is insufficient, and the BH property particularly at low temperatures may be reduced. In some cases, mechanical properties such as total elongation cannot be combined. On the other hand, when the Si content exceeds 2.0% by mass, coarse crystallized substances and precipitates are formed, and bending workability and total elongation may be remarkably lowered, and weldability is also significantly inhibited. May be. Therefore, Si content shall be 0.3-2.0 mass%.

  From the viewpoint of enhancing the BH property at low temperature and providing good mechanical properties, the Si content is preferably 0.4% by mass or more, and more preferably 0.5% by mass or more. Further, from the viewpoint of providing good mechanical properties and weldability, the Si content is preferably 1.8% by mass or less, more preferably 1.5% by mass or less.

[Mg: 0.2 to 2.0% by mass]
Mg is also an essential element for enhancing the BH property by generating an aging precipitate that works on the BH property during the artificial aging treatment such as a paint baking process together with Si. It is also an important element that has the effect of improving solid solution strengthening and total elongation that affects press formability.

  If the Mg content is less than 0.2% by mass, the absolute amount of Mg is insufficient, so that the amount of aging precipitates generated is insufficient, and the BH property particularly at low temperatures may be reduced. In some cases, mechanical properties such as total elongation cannot be combined. On the other hand, if the Mg content exceeds 2.0% by mass, coarse crystallized products and precipitates are formed, and bending workability and total elongation may be significantly reduced, and weldability is also significantly inhibited. May be. Therefore, Mg content shall be 0.2-2.0 mass%.

  From the viewpoint of enhancing the BH property at a low temperature and providing good mechanical properties, the Mg content is preferably 0.3% by mass or more. Further, from the viewpoint of providing good mechanical properties and weldability, the Mg content is preferably 1.8% by mass or less, more preferably 1.5% by mass or less.

[Fe: 0.01 to 0.5% by mass]
Fe is an element for forming an Al-Fe-Si-based crystallized substance and ensuring the necessary strength of the aluminum alloy plate. As a result, at least one of Ni and Co was added, and instead of Si, an Al-Fe-Si- (Ni, Co) -based crystallized material containing at least one of Ni and Co was obtained. Again, the contribution to strength is the same.
When the Fe content is less than 0.01% by mass, the number of crystallized substances contributing to the strength is insufficient, and the strength may be lowered. On the other hand, when Fe exceeds 0.5 mass%, the press formability and bending workability of the aluminum alloy plate may be lowered. Therefore, Fe content shall be 0.01-0.5 mass%.

  The Fe content is preferably 0.02% by mass or more, more preferably 0.05% by mass or more, from the viewpoint of improving the strength. Further, the Fe content is preferably 0.45% by mass or less, more preferably 0.4% by mass or less, from the viewpoint of improving press formability and bending workability.

[One or both of Ni and Co: 0.002 to 0.3% by mass in total]
Ni and Co change the composition of the Al-Fe-Si-based crystallized material to the Al-Fe-Si- (Ni, Co) system, and reduce the amount of Si contained in the crystallized material. It is an important element that increases the amount of dissolved Si. Thereby, even if the coating baking process (artificial age hardening process) is a low temperature of 150 ° C. or less, the amount of fine Mg—Si-based precipitates to be generated can be increased, and the BH property can be improved.

  When the total content of Ni and Co is less than 0.002% by mass, the composition of the crystallized product cannot be sufficiently changed to the Al-Fe-Si- (Ni, Co) system, and In some cases, the amount of Si contained cannot be decreased to increase the amount of dissolved Si. As a result, when the coating baking process is performed at a low temperature of 150 ° C. or lower, the amount of fine Mg—Si based precipitates to be generated is reduced, and the BH property is lowered.

On the other hand, even if the total content of Ni and Co exceeds 0.3% by mass, the number of crystallized substances is limited, so the composition of the crystallized substances is changed to the Al-Fe-Si- (Ni, Co) system. The effect of making it saturated is so that the amount of dissolved Si cannot be increased any more. Moreover, when the said total content exceeds 0.3 mass%, the mechanical property, press formability, bending workability, etc. of an aluminum alloy plate may be lowered on the contrary. Therefore, the total content of Ni and Co is in the range of 0.002 to 0.3 mass%.
The total content of Ni and Co is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and still more preferably 0 from the viewpoint of increasing the amount of dissolved Si. 0.05% by mass or more.

  Conventionally, when Ni or Co is added to a 6000 series aluminum alloy plate, the addition of Ni or Co is performed with the aim of finely dispersing or spheroidizing a crystallized product generated during casting. Another aim is to delay the precipitation behavior of precipitates during soaking (homogenizing heat treatment) so that the precipitates are not coarsened during soaking.

  From a viewpoint different from the above aim by adding Ni or Co, in the present invention, by adding one or both of Ni and Co, the composition of the Al-Fe-Si-based crystallized substance is changed to Al-Fe-Si-. There is also an effect of changing to the (Ni, Co) system, decreasing the amount of Si contained in the crystallized product, and increasing the amount of dissolved Si. This is an effect peculiar to the present invention that is not recognized at all in the prior art.

  Moreover, in order to ensure the amount of solute Si, there has never been an example in which a 6000 series aluminum alloy plate to which Ni and Co are added is tempered under the preferred tempering conditions of the present invention described later. As defined in the present invention, the amount of solid solution Si required for BH properties at low temperatures as in the present invention, the structure secured in advance prior to the paint bake hardening treatment (artificial age hardening treatment or artificial aging treatment), It has not been obtained so far. That is, when Ni and Co are simply added and processing is performed under normal manufacturing conditions, there is a high probability that a solid solution Si amount as defined in the present invention is not obtained in advance.

[Organization]
In the present invention, the structure of the 6000 series aluminum alloy plate is further defined on the premise of the above-described aluminum alloy plate composition. That is, as the structure of the 6000 series aluminum alloy sheet that has been tempered after rolling, the solid solution Si amount necessary for the BH property at low temperature is secured in advance prior to the paint bake hardening process. For this reason, in the aluminum alloy plate having the above composition, the total content of Ni and Co in the residue compound having a particle size of more than 0.1 μm separated from the solution by the residue extraction method using hot phenol is 0.005% by mass. In addition, the ratio of the Si content in the solution to the Si content of the aluminum alloy plate is set to 80% or more.

  The reason why the total content of Ni and Co contained in the residual compound is 0.005% by mass or more is to reduce the amount of Si contained in the crystallized product and increase the dissolved Si. In the present embodiment, the amount of solute Si in the 6000 series aluminum alloy plate is secured in advance, and the composition of the crystallized material includes Ni and Co instead of Si, particularly when improving the bake hardening characteristics at low temperatures. It is characteristic that the composition is changed or replaced. As a result, the Si consumed in the crystallized product is reduced, while the solid solution Si in the aluminum matrix is increased to ensure the BH property at a low temperature.

  When the total content of Ni and Co in the residual compound is less than 0.005% by mass, the Al—Fe—Si based crystallized product is sufficiently obtained as the Al—Fe—Si— (Ni, Co) based crystallized product. The remaining Al—Fe—Si-based crystallized product increases. For this reason, the decrease amount of Si contained in the crystallized substance is reduced, and the solid solution Si amount necessary for the BH property in the coating baking process at a low temperature of 150 ° C. or lower cannot be secured, and the strength (hardness) is reduced. Does not improve.

  On the other hand, the larger the total content of Ni and Co contained in the residual compound, the more preferable is the decrease in Si contained in the crystallized product, which is preferable. Therefore, the total content of Ni and Co The upper limit is not particularly limited. However, considering the upper limit of the total content of Ni and Co in the aluminum alloy sheet composition, the upper limit of the total content of Ni and Co contained in the residual compound is substantially 0.3% by mass.

  The amount of Si in the solution separated from the residue is 80% or more of the Si content of the aluminum alloy plate as the amount of solid solution Si after the tempering treatment is 150 ° C. or less. This is because the amount of Si dissolved in the aluminum alloy plate, which is necessary for the BH property in the low-temperature coating baking process, is secured in advance prior to the baking process. When the Si content in the solution is less than 80% of the Si content of the aluminum alloy plate, the Al-Fe-Si-based crystallized product is sufficiently converted to an Al-Fe-Si- (Ni, Co) -based crystallized product. Even if the amount of decrease in Si contained in the crystallized substance is reduced, the amount of solid solution Si necessary for BH properties in the paint baking process at a low temperature of 150 ° C. or less cannot be secured, and the strength (hardness) ) Does not improve.

  Depending on the production conditions of the plate, the amount of Si contained in the crystallized material decreases, and even if the amount of solid solution Si can be secured (increased) in advance, the solid solution Si thus secured as precipitates. There is also a possibility of precipitation. For this reason, there is a possibility that the solid solution Si amount necessary for the BH property in the coating baking process at a low temperature of 150 ° C. or lower cannot be secured, and the strength (hardness) is not improved. Therefore, as the amount of solute Si in the plate after the tempering treatment, the ratio of the Si content in the solution separated from the residue to the Si content in the aluminum alloy plate is defined as 80% or more, and coating is performed. Guarantee (ensure) the amount of solute Si necessary for BH properties in baking treatment.

  The higher the Si content (solid solution Si content) in the solution, the better the BH property in the coating baking process at a low temperature of 150 ° C. or lower, which is preferable. Therefore, the aluminum alloy having the Si content in the solution is preferable. The upper limit of the ratio with respect to Si content of a board is not prescribed | regulated in particular. However, considering the upper limit of Si content in the aluminum alloy plate composition and the production limit, the upper limit of Si content in the solution is about 95% of the Si content of the aluminum alloy plate.

  Thus, in this embodiment, regarding the improvement of the paint bake hardening characteristics of the 6000 series aluminum alloy plate, the composition of the crystallized substance is changed or replaced with a composition containing Ni and Co instead of Si. Based. As a result, the amount of Si consumed in the crystallized product is reduced, and the solid solution Si in the aluminum matrix is increased, thereby ensuring the BH property. As a result, due to the increase in solute Si, the strength after BH can be stably increased to a high strength (high hardness) even when the coating temperature is low at a heating temperature of 150 ° C. or 135 ° C. .

[Production method]
Next, as an example of a preferable manufacturing method capable of manufacturing the above-described aluminum alloy plate, a method for manufacturing the aluminum alloy plate of the present embodiment will be described.

  The aluminum alloy plate of the present embodiment includes a step of casting an aluminum alloy material having the above composition (casting step), a step of homogenizing heat treatment of the aluminum alloy ingot obtained by casting (homogenization heat treatment step), The aluminum alloy ingot after the homogenization heat treatment can be produced by rolling the aluminum alloy ingot to obtain an aluminum alloy rolled sheet (rolling treatment step) and a tempering treatment step. This tempering treatment step includes a solution hardening treatment step (solution hardening treatment step) in which the aluminum alloy rolled sheet is solution treated and cooled. In addition, the aluminum alloy plate of the present embodiment is manufactured as a tempering treatment step, preferably having a step of performing a preliminary aging treatment (preliminary aging treatment step) after the solution hardening treatment step.

  In the production of the aluminum alloy plate of the present embodiment, by devising a method in the tempering step described later, at least one of Ni and Co is added and solid solution Si in the aluminum matrix is secured ( Si is not deposited). Thereby, excellent BH property is ensured. For this reason, there exists an advantage that the aluminum alloy plate excellent in BH property can be manufactured, without changing the manufacturing process by a conventional method largely.

(Casting process)
First, in the casting process, an aluminum alloy melt adjusted to be dissolved within the above-mentioned 6000 series component composition range is cast by appropriately selecting a normal melting casting method such as a continuous casting method or a semi-continuous casting method (DC casting method). .

  Regarding the casting speed or cooling speed in the casting process, it is preferable to set the casting speed to 40 mm / min or more or the cooling speed to 0.5 ° C./sec or more from the viewpoint of suppressing the formation of coarse compounds. In addition, from the viewpoint of suppressing the occurrence of ingot cracking, “nest (casting)” or “shrinkage” and improving the casting yield, the casting speed is set to 65 mm / min or less, or the cooling speed is set to 1 It is preferably 5 ° C./second or less. Therefore, in the casting process, the casting rate is preferably in the range of 40 to 65 mm / min, and the cooling rate is preferably in the range of 0.5 to 1.5 ° C./second.

(Homogenization heat treatment process)
Prior to the rolling process, the aluminum alloy ingot cast in the casting process is subjected to a homogenizing heat treatment. The purpose of this homogenization heat treatment (soaking) is to homogenize the structure, that is, eliminate segregation in crystal grains in the ingot structure. In order to achieve this object, the homogenization heat treatment temperature is suitably selected from the range of preferably 500 ° C. or higher and less than the melting point, and the homogenization time is preferably 4 hours or more.

(Rolling process)
In the rolling treatment step after the homogenization heat treatment step, the aluminum alloy ingot subjected to the homogenization heat treatment is rolled to obtain an aluminum alloy rolled plate having a predetermined plate thickness. In this rolling treatment step, at least one of a hot rolling treatment and a cold rolling treatment is performed, preferably both of the treatments are performed, and more preferably, after undergoing the hot rolling treatment step, cold rolling is performed. Take processing steps.

  The hot rolling treatment is preferably performed at a starting temperature of 400 ° C. to a solidus temperature. Although annealing (roughening) of the hot-rolled sheet before cold rolling is not necessarily required, it may be performed in order to further improve characteristics such as formability.

  In the cold rolling process, the hot-rolled sheet is rolled into a cold-rolled sheet having a desired final sheet thickness such as for automobile panels. For the same purpose as the roughening, intermediate annealing may be performed between the cold rolling passes.

(Tempering treatment)
The aluminum alloy rolled sheet obtained in the rolling process step is preferably subjected to a tempering process on the cold-rolled sheet. As the tempering treatment, a solution hardening treatment is performed, and preferably a pre-aging treatment is performed after the solution hardening treatment.

  An aluminum alloy rolled sheet, preferably a cold-rolled sheet, is subjected to a solution hardening treatment as a tempering treatment, and preferably a reheating treatment (preliminary aging treatment) followed by a tempered 6000 series aluminum alloy plate. The amount of dissolved Si necessary for the BH property at low temperature is ensured. At this time, there are preferable conditions for securing the amount of solute Si necessary for the BH property of the 6000 series aluminum alloy plate at a low temperature in the solution hardening treatment and the subsequent reheating treatment.

(Solution hardening process)
First, the solution hardening treatment is performed at a heating rate of 5 ° C./second or more to a solution treatment temperature of 520 ° C. or higher and a melting temperature or lower, and the solution treatment temperature is 15 minutes or longer and 45 minutes or shorter. It is preferable to hold. The average cooling rate from the solution treatment temperature to the quenching stop temperature of room temperature (25 ° C.) is preferably increased to 50 ° C./second or more.
The solution-quenching treatment is heated to a solution-quenching treatment temperature in the range of 520 ° C. or higher and below the melting temperature and heated at a heating rate of 5 ° C./second or more and held for 15 minutes or more and 45 minutes or less. The composition can be changed to the Al—Fe—Si— (Ni, Co) system, and the amount of Si contained in the crystallized substance can be decreased to increase the amount of solid solution Si. As a result, even when the coating baking process is performed at a low temperature of 150 ° C. or lower, a lot of fine Mg—Si based precipitates are generated, and the BH property can be improved.

  With such preferable solution hardening treatment conditions, it becomes possible to satisfy the definition of the amount of dissolved Si by the residue extraction method using hot phenol of the aluminum alloy plate having the above composition. That is, the ratio of the Si content in the solution to the Si content of the aluminum alloy plate separated from each other, and the total content of Ni and Co contained in the residual compound having a particle size exceeding 0.1 μm, Each can satisfy the specified range.

  Heating to a solution treatment temperature at a heating rate of 5 ° C./second or more and setting the average cooling rate from the solution treatment temperature to the quenching stop temperature at room temperature to 50 ° C./second or more by water cooling or the like This is because the formation of coarse compounds is suppressed during heating and cooling.

  If a coarse compound is formed, even if Ni and Co are contained, the composition of the crystallized product cannot be sufficiently changed to the Al-Fe-Si- (Ni, Co) system, and There is a high possibility that the amount of Si contained can be reduced and the amount of dissolved Si cannot be increased. As a result, when the coating baking process is performed at a low temperature of 150 ° C. or less, the amount of fine Mg—Si-based precipitates to be generated is reduced, the BH property may be lowered, the strength and formability of the aluminum alloy plate, etc. The mechanical properties may be degraded.

(Preliminary aging treatment process)
Next, in the solution hardening treatment, it is preferable that the cold-rolled sheet quenched and cooled to room temperature (25 ° C.) is subjected to preliminary aging treatment (reheating treatment) without delay. In order to form nanoclusters necessary for improving the BH property as a microstructure of the tempered 6000 series aluminum alloy plate, this preliminary aging treatment is performed after the solution treatment and after quenching to room temperature, for 5 minutes. It is more preferable to carry out within the shortest possible time.
A sufficient amount of nanoclusters can be formed by subjecting an aluminum alloy plate that has been quenched after solution treatment and cooled to room temperature to a pre-aging treatment within 5 minutes after reaching room temperature.

  The holding temperature for the pre-aging treatment is preferably 70 to 120 ° C., and the holding time for the pre-aging treatment is preferably 1 to 20 hours. By these, even when the tempered aluminum alloy sheet is held at room temperature for a long time, it is possible to ensure excellent BH properties.

  As described in detail above, the aluminum alloy plate of the present embodiment has Mg, Si, and Fe contents in specific ranges, and includes one or both of Ni and Co, and the total of Ni and Co. Since the content is in a specific range and has a solid solution Si amount in a specific range, the BH property at low temperature or the paint bake hardening property at low temperature is excellent. The aluminum alloy plate of the present embodiment is excellent in BH property (paint bake-hardening characteristics) under low temperature conditions, and is particularly suitable for transportation equipment members that are required to have excellent paint bake-hardening characteristics such as automobiles. .

  The aluminum alloy plate of the present embodiment includes one or both of Ni and Co in a specific range, so that the composition of the Al-Fe-Si based coarse crystallized product is Al-Fe-Si-Ni. It changes to the system, Al-Fe-Si-Co system or Al-Fe-Si-Ni-Co system, and the amount of Si contained in the crystallized product decreases, and the amount of solute Si increases. As a result, the amount of fine Mg-Si-based precipitates generated by the paint baking process can be increased, so that the strength can be improved after low-temperature paint baking and hardening (artificial age hardening or artificial aging treatment). It becomes.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention. Note that the present invention is not limited by the following examples, and can be implemented with appropriate modifications within a range that can be adapted to the above and the following. Moreover, all of them are included in the technical scope of the present invention.

  In the following Examples and Comparative Examples, a 6000 series aluminum alloy plate (cold rolled plate) was made by changing the presence or absence of addition of Ni or Co and the presence or absence of a pre-aging treatment after solution treatment and quenching treatment. Then, BH properties (paint bake hardening characteristics) of these aluminum alloy plates from a relatively high temperature to a low temperature are subjected to a pre-aging treatment (examples in which the pre-aging treatment is not performed are after solution treatment and quenching treatment), and are performed at room temperature for 30 days. Each was evaluated after being held at (25 ° C.).

Specific production conditions for the aluminum alloy plate are as follows.
That is, ingots having the respective compositions shown in Table 1 were commonly melted by the DC casting method within the range of the preferable casting conditions described above (casting speed 50 mm / min, cooling rate 1.0 ° C./sec). Ingot. Subsequently, these ingots were subjected to homogenization heat treatment at 540 ° C. for 4 hours in common with each example, and then hot rolling was started at a hot rolling start temperature of 500 ° C., and the thickness was 2.5 mm. A hot-rolled sheet was used. In common with each example, this hot-rolled sheet was cold-rolled without any rough firing and without intermediate annealing in the middle of the cold-rolling pass to obtain a cold-rolled sheet having a thickness of 1.0 mm.

  Furthermore, in common with each example, each cold-rolled sheet is subjected to a solution heat treatment for 30 minutes at a temperature of 550 ° C. in a glass furnace, and then immediately cooled to room temperature (25 ° C.) to perform a solution hardening treatment. It was. At this time, the average cooling rate from the solution treatment temperature to the quenching stop temperature at room temperature was set to 50 ° C./second or more. Then, about Example 1 and 2, the preliminary aging treatment was performed on the conditions of 100 degreeC x 5 hours.

  A test plate was arbitrarily cut out from the center of each aluminum alloy plate after the tempering treatment, and the structure and characteristics of each test plate were measured and evaluated as follows.

(Structural evaluation by hot phenol residue extraction method)
Each sample collected from any three locations of the test plate was separated by a filter having a mesh size of 0.1 μm when dissolved with hot phenol, and Ni in the residual compound having a particle size exceeding 0.1 μm. The total content (% by mass) of Co and Co was measured and averaged. Moreover, Si content in the said solution isolate | separated from the residue compound was measured and averaged, and the ratio (%) with respect to Si content of the said aluminum alloy plate was calculated | required.

(Paint bake hardening characteristics / Vickers hardness)
In order to investigate the BH property at the time of artificial aging treatment equivalent to paint baking of the test plate, each example was held at different temperatures of 135 ° C., 150 ° C., and 170 ° C. for 20 minutes in common. The Vickers hardness after the treatment was measured.
Vickers hardness is measured with a micro Vickers hardness tester (manufactured by Matsuzawa Co., Ltd.) by applying a load of 0.5 kg to the test plate and measuring it at any three locations on the surface of the test plate. I took the value.

  The above evaluation results are shown in Table 1 together with the composition and the like.

  Each aluminum alloy plate of Examples 1 and 2 satisfies the chemical composition defined in the present invention including the content of Ni or Co, and pre-aging treatment in the tempering treatment is also preferable including other production conditions. Manufactured with conditions. Therefore, as shown in Table 1, in the aluminum alloy plates of Examples 1 and 2, as the structure, Ni and Co in the residual compound whose particle size separated from the solution by the residual extraction method with hot phenol exceeds 0.1 μm. The total amount of Si was 0.005% by mass or more, and the solid solution Si amount was secured in advance so that the ratio of the Si content in the solution to the Si content of the aluminum alloy plate was 80% or more. .

  As a result, each aluminum alloy plate of Examples 1 and 2 is represented not only by the BH property expressed by the Vickers hardness at a relatively high temperature of 170 ° C but also by the Vickers hardness at a relatively low temperature of 135 ° C and 150 ° C. It is also excellent in BH property, and it can be seen that it is excellent in paint bake-hardening characteristics at low temperatures.

  On the other hand, the aluminum alloy plate of Comparative Example 1 does not contain both Ni and Co, and was manufactured without performing a pre-aging treatment as a tempering treatment. The ratio of the Si content in the solution was less than 80%, and the BH property expressed by Vickers hardness was inferior to that of the examples.

  Since each aluminum alloy plate of Examples 3 and 4 contains Ni or Co and is manufactured under suitable manufacturing conditions, the ratio of the Si content in the solution to the Si content of the aluminum alloy plate is 80% or more was satisfied, and the amount of dissolved Si was secured. Therefore, each aluminum alloy plate of Examples 3 and 4 has higher Vickers hardness at low temperatures of 135 ° C. and 150 ° C. than the aluminum alloy plate of Comparative Example 1, and has good BH properties expressed by the Vickers hardness. Met. On the other hand, since each aluminum alloy plate of Examples 3 and 4 was manufactured without performing pre-aging treatment, the BH property represented by Vickers hardness at each temperature of 135 ° C., 150 ° C., and 170 ° C. The BH properties of Examples 1 and 2 were not as excellent. The difference in BH property is that in the aluminum alloy plates of Examples 1 and 2 manufactured by performing the pre-aging treatment, nanoclusters were formed, and in Examples 3 and 4 manufactured without performing the pre-aging treatment. It is considered that nanoclusters are not formed on the aluminum alloy plate, and this is considered due to the presence or absence of nanocluster formation.

  From the results of the above examples, the structure defined in the present invention can be satisfied by the addition of one or both of Ni and Co and preferable manufacturing conditions, and this structure can improve the BH property under low temperature conditions. It is confirmed that it contributes.

Claims (2)

Mg: 0.2-2.0 mass%,
Si: 0.3-2.0% by mass and Fe: 0.01-0.5% by mass,
Including one or both of Ni and Co in a total amount of 0.002 to 0.3 mass%
The balance is an aluminum alloy plate made of Al and inevitable impurities,
The total content of Ni and Co in the residue compound having a particle size of more than 0.1 μm separated from the solution by the residue extraction method using hot phenol is 0.005% by mass or more, and the Si content in the solution The aluminum alloy plate having a solid solution Si amount in which the ratio of the aluminum alloy plate to the Si content is 80% or more.   The aluminum alloy sheet according to claim 1, which has been subjected to a pre-aging treatment.