JP2000160310A - Production of aluminum alloy sheet suppressed in cold aging property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an Al-Mg-Si aluminum alloy sheet small in cold aging properties and excellent in baking hardenability and formability. SOLUTION: An Al-Mg-Si aluminum alloy contg., by weight, 0.3 to 1.0% Mg and 0.8 to 1.3% Si is subjected to melting and casting, is thereafter subjected to soaking treatment and is next subjected to hot rolling and cold rolling to control its sheet thickness to a desired one, which is subsequently subjected to solution heat treatment of executing heating at 510 to 590 deg.C and holding it to the temp. range for <=60 sec as final heat treatment, is thereafter cooled to 400 deg.C at a cooling rate of >=20 deg.C/sec, is subsequently cooled in the temp. range of 400 to 300 deg.C at a rate of 4 to 10 deg.C/sec and is then cooled to room temp. at a rate of >=4 deg.C/sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a 6000 series aluminum alloy sheet having excellent bake hardenability and formability and low aging at room temperature. More specifically, the present invention relates to a panel material for automobiles, home electric appliances and the like. A method for producing an aluminum alloy sheet which is used after baking coating after forming processing, wherein high curability is obtained during baking coating, excellent in formability such as press and bending, and low in room temperature aging. -Mg
The present invention relates to a method for producing a Si-based aluminum alloy plate.

[0002]

2. Description of the Related Art Conventionally, aluminum alloy materials used as panel materials for automobiles, home appliances, etc. are non-heat-treated aluminum alloys.
-In recent years, for the purpose of further thinning and weight reduction, using a heat treatment type aluminum alloy, utilizing the heating in the baking coating process after forming, Methods have been implemented to increase strength. It is desirable that such a heat-treated aluminum alloy be a material which has low strength at the time of forming processing such as pressing, is easily formed, and has a remarkably increased strength by heat treatment of baking coating after the forming processing. For this reason, Al-M
A g-Si-based aluminum alloy is used, and for example, 6000 alloy and 6016 alloy are practically used in Europe and the United States.

[0003]

The heating conditions at the time of baking in Europe and the United States are high temperatures and long times. But,
At present, the heating conditions at the time of baking painting in Japan are tending to shorten the temperature and shorten the time due to energy saving and diversification of resin parts. For this reason, when the baking coating process is performed at a low temperature for a short time, the A manufactured by a normal manufacturing method is used.
A 1-Mg-Si-based aluminum alloy plate cannot provide sufficient strength. In addition, rapid heating and rapid cooling by a continuous heating furnace have been adopted for the final heat treatment (solution quenching after cold rolling) as a means to improve bake hardenability by low-temperature short-time treatment. Is large,
In an actual use environment in which the substrate is left at room temperature for several months after the final heat treatment until molding, the difference from the initial strength becomes large. For this reason, the amount of springback differs depending on the molding time even for the same plate, and the springback during molding increases as the plate is left for a long period of time, resulting in poor moldability.

[0004] The present invention has been made in view of the above-mentioned problems of the prior art, and has been made by improving a method of manufacturing an Al-Mg-Si-based aluminum alloy plate, and having excellent bake hardenability and formability.
It is another object of the present invention to obtain an Al-Mg-Si-based aluminum alloy plate with reduced aging at room temperature.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the baking hardenability, formability, and aging at room temperature are affected by the quenching and cooling conditions after the solution treatment. I found that it had a great effect. That is, Al-Mg
In the case of -Si alloys, when quenching is performed at an insufficient cooling rate after solution treatment, coarse Mg ₂ Si intermetallic compounds or Si simple particles during cooling particularly in a temperature range from a solution treatment temperature to 400 ° C. It precipitates in large amounts and becomes a source of stress concentration at the time of forming, thereby significantly reducing the formability. At the same time, the solute atomic weight that contributes to hardening during the heat of baking decreases, so that the bake hardenability is significantly reduced. Therefore, in order to improve bake hardenability and formability, it is necessary to perform quenching at a sufficient cooling rate. However, this cooling rate is insufficient in the conventional method for producing an Al-Mg-Si alloy. Because
Sufficient bake hardenability and moldability could not be obtained.

On the other hand, room-temperature aging is caused by the formation of clusters in which solute atoms Mg and Si are combined with atomic vacancies during standing at room temperature after solution quenching. That is, the room-temperature aging property depends on the vacancy concentration after the solution quenching. In the conventional method for producing an Al-Mg-Si alloy, after the solution treatment, a high vacancy concentration close to the equilibrium concentration at the solution temperature is maintained during the solution quenching process to rapidly cool to room temperature or near room temperature. Room temperature aging is increased.

On the other hand, the present inventors, by cooling at a sufficient cooling rate in a temperature range in which coarse particles precipitate,
The present invention has been found to be excellent in bake hardenability and moldability, and subsequently to cool and stabilize the vacancy concentration by cooling a temperature region at a constant cooling rate during quenching, thereby suppressing room-temperature aging. Was.

That is, the method for producing an aluminum alloy sheet according to the present invention is as follows.
i: An Al-Mg-Si-based aluminum alloy containing 0.8 to 1.3% is melt-cast, then soaked, then hot-rolled and cold-rolled to a desired thickness, and then finalized. As a heat treatment, a solution treatment is performed by heating to a temperature of 510 to 590 ° C., and then to 20 ° C./sec up to a temperature of 400 ° C.
Cool at the above cooling rate, then 400 to 300 ° C
Is cooled at a rate of 4 to 10 ° C./sec, and then cooled to room temperature at a rate of 4 ° C./sec or more. The cooling from 300 ° C. in the above method may be performed as follows. In other words, from 300 ° C to 50-8
Cool to 0 ° C. at a rate of 4 ° C./sec or more and keep it at that temperature for 1 to 10 hrs.
After cooling at a speed of at least
Heat to ８０80 ° C. and hold in this temperature range for 1-10 hrs.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting alloy components in the present invention will be described. Mg: Mg is an element that strengthens its own solid solution and imparts strength in cooperation with Si, and precipitates an aging precipitate β′-Mg ² Si. However, if the content is less than 0.3%, sufficient strength (proof strength of the material after solution quenching and the strength after baking at 170 ° C.) cannot be obtained. Mg ₂ Si grows as a crystal, and the elongation is reduced, and the formability is significantly reduced. Therefore, the Mg content is in the range of 0.3 to 1.0%. Si: Si works together with Mg and mainly aging precipitate β'-M
It is an element that imparts strength by precipitation hardening due to precipitation of g ₂ Si. However, if it is less than 0.8%, sufficient strength cannot be obtained, and if it exceeds 1.3%, the equilibrium phase Mg ₂ Si
Are crystallized, or Si alone remains, and the elongation is reduced, thereby deteriorating the formability. Therefore, the Si content is 0.8% or more.
The range is 1.3%.

[0010] The Al-Mg-Si-based aluminum alloy according to the present invention further contains Cu, Mn, Cr and the like as unavoidable impurities. In addition, one or more of these components can be added as needed for the following effects. Cu: Cu is an alloy that imparts strength by aging precipitate θ′-CuAl ₂ . In the present invention, by adding Cu, the precipitate is finely and finely precipitated, the strength is improved, and the bake hardenability by low-temperature baking is improved. However, Cu
If the addition amount is less than 0.03%, the effect of increasing the strength is not recognized, and if it exceeds 0.7%, the corrosion resistance decreases. Therefore, when Cu is added, the content is 0.03% to 0.1%.
The range is 7%. Mn: an element that precipitates the second phase precipitate MnAl ₆ , suppresses recrystallization of the alloy composition, refines crystal grains, and contributes to improvement in formability and increase in strength. However, if the content is less than 0.05%, the effect of refining the crystal grains does not appear, and the precipitation of the second phase precipitate MnAl ₆ is not remarkable, so that no improvement in the formability or strength is observed. On the other hand, if it exceeds 0.2%, coarse crystals are formed, and the moldability is reduced. Therefore, when Mn is added, the content is in the range of 0.05 to 0.2%. Cr: Cr forms an intermetallic compound, and the refined compound suppresses recrystallization, refines the crystal grains, and gives an effect of improving the formability. However, the effect appears when the added amount is less than 0.005%. On the other hand, if it exceeds 0.1%, a coarse intermetallic compound is formed, and the moldability decreases. Therefore, when Cr is added, the content is made 0.005 to 0.1%. Other T
Inevitable impurities such as i, Fe, Zr, and Zn may be contained as long as they are 0.1%, 0.3%, 0.1%, and 0.2% or less, respectively.

Next, the reasons for limitation of the manufacturing method of the present invention will be described. The steps up to the solution treatment of the alloy having the above-described composition, that is, the steps up to forming a rolled sheet having a required product thickness, may be the same as those of an Al-Mg-Si-based alloy in a normal method. This will be briefly described as follows. First, the soaking process after dissolution → casting is to uniformly disperse the segregation of added elements,
This is an important heat treatment to control the size and volume content of the analytical precipitate. If this heat treatment is performed at a temperature lower than 500 ° C., the intermetallic compound comprising the additional element does not form a solid solution and remains with a high volume content, thereby deteriorating the formability. Further, when the treatment is performed at a temperature exceeding 600 ° C., burning occurs and cracks occur during hot rolling. Therefore, the temperature range of the homogenizing heat treatment is set to 500 to 600 ° C. Burning may occur at a temperature of 600 ° C. or lower, and it is preferable that the burning is performed at a temperature that does not cause burning, as high as possible, depending on the composition. Note that the holding time is determined as appropriate. The ingot subjected to the homogenizing heat treatment under the above conditions is subjected to hot rolling → cold rolling to a predetermined thickness. Desirably, in order to further increase the formability between hot rolling and cold rolling, the heating rate is 450 to 52 at a heating rate of 100 ° C./min or more.
It is preferable to perform an intermediate annealing treatment in a temperature range of 0 ° C. for 0 to 30 seconds.

[0012] After the cold rolling is completed to a predetermined thickness, a solution treatment is performed. In the heat treatment to the solution treatment temperature, rapid heating is desirable from the viewpoint of miniaturization of crystal grains. If the temperature of the solution treatment is lower than 510 ° C., the additional elements do not form a solid solution and bake hardenability cannot be obtained. On the other hand, as for the upper limit, a higher solution temperature is preferable for baking hardenability, but if it exceeds 590 ° C., eutectic melting may occur, so that it is preferably 590 ° C. or lower. The holding time in this temperature range is desirably 60 sec or less in view of the line efficiency in the continuous processing line, and may be 0 sec as long as the re-dissolution of the added element can be sufficiently performed. However, it is not particularly limited to this. After the solution treatment, quenching is performed. First, when the cooling rate from the solution temperature to the temperature of 400 ° C. is slower than 20 ° C./sec on average, coarse Mg ₂ Si and elemental Si are cooled during cooling. Precipitates and the formability decreases. In addition, bake hardenability is reduced, and sufficient strength cannot be obtained during baking. Therefore, it is necessary to cool at a rate of 20 ° C./sec or more, preferably 100 ° C./sec or more.

In the temperature range of 400 ° C. to 300 ° C., the material should be cooled in an average range of 4 ° C./sec to 10 ° C./sec in order to lower the atomic vacancy concentration in the material and to suppress the room temperature aging after the plate is manufactured. is necessary. That is, by cooling the temperature range from 400 ° C. to 300 ° C. in the range from 4 ° C. to 10 ° C./sec, the vacancy concentration is reduced, and the aging at normal temperature is suppressed. 4 ℃
When cooled at a rate slower than / sec, coarse Mg ₂ Si
In addition, elemental Si precipitates at the grain boundaries, and the aging resistance at room temperature is reduced, but the bake hardenability is reduced, and sufficient strength is not obtained at the time of coating baking, and the formability is also reduced. Meanwhile, 1
Cooling at a rate exceeding 0 ° C./sec freezes with a high vacancy concentration, so that the baking hardenability is good, but the room temperature aging becomes high. 4 ° C / sec on average from 300 ° C to room temperature
If it is slower, it ages and the material yield becomes higher. In addition, 5
Cool at a rate of 4 ° C / sec or more to 0 to 80 ° C on average,
After maintaining at that temperature range for 1 to 10 hrs, or cooling to room temperature at an average rate of 4 ° C./sec or more,
Heat to 50-80 ° C within min.
When held for 10 hours, precipitation nuclei contributing to hardening during baking coating are formed, which has the effect of improving baking hardenability. According to the manufacturing method described above, it is possible to obtain an aluminum alloy sheet having a reduced aging resistance at room temperature, having a difference in proof stress after standing at 25 ° C. for 7 days and standing at 25 ° C. for 90 days of 20 N / mm ² or less. Becomes At the same time, it is also possible to obtain an aluminum alloy sheet having a proof stress of 200 N / mm ² or more after baking coating at 170 ° C. for 20 minutes and suppressing the aging at room temperature.

[0014]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. (Example 1) The alloy ingot having the composition shown in FIG.
It was produced by a C casting method, and after being homogenized at 540 ° C. × 4 hrs, hot-rolled to a thickness of 2.5 mm. Then 50
Intermediate annealing at 0 ° C (holding time at 500 ° C for 0 sec)
c) Further, final cold rolling was performed to a thickness of 1 mm. Thereafter, the final solution treatment (solution treatment temperature and holding time are uniformly 540 ° C. × 30 sec) under the conditions A to E shown in Table 2.
c) and the second stage of low-temperature heating was performed. In addition, the cooling rate of the final solution treatment was adjusted by standing cooling, forced air cooling, hot water cooling, and water cooling.

[0015]

[Table 1]

[0016]

[Table 2]

The plate obtained as described above was further kept at room temperature for 7 days (25 ° C. × 7 days) and 90 days (25 ° C. × 90 days).
Day) After standing, the mechanical properties of each plate were investigated.
Furthermore, each board is stretched by 2% → 170 ° C × 20 min
Heat treatment (heating equivalent to baking coating) was performed, and characteristics after heating were investigated. Table 3 shows the above results. In Table 3,
Δσ0.2 is the difference between the proof stress after standing for 90 days and the proof stress after standing for 7 days (showing the aging effect at room temperature), and the proof strength after baking means the proof strength after heating equivalent to baking coating. As for the moldability (spring back), those having Δσ 0.2 of 20 N / mm ² or less were evaluated as “○”, and those exceeding 20 N / mm ² were evaluated as “x”. This is because the proof stress can be directly evaluated as the amount of springback, and Δσ0.2 is the difference between the amount of springback when molded after standing for 7 days and the amount of springback when molded after standing for 90 days ( This is because the same aluminum alloy plate can be evaluated as having a variation in the amount of springback, and therefore, a smaller Δσ0.2 (smaller aging at normal temperature) can be evaluated as having a smaller variation in the amount of springback and excellent moldability.

[0018]

[Table 3]

As shown in Table 3, the plate manufactured by the method of the present invention exhibited an increase in proof stress after holding at 25 ° C. × 90 days (Δσ 0.2).
It can be seen that the aging resistance at room temperature is suppressed, the variation of springback due to the aging of the same plate is suppressed, and the proof strength after baking is excellent at 200 N / mm ² or more, even though it is high. On the other hand, the plate manufactured under the conditions shown in the comparative example was subjected to aging at room temperature and a temperature of 25 ° C.
It can be seen that the increase in proof stress (Δσ0.2) after day holding was large, the variation in the amount of springback was large, and the moldability was poor (1D, 1E). In addition, the increase in proof stress (Δσ0.
In the case of 2), the proof stress before baking and the proof stress after baking are low (1C).

Example 2 An alloy ingot shown in Table 1 was produced by a DC casting method, and homogenized at 540 ° C. × 4 hrs.
Hot rolling was performed to a thickness of 2.5 mm. Then 500 ° C
Intermediate annealing of × 0 sec was performed, and final cold rolling was performed to a sheet thickness of 1 mm. Thereafter, a final solution treatment was performed in the process of the present invention (method A in Example 1), and the mechanical properties and formability of each obtained plate were examined in exactly the same manner as in Example 1. did. Table 4 shows the results.

[0021]

[Table 4]

The plate manufactured by the method of the present invention has a small increase in the yield strength (Δσ0.2) after holding at 25 ° C. × 90 days, suppresses the aging at room temperature, and exhibits a variation in springback due to the aging of the same plate. Suppressed and the proof stress after baking is 200N /
Despite its high value of ² mm or more, it has excellent moldability.
On the other hand, Comparative Examples 7 and 8 have low proof stress before and after baking, and Comparative Example 9 has a large increase in proof stress (Δσ0.2) after holding at 25 ° C. × 90 days after aging at room temperature due to the aging. The back has large dispersion and poor moldability, and the proof strength after baking after standing for 90 days is low.

[0023]

According to the present invention, Al-Mg-Si which suppresses the aging at room temperature, and is excellent in moldability and bake hardenability.
Aluminum alloy plate can be manufactured. This Al-Mg
-Si-based aluminum alloy plates can be suitably used for applications such as automobile panels and interior parts.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22F 1/00 686 C22F 1/00 686B 691 691B 691C 692 692A 692B 693 693A

Claims (4)

[Claims] 1. Mg in weight%: 0.3-1.0%, S
i: An Al-Mg-Si-based aluminum alloy containing 0.8 to 1.3% is melt-cast, then soaked, then hot-rolled and cold-rolled to a desired thickness, and then finalized. As a heat treatment, a solution treatment is performed by heating to a temperature of 510 to 590 ° C., and then to 20 ° C./sec up to a temperature of 400 ° C.
Cool at the above cooling rate, then 400 to 300 ° C
A temperature range of 4 to 10 ° C./sec, and then cooling to room temperature at a rate of 4 ° C./sec or more. 2. The aluminum alloy according to claim 1, which is melt-cast, subjected to soaking, then hot-rolled and cold-rolled to a desired thickness, and then subjected to a final heat treatment of 510.
After performing a solution treatment by heating to a temperature of 590 ° C.,
Cooling to a temperature of 00 ° C at a cooling rate of 20 ° C / sec or more, and then increasing the temperature range of 400 ° C to 300 ° C to 4 to 10 ° C
/ Sec, then cool to 50-80 ° C at a rate of 4 ° C / sec or more, or cool to room temperature.
After cooling at a rate of at least
A method for producing an aluminum alloy sheet with reduced aging at room temperature, characterized in that the sheet is heated to 0 to 80 ° C. and kept at 1 to 10 hrs in this temperature range. 3. The room temperature according to claim 1, wherein the difference in proof stress between the aluminum alloy plate after standing at 25 ° C. for 7 days and after standing at 25 ° C. for 90 days is 20 N / mm ² or less. A method for producing an aluminum alloy sheet with suppressed aging. 4. The aging resistance after baking at 170 ° C. for 20 minutes of the aluminum alloy plate is 200 N / mm ² or more, and the aging resistance at room temperature according to claim 1 is suppressed. Manufacturing method of aluminum alloy plate.