JP2003231955A - Process for manufacturing aluminum alloy plate with excellent hemmability and bake-hardening property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for manufacturing an aluminum alloy with excellent hemmability and bake-hardening property. <P>SOLUTION: In the process for manufacturing an aluminum alloy with excellent hemmability and bake-hardening property, an aluminum alloy comprising 0.3-0.7 mass% Mg, 0.7-1.5 mass% Si and the balance being Al and unavoidable impurities is hot-rolled and cold-rolled into a rolled plate with a desirable thickness. The rolled plate is subjected to a solution treatment at 480-580°C for ≤5 min and subsequently cooled to 60-120°C at a cooling rate of ≥10°C/sec in a first cooling step. Immediately after the first cooling step, the plate is cooled to 40°C in a second cooling step according to the formula: (0.0178 T-1.289)<log(R)<1 (wherein R is the average cooling rate (°C/hr) in the second cooling step; T is the finishing temperature (°C) in the first cooling step; and log is the common logarithm). The plate is heated at a temperature-rising rate of ≥5°C/sec, kept at 180-280°C for ≤60 sec and subsequently cooled at a cooling rate of ≥5°C/sec. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an automobile body sheet.
The present invention relates to a method for producing a 6000-series aluminum alloy sheet suitable for use in a sheet and the like, and particularly to a method for producing an aluminum alloy sheet having excellent hem bendability and paint bake hardening.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for weight reduction of vehicle bodies for the purpose of improving fuel efficiency of automobiles, and aluminum alloy plates for automobile body panels and the like have been used as one of means for reducing weight. As an aluminum alloy for automobile body panels, a non-heat treatment type 5000 series alloy (Al-Mg
System) and a heat treatment type 6000 series alloy (Al-Mg-Si)
System) and are used. In recent years, 6000 series alloys are used as body panel materials because the thinness of panels can be aimed at by taking advantage of the fact that the yield strength can be increased by utilizing the heat treatment of paint baking process (paint baking hardenability). Is increasing.

However, in order to obtain a high paint bake hardenability, the conventional general manufacturing method is not sufficient, and JP-A-7-150282, JP-A-8-60314, and JP-A-9-143644 are not sufficient. Various manufacturing methods such as publications have been proposed. The inventors of the present invention also disclosed in JP-A-11-1723.
Japanese Patent Laid-Open No. 90 discloses a method for producing an aluminum alloy sheet which is excellent in paint bake hardenability and has little change with time at room temperature after sheet production and is excellent in press formability. However, in recent years, higher levels of press formability and paint bake hardenability have been required, and excess Si type is often used as an alloy component.
Cu may be added in some cases. The alloy having such a component has a problem that the hem bendability is likely to be lowered, but at present, the required level of the hem bendability is higher.

Here, the hem bending process is performed at a panel end portion such as an engine hood or a trunk lid of an automobile.
It is a bending process of °. Aluminum alloy, especially Al-M
The g-Si alloy is apt to cause defects such as cracks in the bent portion. Considering such severe hem bending, it is difficult to say that the current aluminum alloy has sufficient workability.

[0005]

SUMMARY OF THE INVENTION The present invention has been made under the circumstances described above, and impairs the coating bake hardenability of a 6000 series aluminum alloy sheet which is particularly effective for use in automobile body panels. It is an object of the present invention to provide a method for producing an aluminum alloy sheet having excellent hem bendability and bake hardenability, which can sufficiently cope with hem bending without using the above method.

[0006]

The inventors of the present invention have conducted various studies in order to achieve the above-mentioned object, and as a result, the excellent paint bake hardenability can be secured as it is, and the hem bendability can be further improved. The present invention has been completed by finding a manufacturing method, and the gist thereof is as follows. (1) Mass%, Mg: 0.3 to 0.7%, Si: 0.
An aluminum alloy containing 7 to 1.5% and the balance Al and unavoidable impurities is formed into a rolled plate having a desired plate thickness by hot rolling and cold rolling, and the rolled sheet is heated at a temperature of 480 to 580 ° C for 5 minutes or less. After performing the solution treatment, the first stage cooling is performed at a cooling rate of 10 ° C./s or more to a temperature in the range of 60 to 120 ° C., and immediately after the first stage cooling to 40 ° C., the following formula: (0 .0178T-1.289) <log
Second stage cooling according to (R) <1 (where R: average cooling rate of second stage cooling (° C / h), T: first stage cooling end temperature (° C), log is a common logarithm) , And 5
Heme bendability and baking characterized by performing a heat treatment of holding the temperature in the range of 180 to 280 ° C for 60 seconds or less at a temperature rising rate of ° C / s or more, and then cooling at a cooling rate of 5 ° C / s or more. A method for producing an aluminum alloy plate having excellent curability.

(2) The aluminum alloy is in a mass%
Then, the method for producing an aluminum alloy sheet having excellent heme bendability and paint bake hardenability according to (1) above, which further contains Cu: 0.1 to 0.8%. (3) The aluminum alloy contains Ti: 0.
005-0.15%, B: 0.0001-0.05%,
Mn: 0.03 to 0.4%, Cr: 0.02 to 0.15
%, Fe: 0.03 to 0.3%, Zn: 0.03 to 1%
The method for producing an aluminum alloy sheet having excellent heme bendability and paint bake hardenability according to (1) or (2) above, which further comprises one or more of these.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The inventors of the present invention have proposed a method for producing an aluminum alloy sheet for forming, which has excellent paint bake hardenability, in JP-A No. 11-172390, but further limit the components and increase the second stage cooling rate, The inventors have found that by optimizing the restoration treatment conditions that are continuously performed after the second-stage cooling, the hem bendability is greatly improved while maintaining good paint bake hardenability, and the present invention has been completed.

First, the reason for limiting the preferable component composition range in the present invention will be explained. Mg, Si: Mg and Si are essential basic components of the present invention, and are contained in order to obtain excellent paint bake hardenability and good press moldability. The component range is Mg: 0.3
˜0.7%, Si: 0.7 to 1.5%. If Mg is less than 0.3% and Si is less than 0.7%, good press formability and paint baking effect cannot be obtained. Also, M
This is because when g exceeds 0.7% and Si exceeds 1.5%, grain boundary precipitation is likely to occur and the hem bendability is deteriorated.

Cu: Cu is preferably contained mainly for improving the press moldability. The composition range was Cu: 0.1 to 0.8%. If the Cu content is less than 0.1%, a sufficient effect of improving press moldability cannot be obtained. On the other hand, if the Cu content exceeds 0.8%, the corrosion resistance deteriorates and high hem bendability cannot be secured. Further, if necessary, one or more of Ti, B, Mn, Cr, Fe and Zn may be contained.

Ti and B: Since Ti and B have the effect of refining the crystal grains of the ingot and improving the press formability by adding a small amount, the content of Ti is 0.005 to 0.15%,
The content of B is preferably specified in the range of 0.0001 to 0.05%. If Ti exceeds 0.15% and B exceeds 0.05%, coarse crystallized substances are formed and the formability deteriorates. Further, if Ti is less than 0.005% and B is less than 0.0001%, the grain refining effect of the ingot cannot be sufficiently obtained.

Mn, Cr, Fe and Zn have the effect of improving press formability by improving strength and making crystal grains finer. Mn, Cr, Fe: Mn, Cr and Fe are all elements that improve the formability by improving the strength and refining the crystal grains, and the content thereof is 0.4% of Mn and C.
If r is more than 0.15% and Fe is more than 0.3%, coarse crystallized substances are formed, and the formability is rather lowered. on the other hand,
Mn 0.03%, Cr 0.02%, Fe 0.02
If it is less than%, the above effect cannot be sufficiently obtained. Therefore, Mn: 0.03 to 0.4%, Cr: 0.02 to 0.
15% and Fe: 0.03 to 0.3%.

Zn: Zn has the effect of improving formability by improving strength. If the content is less than 0.03%, the above effect is insufficient, and if it exceeds 1%, the increase in strength becomes too large and the moldability rather deteriorates. Therefore, the range is 0.03 to 1%. In addition to the above elements,
Like the usual aluminum alloys, inevitable impurities are contained, but the amount thereof is acceptable as long as it does not impair the effects of the present invention.

Next, the preferred method for producing the aluminum alloy sheet of the present invention will be described in detail. The aluminum alloy of the present invention may be cast, hot-rolled and cold-rolled in a conventional manner to produce a plate having a desired thickness. In addition, intermediate annealing may be performed between the hot rolling and the cold rolling and during the cold rolling. 48 after cold rolling to desired thickness
Solution treatment is performed at a temperature in the range of 0 to 580 ° C. 48
At temperatures below 0 ° C, the solute atoms that contribute to press formability and paint bake hardenability do not form a solid solution in the Al matrix phase and precipitate as the second phase, so the above performance is sufficiently secured. It is not possible and the hem bendability is reduced. On the other hand, if the solution temperature exceeds 580 ° C., partial dissolution may occur. Therefore, the solution heat treatment temperature was set within the range of 480 to 580 ° C.

Regarding the holding at the solution heat treatment temperature, no holding may be performed (cooling immediately after reaching the solution heat treatment temperature) as long as heating is performed within the above temperature range. Meanwhile, 5
If the amount is kept over the above range, not only the solution effect is saturated and the economical efficiency is impaired, but also the recrystallized grains are coarsened. Therefore, the holding time was set to 5 minutes or less. Cooling after the solution treatment is performed at a cooling rate of 10 ° C./s or more to a temperature range of 60 ° C. or more and 120 ° C. or less. If the cooling rate after the solution treatment is set to less than 10 ° C./s, the Mg ₂ Si or the like second
Phases are precipitated, the heme bendability and press formability are reduced, the supersaturated solid solution amount of solute atoms is reduced, and the paint bake hardenability is also reduced. Therefore, the cooling rate after the solution treatment temperature is set to 10 ° C./s or more. The upper limit is not particularly limited, but if it exceeds 100 ° C./s, problems of shape such as plate warp are likely to occur.

After the first stage cooling described above, up to 40 ° C.,
(0.0178T-1.289) <log (R) <1
(However, R: average cooling rate of second stage cooling (° C / h),
T: The second stage cooling is performed according to the first stage cooling end temperature (° C.), log is a common logarithm. The above formula is derived experimentally, but the purpose of cooling according to this formula is
This is to form a fine β ″ phase by gradually cooling from the 1st stage cooling end temperature to 40 ° C., to secure the paint bake hardenability and to suppress room temperature aging after plate production.

When R is 10 ° C./h or more, the components of the present invention are insufficient in securing the coating bake hardenability and suppressing the change with time in room temperature after plate production. Also, 0.6 ° C./h, which is the (0.0178T−1.289) value when T = 60 ° C.
In the following, the hem bendability is likely to decrease. Furthermore, 5
Heat treatment is performed at a temperature rising rate of C / s or more at a temperature in the range of 180 to 280 C for 60 seconds or less, and then cooling is performed at a cooling rate of 5C / s or more. If the heating temperature is lower than 180 ° C or higher than 280 ° C, good hem bendability cannot be secured.

Further, when the temperature rising or cooling rate is less than 5 ° C./s or when the holding time is 60 seconds or more, grain boundary precipitation is likely to occur and the hem bendability is deteriorated. If the heating temperature is reached, the lower limit of the holding time may be 0 second. That is, no holding is required (cooling immediately after reaching the heating temperature). The upper limits of the temperature rising rate and the cooling rate are not particularly limited, but if the rate exceeds 100 ° C./s, problems such as plate warpage are likely to occur. The temperature range in which cooling is performed at the above cooling rate is preferably from the heating temperature to 40 ° C. This is because if the cooling end temperature is high, the hem bendability may decrease, and 120 ° C. or lower is preferable. There is no particular time constraint from the second stage cooling to this restoration process. As described above, by defining the alloy components and performing the two-step cooling after solution treatment and the restoration treatment in the manufacturing process under appropriate conditions, it is possible to have excellent hem bendability and paint bake hardenability.

[0019]

EXAMPLES The present invention will be described below based on examples. (Example 1) An alloy having a composition as shown in Table 1 was melted, cast, and rolled by a usual method to form a plate having a plate thickness of 1 mm. Then, the rolled plate was subjected to a solution treatment of 550 ° C. for 20 s and air-cooled to 90 ° C. at an average cooling rate of 30 ° C./s, and then subjected to a cooling rate formula of 40 according to the present invention.
The second stage cooling was performed at 3 ° C./h to 0 ° C. 230 ° C thereafter
Restoration processing was performed for 10 seconds. The temperature rising and cooling rates were both 30 ° C./s. After the plate was manufactured, it was allowed to stand at room temperature for 10 days, and then the tensile properties, paint bake hardenability, and hem bendability were evaluated. The evaluation of the paint bake hardenability was carried out by measuring the yield strength when heat treatment was carried out at 175 ° C. for 30 minutes, which corresponds to the paint bake treatment. The hem bendability was evaluated by applying a prestrain of 10%, bending 180 ° with a 1 mm plate sandwiched therebetween, and the cracking condition in the bent portion. The scores were ⊚ good, ○ slightly rough skin, △ fine cracks, and × large cracks. The survey results are shown in Table 1. As for the paint bake hardenability, the amount of strength increase due to the paint bake treatment: 70
The target was at least MPa.

[0020]

[Table 1]

From Table 1, the aluminum alloy sheets 1 to 12 having the components of the present invention have a strength increase of 70 M due to baking.
It is Pa or more, and also has a good hem bendability to the extent that slight rough skin is observed. On the other hand, the alloys 13 and 14 of Comparative Examples having components other than the present invention as essential components cannot achieve both good hem bendability and paint bake hardenability even when produced by the production method of the present invention. Alloy 13 has good hem bendability, but very low paint bake hardenability.
Alloy 14 has insufficient paint bake hardenability and low hem bendability. The alloy 15 satisfies the composition requirement of claim 1, but if the selected component Cu is out of the upper limit thereof, it has a paint bake hardenability but has a low hem bendability. Alloy 16 satisfies the constituent requirements of claim 1, but is an optional constituent M
This is the case where n and Cr are out of the upper limits, and coarse crystallized substances are formed, so that the coating bake hardenability but the hem bendability becomes low.

The alloy 17 also satisfies the component requirements of claim 1, but Fe and Zn which are the selective components are out of the upper limits, and in this case as well, coarse crystallized substances are formed and the coating is bake hardenable. However, the bendability of the hem is low. Alloy 18 satisfies the composition requirements of claim 1, but the selected components Ti and B are out of the upper limits, and although it has paint bake hardenability, it has low hem bendability due to the formation of coarse crystallized substances. I will end up. Thus, in the examples belonging to the present invention,
It was possible to produce an aluminum alloy plate having both good paint bake hardenability and hem bendability.

Example 2 A 1 mm-thick rolled plate having the composition of the invention alloy 6 in Table 1 was subjected to solution treatment by holding at 540 ° C. for 10 seconds, and then subjected to heat treatment conditions shown in Table 2. A test material was produced. For this aluminum alloy plate,
A study similar to that conducted in Example 1 was performed. The survey results are shown in Table 2. Under the manufacturing conditions 1 to 5 of the present invention, the strength increase due to coating baking is 70 MPa or more, and the hem bendability is also good. On the other hand, it is understood that Comparative Examples 6 to 13 of the manufacturing conditions which are out of the present invention cannot have both good hem bendability and paint bake hardenability. Comparative Example 10 was manufactured under the conditions described in JP-A No. 11-172390, but the paint bake hardenability was good, but the hem bendability was poor.

[0024]

[Table 2]

[0025]

As described above, according to the present invention, an aluminum alloy sheet having excellent hem bendability and paint bake hardenability and suitable for automobile bodies can be provided. It can greatly contribute to the weight reduction of. Therefore, it can be said that the industrial value of the present invention is extremely high.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22F 1/00 672 C22F 1/00 672 683 683 683 685 685Z 686 686B 691 691A 691B 691C 692 692A 692B (72) Inventor Sato 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd. Technical Development Department (72) Inventor Asahi Hibino 1-2-1 Kinshi 1-2 Sumida-ku, Tokyo Sky Aluminum Co., Ltd. (72) Inventor Osamu Noguchi Tokyo 1-2-1 Kinshi, Sumida-ku, Sky Aluminum Co., Ltd. (72) Inventor Toshiki Muramatsu 1-2-1, Kinshi, Sumida-ku, Tokyo Sky Aluminum Co., Ltd.

Claims (3)

[Claims] 1. An aluminum alloy containing Mg: 0.3 to 0.7% and Si: 0.7 to 1.5% by mass, with the balance being Al and inevitable impurities. A cold rolled plate having a desired plate thickness is obtained by cold rolling, and a solution treatment is performed at a temperature of 480 to 580 ° C. for 5 minutes or less, and then cooled to a temperature in the range of 60 to 120 ° C. at a cooling rate of 10 ° C./s or more. The following formula is used from immediately after the first stage cooling to 40 ° C .: (0.0178T-1.289) <log (R) <1
(However, R: average cooling rate of second stage cooling (° C / h),
T: Second stage cooling according to the first stage cooling end temperature (° C), log is a common logarithm), and 60 at a temperature in the range of 180 to 280 ° C at a temperature rising rate of 5 ° C / s or more. A method for producing an aluminum alloy sheet having excellent hem bendability and bake hardenability, which comprises cooling at a cooling rate of 5 ° C./s or more after performing a heat treatment for holding for not more than 2 seconds. 2. The aluminum alloy contains C in mass%.
The method for producing an aluminum alloy sheet having excellent hem bendability and paint bake hardenability according to claim 1, further comprising u: 0.1 to 0.8%. 3. The aluminum alloy, in mass%, Ti: 0.005-0.15%, B: 0.0001-0.05%, Mn: 0.03-0.4%, Cr: 0. 0.02 to 0.15%, Fe: 0.03 to 0.3%, Zn: 0.03 to 1%, or one or more kinds thereof are further contained. The method for producing an aluminum alloy sheet having excellent hem bendability and paint bake hardenability according to 1.