JP2001152302A - Aluminum alloy sheet excellent in press formability, and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy sheet for automobile use, having press formability comparable with that of the 5000 series alloys and capable of giving sufficient strength by baking finish. SOLUTION: The aluminum alloy sheet excellent in press formability has a composition consisting of, by mass, 0.1-0.6% Mg, >1.2-1.7% Si, 0.5-1.5% Cu and the balance Al with inevitable impurities and satisfying Mg+Si<=2%, and further, with respect to TS(tensile strength) and YS (0.2% proof stress) before pressing, the value of (TS-YS) is regulated to >=130 MPa, preferably >=140 MPa. This alloy sheet can be manufactured by performing solution heat treatment at 450-580 deg.C after cold rolling and then applying cooling at >=15 deg.C/s cooling rate down to a temperature between room temperature and 70 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a mold having excellent moldability,
The present invention relates to an aluminum alloy sheet suitable for an automobile body sheet and the like and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for weight reduction of a vehicle body for the purpose of improving fuel efficiency of an automobile. As one of means for reducing the weight, use of an aluminum alloy plate for an automobile body sheet or the like has been performed. A material for an automobile body sheet is required to have not only excellent press formability but also excellent strength after baking, corrosion resistance, and the like. Currently used aluminum alloys for automobile body sheets include a non-heat treated Al-Mg alloy and a heat treated A
An l-Mg-Si system is used.

[0003] Al-Mg based alloys have been widely used in automobile body panels in Japan as aluminum alloys having excellent formability, since ductility is improved with an increase in Mg content. However, in Al-Mg based alloys,
Although it has better formability than Al-Mg-Si alloys, the stretcher-strain pattern may appear during press forming to impair the surface quality, or it may soften during baking and dent resistance. There is a problem that it is inferior.

On the other hand, the Al-Mg-Si-based alloy has advantages in that a stretcher-strain pattern essentially does not substantially appear, and that the yield strength can be increased by utilizing heat treatment in a coating baking process. There is a problem that the formability is inferior to that of an Al-Mg alloy, and there is a limit in its application to an automobile body panel. Thus, as an aluminum alloy for automobile body panels,
It is required to have excellent press formability, excellent surface quality after pressing, and sufficient strength by paint baking.

[0005]

To cope with such required characteristics, for example, Japanese Unexamined Patent Publication No. 1-287244 discloses that an Al-Cu-Mg-Si alloy having age-hardening property is used as a core material to form a good molding. There has been proposed an aluminum alloy laminated plate using pure Al as a skin material, which has properties and has no problem with a stretcher-strain pattern, and achieves both press formability and paint bake hardenability. However, there is a concern that the manufacturing cost of the plywood increases and that contact corrosion of dissimilar metals occurs on the end face. SUMMARY OF THE INVENTION An object of the present invention is to provide an aluminum alloy sheet for automobiles having a single plate having press formability comparable to that of a 5000 series alloy and having sufficient strength obtained by coating and baking.

[0006]

Means for Solving the Problems In order to achieve the above object, the inventors first studied various factors affecting the formability of an aluminum alloy sheet. As a result, Al
In an alloy containing Cu as a base based on an Mg-Si system, when a cluster (hereinafter referred to as a low-temperature cluster) formed of solute atoms formed at a temperature near room temperature after solution is formed, the (TS-YS) value becomes Higher and its value is 130
It has been found that a press formability equal to or higher than that of the 5000 series alloy can be obtained if the pressure is at least MPa. But,
This low-temperature cluster is used for G.I. P. Al-Mg, which hinders the precipitation of the zone and cannot be expected to have a large increase in strength at the time of paint baking, is softened by paint baking by specifying the alloy components and manufacturing method.
It was also found that sufficient strength could be obtained, exceeding that of the base alloy.

The present invention has been obtained based on the above findings, and its gist is as follows: (1) mass%, Mg: 0.1 to 0.6%, Si:
More than 1.2 to 1.7%, Mg + Si: 2% or less, Cu:
0.5-1.5%, the balance consists of Al and unavoidable impurities, and in TS (tensile strength) and YS (0.2% proof stress) before pressing, (TS-YS) An aluminum alloy plate excellent in press formability, having a value of 130 MPa or more. (2) mass%, Ti: 0.005 to 0.15%,
B: 0.0001 to 0.05%, Mn: 0.03 to 0.
4%, Cr: 0.02 to 0.15%, Fe: 0.03 to
The aluminum alloy sheet having excellent press formability according to the above (1), further comprising one or more of 0.3% and Zn: 0.03 to 1%.

(3) After the cold rolling, the solution is subjected to a solution treatment at a temperature of 450 to 580 ° C., and then cooled from room temperature to 70 ° C. at a cooling rate of 15 ° C./s or more. ) Or the method for producing an aluminum alloy sheet excellent in press formability according to (2). (4) After performing a solution treatment and cooling to a temperature of room temperature or more and 70 ° C. or less, it is left at room temperature for one day or more,
The method for producing an aluminum alloy sheet excellent in press formability according to the above (3), further comprising performing heat treatment at a temperature of 120 ° C. for 1 to 50 hours. (5) The above-mentioned (3), wherein after performing a solution treatment and cooling to a temperature of room temperature or more and 70 ° C. or less, a heat treatment is further performed at a temperature of room temperature or more and 70 ° C. or less for 1 to 100 hours. 3. The method for producing an aluminum alloy sheet having excellent press formability described in 1. above.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The present inventors have conducted various studies on material factors affecting the formability of an aluminum alloy plate in order to achieve the above object. As a result, the (TS-YS) value of the alloy plate (where TS is the tensile strength, YS is 0.2% proof stress)
It has been found that press formability is improved. Next, in the Al-Mg-Si based alloy which has no stretcher-strain pattern and has age-hardening properties, the inventors carefully studied the influence of the presence state of solute atoms, alloy components and manufacturing conditions on press formability. .

As a result of various studies, in an alloy obtained by adding Cu to an Al-Mg-Si alloy, the ranges of the components of Mg and Si and the added amount of Cu are specified, and the alloy is formed at a temperature near room temperature after solutionizing. When a low-temperature cluster considered to be composed of solute atoms is formed, (TS-
YS) value and formability equivalent to that of the 5000 series alloy is obtained.
It has been found that press formability of at least 000 series alloy can be obtained. Therefore, in order to ensure higher formability, the (TS-YS) value of the alloy is preferably set to 140 or more.

[0011] In addition, the general paint baking conditions of 17
In a heat treatment at a temperature of about 0 to 180 ° C. for less than 30 minutes, since this low-temperature cluster exists relatively stably, the amount of supersaturated solid solution of solute atoms is reduced. P. This hinders zone deposition. As a result, although a large increase in strength cannot be expected during the baking treatment, it was also found that by specifying the alloy components and the manufacturing method, a sufficient strength of a 5000 series alloy or more which is softened by baking paint can be obtained.

The reason for limiting the preferred component composition range in the present invention will be described. Mg, Si, Cu, Mg, S
i and Cu are indispensable basic components of the present invention, and are contained in order to form fine low-temperature clusters and obtain high press moldability and sufficient paint bake hardenability. As the component ranges, Mg: 0.1 to 0.6 mass%, Si: 1.
More than 2 to 1.7 mass%, Cu: 0.5 to 1.5 mass
s% and Mg + Si ≦ 2 mass%. Mg
Is less than 0.1 mass%, Si is less than 1.2 mass%, and Cu is less than 0.5 mass%, a (TS-YS) value of 130 MPa or more cannot be obtained, and sufficient press moldability and paint baking effectiveness can be obtained. I can't.

When Mg exceeds 0.6 mass%, Si exceeds 1.7 mass%, Cu exceeds 1.5 mass%, and Mg + Si> 2 mass%, the effect of improving the (TS-YS) value is not only saturated, but also , Mg ₂ S during solution treatment
A second phase, such as i, Si, an Al-Cu-Mg-Si-based compound, precipitates on the crystal grain boundaries, increases the 0.2% proof stress, and greatly reduces the hem bendability. In the present invention, if necessary, Ti, B, Mn, Cr,
One or more of Fe and Zn may be contained.

[0014] 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 mass%,
It is preferable that the content of B is specified in the range of 0.0001 to 0.05 mass%. Each content is Ti:
If it exceeds 0.15 mass% and B: more than 0.05 mass%, a coarse crystallized substance is formed and the moldability deteriorates. Therefore, it is preferable that the upper limit is 0.15 mass% and 0.05 mass%, respectively. Each content is Ti: 0.
If it is less than 005 mass% and B is less than 0.0001 mass%, the effect of refining the crystal grain of the ingot cannot be sufficiently obtained.
Preferably, the lower limit is 001 mass%.

Since Mn, Cr, Fe, and Zn have the effect of improving the press formability by improving the strength and refining the crystal grains, Mn: 0.03 to 0.4mass, respectively.
s%, Cr: 0.02 to 0.15 mass%, Fe:
It is good to make it contain in the range of 0.03-0.3 mass% and Zn: 0.03-1%. Among them, Mn, Cr, Fe
Are elements that improve press formability by improving strength and refining crystal grains. When the content of Mn exceeds 0.4 mass%, the content of Cr exceeds 0.15 mass%, and the content of Fe exceeds 0.3 mass%, Coarse crystals are formed, and the moldability is rather deteriorated. Further, the content of Mn is 0.03 mass% and the content of Cr is 0.02 mass%.
% And Fe less than 0.02 mass%, the above-mentioned effects cannot be sufficiently obtained.

Zn has the effect of improving press formability by improving strength. Its content is 0.03m
If it is less than ass%, the above effect is insufficient, and 1mas
If it exceeds s%, the increase in strength becomes too large and the press formability is rather deteriorated. Therefore, it is set in the range of 0.03 to 1%. In addition to the above-mentioned elements, unavoidable impurities are contained as in the case of ordinary aluminum alloys, but the amount thereof is acceptable as long as the effects of the present invention are not impaired.

In addition, the production method is based on a method of rapidly cooling to room temperature after the solution treatment to form a solute atom into a supersaturated solid solution and forming a low-temperature cluster by aging near room temperature. In the case where diffusion of solute atoms is slow only by aging at room temperature and sufficient strength characteristics cannot be obtained in a short time, it is effective to continue heat treatment in a temperature range of 50 to 120 ° C. after aging at room temperature. Further, since the low-temperature cluster formation temperature range is about 70 ° C. or less, a method of rapidly cooling to a low-temperature cluster temperature range of room temperature or more and 70 ° C. or less after the solution treatment and aging in that temperature range is also effective.

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 is subjected to casting, hot and cold rolling according to a conventional method. However, in order to form a low-temperature cluster and obtain excellent formability, after the cold rolling, a temperature within a range of 450 to 580 ° C. It is effective to perform a solution treatment at a temperature of not less than room temperature and not more than 70 ° C. at a cooling rate of not less than 15 ° C./s. As the solution treatment conditions in the above step, at a temperature of 450 ° C. or less, the solute atoms contributing to the improvement of the formability and ensuring the baking hardenability of coating (age hardening) do not sufficiently dissolve in the Al matrix, Because of precipitation as a phase, it is not possible to improve the formability and ensure the baking hardenability of the coating, and the hem bending property is reduced. On the other hand, if the solution temperature exceeds 580 ° C., partial melting may occur. Therefore, the solution treatment temperature was set in the range of 450 to 580 ° C. Regarding the above-mentioned holding at the solution temperature, if the solute atoms are sufficiently dissolved, even if no holding (cooling immediately after reaching the solution treatment temperature), a certain holding time is required. Good.

If the cooling rate after the solution treatment is set to less than 15 ° C./s, the second phase precipitates during cooling, the hem bendability decreases, and the supersaturated solid solution amount of solute atoms decreases. The amount of low-temperature cluster formation effective for improving press formability is reduced, and the baking hardenability of the coating is also reduced. Therefore, the cooling rate after the solution treatment temperature is 15 ° C./s
It was above. Further, the reason for defining the temperature range for cooling after the solution treatment is that if the temperature exceeds 70 ° C., not the low-temperature cluster but G.P. P. This is because a zone is formed, and low-temperature clusters are formed below room temperature, but the diffusion of solute atoms is slow, and it takes a long time to form low-temperature clusters. The room temperature here is approximately 25 ° C.

Second, after cold rolling, a solution treatment is performed at a temperature in the range of 450 to 580 ° C., and the solution is cooled to room temperature at a cooling rate of 15 ° C./s or more, and then left at room temperature for 1 day or more. ,
Thereafter, it is effective to perform heat treatment in a temperature range of 50 to 120 ° C. for 1 to 50 hours to obtain excellent moldability. The reasons for setting the solution treatment temperature and cooling rate conditions in the above step are the same as those described above. If the standing time at room temperature after solution treatment is less than 1 day, the amount of low-temperature clusters that contribute to the improvement of moldability will be reduced.

In addition, the diffusion of solute atoms is slow only by aging at room temperature for one day or more, and sufficient strength characteristics cannot be obtained in a short period of time, which may cause a problem from the viewpoint of industrial productivity.
In that case, it is effective to continue the heat treatment in a temperature range of 50 to 120 ° C. after aging at room temperature. The reason for defining the range of this heat treatment is that if the treatment is performed at a temperature lower than 50 ° C. for less than 1 hour, a sufficient increase in strength cannot be obtained.
On the contrary, if the time is longer than the above, the increase in strength becomes too large.

Thirdly, it is preferable to cool to a temperature of from room temperature to 70 ° C. after the solution treatment and then to perform a heat treatment at a temperature of from room temperature to 70 ° C. for 1 to 100 hours to obtain excellent formability. It is effective for The reason for defining the temperature range for cooling after the solution treatment is that if the temperature exceeds 70 ° C. P. This is because zones are formed, and low-temperature clusters are formed at room temperature or lower, but the diffusion of solute is slow and the formation of low-temperature clusters takes a long time.

Further, the reason for defining the heat treatment time is as follows.
In less than one hour, the amount of low-temperature cluster formation is insufficient,
If the time is longer than 100 hours, the strength rise becomes too large. The aluminum alloy plate thus obtained has excellent press formability, and has a 500
A sufficient strength equal to or higher than that of the 0-base alloy can be obtained. Therefore, such an aluminum alloy plate is suitable for an automobile body sheet.

[0024]

The present invention will be described below with reference to examples. (Example 1) An alloy having a component composition as shown in Table 1 was melted, cast and rolled by a usual method to form a plate having a thickness of 1 mm. The rolled sheet was subjected to a solution treatment at 550 ° C. for 20 seconds and then air-cooled to room temperature at an average cooling rate of 30 ° C./s to produce an aluminum alloy sheet. After being left at room temperature for 10 days after the production, tensile properties and moldability (deep drawing test, ball head overhang test) were examined. Further, in order to evaluate the paint bake hardenability, a heat treatment was performed at 170 ° C. for 20 minutes corresponding to the paint bake treatment after applying a 2% pre-strain corresponding to the processing received by the press, and the proof stress was examined. Table 2 shows the results of those investigations.

[0025]

[Table 1]

The object of the present invention is to provide an aluminum alloy sheet having good formability comparable to 5000 series alloy and almost sufficient paint bake hardenability equal to or more than 5000 series alloy. As the performance, the limit aperture ratio: 2.03 or more, Erichsen value: 10.3 or more, preferably the limit aperture ratio: 2.05 or more, Erichsen value: 1
The target was 0.5 or more. Further, as the paint bake hardenability, the yield strength after paint bake was set to 140 MPa or more.

As shown in Table 2, the aluminum alloy sheet 1 of the present invention
Nos. 17 to 17 have excellent moldability and a strength after baking of 13
It turns out that it is more than 0MPa. Also, alloys 18 and 19 of comparative examples having components other than the present invention have low formability,
In addition, paint bake hardenability is low. On the other hand, alloys 20 to 25 have paint bake hardenability, but are inferior in moldability due to departure from the components of the present invention. That is, according to the present invention, it is possible to manufacture an aluminum alloy plate having both good formability and sufficient paint bake hardenability.

[0028]

[Table 2]

Example 2 A 1 mm-thick rolled sheet of Invention Alloy 5 shown in Table 1 was subjected to a solution treatment at 550 ° C. for 20 seconds and then cooled to room temperature by controlling the cooling rate. After air-cooling, after standing at room temperature, heat treatment was continued. Average cooling rate after solution, leaving time from air cooling to heat treatment,
Table 3 shows the heat treatment conditions after standing at room temperature. Investigations similar to those performed in Example 1 were performed on the aluminum alloy plate manufactured as described above. Table 4 shows the results of the investigation. The production conditions were such that the cooling rate was too low to obtain a sufficient supersaturated solid solution, so that the production conditions were insufficient storage at room temperature after solutionization, and good moldability was not obtained. . In addition, the production conditions were such that the initial strength was low due to insufficient heat treatment, and the yield strength after coating baking was insufficient. Under the production conditions, the strength increase due to the heat treatment was too large, and the formability was deteriorated. Thus, it can be seen that the one treated under the production conditions of the present invention is excellent in moldability and has a sufficient amount of paint bake hardening as compared with the production conditions of the above-mentioned comparative example.

[0030]

[Table 3]

[0031]

[Table 4]

Example 3 A 1 mm-thick rolled sheet of invention alloy 5 in Table 1 was subjected to a solution treatment at 550 ° C. for 10 seconds and then to a temperature at an average cooling rate of 25 ° C./s. Air cooled. After air cooling, heat treatment was subsequently performed. Table 5 shows the air cooling temperature after the solution treatment and the conditions of the subsequent heat treatment. Investigations similar to those performed in Example 1 were performed on the aluminum alloy plate manufactured as described above. Table 6 shows the results of the investigation. As shown in Table 6, it can be seen that those treated under the production conditions in the present invention have excellent moldability and a sufficient amount of paint bake hardening in comparison with the production conditions of the above-mentioned comparative example. .

[0033]

[Table 5]

[0034]

[Table 6]

[0035]

According to the present invention, it is excellent in moldability, has sufficient paint baking hardenability, and is suitable for an automobile body or the like that requires moldability and dent resistance after baking. Since an aluminum alloy plate can be provided, it can greatly contribute to reducing the weight of a vehicle. Therefore, it can be said that the industrial value of the present invention is extremely high.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) ) Inventor Ken Takada 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Toshiki Muramatsu 1-2-1 Kinshi, Sumida-ku, Tokyo Sky Aluminum Co., Ltd. (72) Invention Person Osamu Noguchi 1-2-1 Kinshi, Sumida-ku, Tokyo Sky Aluminum Co., Ltd.

Claims (5)

[Claims] 1. Mass%: Mg: 0.1 to 0.6%, Si: more than 1.2 to 1.7%, Mg + Si: 2% or less, Cu: 0.5 to 1.5% And the balance consists of Al and inevitable impurities,
An aluminum alloy sheet excellent in press formability, wherein the value of (TS-YS) in TS (tensile strength) and YS (0.2% proof stress) before pressing is 130 MPa or more. 2. Mass%, Ti: 0.005 to 0.15%, B: 0.0001 to 0.05%, Mn: 0.03 to 0.4%, Cr: 0.02 to 0. The press formability according to claim 1, further comprising one or more of 15%, Fe: 0.03 to 0.3%, and Zn: 0.03 to 1%. Excellent aluminum alloy plate. 3. The method according to claim 1, wherein after the cold rolling, a solution treatment is performed at a temperature of 450 to 580 ° C., and thereafter, the solution is cooled to a temperature of room temperature to 70 ° C. at a cooling rate of 15 ° C./s or more. 3. The method for producing an aluminum alloy sheet having excellent press formability according to item 2. 4. After performing a solution treatment and cooling to a temperature of room temperature or more and 70 ° C. or less, it is left at room temperature for 1 day or more, and then further heat-treated at a temperature of 50 to 120 ° C. for 1 to 50 hours. The method for producing an aluminum alloy sheet having excellent press formability according to claim 3, characterized in that: 5. The method according to claim 1, wherein after performing a solution treatment and cooling to a temperature of room temperature or more and 70 ° C. or less, a heat treatment is continuously performed at a temperature of room temperature or more and 70 ° C. or less for 1 to 100 hours. 4. The method for producing an aluminum alloy sheet having excellent press formability according to 3.