JPH0734208A - Production of aluminum alloy sheet excellent in formability - Google Patents

Abstract

PURPOSE:To produce a high strength Al alloy sheet excellent in formability by subjecting an Al alloy, having a composition which contains specific amounts of Mg, Cu, Mn, and Ti and where the contents of Fe and Si are controlled, to cold rolling, process annealing, and final annealing under respectively specified conditions. CONSTITUTION:An Al alloy, having a composition which contains, by weight, 4-6% Mg, 0.1-0.3% Cu, and 0.05-0.10% Mn and/or 0.02-0.10% Ti as essential components and further contains, if necessary, 0.0001-0.005% B and/or 0.0001-0.005% Be and further 0.1-0.6% Zn and where the contents of Fe and Si as impurities are controlled to 0.05-0.20% and 0.03-0.15%, respectively, is hot-rolled. The resulting hot rolled plate is subjected to primary cold rolling at >=50% cold draft. The resulting sheet is heated rapidly to 450-540 deg.C, held for <=30sec, and cooled rapidly to undergo process annealing. After secondary cold rolling at 5-14% cold draft, the Al alloy sheet is heated rapidly to 450-540 deg.C, held for <=30sec, and cooled rapidly to undergo final annealing.

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 an aluminum alloy sheet suitable for automobile body materials and the like which require good formability.

[0002]

2. Description of the Related Art Conventionally, in an automobile body material, use of an aluminum material has been studied in order to reduce the weight of a vehicle, and a body using a high strength Al-Mg alloy for forming is partially used. A material has been proposed and put into practical use. By the way, severe forming conditions are imposed in the forming process of the body material for automobiles, and therefore the material is required to have excellent formability including deep drawability.

In the body material, the deep drawability is emphasized as the formability, and the so-called Rankford value (r value) is used as the evaluation method. The Lankford value refers to the value of the ratio ε _w / ε _t of the strain in the width direction ε _w and the strain in the thickness direction ε _t in the tensile test, which is 0 in the rolling direction.
R ₀ , r _{45 of} Rankford values of °, 45 ° and 90 °,
weighted average r value of r _{9 0} (equation) is frequently used as an index. The Rankford value described below refers to this r value. r = (r ₀ + 2r ₄₅ + r ₉₀ ) / 4 Generally, the aluminum alloy sheet for forming has a lower Rank Ford value and is inferior in deep drawability as compared with the steel sheet for forming, so the Rank Ford value is increased. The development of aluminum alloy plates is underway.

For example, in JP-A-3-271349 and JP-A-4-301055, in order to improve the r value of an aluminum alloy sheet, an intermediate annealing is performed between two cold working steps, and further, these cold working steps are performed. A method of controlling the working rate in hot working is shown. Specifically, JP-A-4-30
In 1055, after the hot rolling of the obtained ingot, the workability is 50
% Cold cold rolling, then intermediate annealing at 280 ° C. or higher and lower than 440 ° C. for 30 minutes or longer and shorter than 12 hours, and further cold rolling with a workability of 10% or higher and lower than 50%, for final heat treatment. I am offering. Further, JP-A-3-271349 discloses that cold rolling after intermediate annealing is performed at a rolling rate of 15 to 40%.

[0005]

However, in the above-mentioned manufacturing method, the Rank Ford value is 0.7 or 0.75.
In view of the above, it is desirable to obtain a higher Rank Ford value (for example, 0.85 or more) in order to obtain a good deep drawability as an automobile body material. Further, in each of the above-mentioned manufacturing methods, it is stated that if the cold rolling ratio after the intermediate annealing is less than the lower limit, the crystal grains become coarse during the final heat treatment, the formability decreases, and the r value also decreases.

On the contrary, the inventor of the present application, by properly selecting the composition of the aluminum alloy used for the body material, increases the r value after the final annealing as the cold workability after the intermediate annealing becomes lower. I got the result. However, in this method, even if the r value is high, the deep drawability is not always improved and may be decreased, and the overhang property is also decreased, and the overall formability is often decreased. . It is considered that this is because the crystal grains are likely to coarsen, as shown in the above-mentioned manufacturing method. As a result of further research by the inventor of the present application,
By selecting the composition and further controlling the annealing conditions, a Rankford value of 0.85 or more is achieved, good deep drawability is secured, and an aluminum alloy plate with excellent bulging property is obtained. The present invention has completed the present invention by finding a manufacturing method capable of achieving the above.

[0007]

That is, the invention of the present application is
% By weight of Mg: 4-6%, Cu: 0.1-0.3%,
Mn: 0.05-0.10% or Ti: 0.02-
Fe and Si containing 0.10% of one or two kinds as essential components and contained as impurities are Fe: 0.05 to 0.20% and Si: 0.03 to, respectively.
Restricted to 0.15%, and if necessary, B: 0.0
001 to 0.005%, Be: 0.0001 to 0.00
A method for producing an aluminum alloy sheet having excellent formability, which is made of an aluminum alloy containing 5% of 1 type or 2 types, wherein a first cold-rolling rate is controlled to 50% or more after hot rolling. After performing hot rolling, further rapidly heating to 450 to 540 ° C., performing intermediate annealing of holding for 30 seconds and then rapidly cooling, and then performing second cold rolling in which the cold working ratio is controlled to 5 to 14%, Then, the final annealing is performed by rapidly heating to 450 to 540 ° C., holding for 30 seconds and then rapidly cooling.

As a component of the above aluminum alloy, Zn: 0.1 to 0.6% can be further contained in a weight percentage. For intermediate annealing and final annealing, the average heating rate from 200 to 450 ° C. during rapid heating is 10 ° C./second or more, and the average cooling rate from 200 ° C. or less during rapid cooling is 20 to 100 ° C./second. Is desirable.

[0009]

According to the present invention, the Rankford value is 0.9.
As described above, it is possible to obtain an aluminum alloy sheet having an LDR of 2.10 or more and an Erichsen value of 9.7 or more, and having excellent deep drawability and overhangability and good formability. Next, the reasons for limiting the components of the aluminum alloy and the reasons for limiting the production conditions in the present invention will be described.

[Chemical composition] Mg: 4 to 6% Mg enhances the work hardenability of the alloy and improves the overhanging property. As a result, the difference between tensile strength and proof stress is increased,
It also contributes to the improvement of deep drawability. In order to sufficiently obtain these effects, the content of 4% or more is necessary. It should be noted that the higher the Mg content, the higher the r-value can be obtained. However, even if the content exceeds 6%, the effect does not increase any more, and the hot rolling property remarkably deteriorates. Limited to 6%.

Cu: 0.1 to 0.3% Cu prevents softening of the molded product due to heating in the baking process after the molding process and the coating process. Further, like Mg, it enhances the work hardenability, improves the overhanging property, increases the difference between the tensile strength and the proof stress, and contributes to the improvement of the deep drawability. Further, it has an effect of further increasing the r value, and prevents coarsening of crystal grains after final annealing. In order to obtain these effects, the content of 0.1% or more is required. However, if the content exceeds 0.3%, the overhanging property deteriorates. The reason for this is thought to be that even if annealing is performed at a high temperature, Cu precipitated during hot rolling or the like is not completely solutionized and remains as an intermetallic compound. From the above points, C
The u content was limited to 0.1-0.3%.

Mn: 0.05 to 0.10% Ti: 0.02 to 0.10% Both of these elements have the effect of further increasing the r value of the aluminum alloy plate, and the crystals after the final annealing. One or more kinds are added to prevent coarsening of the grains. To obtain these effects, Mn is 0.05% and Ti is 0.02%.
The above contents are required. However, both are 0.10%
If the content exceeds the above range, the amount of the intermetallic compound formed becomes large, and the moldability, particularly the bulging property is remarkably reduced, so the content was limited to the above range. Note that Ti is 0.0
When added in an amount of 2% or more, it is necessary to take a sufficient holding time before the ingot is made to completely dissolve it, unlike the adding method for refining the crystal grains of the ingot which will be described later.

Zn: 0.1 to 0.6% Zn is added if desired in order to improve the zinc phosphate processability. In order to obtain the required effect, it is necessary to add 0.1% or more, while if added over 0.6%, Cu
As in the case, the overhanging property is reduced. The reason for this is
It is considered that, like Cu, it does not become a solution and remains as an intermetallic compound, and secondly, it imparts room temperature age-hardening property, so that it hardens during standing at room temperature. For the above reasons, Zn
Content was limited to 0.1 to 0.6%.

Fe: 0.05% to 0.20% Si: 0.03 to 0.15% These are components contained in the aluminum ingot as unavoidable impurities, but they are contained in excess of their respective upper limits. In both cases, an intermetallic compound is formed and the overhanging property is significantly impaired. However, if the content is too small, the crystal grains after the final annealing are likely to become coarse, so the respective limits are set to the above ranges. B: 0.0001 to 0.005% Be: 0.0001 to 0.005% B is an Al-Ti-B master alloy for refining the crystal grains of the ingot. Add accordingly. Therefore, the intermetallic compound in the Al-Ti-B master alloy is not completely melted before being cast, and therefore if the addition amount is too large, the bulging property is impaired. Therefore, the amounts of Ti and B added immediately before casting are 0.015% and 0.005, respectively.
It must be less than or equal to%. Be is added as necessary to prevent oxidation during casting or homogenization treatment. However, in both cases, if the amount added is too large, the overhanging property is impaired, so an upper limit was set.

[Casting and Homogenization Treatment] In the production of the aluminum alloy ingot of the present invention, a semi-continuous casting method (DC casting method) can be applied according to a conventional method. Before hot rolling, it is desirable to carry out a homogenizing treatment at a temperature range of about 480 to 520 ° C. for 8 to 24 hours for the purpose of improving formability and stabilizing crystal grains. Homogenization temperature is 4
If it is less than 80 ° C, a sufficient homogenizing effect cannot be expected.
Since there is a growth of giant recrystallization at a temperature exceeding 20 ° C, the range of 480 to 520 ° C is desirable.

[Hot Rolling, First Cold Rolling] Hot rolling is performed according to a conventional method, after which the first cold rolling is performed and then intermediate annealing is performed. The rolling ratio in the first cold rolling is 5
The content of 0% or more prevents the crystal grains from coarsening during the intermediate annealing. If this rolling rate is less than 50%, the crystal grains become remarkably coarse and the Rankford value decreases, so a rolling rate of 50% or more is required. For the same reason, it is desirable to set the rolling rate to 60 to 90%.

[Intermediate Annealing] By performing the intermediate annealing by rapid heating, holding for a short time, and rapid cooling, the r value can be improved without causing coarsening of crystal grains. By performing this intermediate annealing at a high temperature of 450 ° C. or higher, it is possible to promote the solution treatment of the additive element and the impurity element and improve the overhanging property. On the other hand, when annealed at a low temperature of less than 450 ° C., the intermetallic compound formed during hot rolling becomes coarse and agglomerated, which makes it difficult to form a solution even when the final annealing is performed at a high temperature. 450 ℃
It is necessary to do the above. Further, if the heating temperature exceeds 540 ° C., the crystal grains are coarsened and the melting point of the aluminum alloy is close to the melting point of the aluminum alloy. From the above, the heating temperature of the intermediate annealing was limited to 450 to 540 ° C.

The heating rate until the temperature is raised to this temperature is
It is desirable to set it to 10 ° C./second or more. This is because the rapid heating in this range has the effect of refining the crystal grains. On the other hand, if it is less than 10 ° C./sec, the crystal grains become coarse, so the above range is a desirable heating rate. The holding time after heating to the above temperature is within 30 seconds as described above, because the crystal grains become coarse when held for more than 30 seconds. Further, in the rapid cooling after holding at the predetermined temperature, it is desirable to cool at a cooling rate of 20 to 100 ° C./sec. Quenching within this range has the effect of refining the crystal grains. On the other hand, if it is less than 20 ° C./sec, the crystal grains become coarse, and if it exceeds 100 ° C./sec, the shape of the plate deteriorates, so the above range is the desirable cooling rate.

[Second Cold Rolling] By limiting the cold working ratio in the second cold rolling after the intermediate annealing to 5 to 14%, the r value is improved without causing the crystal grains to become coarse. Can be made. When the cold working ratio is less than 5%, the final annealing treatment causes coarsening of crystal grains, resulting in deterioration of formability.
Further, if it exceeds 14%, the Rankford value decreases, so the range is limited to the above range. A more preferable cold working rate is 6 to 14%.

[Final Annealing Treatment] Similar to the intermediate annealing treatment, the final annealing treatment is performed by rapid heating, holding for a short time, and rapid cooling. When the heating temperature is less than 450 ° C, the occurrence of stretcher strain marks becomes apparent, and Rankford value r
However, if the temperature exceeds 540 ° C, the crystal grains become coarse. Therefore, the temperature is limited to 450 to 540 ° C.
The temperature is preferably 490 to 520 ° C. The heating rate for heating to this temperature is preferably 10 ° C./second or more. This is because the rapid heating in this range has the effect of refining the crystal grains. On the other hand, if it is less than 10 ° C./sec, the crystal grains become coarse, so the above range is a desirable heating rate.

The holding time after heating to the above temperature is within 30 seconds as described above, because the crystal grains become coarse when held for more than 30 seconds. Further, in the rapid cooling after holding at the predetermined temperature, it is desirable to cool at a cooling rate of 20 to 100 ° C./sec. By quenching in this range, a plate with a good shape in which stretcher strain marks do not occur can be obtained. On the other hand, at less than 20 ° C / sec, stretcher strain marks occur and
If the temperature exceeds 00 ° C / sec, the shape of the plate deteriorates, so the above range is the desirable cooling rate.

[0022]

EXAMPLE An aluminum alloy having the composition shown in Table 1 was melted by a conventional method and DC cast to 600 mm × 1300.
The ingot had a size of mm × 3000 mm. 510 ° C for this ingot
Homogenizing treatment for 16 hours at 7m by hot rolling
It was a plate of m thickness. After that, cold rolling → intermediate annealing → cold rolling → final annealing were performed under the conditions shown in Table 2. In the intermediate annealing of the invention method and the final annealing of the invention method and the comparative method, 2
Rapid heating at a heating rate of 0 ° C / second, holding for 10 seconds, then 25
It was rapidly cooled at a cooling rate of ° C / sec. On the other hand, in the intermediate annealing of the comparative method, the temperature is gradually raised to a predetermined temperature (0.03 ° C./sec),
After holding for 2 hours, it was gradually cooled (0.02 ° C / sec). The thus obtained sheet was examined for mechanical properties in three directions parallel to the rolling direction, 45 ° and 90 °, the Rankford value r and LDR, the Erichsen value, and the crystal grain size. The results are shown in Table 3. In the table, those with a Rank Ford value of less than 0.90 are marked with x, those with a rank of 0.90 or more are marked with o, and those with an LDR of less than 2.10 are marked with x.
.Circle-solid., Those with 2.10 or more are marked with .smallcircle.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

As is clear from Table 3, according to the method of the present invention, high values of r value, LDR, and Erichsen value were obtained, which was excellent in deep drawability and overhangability, and other mechanical properties. It was also excellent in properties. On the other hand, the test piece using the alloy outside the range of the present invention is inferior in one or both of the r value and the Erichsen value even when manufactured according to the process of the present invention. The comparative material 12 was poor in workability and cracked during rolling, so an evaluation test was not conducted. Further, in the case of adopting the intermediate annealing of the comparative method, the r value is good, but it is inferior to the Erichsen value. Further, when the working ratio of the second cold rolling exceeds the upper limit of the invention method, the r value was lowered.

[0027]

As described above, according to the method for producing an aluminum alloy sheet having excellent formability of the present invention, after the aluminum alloy having the specific composition is hot-rolled, the cold working rate is controlled to 50% or more. 1 cold rolling, 450-54
After performing an intermediate anneal of rapidly heating to 0 ° C., holding for 30 seconds and then rapidly cooling, the cold working ratio was controlled to 5 to 14%.
Cold-rolling, followed by rapid heating to 450 to 540 ° C., holding for 30 seconds or less, and then rapid cooling.
A high-strength aluminum alloy plate with excellent deep drawability and overhanging properties is obtained, including automobile body materials,
There is an effect that a lightweight molding plate material suitable for applications requiring severe moldability can be obtained.

Claims (2)

[Claims] 1. Mg: 4-6% by weight, Cu: 0.1
~ 0.3% and Mn: 0.05-0.10% or T
i: 0.02 to 0.10% of one or two kinds as essential components, and Fe and Si contained as impurities, respectively: Fe: 0.05 to 0.20%, S
i: 0.03 to 0.15%, and if necessary, B: 0.0001 to 0.005%, Be: 0.00
A method for producing an aluminum alloy sheet having excellent formability, which comprises an aluminum alloy containing one or two of 01 to 0.005%, wherein a cold working rate is controlled to 50% or more after hot rolling. After performing the first cold rolling, further rapidly heating to 450 to 540 ° C., holding for 30 seconds or less, and then performing an intermediate annealing of rapidly cooling,
The second cold rolling in which the cold working ratio is controlled to 5 to 14% is performed, then the rapid annealing is performed at 450 to 540 ° C., the final annealing is performed in which it is rapidly cooled after being held for 30 seconds. Excellent aluminum alloy plate manufacturing method 2. The method for producing an aluminum alloy sheet having excellent formability according to claim 1, further comprising Zn: 0.1 to 0.6% by weight as a component of the aluminum alloy.