JPH04147936A - High strength aluminum alloy sheet for drawing and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture an Al alloy sheet excellent in drawability, at the time of subjecting the ingot of an Al-Mg-Cu series alloy having a specified compsn. to soaking treatment, hot rolling and cold rolling to work into a sheet material by regulating the grain size of the ingot, its cold rolling ratio and heat treating conditions in the final sheet thickness or the like. CONSTITUTION:The ingot at an Al alloy contg., by weight, 4 to 8% Mg, 0.05 to 0.7% Cu, 0.01 to 0.3% Mn, 0.002 to 0.01% Be and each <0.1% and total <=0.15% Fe and Si, furthermore contg. total <=0.2% of one or >= two kinds among <0.2% Cr, <0.2% Zr and <0.2% V and having <=500mum grain diameter is subjected to soaking treatment and is thereafter subjected to hot rolling and cold rolling. The rolled stock is successively subjected to process annealing and is thereafter subjected to final cold rolling at 10 to 50% working ratio into an Al alloy sheet having a prescribed sheet thickness, which is finally heated to 450 to 54O deg.C and is rapidly cooled at <=200 deg.C/min cooling rate. The Al alloy sheet in which crystalline grains are formed of equi-axed ones and the average grain diameter in the sheet face and cross section is regulated to 30 to 100mum and excellent in drawability and strength after a baking finish can be manufactured.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a high-strength aluminum alloy plate for drawing, and more specifically, it is used for drawing and forming, such as automobile body panels, door inner panel materials, oil pans, etc. Suitable for products that will be painted, with excellent drawing processability.
The present invention relates to a high-strength aluminum alloy plate for drawing that has high strength after baking coating, and a method for manufacturing the same. (Prior art and problems to be solved) Generally, cold-rolled steel sheets have been widely used as materials for parts such as automobile body panels, door inner panel materials, and oil pans, but as automobiles become more sophisticated. The weight of vehicles is increasing with the increase in functionality, and in order to maintain performance and to comply with the recent tightening of North American CAFE regulations due to the issue of global warming due to carbon dioxide gas, the weight of the vehicle body has been reduced. I'm here. There is an increasing demand for using aluminum alloy plates in various parts instead of conventional cold-rolled steel plates. Aluminum alloy plates used in such applications are required to have good drawing workability and high strength after baking the paint. However, conventionally, Mg was added at 2.4 to 5% for these applications.
Containing Al-Mg alloy (5052, 5154, 51
Soft materials such as 82, 5083) are about to be put into practical use. However, although the above-mentioned 5052.5154 alloy has relatively good drawability, it cannot be said that the strength is sufficient.
In order to ensure strength, the plate thickness must be increased. Also,
5086.5182.5083 alloy has relatively high strength, but its drawability is not sufficient, and it cannot handle the increasingly complex shapes of molded products these days, and cracks occur when processing is severe. Then there is a problem. In addition, there is a problem that strength decreases due to relaxation of processing strain during painting baking after processing, and furthermore, thread rust resistance tends to deteriorate. The present invention solves the problems of the prior art described above. To provide an aluminum alloy plate for drawing which has drawability equal to or higher than that of conventional 5052.5154 alloy and strength equal to or higher than 5086.5182,5083 alloy, and to provide a method for producing the same. The purpose is to (Means for Solving the Problems) As a result of intensive research to achieve the above object, the present inventor has optimized the component composition including Mg and Cu, and improved the crystal grains on the plate surface and cross section. We have discovered that this is possible by optimizing the size and further regulating the grain size of the ingot, cold rolling rate, heat treatment conditions at the final plate thickness, etc., and have hereby made the present invention. be. That is, in the present invention, Mg: 4 to 8%, Cu:O. 05-0.7%, Mn: 0.01-0.3% and Be:
Contains 0.002 to 0.01%, and Fe: 0°1
% or less, Si: 0.1% or less, Fe+Si: 0.15
% or less, and if necessary, one of Cr: 0.2% or less, Zr: 0.2% or less, and V: 0.2% or less.
An aluminum alloy plate containing a seed or a total of two or more types at 0.2% or less, and the remainder consisting of Al and unavoidable impurities, the crystal grains are equiaxed grains, and the average crystal grain size of the plate surface and cross section The object of the present invention is to provide a high-strength aluminum alloy plate with excellent drawing workability, which is characterized by a hardness in the range of 30 to 100 μm. In addition, the manufacturing method uses an aluminum alloy having the above-mentioned chemical composition, using an ingot with a crystal grain size of 500μ■ or less, followed by homogenization treatment, hot rolling, cold rolling, intermediate annealing, and then final It is characterized by giving a cold working rate of 10 to 50% to obtain a predetermined plate thickness, heating at 450 to 540°C as a final heat treatment, and then cooling at 200°C/inch or more. The present invention will be explained in more detail below. (Function) First, the reason for limiting the chemical components in the present invention will be explained. Mg: Mg is an essential basic component in the aluminum alloy targeted by the present invention, and is an element that contributes to improving strength and drawability. However, if the amount of Mg is less than 4%, the effect cannot be sufficiently obtained. If it exceeds 8%, although the strength increases, rolling workability deteriorates and cracks tend to occur during rolling, making normal industrial production difficult. Therefore, the Mg amount is in the range of 4 to 8%. Cu: Similar to Mg, Cu is an element that contributes to improving strength and drawing workability, and especially when it coexists with Mg, the effect becomes even greater. It is particularly effective in reducing softening during baking painting. However, if the Cu content is less than 0.05%, the effect is small, and if it exceeds 0.7%, although it is effective in improving strength, eutectic melting tends to occur, making industrial production difficult. Therefore, the amount of Cu is in the range of 0.05 to 0.7%. Mn: Mn is an element that contributes to improving strength and refining recrystallized grains, but if it is less than 0.01%, its effect is small;
If it exceeds 3%, although the strength increases, the recrystallized grains become too fine, producing even coarser crystallized substances, which deteriorates drawing workability, which is not preferable. Therefore, the amount of Mn is 0
．． The range is 0.01 to 0.3%. Be: Be is an element that contributes to preventing oxidation of the molten metal during melting and casting, and the effect is particularly great as the amount of Mg increases. However, the effect is small below 0.002%, and 0,
If it exceeds 0.01%, the effect will be saturated and drawing workability will tend to deteriorate, which is not preferable. Therefore, BeJi is 0. OQ shall be in the range of 2 to 0°01%. Fe, Si: Fe and Si are elements that impart strength, but as their content increases, coarse crystallized substances are formed, which reduces drawing workability. In particular, if each content exceeds 0.1%, the drawability will be significantly reduced. Therefore, Fe
, Si content is 0.1% or less, and Fe and Si content is regulated to 0.15% or less. Cr, Zr, V: Since Cr, Zr, and V are elements effective for improving strength and refining recrystallized grains, one or more of them can be added in an appropriate amount if necessary. The effect can be obtained when each individual addition is 0.2% or less, but the total content of two or more types is 0.2%.
Although it does not affect drawing workability below, 0.2
%, it is not preferable because coarse crystallized substances are produced and the drawing workability is deteriorated. Next, we will explain the structure (crystal grain size) of the aluminum alloy plate having the above chemical components.The grain size is a factor that affects formability, particularly drawing workability. In the present invention,
It is necessary that the grains are equiaxed on the plate surface and in the plate cross section, and that the average crystal grain size is in the range of 30 to 100 μm. If the average crystal grain size is less than 30 μm, drawing workability is poor and high M
Stretcher strain marks (SS marks) peculiar to G are more likely to occur. On the other hand, if it exceeds 100 μm, the effect of improving drawing workability is saturated, and on the other hand, the surface after drawing becomes rough, which is not preferable. Therefore, the average crystal grain size is in the range of 30 to 100 μm, preferably in the range of 40 to 80 μm. Furthermore, the manufacturing process of the present invention will be explained. First, an aluminum alloy having the above chemical components is melted by a conventional method and cast to obtain an ingot. However, since the crystal grain size of the ingot has a large effect on the grain refinement of the product, it needs to be 500 μI or less. This means that when an aluminum alloy ingot with the above composition is homogenized and then hot-rolled and cold-rolled to a predetermined thickness, if the crystal grain size of the ingot exceeds 5゜Oμ, Subsequent processes have little effect on refining the crystal grains of the product.
This is to worsen drawing workability. Conventional methods may be used for the homogenization treatment and hot rolling of this ingot. For example, if necessary, the ingot is subjected to one or two stages of homogenization treatment at 400 to 520°C for 2 to 48 hours, and then hot rolled according to a conventional method. In addition,
After that, it may be adjusted to 350-b as needed. Next, cold rolling is performed. However, the cold rolling is performed at a re-proprietary cold working ratio of 10 to 50% to obtain a predetermined thickness. If the cold working ratio is less than 10%, it will not be possible to obtain uniform crystal grains through subsequent heat treatment, and drawing workability will become uneven and roughness will likely occur. Moreover, if it exceeds 50%, the recrystallized grain size becomes too fine, resulting in poor drawing workability. In this case, in the middle of cold rolling, intermediate annealing may be performed under conventional conditions (330~B).Next, as a final heat treatment, solution treatment is performed at a temperature range of 450~540℃, followed by 200℃/+++in. Cool at the cooling rate above.This heat treatment has a large contribution to drawing workability 1 strength, and is aimed at reducing strength softening during baking painting by making the crystal grain size uniform and making Mg and Cu a solid solution. If the solution temperature is less than 450°C, the conversion of Mg, Cu, etc. into a solid solution and the recrystallization grain size refinement will be insufficient, resulting in poor drawing workability and a decrease in strength. If the temperature exceeds ℃, it should be avoided as it may cause eutectic melting.In cooling after solution treatment, Mg, Cu, etc. are made into a solid solution to improve drawing workability and prevent strength softening. for 20
It is necessary to set the cooling rate to 0° C./+min or more. 20
If it is less than 0° C./min, Mg and Cu compounds will precipitate at the grain boundaries and within the grains, reducing drawing workability and reducing the effect of preventing strength softening, which is not preferable. Note that methods for obtaining such a cooling rate include forced air cooling, water cooling, etc., but from the viewpoint of reducing strain during quenching, it is desirable to apply forced air cooling. (Example) Next, an example of the present invention will be shown. Fubainuki ↓ 480℃
After homogenizing for a long time, hot rolling was carried out between 500 and 280°C to a thickness of 3.5mm, and then the thickness was 1.5+am.
cold rolling to 400~5 as intermediate annealing.
After rapidly heating to 00℃ and holding for 30 seconds or less, 400℃/wi
It was rapidly cooled at an average cooling rate of n. Then, cold rolling was performed (final cold working rate: 30%) to a plate thickness of 1 sm. This 1n+m thick aluminum alloy plate was rapidly heated to 530℃, held at that temperature for 30 seconds, and then heated to 6oO℃/w.
A final heat treatment was performed to rapidly cool the sample at an average cooling rate of 1.5 in, and a test material was obtained. The mechanical properties of the obtained test material and the drawing workability using small test pieces were investigated, and the strength after 5% stretching and heating (17
The strength after 5°C x 20 minutes was examined. The results are also listed in Table 2. Note that drawing workability was evaluated by drawing depth (mm) by performing drawing using an Erichsen tester under the following conditions. Drawing processing conditions Blank diameter: 90++ UO punch diameter: 40+C++ Rodice diameter: 42° 4) Opening rP: 4.5mm rd: 3.0mm Wrinkle pressing force = 2.0tOn As is clear from Table 2, the present invention example All of them have a deep drawing depth, less decrease in strength due to heating after processing, and are excellent in drawing workability and strength. On the other hand, it can be seen that the comparative example is inferior in any of drawing depth, strength, and strength reduction due to heating after processing.

[Left below]

Aluminum alloy NQ having the chemical composition shown in Table 1
2 (within the scope of the present invention) was homogenized and hot-rolled under the same conditions as in Example 1, and the final reduction rate of cold rolling and final heat treatment conditions were changed to reduce the average grain size. Different plates were manufactured and the influence of drawability, SS mark, etc. was investigated. The results are shown in Table 3. As is clear from Table 3, all of the examples of the present invention have a deep drawing depth and exhibit excellent drawing workability, and are also good in terms of SS mark and surface roughness. On the other hand, the comparative example has poor drawing workability, or even if the drawing depth is deep, roughness occurs and the strength is low.

[Left below]

1 (Aluminum alloy Na having the chemical components shown in Table 1)
2 (within the scope of the present invention), aluminum alloy plates were manufactured under various conditions (ingot crystal grain size, final cold working rate, solution treatment temperature, cooling rate) shown in Table 4, and those conditions were We investigated the influence of Note that other conditions were the same as in Example 1. The results are shown in Table 5. As is clear from Table 5, the examples of the present invention have excellent strength and drawing workability, whereas the comparative examples in which any of the manufacturing conditions in Table 4 are outside the scope of the present invention have excellent strength and drawability. Also, the drawability is poor.

[Left below]

(Effects of the Invention) As detailed above, according to the present invention, 5052.515 of the conventional material can be used as an aluminum alloy plate used for formed products that require drawing workability and high strength after painting baking.
It has better drawing workability than 4, etc., and has less strength loss after paint baking, so it is suitable for automobile body panels and other parts, and greatly contributes to reducing the weight of automobiles.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating drawing depth. Patent applicant: Kobe Steel, Ltd. Representative Patent Attorney Takashi Nakamura

Claims (3)

[Claims] (1) In weight% (the same applies hereinafter), Mg: 4 to 8%, Cu
:0.05-0.7%, Mn:0.01-0.3% and Be:0.002-0.01%, and Fe:
0.1% or less, Si: 0.1% or less, Fe+Si: 0
．． 15% or less, with the remainder consisting of Al and unavoidable impurities, the crystal grains are equiaxed grains, and the average crystal grain size on the plate surface and cross section is 30 to 100μ
A high-strength aluminum alloy plate with excellent drawing workability, which is characterized by a drawability in the range of m. (2) The aluminum alloy further contains one of Cr: 0.2% or less, Zr: 0.2% or less, and V: 0.2% or less.
The aluminum alloy plate according to claim 1, wherein the total content of one or more species is 0.2% or less. (3) For an aluminum alloy having the chemical composition according to claim 1 or 2, using an ingot with a grain size of 500 μm or less, after homogenization treatment, hot rolling, cold rolling, and intermediate annealing, Next, a final cold working rate of 10 to 50% is applied to obtain a predetermined plate thickness, and a final heat treatment is performed at 450 to 540°C.
A method for producing a high-strength aluminum alloy plate with excellent drawing workability, the method comprising heating the plate and then cooling the plate at a rate of 200° C./min or more.