JPH1171623A - Aluminum alloy sheet for automotive body panel and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an alloy sheet excellent in press formability, corrosion resistance or the like by a method which does not require high energy even in the case a recycling material of low purity such as scrap is used as the raw material by specifying its compsn. and regulating the number of pieces of the crystallized products in which the maximum size is a specified value or above shown in the cross-section in the rolling direction and number of the crystallized products in which the ratio of the maximum size to the minimum size is a specified value or above, to a specified value or below. SOLUTION: This Al alloy has a comp. contg., by weight, 0.2 to 1.5% Si, <=1.5% Fe, <=1.0% Cu, <=0.20% Mn, 0.2 to 1.5% Mg, <=0.35% Cr, <=0.70% Zn, <=0.20% Ti, and the balance Al, in which the number of pieces of the crystallized products in which the maximum size is >=10 μm shown in the cross-section in the rolling direction of the sheet is regulated to <=300 pieces/mm<2> , and the number of pieces of the crystallized products in which the ratio of the maximum size to the minimum size is >=3.5 is regulated to <=100 pieces/mm<2> . As for the method for producing it, at the time of successively executing melting, casting, soaking treatment, hot and cold rolling and annealing, in the case of the casting, one or more kinds among Na, Sr, Sb, Ca, Te, Ba or the like are added by 0.005 to 0.3% in total to finely disperse and spheroidize the crystallized products.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy sheet which is excellent in press formability and corrosion resistance and is used for an automobile body sheet and a method for producing the same. More specifically, the present invention relates to a method using a recycled material such as scrap as a raw material. Also, the present invention relates to an aluminum alloy sheet for an automobile body panel which can exhibit excellent properties in press formability and corrosion resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, automobile body seats have
Mainly, cold-rolled steel sheets have been used. However, in recent years, the application of an aluminum alloy plate has been studied and implemented due to a demand for a lighter vehicle body. Car body seats include
It is required not only to be excellent in press formability but also to be excellent in chemical conversion property, corrosion resistance, strength after paint baking, and the like.

Hitherto, as aluminum alloys for automobile body sheets, JIS5052, JIS5182,
JP-A-62-27544, JP-B-62-4298.
No. 5, Al-Mg based alloys represented by alloys such as
Al-Mg represented by A6009, AA6010, etc.
-Si based alloy is used. Of these, Al-Mg
-Si-based alloy is an age hardening type alloy,
High strength is obtained by baking paint at 70-200 ° C,
It has the advantage of excellent dent resistance, and is widely used in Europe and the United States mainly for outer plates.

However, since Al-Mg-Si alloys are inferior in formability as compared with Al-Mg alloys, most of the Al-Mg-Si alloys contain impurities such as Fe in order to satisfy the strict press formability comparable to steel plates. It is manufactured from high-purity new bullion, which has been extremely low. Therefore, there is a major problem that not only the material cost is increased, but also a large amount of energy is consumed in the production of new bullion, which leads to destruction of the global environment. For this reason, there is a demand for an aluminum alloy sheet that can exhibit excellent properties in press formability, corrosion resistance, strength after baking, and the like even when a low-purity recycled material such as scrap is used.

[0005]

Regarding the above problems, in the production of secondary metal using aluminum scrap, techniques for removing impurities from the molten metal have been studied (for example, promotion of non-ferrous metal material recycling). Technological research and development: Basic research and research, elemental technology research results report, 1995, Metallic Materials Research and Development Center), the purity has not yet reached the level of new bullion, Since high energy is required along with capital investment, it may rather promote the destruction of the global environment.

The present invention has been made in view of such a situation, and uses a low-purity recycled material such as scrap as a raw material by an inexpensive method that does not require high energy, and has press formability, corrosion resistance, and the like. It is an object of the present invention to provide an aluminum alloy sheet for an automobile body panel having excellent strength after baking.

[0007]

Means for Solving the Problems The present inventors have come up with the idea that impurities are unavoidable in aluminum alloys manufactured using low-purity raw materials.
An attempt was made to achieve the above object by detoxifying the adverse effects of these impurities. That is, the present inventors investigated the effect of the addition of trace elements on the size and shape of the crystallized substance in an aluminum alloy containing a large amount of impurities, and refined the crystallized substance by adding a specific element. Further, they have found that they are spheroidized and can improve press formability and corrosion resistance, leading to the present invention.

That is, according to the present invention, in weight%, S
i: 0.2 to 1.5%, Fe: 1.5% or less, Cu:
1.0% or less, Mn: 0.20% or less, Mg: 0.2 to
1.5% or less, Cr: 0.35% or less, Zn: 0.70
% Or less, Ti: 0.20% or less, and the balance: 30 or less of the crystallized substance consisting of Al and inevitable impurities and having a maximum diameter of 10 μm or more as seen in the cross section in the rolling direction of the sheet.
0 / mm ² or less and the number of crystallized substances whose ratio of maximum diameter to minimum diameter (maximum diameter / minimum diameter) is 3.5 or more is 100
The present invention provides an aluminum alloy plate for an automobile body panel, which is not more than pcs / mm ² .

The method of manufacturing an aluminum alloy sheet for an automobile body panel according to the present invention comprises the steps of sequentially performing melting, casting, soaking, hot rolling, cold rolling and annealing to form a rolled sheet; , Sr, Sb, Ca, T
e, one of Ba, Li, K, Bi, P, As, Se
At least 0.005 to 0.3% by weight of seeds is added.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
First, the reasons for limiting the component composition will be described. In the alloy system of the present invention, Si and Mg are added as essential components, and other components are optional components and may not be added (0%) in some cases. Si is an element that forms a compound together with Mg and contributes to the improvement of the strength, and serves to increase the strength after baking. However, if the content is less than 0.2% by weight, the strength is improved by precipitation hardening. Since the amount of generation of the Mg ₂ Si phase contributing to the above is small, sufficient strength cannot be obtained.
If it exceeds 5% by weight, the strength is saturated, and a large number of grain boundary precipitates are formed, and the hem bending property and the intergranular corrosion resistance decrease. Therefore, the content of Si is set to 0.2 to 1.5% by weight.

[0011] Mg also forms a compound with Si and is strong.
The content is less than 0.2% by weight
Is Mg that contributes to strengthening_TwoLow amount of Si phase
Therefore, sufficient strength cannot be obtained, while exceeding 1.5% by weight
Then, the hem bending property and the intergranular corrosion resistance decrease. Accordingly
Thus, the content of Mg was set to 0.2 to 1.5% by weight. Fe
Is effective for grain refinement or strength,
Sometimes, massive Al _ThreeFe or Al₆Crystallized as Fe
And lowers formability and corrosion resistance. These crystals are
By adding a specific element in the present invention, finer and spherical
However, when the content of Fe exceeds 1.5% by weight,
After all, the effect becomes insufficient, and moldability and corrosion resistance decrease.
I do. Therefore, the content of Fe is 1.5% by weight or less.
did.

[0012] Cu is an element that promotes aging strengthening and increases the strength of the alloy. However, if its content exceeds 1.0% by weight, corrosion resistance and weldability are reduced. Therefore, Cu
Was set to 1.0% by weight. Mn is an element having an effect of refining and stabilizing crystal grains and increasing the strength. However, if it exceeds 0.20% by weight, a coarse intermetallic compound is formed together with Fe to lower the formability. .
Therefore, the upper limit of Mn is set to 0.20% by weight.

[0013] Cr is added as necessary and, like Mn, is an element that has the effect of refining and stabilizing crystal grains and increasing the strength. Reduce the nature. Therefore, the upper limit of Cr is set to 0.35% by weight. Zn is an element effective for improving the strength, but if it exceeds 0.70% by weight, press formability, corrosion resistance and weldability are reduced. Therefore, Zn
The upper limit of the content was 0.70% by weight.

[0014] Ti is generally added alone or in combination with a small amount of B in order to refine the crystal grains of the ingot. In this case, if the content of Ti exceeds 0.20% by weight, the effect is saturated and the formability is also reduced. Therefore, the upper limit of the content of Ti is set to 0.20% by weight.
When B is added simultaneously, the amount of addition is 0.0005 to
0.03% by weight is advantageous.

[0015] An alloy sheet within the above-mentioned range of component composition alone cannot be an alloy sheet suitable for use in an automobile body panel. The present inventors have conducted various investigations on the influence of the size and shape of the crystallized substance on the properties of the alloy sheet. As a result, the maximum diameter of the alloy sheet in the cross section in the rolling direction was 10 μm.
The number of crystallized substances is 300 / mm ² or less and the ratio of the maximum diameter to the minimum diameter (maximum diameter / minimum diameter) is 3.5 or more is 100 / mm 2. ^When it is ² or less, while exhibiting excellent press formability, corrosion resistance, and strength after baking, is the number of crystallized substances having a maximum diameter of 10 μm or more exceeding 300 / mm ² ? Alternatively, when the ratio of the maximum diameter to the minimum diameter (maximum diameter / minimum diameter) is 3.5 or more and the number of crystallized substances exceeds 100 / mm ² , the press formability, corrosion resistance, It was found that the strength and the like after baking were inferior. Therefore, the number of crystallized substances whose maximum diameter seen in the rolling direction cross section of the alloy sheet is 10 μm or more is 300 / mm ² or less, and the ratio of the maximum diameter to the minimum diameter (maximum diameter / minimum diameter) is 3. The number of crystallized substances of 5 or more was limited to 100 / mm ² or less.

Next, a method for manufacturing an aluminum alloy plate according to the present invention will be described. In order to obtain an alloy plate having the above-mentioned crystal size and shape, it is necessary to finely disperse and crystallize the crystal. The present inventors have studied in detail the effect of additional elements on the size and shape of the intermetallic compound crystallized during solidification in an aluminum alloy having the above-described component range, and examined the fine dispersion of the crystallized substance, , Na, Sr, Sb, Ca, Te, Ba, Li,
It has been found that it is very effective to add one or more of the elements K, Bi, P, As, and Se during casting solidification. It is considered that these elements become crystallization nuclei of intermetallic compounds in the form of bubbles or compounds during solidification of the aluminum alloy, and contribute to their fine dispersion and spheroidization. If the amount of addition is less than 0.005% by weight, the above effect is not seen. If the total amount exceeds 0.3% by weight, the above effect is not only saturated, but also the mechanical properties deteriorate. Since there is a danger of brittle cracking during hot working, the total amount of these elements is 0.00
The content was 5 to 0.3% by weight.

In the method for producing an aluminum alloy sheet according to the present invention, the alloy having the above component range is melted by a conventional method, and Na, Sr, Sb, Ca, T
One or more of the elements e, Ba, Li, K, Bi, P, As, and Se are added within a total range of 0.005 to 0.3% by weight. As the addition method, a method of adding these elements as a simple metal, a method of adding these elements as a flux containing these elements, a method of adding Al as a mother alloy of these elements, and the like can be applied. After the casting and solidification, a rolled plate is formed by soaking, hot rolling, cold rolling and annealing by a conventional general plate manufacturing method.

As described above, according to the present invention, the size and shape of the intermetallic compound crystallized during solidification can be controlled by appropriately adjusting the component composition of the alloy and adding a specific element during casting. As a result, even if low-purity alloys such as recycled materials are used as raw materials,
It has become possible to provide an aluminum alloy sheet for an automobile body panel which is excellent in press formability, corrosion resistance, strength after paint baking, and the like.

[0019]

Next, the present invention will be described with reference to examples. (Example 1) An example of an aluminum alloy plate for an automobile body panel according to the present invention will be described in comparison with a comparative example.

Each alloy having the chemical components shown in Table 1 was melted and, at the time of casting, metal N equivalent to 0.1% by weight of the molten metal was used.
After a was added and solidified, face milling, soaking, hot rolling, cold rolling and annealing were performed by a conventional method to produce a cold-rolled sheet having a thickness of 1 mm. The obtained aluminum alloy sheets were evaluated for tensile properties, formability, corrosion resistance, and paint bake hardenability. Tensile properties were determined using JIS No. 5 test pieces. The formability was evaluated by a cylinder deep drawing test, an Erichsen test, and a bending test, and evaluated by a limit drawing ratio (LDR), an Erichsen value, and a minimum inner radius of a 180 ° bending test. Corrosion resistance was obtained by forming a phosphate film on a 70 mm x 150 mm test piece in a fluoride-added phosphate treatment bath, applying 20 μm of cationic electrodeposition coating, intermediate coating, and top coating to a total coating thickness of 80 μm. Make a knife cut to reach the aluminum substrate and spray with salt (5% NaCl, 35%
C) for 1 week, wet (85% relative humidity, 40 ° C.) for 5 days, and exposed to a cycle environment consisting of 1 day left indoors for 8 weeks. . The paint bake hardenability was evaluated by subjecting an alloy plate 7 days after the final annealing to a heat treatment equivalent to paint bake at 170 ° C. × 30 minutes and measuring the 0.2% proof stress. Table 2 shows the evaluation results of those characteristics.

The object of the present invention is to provide an aluminum alloy plate exhibiting good performance even when a low-purity alloy is used as a raw material. The target was set to the same value as that of the alloy plate. Specifically, the following values were used as a guide. Tensile strength 220MPa or more Total elongation 26% or more Critical deep drawing ratio 2.00 or more Erichsen value 9.5 or more Minimum bending radius 0.5t or less (t: plate thickness) Maximum thread rust length 1.0mm or less After paint baking 0.2% proof stress 170 MPa or more As is clear from Table 2, the aluminum alloy plates according to the present invention all achieve the above-mentioned target, but among the aluminum alloy plates as comparative materials, alloys 22, 23, 25 And 28 to 32 do not satisfy the conditions of the present invention in any of the component composition, the size and the shape of the crystallized product, and therefore all have excellent paint bake hardenability, but all have excellent ductility, moldability and The alloy 27 is inferior in corrosion resistance and does not satisfy the conditions of the present invention in any of the component composition, the size and the shape of the crystallized product, so that the ductility, moldability, corrosion resistance and paint bake hardenability are not obtained. In any characteristics, not able to achieve the target. Alloys 21 and 26 satisfy the conditions of the present invention with respect to the size and shape of the crystallized substance, but since the component composition is out of the range of the present invention,
Although excellent in ductility, moldability and corrosion resistance, tensile strength and paint bake hardenability have not achieved the above targets.

The alloy 24 satisfies the conditions of the present invention in terms of the size and shape of the crystallized substance, but the composition is out of the range of the present invention, so that the corrosion resistance is significantly reduced. (Embodiment 2) An embodiment of a method for manufacturing an aluminum alloy plate for an automobile body panel according to the present invention will be described in comparison with a comparative example.

The alloy 2 in Table 1 was melted, and the amount of molten metal was 0.0
Na, Sr, Sb, C in an amount corresponding to 2 to 0.7% by weight
a, Te, Ba, Li, P, As, and Se are added alone or in combination, each as a single metal, in the form of a flux containing these elements, or in the form of a master alloy of Al and these elements. After solidification, the resultant was subjected to face milling, soaking, hot rolling, cold rolling and annealing by a conventional method to produce a cold-rolled sheet having a thickness of 1 mm. The obtained aluminum alloy sheets were evaluated for tensile properties, formability, corrosion resistance and paint bake hardenability in the same manner as in Example 1. Table 3 shows the evaluation results of each characteristic. As the target of the performance of the alloy plate, the same value as in the case of Example 1 was used as a guide.

As is clear from Table 3, the aluminum alloy plate manufactured by the manufacturing method according to the present invention achieves the above-mentioned target, but the aluminum alloy plate manufactured by the comparative method has a crystallized form. Because the conditions of the present invention are not met,
It can be seen that the moldability and the corrosion resistance are inferior.

[0025]

[Table 1]

[0026]

[Table 2]

[0027]

[Table 3]

[0028]

As described above, the aluminum alloy plate according to the present invention exhibits excellent press formability, corrosion resistance, strength after baking, etc. at low cost even when recycled materials such as scrap are used as raw materials. Because it can be used, it can be used for automobile body panels. Therefore, it can be said that the present invention is an invention having extremely high industrial value.

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 631 C22F 1/00 631Z 640 640A 681 681

Claims (2)

[Claims] 1. In weight%, Si: 0.2-1.5%, Fe: 1.5% or less, Cu: 1.0% or less, Mn: 0.20% or less, Mg: 0.2-1.5% 1.5%, Cr: 0.35% or less, Zn: 0.70% or less, Ti: 0.20% or less, and balance: Al and unavoidable impurities, and the maximum seen in the rolling direction cross section of the sheet Diameter 1
The number of the crystallized substances having a diameter of 0 μm or more is 300 / mm ² or less, and the number of the crystallized substances having a ratio of the maximum diameter to the minimum diameter (maximum diameter / minimum diameter) of 3.5 or more is 100 / An aluminum alloy plate for an automobile body panel, which is not more than mm ² . 2. The method for producing an aluminum alloy sheet according to claim 1, wherein the step of melting, casting, soaking, hot rolling, cold rolling, and annealing is sequentially performed to form a rolled sheet.
Na, Sr, Sb, Ca, Te, Ba, L
A method for producing an aluminum alloy sheet for an automobile body panel, comprising adding at least one of i, K, Bi, P, As, and Se in a total amount of 0.005 to 0.3% by weight.