JPH08165538A - Rolled aluminum alloy sheet for automobile body sheet, improved in recycling property, and production thereof - Google Patents

Abstract

PURPOSE: To improve the regeneration rate of iron-containing aluminum scrap, such as automobile scrap, into an aluminum alloy sheet for automobile body sheet by specifying a composition and also permitting high iron content. CONSTITUTION: This alloy sheet has a composition consisting of, by weight ratio, 2.5-8% Mg, 0.3-1.2% Fe, <=0.5% Si, <=0.3% Mn, and the balance Al with inevitable impurities and satisfying Si/Fe<=1.0 and Si×0.6×Fe<=0.9%. Simultaneously, the number of intermetallic compounds with a size of >=10μm is regulated to <=300pieces/mm<2> , and also the size of crystalline grains is regulated to 20-70μm. Moreover, although this composition can further contain prescribed amounts of Cr, Zr, Ni, V, Cu, and Zn, continuous casting velocity and annealing conditions after rolling must be controlled in this case, and also the required number of intermetallic compounds and size of crystalline grains must be satisfied.

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 used for automobile body sheets and a method for producing the same, and more particularly, to a "dirty" aluminum scrap containing a relatively large amount of iron-based material such as steel. A highly recyclable automobile body sheet that can exhibit excellent performance even when manufactured as a raw material, and that it is easy to use once as an automobile body sheet and then recover it and use it again for automobiles. The present invention relates to a rolled aluminum alloy plate for use and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, the use of aluminum alloy sheets for automobile body seats has been studied and implemented due to demands for reduction of fuel consumption and weight reduction of automobiles. As an aluminum alloy plate used for such applications, not only the formability, strength, pretreatment before coating, corrosion resistance after coating, etc. are as good as steel plates, but also materials from conventional steel plates. It is an important issue to be able to suppress the cost increase in the production line, distribution / collection route due to the change.

[0003] By the way, as an aluminum alloy for forming used in a conventional automobile body sheet or an aluminum alloy for forming used which has been considered to be used, an Al-Mg type JIS5182 alloy O material or 50 is used.
82 alloy O material, Al-Mg-Cu system, Al-Mg
There are various alloys such as those based on Al-Mg-Cu-Zn.

[0004]

The conventional aluminum alloys for automobile body sheets as described above have the following properties: formability, strength,
Although there are some similar to steel sheets in terms of pretreatment before coating and corrosion resistance after coating, it is still insufficient in terms of suppressing the cost increase due to the change of automobile body sheet material from steel to aluminum alloy. I don't get.

That is, in general, when an automobile part such as an automobile body sheet is manufactured from an aluminum alloy plate, the aluminum alloy plate is handled on the same line as the manufacturing line for manufacturing the steel plate, and the aluminum alloy plate is used as a product. Plates are often used by joining with steel plates and steel parts. Therefore, when recovering scraps or product scraps generated in the manufacturing process, it is impractical to completely separate and recover the steel plate and the aluminum plate from the viewpoint of cost.・ The fact is that it is inevitable that some steel parts will be mixed in.

Therefore, by reusing aluminum scrap of automobile manufacturing process and automobile parts / products as a melting raw material when manufacturing aluminum alloy materials, it is possible to cope with environmental problems and effectively use resources, and further increase costs accompanying material changes. In order to suppress the above problem, Fe contained in the aluminum scrap and mixed into the aluminum alloy produced by using it as a melting raw material becomes a problem.

It has been recognized that some conventional aluminum alloys for automobile body sheets also contain Fe as an unavoidable impurity, and the addition of a small amount of Fe may be positively recognized. The allowable amount of Fe in an aluminum alloy is far smaller than the amount of Fe mixed in when scrap containing steel such as automobile scrap is used, and therefore it is difficult to utilize a sufficient amount of aluminum scrap. As described above, the upper limit of the amount of Fe in the conventional aluminum alloy for automobile body sheets was restricted to a small amount because the Al-Fe-based intermetallic compound generated when Fe was contained impairs the formability. Therefore, if this problem is solved, the inclusion of a large amount of Fe will be allowed, and along with that, a path for effectively utilizing aluminum scrap such as automobile scrap containing a large amount of Fe as a melting raw material will be opened. it is conceivable that.

Therefore, the present invention uses a large amount of scrap containing a large amount of Fe, such as automobile scrap,
To provide an aluminum alloy for an automobile body sheet having performance comparable to that of a conventional aluminum alloy for an automobile body sheet, thereby promoting effective utilization of scrap, and using the alloy of the present invention once for an automobile body sheet. The purpose of this is to later collect this so that it can be used again easily as a material for automobiles, that is, to enhance recyclability.

[0009]

In order to solve the above problems, the present inventors have studied the function of forming coarse needle-shaped Al--Fe intermetallic compounds that adversely affect the moldability, and as a result, have found that the chemical composition In particular, it has been found that the maximum permissible amount of Fe that can be contained can be increased without impairing the formability by properly adjusting Si and Mn and controlling the manufacturing conditions appropriately. I arrived.

Specifically, the rolled aluminum alloy sheet for automobile body sheet according to the invention of claim 1 has a Mg: 2.5-
8%, Fe: 0.3 to 1.2% included, and Si ≦ 0.
5%, Mn ≦ 0.3%, Si / Fe ≦ 1.0, Si +
0.6 × Fe ≦ 0.9%, the balance consisting of Al and unavoidable impurities, the number of intermetallic compounds having a size exceeding 10 μm is 300 / mm ² or less, and the crystal grain size is 20 to It is characterized by being in the range of 70 μm.

The rolled aluminum alloy sheet for automobile body sheet according to the second aspect of the present invention is Mg: 2.5 to 8%, F
e: Includes 0.3 to 1.2% and Si ≦ 0.5%, M
n ≦ 0.3%, Si / Fe ≦ 1.0, Si + 0.6 × F
e ≦ 0.9%, Cr: 0.01-0.
2%, Zr: 0.01 to 0.2%, Ni: 0.01 to
0.05%, V: 0.01 to 0.05%, containing one or more kinds, and Mn + Cr + Zr + Ni + V
<0.4%, the balance being Al and inevitable impurities, the number of intermetallic compounds having a size exceeding 10 μm is 300 / mm ² or less, and the crystal grain size is 20 to
It is characterized by being in the range of 70 μm.

Furthermore, the rolled aluminum alloy sheet for automobile body sheet according to the third aspect of the present invention is Mg: 2.5 to 8%,
Fe: containing 0.3 to 1.2% and Si ≦ 0.5%,
Mn ≦ 0.3%, Si / Fe ≦ 1.0, Si + 0.6 ×
Fe ≦ 0.9%, Cu: 0.05〜
1.2%, Zn: 0.05 to 1.5% of one or two kinds, the balance consisting of Al and unavoidable impurities, and the number of intermetallic compounds having a size exceeding 10 μm is 300 / Mm ² or less, the grain size is 20 to 70
It is characterized by being in the range of μm.

The rolled aluminum alloy sheet for automobile body sheet according to the invention of claim 4 has a Mg: 2.5 to 8 ratio.
%, Fe: 0.3 to 1.2% included, and Si ≦ 0.5
%, Mn ≦ 0.3%, Si / Fe ≦ 1.0, Si + 0.
6 × Fe ≦ 0.9%, Cr: 0.01
~ 0.2%, Zr: 0.01-0.2%, Ni: 0.0
1 to 0.05%, V: 0.01 to 0.05%
Or two or more, and Mn + Cr + Zr + Ni
+ V <0.4%, and further Cu: 0.05 to 1.2
%, Zn: 0.05 to 1.5%, one or two, and the balance being Al and unavoidable impurities, and the number of intermetallic compounds having a size exceeding 10 μm is 30.
It is characterized in that the number of crystal grains is 0 / mm ² or less and the grain size is in the range of 20 to 70 μm.

Further, the method for producing a rolled aluminum alloy sheet for automobile body sheet according to the fifth aspect of the present invention is Mg: 2.
5 to 8%, Fe: 0.3 to 1.2% included, and Si ≦
0.5%, Mn ≦ 0.3%, Si / Fe ≦ 1.0, Si
+ 0.6 × Fe ≦ 0.9%, Cr: 0.01-0.2%, Zr: 0.01-0.2 as required
%, Ni: 0.01-0.05%, V: 0.01-0.
One or more of 0.05% is included, and Mn +
Cr + Zr + Ni + V <0.4%, and if necessary Cu: 0.05-1.2%, Zn: 0.05-
An alloy containing one or two of 1.5% and the balance Al and inevitable impurities was cast at a casting speed of 40 mm.
/ Min or more, DC casting, then rolling, and then final annealing under conditions of a heating rate of 10 ° C / min or more and an ultimate temperature of 450 ° C or more, which results in the number of intermetallic compounds having a size of more than 10 μm. Is 300 / mm ² or less and the grain size is in the range of 20 to 70 μm.

Furthermore, the method for producing an aluminum alloy rolled sheet for an automobile body sheet according to the invention of claim 6 is Mg:
2.5 to 8%, Fe: 0.3 to 1.2% included, and S
i ≦ 0.5%, Mn ≦ 0.3%, Si / Fe ≦ 1.0,
Si + 0.6 × Fe ≦ 0.9% is regulated, and further Cr: 0.01 to 0.2%, Zr: 0.01 to if necessary.
0.2%, Ni: 0.01 to 0.05%, V: 0.01
To 0.05%, one or more of them are included, and Mn + Cr + Zr + Ni + V <0.4%, and if necessary, Cu: 0.05 to 1.2%, Zn: 0.0
5% to 1.5% of 1 or 2 types, the balance is A
1 and an unavoidable impurity alloy with a plate thickness of 2 to 40
mm is continuously cast and rolled, and then further rolled, followed by final annealing under conditions of a heating rate of 10 ° C./min or more and an ultimate temperature of 450 ° C. or more, whereby the number of intermetallic compounds having a size of more than 10 μm is 300. The feature is to obtain a rolled plate having a number of grains / mm ² or less and a crystal grain size in the range of 20 to 70 μm.

[0016]

First, the reasons for limiting the chemical composition of the alloy in the present invention will be explained.

Mg: Generally, in an aluminum alloy rolled plate, the strength and elongation are improved as the Mg content is increased, and the strength and elongation values are comparable to those of the cold rolled steel plate. However, the Mg content is 8%
If it is added over the range, the hot workability is remarkably reduced and the work becomes difficult. On the other hand, if the Mg content is less than 2.5%, it becomes difficult to obtain the strength and elongation required for an automobile body sheet. Therefore, the Mg content is in the range of 2.5 to 8%.

Fe: Fe is an important element in the present invention. Since the addition of Fe forms a needle-shaped Al-Fe-based intermetallic compound and causes deterioration of formability, when used as an aluminum alloy for automobile body sheets that requires forming, the amount of Fe is generally In general, it is usually suppressed as much as possible. However, as a result of continuous experiments and research conducted by the present inventors, it is a coarse intermetallic compound larger than 10 μm that has a particularly bad effect on formability.
The number of coarse intermetallic compounds exceeding 300 μm / mm
It was found that if it is ² or less, there is little adverse effect on moldability. Based on this result, further research was conducted, and the production of intermetallic compounds was investigated for various alloys with an Fe content of 0.30% or more, which makes it possible to easily control the Fe content even when automobile scrap is used. The presence of Si and Mn contained in accelerating the generation and coarsening of the Al-Fe-based intermetallic compound, and by appropriately controlling the Si content and the Mn content, even if the Fe content is increased to some extent, Coarse Al-F exceeding 10 μm that adversely affects the formability
The number of e-based intermetallic compounds has a small effect on formability. 3
It has been found that the number can be suppressed to 00 pieces / mm ² or less. Specifically, the Si amount is regulated to 0.5% or less and the Mn amount is regulated to 0.3% or less, and the S / Fe ratio is 1.0 or less, Si +.
By controlling the value of 0.6 × Fe to 0.9% or less, even if the Fe content is increased to 1.2%, the number of intermetallic compounds increases, but the Al--Fe-based coarse ( > 1
It was found that the formation of intermetallic compounds (0 μm) can be suppressed. Therefore, in the present invention, Fe is added up to 1.2% so as not to impair the formability, in order to improve the utilization of the aluminum scrap under the above-mentioned restrictions on Si and Mn. If the Fe content exceeds 1.2%, a large number of coarse Al—Fe-based intermetallic compounds exceeding 10 μm will be formed even if the Si content and the Mn content are regulated, and the formability will be remarkably increased. On the other hand, if the Fe content is less than 0.30%, aluminum scrap such as automobile scrap containing a large amount of Fe cannot be sufficiently utilized, which is meaningless in terms of scrap usability and recyclability. Therefore, the Fe content is in the range of 0.30 to 1.2%.

Si: Si reduces the solubility of Fe, and Al-
It is an element that increases the size of a Fe-based or Al-Fe-Si-based intermetallic compound to generate a coarse intermetallic compound and reduces the formability. The coarsening of these intermetallic compounds also depends on the ratio between the amount of Si and the amount of Fe, and in order to obtain the characteristics required for the use of automobile body sheets, the ratio between the amount of Si and the amount of Fe (Si / Fe ) Is required to be 1.0 or less. If the Si content exceeds 0.5%, M
Formability deteriorates due to generation and coarsening of g ₂ Si. Furthermore, the total amount of Si and Fe also affects the formation of coarse intermetallic compounds, and the total amount of Si and 0.6 times the amount of Fe (Si
There is no problem if + 0.6 × Fe) is in the range of 0.9% or less, but if it exceeds this range, the formability deteriorates. Therefore, the Si content is regulated to Si ≦ 0.5% and S
i / Fe ≦ 1.0 and Si + 0.6 × Fe ≦
It is necessary to satisfy the condition of 0.9%.

Mn: Mn coexists with Fe to coarsen the Al--Fe based intermetallic compound and reduce the formability.
Further, in the alloy of the present invention having a large amount of Fe, the number of intermetallic compounds produced is large, but since this intermetallic compound becomes a nucleus for recrystallization, a large number of recrystallization nuclei are produced in the alloy of the present invention. It will be. However, since Mn has an action of suppressing the growth of recrystallized grains, the growth of the recrystallized grains during annealing tends to be insufficient, and therefore the recrystallized grains become finer if the Mn amount is large, and the crystallites to be described later Grain size 20μm
Since the above conditions cannot be satisfied, surface defects such as stretcher strain are likely to occur. However, Mn
If the amount is 0.3% or less, these adverse effects can be removed, so Mn is limited to 0.3% or less.

Cr, Zr, Ni, V: Cr, Zr, N
i and V have an effect of suppressing the growth of recrystallized grains similarly to Mn, and when the crystal grains are likely to become coarse, an appropriate crystal grain size can be obtained by adding one or more of them. . However, if the content of each exceeds 0.2%, the recrystallized grains become too fine to satisfy the condition of the grain size of 20 μm or more, or the giant intermetallic compound is generated to significantly reduce the formability. On the other hand, if the addition amount of these elements is less than 0.01%, a sufficient grain refining effect cannot be obtained. Therefore, when Cr, Zr, Ni, and V are positively added, the addition amount is set to each 0.01 to 0.2%. Even within this range, Cr,
When the total amount of Zr, Ni, V and Mn is 0.4% or more, it becomes difficult to control recrystallization as described above, and therefore Mn + Cr +.
It is necessary to satisfy the condition of Zr + Ni + V <0.4.

Cu, Zn: Cu, Zn is an element effective for improving strength, and in the case of applications requiring strength, one or two kinds are added. If the Cu content is less than 0.02% and the Zn content is less than 0.05%, the strength cannot be sufficiently improved. On the other hand, Cu exceeds 1.2% or Z
If n is added in excess of 1.5%, formability, corrosion resistance,
It impairs general properties such as weldability as an automobile body sheet. Therefore, the Cu addition amount is set within the range of 0.02 to 1.20%, and the Zn addition amount is set within the range of 0.05 to 1.50%.

In addition to the above elements, basically Al and inevitable impurities may be used.

In general aluminum alloys, a small amount of Ti is often added alone or in combination with B in order to refine the crystal grains of the ingot, and addition of these elements is allowed in the present invention. However, if the Ti addition amount exceeds 0.15%, coarse primary crystal TiAl ₃ particles are generated. Therefore, the Ti addition amount is preferably 0.15% or less, and when B is added together with Ti, B addition amount is 5
If it exceeds 00 ppm, coarse TiB ₂ particles will be produced, so the B addition amount is preferably 500 ppm or less. In addition, in the melting and casting of aluminum alloys, a small amount of Be is generally added in order to prevent the oxidation of the molten metal. In the case of the present invention, however, if Be is added in an amount of 500 ppm or less, other properties are particularly deteriorated. There is no such thing.

The rolled aluminum alloy sheet of the present invention having the above-described composition must meet the following metallographic conditions.

Intermetallic Compound Size: The alloy of the present invention containing a large amount of Fe inevitably contains a large amount of Al--Fe based intermetallic compounds. As a result of studying the influence of this intermetallic compound on the formability, it was found that the intermetallic compound of a small size does not have a great influence on the formability, while the intermetallic compound of a large size causes the deterioration of the formability. There was found. In particular, intermetallic compounds with a size exceeding 10 μm are 1
It was found that the presence of more than 300 pieces per mm ² markedly deteriorates the formability. Therefore, in the present invention, the number of intermetallic compounds having a size exceeding 10 μm is 30
It was defined as 0 pieces / mm ² or less. In addition, an intermetallic compound having a size of 10 μm or less does not cause any particular problem in the present invention.

Here, the method of reducing the number of intermetallic compounds having a size of more than 10 μm to 300 / mm ² or less is not particularly limited, but the production method of the present invention as described later is preferable. That is, in the production method according to the present invention, the intermetallic compound size can be controlled by appropriately adjusting the casting speed.

Grain size: In the alloy of the present invention, a large number of Al--Fe intermetallic compounds exist as described above, and these Al--Fe intermetallic compounds become nuclei of crystals in the recrystallization process. . Therefore, in the alloy of the present invention, a large number of recrystallized grains are generated during recrystallization annealing (final annealing), so that the crystal grains tend to become too fine. In particular, when the crystal grain size is less than 20 μm, the elongation is lowered and stretcher strain marks are generated. On the other hand, if the crystal grain size exceeds 70 μm, the rough skin phenomenon is noticeable during molding, resulting in surface defects. Therefore, the crystal grain size needs to be in the range of 20 to 70 μm. The means for keeping the crystal grain size within the range of the present invention is not particularly limited, but the production method of the present invention as described below, particularly control of generation of intermetallic compounds by appropriate casting conditions and appropriate By setting such final annealing conditions, it is possible to obtain an appropriate crystal grain size without excessively refining the crystal grains and without coarsening them.

Next, the manufacturing method of the present invention will be described.

Casting: First, an alloy having the above-mentioned composition is melted and cast according to a conventional method.

The casting may be either DC casting (semi-continuous casting) or continuous casting and rolling (thin plate continuous casting), but a sufficiently high solidification rate is required to make the intermetallic compound produced during casting fine. is necessary. When DC casting is applied, the casting speed is set to 40 mm / min or more, which is faster than the conventional method, and the intermetallic compound size is 10 μm.
m or less can be achieved. On the other hand, in the case of continuous casting and rolling, specific methods thereof are roughly classified into a roll casting method in which hot rolling is not performed and a belt casting method or a block casting method in which hot rolling is performed. Also, if the ingot thickness is 2 to 40 mm,
An intermetallic compound size of 10 μm or less can be achieved.

Soaking / heating: In the method of the present invention, it is not always necessary to perform homogenization treatment on the ingot, but even if homogenization treatment is carried out for the purpose of eliminating inhomogeneity of the ingot, the object of the present invention is It does not impair the performance of the rolled aluminum alloy plate. Further, in the case of the present invention, the homogenization treatment may also be performed by heating the ingot before hot rolling.

Rolling: When the thickness of the ingot does not reach the final plate thickness, it is rolled to a desired plate thickness by hot rolling or cold rolling. When hot rolling is performed, the conditions are not particularly limited, but if the hot rolling start temperature is lower than 300 ° C., the productivity will decrease, while if it exceeds 570 ° C., it becomes brittle and cracks easily occur during rolling. Therefore, the hot rolling start temperature when performing hot rolling is preferably in the range of 300 to 570 ° C. Further, when hot rolling alone cannot achieve a desired strip thickness, cold rolling may be performed once or more, but the cold rolling conditions in this case are not particularly limited. Between the hot rolling and the cold rolling or between the cold rolling and the cold rolling, intermediate annealing may be performed for softening or the like, if necessary. The intermediate annealing may be performed in a batch furnace or a continuous annealing furnace, and the conditions are not particularly limited in either case.

Final annealing: In the final annealing, the heating rate (temperature rising rate) is 10 ° C./min or more, and the ultimate heating temperature is 450.
It must be above ℃. In order to satisfy such conditions, it is desirable to use a continuous annealing furnace. The reason for setting the final annealing conditions as described above is as follows.

That is, in the alloy of the present invention containing a large amount of Fe, a large number of recrystallized nuclei are likely to be formed, and thus the recrystallized grains are likely to be fine as described above. On the other hand, in the conventional general batch annealing (BAF), since the annealing temperature is generally low and the recrystallized grains are difficult to grow even if a large number of recrystallized nuclei are generated, when the batch annealing is applied to the alloy of the present invention,
The grains become extremely fine, and as a result, elongation is reduced and stretcher strains are easily generated. However, if rapidly heated to a high temperature using a continuous annealing furnace,
The crystal grains grow uniformly and are appropriately coarsened, so that high elongation can be obtained, and at the same time, stretcher strain is less likely to occur. However, even if rapid heating of 10 ° C./min or more is performed, if the ultimate temperature is less than 450 ° C., the growth of crystal grains is slow and the desired result cannot be obtained. The ultimate temperature is 450 ° C
If the heating rate is slower than 10 ° C./min even above, the growth of crystal grains becomes non-uniform and abnormal growth occurs,
Huge crystal grains are generated, which causes rough skin during molding. Therefore, it is necessary to set the heating rate to 10 ° C./min or more and the ultimate temperature to 450 ° C. or more. The upper limit of the final annealing temperature is not particularly limited, but usually it is preferably 570 ° C or lower. The cooling rate during the final annealing is essentially arbitrary, but Cu or Z is used as a positive additive component.
When n is added, in order to maintain elongation or impart bake hardness (bake hardenability), 10 ° C /
It is preferable to perform rapid cooling of min or more.

The holding time at the ultimate temperature is
It may be determined in consideration of alloying components, annealing temperature, etc. within a range where the crystal grain size does not exceed 70 μm, but normally no holding (cooling immediately after reaching a predetermined temperature) or holding within 5 minutes is preferable.

The rolled plate obtained as described above may be used as it is for final use, or may be subjected to strain correction and used for final use in some cases.

[0038]

Embodiments of the present invention will be described below.

Table 1 shows the alloy composition of the aluminum alloys A to J used in the examples. Alloy A is an alloy corresponding to claim 1, alloy B is an alloy corresponding to claim 2, alloy C
Is an alloy corresponding to claim 3, and alloys D and E are alloy components corresponding to claim 4. In addition, alloy F is a conventional alloy that uses good quality metal, not scrap, as a raw material.
The amount of e is 0.12%, which is much smaller than that of the alloy of the present invention. The other alloys G through J are comparative alloys that fall outside the compositional range of this invention.

[0040]

[Table 1]

Each of the alloys in Table 1 has a width of 1200 mm and a thickness of 50.
It was cast into a DC ingot having a size of 0 mm and a length of 3500 mm, and chamfering was performed on each of the rolled surface and the side surface by 5 mm. After that, No. 1 to No. After soaking and heating according to No. 13, hot rolling was performed to a plate thickness of 4 mm. This is further plate thickness 1
After cold rolling to mm, final annealing was performed under the conditions shown in Table 2. In Table 2, CAL indicates continuous annealing, and BAF indicates batch annealing.

[0042]

[Table 2]

Characteristic values of each alloy, that is, Erichsen value indicating mechanical properties (tensile strength, proof stress, elongation) and formability, yield elongation, and crystal grain size and 10 μm as structural factors for achieving these characteristics. The number of intermetallic compounds having a size exceeding 1.0 was measured. Table 3 shows the results.

[0044]

[Table 3]

Since the object of the present invention is to provide a highly recyclable aluminum alloy sheet, that is, an aluminum alloy rolled sheet exhibiting excellent performance even when scrap containing a large amount of iron such as automobile scrap is used as a raw material, the alloy As the performance of the rolled plate, a value similar to that of a conventional alloy using a highly pure raw material was targeted. Specifically, the following values were used as a guideline for performance. Elongation 26% or more Erichsen value 9.5 mm or more Yield elongation 0.3% or less

No. 1, No. 2, No. 5, No.
6, No. No. 8 is within the scope of the present invention in terms of alloy composition, structure, and manufacturing method. In these cases, strength and elongation are sufficient values, and Erichsen value,
The yield elongation is also excellent, and the target performance is fully achieved.

No. No. 3 is an example in which the alloy components are within the scope of the present invention, but the annealing condition is set to a low temperature outside the scope of the present invention. In this case, the crystal grain size was out of the range of the present invention, stretcher strain was generated, the appearance was poor, and the yield elongation was also poor.

No. No. 4 is an example in which the alloy composition is within the range of the present invention, but the heating rate did not satisfy the conditions of the present invention by using a batch furnace for final annealing, and in this case as well, the crystal grains were refined and therefore the elongation was increased. It was small and the yield elongation was extremely high, resulting in poor moldability. In addition, stretcher strains also occurred and the appearance was poor.

No. No. 7 is an example in which the alloy composition is within the range of the present invention, but the casting speed is slow.
A large amount of intermetallic compounds exceeding m were produced. Therefore, the elongation and Erichsen value decreased, and the moldability deteriorated.

No. 9 is an example using a conventional alloy,
Good properties are shown in terms of strength and moldability. However, in conventional alloys, the alloy components, especially Fe, are regulated to a very small amount, so it is necessary to use good quality metal (virgin metal) as a raw material, and therefore the cost cannot be reduced, and recycling is not possible. It is also inferior to the alloy of the present invention from the viewpoint of resource reuse, such as difficulty in production.

No. 10 has a high Mn content and Mn
Since the total content of + Cr + Zr + Ni + V is large, a large number of huge intermetallic compounds are generated, which deteriorates the formability, and the recrystallized grains cannot be controlled to an appropriate size and become too fine, resulting in strong stretcher strain. did.

No. 11 has a high Cr content and Mn
Since the total content of + Cr + Zr + Ni + V is large, N
o. As in No. 10, the crystal grains became too fine, and the stretcher strain had a strong result.

No. No. 12 had too much Fe and Mn,
In addition, the total content of Mn + Cr + Zr + Ni + V is large,
As a result, a large number of huge intermetallic compounds were generated, the moldability was deteriorated, the recrystallized grains could not be controlled to an appropriate size, and the stretcher strain was strong.

No. No. 13 has a large amount of Si, so Al-F
A large amount of both the e-Si system and the Mg ₂ Si intermetallic compound were formed, and the elongation was a low value of 24%, which was 30% of that of the present invention.
It was inferior to the value of the growth that extended to.

[0055]

As described above in detail, according to the present invention,
An aluminum alloy rolled plate for forming having strength and formability equal to or higher than that of a conventional alloy in which a small amount of Fe is regulated by appropriately adjusting other components even if the alloy component contains a large amount of Fe. Therefore, even if a large amount of aluminum scrap containing a large amount of steel and iron is used as a melting raw material such as automobile scrap, it is possible to obtain a material comparable to the conventional material using a high-purity raw material as an automobile body sheet. As a result, it becomes possible to utilize a large amount of automobile scraps and the like, and it has become possible to remarkably improve scrap usability. Further, when the rolled aluminum alloy sheet according to the present invention is used for an automobile body sheet, it is possible to realize the recycling of producing an automobile from automobile scraps, which can greatly contribute to effective use of resources. Furthermore, according to the manufacturing method of the present invention, the excellent rolled plate described above can be manufactured stably and easily.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mamoru Matsuo 4-3-18 Nihombashi Muromachi, Chuo-ku, Tokyo Within Sky Aluminum Co., Ltd. (72) Inventor Yukio Sasaki 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Stock Company Technology Development Headquarters (72) Inventor Masao Kikuchi 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Co., Ltd. (72) Inventor Makoto Saga 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Stock Company Technology Development Division

Claims (6)

[Claims] 1. Mg: 2.5 to 8% (weight%, the same applies hereinafter), Fe: 0.3 to 1.2%, and Si ≦ 0.5%, Mn ≦ 0.3%, Si /Fe≦1.0, Si + 0.6 × Fe ≦ 0.9%, the balance consisting of Al and unavoidable impurities, and the number of intermetallic compounds having a size exceeding 10 μm is 3
00 grains / mm ² or less, crystal grain size is 20 to 70 μm
Highly recyclable aluminum alloy rolled sheet for automobile body sheets, characterized by being within the range. 2. Mg: 2.5 to 8%, Fe: 0.3 to 1.2%, and Si ≦ 0.5%, Mn ≦ 0.3%, Si / Fe ≦ 1.0, It is regulated to Si + 0.6 × Fe ≦ 0.9%, and further Cr: 0.01 to 0.2%, Zr: 0.01 to 0.2%, Ni: 0.01 to 0.05%, V: 0.01 to 0.05% of one or more of them, and Mn + Cr + Zr + Ni + V <0.4%, the balance consisting of Al and unavoidable impurities, and of the intermetallic compound having a size of more than 10 μm. Number 3
00 grains / mm ² or less, crystal grain size is 20 to 70 μm
Highly recyclable aluminum alloy rolled sheet for automobile body sheets, characterized by being within the range. 3. Mg: 2.5-8%, Fe: 0.3-1.2% are included, and Si ≦ 0.5%, Mn ≦ 0.3%, Si / Fe ≦ 1.0, It is regulated to Si + 0.6 × Fe ≦ 0.9%, and further contains one or two of Cu: 0.05 to 1.2% and Zn: 0.05 to 1.5%, the balance being Al. And unavoidable impurities, and the number of intermetallic compounds with a size exceeding 10 μm is 3
00 grains / mm ² or less, crystal grain size is 20 to 70 μm
Highly recyclable aluminum alloy rolled sheet for automobile body sheets, characterized by being within the range of. 4. Mg: 2.5-8%, Fe: 0.3-1.2% are included, and Si≤0.5%, Mn≤0.3%, Si / Fe≤1.0, It is regulated to Si + 0.6 × Fe ≦ 0.9%, and further Cr: 0.01 to 0.2%, Zr: 0.01 to 0.2%, Ni: 0.01 to 0.05%, V: It contains one or more of 0.01 to 0.05%, and Mn + Cr + Zr + Ni + V <0.4%, and further Cu: 0.05 to 1.2%, Zn: 0.05 to 1. 5% of 1 type or 2 types, the balance is Al and unavoidable impurities, and the number of intermetallic compounds having a size exceeding 10 μm is 3
00 grains / mm ² or less, crystal grain size is 20 to 70 μm
Highly recyclable aluminum alloy rolled sheet for automobile body sheets, characterized by being within the range. 5. Mg: 2.5-8%, Fe: 0.3-1.2% are included, and Si≤0.5%, Mn≤0.3%, Si / Fe≤1.0, It is regulated to Si + 0.6 × Fe ≦ 0.9%, and if necessary Cr: 0.01 to 0.2%, Zr: 0.01 to 0.2%, Ni: 0.01 to 0.05. %, V: 0.01 to 0.05% of one or more of them, and Mn + Cr + Zr + Ni + V <0.4%, and if necessary, Cu: 0.05 to 1.2%, Zn: An alloy containing one or two of 0.05 to 1.5%, the balance being Al and unavoidable impurities, DC-cast at a casting speed of 40 mm / min or more, and then rolled, After that, the final annealing is performed under the conditions that the heating rate is 10 ° C / min or more and the ultimate temperature is 450 ° C or more. The number of intermetallic compounds with a size exceeding 0 μm is 30
0 grains / mm ² or less and crystal grain size is 20 to 70 μm
A method for producing a highly recyclable aluminum alloy rolled sheet for an automobile body sheet, which comprises obtaining a rolled sheet within the range. 6. Mg: 2.5-8%, Fe: 0.3-1.2% are included, and Si ≦ 0.5%, Mn ≦ 0.3%, Si / Fe ≦ 1.0, It is regulated to Si + 0.6 × Fe ≦ 0.9%, and if necessary Cr: 0.01 to 0.2%, Zr: 0.01 to 0.2%, Ni: 0.01 to 0.05. %, V: 0.01 to 0.05% of one or more of them, and Mn + Cr + Zr + Ni + V <0.4%, and if necessary, Cu: 0.05 to 1.2%, Zn: An alloy containing one or two of 0.05 to 1.5%, with the balance being Al and inevitable impurities, was continuously cast-rolled to a plate thickness of 2 to 40 mm, and then further rolled, and thereafter. Final annealing is performed under the conditions that the heating rate is 10 ° C / min or higher and the ultimate temperature is 450 ° C or higher.
The number of intermetallic compounds with a size exceeding μm is 300 / m
A method for producing a highly recyclable aluminum alloy rolled sheet for an automobile body sheet, which comprises obtaining a rolled sheet having a size of m ² or less and a crystal grain size within a range of 20 to 70 μm.