JPH0853732A - Aluminum alloy sheet for automobile body sheet, its production and its forming method - Google Patents

Abstract

PURPOSE:To inexpensively produce an Al alloy sheet excellent in formability in the case of using low viscosity lubricating oil by a simple process by subjecting the cold rolled sheet of an Al-Mg alloy having a specified compsn. to process annealing, thereafter subjecting it to final cold rolling by a roll having a specified surface roughness and executing final annealing. CONSTITUTION:The ingot of an Al allay contg., by weight, 2.0 to 8.O% Mg and furthermore contg. one or >=two kinds among <1.5% Fe, <l.0% Mn, <0.3% Cr and <0.3% Zr is subjected to hot rolling, is thereafter subjected to cold rolling at <=20% rolling ratio and is next subjected to process annealing at 320 to 550 deg.C to regulate the recrystallized grain size in the surface layer of the Al alloy sheet to 70 to 300mum, which is successively subjected to final cold rolling by a rolling roll having <=0.5mum Pa roll roughness to form into a sheet material in which the recrystallized grain size in the sheet surface layer is regulated to 10 to 50mum and the surface roughness Pa to <=0.5mum, and also, the surface roughness Ra in the case of being applied with 10% stretch is regulated to >=0.8mum. The Al alloy sheet having high formability under low viscosity lubrication only by ordinary roll finishing can be produced at a low cost without subjecting the surface of the Al alloy sheet to special shot dull finishing.

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 suitable for a forming material for automobile body sheets and the like, a method for producing the same, and a method for forming the same. Without finishing
The present invention relates to an aluminum alloy sheet suitable for formability under low-viscosity lubrication only by mill finishing with ordinary rolling rolls, a method for producing the sheet, and a method for forming such a sheet.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been mainly used for automobile outer panels. However, recently, in order to reduce the weight of an automobile body, it has been considered to use an aluminum alloy plate such as an Al-Mg system or an Al-Mg-Si system.
When molding an automobile body sheet, it is common to use a low-viscosity lubricating oil because it is easy to degrease and wash in the subsequent steps. Formability under low-viscosity lubrication is due to the rough surface of the plate, which forms a micropool for retaining lubricating oil on the contact surface with the mold. It is known that the degree Ra is about 0.6 to 1.0). In addition, the shot dull finishing material is made rough by applying sand, steel balls or the like to the surface of the rolling roll, or by making fine irregularities with a laser or the like to make it rough (such a rough surface is called a shot eye). A material obtained by transferring the surface of this roll to a plate by rolling to roughen the surface of the plate.

[0003]

In the case where the above-mentioned shot dull finishing material is an aluminum rolled plate, it is transferred to the surface of the plate by lightly pressing it with a roll having shots in the final pass of cold rolling. Therefore, in the conventional production of a shot dull finishing material, the number of passes is one extra step, and the shot processing of the roll is very expensive, and it is necessary to always hold this roll. Since there is a need for roll replacement, there is a drawback that the cost becomes high.

An object of the present invention is to solve the above-mentioned problems. Specifically, in a milling process using ordinary rolling rolls, in a forming process under lubrication using a low-viscosity oil of 20 cst or less, a plate is produced. An object of the present invention is to provide an aluminum alloy plate and a method for producing the plate that form a micropool on the surface to improve the formability, and to provide a method for forming such a plate.

[0005]

The first aspect of the present invention for solving the above-mentioned problems includes Mg 2.0 to 8.0 wt% and further comprises Fe 1.5 wt% or less, Mn 1.0 wt% or less, Cr 0. An Al alloy plate containing 3 wt% or less and 0.3 wt% or less of Zr or less, and the rest of which is a normal impurity and Al, and the recrystallized grain size of the plate surface layer in the previous step is 70. ˜300 μm, and the recrystallized grain size of the plate surface layer after final annealing in the final finished plate is 10 to 50 μm.
m, surface roughness Ra ≦ 0.5 μm, and 10%
The surface roughness when stretch is added is Ra ≧ 0.8μ
It is an aluminum alloy plate for an automobile body sheet with m.

A second aspect of the present invention relates to a method for producing the Al alloy plate, which comprises hot rolling an ingot having the Al alloy composition and then cold rolling at a rolling rate of 20% or less, Then, after performing intermediate annealing at a temperature of 320 to 550 ° C., final cold rolling is performed using a roll having a roll roughness Ra ≦ 0.5 μm, and a temperature rising rate of 3.0 ° C./sec or more and a holding temperature of 450 to After the final annealing at 550 ° C. and a holding time of 120 sec or less, the recrystallized grain size of the plate surface layer after the intermediate annealing is 7
0 to 300 μm, the recrystallized grain size of the plate surface layer after final annealing in the final finished plate is 10 to 50 μm, the surface roughness Ra ≦ 0.5 μm, and the surface roughness when 10% stretch is added. This is a method for producing an aluminum alloy plate for an automobile body sheet, the degree of which is Ra ≧ 0.8 μm.
A third aspect of the present invention relates to another method for producing the Al alloy plate, which comprises subjecting the ingot having the Al alloy composition to hot rolling at a hot rolling end temperature of 250 to 300 ° C., and thereafter, Annealing at 320 to 550 ° C. is performed, and then cold rolling is performed. At that time, final cold rolling is performed by rolls having a roll roughness Ra ≦ 0.5 μm, and the temperature rising rate is 3.0 ° C./s.
ec or more, holding temperature 450 to 550 ° C, holding time 120
After the final annealing for sec or less, the recrystallized grain size of the plate surface layer after the intermediate annealing is 70 to 300 μm, and the recrystallized grain size of the plate surface layer after the final annealing in the final finished plate is 10 to 50 μm.
And the surface roughness is Ra ≦ 0.5 μm, and the surface roughness when 10% stretch is added is Ra ≧ 0.8 μm.
And a method for producing an aluminum alloy sheet for an automobile body sheet. Further, a fourth aspect of the present invention relates to another method for producing the Al alloy plate, wherein the ingot having the Al alloy composition is subjected to a hot rolling termination pass under a rolling reduction of 20% or less,
Hot rolling is performed at a finishing temperature of 400 ° C. or higher, and then cold rolling is performed, in which case roll roughness Ra ≦ 0.5 μm.
Final cold rolling is performed by using a roll of No. 1, and a final annealing at a temperature rising rate of 3.0 ° C./sec or more, a holding temperature of 450 to 550 ° C., a holding time of 120 sec or less is performed, and the sheet surface layer after hot rolling is re-rolled. The crystal grain size is 70 to 300 μm, and the recrystallized grain size of the plate surface layer after the final annealing in the final finished plate is 1
0 to 50 μm, the surface roughness Ra ≦ 0.5 μm,
And the surface roughness when adding 10% stretch is Ra
A method for producing an aluminum alloy sheet for an automobile body sheet, wherein ≧ 0.8 μm.

Next, a fifth aspect of the present invention relates to a method for forming an Al alloy sheet according to the first aspect of the present invention, wherein the aluminum alloy sheet is rubbed with a low viscosity oil having a lubricating oil viscosity of 20 cSt or less. This is a method for forming an aluminum alloy sheet for an automobile body sheet, which is formed under the condition that the maximum equivalent strain of the moving part is 0.06 or more. The Al alloy plate of the present invention (the first invention) has a special surface manufacturing process (after the second to fourth inventions), which is the re-deposition of the plate surface layer in the previous step (after the intermediate annealing or hot rolling). In addition to adjusting the crystal grain size and the recrystallized grain size of the plate surface layer in the final plate, the surface is roughened by generating grain boundary steps in the crystal grains during material deformation, especially during drawing, and the mill finish material Even if it is present, the surface becomes like a shotdal material, and this grain boundary step becomes a micropool, improving the formability under low viscosity lubricating oil.

[0008]

Next, the reason why the alloy composition of the Al alloy used in the present invention is limited as described above will be explained. When Mg forms a solid solution, the strength is increased, and at the same time, the work hardenability is increased to increase the ductility and contribute to the improvement of the formability. The reason why the addition amount is limited to 2.0 to 8.0 wt% is that the effect is small when it is less than 2.0 wt%,
This is because if it exceeds 0 wt%, the hot workability is deteriorated and the manufacturing cost is increased. Elements such as Fe, Mn, Cr, and Zr all have the effect of increasing the strength, but Fe1.
5 wt%, Mn 1.0 wt%, Cr 0.3 wt%, Zr
If it exceeds 0.3 wt%, the ductility is lowered. Although Cu, Si, Ti, etc. are used as impurities, Cu is 0.5 wt.
% Or less, Si is 0.2 wt% or less, Ti is 0.2 wt% or less.
If it is contained below, the effect of the present invention is not impaired.

Next, in the Al alloy plate of the first invention, the recrystallized grain size of the plate surface layer in the previous step is 70 to 300 μm, and the recrystallized grain size of the plate surface layer after final annealing in the final finished plate is 10 The reason why the surface roughness is Ra ≦ 0.5 μm and the surface roughness when 10% stretch is added is Ra ≧ 0.8 μm will be described. The plate according to the present invention is a pre-process for the final plate even if recrystallization occurs in the final annealing, that is, an intermediate stage process in the entire rolling process,
Specifically, the influence of the recrystallization structure during intermediate annealing or hot rolling remains. When this material is subjected to a forming process, a grain boundary step is generated due to the difference in the orientation of the recrystallized grains in the previous step in addition to the difference in the orientation of the final recrystallized grains, and the roughness is increased. Therefore, a micropool that holds a low-viscosity lubricating oil is formed in the roughened concave portion, and the moldability is improved.

In order to facilitate understanding of this, the relationship between the recrystallized grains in the previous step and the recrystallized grains and the grain boundary step in the final plate will be described with reference to the drawings. FIG. 1A shows coarse recrystallized grains (IG) in the previous step, and FIG. 1B shows a state in which the grains are elongated in the rolling direction by cold rolling. FIG. 1 (c) shows that the cold-rolled structure of FIG. 1 (b) has fine final recrystallized grains (FG) generated in the recrystallized grains (IG) in the previous step due to the final annealing. Indicates that Further, FIG. 2 is an enlarged cross-sectional view of a plate surface layer portion showing a state of a grain boundary step generated in a forming process of an Al alloy plate having the structure shown in FIG. 1 (c). Here, part A is a grain boundary step due to I · G, and part B is a grain boundary step due to F · G. In the molding process, the grain boundary step at the portion A serves as a micropool.

The size of the recrystallized grains in the previous step is 70 to 30.
The range of 0 μm is specified because when the thickness is less than 70 μm, the above-mentioned effect is small, and when it exceeds 300 μm, the effect is large, but roughening occurs and there is a problem in appearance after molding. A more desirable range is 70 to 150 μm.
Further, the recrystallized grain size after final annealing is set to 10 to 50 μm, because when it is less than 10 μm, Luders band is remarkably generated during the forming process, and when it exceeds 50 μm, it may cause skin roughness depending on the application, which is a problem in surface quality. Is not desirable.
A desirable range is 20 to 50 μm. Note that the recrystallized grain size in both the previous step and the final plate was set as the plate surface layer,
This is because the crystal grain size of the plate surface layer is greatly related in the present invention.

Further, in the present invention, the surface roughness is Ra ≦
The reason why the plate of the present invention is 0.5 μm is the mill finish material, and the center line average roughness is Ra ≦ 0.5 μm in order to distinguish the surface state from the shotdal material. The surface roughness of the plate before forming is about the same as that of a normal rolled material. Further, in order to define the degree of occurrence of grain boundary step due to deformation, the condition was that the surface roughness was Ra ≧ 0.8 μm when 10% stretch was added. 10%
When stretch is added, the surface roughening state is Ra
Is less than 0.8 μm, the size of the micropool is small and the effect of improving the moldability is not sufficient.
By using the plate structure as described above, it is possible to perform the molding process in the same manner as the conventional shot dull finishing material.

Next, the reason why the manufacturing conditions are selected as described above in the method for manufacturing an aluminum alloy sheet according to the present invention (the second to fourth inventions) will be described. In the production of the AL alloy plate of the present invention, the rolls used for casting, solution treatment and cold rolling are performed under ordinary conditions. In the manufacturing method according to the second aspect of the present invention, hot rolling is performed in a conventional method of 350 to 4
After performing at 50 ° C, cold rolling is performed at a rolling rate of 20% or less, and then intermediate annealing is performed at a temperature of 320 to 550 ° C.
The recrystallized grain size of the plate surface layer after the intermediate annealing is adjusted to 70 to 300 μm. The recrystallized grains have a final grain size of 10 to 50 μm.
The m crystal grains are mixed with the surface layer of the plate of the final product, and each crystal grain causes a step on the plate surface when the material is deformed.
The above-mentioned intermediate annealing temperature is set to 320 to 550 ° C. is 3
If it is lower than 20 ° C, recrystallization does not occur, and if it exceeds 550 ° C, melting may occur. Next, in the manufacturing method according to the third aspect of the present invention, the hot rolling end temperature is 2
In the case of 50 to 300 ° C, recrystallization does not occur during hot rolling, and the accumulation of dislocations due to hot working remains.
Recrystallization occurs by applying an intermediate annealing at 550 ° C. Further, in the manufacturing method according to the fourth aspect of the invention, recrystallization due to the self-annealing effect occurs during hot rolling by performing the conditions for the hot rolling end pass at a rolling reduction of 20% or less and an end temperature of 400 ° C. or more. Therefore, intermediate annealing is not necessary. In this case, it is specified that the reduction is performed at 20% or less and the finishing temperature is 400 ° C. or more. When the reduction is more than 20%, the driving force for recrystallization is too large, so that the grain size is not sufficiently increased. Temperature is 40
This is because recrystallization due to self-annealing is less likely to occur at less than 0 ° C.

Cold rolling is applied to the recrystallized structures obtained by the manufacturing methods according to the second to fourth aspects of the invention as described above, and a roll having a normal roll roughness Ra ≦ 0.5 is subjected to final cold rolling. Cold-rolling is carried out, and then final annealing is performed at a heating rate of 3.0 ° C.
/ Sec or more, holding temperature 850 to 550 ° C, holding time 1
It is performed in 20 seconds or less. The final annealing was performed at a temperature rising rate of 3.0 ° C./sec or more, a holding temperature of 450 to 550 ° C., and a holding time of 120 sec or less because the temperature rising rate is fast and the crystal orientation becomes a random orientation, so that each crystal grain during material deformation This is because a larger grain boundary step is generated due to the difference in the wobbling direction. The cooling rate is preferably 3.0 ° C./sec or higher from the viewpoint of preventing the Luders band from being generated.

The fifth aspect of the present invention relates to a method for forming an Al alloy sheet produced as described above, but it is defined that a low viscosity oil having a lubricating oil viscosity of 20 cSt or less is used in the forming process. When the viscosity of the lubricating oil exceeds 20 cSt, in the degreasing and cleaning process of the lubricating oil after the molding process,
This is because the removal becomes difficult. Also, the molding was performed under the molding conditions in which the maximum equivalent strain of the sliding part was 0.06 or more. The reason is that when the sliding part of the molded product is deformed by less than 0.06 due to the equivalent strain, This is because the effect of improving the formability is not exhibited because the generation of the interface step is insufficient. The equivalent strain referred to here is the strain represented by the following equation.

[0016]

[Equation 1]

[0017]

EXAMPLES Preferred examples of the present invention will be described below as comparative examples.
Description will be made in comparison with the conventional example. Table 1 shows Al alloy compositions used in the present example, comparative example, and conventional example. An Al alloy having the composition shown in Table 1 was subjected to a homogenizing treatment by a conventional method, and then hot-rolled and cold-rolled (final cold-rolled roll was Ra = 0.4 μm).
Was used), intermediate annealing, and final annealing were performed under the manufacturing conditions shown in Tables 2 and 3 to obtain a plate material having a thickness of 1 mm. In addition, No of Table 2
1 to 9 are Al alloy plates (claim 1) manufactured by the method of the present invention (claims 2 to 4) in the examples of the present invention. Further, Nos. 10 to 18 in Table 3 are Al alloy plates manufactured under the manufacturing conditions deviating from the method of the present invention in Comparative Example, and No. 19
Reference numerals 20 to 20 are conventional examples, which are conventional shot dull finishing plates.
The recrystallized grain size in the previous step, the crystal grain size in the final plate, the Ra of the base plate, and the Ra after 10% stretching were measured for this plate material and shown in Tables 2 and 3. Ra was measured in the direction perpendicular to the rolling direction of the plate. Further, as a forming test, a deep drawing test was performed to measure a drawable depth. In this case, punching diameter φ33 mm, cylindrical drawing with a drawing ratio of 1.94 was used for wrinkle holding force 1000 kgf, lubricating oil viscosity 5 cS
It was performed under the condition of low viscosity anticorrosive oil coating of t. The equivalent strain in the die R portion, which is the sliding portion in this case, was 0.07. The molding conditions correspond to the invention of claim 5. Furthermore, the appearance after molding is ⊚: good, ∘:
There was no problem, Δ: There was a problem, and ×: Luders or rough skin was evaluated. The results are shown in Tables 2 and 3.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

As is clear from Tables 1, 2 and 3, the NO. 1.2.4.5.
No. 6 of the conditions corresponding to claim 6 and claim 1 and 3. 3.7.
No. 8 of the conditions corresponding to Claims 1 and 4. All of 9 have excellent moldability, and the appearance after molding is also good. On the other hand, when molded with the same alloy composition, NO. 1
In No. 0, the condition of the previous step of recrystallization is out of the range of the present invention, the recrystallized grain size in the previous step is small, Ra after 10% stretching is small, and the deep drawing depth is also small. NO. 1
In No. 7, the condition of the previous step is within the range of the present invention, but the final annealing condition deviates from the condition of the present invention.
a is small and the appearance after molding is not good. N0.18 was outside the scope of the present invention in both the conditions of the previous step and the final annealing condition, the final crystal grain size was large, and roughening occurred after molding. In addition, NO. Nos. 11 to 15 and 16 have the conditions of the previous step out of the scope of the present invention, so even if the final annealing is performed, the deep drawing depth,
One of the appearance characteristics after molding is inferior. The aluminum alloy plate according to the present invention has a conventional shotal material NO. It can be seen that compared with Nos. 19 and 20, the moldability is equivalent and the appearance after molding is excellent.

[0022]

As described above, according to the present invention, it is possible to supply a material having the same high moldability as that of the conventional shot dull material, an excellent appearance after molding, and a low cost. Therefore, a remarkable industrial effect can be expected.

[Brief description of drawings]

FIG. 1 is an explanatory view of a metal structure of a plate surface layer portion according to the present invention, in which (a) is a state of coarse recrystallized grains in a previous step, and (b) is a result of cold rolling. In the state of being stretched in the rolling direction, and (c) shows the state of recrystallized grains of the final plate when this is further annealed.

FIG. 2 is an enlarged cross-sectional view of a plate surface layer portion showing a state of a grain boundary step generated in a forming process of an Al alloy plate having the structure shown in FIG. 1 (c).

[Explanation of Codes] I / G Coarse recrystallized grains in previous process F / G Recrystallized grain of final plate A part Grain boundary step due to I / G B part Grain boundary step due to F / G

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C22F 1/047 (72) Inventor Satoshi Kakio 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Industrial Co., Ltd. (72) Inventor Yoichiro Toguji, 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor, Shintaku Yasunaga 1-4-1 Chuo, Wako, Saitama Stock Association Incorporated in Honda R & D Co., Ltd. (72) Inventor Noboru Hayashi 1-4-1 Chuo, Wako, Saitama Stock Company

Claims (5)

[Claims] 1. An element containing 2.0 to 8.0 wt% of Mg, further containing 1.5 wt% or less of Fe, 1.0 wt% or less of Mn, and Cr.
Either 0.3 wt% or less, Zr 0.3 wt% or less 1
Al alloy plate containing 1 or 2 or more kinds and the rest normal impurities and Al, the recrystallized grain size of the plate surface layer in the previous step is 70 to 300 μm, and the recrystallized grain size of the plate surface layer in the final plate Is 10 to 50 μm, and the surface roughness is Ra ≦
An aluminum alloy plate for an automobile body sheet, which has a surface roughness of Ra ≧ 0.8 μm when a stretch of 10% is applied at 0.5 μm. 2. Includes Mg 2.0 to 8.0 wt%, further Fe 1.5 wt% or less, Mn 1.0 wt% or less, Cr
Either 0.3 wt% or less, Zr 0.3 wt% or less 1
After hot-rolling an Al alloy ingot containing Al or two or more kinds and the rest ordinary impurities and Al, cold rolling is performed at a rolling rate of 20% or less, and then intermediate annealing is performed at a temperature of 320 to 550 ° C. After that, final cold rolling is performed by a roll having a roll roughness Ra ≦ 0.5 μm, and the temperature rising rate is 3.0.
C./sec or more, a holding temperature of 450 to 550.degree. C., a holding time of 120 sec or less is subjected to final annealing, and the recrystallized grain size of the plate surface layer after intermediate annealing is 70 to 300 .mu.m. Is 10 to 50 μm, the surface roughness is Ra ≦ 0.5 μm, and the surface roughness when a 10% stretch is added is Ra ≧ 0.8 μm. Manufacturing method. 3. Mg 2.0-8.0 wt%, Fe 1.5 wt% or less, Mn 1.0 wt% or less, Cr
Either 0.3 wt% or less, Zr 0.3 wt% or less 1
Al alloy ingots containing two or more kinds, and the rest ordinary impurities and Al having a hot rolling end temperature of 250 to 30.
Hot rolling at 0 ° C. is performed, annealing is then performed at 320 to 550 ° C., and then cold rolling is performed. At that time, final cold rolling is performed using rolls having a roll roughness Ra ≦ 0.5 μm. This was subjected to final annealing at a temperature rising rate of 3.0 ° C./sec or more, a holding temperature of 450 to 550 ° C., and a holding time of 120 sec or less so that the recrystallized grain size of the plate surface layer after the intermediate annealing was 70.
˜300 μm, the recrystallized grain size of the surface layer of the final plate is 10 to 50 μm, and the surface roughness is Ra ≦ 0.5 μm.
R is the surface roughness when 10% stretch is added in m
A method of manufacturing an aluminum alloy sheet for an automobile body sheet, characterized in that a ≧ 0.8 μm. 4. An element containing 2.0 to 8.0 wt% of Mg, further containing 1.5 wt% or less of Fe, 1.0 wt% or less of Mn, and Cr.
Either 0.3 wt% or less, Zr 0.3 wt% or less 1
Al alloy ingots containing two or more kinds of Al, and the rest of which are normal impurities and Al, are hot-rolled under conditions of a hot-rolling end pass of a rolling reduction of 20% or less and an end temperature of 400 ° C. or more, and then cooled. Rolling is performed, but the roll roughness Ra
Final cold rolling was performed with a roll of ≦ 0.5 μm, and the temperature rising rate was 3.0 ° C./sec or more and the holding temperature was 450 to 5
After the final annealing at 50 ° C. and a holding time of 120 sec or less, the recrystallized grain size of the plate surface layer after hot rolling is 70 to 300 μm.
m, the recrystallized grain size of the plate surface layer in the final plate is 10 to 50
μm and surface roughness Ra ≦ 0.5 μm, 10
The surface roughness when adding% stretch Ra ≧ 0.8
The method for producing an aluminum alloy plate for an automobile body sheet, wherein the aluminum alloy plate has a thickness of μm. 5. An element containing 2.0 to 8.0 wt% of Mg, further containing 1.5 wt% or less of Fe, 1.0 wt% or less of Mn, and Cr.
Either 0.3 wt% or less, Zr 0.3 wt% or less 1
Al alloy plate containing 1 or 2 or more kinds and the rest normal impurities and Al, the recrystallized grain size of the plate surface layer in the previous step is 70 to 300 μm, and the recrystallized grain size of the plate surface layer in the final plate Is 10 to 50 μm, and the surface roughness is Ra ≦
An aluminum alloy plate having a surface roughness of Ra ≧ 0.8 μm when a stretch of 10% was added at 0.5 μm,
A method for forming an aluminum alloy sheet for an automobile body sheet, which comprises using a low-viscosity oil having a lubricating oil viscosity of 20 cSt or less and performing the forming under the condition that the maximum equivalent strain of the sliding portion is 0.06 or more.