JPH04228552A - Production of aluminum alloy sheet for forming - Google Patents

Abstract

PURPOSE:To improve strength, formability, and external appearance and quality characteristics by specifying the conditions at the final process annealing among process annealings at the time of cold-rolling an Al-Mg-Si alloy sheet and also specifying respective cold drafts at cold rollings before and after the final process annealing. CONSTITUTION:A sheet of Al alloy of Al-Mg-Si type belonging to JIS No.600 type is cold-rolled, while process-annealed between the cold rolling stages. At this time, the ratio between draft A at the cold rolling before the final process annealing and draft B at the final cold rolling after the final process annealing, B/A, is regulated to >=0.8. Moreover, draft of finish cold rolling is regulated to >=30% and continuous annealing is done at 300-580 deg.C to exert process annealing, and further, after the final cold rolling, solution treatment is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention is applicable to moldings used for materials for various land transportation vehicles, such as materials for automobile body sheets, and materials for various electrical and mechanical parts, such as chassis for VTRs. The present invention relates to a method of manufacturing an aluminum alloy sheet for processing, and particularly to a method of manufacturing an aluminum alloy sheet that has excellent strength and formability, as well as excellent appearance quality characteristics such as flow lines.

BACKGROUND OF THE INVENTION Recently, aluminum alloys have come into widespread use in automobile body sheets, various other automobile parts, and various electromechanical parts, mainly with the aim of reducing weight.

By the way, conventionally, as aluminum alloys used for various forming processes, A■-Mg series JIS 5182
Alloy O material, 5052 alloy O material, or A■-Mg-S
i-based AA 6009 alloy T4 treated material, 6010 alloy T
4 treated materials were the most widely used.

Problems to be Solved by the Invention Among the conventional aluminum alloys used in the above-mentioned forming process, A■-Mg based alloy soft materials such as 5182 Alloy O material and 5052 Alloy O material have a tendency to form on the surface after forming process. Because Lüders marks are easily generated, it is considered undesirable for automobile panels, etc., which require particularly excellent appearance quality.

On the other hand, A■-Mg-Si alloys such as 6009 alloy T4 treated material and 6010 alloy T4 treated material do not produce Lüders marks due to forming processing, and have strength comparable to that of steel sheets, as well as strength after baking coating. However, on the other hand, a flow line called ridging occurs after the forming process, which impairs the appearance quality, and furthermore, the grain size is coarse, so there is a problem in heavily machined parts. It has drawbacks such as easy skin irritation.

This invention was made against the background of the above-mentioned circumstances, and is suitable for use as a forming aluminum alloy plate for applications such as land transportation vehicles and electromechanical parts. The purpose of the present invention is to provide a method capable of obtaining an aluminum alloy plate having characteristics that do not cause surface roughness in lines or heavily processed parts, that is, excellent appearance quality characteristics, and also having excellent formability. It is something.

Means for Solving the Problems In order to solve the above-mentioned problems, in the method of manufacturing an aluminum alloy plate for forming according to the present invention, a JIS 6000 series A■-Mg-Si aluminum alloy is used as the alloy. In addition, the cold rolling process includes one or more intermediate annealing, and the conditions of the final intermediate annealing and the rolling rate of the cold rolling before and after the final intermediate annealing are It was decided to stipulate it strictly.

That is, the method for manufacturing an aluminum alloy plate for forming according to the present invention is based on A■-Mg-
When performing cold rolling on a continuously cast thin sheet or hot rolled sheet made of Si-based aluminum alloy with one or more intermediate annealing in between, rolling in the cold rolling before the final intermediate annealing. Ratio (B/A) of rolling ratio (A) and rolling ratio (B) in final cold rolling after final intermediate annealing
is 0.8 or more and the rolling rate in the final cold rolling (
B) is cold rolled to 30% or more, and the final intermediate annealing is performed at 300 to 580°C by continuous annealing.
The rolling process is characterized by heating to a temperature within the range of 5 minutes or less, and then carrying out a solution treatment after the final cold rolling.

Function: The alloy used in the manufacturing method of this invention is basically JIS
Any A■-Mg-Si type aluminum alloy belonging to the 6000 series may be used.The specific content of the ingredients is not particularly specified, but in general, Mg0.1 to 2.0wt%, Si0.5
~2.5wt% as an essential alloy component, and if necessary, one or two of Cu1.5wt% or less, Zn2.0wt% or less, and Mn0.6wt% or less, if necessary. , Cr0.3wt% or less, Zr0
．． It is sufficient that the content is 3 wt% or less, and the remainder is A2 and unavoidable impurities.

Such desirable components will be explained below.

Mg: Mg is a basic alloy component in JIS 6000 series aluminum alloys, and coexists with Si to form Mg2S.
i and contributes to improving strength through precipitation hardening.

If Mg is less than 0.1 wt%, the effect of improving strength is insufficient, while if it exceeds 2.0 wt%, elongation occurs and formability decreases. Therefore, it is desirable that Mg be within the range of 0.1 to 2.0 wt%.

Si: Si is also a basic alloy component in 6000 series aluminum alloys. Part of the added Si is metal Si
A■ Present as particles in the alloy matrix to improve formability, especially elongation and bendability. In addition, some other Si coexists with Mg to produce Mg2Si, which contributes to improving the strength through precipitation hardening. Here, regarding the amount of Si added, it is important for strength improvement to be in a state where Si is sufficiently excessive compared to the stoichiometric composition of Mg2Si and metal Si is generated. From the viewpoint of strength improvement, Si (wt%)>0.6×Mg(wt%)+0.4(w
t%). . Note that if the absolute amount of Si is less than 0.5 wt%, the effect of improving strength and moldability cannot be sufficiently obtained, while if the amount of Si exceeds 2.5 wt%, elongation and moldability will deteriorate. The amount is 0.5
It is preferably within the range of 2.5 wt%.

Cu, Zn: Both Cu and Zn are elements that contribute to improving strength,
Either one or both may be added as necessary. Of these, Zn is also effective in improving corrosion resistance, and contributes to preventing pitting corrosion by lowering the potential of the matrix. However, if Cu exceeds 1.5 wt%, moldability and corrosion resistance will deteriorate, and if Zn exceeds 2.0 wt%, corrosion resistance will deteriorate and moldability will decrease due to changes over time at room temperature. Therefore, Cu is 1.5wt%
Hereinafter, it is preferable that Zn be within a range of 2.0 wt% or less.

Mn, Cr, Zr: All of these elements contribute to making crystal grains finer and reducing the occurrence of flow lines during molding, and one or more of these elements may be added as necessary. Ru. However, Mn is 0.6wt%, Cr is 0.3wt%, and Zr is 0.
．． If it exceeds 3 wt%, coarse intermetallic compounds will be produced and formability will deteriorate. Therefore, it is preferable that Mn be 0.6 wt% or less, Cr be 0.3 wt% or less, and Zr be 0.3 wt% or less.

The remainder of each of the above components may basically be A and unavoidable impurities, but a trace amount of Be, a trace amount of Ti, or Ti and B may also be added. Be forms a dense oxide film to prevent oxidation of A and Mg on the surface of the aluminum material, which in turn contributes to a significant improvement in thread rust resistance. However, the amount of Be added is 0.01
If it exceeds 0.01 wt %, the effect will be saturated and the cost will increase, so it is desirable that the amount of Be added is 0.01 wt % or less. Furthermore, Ti has traditionally been added together with B as a grain refining agent for the ingot structure, but addition of Ti is effective not only for grain refining but also for improving corrosion resistance. However, if the amount of Ti added exceeds 1.0 wt%, coarse intermetallic compounds will be generated and the rolling properties and formability will deteriorate, so the amount of Ti added is preferably 1.0 wt% or less. Further, B, which may be added together with Ti, is preferably added to less than 0.01 wt% since corrosion resistance will be adversely affected if it exceeds 0.01 wt%.

Next, a method for manufacturing an aluminum alloy plate according to the present invention will be explained.

First, a molten alloy having the above-mentioned composition is cast. As the casting method here, a DC casting method (semi-continuous casting method) or a continuous casting rolling method (thin plate continuous casting method) may be applied.

The aluminum alloy ingot obtained by DC casting is subjected to homogenization treatment at a temperature within the range of 450°C to 570°C. By performing such homogenization treatment, it is possible to improve moldability and stabilize recrystallized grains. If the temperature of the homogenization treatment is less than 450°C, the above-mentioned effects cannot be obtained, while if it exceeds 570°C, eutectic melting may occur. Note that the time for homogenization treatment is 1 to 4
8 hours is preferable. If the treatment time is less than 1 hour, the above-mentioned effects cannot be sufficiently obtained, while treatment for a long time exceeding 48 hours is not economical. After such homogenization treatment, hot rolling is performed according to a conventional method to obtain a hot rolled plate having a desired thickness.

On the other hand, in the case of a continuously cast thin plate obtained by the continuous casting and rolling method, it is not necessary to perform hot rolling, but it may be subjected to the same homogenization treatment as in the case of the ingot produced by DC casting described above.

The hot rolled plate or continuously cast thin plate obtained as described above is cold rolled with one or more intermediate annealing steps in between, and then subjected to solution treatment. In this invention, the cold rolling conditions before and after the final intermediate annealing in the cold rolling process as described above and the conditions of the final intermediate annealing are controlled to achieve final structure control, improve formability, and improve the flow line. This is extremely important for prevention.

Note that intermediate annealing is generally performed to improve the cold rollability of alloys with large work hardening.
Intermediate annealing is not normally performed during cold rolling of soft alloys such as IS 6000 series, but in the method of the present invention, it plays an extremely important role for microstructural control.

Next, the conditions of the cold rolling process will be explained.

First, the ratio (B) of the rolling rate (A) in cold rolling before final intermediate annealing and the rolling rate (B) in cold rolling after final intermediate annealing (final cold rolling). /A) to 0
．． 8 or more is extremely important for stabilizing the crystal structure during final recrystallization (recrystallization by solution treatment after final cold rolling). Here, the ratio of B/A is 0.8
If the grain size is less than 100, the recrystallized texture during intermediate annealing is weak, so this is called a cube orientation (cubic orientation), which inhibits formability during the subsequent final cold rolling and solution treatment.
A structure with a (001) orientation is formed.

Secondly, it is also important to set the rolling ratio (B) of the final cold rolling after the final intermediate annealing to 30% or more in order to stabilize the crystal structure during the final recrystallization. Here, if the rolling ratio (B) of the final cold rolling is less than 30%, the crystal grains during the final recrystallization (during solution treatment) become coarse, or the formability deteriorates without recrystallization.

Thirdly, the final intermediate annealing is carried out by continuous annealing.
It is extremely important for tissue control to heat to a temperature within the range of 00 to 580° C. without holding or holding for 5 minutes or less. It is generally known that a special recrystallized texture can be obtained by rapid heating in a continuous annealing furnace. In the case of aluminum alloys, the rolling texture has an orientation close to (123) (634), which is called the S orientation, but if this is recrystallized, it becomes an orientation close to the S orientation, which is called the R orientation. , a (100)(001) orientation called a cube orientation is formed, which significantly reduces formability, particularly deep drawability. However, by recrystallizing by rapid heating such as continuous annealing, then final cold rolling at a rolling reduction of 30% or more, and subsequent solution treatment,
It has been found that the formation of cube orientation, which inhibits formability, can be suppressed. Incidentally, there is an X-ray diffraction method as a method for quantitatively measuring the amount of cube orientation produced, and among them, the inverse pole integrated intensity measurement method is the simplest method. By this method, the (200) integrated intensity ratio compared to a standard sample (pure aluminum powder) without texture was 5.
Although it has been empirically found that if the value exceeds the above, the formability, especially the deep drawability, will be significantly reduced. By doing the above (20
0) It was found that the integrated intensity ratio could be suppressed to less than 5. It has also been found that the crystal structure recrystallized by rapid heating during intermediate annealing becomes a uniform structure, and flow lines caused by rough ingot structures and hot rolled structures can be completely removed.

Here, the heating temperature of the final intermediate annealing in continuous annealing is 3
If the temperature is lower than 00°C, recrystallization will not occur and an appropriate texture will not be obtained, resulting in the formation of a structure with strong cube orientation. On the other hand, if the heating temperature exceeds 580°C, there is a risk of eutectic melting, and recrystallized grains will become coarser, resulting in rough skin during molding and poor appearance.
In addition, moldability decreases. Further, if the heating rate is less than 1° C./sec, the formation of cube orientation in the final plate cannot be suppressed, but with normal continuous annealing, rapid heating of 1° C./sec or more can be achieved. An additional retention time of 5
If it exceeds 100%, the recrystallized grains will become coarser, the thickness of the surface oxidized layer will increase, the rust resistance will decrease, and the economical efficiency will also decrease. Therefore, the conditions for the final intermediate annealing must be determined as described above.

After the final intermediate annealing, it is necessary to perform a solution treatment to recrystallize again to refine and stabilize the crystal grains. As conditions for the solution treatment, which is the final recrystallization treatment, it is desirable to maintain the temperature within the range of 300 to 580° C. for 120 minutes or less.

If the temperature of the solution treatment is less than 300° C., recrystallization will not occur and the moldability will deteriorate. On the other hand, if the temperature exceeds 580°C, there is a risk of eutectic melting, and the recrystallized grains will become coarser and rough, resulting in poor appearance and reduced formability, and furthermore, the thickness of the surface oxidation layer will increase. There is a risk that thread rust resistance may decrease. Here, as a guideline for preventing coarsening of recrystallized grains, it is sufficient to set the recrystallized grain size to 150 μm or less. Further solution treatment time is 120
If it exceeds 100%, the thickness of the surface oxidized layer increases and there is a risk that thread rust resistance will decrease. Note that for this solution treatment, either a batch type heat treatment furnace or a continuous type heat treatment furnace may be applied.

Further, rapid cooling is performed after the solution treatment, and it is sufficient if the cooling rate is higher than forced air cooling. Specifically, a cooling rate of 5° C./sec or more is appropriate.

Note that if forced air cooling or water quenching is performed after solution treatment, the plate is likely to warp. In order to remove this, light cold working such as skin pass, leveling, stretching, etc. may be performed as strain forced working after cooling. However, if such light cold working is performed, the moldability will be slightly reduced.

Therefore, in order to restore formability, it is desirable to perform strain relief annealing after the above-mentioned light cold working. The appropriate conditions for this strain relief annealing are the heating rate and cooling rate as shown in FIG. 1, and the temperature and time as shown in FIG. 2.

Of the above processes, in the cold rolling process,
Of course, cold rolling may be performed with two or more intermediate annealing steps in between. In this case, the final intermediate annealing must be performed by continuous annealing under the conditions already mentioned, but the intermediate annealing before that may be performed under any conditions, and in general, in the case of batch annealing, the temperature is 250 to 450°C 0.5～
In the case of continuous annealing for 24 hours, the temperature may be maintained at 300 to 580°C without holding or for 5 minutes or less.

Here, when performing the above-mentioned intermediate annealing (intermediate annealing before the final intermediate annealing) in a batch method, the heating temperature is 250 ° C.
If it is less than that, it is meaningless because the cold rollability will not be improved.
On the other hand, if the temperature exceeds 450°C, the recrystallized grains will become coarser and the thickness of the surface oxidation layer will increase, which may reduce thread rust resistance.If the holding time is less than 0.5 hours, sufficient cold rolling On the other hand, if the heating time exceeds 24 hours, it not only impairs economic efficiency but also increases the thickness of the surface oxidized layer, which may reduce thread rust resistance. In addition, if the above-mentioned intermediate annealing is performed by continuous annealing, it is meaningless if the heating temperature is less than 300°C because the cold rollability will not be improved, while if it exceeds 580°C, there is a risk of eutectic melting and recrystallization. As the grains become coarser, the thickness of the surface oxidation layer increases, which may reduce thread rust resistance.If the holding time exceeds 5 minutes, the recrystallized grains will become coarser and the surface oxidation layer will increase. There is a possibility that the thickness of the layer increases and the thread rust resistance decreases.

The aluminum alloy plate obtained by the method of the present invention as described above has excellent formability and high strength.
In addition, there are no flow lines or rough skin during molding, and the appearance quality is extremely excellent.

Example Alloys having the compositions shown in alloy numbers 1 to 5 in Table 1 were cast into slabs with cross-sectional dimensions of 500 mm x 1200 mm by DC casting, and the ingots were homogenized at 500°C for 6 hours. After that, the plate was hot rolled to a thickness of 4 mm, and then the second
Processing and heat treatments were performed under various conditions shown in symbols A to F in the table. Here, the processing heat treatments with codes I to E are those in which after primary cold rolling, intermediate annealing is performed, then secondary cold rolling (final cold rolling) is performed, and then solution treatment is performed; In the case of , cold rolling was performed only once and solution treatment was performed without intermediate annealing and subsequent cold rolling. In addition, intermediate annealing is performed by rapid heating using an infrared heater, assuming a continuous annealing furnace.
It was then water cooled. In addition, the solution treatment was performed by heating and holding in a batch electric furnace and then cooling with water.

Table 3 shows the results of examining the material properties of each plate after solution treatment.

Note that the mechanical properties and moldability were both measured after aging at room temperature for two weeks after solution treatment. Among the moldability tests, the Erichsen test was conducted according to the JIS-B method, and the stretchability test was conducted using a ball-head punch with a diameter of 100 mm, with a PVC film attached. L.D.
R (limit drawing ratio) was measured using a φ50 mm punch and Johnson wax as a lubricant. Moreover, bendability (mm) indicates the minimum bending radius. Furthermore, the ear rate is φ6
It shows the selvage ratio when a 2 mm blank is squeezed with a φ32 mm punch.

Further, the inverse pole integrated intensity ratio indicates the result of determining the ratio to the integrated intensity of a sample using a pure aluminum powder (random sample) without texture as a standard sample by X-ray diffraction.

Furthermore, Table 4 shows the results of examining the grain size and appearance characteristics of each alloy plate. In Table 4, rough skin was evaluated by observing the surface of a bent sample, and lining was
Evaluation was made by observing the surface of a sample that was extended by 33 mm using a mm punch. These evaluations were divided into three levels: A: Good, B: Slightly noticeable, and C: Very noticeable.

As is clear from Table 3, the aluminum alloy plate obtained by the method of the present invention has the same or higher strength as the aluminum alloy plate obtained by the comparative method, and has the same formability as the aluminum alloy plate obtained by the comparative method. When compared with samples of , it is superior to aluminum alloy plates obtained by conventional methods. Further, as is clear from Table 4, the aluminum alloy plate obtained by the method of the present invention was found to have excellent appearance quality characteristics with almost no occurrence of rough skin or ridging (flow lines).

Effects of the Invention As is clear from the above explanation, the method for producing an aluminum alloy plate for forming according to the present invention has strength equal to or higher than that of conventional aluminum alloy plates for forming, and excellent formability. Moreover, it is possible to obtain an aluminum alloy sheet with extremely excellent appearance quality characteristics that does not cause flow lines or rough skin during forming process, and is therefore suitable for materials such as parts of land transportation vehicles such as automobile bodies or parts for electric machines, etc. Ideal for manufacturing parts materials that require good appearance quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between heating rate, cooling rate, and temperature in strain relief annealing, and FIG. 2 is a diagram showing the relationship between holding time and temperature in strain relief annealing. Applicant Sky Aluminum Co., Ltd. Representative Patent Attorney Takehisa Toyota

Claims (1)

[Claims] When cold rolling a continuously cast thin plate or hot rolled plate made of A-Mg-Si aluminum alloy belonging to JIS 6000 series with one or more intermediate annealing in between, the final The ratio (B/A) of the rolling ratio (A) in the cold rolling before the intermediate annealing to the rolling ratio (B) in the final cold rolling after the final intermediate annealing is 0.8 or more, and the final cold rolling The rolling ratio (B) in rolling is 30
% or more, and the final intermediate annealing is performed by continuous annealing to a temperature within the range of 300 to 580°C, with no holding or holding for less than 5 minutes, and then final cooling. A method for producing an aluminum alloy plate for forming with excellent formability, the method comprising performing solution treatment after rolling.