JP2008163361A - Method for producing magnesium alloy thin sheet having uniformly fine crystal grain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a magnesium alloy thin sheet having uniformly fine crystal grains. <P>SOLUTION: Through a process where the molten metal of a magnesium alloy comprising, by weight, 1.0 to 11% Al, ≤2.0% Zn and 0.1 to 0.5% Mn, and the balance Mg with inevitable impurities is subjected to continuous casting/rolling, so as to be a belt-like magnesium alloy sheet material, and, the magnesium alloy sheet material is subjected to hot rolling after homogenizing treatment or before the treatment, and the draft in the first one pass in the hot rolling stage is controlled to ≥40%, a magnesium alloy thin sheet having uniform fine crystal grains can be produced. Further, in the hot rolling stage, it is possible that the material heating temperature is controlled to the range of 200 to 350°C, and, also, the surface temperature of rolling rolls in a hot rolling device is controlled to the range of 150 to 350°C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for hot rolling a magnesium alloy sheet obtained by continuous casting and rolling, and a method for producing a magnesium alloy sheet having a uniform fine grain structure obtained thereby.

  It is known that the mechanical properties of magnesium alloys are strongly dependent on the crystal grain size, and various excellent properties can be obtained, such as the finer the crystal grains, the higher the strength and elongation, and the easier superplasticity appears. It has been. Conventionally, thermomechanical processing has been used as a method for producing a magnesium alloy plate having a fine crystal grain structure. In many cases, this method controls the dynamic recrystallization phenomenon during hot working, the solid solution of solute elements during the heat treatment during and after warm working, the precipitation and recovery, the recrystallization phenomenon, etc. The above-mentioned phenomena are comprehensively controlled to refine the crystal grains. Recently, a high strain processing method such as an ECAP method (Equal-Channel Angular Pressing) has been developed.

The present invention relates to a method for easily obtaining a magnesium alloy having fine crystal grains. In the conventional rolling method, a region in which strain is difficult to be uniformly introduced is formed during rolling, and elongated grains are formed in the region. appear. When coarse elongated grains are generated, the portion becomes a large structure of crystal grains and becomes non-uniform even in subsequent repeated rolling.
As a method for repeating such rolling, Patent Document 1 discloses a method of performing hot rolling and warm rolling after continuous casting rolling, and Patent Document 2 discloses a process of warm or hot and warm rolling. A method of applying a homogenization heat treatment has been disclosed.
JP-A-6-293944 JP 2006-144043 A

Since the crystal structure of the magnesium alloy is a dense hexagonal crystal, it is difficult to plastically deform at room temperature and cold workability is poor. Therefore, in the conventional manufacturing method from a thick slab, heating and hot or hot rolling are performed. Therefore, even when the heat treatment method is applied, the limit of the crystal grain size of the obtained magnesium alloy plate is about 10 μm. In addition, the high strain processing method such as the ECAP method is still a laboratory level technique and cannot be applied as a mass production technique for magnesium alloy thin plates.
An object of this invention is to provide the manufacturing method of the magnesium alloy thin plate which has a uniform fine crystal grain in a simple method.

In order to achieve the above object, the present invention employs the following configuration.
(1) The present invention contains, in weight percent, Al: 1.0 to 11%, Zn: 2.0% or less, Mn: 0.1 to 0.5%, with the balance being Mg and inevitable impurities. The molten alloy is continuously cast and rolled to be processed into a strip-shaped magnesium alloy sheet, and the magnesium alloy sheet is hot-rolled after or before the homogenization treatment. A method for producing a magnesium alloy thin plate having uniform fine crystal grains, comprising a step of setting a pass reduction ratio to 40% or more.
(2) In the present invention, in the hot rolling step, the heating temperature of the magnesium alloy sheet is in the range of 200 to 350 ° C, and the rolling roll surface temperature of the hot rolling apparatus is in the range of 150 to 350 ° C. It is a manufacturing method of the magnesium alloy thin plate which has the said uniform fine crystal grain.

According to the production method of the present invention, Al: 1.0 to 11% by weight, Zn: 2.0% or less, Mn: 0.1 to 0.5% are contained, and the balance is Mg and inevitable impurities. The molten magnesium alloy is continuously cast and rolled to be processed into a strip-shaped magnesium alloy sheet, and the magnesium alloy sheet is hot-rolled after or before the homogenization treatment. By including the step of setting the rolling reduction rate of 1 pass of 40% or more, a magnesium alloy thin plate having uniform fine crystal grains can be produced.
Moreover, in the said hot rolling process, it is enough by making the heating temperature of the said magnesium alloy board | plate material into the range of 200-350 degreeC, and making the rolling roll surface temperature of a hot rolling apparatus into the range of 150-350 degreeC. It is possible to efficiently produce a magnesium alloy thin plate having uniform fine crystal grains, which is plastic by heating, suppresses reaction due to excessive heating, and has excellent surface properties.

As described above, according to the method for producing a magnesium alloy sheet of the present invention, a magnesium alloy sheet having a uniform fine structure with an average crystal grain size of 6 μm or less can be efficiently produced. Can be improved.
In addition, the magnesium alloy sheet produced according to the present invention has uniform and fine crystal grains, so it has high strength and extensibility, has excellent properties such as plasticity, and has a complicated shape that was previously impossible. Can also be molded. As a result, the range of application of a molded product made of a magnesium alloy can be expanded, and a light product with high structural strength can be provided.

About the manufacturing method of the magnesium alloy thin plate which has the fine crystal grain of this invention, the reason for limitation of the component and various manufacturing process conditions is demonstrated.
The magnesium alloy applied to the production method of the present invention contains Al: 1.0 to 11% by weight, Zn: 2.0% or less, Mn: 0.1 to 0.5%, with the balance being Mg. And a component composition consisting of inevitable impurities.

The Al content is preferably added within a range of 1.0 to 11%, and more preferably within a range of 2 to 4%.
Al is positively added for the purpose of improving mechanical properties such as castability and strength, and corrosion resistance. However, if the amount of Al exceeds 11%, workability in the rolling process is lowered. Moreover, if the addition amount of Al is less than 1%, sufficient castability, strength and corrosion resistance cannot be obtained.

The Zn content may be added within a range of 2.0% or less.
Zn, like Al, contributes to improvement of mechanical properties such as castability and strength. However, if the added amount of Zn exceeds 2.0%, castability deteriorates. Further, if the added amount of Zn is less than 0.2%, the strength may decrease, and as a result, the press formability may decrease.

The Mn content is preferably added within a range of 0.1 to 0.5%.
Mn has an effect of alleviating the influence of elements that lower the corrosion resistance. That is, by adding Mn, the influence of Fe, which is an impurity element that lowers the corrosion resistance, can be mitigated, and by adding within the above range, the effect can be most exerted. If it exceeds 50%, a coarse metal compound is produced during continuous casting and rolling, and the rollability deteriorates.

Next, each process in the manufacturing method of the magnesium alloy thin plate of this invention is demonstrated.
As shown in FIG. 1 (A), the continuous casting and rolling apparatus 1 is used to continuously cast and roll the molten magnesium alloy into a strip-shaped magnesium alloy sheet M having a thickness of 2.5 to 7 mm by, for example, a twin roll method. The magnesium alloy sheet M is hot-rolled in the hot rolling device 3 after being homogenized in the homogenizing device 2 or before being homogenized.
At this time, by setting the reduction ratio of the first pass in the hot rolling process to 40% or more, the reduction during the hot rolling can be increased, and the strain can be uniformly introduced to the center of the plate thickness of the material. As a result, generation of elongated grains can be suppressed.
In the hot rolling step, the material heating temperature can be in the range of 200 to 350 ° C, and the surface temperature of the rolling roll 6 of the hot rolling apparatus 3 can be in the range of 150 to 350 ° C.

When the hot-rolled magnesium alloy sheet M1 is warm-rolled using the warm-rolling device 4 and thinned to a predetermined target plate thickness, the magnesium alloy has a uniform fine structure with an average crystal grain size of 6 μm or less. A thin plate M2 is obtained.
Furthermore, intermediate annealing (apparatus not shown) may be performed during the warm rolling process.

"Continuous casting and rolling"
In this step, the molten magnesium alloy is supplied between, for example, a pair of water-cooled twin rolls 5 as shown in FIG. 1 (A), the supplied metal is cooled and solidified, and rolled continuously. This is a step of casting and rolling into a thin strip-shaped magnesium alloy sheet M. At the same time, the cast structure in the solidified metal is homogenized to some extent.
In general, casting is a process in which a molten metal melted at a high temperature is poured into a mold and cooled to form an ingot. In order to produce a product, it is necessary to reheat and then divide it into pieces. In the continuous casting and rolling method, the strip-shaped magnesium alloy sheet M can be made as it is from the molten metal without going through the cooling / bundling process, which is excellent in terms of productivity and energy saving, and is an extremely efficient magnesium alloy sheet. Is possible.

"Homogenization treatment"
This process is a heat treatment for eliminating segregation at a high concentration at the dendrite cell boundary and the center of the plate thickness of the Al and Zn solute elements in the rapidly solidified magnesium alloy plate material M. The magnesium alloy sheet M that has been continuously cast and rolled is wound up into a coil R1, and the coil R1 is heat-treated in a heating furnace 7 as shown in FIG. Alternatively, after continuous casting and rolling, the magnesium alloy sheet M1 that has been hot-rolled as shown in FIG. 1C is wound into a coil R2, and the coil R2 is heat-treated in the heating furnace 7 as shown in FIG. I do.
As heat treatment conditions, it is preferable to carry out at a temperature range of 370 to 470 ° C. for 1 hour or longer. The segregation is eliminated by this heat treatment, and a magnesium alloy sheet M having excellent rolling properties thereafter can be obtained.

"Hot rolling"
This step is a step for processing the magnesium alloy plate material M having a predetermined thickness into the magnesium alloy plate material M1 having a predetermined thickness. As shown in FIG. 1 (D) after the homogenization treatment, the magnesium alloy sheet material M that has been continuously cast and rolled, or before the homogenization treatment, as shown in FIG. And supplying between the pair of rolling rolls 6 and rolling.
Here, by setting the first one-pass reduction ratio to 40% or more, uniform fine crystal grains can be obtained. The upper limit of the first one-pass rolling reduction is, for example, 75%. It is preferable that the heating temperature of the magnesium alloy sheet M is in the range of 280 to 350 ° C, and the surface temperature of the rolling roll 6 is in the range of 150 to 350 ° C. When performed at a temperature lower than these ranges, the resulting magnesium alloy sheet M1 may have insufficient plasticity due to insufficient heating. Conversely, when performed at a temperature higher than these ranges, the activity is high. In some cases, magnesium reacts with the apparatus, the product adheres to the surface of the obtained magnesium alloy sheet M1, and the surface properties may deteriorate.

"Warm rolling"
In this step, the magnesium alloy sheet M1 heat-treated after hot rolling or the magnesium alloy sheet M1 without heat treatment is processed as shown in FIG. 1 (F) to a magnesium alloy sheet M2 having a predetermined thickness. It is this process. The heating temperature of the magnesium alloy sheet M1 is preferably less than 300 ° C., and the surface temperature of the rolling roll 8 in the warm rolling device 4 is preferably 120 ° C. or less. When it is carried out at a temperature higher than these ranges, highly active magnesium may react with the apparatus, the product may adhere to the surface of the obtained magnesium alloy plate M2, and the surface properties may deteriorate.
The number of passes in the warm rolling process may be one time rolling or multiple times rolling, and is not particularly limited. Depending on the product, cold rolling and further final annealing may be performed after warm rolling.

"Intermediate annealing"
This step is an annealing step that is performed at a temperature higher than the recrystallization temperature in order to soften the plastically processed material in a temperature range where strain hardening occurs and to facilitate the processing. It is preferably provided between the hot rolling process and the warm rolling process or when the rolling reduction of the warm rolling exceeds 80%. Even if the reduction ratio in one warm rolling process is 80% or less, if the total reduction ratio in two or more warm rolling processes exceeds 80%, this intermediate annealing process is provided. It is preferable to provide a final warm pressure step.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
It should be noted that the present invention is not limited by this embodiment, and can of course be appropriately modified within a compatible range, all of which are included in the technical scope of the present invention.

<Manufacturing method and measuring method>
Magnesium alloy (sample number 1) having an alloy composition of Al: 3.1%, Zn: 0.79%, Mn: 0.38%, and Al: 5.8%, Mn: 0.32% A continuous casting and rolling by a twin roll method as shown in FIG. 1 was performed on a molten magnesium alloy (test material number 2) having an alloy composition to produce a strip-shaped magnesium alloy sheet having a thickness of 6.4 mm.
The obtained magnesium alloy sheet was subjected to a homogenization treatment at 450 ° C. for 8 hours, and then the reduction rate of the first one pass in the hot rolling process was compared with 40%, 48%, and 57% in the examples. In the example, hot rolling was performed at 32% (heating temperature of the plate material of 300 ° C. and rolling roll surface temperature of 250 ° C. in both Examples and Comparative Examples), and the thickness was further 2.5 mm by hot rolling. Further, after intermediate annealing, a magnesium alloy thin plate having a thickness of 0.80 mm was manufactured by warm rolling.
The average particle diameter was measured by a cutting method using a photomicrograph taken in the longitudinal section of the manufactured thin plate.
<Evaluation results>
The results of Examples 1 to 4 and Comparative Example 1 are shown in Table 1.

As the rolling reduction of the first pass in the hot rolling process increased, the formation of coarse elongated grains was suppressed, and the number of coarse elongated grains decreased and the size of coarse elongated grains also decreased.
In the comparison of the magnesium alloy sheet with a plate thickness of 0.8 mm, the average grain size was as small as 6 μm or less when the first rolling reduction in the hot rolling process was 40% or more.
As shown in Table 1, the crystal grains of the magnesium alloy thin plates of Examples 1 to 4 obtained according to the present invention are clearly made finer than those of Comparative Example 1.

It is a figure which shows the manufacturing process of one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Continuous casting rolling apparatus, 2 ... Homogenization processing apparatus, 3 ... Hot rolling apparatus, 4 ... Warm rolling apparatus, 5 ... Twin roll, 6 ... Roll, 7 ... heating furnace, 8 ... rolling roll M ... magnesium alloy sheet, M1 ... magnesium alloy sheet, M2 ... magnesium alloy sheet, R1 ... coil, R2 ... coil

Claims (2)

A magnesium alloy molten metal containing Al: 1.0 to 11% by weight, Zn: 2.0% or less, Mn: 0.1 to 0.5%, the balance being Mg and inevitable impurities,
Continuous casting and rolling, processing into a strip-shaped magnesium alloy sheet,
The magnesium alloy sheet is hot-rolled after the homogenization treatment or before the treatment,
A method for producing a magnesium alloy thin plate having uniform fine crystal grains, comprising a step of setting the rolling reduction ratio of the first pass in the hot rolling step to 40% or more.   The uniform fineness according to claim 1, wherein in the hot rolling step, the heating temperature of the magnesium alloy sheet is in the range of 200 to 350 ° C, and the rolling roll surface temperature of the hot rolling apparatus is in the range of 150 to 350 ° C. Of manufacturing a magnesium alloy thin plate having various crystal grains.

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