KR20090121792A - Method of manufacturing fine-grained mg alloy sheets by static recrystallization - Google Patents

Abstract

PURPOSE: A method of manufacturing fine-grained Mg alloy sheets by static re-crystallization is provided to have high intensity, high tenacity and excellent elongation ratio at the molding temperature by adopting fine-grains. CONSTITUTION: The board material is made by rolling the Mg alloy sheets at the re-crystallization temperature or less(10). The fine-grains is formed by heat-processing and re-crystallizing the board material(20). At the temperature of 200°C ~ 350°C, the Mg alloy sheets is processed for 9~15 hours. The Mg alloy sheets are rolled with uniform speed. The Mg alloy sheets are rolled under the condition of the roll speed ratio of 1.1:1~3:1. The Mg alloy sheets are repetitively cooling-rolled at the roll temperature of 80°C~150°C with the shrinkage ratio of 1~10%.

Description

Method for manufacturing fine grained magnesium alloy rolled sheet using static recrystallization {Method of manufacturing fine-grained Mg alloy sheets by static recrystallization}

The present invention relates to a method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method, and more particularly, to a method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method to improve mechanical molding properties of a magnesium alloy sheet. It is about.

In general, magnesium alloy is a compact hexagonal lattice (HCP) structure, the slip system required for plastic processing is limited, so it is very difficult to mold and manufacture the product at room temperature, so the molded product must be manufactured through hot working.

Accordingly, improvement of formability is absolutely necessary for the development of intermediate materials and products of magnesium alloys. For example, the formability for magnesium alloys is the most effective method to improve the elongation by making the grain size of the magnesium alloy fine to improve the elongation, or to operate the limited slip system of the compact hexagonal grid structure.

However, when the demand for magnesium plate is gradually increased, it is not efficient to manufacture magnesium alloy plate having good room temperature formability by providing the microstructure required in commercially available magnesium alloy or increasing the possibility of operation of non-base slip type. It is true.

In addition, in the case of a plate manufacturing method of the conventional magnesium alloy, it is necessary to increase the reduction ratio during rolling in order to refine the grains. In the conventional manufacturing process, the grain size is limited because of the severe reduction in the thickness, and thus the grain size is limited and repeated. Since the grains were refined by hot re-rolling and the dynamic recrystallization, the bottom surface texture was largely developed, and the anisotropy of the sheet was increased and the formability was deteriorated.

That is, the conventional magnesium alloy sheet manufacturing method has a limitation in miniaturizing the grains by dynamic recrystallization during hot working, and has a problem in that the anisotropy of the sheet due to the development of the aggregate structure, which is unfavorable to the molding, increases, resulting in deterioration of the formability. .

The present invention has been made to solve the conventional problems as described above, an object of the present invention is to provide a processing method in which static recrystallization can occur very efficiently in the production of magnesium alloy sheet material of the magnesium alloy sheet having fine grains The fine grains formed by the static recrystallization by fabrication and heat treatment after rolling have less basal texture than the grains formed by the dynamic recrystallization, and the temperature at which the magnesium alloy sheet is formed as the grains become uniform / fine. Elongation is greatly increased in the range, uniform / high-speed deformation is also increased to provide a magnesium alloy sheet manufacturing method that can improve the moldability of the magnesium alloy sheet.

In order to achieve the above object, the method for producing a fine-grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention comprises the step of making a sheet by rolling the magnesium alloy cast material below the recrystallization temperature and the plate produced in the rolling step Heat treatment to form fine grains by static recrystallization.

In addition, the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention further includes a pretreatment step of homogenizing and solidifying the magnesium alloy cast material before the rolling step.

In addition, in the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, the pretreatment step is characterized in that for 9 to 15 hours at a temperature of 200 ℃ ~ 350 ℃.

In addition, in the method for producing a fine-grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, the rolling step is characterized in that the repeated repeated hot rolling with a thickness shrinkage of 10 to 25% in the temperature range of 150 ℃ to 250 ℃. It is done.

In addition, in the method for producing a fine-grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, the rolling step is a constant velocity rolling process, or a constant-speed rolling process with a vertical roll speed ratio of 1.1: 1 to 3: 1 after constant velocity rolling. It is characterized by that.

In addition, in the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, the rolling step is 1 to 10 in the temperature range of the roll temperature 80 ℃ ~ 150 ℃ without heating the magnesium alloy casting material It is characterized in that repeated cold rolling at a thickness shrinkage of%.

In addition, in the method for producing a fine-grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, the heat treatment step is characterized in that the heat treatment for 5 to 10 minutes at a temperature range of 220 ~ 270 ℃ plate subjected to the rolling step It is done.

In addition, in the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, the heat treatment step is a static recrystallization temperature in a temperature range plus 50 ℃ to 80% recrystallization of the magnesium alloy rolled product recovery It is characterized by setting and heat treatment.

In addition, in the method for producing a fine-grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, in the rolling step, the crystal grains produced by dynamic recrystallization due to the temperature rise of the magnesium alloy is 30% or less of the total, and The remaining crystal grains are formed by the static recrystallization by the heat treatment after the rolling step.

According to the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention having the above configuration, the fine grains may be formed by the static recrystallization of the magnesium alloy sheet through a rolling-heat treatment process.

In addition, the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method of the present invention has a fine crystal structure, and thus exhibits mechanical properties having high strength and high toughness in the room temperature region where the alloy is actually used. It is possible to provide a magnesium alloy sheet having excellent elongation at the forming temperature to improve moldability.

In addition, according to the method of manufacturing a fine grained magnesium alloy rolled sheet using the static recrystallization method of the present invention, it is possible to produce a sheet of magnesium alloy through two-speed and constant velocity rolling, and the magnesium sheet thus manufactured has fine grains by static recrystallization. The fine grains formed by heat treatment after rolling are relatively less aggregated than the grains formed by dynamic recrystallization, and as the grains become uniform / fine, the elongation at the temperature range at which the magnesium alloy sheet is formed increases. In addition, the moldability is very excellent because the uniform / fast deformation ability is also increased.

Therefore, the method for producing a fine grained magnesium alloy rolled sheet material using the static recrystallization method of the present invention enables the weight reduction of road, aviation, and rail transportation means, and is used as exterior materials for electronic / communication products such as mobile communication, notebook computers, and cameras. It is possible to provide a magnesium alloy sheet material that can be widely applied.

Hereinafter, with reference to the accompanying drawings a preferred embodiment of a method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method according to the present invention. The terms to be described below are terms defined in consideration of functions in the present invention, which may vary depending on the intention or convention of a user or an operator. Therefore, definitions of these terms should be made based on the contents throughout the specification.

In addition, the following examples are not intended to limit the scope of the invention, but merely illustrative of the components set forth in the claims of the present invention, which are included in the technical spirit throughout the specification of the present invention and components of the claims Embodiments including a substitutable component as an equivalent in may be included in the scope of the present invention.

As shown in Figure 1, the method for producing a fine-grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention comprises the step (10) of manufacturing a magnesium alloy sheet by rolling a magnesium alloy cast material and the rolled product after the rolling ( Heat treatment of the plate) to form fine grains by static recrystallization (20).

Here, the rolling step 10 is to repeatedly roll to a thickness of 0.3 ~ 1.5 mm at a thickness shrinkage rate at which recrystallization does not occur at a temperature below which recrystallization occurs in the magnesium alloy casting during rolling. The heat treatment step 20 is to heat-treat the rolled material (plate) for a predetermined time at a temperature at which static recrystallization occurs.

The step (10) of rolling the plate to adjust the rolling processing conditions such that the production of crystal grains is 30% or less of the total by dynamic recrystallization due to the temperature rise of the magnesium alloy. In addition, the rolling step 10 includes a cold-warm constant rolling process, and may include a two-speed rolling process having a vertical roll speed ratio of 1.1: 1 to 3: 1.

After the rolling step 10, the step 20 of forming the remaining crystal grains by static recrystallization by heat treatment is performed. The temperature of the recrystallization of the magnesium alloy rolled product is 80%, and the temperature is 50 ° C. plus the static recrystallization temperature. The magnesium plate having fine grains having a size of 3 to 4 μm is prepared by static recrystallization by heat treatment.

Conventional magnesium alloy was not able to secure the workability at room temperature, but according to the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method of the present invention, the magnesium alloy sheet can be processed in a variety of ways in the temperature range that is formed Therefore, in the present invention, the room temperature and warm processing are performed in order to obtain a healthy processed material, and the processing temperature of the cast material is set to a range capable of securing the integrity of the processed material through experiments.

In the following examples, the elongation, yield, and tensile strength of each plate manufactured by the present invention are measured and measured by a room temperature tensile test. Among them, a representative plate is selected to confirm the grain size of the magnesium alloy plate through an optical microscope, The process of setting the heat treatment temperature by analyzing the rolled material (plate material) through a differential scanning calorimeter to solve the residual stress and to measure the temperature at which recrystallization can occur is described.

Hereinafter, an embodiment of a method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method according to the present invention will be described with reference to FIGS. 2 to 11.

Table 1 below is a table measuring the yield strength, tensile strength, room temperature elongation of the alloy composition of various embodiments to be described later made into a plate through the process of casting, cold and warm constant speed and double speed, hot constant speed and double speed.

In the present embodiments, molten metals of the ZE41, ZE20, and ZE31 alloys and the AZ31 alloy, which is a commercial magnesium alloy, are prepared and a casting material is obtained by a casting method. ZE41 and AZ31 alloys are made by heating a carbon crucible at 700 ° C in an electric induction furnace to melt magnesium, and then adding other additives to form an alloy molten metal and injecting the molten alloy into a casting mold cooled with cooling water. to be. In addition, the ZE20 and ZE31 alloys are cast materials manufactured using a twin roll strip casting method.

At this time, according to the embodiment to be described later the cold cast warm plate made of constant-speed and double-speed rolling, and heat treatment to form fine grains through static recrystallization and the tensile test results are shown in Table 1 .

Example 1

Example 1 processes the casting material of the ZE41 alloy shown in Table 1 by warm constant velocity rolling. The processing method is to reduce the thickness of the cast material by 20% at the material temperature of 200 ℃, and to manufacture magnesium plate by repeatedly isotropically rolling until the thickness of the cast material is 0.6mm, and fine grains are formed through static recrystallization after rolling. Heat treatment at 250 ° C. for 5 minutes to form.

FIG. 2 is an optical micrograph of a plate made of a ZE41 alloy through a constant isothermal rolling process, showing that the crystal grains are not properly generated because dynamic recrystallization does not occur.

3 is an optical micrograph of a plate prepared by heat treatment of the ZE41 alloy after a constant isothermal rolling and shows that fine grains of 3 to 4 μm were formed in α-Mg structure by static recrystallization.

FIG. 4 is an optical micrograph of a plate made of a commercial magnesium alloy AZ31 alloy in the same manner as in Example 1 through a constant constant rolling process and a heat treatment process, 3 to 4 in the α-Mg structure by the static recrystallization during the heat treatment process It is shown that fine grains were formed in μm.

FIG. 5 is an optical photomicrograph for comparison with FIG. 4, wherein a plate made of a ZE41 alloy through general hot rolling at 400 ° C. and a thickness shrinkage of 30% has a grain size of 10 to 15 μm through dynamic recrystallization. Show what is formed.

Example 2

In Example 2, the casting material of the ZE41 alloy shown in Table 1 is subjected to a solid solution treatment at 350 ° C. for 15 hours and then processed by warm constant speed and double speed rolling. The processing condition is a method of reducing the thickness by 20% at a material temperature of 200 ° C. by using a cast material. Accordingly, the sheet is repeatedly subjected to constant isotropic rolling until the thickness reaches 1.0 mm, and is repeatedly repeated to 0.5 mm. 1) to prepare a magnesium plate, and then heat-treated at 250 ℃ for 5 minutes to form fine grains through static recrystallization after rolling.

Example 3

Example 3 processed the casting material of the ZE31 alloy shown in Table 1 by cold constant speed rolling. The processing condition is to reduce the thickness by 10% at a roll temperature of 120 ℃ without heating the material using a cast material. Heat treatment at 220 ℃ for 10 minutes to form a fine grain through.

FIG. 6 is an optical photomicrograph of a plate fabricated from a ZE31 alloy through a cold isotropic rolling process and a heat treatment process, showing that micronized grains having a size of 3 to 4 μm were formed in α-Mg structure by static recrystallization during heat treatment.

FIG. 7 is an optical micrograph of a plate made of AZ31 alloy, which is a commercial magnesium alloy, by cold isothermal rolling and heat treatment, wherein fine grains of 3 to 4 μm are formed in α-Mg structure by static recrystallization during heat treatment. Shows.

Example 4

In Example 4, the casting material of the ZE31 alloy shown in Table 1 is subjected to homogenization and solid solution treatment at 200 ° C. for 9 hours, followed by cold constant speed and double speed rolling. The processing condition is to reduce the thickness by 10% at the roll temperature of 120 ℃ without heating the material by using the cast material. Repeated constant rolling until the thickness reaches 1.5 mm and repeated double rolling up to 0.8 mm (up and down roll speed ratio) 2: 1) to prepare a magnesium sheet and heat-treated at 220 ° C. for 10 minutes to form fine grains through static recrystallization after rolling.

Example 5

In Example 5, after casting the ZE41 alloy shown in Table 1, the casting material was repeatedly warmed to a thickness of 0.3 to 1.5 mm at a shrinkage rate of 10 to 25% at 100 to 250 ° C. through the same process as in Examples 1 to 2. It is made of ZE41 alloy plate material by constant speed and double speed rolling (up-down roll speed ratio 1.1: 1 to 3: 1).

The prepared ZE41 alloy sheet was heat-treated at 250 ° C. for 5 minutes, and the elongation obtained through a tensile test at strain ¹ × 10 ⁻³ s ⁻¹ at room temperature was measured, and the results are shown in Table 1. 8 is a graph showing the room temperature tensile test data of the ZE41 alloy.

Example 6

Example 6 casts the ZE20 and ZE31 alloys shown in Table 1, and then casts the cast material through the same process as in Examples 3 to 4 with a shrinkage of 1 to 10% at a roll temperature of 80 to 150 ° C at a thickness of 0.3 to 1.5. It is made of ZE20, ZE31 alloy plate material by repeated cold constant speed and double speed rolling (up to down speed ratio 1.1: 1 to 3: 1) to mm. Subsequently, the plate was heat-treated at 250 ° C. for 5 minutes, and the elongation obtained through a tensile test at strain ¹ × 10 ⁻³ s ⁻¹ at room temperature was measured, and the results are shown in Table 1.

As described above, the magnesium alloy sheet prepared as shown in Examples 5 and 6 showed a reliable strength of 140 MPa or more and a high elongation of 23% to 33% in all compositions subjected to the tensile test.

On the other hand, Figure 9 is a graph showing the room temperature tensile test data of the ZE20, ZE31 alloy, Figure 10 is a strain 1x10 ^-3 s ^-1 , at 150 ℃ of the ZE20 alloy 1x10 ^-2 s ^-1, 1x10 ^-1 s as a tensile test graph showing the tensile test data to ^-1, as shown, there is a significant change in elongation in rapid deformation and slow strain 150 ℃, 1x10 ^-1 s ^- Since a high elongation of 65% or more is shown at a high strain rate of ^1, the plate produced by the method for producing a fine grained magnesium alloy rolled plate using the static recrystallization method according to the present invention is formed at a high strain rate at a molding temperature of 150 ° C. during press forming. This becomes possible.

11 is a graph illustrating an analysis method for setting a temperature at which the static recrystallization occurs in the heat treatment step of the above-described embodiment. The temperature of recrystallization in the heat treatment step after rolling the cast material is analyzed through a differential scanning calorimeter. It is a graph. Referring to FIG. 11, it can be seen that the casting material starts to recover from about 130 ° C. and all residual stresses are resolved at about 235 ° C. FIG. Therefore, the heat treatment temperature for forming the crystal grains through the static recrystallization may be set to 220 ~ 270 ° C plus 50 ° C to 220 ° C, which is the point of recovery of 80% or more.

In the case of the AZ31 alloy, the recrystallization temperature was set by the same method through the differential scanning calorimeter, and other magnesium alloys can be set the static recrystallization temperature during the heat treatment using the same method.

Therefore, the magnesium alloy sheet produced by the method for producing a fine grained magnesium alloy rolled sheet using the static recrystallization method according to the present invention, compared with the conventional magnesium alloy for forming a sheet, the processing of the static recrystallization can occur very efficiently during sheet manufacturing Due to the method, it has very fine grains, and the fine grains formed by heat treatment after rolling have relatively less aggregate structure than the grains formed by dynamic recrystallization, and the temperature at which magnesium alloy sheet is formed as the grains become uniform / fine. Since the elongation in the range is greatly increased and the uniformity / high speed deformation ability is also increased, the formability of the sheet can be improved, and the formability of the manufactured magnesium sheet can be greatly increased.

1 is a flow chart of a method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method according to the present invention.

Figure 2 is a plate prepared by the rolling process of the ZE41 alloy according to Example 1 of the present invention, an optical microscope tissue photograph showing that no crystal grains before heat treatment.

FIG. 3 is an optical micrograph of α-Mg structure in which a ZE41 alloy according to Example 1 of the present invention is manufactured by a warm rolling process, in which fine grains are formed at 3 to 4 μm by static recrystallization after heat treatment.

FIG. 4 is an optical micrograph of α-Mg structure in which AZ31 alloy according to Example 1 of the present invention is manufactured by a warm rolling process, in which fine grains are formed at 3 to 4 μm by static recrystallization after heat treatment.

FIG. 5 is a photomicrograph of a ZE41 alloy produced by a general hot rolling process, wherein the grain size of α-Mg structure is 10 to 15 μm formed by dynamic recrystallization.

FIG. 6 is an optical micrograph of α-Mg structure in which a ZE31 alloy according to Example 3 is manufactured by a cold constant velocity rolling process, in which fine grains are formed at 3 to 4 μm by static recrystallization after heat treatment.

FIG. 7 is an optical micrograph of α-Mg structure in which AZ31 alloy according to Example 3 of the present invention is manufactured by a warm rolling process, in which fine grains are formed at 3 to 4 μm by static recrystallization after heat treatment.

8 is a graph showing room temperature tensile test data (Data) of the ZE41 alloy according to Example 5 of the present invention.

9 is a graph showing room temperature tensile test data (Data) of ZE20 and ZE31 alloys according to Example 6 of the present invention.

10 is a graph showing 150 ° C tensile test data (Data) of the ZE20 alloy according to Example 6 of the present invention.

11 is a graph illustrating an analysis method for setting a temperature at which recrystallization occurs in a heat treatment step after rolling a magnesium alloy according to the present invention.

Claims (10)

Rolling the magnesium alloy casting material at a temperature below the recrystallization temperature to form a sheet (10); And Heat-treating the plate material produced in the rolling step 10 to form fine grains by static recrystallization (20). The method of claim 1, The method of manufacturing a fine grained magnesium alloy rolled sheet using the static recrystallization method, characterized in that it further comprises a pre-treatment step of homogenizing and solidifying the magnesium alloy casting material before the rolling step. The method of claim 2, wherein the pretreatment is a step of treating the magnesium alloy cast material at a temperature of 200 ° C. to 350 ° C. for 9 to 15 hours. The method according to claim 1 or 2, The rolling step (10) is a method for producing a fine-grained magnesium alloy rolled sheet using a static recrystallization method, characterized in that the repeated repeated hot rolling at a thickness shrinkage of 10 to 25% in the temperature range of 150 ℃ ~ 250 ℃. The method of claim 4, wherein The rolling step (10) is a method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method, characterized in that the constant rolling process, or a continuous rolling process of the up and down roll speed ratio of 1.1: 1 to 3: 1 after constant velocity rolling. The method according to claim 1 or 2, The rolling step 10 is a fine grain using a static recrystallization method characterized in that the cold rolling is repeated at a thickness shrinkage of 1 to 10% in the temperature range of the roll temperature 80 ℃ ~ 150 ℃ without heating the magnesium alloy casting material Method of manufacturing magnesium alloy rolled sheet. The method of claim 6, The rolling step (10) is a method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method, characterized in that the constant rolling process, or a continuous rolling process of the up and down roll speed ratio of 1.1: 1 to 3: 1 after constant velocity rolling. The method according to claim 1 or 2, The heat treatment step 20 is a method for producing a fine-grained magnesium alloy rolled plate using a static recrystallization method, characterized in that for 5 to 10 minutes heat treatment in the temperature range of 220 ~ 270 ℃ the plate passed through the rolling step (10). The method of claim 1, The heat treatment step 20 of the fine-grained magnesium alloy rolled sheet using the static recrystallization method characterized in that the static recrystallization temperature is set to a temperature range plus 50 ℃ to a temperature where the recrystallization of the magnesium alloy rolled product is recovered 80% Manufacturing method. The method of claim 1, In the rolling step 10, the crystal grains produced by the dynamic recrystallization due to the temperature rise of the magnesium alloy is 30% or less of the total, and the remaining crystal grains are formed by the static recrystallization by the heat treatment after the rolling step 10. A method for producing a fine grained magnesium alloy rolled sheet using a static recrystallization method.

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