KR101610360B1 - Magnesium alloy sheet, method for manufacturing the same - Google Patents

Abstract

The present invention relates to a magnesium alloy plate, and to a manufacturing method thereof. More specifically, provided is the magnesium alloy plate, comprising 2 to 4 wt% of Al; 0.5 to 1.5 wt% of Zn; and the remaining consisting of Mg and unavoidable impurities. The magnesium alloy plate comprises a twin spot inside a microtissue, wherein a surface fraction of the twin spot with respect to the entire surface (100%) of the microtissue is greater than or equal to 10%. In addition, provided is the method for manufacturing a magnesium alloy plate, by controlling a rolling step.

Description

TECHNICAL FIELD [0001] The present invention relates to a magnesium alloy sheet, and a method of manufacturing the same. BACKGROUND ART [0002]

A magnesium alloy plate, and a method of manufacturing the same.

At present, the limitation of carbon dioxide emission in the international society and the importance of renewable energy are becoming a hot topic, and lightweight alloys, which are a structural material, are recognized as a very attractive research field.

Particularly, magnesium has a density of 1.74 g / cm 3, which is the lightest metal, compared with other structural materials such as aluminum and steel, and has various advantages such as vibration absorption ability and electromagnetic shielding ability. Research is actively being carried out.

Such magnesium-containing alloys are currently being applied not only in the field of electronic devices but also in automobile fields, but they have a fundamental problem in corrosion resistance, flame retardancy, and moldability, and thus there is a limit to further expand the application range thereof.

Especially with regard to moldability, magnesium has a HCP structure (Hexagonal Closed Packed Structure). That is, a large amount of heat is required in the magnesium processing step, leading to an increase in the process cost.

On the other hand, among the magnesium alloys, the AZ-based alloys include aluminum (Al) and zinc (Zn), which are inexpensive and yet commercially available magnesium alloys, while securing adequate strength and ductility.

However, the above-mentioned physical properties mean an appropriate level of magnesium alloy, and the strength is lower than that of aluminum (Al) which is a competitive material.

Therefore, it is necessary to improve the physical properties such as low moldability and strength of the AZ-based magnesium alloy, but the research on this is still insufficient.

Accordingly, the present inventor intends to provide a magnesium alloy plate having improved strength and formability as compared with a conventionally commercialized AZ-based magnesium alloy, and a method of manufacturing the same.

Specifically, in one embodiment of the present invention, it is possible to provide a magnesium alloy plate having an area fraction of twinning in the microstructure of 10% or more.

In another embodiment of the present invention, it is possible to provide a method of manufacturing such a magnesium alloy plate by controlling the rolling step.

In one embodiment of the present invention, it comprises twinning in the microstructure, comprising 2 to 4 wt% of Al and 0.5 to 1.5 wt% of Zn, the balance consisting of Mg and unavoidable impurities, Wherein the area fraction of the twin with respect to the area (100%) is 10% or more.

Specifically, the microstructure of the magnesium alloy sheet will be described in detail as follows.

The area fraction of the twin with respect to the total area (100%) of the microstructure may be 20% or more.

In addition, the microstructure of the magnesium alloy sheet may include crystal grains refined by the twin crystal.

At this time, the grain size of the crystal grains may be 1 to 5 mu m.

The yield strength, the limit dome height, and the elongation of the magnesium alloy sheet will be described in detail as follows.

The yield strength of the magnesium alloy sheet may be 230 MPa or more.

In addition, the limiting dome height of the magnesium alloy sheet may be 4 mm or more.

On the other hand, the elongation percentage of the magnesium alloy sheet may be 12 to 15%.

In another embodiment of the present invention, there is provided a method for producing a magnesium alloy casting, comprising: casting a molten metal containing 2 to 4 wt% of Al and 0.5 to 1.5 wt% of Zn and the balance of Mg and unavoidable impurities to obtain a magnesium cast plate; A solution annealing process of the casting plate; Rolling the solution-treated casting plate; Heat treating the rolled casting plate to obtain a magnesium alloy sheet, wherein the obtained magnesium alloy sheet comprises twinned in a microstructure, and wherein the twinned steel sheet has a total area (100%) of the microstructure, Wherein the area fraction of the magnesium alloy sheet is 10% or more.

Specifically, the step of rolling the solution-treated casting plate is explained as follows.

The rolling may be performed at a temperature of 150 to 400 캜.

The alloy sheet material may be quenched simultaneously with the rolling.

The temperature of the casting plate quenched at the same time as the rolling may be 30 to 200 캜.

The step of rolling the solution-treated casting plate may be carried out at least once.

Further, a detailed explanation of the obtained magnesium alloy plate is as follows.

The area fraction of the twin crystal relative to the total area (100%) of the microstructure of the obtained magnesium alloy sheet may be 20% or more.

The microstructure of the obtained magnesium alloy sheet may include crystal grains refined by the twin crystal.

At this time, the grain size of the crystal grains may be 1 to 5 mu m.

On the other hand, the yield strength of the obtained magnesium alloy sheet may be 230 MPa or more.

In addition, the limiting dome height of the obtained magnesium alloy sheet may be 4 mm or more.

In addition, the elongation of the magnesium alloy sheet obtained may be 12 to 15% or more.

The steps of the method for manufacturing the magnesium alloy plate will be described below.

Further, the step of heat-treating the rolled casting plate to obtain a magnesium alloy sheet may be performed at a temperature of 150 to 400 ° C.

The solution annealing process of the casting plate may include heating the casting plate to 150 to 400 ° C, Quenching the heated casting plate to 25 to 150 캜; And maintaining the quenched casting plate at room temperature.

According to an embodiment of the present invention, the area fraction of the twins in the microstructure is increased as compared with the conventional AZ-based magnesium alloy plate, thereby providing a magnesium alloy plate having improved strength and moldability.

According to another embodiment of the present invention, a method of manufacturing a magnesium alloy sheet as described above can be provided by maximizing the formation of twinning by controlling the rolling step.

1 is a photograph showing microstructure of a magnesium alloy sheet according to an embodiment of the present invention.
2 is a photograph showing microstructure of a magnesium alloy sheet according to a comparative example of the present invention.
3 is a table comparing the mechanical properties of each magnesium alloy sheet according to one embodiment of the present invention and one comparative example.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

In one embodiment of the present invention, it comprises twinning in the microstructure, comprising 2 to 4 wt% of Al and 0.5 to 1.5 wt% of Zn, the balance consisting of Mg and unavoidable impurities, Wherein the area fraction of the twin with respect to the area (100%) is 10% or more.

Specifically, it may be 2.5 to 3.5% by weight of Al and 0.7 to 1.3% by weight of Zn.

This is a so-called AZ-based magnesium alloy plate containing Al and Zn. Due to the high area fraction of twinning in the microstructure as compared with a generally known AZ-based magnesium alloy plate (less than about 10% twinning fraction) ) Strength, and 2) a moldability improved magnesium alloy plate.

1) In general, twinning means that two homogeneous crystals are symmetrical in one plane or two straight lines in a symmetry axis, and have a boundary.

Since the boundary of the twin crystal has energy such as a grain boundary, the boundary of the twin crystal can act as a grain boundary, and the twin crystal can interfere with the movement of the dislocation.

In this regard, the magnesium alloy plate provided in one embodiment of the present invention includes a twin of a high area fraction in the microstructure as compared with a generally known AZ-based magnesium alloy plate, so that the movement of the dislocation is disturbed by the twin The effect of this is more pronounced, which can lead to improved yield strength characteristics.

2) On the other hand, the known AZ-based magnesium alloy plate has a basal plane texture and the C-axis is perpendicular to the rolling direction in HCP (Hexagonal Close Packed) structure.

On the other hand, in the case of the magnesium alloy plate provided in one embodiment of the present invention, the C axis of the HCP structure is rotated about 86 degrees about <11-20> by the twinning occupying a high area fraction in the microstructure As a result, the basal plane texture is weakened and transformed into the non-basal plane texture, which can result in improved formability.

Hereinafter, the magnesium alloy plate provided in one embodiment of the present invention will be described in detail, and its strength and formability will be more specifically described in the examples.

First, the microstructure of the magnesium alloy sheet will be described in detail.

As described above, the area fraction of the twin with respect to the total area (100%) of the microstructure may be 10% or more, and more specifically, 20% or more.

This corresponds to a higher twinning fraction than that of a generally known AZ-based magnesium alloy plate. In this case, the above-mentioned effect is maximized, and the strength and moldability of the magnesium alloy plate can be greatly improved.

In addition, the microstructure of the magnesium alloy sheet may include crystal grains refined by the twin crystal.

When the twin crystal exists in the crystal grains constituting the microstructure of the magnesium alloy plate, the crystal grains can be differentiated by the boundary of the twin crystal serving as a crystal grain boundary. Particularly, the crystal grains can be further finely divided by twinning occupying an area fraction of 10% or more (specifically, 20% or more) in the microstructure.

At this time, the grain size of the crystal grains may be 1 to 5 mu m.

In this connection, generally known AZ-based magnesium alloy plates include crystal grains having an average size of more than 5 mu m and not more than 20 mu m in the form of a rolled material or an extruded material and have an average size of 20 mu m or more in the form of a die casting material .

Specifically, since the generally known AZ-based magnesium alloy sheet contains less than 10% of twin crystal, such a small amount of twin crystal can not produce finer crystal grains of less than 5 탆.

On the other hand, when a twin crystal having a high area fraction in the crystal grains constituting the microstructure of the magnesium alloy sheet is included, the grain size of the crystal grains can be miniaturized as described above.

In addition, the twin crystal may be uniformly distributed in the microstructure of the magnesium alloy plate.

The yield strength, the critical dome height, and the elongation of the magnesium alloy sheet will be described in detail as follows, and can be more specifically supported by Examples and Test Examples described later.

First, the yield strength of the magnesium alloy sheet may be 230 MPa or more, specifically 230 to 250 MPa.

Generally, the yield strength refers to the stress at which the material starts to undergo macroscopic plastic deformation, which means that plastic deformation of the material becomes difficult as the yield strength increases.

The above limited range corresponds to an increased yield strength as compared with a generally known AZ-based magnesium alloy plate due to an increase in the area fraction of the twin in the microstructure, and the causal relationship is as described above. However, the value less than 230 MPa corresponds to the yield strength of a generally known AZ-based magnesium alloy plate, and thus the range is limited.

In addition, the limiting dome height of the magnesium alloy sheet may be 4 mm or more, specifically, 4.5 to 5 mm.

In general, the limit dome height (LDH) is used as an index for evaluating the formability (in particular, compressibility) of a material, which means that the moldability of the material is improved as the height of the limit dome increases.

The above limited range corresponds to an increased limit dome height relative to a generally known AZ-based magnesium alloy plate due to the increased area fraction of the twin in the microstructure.

Specifically, the magnesium alloy plate has higher moldability because the non-hypothetical texture is formed due to the causal relationship described above, and accordingly, the magnesium alloy plate can have an increased critical dome height as described above.

Meanwhile, the elongation of the magnesium alloy sheet may be 12 to 15%.

Generally, the elongation is a value obtained by dividing a specimen after rupture in a tensile test and calculating the amount of deformation between the points. The elongation means that the ductility decreases as the elongation decreases.

In the above-mentioned limited range, due to an increase in the area fraction of the twin in the microstructure, the crystallinity of the microstructure of the magnesium alloy sheet becomes finer and the ductility is lowered. As a result, the AZ- Lt; RTI ID = 0.0 &gt; elongation.

In another embodiment of the present invention, there is provided a method for producing a magnesium alloy casting, comprising: casting a molten metal containing 2 to 4 wt% of Al and 0.5 to 1.5 wt% of Zn and the balance of Mg and unavoidable impurities to obtain a magnesium cast plate; A solution annealing process of the casting plate; Rolling the solution-treated casting plate; Heat treating the rolled casting plate to obtain a magnesium alloy sheet, wherein the obtained magnesium alloy sheet comprises twinned in a microstructure, and wherein the twinned steel sheet has a total area (100%) of the microstructure, Wherein the area fraction of the magnesium alloy sheet is 10% or more.

This corresponds to a method of manufacturing a magnesium alloy plate having the above-mentioned characteristics by maximizing the formation of twins by controlling the rolling step.

More specifically, the step of rolling the solution-treated casting plate is explained as follows.

The rolling may be performed at a temperature of 150 to 400 캜.

If the alloy is rolled at a high temperature exceeding 400 ° C, the crystal grains may be grown to lower the strength of the finally obtained magnesium alloy plate. When the temperature is lower than 150 ° C, the solution- There is a problem that a crack or breakage phenomenon occurs, and the rolling temperature is limited as described above.

That is, by limiting the rolling temperature in this way, twinning of an improved area fraction can be formed as described above.

Further, the casting plate may be quenched simultaneously with the rolling.

For example, when the casting plate subjected to the solution treatment is rolled using twin roll, the rolling temperature is set to 300 ° C, and the speed through the roll bite is controlled to 100 mpm, May be quenched and its temperature may be 30 to 200 占 폚, specifically 50 to 150 占 폚.

Concretely, the temperature of the casting plate quenched at the same time as the rolling depends on the thickness of the casting plate, and the thinner the thickness, the closer it can be to 50 캜.

Further, the step of rolling the solution casting casting plate until the final thickness of the magnesium alloy plate (for example, 0.1 to 5 mm) is reached, is repeatedly carried out, Can be repeated.

That is, the step of rolling the solution-treated casting plate may be performed at least once.

This is supported by the following embodiments.

The magnesium alloy plate thus obtained is described as follows, and a detailed description thereof will be omitted since it is as described above.

The area fraction of the twin crystal relative to the total area (100%) of the microstructure of the obtained magnesium alloy sheet may be 20% or more.

The microstructure of the obtained magnesium alloy sheet may include crystal grains refined by the twin crystal.

At this time, the grain size of the crystal grains may be 1 to 5 mu m.

On the other hand, the yield strength of the obtained magnesium alloy sheet may be 230 MPa or more, specifically 230 to 250 MPa.

The limiting dome height of the obtained magnesium alloy sheet may be 4 mm or more, specifically 4.5 to 5 占 퐉.

In addition, the elongation of the magnesium alloy sheet obtained may be 12 to 15% or more.

The steps of the method for manufacturing the magnesium alloy plate will be described below.

First, the step of rolling the solution-treated casting plate may be carried out at a temperature of 150 to 400 ° C.

Further, the step of heat-treating the rolled casting plate to obtain a magnesium alloy sheet may be performed at a temperature of 150 to 400 ° C.

If the heat treatment is performed at a high temperature exceeding 400 ° C, the surface of the rolled casting plate may be locally melted and the crystal grains in the microstructure may grow excessively. On the other hand, at a temperature lower than 150 ° C, the stress caused by the rolling may be released. In consideration of this, the heat treatment temperature is limited as described above.

The solution annealing process of the casting plate may include heating the casting plate to 150 to 400 ° C, Quenching the heated casting plate to 50 to 150 캜; And a step of maintaining the normally quenched casting plate at a normal temperature.

The description thereof is omitted since it is generally known.

Hereinafter, preferred examples and test examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples.

Example : In microstructure Twinning  area Fraction Increased AZ31 Manufacture of Magnesium Alloy Sheet

A magnesium cast plate was obtained by casting a molten metal consisting of Al: 3 wt%, Zn: 1 wt% Mg, Mg: 0.3 wt%, and the balance of Mg and unavoidable impurities in a conventional roll casting system.

Thereafter, the casting plate was solution annealed. Specifically, the casting plate was heated at 420 DEG C for 24 hours, quenched at 150 DEG C for 30 minutes, and kept at room temperature.

The solution casting plate was rolled at 300 캜 using a twin-roll rolling machine. At this time, the speed at which the casting plate passed through the roll bite was set to 100 mpm, and the temperature of the casting plate passed through the roll bite and simultaneously coincided with the rolling was dependent on the thickness of the casting plate rolled.

Specifically, when the casting plate is rolled to a thickness of 4 to 5 mm, the temperature of the casting plate is rapidly reduced to about 150 ° C. When the casting plate is rolled to a thickness of 3 to 4 mm, , It was confirmed that it was rapidly cooled to about 100 ° C when it was rolled to a thickness of 1.5 to 2 mm and to about 50 ° C when it was rolled to a thickness of 1.0 to 1.5 mm.

That is, immediately quenching is performed simultaneously with the rolling of the casting plate, and the temperature can be further lowered as the thickness of the rolled casting plate becomes thinner.

Thereafter, the rolled casting plate was heat-treated at 400 ° C. for 10 hours, and thus a magnesium alloy sheet according to an embodiment of the present invention was obtained.

In summary, the temperature of the plate was raised to 400 ° C., and the temperature was controlled to 300 ° C. when the mixture was fed into a twin-roll rolling machine. The temperature of the quenched casting plate after rolling was 150 ° C. or lower , And it was confirmed that the thinner the rolled thickness of the casting plate was, the lower it was. Thereafter, the steel sheet was reheated to 400 DEG C until the final target thickness reached 1.0 mm, and the rolling and quenching process was repeated.

Comparative Example : Conventional commercialized AZ31 Manufacture of Magnesium Alloy Sheet

In the above examples, the rolling process of the solution casting plate at 250 DEG C, the heat treatment and rolling were not repeated, and the rolling and the quenching were not simultaneously performed. An AZ31-based magnesium alloy plate could be obtained by the same process.

Test Example  1: Observation of microstructure of magnesium alloy plate

Scanning Electron Microscope (SEM) photographs were taken to observe the microstructure of each magnesium alloy sheet prepared in the above Examples and Comparative Examples.

Fig. 1 shows the result of the above embodiment, Fig. 2 shows the result of the comparative example, The area of the microstructure of the magnesium alloy plate shown in each SEM photograph was calculated and then the area occupied by the twin in each of the SEM photographs was calculated to calculate the area fraction of the twin in the microstructure.

According to Fig. 1, it was confirmed that the area fraction of twinning in the microstructure of the Example was not less than 20% by volume. On the other hand, according to Fig. 2, it was confirmed that the area fraction of the twins in the microstructure of the comparative example was as low as 5% or less.

On the other hand, when comparing FIGS. 1 and 2, grain sizes of crystal grains constituting each microstructure of Examples and Comparative Examples are observed to be similar. Nevertheless, it can be inferred that the area fraction of twinning in the microstructure of the embodiment was greatly increased compared with the comparative example because the rolling process was controlled by the process of cooling simultaneously with rolling.

Test Example  2: Evaluation of Mechanical Properties of Magnesium Alloy Plate

The yield strength, tensile strength, elongation, and limit dome height of the respective magnesium alloy sheets prepared in the above Examples and Comparative Examples were measured and recorded in FIG. 3, respectively.

Specifically, uniaxial tensile tests were conducted on each of the magnesium alloy sheets of the above Examples and Comparative Examples under a strain rate of 6.4X10 &lt; ^-4 &gt; / s at room temperature to measure the yield strength, tensile strength and elongation Could.

Independently of this, in the case of the limit dome height, each manufactured test piece was inserted between the upper die and the lower die, and the outer circumferential portion of each test piece was fixed with a force of 5 kN, and a known press oil was used as the lubricating oil. Then, a spherical punch having a diameter of 30 mm was used to deform at a speed of 5 to 10 mm / min. After the punch was inserted until each of the test pieces was broken, the deformation height .

Hereinafter, the evaluation results of the properties will be described in detail with reference to FIG. 3

Yield strength

The yield strengths of the examples were 230-250 MPa, while the yield strengths of the comparative examples were measured to be 200-210 MPa.

The reason why the yield strength of the example was increased by as much as 40 MPa as compared with the comparative example is that the area fraction of the twin in the microstructure of the above example is increased as compared with the comparative example .

The tensile strength

On the other hand, the tensile strengths of Examples and Comparative Examples were all measured to be 270 to 280 MPa.

Thus, it can be seen that even if the yield strength is increased as compared with the comparative example of the above embodiment, the characteristics of the tensile strength can still be secured.

Elongation

The elongation of the above example was measured to be 12 to 15%, while the elongation of the comparative example was measured to be 15 to 18%.

The reason why the elongation percentage of the example was decreased compared with the comparative example is as follows. As shown in the test example 1, the area fraction of the twin in the microstructure of the example is evaluated to be increased due to the increased characteristics as compared with the comparative example.

Limit dome height

The limit dome height of the example was 4.5 to 5 mm while the limit dome height of the comparative example was measured to be 2 to 3 mm.

As compared to the comparative example, the limit dome height of the embodiment can be increased by more than two times. Also, as shown in Test Example 1, the area fraction of the twin in the microstructure of the embodiment is increased .

Specifically, the comparative example has a basal plane texture, but the embodiment has higher moldability because the non-basal plane texture is formed by the causal relationship described above, and thus has a much higher critical dome height than the comparative example You can.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (20)

2 to 4 wt% of Al, and 0.5 to 1.5 wt% of Zn, the balance being Mg and unavoidable impurities.
Including twinning in microstructures,
Wherein the area fraction of the twin with respect to the total area (100%) of the microstructure is 20% or more.
Magnesium alloy plate.
delete The method according to claim 1,
The microstructure of the magnesium alloy plate may be,
And the crystal grains are micronized by the twin crystal.
Magnesium alloy plate.
The method of claim 3,
The grain size of the above-
1 to 5 [mu] m.
Magnesium alloy plate.
The method according to claim 1,
The yield strength of the magnesium alloy sheet,
230 MPa or more,
Magnesium alloy plate.
The method according to claim 1,
The limiting dome height of the magnesium alloy sheet may be,
4 mm or more,
Magnesium alloy plate.
The method according to claim 1,
The elongation percentage of the magnesium alloy sheet is,
12 to 15%.
Magnesium alloy plate.
Casting a molten metal containing 2 to 4 wt% of Al and 0.5 to 1.5 wt% of Al and the remainder of Mg and unavoidable impurities to obtain a magnesium cast plate;
A solution annealing process of the casting plate;
Rolling the solution-treated casting plate at a temperature of 150 to 350 캜; And
Heat treating the rolled casting plate to obtain a magnesium alloy plate,
Wherein the obtained magnesium alloy sheet comprises twinning in the microstructure, and the area fraction of the twin with respect to the total area (100%) of the microstructure is 20% or more.
A method for manufacturing a magnesium alloy plate.
delete 9. The method of claim 8,
Rolling the solution-treated casting plate;
And the casting plate is quenched at the same time as the rolling.
A method for manufacturing a magnesium alloy plate.
11. The method of claim 10,
The temperature of the casting plate quenched at the same time as the above-
RTI ID = 0.0 &gt; 200 C, &lt; / RTI &
A method for manufacturing a magnesium alloy plate.
11. The method of claim 10,
Rolling the solution-treated casting plate;
Lt; RTI ID = 0.0 &gt; at least &lt; / RTI &
A method for manufacturing a magnesium alloy plate.
delete 9. The method of claim 8,
The microstructure of the magnesium alloy sheet thus obtained,
And the crystal grains are micronized by the twin crystal.
A method for manufacturing a magnesium alloy plate.
15. The method of claim 14,
The grain size of the above-
1 to 5 [mu] m.
A method for manufacturing a magnesium alloy plate.
9. The method of claim 8,
The yield strength of the obtained magnesium alloy sheet is,
230 MPa or more,
A method for manufacturing a magnesium alloy plate.
9. The method of claim 8,
The limiting dome height of the magnesium alloy sheet obtained is,
4 mm or more,
A method for manufacturing a magnesium alloy plate.
9. The method of claim 8,
The elongation percentage of the obtained magnesium alloy sheet was,
12 to 15%.
A method for manufacturing a magnesium alloy plate.
9. The method of claim 8,
Heat treating the rolled casting plate to obtain a magnesium alloy plate,
Lt; RTI ID = 0.0 &gt; 150 C &lt; / RTI &gt;
A method for manufacturing a magnesium alloy plate.
9. The method of claim 8,
A solution annealing process of the casting plate;
Heating the casting plate to 150 to 400 캜;
Quenching the heated casting plate to 25 to 150 캜; And
Maintaining the normally quenched casting plate at ambient temperature.
A method for manufacturing a magnesium alloy plate.

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