JP2020524219A - Magnesium alloy sheet material and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a magnesium alloy sheet material and a method for manufacturing the same. According to one embodiment of the present invention, Al: 2.7-5.0 wt%, Zn: 0.75-1.0 wt%, Ca: 0.1-1. 0% by weight, Mn: 1.0% by weight or less (excluding 0% by weight), the balance including Mg and other unavoidable impurities, and the volume fraction of the bottom surface crystal grains is 100% by volume of the crystal grains of the entire magnesium alloy sheet. Provided is a magnesium alloy plate material in which the content is 30% or less and the bottom surface crystal grains are crystal grains of <0001>//C axis orientation.

Description

One embodiment of the present invention relates to a magnesium alloy sheet and a method for manufacturing the same.

At present, the importance of carbon dioxide emission restriction and new renewable energy in the international community has emerged as a pending issue, and as a result, lightweight alloys, which are a type of structural material, are recognized as a very attractive research field. Has been done.

In particular, magnesium is the lightest metal with a density of 1.74 g/cm ^{3 over} other structural materials such as aluminum and steel, and has various advantages such as vibration absorption ability and electromagnetic wave shielding ability. , Research on related industries to utilize this is being actively conducted.

Such magnesium-containing alloys are mainly applied not only to the current electronic device field but also to the automotive field, but they have fundamental problems in corrosion resistance, flame retardancy, and formability. The current situation is that there is a limit to further expansion.

Particularly in relation to formability, magnesium has an HCP structure (Hexagonal Closed Packed Structure), and the slip system at room temperature is not sufficient, so there are many difficulties in the processing process. That is, a lot of heat is required in the magnesium processing step, which leads to an increase in process cost.

On the other hand, among the magnesium alloys, the AZ-based alloy contains aluminum (Al) and zinc (Zn), belongs to a cheaper one while ensuring a certain level of appropriate strength and soft physical properties, and is commercialized. Equivalent to a magnesium alloy.

However, the above-mentioned physical properties mean that they are in a proper level among magnesium alloys, and have a lower strength than aluminum (Al) which is a competitive material.

Therefore, it is necessary to improve the physical properties such as low formability and strength of the AZ-based magnesium alloy, but the present situation is that research on it has been insufficient.

Provided are a magnesium alloy sheet material and a method for manufacturing the same.

Specifically, it is intended to suppress center segregation composed of Al-Ca secondary phase particles and improve the formability of the magnesium plate material. Therefore, the magnesium alloy plate material in which the Al-Ca secondary phase is not segregated in the center but dispersed is provided.

Not only that, the twin pass structure is controlled by skin pass rolling to maintain formability and improve strength. Specifically, the skin pass rolling can minimize the development change of the (0001) texture and improve the strength while maintaining the formability.

The magnesium alloy sheet material according to one embodiment of the present invention has Al: 2.7 to 5.0 wt%, Zn: 0.75 to 1.0 wt%, and Ca: 0.1 to 100 wt% as a whole. 1.0% by weight, Mn: 1.0% by weight or less (excluding 0% by weight), balance Mg and other unavoidable impurities, and the volume fraction of the bottom crystal grains with respect to 100 volume% of the crystal grains of the entire magnesium alloy sheet. The ratio is 30% or less, and the bottom surface crystal grain can provide a magnesium alloy plate material in which <0001>//C axis orientation crystal grain.

The magnesium alloy plate material contains Al-Ca secondary phase particles, and is composed of a quarter part that is a quarter point from the surface of the magnesium alloy plate material and an Al part that is a half point from the surface of the magnesium alloy plate material. The difference in the area fraction of the -Ca secondary phase particles may be 10% or less.

Specifically, the ratio of the length of the intermediate segregation to the entire length of the magnesium alloy sheet in the rolling direction may be less than 5%.

The thickness ratio of the intermediate segregation to the total thickness of the magnesium alloy sheet may be less than 2.5%. Accordingly, in the magnesium alloy plate material, Al-Ca secondary phase particles may not be segregated in the central portion of the magnesium alloy material but may be evenly distributed.

The Al-Ca secondary phase particles, Al: 20.0 to 25.0% by weight, Ca: 5.0 to 10.0% by weight, Mn: 0.1 to 0.5, based on 100% by weight as a whole. % By weight, Zn: 0.5 to 1.0% by weight, the balance Mg and other unavoidable impurities.

The average particle size of the Al-Ca secondary phase particles may be 0.01 to 4 μm.

The Al-Ca secondary phase particles may be included in an amount of ^{2 to} 15 per 100 µm ^{2 of the} magnesium alloy plate material.

The limit dome height (LDH) of the magnesium alloy plate material may be 7 mm or more.

The maximum collective strength may be 1 to 4 based on the (0001) surface of the magnesium alloy plate material.

The yield strength of the magnesium alloy sheet material may be 150 to 190 MPa.

A magnesium alloy sheet material according to another embodiment of the present invention comprises Al: 2.7 to 5.0% by weight, Zn: 0.75 to 1.0% by weight, Ca: 0. 1 to 1.0% by weight, Mn: 1.0% by weight or less (excluding 0% by weight), balance Mg and other unavoidable impurities, and the area of the twinning structure is 100% of the total area of the magnesium alloy sheet. A magnesium alloy sheet material having a rate of 35% or less can be provided.

Specifically, the area fraction of the twinning structure may be 5 to 35% with respect to 100% of the total area of the magnesium alloy sheet.

A volume fraction of bottom surface crystal grains is 30% or less with respect to 100% by volume of crystal grains of the whole magnesium alloy plate material, and the bottom surface crystal grains are crystal grains of <0001>//C axis orientation. Can be provided.

The limit dome height of the magnesium alloy plate material may be 7 mm or more.

The maximum collective strength may be 1 to 4 based on the (0001) surface of the magnesium alloy plate material.

The yield strength of the magnesium alloy sheet may be 200 to 300 MPa.

The magnesium alloy sheet according to the embodiment of the present invention can disperse the central segregation composed of Al-Ca secondary phase particles and improve the formability of the magnesium sheet. Accordingly, the magnesium alloy sheet according to the embodiment of the present invention can provide a magnesium alloy sheet in which the Al-Ca secondary phase is dispersed without being segregated in the center. Specifically, the area fraction of Al-Ca secondary phase particles in the quarter part which is a 1/4 point from the surface of the magnesium alloy sheet and the central part which is a 1/2 point from the surface of the magnesium alloy sheet. It is possible to provide a magnesium alloy sheet material having a difference of 10% or less.

A magnesium alloy sheet material according to another embodiment of the present invention can obtain a magnesium alloy sheet material having an area fraction of twin structure of 35% or less based on 100% of the total area of the magnesium alloy sheet material by skin pass rolling. it can. Specifically, the skin pass process can improve the strength by controlling the twinning structure while minimizing the development of the (0001) texture and maintaining the formability.

1 is a schematic flowchart of a method for manufacturing a magnesium alloy sheet according to an embodiment of the present invention. It is an optical microscope (Optical microcopy) photograph of the magnesium alloy plate material manufactured in Example 1a. It is an optical microscope photograph of the magnesium alloy plate material manufactured in Comparative Example 1a. It is a secondary electron microscope (Secondary Electron Microscopy) photograph of the magnesium alloy plate material manufactured in Example 1a. It is the figure which showed the result of having measured the limiting dome height of the magnesium alloy board|plate material manufactured in Example 1a. It is the figure which showed the aggregate strength of the maximum (0001) plane of Example 1a. It is a figure showing the maximum (0001) plane aggregate strength of comparative example 1a. It is the result of having analyzed the magnesium alloy plate material manufactured in Example 1a by EBSD(Electron Backscatter Diffraction). It is the figure which showed the fraction of the crystal orientation of Example 1a with the graph. It is the result of the EBSD analysis of the magnesium alloy sheet material based on the skin pass reduction ratio. It is a figure which showed the maximum assembly strength of the (0001) surface of Example 2 and Comparative Example 2 by skin pass conditions.

Advantages and features of the present invention, as well as methods of achieving them, will become apparent with reference to the embodiments described in detail below in connection with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various forms different from each other. The present embodiments merely complete the disclosure of the present invention, and the technical field to which the present invention belongs. The present invention is defined only by the scope of the claims, which is provided to inform those who have ordinary knowledge in the full scope of the invention. Like reference numerals refer to like elements throughout the specification.

Therefore, in some embodiments, well-known techniques are not described in detail to avoid obscuring the present invention. Unless defined otherwise, all terms (including technical and scientific terms) used herein have the meaning commonly understood by one of ordinary skill in the art to which this invention belongs. Be seen. When a part of an entire specification includes “a component”, it means that the component may further include other components, not excluding other components, unless otherwise specified. To do. In addition, the singular forms include the plural forms unless otherwise specified.

The magnesium alloy sheet according to the embodiment of the present invention has Al: 2.7 to 5.0% by weight, Zn: 0.75 to 1.0% by weight, Ca: 0. 1 to 1.0% by weight, Mn: 1.0% by weight or less (excluding 0% by weight), the balance Mg and other unavoidable impurities may be contained.

Hereinafter, the reasons for limiting the components and the composition will be described.

First, aluminum (Al) improves the mechanical properties of the magnesium alloy sheet material and improves the castability of the molten metal. When Al is added in an amount of more than 5.0% by weight, there may occur a problem that the castability rapidly deteriorates. If Al is added in an amount less than 2.7% by weight, the mechanical properties of the magnesium alloy sheet material may deteriorate. Therefore, the range of the Al content can be adjusted to the range described above.

Zinc (Zn) improves the mechanical properties of the magnesium alloy plate material. When Zn is added in an amount of more than 1.0% by weight, a large amount of surface defects and center segregation may be generated, which may cause a problem that casting property is rapidly deteriorated. When Zn is added in an amount of less than 0.75% by weight, However, a problem may occur in which the mechanical properties of the magnesium alloy sheet material deteriorate. Therefore, the range of Zn content can be adjusted to the range described above.

Calcium (Ca) imparts flame retardancy to the magnesium alloy plate material. When Ca is added in an amount of more than 1.0% by weight, the fluidity of the molten metal is reduced, the castability is deteriorated, and the center segregation composed of Al-Ca-based intermetallic compound is increased to improve the formability of the magnesium alloy sheet material. Problems can be exacerbated. When Ca is added in an amount less than 0.1% by weight, the problem that flame retardancy is not sufficiently imparted may occur. Therefore, the range of Ca content can be adjusted to the range described above. More specifically, Ca may be included in an amount of 0.5 to 0.8% by weight.

Manganese (Mn) improves the mechanical properties of the magnesium alloy sheet material. If Mn is added in an amount of more than 1.0% by weight, heat dissipation may be deteriorated, and at the same time, it may be difficult to control uniform distribution. Therefore, the range of the Mn content can be adjusted to the range described above.

The volume fraction of the bottom crystal grains may be 30% or less based on 100 volume% of the crystal grains of the entire magnesium alloy plate material.

In one embodiment of the present invention, the bottom surface crystal grain means a crystal grain having a bottom surface orientation. Specifically, magnesium has an HCP (Hexagonal Closed Pack) crystal structure. At this time, a crystal grain in which the C axis of the crystal structure is parallel to the thickness direction of the plate material is a crystal having a bottom crystal orientation. It is called a grain (that is, a bottom crystal grain). Therefore, in the present specification, the bottom surface crystal grains are represented by "<0001>//C axis".

More specifically, when the fraction of the bottom surface crystal grains is in the above range, it is possible to obtain a magnesium alloy sheet material having excellent formability.

Specifically, the volume fraction of the crystal grains having a <0001>//C axis orientation relationship with respect to 100 volume% of the crystal grains of the entire magnesium alloy sheet may be 30% or less. More specifically, the volume fraction of crystal grains in the <0001>//C axis direction may be 25% or less with respect to 100 volume% of the crystal grains of the entire magnesium alloy sheet material. More specifically, it may be 20% or less. The lower limit of the volume fraction of the crystal grains having the <0001>//C axis orientation relationship may be more than 0%. This means that the present invention can be included within the range where the volume fraction of the crystal grains having the <0001>//C axis orientation relationship exists.

In the magnesium alloy plate material, the crystal grain fraction in the <0001>//C axis direction may decrease due to an increase in the crystal grain orientation distribution.

As a result, when the crystal grain fraction range of <0001>//C-axis orientation is satisfied, the aggregate strength of the magnesium alloy sheet material can be lowered, and the magnesium alloy sheet material excellent in formability can be obtained.

The magnesium alloy sheet material according to an embodiment of the present invention may include Al-Ca secondary phase particles.

Specifically, the magnesium alloy sheet material according to the embodiment of the present invention may include Al-Ca secondary phase particles and may include almost no center segregation. More specifically, the magnesium alloy sheet material according to an embodiment of the present invention may have a form in which Al-Ca secondary phase particles are evenly dispersed. The center segregation means that Al-Ca secondary phase particles are segregated at the center of the thickness direction (ND) of the magnesium alloy sheet, and as described above, when the center segregation increases, the formability of the magnesium alloy sheet is increased. Can be exacerbated.

Therefore, the magnesium alloy sheet according to the embodiment of the present invention has an area of the Al-Ca secondary phase particles in the quarter portion which is ¼ point from the surface and the central portion which is ½ point from the surface of the magnesium alloy sheet material. The difference in fraction can be 10% or less. As a result, the Al-Ca secondary phase particles are not segregated in the central portion and are dispersed uniformly throughout, and the moldability can be improved. Here, the area fraction means the fraction of the area of the Al-Ca secondary phase particles per the same area in the quarter part and the central part.

More specifically, the ratio of the length of the intermediate segregation to the total length of the magnesium alloy sheet material in the rolling direction (RD) may be less than 5%. The thickness ratio of the intermediate segregation may be less than 2.5% with respect to the total thickness of the magnesium alloy sheet material in the thickness direction (ND).

This means that the center segregation is scarcely formed in the base material, which is a range where the segregation length and thickness are all reduced as compared with the center segregation generated when Al and Ca are added. As a result, the magnesium alloy sheet material according to the embodiment of the present invention can have improved formability.

The whole length of the magnesium plate material is based on a magnesium plate material having a constant length unit. Specifically, the length unit may be 1,000 to 3,000 μm.

Specifically, Al: 20.0 to 25.0 wt%, Ca: 5.0 to 10.0 wt%, Mn: 0.1 to 100 wt% of the Al-Ca secondary phase particles as a whole. 0.5 wt%, Zn: 0.5 to 1.0 wt%, the balance Mg and other unavoidable impurities may be included.

In general, when Al and Ca are added to magnesium for alloying, center segregation of Al-Ca secondary phase particles is generated, which greatly deteriorates formability. On the other hand, the magnesium alloy sheet according to the embodiment of the present invention can improve the formability of the magnesium sheet by suppressing the formation of center segregation composed of Al-Ca secondary phase particles. Specifically, it is possible to provide a magnesium alloy sheet material in which Al-Ca secondary phase particles are dispersed.

The average particle size of the Al-Ca secondary phase particles may be 0.01 to 4 μm. The larger the average particle size of the Al-Ca secondary phase particles, the more the formability may decrease due to the formation of center segregation as described above. It exhibits improved formability in the particle size range described above.

The Al-Ca secondary phase particles may be included in an amount of ^{2 to} 15 per 100 μm ^{2 of the} magnesium alloy plate material. By including the number of Al-Ca secondary phase particles in the above range, the formability of the magnesium alloy sheet material can be improved.

In an embodiment of the present invention, Al, Zn, Mn, and Ca composition ranges, temperature and time conditions during homogenizing heat treatment, temperature and rolling rate during warm rolling in order to control Al-Ca secondary phase particles. Etc. can be precisely adjusted.

The magnesium alloy sheet material according to an embodiment of the present invention includes crystal grains, and the average grain size of the crystal grains may be 5 to 30 μm. Formability can be improved within the grain size range of the crystal grains.

Also, the limiting dome height of the magnesium alloy sheet material according to an embodiment of the present invention may be 7 mm or more. More specifically, it can be 7-10 mm.

Generally, the limit dome height is utilized as an index for evaluating the formability (particularly, compressibility) of a material, and it means that the formability of the material improves as the limit dome height increases.

The limited range is due to an increase in the orientation distribution of the crystal grains in the magnesium alloy plate material, and is a significantly high limit dome height as compared with the generally known magnesium alloy plate material.

Therefore, the magnesium alloy sheet may have a maximum collective strength of 1 to 4 with reference to the (0001) plane. When it exceeds the above-mentioned range, the formability of the magnesium alloy sheet is poor.

In addition, the yield strength of the magnesium alloy sheet according to the embodiment of the present invention may be in the range of 150 to 190 MPa.

The magnesium alloy sheet according to an embodiment of the present invention may have an area fraction of twin structure of 35% or less with respect to 100% of the entire area of the magnesium alloy sheet by skin pass rolling in a manufacturing step described later. More specifically, the area fraction of the twinning structure may be 5 to 35%. More specifically, the area fraction of the twinning structure may be 5-33%. By controlling the twinning structure fraction within the above range, the yield strength of the magnesium alloy sheet material according to an embodiment of the present invention may be 200 to 300 MPa. Such a range is considered to be an excellent range for the magnesium plate material of the component according to the embodiment of the present invention.

In addition, the thickness of the magnesium alloy sheet according to the embodiment of the present invention may be 0.4 to 3 mm. The magnesium plate material according to an embodiment of the present invention may be selected according to the characteristics required in the above thickness range. However, the present invention is not limited to this thickness range.

FIG. 1 schematically shows a flowchart of a method for manufacturing a magnesium alloy sheet material according to an embodiment of the present invention. The flowchart of the method for manufacturing a magnesium alloy sheet material of FIG. 1 is merely for illustrating the present invention, and the present invention is not limited to this. Therefore, the manufacturing method of the magnesium alloy sheet material can be variously modified.

A method for manufacturing a magnesium alloy sheet according to an embodiment of the present invention is as follows: Al: 2.7 to 5.0 wt%, Zn: 0.75 to 1.0 wt%, Ca: 0.0. 1 to 1.0 wt%, Mn: 1.0 wt% or less (excluding 0 wt%), a step of casting a molten metal containing the balance Mg and other inevitable impurities to produce a cast material (S10); The method includes the step of homogenizing heat treatment (S20); and the step of warm rolling the casting material subjected to the homogenizing heat treatment (S30).

In addition, the method for manufacturing the magnesium alloy sheet material may further include other steps, if necessary.

First, Al: 2.7 to 5.0% by weight, Zn: 0.75 to 1.0% by weight, Ca: 0.1 to 1.0% by weight, Mn: 1. A step (S10) of manufacturing a cast material by casting a molten metal containing 0% by weight or less (excluding 0% by weight) and the balance Mg and other unavoidable impurities may be performed.

The reason for limiting the numerical value of each component is as described above, and thus the duplicate description will be omitted.

At this time, the method of manufacturing the casting material (S10) may be a method of die casting, strip casting, billet casting, centrifugal casting, tilt casting, sand casting, direct chill casting or a combination thereof. it can.

More specifically, the strip casting method can be used. However, it is not limited to this.

More specifically, the reduction force in the step of manufacturing the cast material (S10) may be 0.2 ton/mm ² or more. More specifically, it may be 1 ton/mm ² or more. More specifically, it can be 1 to 1.5 ton/mm ² . When the casting material solidifies and receives a rolling reduction force at the same time, the formability of the magnesium alloy sheet material can be improved by adjusting the rolling reduction force to fall within the above range.

Then, a step of homogenizing and heat treating the cast material (S20) may be performed.

At this time, the heat treatment may be performed at a temperature of 350° C. to 500° C. for 1 to 28 hours. More specifically, the homogenizing heat treatment can be performed for 18 to 28 hours.

In the temperature range lower than 350° C., the homogenizing heat treatment may not be performed properly, and a problem may occur that the beta phase such as Mg ₁₇ Al ₁₂ does not form a solid solution in the matrix.

In the temperature range higher than 500° C., the beta phase condensed in the main material may melt to cause a fire, or holes may occur in the magnesium plate material. Therefore, the homogenizing heat treatment can be performed within the above-mentioned temperature range.

Thereafter, a step of warm rolling the homogenized heat treated casting material (S30) may be performed.

At this time, the temperature condition of the warm rolling may be 150°C to 350°C. In the temperature range lower than 150° C., there may be a problem that many edge cracks occur. In the temperature range higher than 500° C., problems unsuitable for mass production may occur. Therefore, warm rolling can be performed within the above-mentioned temperature range.

The warm rolling step may be performed multiple times, and the hot rolling may be performed at a reduction rate of 10 to 30% per time. The reduction ratio of the warm rolling means a% value with respect to the thickness 100% (length %) of the cast material before the warm rolling. By performing the warm rolling a plurality of times, it is possible to finally roll to a thin thickness of about 0.4 mm.

The method may further include one or more steps of intermediate annealing between a plurality of warm rollings. By further including the step of intermediate annealing, the formability of the magnesium alloy sheet material can be further improved. Specifically, the step of intermediate annealing may be performed at a temperature of 300 to 500° C. for 1 to 10 hours. More specifically, it may be carried out at a temperature of 450 to 500°C. Within the above range, the formability of the magnesium alloy sheet material can be further improved.

The method may further include a post heat treatment step after the warm rolling step. By further including the post heat treatment step, the formability of the magnesium alloy sheet material can be further improved. The post heat treatment step may be performed at 300 to 500° C. for 1 to 15 hours. Specifically, it can be carried out for 1 to 10 hours. Within the above range, the formability of the magnesium alloy sheet material can be further improved.

Another method for manufacturing a magnesium alloy sheet according to an embodiment of the present invention is as follows: Al: 2.7-5.0 wt%, Zn: 0.75-1.0 wt%, Ca: 100 wt% : 0.1-1.0 wt%, Mn: 1.0 wt% or less (excluding 0 wt%), casting a molten metal containing the balance Mg and other unavoidable impurities to produce a cast material; Homogenizing heat treatment; warm rolling the homogenized heat treating cast material to produce a rolled material; post heat treating the rolled material; and performing a skin pass on the post heat treated rolled material. The method may include manufacturing a magnesium alloy sheet material.

First, Al: 2.7 to 5.0% by weight, Zn: 0.75 to 1.0% by weight, Ca: 0.1 to 1.0% by weight, Mn: 1. A step of casting a molten metal containing 0% by weight or less (excluding 0% by weight), the balance Mg and other unavoidable impurities to produce a cast material can be carried out.

The molten metal may be AZ31 alloy, AL5083 alloy, or a combination thereof which has already been commercialized at the above stage. However, it is not limited to this.

More specifically, the molten metal can be prepared in the temperature range of 650 to 750°C. Then, the molten metal may be cast to manufacture a cast material. At this time, the cast material may have a thickness of 3 to 7 mm.

At this time, the casting material may be manufactured by die casting, strip casting, billet casting, centrifugal casting, tilt casting, sand casting, direct chill casting, or a combination thereof. More specifically, the strip casting method can be used. However, it is not limited to this.

More specifically, the rolling force in the step of manufacturing the cast material may be 0.2 ton/mm ² or more. More specifically, it may be 1 ton/mm ² or more. More specifically, it can be 1 to 1.5 ton/mm ² .

After this, a step of homogenizing and heat treating the cast material may be performed.

More specifically, the homogenizing heat treatment of the cast material may include a primary heat treatment step in a temperature range of 300°C to 400°C; and a secondary heat treatment step in a temperature range of 400°C to 500°C. .. The temperature ranges of the first heat treatment step and the second heat treatment step may be different.

More specifically, the first heat treatment step in the temperature range of 300°C to 400°C may be performed for 5 hours to 20 hours. Also, the secondary heat treatment step in the temperature range of 400° C. to 500° C. may be performed for 5 hours to 20 hours.

By performing the first heat treatment step in the temperature range, the Mg-Al-Zn ternary pi phase generated in the casting step can be removed. The presence of the ternary pi phase adversely affects the subsequent processes. Further, the stress in the slab can be released by performing the secondary heat treatment step within the above temperature range. Further, recrystallization formation of the cast structure can be more actively induced.

Then, a step of manufacturing the rolled material by performing hot rolling on the homogenized heat treated casting material may be performed.

The heat-treated cast material may be rolled 1 to 15 times to a thickness of 0.4 to 3 mm. Also, the rolling may be performed at 150 to 350°C.

More specifically, if the rolling temperature is lower than 150° C., cracks may be induced on the surface during rolling, and if it exceeds 350° C., it is not suitable for actual mass production equipment. Therefore, it can be rolled at 150°C to 350°C.

Then, an intermediate annealing of the rolled material may be performed. When it is rolled multiple times in the rolling step, it may be heat-treated in a temperature range of 300° C. to 550° C. for 1 hour to 15 hours in an interval between the passes.

For example, it may be rolled twice and then subjected to intermediate annealing once and rolled to a final target thickness. As another example, rolling may be performed three times and then annealing may be performed once to roll to a final target thickness. More specifically, when the rolled cast material is annealed in the above temperature range, the stress generated by rolling can be released. Therefore, it can be rolled several times to the desired thickness of the cast material.

Then, a step of post-heat treating the rolled material may be performed.

The post heat treatment step may be performed at 300 to 500° C. for 1 to 15 hours. Specifically, it can be carried out for 1 to 10 hours. Within the range described above, the formability of the magnesium alloy sheet material can be further improved.

Finally, a skin pass may be performed on the post-heat treated rolled material to produce a magnesium alloy sheet material.

More specifically, the skin pass is also referred to as temper rolling or temper rolling, meaning that the deformed pattern generated in the cold-rolled steel sheet after treatment is removed and cold rolling is performed with a light pressure to improve hardness. To do.

Therefore, in an embodiment of the present invention, the skin pass may be performed once in the temperature range of 250°C to 350°C.

The magnesium alloy sheet material manufactured by performing the skin pass may be rolled at a reduction rate of 2 to 15% with respect to the thickness of the rolled material. More specifically, the reduction rate may be linked to the skin pass temperature.

As a specific example, when the skin pass temperature is 250° C., the skin pass rolling reduction ratio may be 5 to 15%. At this time, the yield strength may be 200 to 260 MPa. At this time, the limit dome height may be in the range of 7.3 to 8.1.

As a specific example, when the skin pass temperature is 300° C., the skin pass reduction ratio may be 5 to 15%. More specifically, it can be 7-12%. At this time, the range of yield strength may be 200 to 250 MPa. At this time, the limit dome height may be in the range of 7.3 to 8.1.

In the present application, the limit dome height (Limit Dome Height, LDH) is an index for evaluating the formability of a plate material, particularly pressability, and the formability is measured by deforming a test piece and measuring the deformed height. To measure. When the limit dome height value is high, it means that the plate material is excellent in formability.

More specifically, in the case of skin-passing under the above-mentioned temperature and pressure conditions, the development of the (0001) texture is reduced, so moldability can be ensured. That is, when the skin pass is performed under the above conditions, the change in the texture strength can be minimized and the strength can be improved.

Hereinafter, detailed description will be made with reference to examples. However, the following examples only illustrate the present invention, and the contents of the present invention are not limited by the following examples.

Example 1
The amounts of Al and Ca were as disclosed in Table 1 below with respect to 100% by weight as a whole, and a melt containing 0.8% by weight of Zn, 0.5% by weight of Mn, the balance Mg and inevitable impurities was prepared.

The molten metal was passed between two cooling rolls to manufacture a magnesium cast material. At this time, the rolling force of the cooling roll is as disclosed in Table 1 below.

Then, the magnesium cast material was subjected to homogenizing heat treatment at 400° C. for different times as disclosed in Table 1 below.

The homogenized heat-treated cast material was warm-rolled at a temperature of 250° C. and a reduction rate of 15%. After that, the sheet was annealed for 1 hour at the temperature disclosed in Table 1 below, and then warm-rolled again at a temperature of 250° C. at a reduction rate of 15% to produce a magnesium alloy sheet material.

Comparative Example 1
A molten metal containing Al and Ca as disclosed in Table 1 below, relative to 100% by weight in total, and 0.8% by weight of Zn, the balance Mg and inevitable impurities was prepared.

A magnesium alloy sheet was manufactured in the same manner as in Example 1 except for the conditions disclosed in Table 1 below.

The following test examples were carried out in order to compare and evaluate the physical properties of the previously produced examples and comparative examples.

Test Example 1: Observation of Microstructure of Magnesium Alloy Plate Material Using a scanning electron microscope (SEM, Scanning Electron Microscope), the microstructure of the magnesium alloy plate materials manufactured in Examples and Comparative Examples was observed.

This is disclosed in Figures 2-4 of the present application.

FIG. 2 is a scanning electron microscope (SEM) photograph of the magnesium alloy sheet produced in Example 1a. FIG. 3 is a scanning electron micrograph of the magnesium alloy sheet produced in Comparative Example 1a.

Specifically, the horizontal direction in FIGS. 2 to 3 means the rolling direction (RD) of the magnesium alloy sheet material, and the vertical direction means the thickness direction (ND).

As disclosed in FIG. 2, in the case of Example 1a, it is found that center segregation is hardly generated in the magnesium alloy sheet material. Specifically, it can be seen that the ratio of the length of the center segregation to the total length in the rolling direction of Example 1a of about 2000 μm is less than 5%.

On the other hand, as disclosed in FIG. 3, in the case of Comparative Example 1a, it can be seen that a large amount of center segregation occurred. Specifically, it can be seen that in Comparative Example 1a, the ratio of the length of central segregation to the total length of about 2000 μm in the rolling direction is 5% or more. Further, in Comparative Example 1a, the thickness of the intermediate segregation was confirmed to be about 30 μm with respect to the total thickness of about 1200 μm in the thickness direction. From this, it is understood that the thickness ratio of the intermediate segregation is 2.5% with respect to the total thickness of the magnesium alloy sheet material in the thickness direction. Therefore, in Comparative Example 1a, it was confirmed that a large amount of center segregation occurred.

As a result, the center segregation is a factor that deteriorates the formability of the magnesium alloy sheet, so that it is possible to obtain a magnesium alloy sheet having excellent formability such that center segregation is not generated.

FIG. 4 is a secondary electron microscope (SEM) photograph of the magnesium alloy sheet produced in Example 1a.

White dots in FIG. 4 mean Al-Ca secondary phase particles. More specifically, as a result of the component analysis of the white dots in FIG. 4, analysis was made with Al 24.61% by weight, Ca 8.75% by weight, Mn 0.36% by weight, Zn 0.66% by weight, the balance Mg and other unavoidable impurities. Was done.

From this, it was confirmed that the magnesium alloy plate material according to Example 1a contained Al-Ca secondary phase particles. Specifically, it can be seen from FIG. 4 that 50 Al-Ca secondary phase particles are distributed per 1600 μm ² area of the magnesium alloy sheet.

However, as shown in FIG. 4, in the case of Example 1a, it is found that the Al—Ca secondary phase is not segregated and is dispersed. As a result, as disclosed in Table 2 below, the limit dome height of Example 1a of the present application is 9.4 mm, while the limit dome height of Comparative Example 1a is 2.5 mm, compared to the Examples. It can be seen that the moldability is poor.

Test Example 2: Measurement of Limit Dome Height of Magnesium Alloy Plate Material The limit dome height (Limit Dome Height, LDH) in the present application is an index for evaluating the formability of the plate material, particularly the pressability, and is transformed into a test piece. And the deformed height can be measured to measure the formability.

The limit dome height was obtained by inserting the magnesium alloy sheet materials according to the examples and comparative examples between the upper die and the lower die, fixing the outer peripheral portion of each test piece with a force of 5 kN, and using a known press oil as the lubricating oil. Used, and using a spherical punch having a diameter of 20 mm, deformed at a speed of 5 to 10 mm/min, and after inserting the punch until each test piece ruptured, the deformation height of each test piece at the time of rupture It was measured by the method of measuring the height. That is, the height at which the test piece was deformed was measured.

This is disclosed in FIG. 5 of the present application.

FIG. 5 is a diagram showing a result of measuring a limiting dome height of the magnesium alloy sheet material manufactured in Example 1a.

As disclosed in FIG. 5, it can be seen that the magnesium alloy sheet according to Example 1a has excellent formability.

This can be confirmed from Tables 2 and 3 below.

Test Example 3: Crystal Orientation Analysis of Crystal Grains The crystal orientation of crystal grains of magnesium alloy sheet materials according to Examples and Comparative Examples was confirmed with an XRD analyzer and shown in FIGS. 6 to 11. Specifically, the texture of crystal grains was shown by using the XRD pole figure method.

More specifically, the pole figure is a diagram in which the direction of an arbitrarily fixed crystal coordinate system is stereo-projected onto the test piece coordinate system. More specifically, a pole figure can be shown by displaying the poles on the {0001} plane of crystal grains of various orientations in the reference coordinate system and drawing a density contour line according to the pole density distribution. At this time, the poles are fixed in a specific lattice direction by the Bragg angle, and some poles can be displayed on the single crystal.

Therefore, it can be interpreted that the smaller the density distribution value of the contour lines shown by the pole figure method, the more the crystal grains of various orientations are distributed, and the larger the density distribution value is, the more the crystal grains of <0001>//C axis orientation are distributed. it can.

This can be compared with FIGS. 6 and 7 of the present application.

FIG. 6 is a diagram showing the maximum aggregate strength of the (0001) plane of Example 1a. FIG. 7 is a diagram showing the maximum aggregate strength of the (0001) plane of Comparative Example 1a.

Specifically, the maximum aggregate strength of the (0001) plane in FIGS. 6 and 7 is the result of analyzing the crystal orientation of the magnesium alloy sheet material by the XRD analyzer described above.

As disclosed in FIG. 6, in the example, the maximum density distribution value (collection strength) of the (0001) plane is 2.73, which is low, whereas in the comparative example, it is 12.1 and is higher than the example. I was able to confirm.

That is, it can be deduced from the examples that the maximum aggregate strength value is small, the contour lines are widely spread, and the crystal grains of various orientations are distributed.

On the other hand, in the comparative example, the maximum aggregate strength value is large and the contour lines are dense, so it can be seen that the comparative example contains more crystal grains of <0001>//C-axis orientation than the example.

From this, it can be seen that the examples are more excellent in moldability.

This can be seen from FIGS. 8 and 9 of the present application.

FIG. 8 is a result of analyzing the magnesium alloy sheet manufactured in Example 1a by EBSD (Electron Backscatter Diffraction).

FIG. 9 is a graph showing the fraction of the crystal orientation of Example 1a.

First, as disclosed in FIG. 8, the crystal orientation of crystal grains can be measured by using EBSD. More specifically, the EBSD can inject electrons into a test piece through an e-electron beam and measure the crystal orientation of crystal grains using inelastic scattering diffraction behind the test piece.

Further, as disclosed in FIG. 9, crystal grains having a misorientation angle between grains of 20° or less can be said to be bottom crystal grains. From this, it was confirmed that the volume fraction of <0001>//C-axis oriented crystal grains was distributed about 18.5% with respect to the volume fraction of 100% of the whole crystal grains.

Further, as shown in FIG. 8, it was found that crystal grains having various orientations were distributed in various colors, and crystal grains (red) corresponding to crystal grains having <0001>//C-axis orientation were designated as EBSD. The result could be confirmed with the naked eye.

As a result, it was confirmed that in Comparative Examples 1a to 1d that did not satisfy the conditions of the homogenizing annealing time, the rolling temperature, and the intermediate annealing temperature, the formability was inferior to that of the Examples. Not only that, the yield strength is inferior to that of the example. In the case of Comparative Example 1c, the average size of the crystal grains was 40 μm, which was relatively excellent in formability as compared with the other Comparative Examples, but was at a level not reaching that of the Examples.

Example 2
A molten metal containing Al: 3.0% by weight, Zn: 1.0% by weight, Ca: 1.0% by weight, Mn: 0.3% by weight, and the balance Mg and other inevitable impurities with respect to 100% by weight as a whole. Got ready.

A casting material was manufactured by casting the molten metal.

The cast material was subjected to primary homogenization heat treatment at 350° C. for 10 hours. The first homogenized heat treated casting material was subjected to a second homogenized heat treatment at 450° C. for 10 hours.

The homogenized heat treated cast material was rolled to produce a rolled material.

Then, the rolled material was post-heat treated at 400° C. for 10 hours.

Finally, the post-heat treated rolled material was skin-passed to manufacture a magnesium plate, and the skin-passing execution temperature and reduction rate are as disclosed in Table 2.

Comparative example 2
A magnesium alloy sheet material was produced in the same manner as in Example 2 except for the conditions of skin pass temperature and rolling reduction.

The following test examples were carried out in order to compare and evaluate the physical properties of the examples and the comparative examples. In addition, the measurement of the limit dome height, the crystal orientation analysis, and the test example are also performed, and the test method is as described above.

Test Example 4: Comparison of physical properties by skin pass reduction rate and temperature

As disclosed in Table 3, the magnesium alloy having the same composition and composition was skin-passed, and as a result, the yield strength could be improved without a large change in formability. More specifically, the formability can be compared by the numerical values of the elongation rate and the limit dome height.

In addition, this was able to ensure moldability by minimizing the change in texture, and the change in texture due to the skin pass reduction ratio can be confirmed from FIG. 10.

FIG. 10 shows the results of EBSD analysis of magnesium alloy sheet materials according to the skin pass reduction ratio.

As disclosed in FIG. 10, it can be confirmed that the crystal grains in various orientations are distributed even when skin pass is further performed after rolling. Furthermore, when rolling with a higher skin pass reduction, twinning (black) texture and dislocation development minimized the orientation change of the texture and improved the strength.

Specifically, when the skin pass reduction ratio was 2 to 6%, the area fraction of the twinned structure was confirmed to be 15% with respect to the entire area of 100%. When the skin pass reduction rate was 6 to 15%, the area fraction of the twinned structure was confirmed to be 30% with respect to the total area of 100%.

As described above, the twinning structure and dislocation can maintain the strength of the magnesium alloy sheet material and improve the formability.

Therefore, when rolling is performed with a rolling reduction of more than 15% (Comparative Example 2a), the texture of the (0001) plane may be developed again and the formability may be deteriorated.

FIG. 11 is a diagram showing the collective strength of the (0001) planes of Example 2 and Comparative Example 2 according to the skin pass conditions.

As disclosed in FIG. 11, it can be seen that even if the skin pass is performed, the change in the texture of the example is not large. However, as in Comparative Example 2a, it was found that when the skin pass reduction rate was excessive, the strength of the texture significantly changed. As a result, as disclosed in Table 3, it was confirmed that Comparative Example 2a had an excellent effect of increasing the yield strength, but the elongation rate was very poor.

It can also be confirmed that the effect of increasing the yield strength due to the skin pass reduction ratio is greater than the effect of increasing the yield strength due to the change in skin pass temperature.

Although the embodiments of the present invention have been described with reference to the accompanying drawings, those having ordinary knowledge in the technical field to which the present invention pertains do not change the technical idea or essential features of the present invention. It can be understood that it can be implemented in a specific form.

Therefore, it should be understood that the above-described embodiment is illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the scope of the claims to be described later than the detailed description, and the meaning and scope of the scope of the claims and all modifications or modified forms derived from the equivalent concept thereof fall within the scope of the present invention. Must be construed to be included.

Claims (10)

Al: 2.7-5.0% by weight, Zn: 0.75-1.0% by weight, Ca: 0.1-1.0% by weight, Mn: 1. 0% by weight or less (excluding 0% by weight), balance Mg and other inevitable impurities,
The volume fraction of the bottom crystal grains is 30% or less with respect to 100 volume% of the crystal grains of the entire magnesium alloy plate material,
The bottom surface crystal grains are crystal grains of <0001>//C axis orientation,
Magnesium alloy plate material. The magnesium alloy plate material contains Al-Ca secondary phase particles,
The difference in area fraction of Al-Ca secondary phase particles between the quarter part, which is ¼ point from the surface of the magnesium alloy plate material, and the central part, which is ½ point from the surface of the magnesium alloy plate material, is 10%. Is less than
The magnesium alloy plate material according to claim 1. The magnesium alloy sheet according to claim 2, wherein the ratio of the length of the intermediate segregation to the entire length of the magnesium alloy sheet in the rolling direction is less than 5%. The magnesium alloy plate material according to claim 3, wherein the thickness ratio of the intermediate segregation is less than 2.5% with respect to the total thickness of the magnesium alloy plate material in the thickness direction. The limit dome height (LDH) of the magnesium alloy plate material is 7 mm or more,
The maximum collective strength is 1 to 4 with reference to the magnesium alloy plate material (0001) surface,
The magnesium alloy plate material according to claim 4. Al: 2.7-5.0% by weight, Zn: 0.75-1.0% by weight, Ca: 0.1-1.0% by weight, Mn: 1. 0% by weight or less (excluding 0% by weight), balance Mg and other inevitable impurities,
The area fraction of the twinned structure is 35% or less with respect to 100% of the total area of the magnesium alloy sheet.
Magnesium alloy plate material. The magnesium alloy plate material according to claim 6, wherein the area fraction of the twinning structure is 5 to 35% with respect to 100% of the total area of the magnesium alloy plate material. The volume fraction of the bottom crystal grains is 30% or less with respect to 100 volume% of the crystal grains of the entire magnesium alloy plate material,
The bottom surface crystal grains are crystal grains of <0001>//C axis orientation,
The magnesium alloy plate material according to claim 7. The limit dome height of the magnesium alloy plate material is 7 mm or more,
The maximum collective strength is 1 to 4 with reference to the magnesium alloy plate material (0001) surface,
The magnesium alloy plate material according to claim 8. The magnesium alloy plate material according to claim 9, wherein the yield strength of the magnesium alloy plate material is 200 to 300 MPa.

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