KR101502751B1 - Method for manufacturing cold rolled magnesium alloy sheet having enhanced formability, yield strength and tensile strength and cold rolled magnesium alloy sheet having enhanced formability, yield strength and tensile strength manufactured thereby - Google Patents

Abstract

The present invention provides a method for manufacturing a magnesium alloy cold rolled plate having improved moldability at room temperature and a magnesium alloy cold rolled plate manufactured thereby. More particularly, the present invention relates to a method of manufacturing a steel plate, which comprises (a) a plate made of a magnesium alloy and a constraining member made of steel and suppressing plastic deformation of the plate in a transverse direction (TD) Preparing a composite sheet; (b) cold rolling the composite sheet material; And (c) separating the cold rolled plate made of the magnesium alloy from the cold-rolled composite sheet obtained in the step (b) to produce a magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength And a magnesium alloy cold-rolled sheet produced by the method, and having improved formability, yield strength and tensile strength. According to the method for manufacturing a magnesium alloy cold rolled plate according to the present invention, a magnesium alloy sheet material having improved formability at room temperature can be manufactured, and a sheet material can be manufactured through cold rolling. Therefore, The magnesium alloy sheet produced by the manufacturing method according to the present invention has improved moldability at room temperature and is widely used in various technical fields such as automobiles and aircrafts Lt; / RTI >

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength, and a magnesium alloy cold rolled plate having the improved formability, yield strength and tensile strength, enhanced formability, yield strength and tensile strength and cold rolled magnesium alloy sheet having enhanced formability,

The present invention relates to a method for manufacturing a magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength, and a magnesium alloy cold rolled plate having the improved formability, yield strength and tensile strength produced by the method, , A method of manufacturing a magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength by using a composite plate including a constraining member for suppressing plastic deformation in a transverse direction (TD) of a magnesium alloy plate material, and And a magnesium alloy cold-rolled sheet manufactured by the method, which has improved moldability, yield strength and tensile strength.

A variety of plate material processing methods such as press working are used for the processing of plate materials in automobile and aircraft industries. During the processing of plate materials using these materials, the material may be stretched locally or wholly, bending, Deformation such as flanging, deep drawing, or the like, or a combination thereof, occurs.

Therefore, the formability of the plate material, which means the degree to which the plate material can be plastic deformed without causing fracture, is more important than any physical property in the processing of the plate material.

On the other hand, the magnesium alloy has been attracting attention as an alloy for a structural material exhibiting low specific gravity, good specific strength and rigidity, but it has a crystal structure of hexagonal close packed (HCP) and has a sufficient slip system at room temperature In a basal texture formed in a magnesium alloy by hot rolling or extrusion, this slip system has a Schmid factor (Schmid factor) close to zero for strain along the c axis, ), The moldability at room temperature is lowered and the use thereof is not widespread.

Therefore, in order to use a magnesium alloy sheet in a variety of fields, it is desired to develop a magnesium alloy sheet having excellent moldability at room temperature and having improved yield strength and tensile strength.

SUMMARY OF THE INVENTION The present invention provides a method for manufacturing a cold rolled magnesium alloy sheet having improved yield strength and tensile strength as well as moldability at room temperature, and a magnesium alloy cold rolled sheet manufactured by the method.

In order to accomplish the above object, the present invention provides a method of manufacturing a steel plate, comprising the steps of: (a) forming a plate made of a magnesium alloy and steel and suppressing plastic deformation of the plate in a transverse direction (TD) Preparing a composite sheet including a constraining member; (b) cold rolling the composite sheet material; And (c) separating the cold rolled plate made of the magnesium alloy from the cold-rolled composite sheet obtained in the step (b) to produce a magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength Method.

Further, the present invention proposes a magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength, produced by the above-described production method.

The magnesium alloy cold-rolled sheet manufacturing method according to the present invention can produce a magnesium alloy sheet having improved yield strength and tensile strength and improved moldability at room temperature, It is not accompanied by problems such as an increase in cost due to hot working or a complicated process as in the case of the conventional magnesium alloy sheet material production because the plate material can be manufactured through rolling.

In addition, the magnesium alloy sheet produced by the method of the present invention exhibits improved yield strength and tensile strength, and has excellent moldability at room temperature, and thus can be widely used in various technical fields such as automobiles and aircraft.

1 is a schematic view showing an example of a composite plate used in a method of manufacturing a magnesium alloy cold rolled plate having improved formability according to the present invention.
2 (a) to 2 (c) are graphs showing the relationship between the center of the specimen and the center of gravity along the transverse direction (TD) in a plane perpendicular to the rolling direction (RD) of the magnesium alloy specimen produced in the embodiment / 4, optical micrographs of the surface microstructure observed at the edge.
3 is a graph showing the results of tensile test at 100 ° C (FIG. 3 (a)) and tensile test at room temperature (FIG. 3 (a)) of magnesium alloy specimens prepared in the examples of the present invention and magnesium alloy specimens prepared in the comparative examples (b)).
FIG. 4 shows the results of the limit dome height (LDH) test for the magnesium alloy specimens prepared in the examples of the present invention and the magnesium alloy specimens prepared in the comparative examples.

Hereinafter, the present invention will be described in detail.

A method for manufacturing a magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength according to the present invention comprises the steps of: (a) forming a plate made of a magnesium alloy and steel, Preparing a composite plate including a constraining member for suppressing plastic deformation in a transverse direction (TD); (b) cold rolling the composite sheet material; And (c) separating the cold rolled plate made of the magnesium alloy from the cold rolled composite sheet obtained in the step (b). Each step will be described in detail below.

The step (a) of the manufacturing method according to the present invention comprises a plate made of a magnesium alloy and a constraining member for suppressing plastic deformation of the plate in the transverse direction (TD) To form a composite sheet material.

In the present specification, the composite plate comprises a magnesium alloy and a different material of steel, each of which is an independent individual member of a plate and a restraining member, Are defined as having a plate shape.

In the composite plate, a plate made of a magnesium alloy is intended to be formed through cold rolling. The plate is perpendicular to the rolling direction (RD) of the plate material in the cold rolling process and in the TD direction parallel to the rolled surface And is contained in the composite plate according to the present invention.

Here, the shape of the constraining member is not particularly limited as long as it can apply compressive stress that suppresses plastic deformation of the plate in the TD direction during rolling.

For example, when preparing the composite plate 1 having the shape and structure shown in Fig. 1, a constraining member 3 having a concave portion is formed by processing a hot rolled plate made of steel or the like, Rolled plate material or the like is processed so as to have a size conforming to the shape of the concave portion to manufacture the plate material 2 and then the plate material 2 is positioned so as to be embedded in the concave portion of the restraint member 3, Can be completed. If necessary, it is also possible to adhere the plate member 2 and the restraint member 3 so that the composite plate can be provided without interruption in the cold rolling step to be described below.

On the other hand, with respect to the kind of the magnesium alloy constituting the plate and the type of the steel constituting the constraining member, the type is not particularly limited as long as the steel can be rolled at a desired reduction ratio and its stiffness is larger than the magnesium alloy stiffness. If the rigidity of the steel constituting the restraining member is greater than the rigidity of the magnesium alloy constituting the plate, the restraining member is subjected to cold rolling in the step (b) described below by applying compressive stress against the TD direction of the plate during rolling of the composite plate. It is effective in improving the rolling property of the plate material.

Step (b) of the production process according to the present invention can be carried out using a known rolling method using a known rolling mill as cold rolling the composite sheet prepared in the step (a).

In this step, cold rolling is performed using the composite plate described above in detail, so that a magnesium alloy plate which is to be hot rolled at a sufficiently high temperature of 230 DEG C or more in order to avoid occurrence of cracks in the past, For example, a plate material having a sound microstructure can be produced even through cold rolling at a temperature of from room temperature to 100 deg.

Specifically, a constraining member made of steel compressively stresses the magnesium alloy sheet in the TD direction during the cold rolling process to prevent the occurrence of edge cracks and to form tensile twinning, It is possible to manufacture a high-quality plate material through cold rolling.

Therefore, according to the present invention, it is possible to manufacture a plate material of high quality through cold rolling even for a magnesium alloy material, which had to be hot-worked inevitably due to low ductility at room temperature and low workability. It is possible to prevent the shortening of the lifetime of the roll due to the heating, and the production cost can be reduced according to the energy consumption, so that it is possible to manufacture the plate of excellent quality economically.

The step (c) of the manufacturing method according to the present invention is a step of separating the cold rolled plate made of the magnesium alloy from the cold rolled composite sheet obtained in the step (b), wherein the magnesium alloy cold rolled plate can be separated from the constraining member If so, there is no limit to the means or method.

On the other hand, the magnesium alloy cold-rolled sheet produced by the above-mentioned method has remarkably improved formability at room temperature compared with the sheet before cold rolling, thereby making it possible to economize and simplify the process in various industrial fields such as automobiles and airplanes It is expected that the application field of magnesium alloy sheet will be greatly expanded.

Specifically, the magnesium alloy cold rolled plate having improved moldability according to the present invention is characterized in that the limit dome height (LDH) value at room temperature is increased by 20% or more before the cold rolling process.

Here, the LDH is an index widely used for evaluating the press performance among the formability of the plate material. The LDH is an index widely used to fix the outer circumferential portion of a disk specimen of a certain standard with a constant force and to deform at a constant speed using a spherical punch having a constant diameter. When the specimen is broken, it is defined as the deformed height of the specimen as the punch moves until the specimen breaks.

Hereinafter, the present invention will be described in detail on the basis of embodiments. The presented embodiments are illustrative and are not intended to limit the scope of the invention.

<Examples>

A sample of hot-rolled commercial AZ31 (Al: 3 wt%, Zn: 1 wt%, Mn: 0.3 wt%, Mg: balance) plate having a thickness of 1.2 mm was processed to obtain a specimen having a size of 90 mm x 12 mm x 1.2 mm The specimen was inserted into a concave portion formed across both ends of one side of hot-rolled steel (C: 0.12 wt%, Si: 0.20 wt%, Mn: 0.87 wt%, Fe: A composite sheet having the shape and structure shown in Fig.

Next, immediately after homogenization of the composite sheet at a low temperature of 100 DEG C for 20 minutes, the homogenization was carried out under the conditions of a rolling temperature of 100 DEG C and a rolling speed of 2 rpm, which were the same as the homogenization temperature, using a rolling mill having a roll diameter of 250 mm After cold rolling at a reduction ratio of 3%, a magnesium alloy specimen was separated from the rolled composite sheet.

2 (a) to 2 (c) are graphs showing the relationship between the three points (the center, the quarter, and the edge) of the specimen along the TD direction in a plane perpendicular to the RD direction in the specimen manufactured in this embodiment The microscopic photographs of the microstructures showed that the frequency of twinning was increased with the direction of the specimen.

<Comparative Example>

A sample of hot-rolled commercial AZ31 (Al 3 wt%, Zn 1 wt%, Mn 0.3 wt%, Mg balance) plate having a thickness of 1.2 mm was processed to produce specimens having dimensions of 90 mm x 12 mm x 1.2 mm.

< Experimental Example > In the Examples and Comparative Examples  Measurement of strength and formability of prepared specimens

Tensile strength and formability of the magnesium alloy plate specimens prepared in Examples and Comparative Examples were measured as follows.

That is, a tensile test specimen having a gauge length of 25 mm, a gauge width of 6 mm and a thickness of 1.16 mm was prepared for a tensile test, and a tensile test was conducted at a strain rate of 0.001 s ^-1 at 100 ° C. and room temperature, The results are shown in Figs. 3 (a) and 3 (b), respectively.

Then, a disc-shaped specimen having a diameter of 50 mm and a thickness of 1.16 mm was prepared for the LDH test, and the specimen was inserted between the upper die and the lower die of the LDH test apparatus, and then the specimen was fixed with a force of 15 kN. The specimen was subjected to deformation at a rate of 0.02 mm / sec using a 25 mm diameter spherical punch to measure the deformation height until fracture of the specimen. The results are shown in FIG.

The tensile strength of the cold-rolled magnesium alloy specimen prepared in the example and the tensile strength of the magnesium alloy specimen prepared in the comparative example were 275 MPa and 272 MPa, respectively, as shown in Fig. 3 (a) MPa. On the other hand, the yield strength was increased to 187 MPa and 144 MPa, respectively. On the other hand, according to FIG. 3 (b) showing the tensile test result at room temperature, The tensile strengths of the specimens prepared in the comparative examples were 308 MPa and 293 MPa, respectively, and the yield strengths were 240 MPa and 177 MPa, respectively. Thus, at room temperature, the specimens prepared in the examples were higher in yield strength Of course, the tensile strength is remarkably improved.

From FIG. 4, it can be seen that the cold-rolled magnesium alloy specimen produced in the example exhibits remarkably improved moldability as much as 23% as compared with the magnesium alloy specimen prepared in the comparative example.

1: composite plate
2: Sheet
3:

Claims (8)

(a) a plate made of a magnesium alloy, and a restraining member made of steel and suppressing plastic deformation in a transverse direction (TD) of the plate during rolling, The method comprising: preparing a composite plate having a concave portion formed on both sides of the concave portion;
(b) cold rolling the composite sheet at a temperature of from room temperature to 100 ° C; And
(c) separating a cold-rolled plate made of a magnesium alloy from the cold-rolled composite sheet obtained in the step (b), and a step of separating the cold-rolled plate made of a magnesium alloy from the cold- . delete The method according to claim 1, wherein both sides of the plate made of magnesium alloy are in contact with the restraining member without being separated from each other. The method of claim 1, wherein the plate made of magnesium alloy in step (a) has a composition of Al 3% by weight, Zn 1% by weight, Mn 0.3% by weight and Mg balance and is hot rolled AZ31 plate A method of producing a magnesium alloy cold rolled plate having moldability, yield strength and tensile strength. delete The method according to claim 1, wherein the plate member and the restraining member are bonded and bonded to each other in the composite plate, wherein the plate member and the restraining member are bonded to each other. A magnesium alloy cold rolled plate having improved formability, yield strength and tensile strength, produced by the production method according to claim 1, 3, 4 or 6. The magnesium alloy cold rolled plate according to claim 7, wherein the value of the critical dome height (LDH) is increased by at least 20% as compared to that before cold rolling.

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