KR20130001511A - Forming method of high-strength magnesium blanks employing the tailored softening process, and magnesium plate thereby - Google Patents

Abstract

PURPOSE: A processing method for molding a high strength magnesium board through a local softening process by rapid heating, and a molded high strength magnesium board component by the same are provided to apply a magnesium board component to a transporting machine, thereby maintaining a high mechanical strength, and reduce the weight. CONSTITUTION: A processing method for molding a high strength magnesium board through a local softening process includes: a local softening step(step 1) for locally improving the elongation ratio by applying heat treatment to a region where the molding occurs in high strength magnesium board(H-temper); and a step(step 2) of applying a molding process to the locally softened magnesium board to step 1. The local softening at step 1 is accomplished at a temperature of 110 to 400°C. The local softening at step 1 is suitable for a continuous process(In-line) since a rapid heat treatment is accomplished for 1 to 120 seconds. The rapid heat treatment at step 1 is accomplished by one heating element which is chosen from a group of a high-frequency wave, a laser, and a halogen lamp.

Description

Forming method of high strength magnesium sheet by localized softening process by rapid heating and forming high strength magnesium sheet molded part formed by this process {Forming method of high-strength magnesium blanks employing the tailored softening process, and magnesium plate hence}

The present invention relates to a molding process of a high strength magnesium sheet through a local softening process and a high strength magnesium sheet molded part molded thereby.

Recently, the government's policy and R & D direction has been promoted in order to meet the social demand for efficient use of energy resources and reducing environmental pollution, which are facing exhaustion. In particular, regulations to reduce environmental pollution caused by carbon dioxide and various exhaust gases, which are the main causes of global warming, have been enacted in stages, and research and development for efficient use of limited energy resources are being actively conducted.

In order to reduce environmental pollution and improve the efficiency of energy resource utilization, the technology to make the weight of transportation equipment lightweight by replacing the existing steel materials by applying lightweight materials to various transportation equipment is considered as the core technology. In order to achieve the purpose, magnesium has a specific gravity less than 1/4 of iron and high specific strength is attracting attention as the most powerful lightweight material.

On the other hand, compared to the production process of magnesium casting material which is technically mature, the manufacturing technology of magnesium plate parts using plastic processing process is very weak in technical foundation, and recently, R & D has started in the world. It is in the early stages of technology development. Therefore, in order to revitalize the domestic parts and materials industry and to apply high-value-added magnesium plate parts to the automobile industry and the electronics industry, it is urgently required to develop a variety of magnesium plate forming processes and parts manufacturing technology.

Magnesium material with Hexagonal Close Packed (HCP) has very poor formability at room temperature, so it is a common metal sheet forming process such as stamping, press forging, deep drawing, etc. It is impossible to manufacture the plate molded parts through the steel molding, so the hot forming method should be applied. However, molding at a high temperature causes a decrease in strength of the material after molding, and thus, there is an urgent need for development of a molding method at a low temperature or room temperature to maintain the strength of the raw material.

Therefore, the inventors of the present invention while studying the method to improve the formability while maintaining the overall strength of the molded part of the magnesium material at the level of strength before molding, during the manufacturing of magnesium plate material does not perform the last annealing after rolling to have a high strength Locally rapid heating of only the parts that need to be molded into magnesium plate material (H-temper) to improve elongation, without maintaining or decreasing the strength of the parts that do not require molding or need small amount of molding to the strength of the raw materials Development of a magnesium plate forming processing method capable of local molding has completed the present invention.

SUMMARY OF THE INVENTION An object of the present invention is to provide a molding method of a high strength magnesium sheet through a local softening process by rapid heating and a high strength magnesium sheet molded part molded thereby.

In order to achieve the above object, in the present invention, localized softening step (step 1) of locally increasing the elongation by rapidly heat-treating only a portion of the high-strength magnesium plate (H-temper) that requires molding; And

Provided is a magnesium plate forming process through a local softening process comprising the step (step 2) of forming a locally softened magnesium plate in step 1.

Forming process of high strength magnesium sheet material through local softening process by rapid heating according to the present invention and the high strength magnesium plate molded part molded thereby are to selectively localize only the portion that needs to be molded to increase the elongation and thereby formability In this case, the processing is not required or the amount of processing is small and the portion to maintain high strength has no effect of maintaining the initial mechanical properties of the magnesium plate before molding is performed only by no heating or minimal heating. In addition, by forming simultaneously with the local heating, there is an additional effect of improving the mechanical properties of the molded part by utilizing the dynamic recrystallization phenomenon generated in the high-strength magnesium plate microstructure by the action of heat and deformation. Accordingly, in the high strength magnesium sheet according to the present invention, the site where the heating is not maintained maintains the mechanical properties of the raw material and the site where the heating is locally improves the formability, thereby forming the desired part shape. The magnesium sheet molded part according to the invention maintains the excellent mechanical properties of the initial high strength magnesium sheet. Therefore, by applying the magnesium plate molded parts according to the present invention to the transport equipment, while maintaining a high mechanical strength and exhibits the maximum weight loss effect, it is possible to save energy through the fuel economy of the transport equipment.

1 is a photograph showing specimen deformation before and after molding;
2 is a graph measuring the Vickers hardness value change after the test piece is deformed;
3 is a photograph observing the microstructure after the specimen is deformed.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention

A local softening step (step 1) of locally increasing the elongation by heat-treating only a portion of the high-strength magnesium plate (H-temper) that requires molding; And

Provided is a molding method of a magnesium sheet through a local softening process comprising the step (step 2) of forming a locally softened magnesium sheet in step 1.

Hereinafter, the present invention will be described in detail step by step.

In the molding method of the magnesium plate according to the present invention, step 1 is a step of local softening step of locally increasing the elongation by rapidly heat-treating the high strength magnesium plate (H-temper) only to the portion requiring molding. In the existing magnesium sheet forming process, the entire sheet is heated and molded to form a part that does not require molding or requires a small amount of molding. Accordingly, the mechanical properties are deteriorated due to the effect of annealing and softening the entire sheet. There was a problem of losing the high strength of the material. However, in the molding process according to the present invention, by heating only the portion of the magnesium plate raw material that needs to be molded, while maintaining the mechanical properties of the portion that does not require molding, while improving the elongation of the portion requiring the forming of the plate to improve the formability Can be.

The rapid heating heat treatment of step 1 may be performed by heating using a heat source such as a high frequency, a laser, and a halogen lamp, and preferably, may be performed through a warm forming mold in which a heating element is inserted only in a molding part. have.

At this time, the rapid heat treatment for the local softening is preferably carried out at a temperature of 150 to 400 ℃. If the rapid heat treatment is performed at less than 150 ℃, there is a problem that can not obtain the desired level of formability, if the rapid heat treatment is performed at a temperature exceeding 400 ℃ formability increases but mechanical problems are excessively deteriorated have.

The rapid heat treatment is performed within 1 to 120 seconds, which is suitable for the sheet forming process in an in-line process. The longer the rapid heat treatment is performed, the more delayed the forming process of the magnesium plate material, and thus the productivity decreases. However, in the molding process according to the present invention, by softening the magnesium plate locally through rapid heat treatment, production through a continuous process is possible, and productivity may be improved.

In the molding method of the magnesium plate according to the present invention, step 2 is a step of forming the locally softened magnesium plate in step 1. The molding process of step 2 is to be processed through a plastic deformation process such as stamping, press forging, etc. according to the field and the degree of processing to apply the plate material, there is no particular limitation.

Molding of the step 2 may be carried out at a temperature of room temperature to 400 ℃ or less, most preferably at room temperature. By performing the molding in step 2 at a temperature in the above range it is possible to maintain the mechanical properties while performing the molding of the magnesium plate. In addition, by utilizing the dynamic recrystallization phenomenon caused by the combined effect of heat and deformation in the above temperature range it can be obtained an additional effect that the mechanical properties of the molded part is improved. Accordingly, the magnesium plate formed by the present invention is characterized by excellent strength.

Molding method of the magnesium plate according to the present invention can be carried out simultaneously by the local softening by the rapid heat treatment of step 1 and the molding process of step 2 by a mold including a heating element, thereby a continuous process This improves productivity. In this case, the heat source of the mold may be a high frequency, a laser, a halogen lamp and the like, but is not particularly limited thereto.

In addition, the present invention provides a molded magnesium molded part through the molding process.

Magnesium and magnesium alloy sheet material having a dense hexagonal lattice (HCP) crystal structure is formed using a conventional plastic working process applied to carbon steel having a body-centered cubic (BCC) crystal structure and aluminum alloy having a face-centered cubic (FCC) crystal structure. This is difficult. This is because the slip system acting on external stress is extremely limited due to the low symmetry characteristic of the dense hexagonal crystal structure and the large anisotropy of the rolled sheet material, which is shown by the preferential arrangement of the dense surface parallel to the rolling direction during the rolling process. In order to solve such a difficult formation of magnesium plate material, forming or processing at high temperature where the non-dense surface slip system is activated to improve moldability is inevitable, and thus there is a problem that the mechanical strength of the raw material is degraded by forming at high temperature. .

However, the magnesium plate molded part according to the present invention selectively improves the moldability by heating only the portion that needs to be molded, and the portion that does not need to be heated does not heat to maintain the mechanical properties of the original magnesium plate. And molding is performed. This solves the conventional problem that the mechanical properties are degraded by applying high-temperature heat to the whole plate to process the magnesium plate, there is an effect that can improve the formability and maintain or improve the mechanical properties of the magnesium plate.

<Dense hexagonal lattice crystal structure>

On the other hand, the magnesium plate molded part according to the present invention can be used as a vehicle body or an electronics case of a transportation device. By using the magnesium plate molded part according to the present invention as a large-area part of the transporting device, it is possible to reduce the weight of the transporting device, thereby improving fuel economy and thus saving energy. In addition, by applying to electronic products such as notebooks, it is possible to obtain a lightening effect of the electronic products and to improve the strength of the electronics case to protect from external impact.

For example, large-area parts such as a car's ceiling are subjected to changes in dimensions and shapes due to buckling caused by the difference in coefficient of thermal expansion in the heat treatment process after painting, in order to minimize 200 MPa Yield strength above is required. It is difficult to maintain such high yield strength values by the conventional method of heating the entire sheet to be processed. However, when the magnesium sheet formed by the present invention is applied to the vehicle body, it is preferable to increase the elongation only at the edge of the sheet. By processing the main body, it is possible to maintain the yield strength value to be applied to the vehicle body and to process it in the desired form, and to improve fuel efficiency and energy saving effect due to the weight reduction due to the application of magnesium plate.

Hereinafter, the present invention will be described in detail through examples. However, the following examples are merely to illustrate the present invention, but the content of the present invention is not limited by the following examples.

Example 1 Local Molding of High Strength Magnesium Alloy Plate 1

Step 1: After processing a 1 mm thick H-Temper High Strength Magnesium Alloy (AZ31-H24) sheet into 150 mm long and 15 mm wide specimens, the center of the specimen was heated to 150 ° C. at a heating rate of 40 ° C./sec using an electrical resistance heating method. A local softening heat treatment was performed to heat to and hold for 60 seconds. At this time, temperature was measured using the thermocouple spot-welded to the test piece to the left-right 40mm from the center which heats.

Step 2: The locally softened magnesium sheet test specimen in Step 1 was uniaxially stretched at a crosshead speed of 0.3 mm / sec to form a high strength magnesium alloy sheet.

Example 2 Local Molding of High Strength Magnesium Alloy Plate 2

A high-strength magnesium alloy plate was formed in the same manner as in Example 1 except that the central portion of the test piece was heated to 200 ° C. in Step 1 of Example 1 to perform a local softening heat treatment.

&Lt; Comparative Example 1 &

Without performing step 1 of Example 1, the high strength magnesium alloy sheet was formed by uniaxial stretching until breakage of the test piece occurred at room temperature.

Experimental Example 1 Measurement of Elongation of Magnesium Sheet

In order to analyze the elongation of the high strength magnesium alloy sheet formed in Examples 1 and 2 and Comparative Example 1, the local elongation was measured from the change in position of the grid indicated on the test piece, and the results are shown in FIGS. .

Heating temperature (℃) Elongation (%)
Local heating
5 mm Elongation (%)
Local heating
10 mm Elongation (%)
Local heating
15 mm Elongation (%)
Local heating
20 mm Example 1 150 66 25 14 7 Example 2 200 87 31 13 6 Comparative Example 1 - 17.8 3 0 0

As shown in FIG. 1 and Table 1, the magnesium plate material uniaxially stretched according to Example 1 and Example 2 of the present invention showed a significant improvement in local elongation, i.e., formability, due to deformation after local heating, It was confirmed that the magnesium plate of Comparative Example 1 which was uniaxially stretched in the heated state did not exhibit the effect of increasing the formability due to local heating and thus the AZ31 H-temper plate exhibited a value of the elongation range of 15-20% as ordinarily shown. Through this, it was confirmed that the molding process according to the present invention can improve the formability of the high strength magnesium sheet.

Experimental Example 2 Vickers Hardness Measurement

After the molding of the high-strength magnesium plate (H-temper) subjected to local heating by Examples 1 and 2 of the present invention was performed, the Vickers hardness value was measured to a position 50 mm away from the local heating source, and the results are shown in FIG. 2. Indicated on

As shown in FIG. 2, the magnesium sheet formed in Examples 1 and 2 is compared with the hardness value of the magnesium plate (O-temper) in which the hardness value of the molded portion is completely annealed by the combined action of local heating and molding. It can be seen that it is very high. This is due to the dynamic recrystallization generated in the microstructure by the combined action of local heating and molding of high strength magnesium plate (H-temper), the addition of the improved mechanical properties of the molding site by using the molding process according to the present invention It was confirmed that an effective effect can be obtained.

Experimental Example 3 Scanning Electron Microscope Analysis

The microstructure of the high strength magnesium plate (AZ31 H-temper) subjected to localized heating by Example 1 according to the present invention was observed by scanning electron microscope, and the results are shown in FIG. 3.

As shown in FIG. 3, dynamic recrystallization occurred extensively in the grain boundary and twin phase interface by the combined action of heating and molding in the molded part of the high-strength magnesium plate subjected to local heating according to Example 1, and thereby grain size. It can be seen that is very small. That is, it was confirmed that the grain refinement due to the dynamic recrystallization phenomenon is caused by softening and forming by local heating according to the present invention, thereby improving the moldability of the part requiring processing and improving the mechanical properties of the molded part after molding. .

Claims (9)

Localized softening step of heat-treating only the portion of the high-strength magnesium plate (H-temper) needs to be processed to locally increase the elongation (step 1); And
Molding method of high-strength magnesium sheet through a local softening process comprising the step (step 2) of forming a locally softened magnesium plate in step 1.
The method of claim 1, wherein the local softening of the step 1 is carried out at a temperature of 150 to 400 ℃ forming method of magnesium plate material through a local softening process.
The method of claim 1, wherein the local softening of step 1 is rapid heat treatment is carried out for 1 to 120 seconds to suit the continuous process (In-line), characterized in that the forming process of magnesium plate material through a local softening process.
The method of claim 1, wherein the heat treatment of the metal of step 1 of the magnesium alloy sheet through a local softening process, characterized in that performed by any one heat source (Heating element) selected from the group consisting of a high frequency, a laser and a halogen lamp. Molding process.
The method of claim 1, wherein the molding process of step 2 is carried out at a temperature of room temperature to 400 ℃ a molding process of the magnesium alloy sheet through a local softening process.
The method of claim 1, wherein the forming process of step 2 is carried out through any one process selected from the group consisting of stamping, pressing forging and bending (bending) process. Forming process of magnesium alloy plate through the process.
The method of claim 1, wherein the local softening of step 1 and the molding process of step 2 are performed simultaneously by a mold including a heating element.
A magnesium alloy molded part molded by the molding process according to any one of claims 1 to 7.
The magnesium molded part according to claim 8, wherein the molded magnesium molded part is applied to a large area part of a transportation device or an electronic product and an electronic device.

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