KR20160041485A - Method of modifying of metal structure using friction stir process - Google Patents

Abstract

According to the present invention, for a method of modifying a metal structure using a friction stir process at low costs, provided is a method of modifying a metal structure using a friction stir process, comprising: a step of preparing a metal material; a step of partially coating a heat conductive composite on a surface portion of the metal material; and a step of forming a region wherein the metal material reacts to the heat conductive composite by friction stirring the metal material partially coated with the heat conductive composite at least once.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of modifying a metal structure using friction stir,

TECHNICAL FIELD The present invention relates to a metal material technology, and more particularly, to a method of modifying a metal structure using friction stir.

Friction Stir Welding (FSW) is a technique in which a non-consumable friction stir tool rotating at high speed is inserted into a material to be bonded and heat generated by friction between the friction stir tip and the material to be bonded and plastic flow of the material to be welded softened by frictional heat Although it is a new welding method which has been developed only by TWI (The Welding Institue) of England in 1991 and has been only twenty years since 1991, solid state welding process which does not involve melting and solidification during the process Then, the welded part is excellent in mechanical properties, and has been attracting attention as a welding process of a light metal such as an aluminum alloy or a magnesium alloy.

Recently, it has been actively used in various angles such as manufacturing of metal matrix composites through modification of base material and dispersion of carbon materials by using friction stir welding (FSP) method applying the principle of friction stir welding .

However, such surface modification of the material by friction stir can only partially change the metallurgical characteristics such as crystal grain structure or redistribution on the powder phase in the material of the same chemical composition. On the other hand, when specific surface properties such as abrasion resistance and corrosion resistance are required on the surface of the material, it is difficult to satisfy the required performance by surface modification by friction stir alone.

On the other hand, although various coating techniques can be applied to the surface modification requiring such a special function, it is difficult to secure the mechanical strength between the member and the coating layer interface, and there is a limit in that molding or machining of the member after coating is difficult.

<Prior Art Literature>

Korean Patent No. 10-0815653 (Mar. 14, 2008)

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for modifying a metal structure using friction stir, which can be implemented at low cost, solving various problems including the above problems. However, these problems are exemplary and do not limit the scope of the present invention.

According to an aspect of the present invention, there is provided a method of manufacturing a metal material, comprising the steps of: preparing a metal material; contacting a surface of the metal material with a friction stir tip; rotating the friction stir tip to an inner region And a step of finely finishing the grain size of the metal material by rotating the friction stir tip before the rotation of the friction stir tip.

Wherein the metal material comprises carbon (C): 0.42 wt% to 0.48 wt%, silicon (Si): 0.15 wt% to 0.35 wt%, manganese (Mn): 0.60 wt (P): 0.030 wt% or less (more than 0 wt%), sulfur (S): 0.035 wt% or less (more than 0 wt%), copper (Cu): less than 0.30 wt% (More than 0 wt%), chromium (Cr): not more than 0.20 wt% (more than 0 wt%), nickel (Ni): not more than 0.20 wt%

In the method of modifying the metal structure using the friction stir, the step of making the grain size of the metal material finer than before the rotation of the friction stir tip may include the steps of: It can only be implemented by rotation.

The method of modifying a metal structure using the friction stirrer includes the step of bringing at least a part of the friction stir tip into the surface of the metal material after the step of contacting the friction stir tip on the surface portion of the metal material .

According to an embodiment of the present invention as described above, a method of modifying a metal structure using friction stir, which can be implemented at a low cost, can be realized. Of course, the scope of the present invention is not limited by these effects.

1 is a flowchart schematically showing a method of modifying a metal structure using friction stir according to embodiments of the present invention.
2 is a view schematically showing a method of modifying a metal structure using friction stir according to embodiments of the present invention.
FIG. 3 is a graph schematically showing the progress speed according to the rotation speed of the friction stir tip according to the embodiments of the present invention. FIG.
4 is a schematic view showing a cross-sectional area of a metal material according to Experimental Example 4 of the present invention.
5 is a view schematically showing a cross-sectional area of a microstructure according to a site of an SM45C steel according to an embodiment of the present invention.
6 is a graph and a photograph showing the deformation rate according to the strength of the metal material according to Experimental Example 4 of the present invention.
7 is a photograph of a specimen on which an impact characteristic test according to Experimental Examples of the present invention is performed.
8 is a photograph schematically showing wear resistance characteristics of Experimental Example 2 and Experimental Example 4 of the present invention.
9 is a graph schematically showing fatigue characteristics of Experimental Example 2 and Experimental Example 4 of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, Is provided to fully inform the user. Also, for convenience of explanation, the components may be exaggerated or reduced in size.

1 is a flowchart schematically showing a method of modifying a metal structure using friction stir according to embodiments of the present invention. 2 is a view schematically showing a method of modifying a metal structure using friction stir according to embodiments of the present invention.

Referring to FIGS. 1 and 2, a method of modifying a metal structure using friction stir according to embodiments of the present invention includes a step of preparing a metal material (S10), a step of contacting a friction stir tip (S30) in which the grain size of the metal material is made finer than before the rotation of the friction stir tip by performing a sintering process to the inner region below the surface portion of the metal material by rotating the friction stir tip .

Further, the method may further include, after the step (S20) of contacting the friction stir tip on the surface of the metal material, at least a part of the friction stir tip is embedded in the surface of the metal material.

For example, as shown in Fig. 2 (a), a metal material 10 is prepared.

Then, as shown in FIG. 2 (b), the friction stir tip 16 can be mounted on the surface portion of the metal material 10. At this time, optionally, at least a portion of the friction stir tip 16 may be recessed from the surface of the metal material 10 into the interior.

Then, as shown in FIG. 2C, the friction stir tip 16 is rotated and moved at a high speed to locally perform plastic working to the inner region below the surface portion of the metal material 10 by the friction stir process Can be performed.

The size of the crystal grains of the metal material 10 is made smaller than before the rotation of the friction stir tip 16, that is, before the friction stir process is performed, by locally performing the plastic working to the inner region below the surface portion of the metal material 10. [ It can be made fine. In addition, the region of the metal material 10 performing the friction stir process locally may be processed physically differently from the region of the metal material 10 where the friction stir process is not performed. This is because the crystal grains of the metal material 10 can be miniaturized by heat generation and recrystallization by strong plastic working.

The area of the metal material 10 subjected to the above-described friction stir process is not subjected to the friction stir process only by the rotation of the friction stir tip 16, that is, the above-described friction stir process, without a separate heat treatment process But may be physically different in properties from the region of the non-metallic material 10.

FIG. 3 is a graph schematically showing the progress speed according to the rotation speed of the friction stir tip according to the embodiments of the present invention. FIG.

Referring to FIG. 3, the friction stir process may be performed in the region A where the defects do not exist, rather than the region B where defects exist, as the friction stir tip is rotated at high speed.

For example, when the rotational speed of the friction stir tip is set to 100 RPM, the friction stir process is performed in the region (B) where defects exist in both of the advancing speeds of 100 mm / min, 200 mm / min and 300 mm / . Also, when the rotation speed of the friction stir tip is set to 200 RPM and 300 RPM, the friction stir process may be performed in a region (B) where defects exist at 100 mm / min and 400 mm / min progress speed, At an advancing speed of 200 mm / min and 300 mm / min, it can be carried out in the region (A) where no defect exists.

On the other hand, when the rotation speed of the friction stir tip is set to 400 RPM, the friction stir process is performed at a speed of 100 mm / min, 200 mm / min, 300 mm / min and 400 mm / (A). &Lt; / RTI &gt;

Generally, in order to mold a mold into a desired shape, a process of heat-treating the entire mold and post-processing it has been required. In addition, problems such as high cost and delay in delivery due to the heat treatment and post-processing have occurred. However, the metal material according to the above-described embodiments of the present invention can omit the heat treatment and post-processing due to local strengthening by the friction stir process.

In addition, it is possible to solve problems such as high cost and delay in delivery time due to the heat treatment and post-processing, and also it is possible to secure a low-cost mold manufacturing technology by using a low-cost metal material.

Wherein the metal material comprises 0.42 wt% to 0.48 wt% of carbon (C), 0.15 wt% to 0.35 wt% of silicon (Si), 0.60 wt% to 0.90 wt% of manganese (Mn) S: not more than 0.035 wt% (more than 0 wt%), Cu: not more than 0.30 wt% (not more than 0 wt%), nickel (Ni): not more than 0.20 wt% (Greater than 0 wt%), and chromium (Cr): less than 0.20 wt% (greater than 0 wt%). For example, SM45C steel, and the like.

Further, the carbon steel material including the SM45C steel may form martensite according to a rapid temperature drop immediately after the friction stir process.

5 is a view schematically showing a cross-sectional area of a microstructure according to a site of an SM45C steel according to an embodiment of the present invention.

Referring to FIG. 5, the SM45C steel material subjected to the friction stir at least once was found to have a grain size smaller than that of the region (b) in which the friction stir processing was performed and the grain in the region (a) Able to know. It can be seen that the crystal grains are refined by heat generation and recrystallization by plastic working of SM45C steel.

It is also confirmed that the pearlite structure observed in the region (b) without the friction stir process is pulverized in the region (a) where the friction stir process is performed. In the outer region (c) subjected to the friction stir process, no coarsening or other phases of the grains were found to degrade the mechanical properties.

On the other hand, the surface of the metal material may further include a thermally conductive composition to improve thermal conductivity. The thermally conductive composition may include at least one of graphite, carbon nanotube (CNT), and graphene, for example. For example, a thermally conductive composition paste containing silicon carbide (SiC) is coated on the surface portion of a metal material (10 in Fig. 2), and then a friction stir tip (16 in Fig. 2) And rotate it.

Further, the thermally conductive composition may contain at least one member selected from the group consisting of, for example, an organic compound, a silicone oil, and a lightweight polymer. The organic compound may be selected from organic compounds having a functional group such as an ether, an alcohol, an amine, an alkyl halide, a carboxyl group, an aldehyde group, a ketone group and an ester group.

Hereinafter, an experimental example to which the technical idea described above is applied will be described in order to facilitate understanding of the present invention. It should be understood, however, that the following examples are for the purpose of promoting understanding of the present invention and are not intended to limit the scope of the present invention.

Experimental Example 1)

Carbon (C): 1.40 wt% to 1.60 wt%, silicon (Si): 0.4 wt% or less (more than 0 wt%), manganese (Mn): less than 0.60 wt% 0.030 wt% or less (more than 0 wt%), sulfur (S): 0.030 wt% or less (more than 0 wt%), chromium (Cr): 11.0 wt% to 13.0 wt%, molybdenum Hardness, tensile properties, impact properties, abrasion resistance and fatigue properties of SKD-11 steel containing 1.2 wt% and vanadium (V) of 0.8 wt% to 1.2 wt% were measured.

Experimental Example 2)

SKD-11 steel having the same composition as in Experimental Example 1 was heat-treated, and then hardness, tensile characteristics, impact characteristics, wear resistance characteristics and fatigue characteristics were measured.

Experimental Example 3)

The hardness, tensile, impact, wear resistance and fatigue properties of SM45C steels were measured.

Experimental Example 4)

The SM45C steel was contacted and rotated on the surface of the SM45C steel, and the SM45C steel was friction-agitated at least one time to plastic work to the area below the surface of the SM45C steel. Then, hardness, tensile properties, impact properties, wear resistance characteristics and fatigue properties were measured.

4 is a schematic view showing a cross-sectional area of a metal material according to Experimental Example 4 of the present invention. The hardness of Experimental Example 4 was measured by measuring the hardness of the portions indicated by the red dot in FIG. 4, and the hardness of Experimental Example 1, Experimental Example 2 and Experimental Example 3 was measured with respect to the hardness measuring region of Experimental Example 4 Table 1 shows the results.

                                                         Unit: HRC Experimental Example 1 Experimental Example 2 Experimental Example 3 Experimental Example 4 Average 17.2 42.8 14.4 34.2

4 and Table 1, the average hardness of Experimental Example 1 was 17.2 HRC, the average hardness of Experimental Example 2 was 42.8 HRC, the average hardness of Experimental Example 3 was 14.4 HRC, and the average hardness of Experimental Example 4 was 34.2 HRC . &Lt; / RTI > It can also be seen that the cases of Experimental Examples 2 and 4 have higher average hardness than those of Experimental Examples 1 and 3.

6 is a graph and a photograph showing the deformation rate according to the strength of the metal material according to Experimental Example 4 of the present invention. The tensile properties according to Experimental Example 2, Experimental Example 3 and Experimental Example 4 are shown in Table 2.

Experimental Example 2 Experimental Example 3 Experimental Example 4 Tensile Strength (MPa) 590 450.26 799.12 Strain (%) 0.8 20.4 7.27

Referring to Table 2 and FIG. 6, in the case of Experimental Example 4, the tensile strength was 799.12 MPa and the strain was 7.27%, which indicates that the tensile strength was superior to that of Experimental Example 2 and Experimental Example 3 .

7 is a photograph of a specimen on which an impact characteristic test according to Experimental Examples of the present invention is performed. The impact characteristics according to Experimental Example 2, Experimental Example 3 and Experimental Example 4 are shown in Table 3. At this time, in Experimental Example 4, the impact characteristics of No. 3 were measured under the same conditions, and Table 3 shows Experimental Examples 4 (1), 4 (2) and 4 (3).

                                                            Unit: J Experimental Example 2 Experimental Example 3 Experimental Example 4 (1) Experimental Example 4 (2) Experimental Example 4 (3) Shock absorption energy (per mm ² )
2.3
0.43
1.58
1.60
1.77

 Referring to Table 3 and FIG. 7, the impact absorption energy per square millimeter was lowest in the case of Experimental Example 3 and 2.3 J, and the values of Experimental Example 2, Experimental Example 4 (1), Experimental Example 4 (2 And 2.3 J, 1.58 J, 1.60 J and 1.77 J in Experimental Example 4 (3), respectively.

8 is a photograph schematically showing wear resistance characteristics of Experimental Example 2 and Experimental Example 4 of the present invention. The abrasion resistance characteristics of Experimental Example 2 and Experimental Example 4 are shown in Table 4.

                                                              Unit: g Psalter Before the test after the test Wear amount Experimental Example 2 150.45 148.86 1.59 Experimental Example 4 140.51 138.63 1.88

Referring to Table 4 and FIG. 8, in the case of Experimental Example 2 (FIG. 8A) and Experimental Example 4 (FIG. 8B), the wear amounts were 1.59 g and 1.88 g, respectively, . &Lt; / RTI >

9 is a graph schematically showing fatigue characteristics of Experimental Example 2 and Experimental Example 4 of the present invention. The fatigue characteristics of Experimental Example 2 and Experimental Example 4 are shown in Table 5.

400 300 250 200 150 Experimental Example 2 7.2 * 10 ⁵ 9.8 * 10 ⁵ 1.3 * 10 ⁶ 3.2 * 10 ⁶ 8.0 * 10 ⁶ Experimental Example 4 1.5 * 10 ⁶ 3.4 * 10 ⁶ 4.9 * 10 ⁶ 7.3 * 10 ⁶ 9.9 * 10 ⁶

Referring to Table 5 and FIG. 9, it can be seen that the fatigue life according to the stress amplitude is better in the case of Experimental Example 4 than in the case of Experimental Example 2. In addition, it can be seen that, in the case of Experimental Example 4 and Comparative Example 2, the case of Experimental Example 4 is judged to be more than 100% as compared with the case of Experimental Example 2.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

10: metal material
16: Friction stir tip

Claims (4)

Preparing a metal material;
Contacting a friction stir tip on a surface portion of the metal material; And
Rotating the friction stir tip to plastic work the surface of the metal material to an area below the surface of the metal material to make the grain size of the metal material finer than before rotation of the friction stir tip;
Wherein the metal structure is modified by friction stir. The method according to claim 1,
Wherein the metal material comprises 0.42 wt% to 0.48 wt% of carbon (C), 0.15 wt% to 0.35 wt% of silicon (Si), 0.60 wt% to 0.90 wt% of manganese (Mn) S: not more than 0.035 wt% (more than 0 wt%), Cu: not more than 0.30 wt% (not more than 0 wt%), nickel (Ni): not more than 0.20 wt% (More than 0 wt%) and chromium (Cr): not more than 0.20 wt% (more than 0 wt%). The method according to claim 1,
Making the grain size of the metal material finer than before rotating the friction stir tip,
Wherein the metal material is implemented only by rotation of the friction stir tip without a separate heat treatment process. The method according to claim 1,
Contacting a friction stir tip on a surface portion of the metal material; Since the
And inserting at least a portion of the friction stir tip internally at the surface of the metal material.

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