KR100878447B1 - Welding method using nanoparticles to suppress deformation during welding - Google Patents

Abstract

The present invention relates to a method of welding using nanoparticles during welding in order to suppress deformation such as cracking and torsion.

The present invention implements a new type of welding method in which nanoparticles are inserted into a welding rod, a welding base material, and a welding part when welding two materials, thereby reducing thermal conductivity during welding, thereby lowering thermal diffusivity. As a result, sufficient time for lattice matching between the molten metal and the weld metal can be secured, and thus, a method of welding using nanoparticles that can reduce cracking or torsional deformation of the weld structure after welding is provided.

The welding method provided by the present invention can increase the stability and durability of all mechanical parts used for welding by suppressing cracking and torsional phenomena occurring during welding, thereby improving the mechanical strength of the welded portion and the stability of the welded structure.

Welding, welding rod, torsion, crack, thermal conductivity, thermal diffusivity, nanoparticles

Description

Nanostructured welding method for reducing deformation

1 is a photograph showing a welding surface after a typical welding

2 is a schematic view showing a method of welding using nanoparticles according to an embodiment of the present invention.

Figure 3 is a schematic diagram showing the thermal phenomenon of the welding portion in the method of welding using nanoparticles according to an embodiment of the present invention.

Figure 4 represents the thermal conductivity of the nanoparticles as claimed findings that it is possible to lower the thermal conductivity of the solid, In _{0 .53} Ga _{0 .47} As alloy and In _{0 .53} Ga _{0 .47} As alloy nanoparticles into a ErAs graph

<Description of the symbols for the main parts of the drawings>

10: electrode 20: electrode

30: base material 40: molten metal

50: nanoparticle 60: alloy atom

The present invention relates to a method of welding using nanoparticles to suppress deformation during welding, and more particularly, by reducing the thermal conductivity by using nanoparticles during welding, and eventually lowering the thermal diffusion rate, crack or torsional deformation It relates to a welding method that can reduce the.

Generally, as a method of joining metal materials of the same type or different types, there are largely divided welding methods and welding methods.

Among them, the welding method is a method in which a metal material is heated and melted at a joint to rearrange and bond atomic bonds of two different materials, such as arc welding, gas welding, and thermite welding.

The most representative TIG (Tungsten Inert Gas) welding of arc welding is arc welding between the tungsten electrode and the base metal with the highest melting point, and welding to protect the welding part with Ar gas to prevent oxidation and nitriding during welding.

In the normal welding including the TIG welding as described above, a lot of cracks are generated on the welding surface.

For example, FIG. 1 is a photograph showing a cross section of a welding surface. Here, a welding wire 1 (Filler wire, filler metal) is used.

It can be seen that the cracks generated in the weld surface as shown in the picture A to D, in particular, in the case of the picture D can be seen that a lot of cracks generated on the weld surface.

The main reason is that the molten metal cools rapidly and there is not enough time to become a lattice match with the welded metal, causing cracks and twists.

In other words, due to the high thermal diffusivity of the electrode during welding, the time for the lattice to match each other is insufficient, resulting in cracking or torsional deformation, resulting in a decrease in the mechanical strength or stability of the weld.

Accordingly, the present invention has been made in view of the above, and an object of the present invention is to implement a new type of welding method in which nanoparticles are put in a welding rod, a welding base material, and a welding part when welding two materials, thereby improving thermal conductivity during welding. By reducing, eventually lowering the thermal diffusion rate, a sufficient time for lattice matching between the molten metal and the weld metal can be obtained, thus providing a method of welding using nanoparticles that can reduce cracking or torsional deformation. have.

The present invention for achieving the above object is to put the nanoparticles when welding two materials, the nanoparticles in the molten metal scatters the energy carriers (phonon, electrons) to reduce the thermal conductivity, it is possible to eventually lower the thermal diffusion rate It is done.

In addition, the present invention is characterized in that the nanoparticles are put in a welding rod, or put in a welding portion of a welding base material, or put in a welding base material to weld.

Hereinafter, a method of welding using nanoparticles according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Figure 2 is a schematic diagram showing a method for welding using nanoparticles according to an embodiment of the present invention.

The welding method using the nanoparticles provided in the present invention can be applied to various types of welding methods performed at temperatures higher than the melting point of the base material, such as arc welding, gas welding, thermite welding, and the like. In the example, a method using nanoparticles for Tungsten Inert Gas (TIG) welding will be described as an example.

The welding method of the present invention is a method that can reduce the deformation, such as cracks and twisting by gradually cooling the molten portion of the metal by using insoluble nanoparticles.

To this end, as shown in FIG. 2, the base material 30 to be welded, for example, an aluminum alloy or a copper alloy, an electrode 20 for performing a welding operation, and a welding rod fused to a molten part ( 10) is provided, the welding proceeds with the arc generation.

Here, reference numeral 40 denotes a molten metal.

The form of using the nano-particles during welding may be a form of using the nano-particles in the electrode, the form of the nano-particles in the welding site of the welding base material, the nano-particles in the welding base material.

By inserting and using nanoparticles during welding, the thermal diffusion rate of the molten portion, for example, the molten metal portion, can be dramatically lowered. Consequently, cracks or torsional deformations occur due to excessive residual thermal stress, which is a problem of conventional welding. Can be reduced.

For example, the time taken for the molten metal to cool down can be calculated by the following equation.

t = √l ² / α = √l ² / k / ρc _p

Where l is the length of the molten site and α is the thermal diffusivity (m ² / s).

The thermal diffusion rate is a value obtained by dividing the thermal conductivity k by the heat capacity.

It has been suggested experimentally and theoretically by the present inventors that nanoparticles can be added to lower the thermal conductivity of materials.

The present invention aims to reduce thermal stress and torsion during welding by lowering the thermal diffusivity by focusing on these prior studies.

Therefore, as can be seen in the above equation, if the thermal conductivity is lowered, the thermal diffusion rate is lowered, so that the molten portion cools down slowly, and eventually the lattice is enough time to match each other, so that the cracks are reduced.

If this is described in more detail, as shown in Figure 3, here shows the thermal phenomenon that occurs when the nanoparticles are inserted during welding, when there is a temperature difference in the site of melting (HOT → COLD) at the site of melting A thermal energy carrier called a phonon (phonon) is generated, and in this case, the nanoparticles 50 or the alloy atoms 60 can scatter the phonons to lower the thermal conductivity of the molten portion, thereby reducing the thermal diffusion rate.

For example, the thermal conductivity is expressed by the following equation.

k = 1 / 3C _v vl

Where C _v is the heat capacity, v is the speed of sound, and l is the mean free path.

As the nanoparticles scatter the phonons, the average free path of the phonons is shortened.

Since the thermal conductivity is proportional to the free path, the thermal conductivity is lowered and eventually the thermal diffusion rate is lowered.

Therefore, by lowering the high thermal conductivity of the molten portion that causes cracking or torsional deformation, it is possible to reduce the cracking or torsional deformation by lowering the thermal diffusion rate.

In the welding method according to an embodiment of the present invention, the nanoparticles may be applied to any one as long as the material is different from a welding rod or a welding base material, and nanoparticles having a small size are preferable.

In addition, in the welding method according to an embodiment of the present invention, by applying nanoparticles having a higher melting point than a welding rod and a welding base material, the welding method does not melt even when mixed with the welding rod or the welding base material.

For example, when a base material is aluminum, melting | fusing point of aluminum will be about 500-600 degreeC.

Therefore, when the ceramic nanoparticles having a high melting point are inserted, they do not melt during welding.

On the other hand, in order to apply nanoparticles, by using powder metallurgy in the welding rod can be produced by adding nanoparticles when manufacturing, the welding part can be put together with the solution containing nanoparticles in the welding, Before welding, the nanoparticles can be put in the site before welding.

At this time, the concentration of the nanoparticles may be about 1 to 10%.

Figure 4 represents the thermal conductivity of the nanoparticles as claimed findings that it is possible to lower the thermal conductivity of the solid, In _{0 .53} Ga _{0 .47} As alloy and In _{0 .53} Ga _{0 .47} As alloy nanoparticles into a ErAs It is a graph.

4, the data herein shows the measured thermal conductivity and electrical properties for being placed for example ErAs particles of nanoparticles, for example, the _{In 0 .53 Ga 0 .47 As alloy} .

It can be seen that by putting the nanoparticles in the solid as described above, the thermal conductivity can be changed while maintaining the electrical properties.

In (a), the thermal conductivity of the materials with and without nanoparticles (in this case, ErAs nanoparticles) was compared.

In (a), points represent experimental data and lines represent theoretical analysis.

As can be seen in the figure, the thermal conductivity was lowered by about two times at room temperature by adding nanoparticles.

In this case, the concentration of nanoparticles is only 0.3%.

(b) shows the normalized properties.

Application of the nanoparticles loaded ErAs In _{0 .53} Ga _{0 .47} As alloy is a thermoelectric semiconductor.

The performance of thermoelectric semiconductors can be expressed by the thermoelectric figure of merit, ZT = (S ² σT) / k.

In order to improve the performance of thermoelectric semiconductors, ZT should be increased.

Here, (S ² sigma) is a power factor, and represents an electrical property of the thermoelectric semiconductor.

As shown in (b), the thermal conductivity decreased by almost half, but the electrical power factor was almost unchanged, and the crystal structure of the solid did not change as shown in the TEM diagram of (a).

As a result, ZT doubled.

In other words, the thermal conductivity can be reduced by 2 times while maintaining the electrical properties and crystal structure.

As described above, the present invention can significantly lower the thermal diffusivity by lowering the thermal conductivity using nanoparticles during welding, thereby increasing the mechanical strength of the welded portion and ensuring the stability of the welded structure. There is an effect that can greatly improve the stability and durability of all mechanical parts used for welding, such as ships.

Claims (4)

When welding between two alloying base materials between aluminum alloys or copper alloys, nanoparticles are put in, so that the nanoparticles in the molten metal can scatter energy carriers (phonon, electrons) to lower the thermal diffusion rate. Welding by using nanoparticles. The method of claim 1, wherein the nanoparticles are welded by placing them in a welding rod. The method according to claim 1, wherein the nanoparticles are welded by placing the nanoparticles in a welded portion of the welding base material. The method of claim 1, wherein the nanoparticles are welded by being placed in a welding base metal.

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