JP2013071164A - Coated rotary tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tool for friction stir welding which can provide stable welding strength and welding quality from the early stage of welding start, and which has excellent durability.SOLUTION: The tool 1 for friction stir welding includes a base material 2, and coating layers 3 deposited on a region on the base material, in contact with at least a material to be welded. At least one layer of the coating layers is deposited by the physical vapor deposition method. The coating layer at the region in contact with the material to be welded has a thickness of ≥3 μm and ≤50 μm, and a surface roughness Ra of ≥0.005 μm and ≤0.2 μm.

Description

  The present invention relates to a friction stir welding tool.

  In the United Kingdom in 1991, friction stir welding technology for joining metal materials such as aluminum alloys was established. In the present technology, frictional heat is generated by rotating while pressing a cylindrical friction stir welding tool having a small-diameter protrusion formed at the tip of a joining surface between metal materials for joining. Then, the metal materials are joined together by softening the metal material at the joining portion with this frictional heat to cause plastic flow.

  Here, the “joining portion” refers to a joining interface portion where joining of metal materials is desired by abutting metal materials or placing metal materials in an overlapping manner. In the vicinity of the bonding interface, the metal material is softened to cause plastic flow. When the metal material is stirred, the bonding interface disappears and bonding is performed. Furthermore, since dynamic recrystallization occurs simultaneously in the metal material, the metal material in the vicinity of the bonding interface is atomized by the dynamic recrystallization, and the metal materials can be bonded with high strength (Patent Document 1). ).

  When an aluminum alloy is used as such a metal material, plastic flow occurs at a relatively low temperature of about 500 ° C., so even if a friction stir welding tool made of inexpensive tool steel is used, there is little damage and frequent friction stir It is not necessary to replace the joining tool. For this reason, the friction stir welding technology is low in the cost of joining aluminum alloys, and as a joining method that replaces the resistance welding method in which aluminum alloys are melted and joined, structural components for railway vehicles, automobiles, and airplanes. Has already been put to practical use in various applications.

  At present, the friction stir welding technique is mainly applied to non-ferrous metals that cause plastic flow at a relatively low temperature, such as aluminum alloys and magnesium alloys. Such a friction stir welding technique is superior to the resistance welding method in terms of the cost and time required for joining, the strength of the joined portion, and the like. For this reason, there is a need to apply not only to joining materials that cause plastic flow at low temperatures, but also to joining copper alloys and steel materials that cause plastic flow at high temperatures of 1000 ° C. or higher.

  In order to improve the wear resistance and welding resistance of the friction stir welding tool and to improve the tool life of the friction stir welding tool, it is attempted to coat various coating layers on the surface of the friction stir welding tool. ing. For example, in Japanese Patent Application Laid-Open No. 2003-326372 (Patent Document 1), a surface of a friction stir welding tool is coated with a diamond film on a portion in contact with a material to be joined, thereby increasing the surface hardness. The friction stir welding tool having such a coating layer is welded to the friction stir welding tool even when non-ferrous metal such as aluminum alloy, magnesium alloy, copper alloy is friction stir welded. And has excellent hardness, wear resistance, and a low coefficient of friction, so that long life and good bonding can be achieved.

  Further, in Japanese Patent Application Laid-Open No. 2005-152909 (Patent Document 2), in order to prevent the metal constituting the material to be bonded from adhering to the friction stir welding tool, the surface of the friction stir welding tool is covered. An adhesion preventing film is coated on a portion in contact with the bonding material. This adhesion preventing film is made of any of diamond-like carbon, TiN, CrN, TiC, SiC, TiAlN, and AlCrSiN. In this patent document, in order to prevent cracking of the anti-adhesion film, improve adhesion, and improve wear resistance, a layer made of any one of TiN, CrN, TiC, SiC, TiAlN, or AlCrSiN is used as the base of the anti-adhesion film. Coated.

  Further, in JP 2007-268605 A (Patent Document 3), as a friction stir welding tool for joining steel materials, a base layer made of aluminum oxide or titanium carbide in a region in contact with a material to be joined, A friction stir welding tool coated with a film composed of a surface layer made of titanium nitride covering the surface of the base layer is disclosed. Japanese Unexamined Patent Application Publication No. 2008-030096 (Patent Document 4) discloses a friction stir welding tool in which a film made of aluminum nitride is coated on a region in contact with a material to be bonded. By coating the surface layer made of titanium nitride having low chemical reactivity as in Patent Document 3, or by coating the film made of aluminum nitride having low affinity with the material to be joined as in Patent Document 4, Wear due to a chemical reaction between the bonding material and the friction stir welding tool can be prevented, and the life of the friction stir welding tool can be extended.

JP 2003-326372 A JP 2005-152909 A JP 2007-268605 A JP 2008-030096 A

  In Patent Document 1, a diamond film having a thickness of 1 μm or more and 30 μm or less is coated on the surface of a cemented carbide or silicon nitride substrate. In Patent Documents 3 and 4, the surface of a base material mainly composed of silicon nitride is coated with a coating layer having a thickness of 1 μm to 20 μm using chemical vapor deposition, physical vapor deposition, or thermal spraying. . Patent Document 3 is a coating layer made of aluminum oxide, and Patent Document 4 is a coating layer made of aluminum nitride.

  In order to improve the wear resistance of the friction stir welding tool, it is preferable to increase the thickness of the coating layer to such an extent that the coating layer does not peel off. However, as the thickness of the coating layer is increased with emphasis on wear resistance, the surface roughness of the coating layer becomes rougher, and when joining a soft metal such as aluminum, the material to be joined is the surface of the friction stir welding tool. It becomes easy to adhere to.

  Also, when the friction stir welding tool is new, frictional heat is likely to be generated because the surface roughness of the coating layer is large, but the friction stir welding tool after several spot welding is Since the convex portion is worn and the surface roughness of the surface coating layer of the coating layer is reduced, frictional heat is hardly generated. Therefore, if the welding conditions are set in accordance with the stable surface roughness of the friction stir welding tool after several spot welding, the temperature of the material to be joined is likely to increase in joining from a new tool to several spots, There is a problem that the shoulder of the friction stir welding tool is inserted deeply into the material to be joined, resulting in burrs at the joint or unstable joint strength.

  Further, when a ceramic material such as silicon nitride or aluminum oxide is used for the base material, there is a problem that the temperature of the friction stir welding tool rises too much at the beginning of the joining and breaks due to thermal cracks. On the other hand, when a cemented carbide or a refractory metal is used for the base material, there is a problem that the friction stir welding tool is plastically deformed at the beginning of joining.

  The present invention has been made in view of the above-described situation, and an object of the present invention is to provide a friction stir welding tool capable of obtaining stable joining strength and joining quality from the beginning of joining and having excellent durability. Is to provide.

  The friction stir welding tool of the present invention includes a base material and a coating layer formed on a portion of the base material that contacts at least a material to be joined, and at least one of the coating layers includes: It is formed by a physical vapor deposition method, and the coating layer in the part which contacts a to-be-joined material is 3 micrometers or more and 50 micrometers or less thickness, and is surface roughness Ra of 0.005 micrometers or more and 0.2 micrometers or less. Features.

  It is preferable that the coating layer in the part which contacts a to-be-joined material is 0.01 micrometer or more and 0.1 micrometer or less surface roughness Ra. It is preferable that the coating layer in the part which contacts a to-be-joined material should carry out the grinding | polishing process after forming a coating layer.

  In the coating layer in the portion that contacts the material to be joined, the surface roughness of the side surface of the shoulder portion is preferably larger than the surface roughness of the probe portion.

  In the coating layer in the part that contacts the material to be joined, the surface roughness of the probe part is preferably equal to or greater than the value of the surface roughness at the lower end of the shoulder part.

  The covering layer is selected from the group consisting of one or more elements selected from the group consisting of group IVa elements, group Va elements, group VIa elements, Al, Si and B in the periodic table, and carbon, nitrogen, oxygen and boron. It is preferable that it consists of a compound with 1 or more types of elements. At least one of the coating layers is preferably formed by a sputter deposition method.

  Since the friction stir welding tool of the present invention has the above-described configuration, it exhibits an effect that a stable bonding strength and bonding quality can be obtained from the beginning of bonding and that it has excellent durability.

It is a schematic sectional drawing which shows an example of the tool for friction stir welding of this invention. It is a schematic sectional drawing which shows another example of the tool for friction stir welding of this invention.

Hereinafter, the present invention will be described in more detail.
<Friction stir welding tool>
FIG. 1 is a schematic cross-sectional view of the friction stir welding tool of the present invention. As shown in FIG. 1, the friction stir welding tool 1 of the present invention includes a base material 2 and a coating layer 3 formed on the base material 2. The friction stir welding tool 1 of the present invention having such a configuration can be used extremely usefully for, for example, a wire welding (FSR: Friction Stir Welding) application, a point welding (spot FSW) application, and the like. The friction stir welding tool 1 of the present invention has a shape including a probe portion 4 having a small diameter (diameter 2 mm or more and 8 mm or less) and a cylindrical portion 5 having a large diameter (diameter 4 mm or more and 20 mm or less). When this is used for joining, the member to be joined is joined by rotating the probe portion 4 in a state where it is inserted or pressed into the joining portion of the joined material. In this case, in the wire bonding application, the probe portion 4 is pressed or inserted into two materials to be bonded in a laminated or line contact state, and the rotating probe portion 4 is linear with respect to the laminated or abutted portion. To be joined together. On the other hand, in the point joining application, the probe part 4 that rotates to a desired joining location of two joined materials that are stacked or abutted on each other is pressed, and the probe part 4 is continuously rotated at that location. Join materials together. The friction stir welding tool of the present invention is not limited to non-ferrous metals that cause plastic flow at relatively low temperatures such as aluminum alloys and magnesium alloys, but also to copper alloys and steel materials that cause plastic flow at high temperatures of 1000 ° C or higher. It can also be used.

  FIG. 2 is a schematic sectional view of a preferred embodiment of the friction stir welding tool of the present invention. As shown in FIG. 2, the friction stir welding tool 1 of the present invention preferably has a chuck portion 7 so that the cylindrical portion 5 is chucked by the holder. The chuck portion 7 is formed, for example, by cutting a part of the side surface of the cylindrical portion 5. On the other hand, a portion that comes into contact with the material to be joined at the time of joining processing is called a shoulder portion 6.

  Further, as shown in FIG. 2, the covering layer 3 is preferably formed at least on a portion of the base material 2 that is in contact with the material to be joined at the time of joining processing. Thus, by forming the coating layer 3 in the portion in contact with the material to be joined, heat generated by friction is hardly transmitted to the base material 2. Thereby, the thermal crack and plastic deformation of the base material 2 can be effectively prevented, and the life of the friction stir welding tool can be extended.

<Base material>
As the base material 2 of the friction stir welding tool of the present invention, a conventionally known material known as such a base material 2 for joining processing can be used without particular limitation. For example, cemented carbide (for example, WC base cemented carbide, including WC, including Co, or further including carbonitride such as Ti, Ta, Nb, etc.), cermet (TiC, TiN, TiCN, etc.) High-speed steel, tool steel, ceramics (such as titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, sialon, and mixtures thereof), cubic boron nitride sintered body Examples of the substrate 2 include diamond sintered bodies, hard materials in which cBN particles are dispersed, and the like.

  When a cemented carbide is used as the substrate 2, the effect of the present invention is exhibited even if such a cemented carbide includes an abnormal phase called free carbon or η phase in the structure.

<Coating layer>
In the friction stir welding tool of the present invention, the coating layer 3 may be a single layer or two or more layers. The coating layer 3 may be formed by alternately laminating a plurality of layers having different compound compositions, but is preferably composed of two or more layers. The coating layer of the present invention is preferably formed so as to cover the entire surface of the base material. However, a part of the base material is not covered with the coating layer, or is covered on any part of the base material. Even if the constitution of the layers is different, it does not depart from the scope of the present invention. Note that the coating layer in the present invention is preferably formed at least on the base material as described above, and at least on the part that contacts the material to be joined at the time of joining processing, and may be formed on the entire surface or part of the chuck part. preferable.

  In the present invention, the coating layer preferably has a thickness of 3 μm or more and 50 μm or less. Thus, by setting it as thickness of 3 micrometers or more, abrasion resistance improves and it becomes possible to extend tool life significantly. When the thickness of the coating layer is less than 3 μm, the wear resistance and the antioxidant property of the substrate are deteriorated, which is not preferable. When the thickness is more than 50 μm, the coating layer easily peels due to the compressive stress accumulated in the coating layer. Therefore, it is not preferable. The thickness of the coating layer is more preferably 5 μm or more and 20 μm or less. When the thickness is 5 μm or more, the wear resistance is further improved, and when the thickness is 20 μm or less, the coating layer has an advantage that it is more difficult to peel off and the time required for the polishing process described later can be shortened.

  In the present invention, the “thickness of the coating layer” refers to the thickness of the coating layer at the portion in contact with the material to be joined, for example, the thickness of the coating layer formed on the base material of the friction stir welding tool The thickness of the coating layer at the tip of the probe portion.

  In the present invention, the coating layer in the part that contacts the material to be bonded has a surface roughness Ra of 0.005 μm or more and 0.2 μm or less. With such a surface roughness, frictional heat is appropriately generated during the joining process, the joined material is easily softened, and the strength of the joined portion of the joined material is stabilized. In addition, since the friction stir welding tool does not become too hot, thermal cracks hardly occur and plastic deformation hardly occurs.

  Here, in the present invention, the “surface roughness Ra” is defined by JIS standard B0601. When the surface roughness Ra is less than 0.005 μm, the surface of the coating layer is too smooth, and frictional heat hardly occurs during the joining process, and it takes time to soften the materials to be joined. Moreover, the time required for polishing the coating layer, which will be described later, is too long, which is not preferable. On the other hand, if the surface roughness Ra exceeds 0.2 μm, when the soft metal workpiece is joined, the workpiece will adhere to the surface of the friction stir welding tool, or too much frictional heat will be generated. This is not preferable because the temperature of the bonding material becomes high and burrs are generated at the bonded portion of the material to be bonded or the strength of the bonded portion is not stable. Further, the temperature of the friction stir welding tool rises too much due to frictional heat, causing a thermal crack in the friction stir welding tool, resulting in damage or plastic deformation.

  A preferable range of the surface roughness of the coating layer at the portion in contact with the material to be joined is 0.01 μm or more and 0.1 μm or less. If Ra is 0.01 μm or more, it can be polished in a relatively short time, and if it is 0.1 μm or less, the temperature increase of the friction stir welding tool and the material to be joined is suppressed, so that the joining quality and strength The friction stir welding tool can be prolonged.

  The friction stir welding tool of the present invention stably generates frictional heat from the beginning of welding, and suppresses the occurrence and wear of thermal cracks as a whole, and the side and lower ends of the shoulder portion and the probe portion. It is preferable to make the surface roughness different depending on each part. That is, the surface roughness of the side surface of the shoulder portion is preferably larger than the surface roughness of the probe portion in the covering layer in the portion that contacts the material to be joined, and the surface roughness of the probe portion is the surface of the lower end of the shoulder portion. More preferably, the roughness value is not less than the roughness value. Among the parts in contact with the material to be joined, the lower end of the shoulder portion achieves the purpose of softening the material to be joined by friction with the material to be joined, so that the surface roughness of the coating layer at this part can be minimized. preferable. As a result, frictional heat is stably generated from the beginning of the joining, and the joining strength and joining quality can be stabilized. The probe part is a part for stirring the material to be joined, but if the probe part is excessively heated, the occurrence of thermal cracks and wear tends to progress, so the surface roughness of the coating layer of the probe part is It must be the same as or larger than the lower end of the shoulder. Of the parts that come into contact with the material to be joined, the side surface of the shoulder part is the part that comes into contact with the material to be joined at the end of the joining process, and the contribution of frictional heat generation is compared to the probe part and the lower end of the shoulder part. Since it is low, the surface roughness of the coating layer may be the largest. In addition, since the side surface of the shoulder portion is exposed to the atmosphere at a high temperature during bonding, if the surface is excessively polished to reduce the surface roughness, pinholes are generated in the coating layer, and the base material is oxidized. This is not preferable because Summarizing the above magnitude relationship of the surface roughness, it is preferable that the side surface of the shoulder portion> the probe portion ≧ the lower end of the shoulder portion.

  As the coating layer of the present invention, a coating having a conventionally known composition can be employed without any particular limitation, and from the group consisting of IVa group element, Va group element, VIa group element, Al, Si, and B in the periodic table. It is preferably composed of a compound composed of at least one element selected and at least one element selected from the group consisting of carbon, nitrogen, oxygen, and boron. Thereby, abrasion resistance can be improved further.

Examples of such compounds include carbides, nitrides, carbonitrides, oxides of at least one element selected from the group consisting of group IVa elements, group Va elements, group VIa elements, Al, and Si in the periodic table. And at least one compound selected from the group consisting of carbonate, carbonitride, boronitride, and borocarbonitride. More specifically, TiAlN, Al _x Ti _1-x N, Al _x Cr _{1 -x N, Ti 1-x Si} x N, AlxTi 1-xy Si y N, Al x Cr 1-xy Si y N, TiCN, like Al ₂ O _3, or the like. Since the coating layer having such a composition has high hardness, it has excellent wear resistance and excellent oxidation resistance, so that the life of the friction stir welding tool can be improved. Among the above compounds, Al _x Cr _1-x N, Al _x Ti _1-xy Si _y N, and Al _x Cr _1-xy Si _y N are preferable because they have particularly excellent oxidation resistance.

<Method for forming coating layer>
As described above, at least one of the coating layers of the present invention is preferably formed by a physical vapor deposition (PVD) method. As the PVD method, for example, a vacuum arc vapor deposition method, a sputtering method, or the like can be used. Since the coating layer formed by the PVD method has a compressive stress, the coating layer has high hardness and excellent wear resistance. Moreover, since the coating layer becomes dense, it is excellent in preventing oxidation of the substrate. At least one of the coating layers is more preferably a sputter deposition method among the PVD methods described above. Since the sputter deposition method can form a coating layer having a surface roughness smaller than that of the vacuum arc deposition method, the surface roughness of the roughness of the present invention can be obtained in a shorter polishing process.

<Surface polishing treatment of coating layer>
In the PVD method, molten particles called droplets flying from the raw material target adhere to the surface of the substrate and grow as a nucleus to form a coating layer. The surface roughness of the coating layer formed in this manner increases as the thickness increases. Therefore, in order to realize a thickness of 3 μm or more and 50 μm or less and a surface roughness Ra of 0.005 μm or more and 0.2 μm or less, it is preferable to polish the surface of the coating layer after coating the coating layer.

  As said grinding | polishing processing method, well-known techniques, such as brush grinding | polishing, film grinding | polishing, buff grinding | polishing, and wet blasting, can be used. A soft media blast that injects soft media with abrasive particles onto the surface to be polished by centrifugal force is preferable because it easily polishes the three-dimensional shape uniformly and the edges are not preferentially polished.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these. In addition, the thickness of the coating layer in an Example was measured by directly observing the cross section using a scanning electron microscope (SEM: Scanning Electron Microscope) or a transmission electron microscope (TEM: Transmission Electron Microscope). In the present invention, the element ratio (atomic ratio) of each metal constituting the nitride layer was determined by SDX-attached EDX or EPMA, or TEM-attached EDX or EPMA.

  In the following, the coating layer is formed by the vacuum arc deposition method or the unbalanced magnetron sputtering method (UBM sputtering method), but the coating layer may be formed by, for example, a balanced magnetron sputtering method.

<Examples 1-30, Comparative Examples 1-4>
The friction stir welding tool of each example and each comparative example is provided with a substantially cylindrical column part 5 having a diameter of 10 mm and a height of 20 mm, and projecting concentrically with the column part 5 at the center of the tip of the column part 5. And the probe portion 4. The probe portion 4 has a substantially cylindrical shape with a diameter of 4 mm and a height of 2 mm.

  And as shown in FIG. 2, it has the chuck | zipper part 7 so that the cylindrical part 5 may be chucked by the holder. The chuck portion 7 is scraped from two opposite directions on the side surface of the cylindrical portion 5 at a portion 10 mm from the upper surface of the cylindrical portion 5. When the chuck portion 7 is viewed from the holder side, the length of the chord formed by cutting is 7 mm.

(Production of friction stir welding tool)
First, the base material which has the above tool shapes was prepared as a base material of the tool for friction stir welding. The material of the base material is a cemented carbide made of 6 wt% Co, 15 wt% TaNbC, and the balance of WC crystal grains. The surface of the WC crystal grains is the surface of the base material (interface portion with the coating layer). The one had an average particle size of 3 μm. The base material of the friction stir welding tool was set on a base material holder in the chamber of the film forming apparatus.

(Formation of coating layer)
Next, the friction stir welding tool shown in FIG. 2 was produced by forming a coating layer on the probe portion and the shoulder portion 6 so as to be in direct contact with the base material. Specifically, a coating layer having the composition shown in the “Composition” column of Table 1 was formed by the method shown in “Coating method” of Table 1 with the thickness shown in the “Thickness” column of Table 1.

In Examples 1-16 and Comparative Examples 1-4, as shown in Table 1, the coating layer was formed using the vacuum arc evaporation method. The alloy target of the metal component of the coating layer was set in the vacuum arc deposition apparatus. For example, in Example 1, in order to form a coating layer made of Al _0.57 Ti _0.38 Si _0.05 N, an alloy target having a composition of Al _0.57 Ti _0.38 Si _0.05 was set. Then, the inside of the chamber of the vacuum arc vapor deposition apparatus is depressurized by a vacuum pump, and the temperature of the substrate is heated to 450 ° C. by a heater installed in the apparatus, and the pressure in the chamber is 1.0 × 10 ^−4. Vacuuming was performed until Pa was reached.

  Next, argon gas is introduced to maintain the pressure in the chamber at 3.0 Pa, the substrate bias power supply voltage of the base material is gradually increased to −1500 V, and the W filament is heated to emit thermoelectrons. The surface of the substrate was cleaned for 15 minutes. Thereafter, argon gas was exhausted.

Next, N ₂ gas was introduced so that the pressure in the chamber was 3 Pa, and the substrate DC bias voltage was set to −50V. An Al _0.57 Ti _0.38 Si _0.05 target was ionized with an arc current of 200 A and reacted with N ₂ gas to form a coating layer made of Al _0.57 Ti _0.38 Si _0.05 N on the probe and shoulder portions of the substrate.

In Example 16, Ti was used as a metal target, and a coating made of TiCN was introduced by introducing gas into the chamber so that the N ₂ gas partial pressure was 1.5 Pa and the CH ₄ gas partial pressure was 1.5 Pa. A layer was formed.

In Examples 17-30, as shown in Table 1, the coating layer was formed using the unbalanced magnetron sputtering method. For example, in Example 17, an alloy target having a composition of Al _0.57 Ti _0.38 Si _0.05 was set to form a coating layer made of Al _0.57 Ti _0.38 Si _0.05 N.

Then, the inside of the chamber of the vacuum arc vapor deposition apparatus is depressurized by a vacuum pump, and the temperature of the substrate is heated to 450 ° C. by a heater installed in the apparatus, and the pressure in the chamber is 1.0 × 10 ^−4. Vacuuming was performed until Pa was reached.

  Next, argon gas was introduced, the pressure in the chamber was maintained at 3.0 Pa, the DC bias voltage was gradually increased to −1000 V, and the surface of the substrate was cleaned for 15 minutes. Thereafter, argon gas was exhausted.

Then, Ar gas and N ₂ gas as the pressure in the chamber becomes 0.6 Pa 1: 1 in introduced at a rate ratio was the substrate DC bias voltage -90 V. A DC sputtering power of 4500 W was applied to the target for ionization and reaction with N ₂ gas to form a coating layer made of Al _0.57 Ti _0.38 Si _0.05 N on the substrate.

(Surface polishing of coating layer)
Next, the surface of the coating layer was polished using the method shown in “Polishing Method” in Table 1. Specifically, in Examples 1 to 10, 14, 17 to 26, and Comparative Examples 1, 2, and 4, the surface of the coating layer was polished by soft media blasting using media with diamond abrasive grains of # 3000. did. The surface roughness of the coating layer was adjusted by the polishing time. However, in Comparative Example 2, since the thickness of the coating layer was too thick at 52.4 μm, the stress of the coating layer was high and the coating layer was peeled off by the surface polishing treatment.

In Examples 11 to 13, 15, and 16, the surface of the coating layer was polished by a brush wrap using a brush with diamond abrasive grains of # 3000. The surface roughness of the coating layer was adjusted by the polishing time. In Examples 27 to 30 and Comparative Example 3, the coating layer was not polished. The surface roughness of the coating layer on the probe portion, the lower end of the shoulder portion, and the side surface before and after surface polishing was measured with a stylus type surface roughness meter. The measurement conditions are as follows, and the measurement results of the surface roughness of each part before and after the polishing treatment are shown in the column of “Surface roughness Ra” in Table 1.
Evaluation length: 1.25mm
Cut-off: 0.25mm
Measurement speed: 0.06 mm / s.

<Evaluation of friction stir welding tool>
For each of the friction stir welding tools of each Example and each Comparative Example, wear resistance was evaluated by performing point joining (spot FSJ) by superposing two steel sheets under the conditions shown below.
Joined material: 1.2 mm thick 980 MPa class high strength steel tool rotation speed: 1500 rpm
Bonding load: 1300kgf
Joining time: 2.0 seconds.

  The evaluation was performed by measuring the diameter of the probe portion after spot bonding of 1000 spots and measuring the wear amount of the probe diameter (a decrease in diameter). The evaluation results of the wear resistance are shown in the column “Change in probe diameter” in Table 2. The smaller the probe diameter change value, the better the wear resistance. Moreover, in order to confirm the quality at the initial stage of joining, it was visually confirmed whether or not burrs were generated in the joined portions of the materials to be joined at the first to fifth spots. When the burr is confirmed visually, “Yes” is entered in the column of “1-5 spot burr generation” in Table 2, and when the burr is not confirmed visually, “1-5 spot burr” in Table 2 is displayed. “None” was entered in the “Occurrence” column.

  As is apparent from Table 2, the friction stir welding tools of Examples 1 to 30 have almost no wear and excellent wear resistance because the amount of change in probe diameter is 0.02 mm or less. I understand that. Moreover, since all the tools for friction stir welding of Examples 1-30 did not generate | occur | produce the burr | flash in 1-5 spot joining of the joining initial stage, it turns out that the quality of joining is stable from the joining initial stage.

  On the other hand, in Comparative Example 1, since the thickness of the coating layer was too thin at 2.6 μm, the wear resistance was poor, and the wear amount of the probe after 1000 spots was large. In Comparative Example 2, since the thickness of the coating layer was too thick at 52.4 μm, the stress of the coating layer was high, and the coating layer was peeled off during the surface polishing treatment, and thus was not evaluated.

  In Comparative Example 3, since the coating layer was not polished, the surface roughness of the coating layer was rough, and heat generation due to friction with the materials to be joined during the joining process increased, and the temperature of the friction stir welding tool increased excessively. A large crack occurred in the friction stir welding tool at the third spot and it was damaged. Moreover, in the comparative example 3, the burr | flash produced in the junction part of the to-be-joined material by joining to 5 spots of joining initial stage. The occurrence of burrs is considered to be due to the fact that the material to be joined was softened too much and was pushed into the material to be joined to the shoulder of the friction stir welding tool due to the large amount of heat generated during the joining process.

  In Comparative Example 4, since the polishing time of the coating layer was short and the surface roughness after polishing was too rough, 0.297 μm, the friction stir welding tool generated a large amount of heat, and the friction stir welding tool cracked at 436 spots. Occurred and damaged. Moreover, in the comparative example 4, the burr | flash produced in the junction part of the to-be-joined material by joining to 5 spots of the joining initial stage. The occurrence of burrs is considered to be due to the fact that the material to be joined was softened too much and was pushed into the material to be joined to the shoulder of the friction stir welding tool due to the large amount of heat generated during the joining process.

  As a result of the above, the friction stir welding tool according to the present invention of Examples 1 to 30 has a stable joining strength and joining quality from the beginning of joining compared to the friction stir welding tool of Comparative Examples 1 to 4. And, it was confirmed that it had excellent durability.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 Friction stir welding tool, 2 base material, 3 coating layer, 4 probe part, 5 cylinder part, 6 shoulder part, 7 chuck part.

Claims (7)

A friction stir welding tool comprising a base material and a coating layer formed on a part of the base material that contacts at least a material to be joined,
At least one of the coating layers is formed by physical vapor deposition,
The tool for friction stir welding, wherein the coating layer in a portion in contact with the material to be joined has a thickness of 3 μm to 50 μm and a surface roughness Ra of 0.005 μm to 0.2 μm.   2. The friction stir welding tool according to claim 1, wherein the coating layer in a portion in contact with the material to be joined has a surface roughness Ra of 0.01 μm or more and 0.1 μm or less.   3. The friction stir welding tool according to claim 1, wherein the coating layer in a portion in contact with the material to be bonded has a surface polished after the coating layer is formed. 4.   The friction stir welding tool according to any one of claims 1 to 3, wherein a surface roughness of a side surface of the shoulder portion is larger than a surface roughness of the probe portion in the covering layer in a portion in contact with the material to be bonded.   The friction stir welding according to any one of claims 1 to 4, wherein the surface roughness of the probe portion is equal to or greater than the value of the surface roughness of the lower end of the shoulder portion in the coating layer in the portion in contact with the material to be joined. Tools.   The coating layer includes one or more elements selected from the group consisting of group IVa elements, group Va elements, group VIa elements, Al, Si and B in the periodic table, and a group consisting of carbon, nitrogen, oxygen, and boron. The friction stir welding tool according to any one of claims 1 to 5, comprising a compound with one or more selected elements.   The friction stir welding tool according to any one of claims 1 to 6, wherein at least one of the coating layers is formed by a sputter deposition method.

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