JP2007175764A - Friction stir joining tool and joining method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction stir joining tool, which has a superior stirring effect of material, can increase pushing-in effect to base material plastically fluidized by the friction stirring, can suppress occurrence of burr during joining, and can prevent occurrence of un-filled defects, and whose pin part has a tough fracture resistance as well as an excellent wear resistance. <P>SOLUTION: The friction stir joining tool 100 is provided with a columnar body 2 and the pin 1 attached at the top of the body 2 almost coaxially with the body 2. The outer peripheral face of the pin 1 has at least one of square or triangle flat faces 3 and small flat sections 4 forming almost right angles and continuing to the flat faces 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tool used for welding metal materials, for example, a friction stir welding tool used for joining and integrating metal materials such as aluminum materials, steel materials, alloy materials thereof, and MMC materials (metal matrix composite materials). And a joining method using the same.

  There are friction welding method, laser welding method, mechanical joining method, adhesion method, etc. as the joining method of metal materials instead of arc welding method using conventional inert gas, these are in terms of workability and reliability, or Currently, the field to which each bonding method is applied is limited due to the high cost of the apparatus.

  In particular, the friction welding method is a technology that has been used for a long time, and the frictional heat generated from the bonded surfaces is produced by rotating the bonded materials to be bonded relatively fast and rubbing the bonded surfaces of the bonded materials together. Then, when the joining surface reaches the melting point, the members to be joined are further pressed together and joined while rotating. This technique has been put into practical use, for example, in joining a grip of a metal bat. However, this friction welding method is limited to materials to be joined that have a relatively small joining area, such as a columnar shape such as a cylinder or a cylindrical tube, or a hollow shape. It had the subject that it was difficult to apply to joining.

  By the way, in recent years, there is a friction stir welding method as a method of joining using frictional heat generated from a material to be joined, like the above-described friction welding method.

  In the friction stir welding, in order to obtain a good joint, it is important to improve the stirring efficiency of a material to be joined that is plastically flowed by friction stirring of the joint. In addition, in order to suppress the occurrence of burrs and build-up of the welded material that occurs in the joint, and to prevent defects (voids) that occur in the joint after joining, There is a need for the action of pushing into the flow region. Furthermore, a friction stir welding tool that can be used for joining difficult-to-join materials such as iron and stainless steel is also required. There are also demands for longer life such as prevention of breakage of pins of the friction stir welding tool and improvement of wear resistance.

  Here, as means for solving the above-mentioned problem, as shown in FIGS. 9A to 9D, a columnar shape inserted into a material to be joined at the tip of a substantially columnar body 22 that rotates about an axis. There has been proposed a friction stir welding tool 210 in which a protrusion 31 or a recess groove 32 is provided in a spiral shape on at least a part of the pin 21 in the axial direction on the outer peripheral surface of the pin 21. According to these friction stir welding tools 210, the plastic flow of the material to be joined around the ridges 31 and the concave grooves 32 can be efficiently generated, and the internal plastic flow is made larger than the vicinity of the surface of the joint portion. It is supposed to be possible. From this, it is said that the material structure of the material to be joined at the joint portion can be uniformly stirred to obtain a stable and homogeneous joint structure. Furthermore, even if the oxide film on the surface of the material to be joined is caught inside the plastic flow region, the oxide film is finely divided by the effective plastic flow as described above, and the influence of the oxide film on the joint portion is also affected. It is said that there is almost no (refer patent document 1).

  Also, as shown in FIGS. 10A and 10B, a cylindrical pin 21 is provided concentrically at the tip of the main body 22, and a spiral groove (not shown) is formed on the end face 25 of the main body. Furthermore, a friction stir welding tool 220 has been proposed in which the depth of a spiral groove (not shown) is shallower as it approaches the pin 21. According to this friction stir welding tool 220, the effect of pushing the material to be joined that plastically flows into the plastic flow region can be increased by the effect of the spiral groove (not shown), and the occurrence of defects (voids) in the joined portion can be increased. It can be prevented. Furthermore, it is said that the helical groove 34 is also formed on the outer peripheral surface of the pin 21 to further increase the action of pushing the material to be joined that plastically flows into the plastic flow region (see Patent Document 2).

  Further, as shown in FIGS. 11A and 11B, the tip of the pin 21 to be inserted into the material to be joined has an inclined surface 35, and more preferably, the tip of the pin 21 has a projection shape such as unevenness. A friction stir welding tool 230 provided with (not shown) has been proposed. Conventionally, when joining materials to be joined arranged on a flat jig (not shown), there is an interval between the tip of the pin 21 of the friction stir welding tool 230 and the jig, and the interval Then, it was a part where plastic flow does not occur. For this reason, there has been a problem that the butted surface of the material to be joined on the back side of the bead remains without being joined. According to this friction stir welding tool 230, plastic flow is also generated in the gap between the jig and the pin 21. It is supposed that the unjoined portion of the butted surface on the back side of the bead does not remain (see Patent Document 3).

Furthermore, as shown in FIG. 12, a spiral groove 33 is formed on the end face 25 of the main body 22 so as to surround the pin 21, and a longitudinal groove 36 extending in the axial direction of the pin 21 is formed on the outer peripheral surface of the pin 21. There has been proposed a friction stir welding tool 240 provided with. According to this friction stir welding tool 240, it is possible to improve the stirring force by the pin 21 and increase the joining speed (see Patent Document 4).
JP H10-249551 JP 2003-48083 A JP 2000-153374 A JP 2004-141897 A

  However, in the friction stir welding tool 210 described in Patent Document 1, the groove width 32 of the pin 21 is set to have a groove width of 0.5 to 1.0 mm and a groove depth of about 0.1 to 0.8 mm. However, when the groove width is set to be narrow, even if the groove depth is set to be wide, the material of the material to be joined is clogged in the concave groove 32 during stirring of the material to be joined, and the stirring efficiency is reduced. Challenges arise. Moreover, when the groove width and the groove depth of the recessed groove 32 are set wide, the mechanical strength of the pin 21 is lowered, and there arises a problem that the pin 21 is broken during stirring. Moreover, although the protruding item | line 31 is set with the protruding item | line width of 0.5-1.3 mm and the protruding item | line height of 0.1-0.8 mm, the deformation | transformation of the protruding item | line 31 generate | occur | produces with the frictional heat which generate | occur | produces at the time of a process. Or a problem that the protrusion 31 itself is missing. Furthermore, the problem that the protruding item | line 31 is missing also when inserting in a to-be-joined material arises.

  Further, the friction stir welding tool 220 described in Patent Document 2 has a problem that stress concentration occurs on the bottom surface of the spiral groove 34 of the pin 21 and the pin 21 being stirred is easily damaged. Further, even if the action of pushing the material to be joined that plastically flows into the plastic flow region in the spiral groove can be increased, the spiral groove 34 of the pin 21 only improves the stirring efficiency in the vicinity of the pin 21. Therefore, there arises a problem that the stirring efficiency in the depth direction cannot be improved.

  Furthermore, in Patent Document 3, since the inclined surface 35 rotates the main body 22 to generate a substantially conical space at the center of the rotation axis, there is a problem that the stirring effect is insufficient. Further, the protrusions and grooves on the end face of the pin 21 are very easily damaged at the edge of the protrusion and the groove when the material to be joined is preheated when the pin 21 is inserted, and difficult to join with high hardness such as iron or stainless steel. In the case of wood, there was a problem that the tendency was particularly strong.

  Moreover, in patent document 4, although the vertical groove 36 of the pin 21 is set as 4-8 mm and also the curvature radius of 4-16 mm is a preferable range, since the shape of the vertical groove 36 is too large, There is a problem that stress is concentrated on the pin 21 during the agitation and is easily damaged, and the tool life is short.

  In order to solve the above problems, a friction stir welding tool according to the present invention is a friction stir welding tool having a cylindrical main body and a pin provided substantially coaxially with the main body at the tip of the main body. At least one or more triangular or quadrangular plane portions, and a small face portion that forms a substantially right angle to the plane portions and continues in a direction away from the axis.

  The pin is tapered toward the tip.

  Further, the pin is made of a silicon nitride sintered body.

  Furthermore, the pin is made of a boron carbide sintered body.

  Furthermore, the planar portion is larger than the area of the small surface portion.

  Further, three or more plane portions and small surface portions are provided.

  The joining method of the present invention uses the friction stir welding tool.

  According to the friction stir welding tool of the present invention, the pin has at least one triangular or quadrangular plane portion on the outer peripheral surface of the pin, and has a small surface portion that forms a substantially right angle to the plane portion. Therefore, by suppressing the burrs generated at the bonded portion of the material to be bonded, since there is no material thinning at the bonded portion, it is possible to obtain a bonded body in which defects (voids) in the bonded portion are not generated. Furthermore, since there is no spiral groove on the outer peripheral surface of the pin, the stress concentration on the pin is small and the pin 1 is not easily broken (broken) when stirring the material to be joined, so that the life can be extended.

  Further, since the flat surface portion and the small surface portion have an effect of pushing the plastic flow into the plastic flow region, a more homogeneous and stable plastic flow can be generated and highly efficient joining can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 (a) and 1 (b) are perspective views showing a tip portion of a tool showing an embodiment of a friction stir welding tool of the present invention.

A friction stir welding tool 100 according to the present invention has a cylindrical main body 2 that rotates about its axis, and a cylindrical pin 1 that is inserted into a material to be joined concentrically with the main body 2 at the tip of the main body 2. It becomes.

  The pin 1 is formed on the front end surface 5 of the main body 2, and the main body 2 and the pin 1 have substantially the same axis. Since the main body 2 is chucked and rotated at the time of joining, if the coaxiality of the pin 1 and the main body 2 is substantially the same, the rotation of the pin 1 accompanying the rotation of the main body 2 will not be shaken, so The pin 1 can be prevented from being damaged when inserted into the material. Further, in order to prevent the pin 1 from being bent from the main body 2 due to the friction with the material to be bonded due to the rotation at the time of bonding and the plastic flow of the material to be bonded, the pin 1 and the main body 2 are not integrated. It is preferable that

  The friction stir welding tool 100 of the present invention has a plurality of triangular planar portions 3 on the outer peripheral surface of the pin 1 as shown in FIG. 1A and a rectangular planar portion 3 as shown in FIG. In addition, it is important that each flat surface portion 3 has a small surface portion 4 that forms a substantially right angle and continues in a direction away from the shaft.

  The reason for this will be described with reference to the relationship between the plastic flow of the material to be joined that occurs during joining and the friction stir welding tool 100 shown in FIGS.

  At the time of joining, the friction stir welding tool 100 inserts the pin 1 in the vicinity of the abutting surface 7 between the end faces of the material to be joined 500 while rotating in the ω direction in FIG. 2, thereby friction between the pin 1 and the end face 5 of the main body 2. Heat is generated, and the plastic flow 8 is generated in the material to be bonded 500 by this frictional heat. The direction of the plastic flow 8 in FIG. 2 is schematically indicated by an arrow.

  Next, the tool 100 is rotated and moved in the X direction in FIG. 2, and the material to be bonded 500 is bonded to the bonded material 500 while the bonding portion 10 is formed at the center of the butted surface 7.

  At this time, since the small surface portion 4 formed on the pin 1 is continuously formed at a substantially right angle to the flat surface portion 3, the joined surface has flowed into the space formed by the flat surface portion 3 and the end surface 5 of the main body 2. The plastic flow 8 of the material 500 is pushed back by the small face portion 4 and has the effect of being pushed into the plastic flow region 9. That is, since the end surface 5 of the main body 2 is also pushed into the material to be bonded 500 at the time of bonding, a pressing pressure by the end surface 5 of the main body 2 acts on the material to be bonded 500. Therefore, a part of the material to be joined 500 in the state of the plastic flow 8 is pushed upward by the end face 5 of the main body 2. However, in the friction stir welding tool 100 of the present invention, the plastic flow 8 is directed downward by the small face portion 4. The material to be joined 500 that is pressed by the end surface 5 of the main body 2 and pushed upward can be pushed into the plastic flow region 9. Moreover, the to-be-joined material 500 extruded upward remains as a burr | flash or a built-up part around the joining part 10, and the joined part 10 after joining reduces in thickness and material thinning. However, by using the friction stir welding tool 100 of the present invention, as described above, in order to suppress the upward extrusion of the material to be bonded 500, the burrs generated near the bonded portion 10 of the material to be bonded 500 obtained A built-up portion can be suppressed.

  Furthermore, since the small surface part 4 improves the stirring efficiency of the to-be-joined material 500 which plastically flows, it can aim at the improvement of joining strength.

  In addition, the angle formed by the plane portion 3 and the small surface portion 4 in the present invention is a substantially right angle indicates that the angle α formed by both is 80 to 120 °, and further, the angle α is 80 to 100 °. It is preferable to make it into a range, and thereby, the above-described pushing-back action of the plastic flow 8 can be obtained more efficiently. This is because if the angle α is smaller than 80 degrees, the effect of facing the small surface portion 4 of the plastic flow 8 by the flat surface portion 3 is lowered. If the angle α is larger than 100 degrees, the plastic flow 8 by the small surface portion 4 is made to flow in the plastic flow region 9. This is because the effect of pushing into the inside of the glass decreases.

  Further, as shown in FIG. 2 (b), the plane portion 3 serves to make the plastic flow 8 generated along the outer periphery of the pin 1 face the small surface portion 4, and the efficiency of the plastic flow 8 by the small surface portion 4. Can be further improved. Therefore, the friction stir welding tool 100 of the present invention can further improve the efficiency of the plastic flow 8 by the combination of the flat surface portion 3 and the small surface portion 4, and can obtain the joint portion 10 with less burr due to the effect of the small surface portion 4. In addition, since the material thinning does not occur in the joint 10, it is possible to obtain the bonded body 500 in which the defect (void) of the joint 10 does not occur. Further, since there is no spiral groove or the like on the outer peripheral surface of the pin 1, the stress concentration on the pin 1 is small and the pin 1 is not easily broken (broken) when the material to be bonded 500 is stirred. be able to.

  On the other hand, when the angle formed between the flat surface portion 3 and the small surface portion 4 on the outer peripheral surface of the pin 1 as shown in FIG. Since the plastic flow 8 generated along the outer periphery of the steel plate cannot be guided to the small face portion 4 and the plastic flow region 9 is reduced and the stirring efficiency is lowered, the bonded object 500 having high bonding strength is obtained. It becomes difficult.

  Further, as shown in FIG. 3, the ratio of the peripheral curve of the tip surface of the pin 1, that is, the ratio of the thick line A in FIG. 3 is indicated by the virtual periphery of the tip of the pin 1, that is, the broken line in FIG. It is preferably formed in the range of 40 to 60% with respect to the peripheral edge B corresponding to the circle.

  When the proportion of the thick line is smaller than 40%, the resistance when the pin 1 is inserted into the material to be joined is increased, and the frictional wear of the peripheral edge of the pin 1 is increased, or the peripheral edge is easily broken and chipped. On the other hand, when it exceeds 60%, the area of the flat surface portion 3 is inevitably reduced, and the effect of pushing the plastic flow 8 by the flat surface portion 3 and the small surface portion 4 into the plastic flow region 9 is reduced.

  Furthermore, it is preferable that the number of the plane parts 3 formed in the outer peripheral surface of the pin 1 is 2-4. This is because when the number of the plane portions 3 is one, the effect of pushing the plastic flow 8 by the plane portions 3 and the small surface portions 4 into the plastic flow region 9 is reduced. Further, if the number of the plane portions 3 is larger than 4, the area of each plane portion 3 is reduced, and the effect of facing the small surface portion 4 of the plastic flow 8 by the plane portion 3 is reduced. The ratio of the curve of the peripheral edge of the pin 1 is reduced, the resistance when the pin 1 is inserted into the material to be joined is increased, the frictional wear of the peripheral edge of the pin 1 is increased, and the peripheral edge is easily cracked and chipped.

  Particularly preferably, when the number of the plane portions 3 is 3, the effect of pushing the plastic flow 8 into the plastic flow region 9 while preventing deterioration of mechanical properties such as frictional wear, cracking and chipping of the pin 1 is obtained. You can get to the maximum.

  Moreover, when the plane part 3 formed in the outer peripheral surface of the pin 1 is a triangle, it is preferable that the ridgeline of the plane part 3 and the small surface part 4 is curvilinear as shown to Fig.4 (a). FIG. 4B schematically shows the state of the plastic flow 8 when the friction stir welding tool 100 of FIG. 4A is used, and smoothly follows the shape of the facet 4 by the curved ridgeline. Therefore, it is possible to increase the action of pushing the material 500 to be joined into the plastic flow region 9, thereby further generating burrs in the material 500. Since it can suppress and there is no material thinning in the junction part 10, the generation | occurrence | production of the defect (void | void) in the junction part 10 can be prevented, and the favorable junction part 10 can be obtained. Further, the apex angle of the small face portion 4 facing the end face of the pin is increased, and the plastic flow 8 is effectively opposed over almost the entire area of the small face portion 4, so that the effect of pushing into the plastic flow region 9 is exerted. Can be increased. On the other hand, in FIG.4 (c), the ridgeline of the small surface part 4 is a straight line, and the direction of the plastic flow 8 is rapidly changed to the downward direction in the apex part by the side of the end surface 5 at the side of a triangular main body. Therefore, the downward plastic flow 8 is generated even in the shape of FIG. 4C, but a part of the plastic flow 8 does not flow downward compared to FIG. End up.

  In addition, the plane part 3 which is a triangle may have a curved corner.

  Next, the case where the flat surface portion 3 formed on the outer peripheral surface of the pin 1 of the friction stir welding tool 100 of the present invention is a square will be described with reference to FIGS. 5 and 6.

  FIG. 5A shows that the small surface portion 4 is formed so as to extend over two sides of the rectangular flat surface portion 3, and FIG. 5B shows that the small surface portion 4 is formed only on one side of the rectangular flat surface portion 3. It is formed to be continuous. The plastic flow 8 at the time of joining using these friction stir welding tools 100 is shown to Fig.6 (a) and (b), respectively. In FIG. 6A, since the small surface portion 4 is formed so as to be continuous over the two sides of the square of the flat surface portion 3, the upward plastic flow 8 is effectively suppressed by the small surface portion 4 facing the end surface of the pin 1. It becomes possible. In addition, as shown in FIG. 6B, when the small surface portion 4 is formed so as to be continuous with only one side of the quadrilateral of the flat surface portion 3, the bonded material 500 that undergoes the plastic flow 8 below the small surface portion 4. It is possible to increase the action of pushing the inside into the plastic flow region 9, but an upward plastic flow 8 may be generated in the upper part of the small face portion 4, and further, the end face 5 of the main body 2 may be rotated to rotate. A plastic flow 8 in the opposite direction may occur on the surface portion of the material 500. Therefore, it is more preferable that the flat portion 3 is formed so as to be continuous over two sides of the square facet 4 and the square of the flat portion 3.

  Note that the quadrangular flat surface portion 3 may have a trapezoidal shape with a long bottom bottom on the pin 1 side and a short top bottom on the end surface 5 side of the main body 2, or may have a curved corner portion.

  In the friction stir welding tool 100 of the present invention, as shown in FIGS. 7A and 7B, the pin 1 is preferably tapered toward the tip. In this case, since the resistance to the pin 1 is reduced at the time of insertion into the material to be joined, breakage can be prevented. Furthermore, the stress concentration at the boundary between the pin 1 and the main body 2 can be alleviated, and the breakage and breakage of the pin 1 can be prevented more reliably. In addition, since the pin 1 has a tapered shape, the volume of the plastic flow region 9 can be increased by reducing the volume of the pin 1 itself, the joining efficiency can be improved, and the volume of the plastic flow region 9 can be improved. Since the surface oxide of the material to be bonded 500 can be pulverized and dispersed, the influence of the oxide film on the bonded portion 10 can be reduced.

  Further, the friction stir welding tool 100 of the present invention is preferably formed of ceramics such as a silicon nitride sintered body, a boron carbide sintered body, an alumina sintered body, and a silicon carbide sintered body. As a result, the wear resistance of the pin 1 and the end face 5 of the main body 2 is improved, resulting in a long life. In addition, since ceramics have extremely high heat resistance, they can withstand use under higher load conditions, and because of their high hardness, they can be used for joining difficult-to-join materials such as steel, stainless alloy, titanium alloy, and MMC. Applicable to many kinds. Among these ceramics, a silicon nitride sintered body is particularly preferable, and since the high-temperature strength is higher than that of an alumina sintered body or a silicon carbide sintered body, the material of the friction stir welding tool 100 that performs bonding by frictional heat. Is suitable. Further, since the compressive strength is about 4000 MPa and the three-point bending strength is about 1000 MPa, which is excellent in mechanical properties, it is suitable for high load bonding. Furthermore, since the apparent density is small, when the main body 2 is rotated at a high speed, the load on the apparatus itself can be reduced, and the thermal conductivity is about 15 to 30 W / m · K, which is a friction stir welding than in the past. Since the thermal conductivity of die steel, high-speed steel, and stainless steel, which have been used as tools, is almost the same, there is no need to greatly change the processing conditions.

  Further, since the boron carbide sintered body has a high Vickers hardness of about 50 GPa, excellent wear resistance, and a high melting point of 2350 to 2470 ° C., it is more difficult to join. Can be used for materials.

  Next, the details of the joining method using the friction stir welding tool 100 as described above will be described with reference to FIGS.

  FIG. 8A shows a schematic diagram in the case of joining around the butting surface 7 where the end faces of the materials to be joined 500 are abutted with each other, and FIG. The schematic diagram in the case of joining centering on the part 6 is shown.

  First, the pin 1 is embedded while rotating the tool 100 in the vicinity of the butting surface 7 of the prepared material 500 or the overlapping portion 6. Here, the rotation direction ω of the tool 100 is set so that the small surface portion 4 provided on the pin 1 faces the rotation direction, and the main body 2 is moved relative to the material 500 to be joined. According to this joining method, a downward plastic flow can be generated by the action of the rectangular or triangular flat surface portion 3 provided on the outer peripheral surface of the rotating pin and the small surface portion 4 continuous with the flat surface portion. A bonded structure can be stably formed, and a high-quality bonded portion with few burrs and built-up portions around the bonded portion 10 can be obtained.

  It should be noted that the present invention is not limited to the embodiments, and various modifications can be made without departing from the spirit of the present invention.

(A), (b) is a fragmentary perspective view which shows one Embodiment of the friction stir welding tool of this invention, (a) is a small face part is a triangle, (b) is an embodiment whose face part is a rectangle. Indicates. (A) is a conceptual diagram which shows the state which joins a to-be-joined material using the friction stir welding tool of this invention, (b) saw the mode at the time of joining of the figure (a) from the upper surface of the junction part. It is a conceptual diagram, (c) is the conceptual diagram which looked at the mode at the time of joining using the friction stir welding tool of the conventional embodiment from the upper surface of the joined part. The top view seen from the front end surface of the pin of the friction stir welding tool of Fig.1 (a) is shown. (A) is a fragmentary perspective view which shows another embodiment of the friction stir welding tool of this invention, (b), (c) is the time of joining using the various friction stir welding tools of the same figure (a). It is a conceptual diagram which shows a mode. (A), (b) is a partial perspective view which shows various embodiment of the friction stir welding tool of this invention. (A) is a conceptual diagram which shows the mode at the time of joining using the friction stir welding tool of Fig.5 (a), (b) is a mode at the time of joining using the friction stir welding tool of FIG.5 (b). FIG. (A), (b) is a fragmentary perspective view which shows another embodiment of the friction stir welding tool of this invention. (A), (b) is a conceptual diagram for demonstrating the joining method using the tool for friction stir welding of this invention. (A), (b) is a top view which shows the conventional friction stir welding tool, (c) (d) is the top view which looked at the same figure (a), (b) from the H direction. (A) is a top view which shows another example of the conventional friction stir welding tool, (b) is the top view which looked at the same figure (a) from the direction of I. (A) is a top view which shows another example of the conventional friction stir welding tool, (b) is the top view which looked at the same figure (a) from the direction of J. (A) is a top view which shows another example of the conventional friction stir welding tool, (b), (c) is the top view which looked at the same figure (a) from the L direction.

Explanation of symbols

100, 210, 220, 230, 240: Friction stir welding tool 21, 21: Pin 2, 22: Main body 3: Plane portion 4: Small surface portion 5, 25: End surface 6: Overlapping portion 7: Butting surface 8: Plastic flow 9 : Plastic flow region 10: Joint part 31: Convex part 32: Concave groove 33: Spiral groove 34: Spiral groove 35: Inclined surface 36: Vertical groove 500: Material to be joined

Claims (7)

In the friction stir welding tool having a cylindrical main body and a pin provided substantially coaxially with the main body at the tip of the main body, at least one or more triangular or quadrangular plane portions on the outer peripheral surface of the pin, and the plane A tool for friction stir welding, comprising: a small face portion that forms an angle substantially perpendicular to the portion and is continuous in a direction away from the shaft. The friction stir welding tool according to claim 1, wherein the pin is tapered toward the tip. The friction stir welding tool according to claim 1 or 2, wherein the pin is made of a silicon nitride sintered body. The friction stir welding tool according to claim 1 or 2, wherein the pin is made of a boron carbide sintered body. The friction stir welding tool according to any one of claims 1 to 4, wherein the flat portion is larger than an area of the small face portion. The friction stir welding tool according to any one of claims 1 to 5, wherein three or more flat portions and small surface portions are provided. The joining method characterized by performing joining using the friction stir welding tool in any one of the said Claims 1 thru | or 6.

Images