JP7544683B2 - Friction stir welding tool and friction stir welding method - Google Patents

Description

The present invention relates to a friction stir welding tool for joining workpieces using frictional heat generated by the rotation of a probe, a friction stir welding method using the friction stir welding tool, and a friction stir welding joint obtained by the friction stir welding method.

Friction stir welding (FSW) is a method in which a probe attached to the tip of a tool is rotated while the tip face of the probe is pressed against the butt joint of the materials to be joined, and the probe is moved along the butt joint while pressed into the materials to be joined, thereby joining the materials to be joined by frictional heat and stirring.
However, while good welding can be achieved near the rotating probe or when materials with high fluidity are used as the welding materials, welding is difficult at locations far from the probe or materials with low plastic fluidity. Furthermore, since the probe is generally cylindrical, plastic flow is unlikely to occur even near the center of rotation of the probe, making it difficult to obtain good welding.

Therefore, in order to obtain good welding quality for such friction stir welding, tools equipped with probes of various shapes have been proposed.

For example, Patent Document 1 discloses a friction stir welding tool in which an outer peripheral recess is formed on the outer peripheral surface of the probe, the outer peripheral surface extending to the tip surface, and a tip recess is formed on the tip surface, the tip recess also extending to the outer peripheral surface so as not to communicate with the outer peripheral recess.

Patent Document 2 also discloses a friction stir tool in which an uneven shape is provided on the side of the probe. The uneven shape of the friction stir tool is a shape that includes multiple edge portions that abruptly change the distance from the axial center toward the inside of the radial direction of the probe, and a diameter-changing portion having a spiral shape in which the distance from the axial center gradually changes from the edge of the edge portion toward the diameter of the circumscribing circle of the probe.

JP 2020-163444 A Patent No. 6329351

Figure 12 is a cross-sectional view showing a joint when a pair of plate materials are joined by a conventional friction stir welding method, and Figure 13 is an enlarged view of part A in Figure 12. Also, Figure 14 is a schematic diagram showing the occurrence of defects when a back bending test is performed on a joint having a root flow.

As shown in Figures 12 and 13, when plate materials 21 and 22 are placed butted together and friction stir welding is performed from the front surface 26a side of the butt joint 26, if stirring by the probe is insufficient, a boundary line called a root flow 27 is likely to remain on the back surface 26b side of the butt joint 26. Note that the front surface 26a side of the butt joint 26 refers to the surface against which the probe is pressed, and the back surface 26b side of the butt joint refers to the opposite surface.

As shown in FIG. 14, when a joint 20 having a root flow 27 is bent by pressing or the like so that the back surface 26b side has a convex shape, the root flow 27 may become a crack 28, and this crack 28 may progress and become the starting point of a crack. It is difficult to sufficiently suppress the occurrence of such a root flow 27 even if the friction stir welding tool or friction stir tool described in the above-mentioned conventional Patent Documents 1 and 2 is used.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a friction stir welding tool that can promote stirring of the probe at the butt joint of the workpieces to be welded and suppress the occurrence of root flow, a friction stir welding method using the friction stir welding tool, and a friction stir welding joint obtained by the friction stir welding method.

As a result of intensive research into solving the above problems, the inventors have found that by forming a probe with a recess (groove) consisting of a wall surface and a continuous surface, and by forming the continuous surface starting from the separation portion so that it approaches the tip along the coaxial circumferential direction or toward the radial center, the stirring effect can be significantly improved, the stirring area can be expanded, and the occurrence of root flow can be suppressed. The present invention was made based on these findings.

The above object of the present invention is achieved by the following configuration [1] for a friction stir welding tool.

[1] A friction stir welding tool that rotates a cylindrical probe and presses a tip of the probe against workpieces to generate frictional heat to weld the workpieces,
The probe comprises:
At least one contact portion extending from approximately the center of the tip of the probe to a radial end portion and contacting the surface of the workpiece in a linear or planar manner;
At least one wall surface extending from the abutment portion substantially parallel to an axis of the probe;
a continuous surface formed continuously with the wall surface and extending in a direction away from the wall surface,
A friction stir welding tool, wherein the continuous surface has a separation portion at a position farthest from the tip of the probe, and is formed so as to approach the tip of the probe from the separation portion in at least one of a coaxial circumferential direction of the probe and a radial center direction of the probe.

Furthermore, preferred embodiments of the present invention relating to a friction stir welding tool relate to the following [2] to [7].

[2] The probe has a plurality of contact portions,
The friction stir welding tool according to [1], wherein the wall surface and the continuous surface are formed between the plurality of abutment portions.

[3] The friction stir welding tool according to [1] or [2], in which the linear contact portion that contacts the surface of the workpiece or the ridgeline between the planar contact portion and the wall surface is substantially linear, and the wall surface is substantially planar.

[4] The friction stir welding tool described in any one of [1] to [3], in which the continuous surface is inclined from the separation portion toward the radial center of the probe toward the tip.

[5] The friction stir welding tool described in any one of [1] to [3], wherein the continuous surface has a stepped shape that gradually approaches the tip from the separated portion toward the radial center of the probe.

[6] The friction stir welding tool described in any one of [1] to [5], in which the continuous surface is inclined from the separated portion in a direction approaching the tip along the coaxial circumferential direction of the probe.

[7] The friction stir welding tool described in any one of [1] to [5], wherein the continuous surface has a stepped shape that gradually approaches the tip from the separated portion along the coaxial circumferential direction of the probe.

The above object of the present invention is also achieved by the following configuration [8] relating to the friction stir welding method.

[8] A friction stir welding method for joining a pair of plate materials using the friction stir welding tool according to any one of [1] to [7],
a step of butting a pair of plate materials together to form a butt joint;
setting the length of the probe so that a residual thickness obtained by subtracting the length of the probe from a thickness of the plate material is greater than 0 (mm);
and pressing one surface of the butt joint with the probe while rotating the probe, thereby friction-stirring the butt joint so that a stirring region stirred by the rotation of the probe reaches the other surface of the butt joint.

In addition, a preferred embodiment of the present invention relating to the friction stir welding method relates to the following [9].

[9] The friction stir welding method described in [8], in which, in the step of friction stirring the butt joint, the length and rotation speed of the probe are adjusted so that the stirring area reaches the other surface of the butt joint.

The above object of the present invention is also achieved by the following configuration [10] relating to a friction stir welded joint.

[10] A friction stir welded joint obtained by the friction stir welding method according to [8] or [9],
The stirring region is formed in a cross section perpendicular to the direction in which the butt portions extend, the stirring region having an average particle diameter that is half or less of the average particle diameter of the particles constituting the pair of plate materials,
The stirring region has a semi-elliptical portion having a major axis in a direction perpendicular to the thickness direction of the plate material and an arc protruding toward the other surface of the butt portion,
A friction stir welded joint, wherein the arc reaches the other surface of the butt joint.

In addition, a preferred embodiment of the present invention relating to a friction stir welded joint relates to the following [11].

[11] A friction stir welded joint as described in [10], in which, when an ellipse is assumed based on the semi-elliptical portion, the ratio of the major axis to the minor axis of the ellipse is 3.0 or less.

The present invention provides a friction stir welding tool that can promote stirring of the probe at the butt joint of the workpieces to be welded and suppress the occurrence of root flow, a friction stir welding method using the friction stir welding tool, and a friction stir welding joint obtained by the friction stir welding method.

FIG. 1 is a perspective view showing a friction stir welding tool according to an embodiment of the present invention. FIG. 2 is an enlarged perspective view showing the tip shape of the friction stir welding tool in FIG. FIG. 3 is a perspective view showing a method for welding a butt joint using the friction stir welding tool according to the embodiment of the present invention. FIG. 4 is a perspective view showing an example of the shape of the probe. FIG. 5 is a perspective view showing another example of the shape of the probe. FIG. 6 is a perspective view showing still another example of the shape of the probe. FIG. 7 is a schematic diagram showing the friction stir welding method according to this embodiment. FIG. 8 is a cross-sectional view showing a friction stir welded joint obtained by the friction stir welding method according to this embodiment. FIG. 9 is a photograph showing an enlarged view of a part of the cross-sectional view shown in FIG. FIG. 10 is a photograph showing the state of the joints after the back bending test for the test pieces of the invention example and the comparative example. FIG. 11 is a photograph showing the stirring region in cross section of the test pieces of the invention example and the comparative example. FIG. 12 is a cross-sectional view showing a joint when a pair of plate materials are joined by a conventional general friction stir welding method. FIG. 13 is an enlarged view of a portion A in FIG. FIG. 14 is a schematic diagram showing the occurrence of defects when a back bending test is performed on a joint having a root flow.

The following describes in detail an embodiment of the present invention. Note that the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the spirit of the present invention.

[Friction stir welding tools]
Fig. 1 is a perspective view showing a friction stir welding tool according to an embodiment of the present invention. Fig. 2 is a perspective view showing an enlarged tip shape of the friction stir welding tool in Fig. 1. As shown in Fig. 1, the friction stir welding tool 10 has a rotating part 11 rotatably supported by a rotation drive motor 17, a cylindrical probe 12 fixed coaxially with the rotating part 11 at the tip of the rotating part 11, and a main body part 18 supporting the rotating part 11.

As shown in FIG. 2, the probe 12 has four contact portions 13 that contact the upper surface of the workpiece in a linear manner, wall surfaces 14 that extend from each contact portion 13 approximately parallel to the axis S of the probe 12, and a continuous surface 15 that is formed continuous with the wall surfaces 14 and extends in a direction away from the wall surfaces 14.

The continuous surface 15 has a separation portion 15a at a position farthest from the tip of the probe 12, and is inclined from the separation portion 15a toward the adjacent abutment portion 13 so as to approach the tip, and also inclined toward the radial center of the probe 12 so as to approach the tip. In this embodiment, the separation portion 15a is located on the boundary line 14a between the wall surface 14 and the continuous surface 15, and is located on the outermost radial side of the probe 12.

The linear abutment portion 13 extends linearly from approximately the center of the tip of the probe 12 to the radial end, and the continuous surface 15 extending from the abutment portion 13 is planar. Although it is preferable that the abutment portion 13 passes through the center of the tip of the probe 12, it is not necessary for it to be exactly at the center, as long as it passes through approximately the center. Furthermore, the wall surface 14 does not need to extend strictly parallel to the axis S of the probe 12, as long as it is approximately parallel to the axis S.

A method for joining the butt joints of a pair of aluminum alloy plates (plate materials) using the friction stir welding tool 10 configured as described above will be briefly described below. Note that the specific shape of the tip of the probe is omitted in Fig. 3.
3, first, a pair of aluminum alloy plates 1, 2, which are the materials to be joined, are arranged so that their end faces face each other to butt against each other to form an butt joint 16. Next, while rotating the rotating part 11, the probe 12 is pressed against an upper surface (one surface) 16a of the butt joint 16, thereby press-fitting the probe 12 into the butt joint 16.
Thereafter, while rotating the probe 12, the friction stir welding tool 10 is moved along the butted portion 16 in the direction of the arrow Y shown in FIG.

At this time, the periphery of the probe 12, which is pressed into the butt joint 16, is heated by frictional heat, causing plastic flow. Then, by moving the probe 12 along the butt joint 16, the aluminum alloy plates 1 and 2 undergo plastic flow along the direction of movement of the probe 12, and the aluminum alloy plates 1 and 2 are joined at the butt joint 16.

In this embodiment, as described above, a groove consisting of a wall surface 14 and a continuous surface 15 is formed between the four abutment portions 13 at the tip of the probe 12. In addition, a continuous surface 15 is formed that is inclined toward the tip from the separated portion 15a toward the adjacent abutment portion 13 in the circumferential direction of the probe 12 and along the coaxial circumferential direction of the probe 12. This continuous surface 15 is also inclined toward the tip in the direction toward the radial center of the probe 12.

In this way, when the continuous surface 15 is inclined and the wall surface 14 extends parallel to the axis S of the probe 12, as the probe 12 rotates, the plastically flowed material moves along the continuous surface 15, collides with the wall surface 14, and moves toward the tip of the probe 12. This makes it possible to expand the stirring area stirred by the rotation of the probe 12, particularly the stirring area on the tip side. As a result, it is possible to prevent the occurrence of unjoined root flow on the back side of the butt portion 16.

In this embodiment, the linear abutment portion 13 extends linearly from the center of the tip of the probe 12 to the radial end, but the abutment portion 13 may be curved so as to be convex in the rotation direction of the probe, or may be curved so as to be convex in the direction opposite to the rotation direction. The abutment portion may be planar, and the ridge between the planar abutment portion and the wall surface may be curved so as to be convex in the rotation direction of the probe, or may be curved so as to be convex in the direction opposite to the rotation direction. The linear abutment portion 13 or the ridge between the planar abutment portion and the wall surface can enhance the stirring effect by being linear rather than curved so as to be convex in the rotation direction of the probe, and further, if it is curved so as to be convex in the direction opposite to the rotation direction of the probe, the stirring effect can be further enhanced. However, from the viewpoint of processability when processing the probe 12, it is preferable that the linear abutment portion 13 or the ridge is approximately linear.

In the present invention, the continuous surface 15 does not need to be formed so as to approach the tip surface from the separated portion 15a along the coaxial circumferential direction of the probe 12, or in the radial center direction. Other examples of the shape of the probe 12 are described below with reference to Figures 4 to 6.

The probe 32 shown in FIG. 4 has four contact portions 33 that contact the upper surface of the workpiece in a planar manner, wall surfaces 34 that extend from each contact portion 33 approximately parallel to the axis of the probe 32, and a continuous surface 35 that is formed continuous with the wall surfaces 34 and extends in a direction away from the wall surfaces 34. The ridge line 33a between the contact portions 33 and the wall surfaces 34 is linear, and the wall surfaces 34 are formed flat. The continuous surface 35 also has a separation portion 35a at a position farthest from the tip of the probe 32.

In the present embodiment shown in FIG. 4, the continuous surface 35 is formed continuously with the wall surface 34, and indicates the entire surface up to the adjacent abutment portion 33. The separated portion 35a indicates a linear portion extending from the outermost surface side of the probe 32 on the wall surface 34 along the outer circumferential surface of the probe 32. The continuous surface 35 is inclined from the separated portion 35a toward the radial center of the probe 32 so as to approach the tip. The continuous surface 35 has a stepped shape that gradually approaches the tip side from the separated portion 35a along the coaxial circumferential direction of the probe 32.

The probe 42 shown in FIG. 5, like the probe 32 described above, has four contact portions 43 that contact the upper surface of the workpiece in a planar manner, wall surfaces 44 that extend from each contact portion 43 approximately parallel to the axis of the probe 42, and a continuous surface 45 that is formed continuous with the wall surfaces 44 and extends in a direction away from the wall surfaces 44. The ridge line 43a between the contact portions 43 and the wall surfaces 44 is linear, and the wall surfaces 44 are formed flat.

In the present embodiment shown in FIG. 5, the continuous surface 45 is formed continuously with the wall surface 44, and shows the entire surface up to the adjacent abutment portion 43. The continuous surface 45 also has a planar separation portion 45a perpendicular to the axis at the position furthest from the tip of the probe 42. In this embodiment, the continuous surface 45 is not inclined from the radial end of the probe 42 toward the radial center. However, the continuous surface 45 has a spiral staircase shape that gradually approaches the tip side of the probe 42 from the separation portion 45a along the coaxial circumferential direction of the probe 42.

The probe 52 shown in FIG. 6 has four contact portions 53 that contact the upper surface of the workpiece in a planar manner, wall surfaces 54 that extend from each contact portion 53 approximately parallel to the axis of the probe 52, and a continuous surface 55 that is formed continuous with the wall surfaces 54 and extends in a direction away from the wall surfaces 54. The ridge line 53a between the contact portions 53 and the wall surfaces 54 is linear, and the wall surfaces 54 are formed flat. The continuous surface 55 also has a separation portion 55a at a position farthest from the tip of the probe 52.

In the present embodiment shown in FIG. 6, the separation portion 55a is a linear portion extending from the outermost surface side of the probe 52 on the wall surface 54 along the outer circumferential surface of the probe 52. The continuous surface 55 is inclined from the separation portion 55a toward the radial center of the probe 52 so as to approach the tip of the probe 52. Note that the continuous surface 55 is not inclined from the boundary between the wall surface 54 and the continuous surface 55 along the coaxial circumferential direction of the probe 52.

In this way, the probe has a recess (groove) consisting of a wall surface and a continuous surface, and the continuous surface is formed so that it approaches the tip along the coaxial circumferential direction or toward the radial center starting from the separation part, thereby significantly improving the stirring effect and expanding the stirring area.

As shown in Figures 2 and 4 to 6, the continuous surface may be formed so as to approach the tip of the probe along the coaxial circumferential direction of the probe, or may be formed so as to approach the tip only toward the radial center of the probe. The continuous surface may not be an inclined surface, but may be a stepped shape that approaches the tip in stages. Furthermore, the separation portion may be in the shape of a point, a line, or a surface. Although it is sufficient for there to be at least one contact portion, it is preferable to have multiple contact portions, as this can improve the stirring efficiency.

[Friction stir welding method]
Next, the friction stir welding method according to this embodiment will be specifically described with reference to the drawings.
The friction stir welding method according to the present embodiment is a method for joining a pair of plate materials using the above-mentioned friction stir welding tool. Specifically, as shown in Fig. 3 and Fig. 7, first, a pair of aluminum alloy plates (plate materials) 1, 2 are arranged so that their end faces face each other to form a butt joint 16. Next, the length T2 of the probe 12 is set so that the remaining thickness T3 of the portion obtained by subtracting the length T2 of the probe 12 from the plate thickness T1 of the aluminum alloy plates 1, 2 exceeds 0 (mm), that is, so that the tip of the probe 12 does not reach the back surface (other surface) 16b side of the butt joint 16.

Next, while rotating the probe 12, pressure is applied from the upper surface (one surface) 16a of the butt joint 16, and the probe 12 is pressed into the butt joint 16. Thereafter, while maintaining the probe 12 rotated, the friction stir welding tool 10 is moved along the butt joint 16. At this time, a stirring region made of fine particles is formed below and around the probe 12 due to the rotation of the probe 12. In this embodiment, the butt joint 16 is friction stirred so that the stirring region reaches the back surface (the other surface) 16b of the butt joint 16.

As a method of friction stirring so that the tip of the probe 12 does not reach the back surface 16b of the butt joint 16 and the stirring area reaches the back surface 16b, a method of adjusting the length T2 and rotation speed of the probe 12 is included. By performing friction stir welding in the above-mentioned manner, it is possible to prevent the occurrence of unjoined root flow on the back surface 16b of the butt joint 16.

The friction stir welding method according to this embodiment can prevent the occurrence of unjoined root flow when joining a butt joint, but the joint shape is not limited to joining a butt joint, and can also be applied to joining lap joints, etc. When joining a lap joint, there is no risk of poor joining of the root flow to begin with, but according to this embodiment, the stirring region spreads toward the tip of the probe, so the stirring region can be formed deep down, resulting in a joint with higher strength.

[Friction stir welded joint]
Next, a friction stir welded joint obtained by the above-described friction stir welding method according to this embodiment will be described.
As shown in Fig. 8, by the above-mentioned friction stir welding method, a stirring region 19 is formed in a cross section perpendicular to the extending direction of the butt portion 16. The stirring region 19 indicates a region constituted by particles finer than the particles constituting the aluminum alloy plates 1 and 2.

In a cross section perpendicular to the direction in which the butt joint 16 extends, the stirring region 19 has a semi-elliptical portion 60 with a major axis Rw perpendicular to the thickness direction of the aluminum alloy plates 1 and 2 and an arc 60a protruding toward the back surface 16b of the butt joint 16, and the shape widens as it approaches the upper surface 16a of the butt joint 16. In addition, in FIG. 8, for convenience, the arc 60a does not reach the back surface 16b of the butt joint 16, but as described above, according to the friction stir welding method of this embodiment, friction stirring is performed so that the stirring region 19 reaches the back surface 16b, so that the arc 60a reaches the back surface 16b of the butt joint 16.

When the distance between the stirring region 19 and the back surface 16b is H (mm), the state in which the arc 60a has not reached the back surface 16b of the butt joint 16 is H>0. The state in which the bottom end of the arc 60a just overlaps with the back surface 16b of the butt joint 16, and the state in which the bottom end of the arc 60a is cut off by the back surface 16b of the butt joint 16 are H≦0. Therefore, the fact that the arc 60a has reached the back surface (the other surface) 16b of the butt joint 16 indicates that H≦0.

Furthermore, the friction stir welding tool 10 according to this embodiment has a characteristic tip shape of the probe 12, and compared to conventional friction stir welding tools, it is possible to widen the stirring area 19 stirred by the rotation of the probe 12, particularly the stirring area at the tip side. Therefore, when an ellipse 61 is assumed based on the above-mentioned semi-elliptical shaped portion 60, it is preferable that the ratio of the major axis Rw to the minor axis Rt of the ellipse 61 (Rw/Rt) is 3.0 or less.

9 is a drawing substitute photograph showing an enlarged part of the cross-sectional view shown in FIG. 8. The state of the particles in the cross-section can be observed by a microscope after the cross-section is electrolytically etched to change the characteristics of the grain boundary surface. As shown in FIG. 9, the size of the particles P _B present in the region B of the stirring region 19 is extremely small compared to the size of the particles P _A present in the region A (region separated from the stirring region 19) in the aluminum alloy plate 2, and therefore it can be confirmed by visually inspecting the micrograph. In the present specification, the region having an average particle size of 1/2 or less of the average particle size of the particles constituting the aluminum alloy plates 1 and 2 when the cross-section is observed is defined as the stirring region 19.

The boundary between the region constituting the aluminum alloy plates 1, 2 themselves and the stirring region 19 can be set, for example, as follows. First, a tentative boundary line 62 is visually set, and an auxiliary line 63 extending in a direction perpendicular to the tentative boundary line 62 is created. Next, the number of particles present per unit length (e.g., 200 μm) is measured at a position within the auxiliary line 63 and sufficiently separated from the butt joint 16, i.e., the number of particles constituting the aluminum alloy plates 1, 2. Then, the unit length is divided by the number to calculate the average particle diameter of the particles P _A constituting the aluminum alloy plates 1, 2.

Thereafter, within the auxiliary line 63, the measurement position is moved closer to the stirring region 19, and the average particle diameter of the particles at that position is calculated from the number of particles present per unit length in the same manner. Then, when the obtained average particle diameter becomes ½ or less of the average particle diameter of the particles P _A constituting the aluminum alloy plates 1 and 2, the center of the unit length is set as the boundary point.
Thereafter, temporary boundary lines and auxiliary lines are created at different positions, and multiple boundary points are set in a similar manner. By connecting these, it is possible to set the boundary line between the region constituting the aluminum alloy plates 1, 2 themselves and the stirring region 19, and it is possible to draw the arc 60a in the semi-elliptical portion 60 shown in FIG. 8.

The effects of the present invention will be specifically explained below using examples of the present invention and comparative examples, but the present invention is not limited to these.

<Friction stir welding>
As an example of the invention, a friction stir welding tool 10 having a probe 12 shaped as shown in Fig. 2 was prepared, and as a comparative example, a friction stir welding tool having a probe with a flat tip was prepared, and friction stir welding was performed using each tool by using the friction stir welding method shown in Fig. 3. Specifically, a pair of aluminum alloy plates 1, 2 were arranged so that their end faces faced each other, and a butt joint 16 was formed. Next, while rotating the rotating part 11, the probe 12 was pressed against the upper surface 16a of the butt joint 16, thereby pressing the probe 12 into the butt joint 16. The length of the probe 12 was variously changed to change the remaining thickness T3.
Thereafter, the friction stir welding tool 10 was moved along the butted portions 16 in the direction of arrow Y shown in FIG. 3 while rotating the probe 12, thereby obtaining a joint.

<Evaluation of joints>
(Back bending test)
A back bending test was performed as shown in Fig. 14 so that the back surface 16b side of the butt joint 16 would be convex, and the presence or absence of root flow was observed. The joining conditions and evaluation method are shown below. The state of the joint after the back bending test is shown in Fig. 10.

Friction stir welding tool: Example of the invention (probe 12 having the shape shown in FIG. 2), comparative example (probe with a flat tip)
Tool movement speed: 1.0 m/min. Rotation speed of rotating part: 2000 rpm
Material to be joined: Aluminum alloy plate AA5182-O
Plate thickness T1 of the workpiece to be joined: 2.3 mm
Residual thickness T3: 0.3mm, 0.2mm, 0.1mm
Evaluation method: Reverse bending test (angle 90°, bending radius 2.5 mm)

(Observation of the stirring region)
In addition, friction stir welded joints were formed under the same conditions as in the above welding method, and a cross section perpendicular to the direction in which the butt joint 16 extends was electrolytically etched and then observed under a microscope. The stirring region in the cross section of each friction stir welded joint is shown in Figure 11. In Figures 10 and 11, the invention example refers to an example in which the friction stir welding tool according to the embodiment of the present invention is used.

(Measurement of size of stirring area and distance from back surface)
The cross section of each test piece shown in FIG. 11 was observed, and as shown in FIG. 8, the arc 60a of the semi-elliptical portion 60 was visually drawn, and an ellipse 61 was drawn based on the semi-elliptical portion 60, and the minor axis Rt and major axis Rw of the obtained ellipse 61 were measured. In addition, the ratio of the major axis Rw to the minor axis Rt of the ellipse (Rw/Rt) was calculated. Furthermore, the distance H between the stirring region 19 and the back surface 16b was measured. The distance H between the stirring region 19 and the back surface 16b indicates the distance between the back surface 16b in the butt portion 16 and the position closest to the back surface in the stirring region 19 (the most protruding position of the arc 60a). The measurement results and calculation results are shown in Table 1 below.

(Measurement of particle size)
For Example No. 2, the average particle size of the particles in the stirring region (region B in FIG. 9) was compared with the average particle size of the particles in the region separated from the stirring region (region A in FIG. 9) based on Example No. 2 in FIG. 11 and its enlarged view in FIG. 9.
The average particle size was calculated by measuring the particle size of each of three randomly selected particles in each region. The particle sizes and average particle sizes of the test pieces of the invention examples are shown in Table 2 below.

As shown in Table 2 above, the average particle size in the stirring region was 1/2 or less of the average particle size of the particles in the aluminum alloy plate. Also, as shown in Figures 10 and 11 and Table 1 above, in all test pieces, a stirring region having an average particle size that was 1/2 or less of the average particle size of the particles in the aluminum alloy plate and a semi-elliptical portion could be observed. In particular, in the test piece of invention example No. 3, no root flow was formed, and excellent results were obtained in the back bending test.

In Comparative Examples 1 to 3 and Invention Examples 1 and 2, root flow was formed at the location indicated by the arrow in Figure 10, but the distance H between the stirring region that is the source of root flow and the back surface was smaller in the invention examples at any remaining thickness. This means that, as shown by the results of Rw/Rt, the invention examples have Rw/Rt values of 3.0 or less, which is smaller than the comparative examples, and the stirring region spreads toward the tip side of the probe. In other words, by using the friction stir welding tool according to the present invention, even if the remaining thickness is more than 0 mm, the arc of the stirring region can reach the back surface, making it easier to suppress the occurrence of root flow.

REFERENCE SIGNS LIST 10 friction stir welding tool 11 rotating part 12 probe 13 contact part 14 wall surface 14a boundary line 15 continuous surface 15a separation part S axis

Claims (10)

A friction stir welding tool that rotates a cylindrical probe and presses a tip of the probe against workpieces to generate frictional heat and join the workpieces,
The probe comprises:
At least one contact portion extending from approximately the center of the tip of the probe to a radial end portion and contacting the surface of the workpiece in a linear or planar manner;
At least one wall surface extending from the abutment portion substantially parallel to an axis of the probe;
a continuous surface formed continuously with the wall surface and extending in a direction away from the wall surface,
the continuous surface has a separated portion at a position farthest from the tip of the probe, and is formed so as to approach the tip of the probe from the separated portion in at least one of a coaxial circumferential direction of the probe and a radial center direction of the probe ,
A friction stir welding tool, wherein the ridgeline between the linear abutment portion that abuts against the surface of the workpiece or the planar abutment portion and the wall surface is approximately linear, and the wall surface is approximately planar . A friction stir welding tool that rotates a cylindrical probe and presses a tip of the probe against workpieces to generate frictional heat and join the workpieces,
The probe comprises:
At least one contact portion extending from approximately the center of the tip of the probe to a radial end portion and contacting the surface of the workpiece in a linear or planar manner;
At least one wall surface extending from the abutment portion substantially parallel to an axis of the probe;
a continuous surface formed continuously with the wall surface and extending in a direction away from the wall surface,
the continuous surface has a separated portion at a position farthest from the tip of the probe, and is formed so as to approach the tip of the probe from the separated portion in at least one of a coaxial circumferential direction of the probe and a radial center direction of the probe ,
A friction stir welding tool , wherein the continuous surface has a stepped shape that approaches the tip in stages from the separated portion toward a radial center of the probe. A friction stir welding tool that rotates a cylindrical probe and presses a tip of the probe against workpieces to generate frictional heat and join the workpieces,
The probe comprises:
At least one contact portion extending from approximately the center of the tip of the probe to a radial end portion and contacting the surface of the workpiece in a linear or planar manner;
At least one wall surface extending from the abutment portion substantially parallel to an axis of the probe;
a continuous surface formed continuously with the wall surface and extending in a direction away from the wall surface,
the continuous surface has a separated portion at a position farthest from the tip of the probe, and is formed so as to approach the tip of the probe from the separated portion in at least one of a coaxial circumferential direction of the probe and a radial center direction of the probe ,
A friction stir welding tool , wherein the continuous surface has a stepped shape that approaches the tip in stages from the separated portion along a coaxial circumferential direction of the probe. The friction stir welding tool according to claim 1 or 3 , wherein the continuous surface is inclined from the separated portion toward a radial center of the probe and in a direction approaching the tip. The friction stir welding tool according to claim 1 , wherein the continuous surface has a stepped shape that approaches the tip in a stepwise manner from the separated portion toward a radial center of the probe. 3. The friction stir welding tool according to claim 1 , wherein the continuous surface is inclined from the separated portion toward the tip along a coaxial circumferential direction of the probe. The friction stir welding tool according to claim 1 or 2 , wherein the continuous surface has a stepped shape that approaches the tip in a stepwise manner from the separated portion along a coaxial circumferential direction of the probe. The probe has a plurality of contact portions,
The friction stir welding tool according to claim 1 , wherein the wall surface and the continuous surface are formed between the plurality of contact portions. A friction stir welding method for joining a pair of plate materials using the friction stir welding tool according to any one of claims 1 to 8 ,
a step of butting a pair of plate materials together to form a butt joint;
setting the length of the probe so that a residual thickness obtained by subtracting the length of the probe from a thickness of the plate material is greater than 0 (mm);
and pressing one surface of the butt joint with the probe while rotating the probe, thereby friction-stirring the butt joint so that a stirring region stirred by the rotation of the probe reaches the other surface of the butt joint. The friction stir welding method according to claim 9 , wherein in the step of frictionally stirring the butt joint, a length and a rotation speed of the probe are adjusted so that the stirring region reaches the other surface of the butt joint.

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