JP6041499B2 - Friction stir welding method - Google Patents

Description

  The present invention relates to a method for joining two metal plates having different hardnesses, and relates to a friction stir welding method capable of easily obtaining a good joint free from joining defects such as unjoined portions and holes.

  Examples of the dissimilar metal joining of two metal members having different melting points, such as an aluminum material and a steel material, and an aluminum material and a copper material, include MIG welding, TIG welding, and laser welding. However, in the dissimilar metal joining by fusion welding, there is a problem that a brittle intermetallic compound is formed at the interface between the dissimilar metals, and the joining strength is low due to the occurrence of blowholes in the welded part. Applying friction stir welding as a method for joining dissimilar metals without reducing the joining strength has been proposed and put into practical use.

  Solid phase bonding by the friction stir welding method is a widely known technique. In the friction stir welding method, a probe of a rotary bonding tool is inserted into the abutting surface of a bonding member, and the rotary bonding tool is moved while rotating. The joining member is softened by frictional heat, and the joining member is joined by plastic flow of the butted surfaces and stirring and mixing. Friction stir welding has the advantage that there is no reduction in strength after joining and the strain is small because the joining members are joined at a temperature below the melting point.

  The friction stir welding method is applied mainly to aluminum materials, and in many cases, it is used for joining similar materials such as aluminum alloys having the same composition. In recent years, attempts have been made to apply to bonding of dissimilar materials.

  Non-Patent Document 1 describes a method for joining a copper material and an aluminum material, which are different metals. A probe provided coaxially at the tip of the rotary joining tool is inserted into the aluminum material having a low hardness, and friction stir welding is performed while a screw portion provided on the probe is in contact with the copper material interface. The resulting bonded body has a tensile strength equivalent to that of the aluminum base material.

  Patent Document 1 describes that friction stir welding is performed by attaching a hard metal plate and a soft metal plate having different hardnesses together. The probe provided coaxially at the tip of the rotary welding tool is inserted 0.05mm or more into the hard metal plate side with respect to the butt line between the soft metal plate and the hard metal plate, and most of the probe is placed on the soft metal plate side. It is what is joined. It is said that the bonding strength can be improved by joining the probe by slightly penetrating the hard metal plate side by scraping the end surface of the hard metal plate to scrape the new surface and causing the soft metal plate to plastically flow.

  Patent Document 2 describes that friction stir welding is performed by attaching a hard metal plate and a soft metal plate having different hardnesses together. By making the thickness of the soft metal plate larger than that of the hard metal plate, a step is provided at the abutting part so that a gap is formed between the shoulder and the hard metal plate, and the soft plastic that is plastically flowed by the rotation of the rotary joining tool The metal plate is joined while entering the gap. Thereby, it is said that joint defects such as voids in the joint portion can be prevented.

  In Patent Document 3, a probe of a rotary joining tool is inserted from the surface side of the plate material to join the soft plate material and the hard plate material, and then a probe of the rotary joining tool is also inserted from the back side of the plate material to join both plate materials. It is also shown that a bobbin tool is applied. As a result, it is possible to prevent the occurrence of an unjoined portion due to insufficient agitation in the vicinity of the probe tip.

Hisaoka Okamura, Shinya Aoda, Yasuhisa Aono, “Friction stir welding of dissimilar metals using friction stir action (1st report)”, Outline of the National Conference of the Japan Welding Society, Japan Welding Society, September 3, 2002, 71. p. 442-443

JP 2003-39183 A Japanese Patent No. 4336744 JP 2009-202212 A

  However, as described in Non-Patent Document 1 and Patent Document 1, in the method in which the probe of the rotary tool is arranged on the soft metal plate side and the friction stir welding is performed, the soft metal plate is mainly plastically flowed between the two materials. Therefore, all the minute voids that may be generated in the butted portions of both materials are supplemented with the soft metal plate. For this reason, a bonding defect such as a gap or a decrease in density occurs between the bonding portion or the shoulder of the rotary bonding tool and the surface of the plate material, which may cause a decrease in bonding strength. Patent Document 1 shows that a plating layer or a brazing material that can be easily bonded to different metals is clad on the butt surface, and the probe is plated by inserting a rotary bonding tool at an angle to the butt surface. There are shown a method in which the probe is brought into contact with the layers and a method in which the abutting surface is inclined to bring the probe tip into contact with the hard metal plate. However, there is a problem that the manufacturing process increases to increase the cost for forming the plating layer.

  A method of scraping the hard metal plate by inserting the probe slightly on the hard metal plate side as in Patent Document 2 is effective. However, even in normal friction stir welding, the probe tip has a low joining temperature and the stirring force is insufficient, and an unjoined part called a kissing bond may be formed on the back side. In order to perform offset bonding, similarly to Non-Patent Document 1 and Patent Document 1, the bonding method of Patent Document 2 also has a problem that an unbonded portion is likely to occur on the back surface of the bonded portion. Further, if the probe center is removed from the abutting surface using a probe with a chamfered tip, the distance between the probe tip and the abutting surface back surface increases, and an unjoined portion is more likely to occur on the back surface side. There was a problem.

  With respect to the occurrence of such an unbonded portion on the back surface side, in Patent Document 3, there is a problem in using a method of bonding by inserting a probe from both the front surface side and the back surface side, or a method of bonding using a bobbin tool. Trying to solve. However, in this method, joining has to be performed twice, resulting in an increase in the number of steps, leading to an increase in cost, and there is a problem that a brittle intermetallic compound at the interface between both plate materials is likely to grow. In addition, the bobbin tool has a narrow condition range for obtaining a good joint as compared with the friction stir welding using a normal tool, and there is a problem in the joining stability.

  An object of the present invention is to provide a friction stir welding method that prevents formation of an unbonded portion on the back surface that is likely to occur in the above-described dissimilar metal bonding, and that can easily provide a good dissimilar metal bonding material.

The present invention relates to the friction stir welding method according to claim 1, wherein the hard metal plate and the soft metal plate having a smaller hardness are abutted, and the rotary joining tool is rotated and moved along the abutting surface to join the two metal plates. In
The rotary joining tool has a substantially cylindrical base, a shoulder provided on both metal plate sides of the base, and a probe suspended concentrically with the base from the surface of the shoulder,
The hard metal plate is disposed on the side where the rotation direction of the rotary bonding tool is coincident with the bonding direction, and the soft metal plate is disposed on the side where the rotation direction of the rotary bonding tool is opposite to the bonding direction,
Both probes are inserted so that the probe is inclined with respect to the abutting surface toward the soft metal plate and the contact area of the shoulder with the soft metal plate is larger than the contact area with the hard metal plate. While rotating the rotary joining tool in contact with the metal plate, the two metal plates are joined by moving along the butt surface while rotating .
Friction stirrer, characterized in that an inclination angle φ (°) when the probe is inserted to be inclined toward the soft metal plate with respect to the abutting surface is defined by the following expressions (1) and (2): A joining method was adopted.
sin ⁻¹ {(0.01 + T−t) / R)} ≦ φ ≦ sin ⁻¹ {(0.03 + T−t) / R)} (1)
−0.5 <T−t <0.5 (2)
Here, T: plate thickness (mm) of the hard metal plate, t: plate thickness (mm) of the soft metal plate, and R: radius of the shoulder (mm).

The invention Oite to claim 2, claim 1, the minimum distance d of the end center and abutting surface of the probe (mm) is a radius of r (mm), the positive soft metal plate side of the d of the probe As follows, it shall join while satisfy | filling following formula (3).
0 ≦ d ≦ r−0.1 (3)

According to a third aspect of the present invention, in the first or second aspect , the shoulder surface has a substantially spherical convex surface or a tapered taper surface facing both metal plates, or a chamfer having a corner portion of R1.0 or more or C1 or more. The shoulder surface is a groove extending from the outer peripheral side to the shaft center portion, and both metal plates plastically flowed by the rotation of the rotary joining tool flow into the shoulder surface to the shaft center portion of the shoulder. It was assumed that grooves to be collected were formed.

According to the first aspect, the hard metal plate that is hard and difficult to plastically flow is disposed on the side where the rotation direction of the rotary joining tool having a large plastic flow action coincides with the joining direction, and the soft metal plate that is easy to plastically flow is provided. By arranging the rotational direction of the rotary joining tool having a relatively small plastic flow action on the side opposite to the joining direction, it is possible to achieve a good balance of plastic flow in both metal plates.
Furthermore, since the probe is inclined and inserted into the soft metal plate side with respect to the abutting surface, the bonding temperature can be lowered compared to the case where the probe is mainly inserted into the hard metal plate side. The growth of fragile intermetallic compounds existing at the interface of the plate can be suppressed. In addition, by inserting the probe while tilting, the probe tip close to the back side is inserted into the hard material, so plastic flow on the back side of the abutting surface is activated and unbonded on the back side of the abutting surface. Generation of a portion (kissing bond) can be prevented.
In addition, a hard metal plate that tends to increase the joining temperature due to a large pressing load by bringing the shoulder into contact with both metal plates so that the contact area of the shoulder with the soft metal plate is larger than the contact area with the hard metal plate. As a result, it is possible to prevent internal defects such as vacancies and tunnel defects generated by excessive plastic flow, and appearance defects such as large thinning and burrs.

  According to the second aspect, as defined in the formula (2), if the difference in thickness between the hard metal plate and the soft metal plate is less than 0.5 mm, the inclination angle φ defined by the formula (1) is set. By providing, a good joint can be produced. Further, even though a metal plate distributed in the market is called, for example, a plate thickness of 1.5 mm, it actually has variations such as 1.481 mm and 1.510 mm, and it is rare that the plate thickness is exactly the same. In the case of metal plates having different hardness, such a slight difference in plate thickness also affects the bondability. However, it is possible to obtain a good joint by providing the inclination angle φ obtained by the equation (1).

  According to the third aspect, the minimum distance d (mm) between the tip center of the probe and the butting surface is defined so as to satisfy the expression (3), and the probe center position is offset from the butting line toward the soft metal plate. . In other words, the probe is inserted more into the soft metal plate than the hard metal plate, so that the contact area of the shoulder with the soft metal plate can be reduced even when the metal plates having greatly different melting points and hardnesses are joined. It can be made larger than the contact area. As a result, the joining temperature and the plastic flow amount of the hard metal plate and the soft metal plate can be optimized, and a good joint free from voids and tunnel defects can be obtained.

  According to claim 4, the shoulder surface is a substantially spherical convex surface or a tapered taper surface facing both metal plates, or a chamfered plane with corners of R1.0 or more or C1 or more, and the shoulder surface. In addition, one or more grooves extending from the outer peripheral side to the shaft center part, and formed by the rotation of the rotary joining tool, the two metal plates that have been plastically flowed into the interior and collected in the shaft center part of the shoulder are formed. By doing so, it becomes possible to effectively suppress the occurrence of burrs due to the shoulder end being pushed into the metal plate, and a joint with a good appearance can be obtained. Further, the contact area can be adjusted more effectively by setting the inclination angle φ.

  As described above, by using the friction stir welding method according to the present invention, it is possible to satisfactorily friction stir weld two metal plates having different hardness from each other, and join unjoined portions, holes, and the like. A joint having no defect can be easily obtained.

It is a top view which shows the 1st embodiment of this invention. It is a front view which shows the 1st embodiment of this invention. It is a top view which shows the 2nd embodiment of this invention. It is a front view which shows the 2nd embodiment of this invention. It is a front view which shows the 3rd embodiment of this invention. It is a front view which shows the Example and comparative example of this invention.

  The first embodiment of the present invention will be specifically described below with reference to the drawings. 1 and 2 show a plan view and a front view, respectively, of the first embodiment of the present invention. The rotary joining tool 1 has a configuration similar to that of a conventional tool, and has a substantially columnar base 2, a shoulder 2 a provided on both metal plate sides of the base 2, and a droop concentric with the base 2 from the surface of the shoulder 2 a. The probe 3 is configured. One of the two metal plates is a hard metal plate 4a, and the other is a soft metal plate 4b. The probe 3 is inserted into both the metal plates 4a and 4b. The metal plates 4a and 4b are pressed by the shoulder 2a from above. The hard metal plate 4a and the soft metal plate 4b are different in hardness, may be different metals, or may be the same type of metal and different in composition and tempering. In the present invention, aluminum alloys having different tempering or composition are preferably used. For example, the hard metal plate 4a is AA6101 alloy and the soft metal plate 4b is AA1050 alloy. Alternatively, both metal plates may be AA6101 alloy, the hard metal plate 4a may be AA6101-T6, and the soft metal plate 4b may be AA6101-T4.

  The hard metal plate 4a and the soft metal plate 4b are butted at the butting surface 5, and both the metal plates 4a and 4b are fixed using a jig such as a clamp (not shown). The hard metal plate 4a is on the side where the rotational direction R and the joining direction F of the rotary joining tool 1 coincide (the left side in FIGS. 1 and 2 is referred to as “advance side”), and the soft metal plate 4b is the rotation of the rotary joining tool 1. It is arranged on the side where the direction R and the joining direction F are opposed to each other (the right side in FIGS. 1 and 2 is referred to as “retreat side”). The joining direction F shown in FIG. 2 is from the front surface to the back surface in the drawing.

  In order to satisfactorily friction stir weld the metal plates 4a and 4b having different hardness without defects, it is necessary to appropriately balance the joining temperature of both the metal plates 4a and 4b and the amount of plastic flow between them. That is, the hard metal plate 4a having a high hardness and difficult to plastically flow is disposed on the forward side where the plastic flow is active, and the soft metal plate 4b having a lower hardness and easier to plastically flow is disposed on the backward side where the plastic flow is less active than the forward side. The plastic flow amount can be appropriately balanced by disposing in the above.

  The probe 3 is inserted with an inclination toward the soft metal plate 4b with respect to the abutting surface 5. That is, in the direction orthogonal to the joining direction F in FIG. 1, it is inserted inclined from the butt surface 5 (vertical surface) to the soft metal plate 4 b side. At this time, the hard metal plate 4 a and the soft metal plate 4 b are moved in the width direction, and a gap is likely to be generated on the abutting surface 5. Since the gap generated in the abutting surface 5 causes a defect, it is necessary to sufficiently fix both the metal plates so as not to move.

  When the thickness of the hard metal plate 4a and that of the soft metal plate 4b are substantially the same, the direction in which the probe 3 is inclined is on the side of the soft metal plate 4b having a low hardness. Since the probe 3 is inserted with an inclination with respect to the abutting surface 5, both metal plates are actively plastically flowed near the back surface at the tip of the probe 3 as compared with the case where the probe 3 is inserted without being inclined. As a result, this backside kissing bond can be prevented. Further, since the bonding temperature can be lowered as compared with the case where the probe is mainly inserted on the side of the hard metal plate, the growth of fragile intermetallic compounds existing at the interface between the two metal plates can be suppressed.

  When the probe 3 is inserted into the two metal plates 4a and 4b so as to be inclined as described above, a gap is generated between the end portions of the shoulder 2a of the hard metal plate 4a having high hardness, and the soft metal plate 4b and the shoulder 2a are brought into contact with each other. The area can be made larger than the contact area between the hard metal plate 4a and the shoulder 2a. Thereby, the joining temperature of a hard metal plate can be suppressed low, an internal defect can be prevented, and appearance defects such as large thinning and burrs can also be prevented.

  As described above, the hard metal plate is placed on the forward side and the soft metal plate is placed on the backward side, the probe is inserted inclined to the soft metal plate side with respect to the abutting surface, and the shoulder soft metal plate and The metal plates are agitated by moving the rotary joining tool along the abutting surface while rotating the rotary joining tool in a state where the shoulder is in contact with both metal plates so that the contact area is larger than the contact area with the hard metal plate. This enables good friction stir welding.

The inventors have studied in detail the angle φ (°) at which the probe is inclined toward the soft metal plate with respect to the butted surface. As a result, it was found that the plastic flow amount of both metal plates can be appropriately balanced by defining the inclination angle φ (°) by the following formulas (1) and (2).
sin ⁻¹ {(0.01 + T−t) / R)} ≦ φ ≦ sin ⁻¹ {(0.03 + T−t) / R)} (1)
−0.5 <T−t <0.5 (2)
Here, T: thickness of the hard plate (mm), t: thickness of the soft plate (mm), R: radius of the shoulder (mm).

  When both the metal plates 4a and 4b have substantially the same thickness, the end of the shoulder 2a and the hard metal plate 4a are defined by φ (°) in the range defined by the equations (1) and (2). A gap of 0.01 to 0.03 mm can be set in between. If the gap is less than 0.01 mm, the joining temperature is too high as described above, and the soft metal plate 4b excessively plastically flows, resulting in a large amount of burrs and internal defects. On the other hand, if the gap exceeds 0.03 mm, the plastic flow of the soft metal plate 4b becomes excessive due to insufficient plastic flow of the hard metal plate 4a, and a large amount of burrs and internal defects are generated.

  Next, a second embodiment of the present invention will be specifically described with reference to the drawings. 3 and 4 are a plan view and a front view, respectively, of the second embodiment of the present invention. This embodiment is composed of (1) friction stir welding of a hard metal plate 4a and a soft metal plate 4b having a smaller hardness, (2) a substantially cylindrical base 2, a shoulder 2a, and a probe 3. (3) The hard metal plate 4a is disposed on the forward side and the soft metal plate 4b is disposed on the backward side. (4) The probe 3 is soft metal with respect to the butting surface 5. The shoulder 2a was inserted into the side of the plate 4b, and the shoulder 2a was brought into contact with both the metal plates 4a and 4b so that the contact area of the shoulder 2a with the soft metal plate 4b was larger than the contact area with the hard metal plate 4a. (5) The inclination angle φ when the probe 3 is inserted in an inclined manner toward the soft metal plate 4b with respect to the abutting surface 5 while rotating the rotary joining tool 1 in the state. (°) with the above formula (1) and It is the same as that of the first embodiment that the expression (2) is defined, and these functions and effects are also as described in the first embodiment.

  Further, the hard metal plate 4a and the soft metal plate 4b are different in hardness and softening temperature, and similar to the first embodiment, different metals may be used, and the same type of metals may be used, and the composition and tempering may be different. It may be between each other. In the second embodiment, for example, tough pitch copper is used as the hard metal plate 4a, and AA1050 alloy is used as the soft metal plate 4b.

As shown in FIG. 4, the second embodiment differs from the first embodiment in that the minimum distance d (mm) between the center of the tip of the probe 3 and the butting surface is r (mm), The positive direction of d is the soft metal plate 4b side, and is joined while satisfying the following formula (3).
0 ≦ d ≦ r−0.1 (3)

  By setting d so as to satisfy Equation (3), the contact area with the shoulder hard metal plate 4a can be further reduced, and the joining temperature can be suppressed low. As a result, it is possible to further enhance the action of preventing internal defects and appearance defects and the action of suppressing the growth of fragile intermetallic compounds formed at the interface between both metal plates. Furthermore, since most of the probe tip is inserted into the soft metal plate 4b, the plastic flow on the back side of the abutting surface is activated to move and curve the interface between the two metal plates and prevent kissing bonds. The effect can be further enhanced. In this second embodiment, both metal plates differ not only in hardness but also in softening temperature, but the contact area between the hard metal plate 4a and the shoulder 2a is smaller than the contact area between the soft metal plate 4b and the shoulder 2a. Therefore, in addition to the effect of preventing internal defects and appearance defects and the effect of suppressing the growth of intermetallic compounds, the effect of preventing melting of the soft metal plate 4b is also exhibited.

Next, modified examples of the first and second embodiments will be described.
As for the surface shape of the shoulder, the surface as in the first and second embodiments shown in FIG. 2 and FIG. 4 is replaced with a flat shoulder, and a substantially spherical convex shape as shown in FIG. It is good also as a taper surface tapered toward the surface, or a chamfered plane with corners of R1.0 or more or C1 or more. Thus, by making the surface shape of the shoulder into a substantially spherical convex shape,
When the work angle is provided, the contact area between the hard metal plate and the shoulder can be more sufficiently suppressed. Furthermore, the effect of suppressing the amount of the soft metal plate (burrs) discharged by the shoulder end portion can be obtained.

  Moreover, as shown in FIG. 5, you may form the groove | channel 6 in the shoulder surface. Such a groove 6 extends from the outer peripheral side of the shoulder 2a to the axial center portion, and a spiral, curved or linear one is preferably used. These grooves generate a centripetal force that collects both plastic plates that have flowed into the groove at the center of the shoulder shaft, and prevent the two metal plates that have flowed plastic from scattering as burrs. One or more such grooves are formed on the shoulder surface.

  As the probe shape, instead of the surface having a smooth substantially cylindrical shape as in the first and second embodiments shown in FIGS. 2 and 4, the surface has a spiral in a direction descending with respect to the rotation direction during processing. It is preferable to provide a groove. Instead of the spiral groove, it may be an intermittent inclined groove, or both grooves may coexist. By such a groove | channel, the metal plate which carried out the plastic flow can be stirred effectively. Further, instead of the columnar probe, a tapered probe whose diameter decreases toward the tip may be used. Furthermore, instead of a probe having a substantially circular cross section perpendicular to the center line, a probe having a multi-plane with chamfered side surfaces of about 3 to 6 may be used.

  Finally, you may provide the advancing angle which inclines a rotary joining tool back with respect to the joining direction F at the time of joining. By setting the advance angle, the amount of heat input can be increased and the joining speed can be improved. However, setting the excessive advance angle increases the contact between the hard metal plate and the shoulder. In order to effectively obtain the advance angle effect, the advance angle range is preferably set to 0 to 1.0 °.

  Next, the present invention will be described in more detail based on examples and comparative examples, but the present invention is not limited thereto.

Examples 1-7 and Comparative Examples 8-9
As shown in FIG. 6, the example and the comparative example were examined. Table 1 shows the materials of the hard metal plate 4a and the soft metal plate 4b, their respective thicknesses T and t, and joining conditions (inclination angle φ, distance d between the probe tip center and the abutting surface, rotational speed, joining speed, advance angle). Shown in The rotary joining tool 1 used in the above examples and comparative examples has a cylindrical shape with a shoulder diameter of 12 mm, and the probe has an M4 screw (radius: 2.0 mm, length: 0.0 mm from the smaller of T and t). 1 mm shorter) was used. In addition, two spiral grooves were provided on the shoulder surface. The number of circumferences of each groove was 1, groove width 0.5 mm, groove depth 0.5 mm, and groove interval 0.5 mm.

  In Examples 1 to 6, the inclination angle φ satisfies the ranges of the above formulas (1) and (2), and the distance d between the probe tip center and the butting surface also satisfies the above formula (3). On the other hand, in Comparative Examples 8 and 9, the inclination angle is not set, and in Example 7, the distance d does not satisfy the above formula (3), and the probe is not inserted into the hard metal plate 4a.

  The following evaluation was performed about the obtained joining material. First, a JIS No. 5 tensile test piece was cut out so that the joining direction and the test direction were perpendicular to each other, and a tensile test was performed. As a result, in all of Examples 1 to 7, it was confirmed that the fracture was caused by the base material of the soft metal plate 4b and the bonding was good. Further, a back bending test was performed with a bending R = 10 mm, and the presence of cracks (unbonded portions) on the back side of the bonded portion was observed. As a result, in Examples 1-6, it has confirmed that there was no crack in the back surface side of a junction part. However, in Example 7, some cracks occurred. On the other hand, all of the bonding materials of Comparative Examples 8 and 9 were broken at the bonded portion by the tensile test, and cracks were observed on the back surface side of the bonded portion in the back bending test.

  As described above, by the friction stir welding method according to the present invention, good dissimilar alloy joints or dissimilar metal joint joints having no internal defects and unjoined parts were obtained from metals having different hardnesses.

  By the friction stir welding method according to the present invention, different metals used for electrodes, terminals, wirings, etc. of batteries, electronic devices, wire harnesses, etc. Friction stir welding is possible.

DESCRIPTION OF SYMBOLS 1 ... Rotary joining tool 2 ... Base 2a ... Shoulder 3 ... Probe 4a ... Hard metal plate 4b ... Soft metal plate 5 ... Butting surface 6 ... Groove φ ..Inclination angle when the probe is inserted inclined to the soft metal plate side with respect to the abutting surface T ... Thickness of the hard metal plate t ... Thickness of the soft metal plate d ... of the probe Minimum distance between tip center and butt face R ・ ・ ・ Rotational direction of rotary welding tool F ・ ・ ・ Direction of rotational welding tool

Claims (3)

In a friction stir welding method in which a hard metal plate and a soft metal plate having a smaller hardness are abutted and both the metal plates are joined by moving the rotary joining tool along the abutting surface while rotating.
The rotary joining tool has a substantially cylindrical base, a shoulder provided on both metal plate sides of the base, and a probe suspended concentrically with the base from the surface of the shoulder,
The hard metal plate is disposed on the side where the rotation direction of the rotary bonding tool is coincident with the bonding direction, and the soft metal plate is disposed on the side where the rotation direction of the rotary bonding tool is opposite to the bonding direction,
Both probes are inserted so that the probe is inclined with respect to the abutting surface toward the soft metal plate and the contact area of the shoulder with the soft metal plate is larger than the contact area with the hard metal plate. While rotating the rotary joining tool in contact with the metal plate, the two metal plates are joined by moving along the butt surface while rotating .
Friction stirrer, characterized in that an inclination angle φ (°) when the probe is inserted to be inclined toward the soft metal plate with respect to the abutting surface is defined by the following expressions (1) and (2): Joining method.
sin ⁻¹ {(0.01 + T−t) / R)} ≦ φ ≦ sin ⁻¹ {(0.03 + T−t) / R)} (1)
−0.5 <T−t <0.5 (2)
Here, T: plate thickness (mm) of the hard metal plate, t: plate thickness (mm) of the soft metal plate, and R: radius of the shoulder (mm). The minimum distance d (mm) between the center of the tip of the probe and the butting surface is joined while satisfying the following formula (3) with the radius of the probe being r (mm) and the positive direction of d being the soft metal plate side. 2. The friction stir welding method according to 1.
0 ≦ d ≦ r−0.1 (3) The surface of the shoulder is a substantially spherical convex surface or tapered surface tapered toward both metal plates, or a chamfered flat surface having a corner portion of R1.0 or more or C1 or more. a groove extending in the axial section from the side, both metal plates and plastic flow by the rotation of the rotating welding tool is a groove which is collected in the axial center of the shoulder and into the interior is formed, according to claim 1 or 2 The friction stir welding method described in 1.

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