Joining method

Abstract

To provide a joining method (lamination feature) which facilitates widening of a joining condition range for aluminum and a dissimilar metal with little wear of a rotation tool when the aluminum and the dissimilar metal are joined.SOLUTION: A joining method for friction-stirring a first metal member 1 and a second metal member 2 by using a rotation tool F comprises: a stacking step; and a joining step of rotating and inserting the rotation tool F into the first metal member 1 and joining the first metal member 1 and the second metal member 2 without contacting the rotation tool F with the second metal member 2. The rotation tool F includes a base 42 and a roughly conical tip 43. The tip 43 has a tapered side surface part 45 on the side surface, and a tip surface 46 at the tip. The tip 43 is provided with a helical groove 47 on the side surface 45. In the joining step, the tip 43 is contacted with the first metal member 1.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a bonding method. [Background technology]

[0002] Explosive welding, brazing, diffusion welding, and friction welding are known as techniques for joining aluminum or aluminum alloys to metals with higher melting points than aluminum (dissimilar metals). Explosive welding, which is not limited by size, is used to produce dissimilar metal joints such as aluminum / carbon steel and aluminum / SUS for ships and LNG tankers, but explosive welding has the problem of limiting manufacturing destinations because it uses explosives. Aluminum / SUS joints are also produced using brazing and diffusion welding, but there are restrictions on the product size and shape. Rotary friction welding, which can join dissimilar metals relatively easily, can only join circular shapes.

[0003] Therefore, dissimilar metal joining using the same solid-state joining method, friction stir welding (FSW), is being investigated. Development examples include joining steel and aluminum, stainless steel and aluminum, and titanium and aluminum. Joining copper and aluminum for conductive materials and thermal products is also being considered.

[0004] When FSW is performed by overlapping aluminum and dissimilar metals, the rotating tool is inserted into the aluminum side. The method is divided into two: either the tip of the rotating tool is brought into contact with the dissimilar metal, or it is not brought into contact. When the tip of the rotating tool is brought into contact with the dissimilar metal, a mixed region of the aluminum and dissimilar metal is formed, resulting in a strong joint. However, when the rotating tool comes into contact with hard metals other than Cu (steel, SUS, Ti, Mo, etc.), the rotating tool is severely worn and a stable joint cannot be achieved.

[0005] As an example of a method for joining dissimilar metals without contacting the tip of the rotary tool, Patent Document 1 describes a method for joining dissimilar metal members using a rotary tool having a shoulder surface and a cylindrical protrusion protruding from the shoulder surface at its tip. In Patent Document 1, a first metal member made of a steel plate and a second metal member made of an aluminum alloy plate are overlapped with the second metal member facing up, and the rotary tool is rotated while inserting its tip from the surface of the second metal member and advancing until the shoulder surface abuts the surface of the second metal member. When the rotary tool is inserted, the protrusion of the rotary tool maintains a distance from the first metal member without directly contacting it, and the metal of the second metal member is stirred while generating frictional heat, forming a stirred region that reaches the first metal member, thereby joining the first metal member and the second metal member. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-275876 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventionally, when joining dissimilar metals by FSW without contacting the rotating tool with the dissimilar metals, the range of joining conditions is very narrow, making it difficult to join aluminum to materials other than Cu. Furthermore, when a rotary tool having a shoulder surface and a cylindrical protrusion at its tip that protrudes from the shoulder surface is used, as in Patent Document 1, the joining range between aluminum and the dissimilar metal is limited to the range corresponding to the protrusion, resulting in a narrow width of the joining area.

[0008] From this perspective, the present invention aims to provide a joining method (lamination technology) that reduces wear on the rotary tool when joining aluminum and dissimilar metals and makes it easier to expand the range of joining conditions between aluminum and dissimilar metals. [Means for solving the problem]

[0009] (1) In order to solve the above problems, the present invention provides a method for joining a first metal member made of aluminum or an aluminum alloy and a second metal member made of a metal having a melting point higher than that of aluminum by friction stirring using a rotary tool, the method comprising: an overlapping step of overlapping the first metal member and the second metal member; and a joining step of inserting the rotary tool into the first metal member while rotating, without bringing the rotary tool into contact with the second metal member, causing plastic flow of the metal material of the first metal member by friction stirring and diffusion bonding it to the metal material of the second metal member, thereby joining the first metal member and the second metal member; the rotary tool has a base and a generally conical tip portion continuous with the base, the tip portion having a tapered side surface centered on the rotation axis of the rotary tool and a tip surface portion at a tip end perpendicular to the rotation axis of the rotary tool, and the side surface of the tip portion has a spiral groove; and the tip portion is brought into contact with the first metal member in the joining step.

[0010] (2) The joining method according to (1), wherein the spiral groove has a step portion consisting of step side surfaces extending in a direction approximately parallel to the rotation axis of the rotary tool and a step bottom surface facing in a direction approximately perpendicular to the rotation axis, and the step portion is formed so that, as the step portion spirals around, the step bottom surface of the step portion is adjacent to the step side surface of the step portion located on the outer periphery of the tip portion, and the step side surface of the step portion is adjacent to the step bottom surface of the step portion located on the inner periphery of the tip portion, and a recess recessed in the direction of the rotation axis is provided in the step bottom surface.

[0011] (3) The joining method according to (1), wherein the depth of the spiral groove is 0.1 mm or more and 1.0 mm or less.

[0012] (4) The joining method according to (1), wherein the width of the spiral groove is 1 mm or more and 5 mm or less.

[0013] (5) The joining method according to (1), wherein the ratio of the depth of the spiral groove to the width of the spiral groove is 0.2 or more and 2.0 or less.

[0014] (6) The bonding method according to (2), wherein the depth of the recess is 0.1 mm or more and 0.5 mm or less.

[0015] (7) The joining method according to (2), wherein the ratio of the depth of the recess to the width of the spiral groove is 0.1 or more and 0.9 or less.

[0016] (8) The joining method according to (1), wherein the tip has a taper angle of 120° or more and 175° or less.

[0017] (9) The joining method according to (1), wherein in the joining step, the distance between the lower end of the tip surface portion and the surface of the second metal member is 0.05 mm or more and 0.2 mm or less.

[0018] (10) The joining method described in (1), wherein in the joining process, the tip portion is inserted into the first metal member, and the base end portion of the tip portion on the base portion side and the base portion are not inserted into the first metal member.

[0019] (11) The joining method according to (1), wherein in the joining step, the plasticized regions of the first metal members formed in adjacent joining paths are joined by overlapping each other.

[0020] (12) The joining method according to (1), wherein in the joining step, the first metal member and the second metal member are joined by overlapping the joining regions formed in adjacent joining paths.

[0021] (13) The joining method according to (1), wherein the first metal member is an aluminum alloy having a solidus temperature of 600°C or higher and a thermal conductivity of 160 W / m·K or higher.

[0022] (14) The joining method according to (1), wherein in the joining step, the contact length of the rotary tool per unit plate thickness is set to 50 mm or more.

[0023] (15) The joining method according to (1), wherein the second metal member comprises at least one selected from the group consisting of steel, stainless steel, titanium, titanium alloy, molybdenum, molybdenum alloy, copper, or copper alloy. [Effects of the Invention]

[0024] According to the joining method of the present invention, when joining aluminum and dissimilar metals, wear on the rotary tool is small and the range of joining conditions for joining aluminum and dissimilar metals can be easily expanded. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 2 is a side view showing a rotary tool according to an embodiment of the present invention. [Figure 2] FIG. 2 is a bottom view of the rotation tool according to the embodiment. [Figure 3] FIG. 2 is an enlarged side cross-sectional view of the rotary tool according to the embodiment. [Figure 4] 1 is a perspective view showing a joining method according to the present embodiment. [Figure 5] FIG. 2 is a front view showing a joining method according to the present embodiment. [Figure 6] FIG. 10 is a front view (after reciprocation) showing the joining method according to the present embodiment. [Figure 7] FIG. 10 is a front view showing a comparative example test. [Figure 8] 10 is a graph showing the relationship between insertion depth and tensile strength in a comparative example test. [Figure 9] FIG. 1 is a cross-sectional view of a joint in a comparative example test (insertion depth 1). [Figure 10] FIG. 10 is a cross-sectional view of a joint in a comparative example test (insertion depth 2). [Figure 11] 1 is a graph showing the relationship between the taper angle of the rotary tool and the tensile strength in Example Test 1. [Figure 12] FIG. 1 is a cross-sectional view of the structure of a joint in Example Test 1. [Figure 13]FIG. 1 is an enlarged view of a bonded portion (bonded interface) in Example Test 1. [Figure 14] FIG. 1 shows elemental mapping in Example Test 1. [Figure 15] 10 is a graph showing the relationship between the thickness of an aluminum alloy plate and the contact area between the aluminum and a rotary tool in Example Test 3. [Figure 16] 10 is a graph showing the relationship between the plate thickness of an aluminum alloy in Example Test 3 and the contact length of a rotary tool per unit plate thickness. [Figure 17] 1 is a schematic plan view of Example Test 4. [Figure 18] FIG. 10 is a schematic cross-sectional view in Example Test 4. [Figure 19] 1 is a graph showing the relationship between time and temperature (up to 1600 seconds) in Example Test 4. [Figure 20] 1 is a graph showing the relationship between time and temperature (up to 1100 seconds) in Example Test 4. DETAILED DESCRIPTION OF THE INVENTION

[0026] Embodiments of the present invention will be described with reference to the drawings as appropriate. The present invention is not limited to the following embodiments. Furthermore, the components in the embodiments can be combined in part or in whole as appropriate. Furthermore, "front surface" means the surface opposite to the "rear surface." In this specification, a numerical range expressed by "to" indicates "greater than or equal to" or "less than or equal to," and is intended to include both values. Furthermore, the drawings are intended to conceptually explain the present invention, and the dimensions and ratios of each component shown may differ from the actual ones.

[0027] [1. Rotation Tool] First, the rotary tool used in the joining method of the present invention will be described. As shown in Figs. 1 to 3, the rotary tool F is a tool that softens a metal material by pressing it against the metal material while rotating. The rotary tool F is made of tool steel. The rotary tool F includes a base end portion 41, a base portion 42, and a tip end portion 43. A spiral groove 47 is formed on the surface of the tip end portion 43. The rotary tool F is rotated in the circumferential direction as described below, and the tip end portion 43 is brought into contact with the metal material.

[0028] The base end 41 is a cylindrical portion that is attached to a machining center, a friction stirring device, etc. (not shown). The base 42 is, for example, cylindrical, and a flange 44 that protrudes outward from the base end 41 side is formed.

[0029] The tip portion 43 has a generally conical shape that tapers from the base portion 42 toward the tip. The tip portion 43 has a tapered side surface portion 45 on its side surface that is centered on the rotation axis C of the rotary tool F. In a cross-sectional view parallel to the rotation axis C and passing through the rotation axis C, the side surface portion 45 may be linear, may have a convex shape that bulges outward, or may have a concave shape that is recessed inward. The tip portion 43 may have a pointed conical shape or a truncated cone shape with a flat portion at the tip. In this embodiment, the tip portion 43 has a tapered side surface portion 45 on its side surface that is centered on the rotation axis C of the rotary tool F, and a flat tip surface portion 46 at its tip that is continuous with the side surface portion 45 toward the tip and perpendicular to the rotation axis C of the rotary tool F. In this embodiment, the side surface portion 45 of the tip portion 43 is linear in a cross-sectional view parallel to the rotation axis C and passing through the rotation axis C.

[0030] The taper angle θ1 of the tip portion 43 is preferably an obtuse angle. More specifically, the taper angle θ1 of the tip portion 43 is preferably 120 to 175°. The taper angle θ1 is more preferably 130 to 165°, even more preferably 140 to 160°, and particularly preferably 145 to 155°.

[0031] The spiral groove 47 is provided so as to spirally wrap around from the center side of the rotary tool F and expand toward the outer periphery. The number of turns of the spiral groove 47 is preferably one or more, more preferably two or more, even more preferably three or more, and particularly preferably five or more. The spiral groove 47 may be formed by a single spiral groove wrapping around, or may be formed by two or more spiral grooves wrapping around in parallel to each other.

[0032] 3, the spiral groove 47 has a step portion 53 made up of a step side surface 51 extending in a direction substantially parallel to the rotation axis C of the rotary tool F and a step bottom surface 52 facing in a direction substantially perpendicular to the rotation axis C. When the rotary tool F is viewed in cross section on a plane passing through the rotation axis, the step portion 53 spirally wraps around the side surface portion 45, and the step side surface 51 and step bottom surface 52 of step portions 53 at different wraparound locations are adjacent to each other and are repeatedly formed.

[0033] Specifically, the stepped portion 53 spirals around, forming, from the outer periphery, a first stepped portion 53a consisting of a first stepped side surface 51a and a first stepped bottom surface 52a, a second stepped portion 53b consisting of a second stepped side surface 51b and a second stepped bottom surface 52b, and a third stepped portion 53c consisting of a third stepped side surface 51c and a third stepped bottom surface 52c in this order. In this case, the second stepped bottom surface 52b of the second stepped portion 53b is adjacent to the first stepped side surface 51a of the first stepped portion 53a located on the outer periphery side of the tip portion 43. Furthermore, the second stepped side surface 51b of the second stepped portion 53b is adjacent to the third stepped bottom surface 52c of the third stepped portion 53c located on the inner periphery side of the tip portion 43. In this way, the step portions 53 are formed adjacent to each other repeatedly in a spiral around the side surface 45, and there is no tapered surface formed by the taper angle of the tapered tip portion 43 between adjacent step portions 53.

[0034] The stepped bottom surface 52 has a recess 54 recessed in the direction of the rotation axis C. The stepped bottom surface 52 and the recess 54 form a stepped bottom 55. That is, the stepped portion 53 spirally wraps around the side surface 45, with the second step bottom 55b of the second step portion 53b adjacent to the first step side surface 51a of the first step portion 53a located on the outer periphery, and the second step side surface 51b of the second step portion 53b adjacent to the third step bottom 55c of the third step portion 53c located on the inner periphery. The stepped side surface 51 located on the outer periphery of the stepped bottom surface 52 and the recess 54 provided in the stepped bottom surface 52 form a protruding portion 56 that protrudes in the direction of the rotation axis C toward the tip of the tool. As described above, the shape of the spiral groove 47 is neither stepped (stepped) nor screw-shaped.

[0035] The cross-sectional shape of the recess 54 provided in the spiral groove 47 is arc-shaped in this embodiment, but it may be elliptical, rectangular, triangular, etc. From the viewpoint of preventing the metal material from accumulating in the recess 54, it is preferable that the cross-sectional shape of the recess 54 be arc-shaped.

[0036] The recess 54 may be provided over the entire step bottom surface 52, or may be provided on a portion of the step bottom surface 52 by being spaced apart from the inner or outer peripheral end of the step bottom surface 52. By providing the recess 54 at a distance from the inner peripheral end of the step bottom surface 52, an inner peripheral step bottom surface 57 is formed. By providing the recess 54 at a distance from the outer peripheral end of the step bottom surface 52, an outer peripheral step bottom surface 58 is formed. By providing the recess 54 at the outer peripheral end of the step bottom surface 52, the protruding portion 56 has a pointed shape toward the tip of the tool. When the recess 54 is provided at the outer peripheral end of the step bottom surface 52, the pointed protruding portion 56 is more susceptible to wear. For this reason, it is preferable that the recess 54 be spaced apart from the outer peripheral end of the step bottom surface 52 to form the outer peripheral step bottom surface 58. In this embodiment, at the step bottom surface 52. On the inner and outer circumferential sides where the recesses 54 are provided, an inner circumferential step bottom surface 57 and an outer circumferential step bottom surface 58 remain as flat portions where the recesses 54 are not formed.

[0037] Furthermore, it is preferable that recess 54 is lower (shallower) than the height of protruding portion 56 formed in step portion 53 located on the outer periphery of step bottom surface 52 where recess 54 is provided. It is also preferable that the depth of recess 54 at step bottom 55 where recess 54 is provided is lower (smaller) than the height of step side surface 51. This makes it possible to prevent the metal material from accumulating in recess 54, and makes it easier for tip portion 43 to uniformly extrude the metal material.

[0038] The depth H2 of the spiral groove 47 is preferably 0.1 mm to 1.5 mm. The depth H2 refers to the length, in the direction of the rotation axis C of the rotary tool F, between the deepest portion of the recess 54 provided in the step bottom surface 52 and the deepest portion of the protruding portion 56 of the step side surface 51 adjacent to the inner periphery of the step bottom surface 52. The depth H2 is more preferably 0.3 to 1.3 mm, even more preferably 0.4 to 1.2 mm, and particularly preferably 0.5 to 1.0 mm. The depth H2 of the spiral groove 47 is preferably 5 to 30% of the height (total length) of the tip portion 43, more preferably 8 to 27%, and even more preferably 11 to 25%. Note that, when there are multiple spiral grooves 47 with different depths H2, the average value of these depths H2 is calculated. The same applies to other dimensions related to the shape of the spiral groove 47.

[0039] The width R1 of the spiral groove 47 is preferably 1 to 5 mm. The width R1 of the spiral groove 47 is, for example, the distance from the second step side surface 51b to the third step side surface 51c. The width R1 of the spiral groove 47 is more preferably 1.2 to 4 mm, even more preferably 1.3 to 3 mm, and particularly preferably 1.5 to 2 mm.

[0040] The ratio of the depth H2 of the spiral groove 47 to the width R1 of the spiral groove 47 is preferably 0.2 to 2.0, and more preferably 0.3 to 1.8.

[0041] The depth of the recess 54 is preferably 0.1 to 0.5 mm, and more preferably 0.2 to 0.4 mm.

[0042] The ratio of the depth of the recess 54 to the width R1 of the spiral groove 47 is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and even more preferably 0.3 to 0.7.

[0043] The pitch (interval) P1 of the spiral groove 47 is preferably 0.5 to 2.5 mm. The pitch P1 refers to the average interval between the spiral grooves 47 formed in a plane perpendicular to the rotation axis C of the rotary tool F, spiraling around from the center of the rotation axis C and spreading outward. The pitch P1 is more preferably 0.7 to 2.0 mm, even more preferably 1.0 to 1.8 mm, and particularly preferably 1.2 to 1.5 mm. The pitch of the spiral groove 47 is preferably 2 to 15% of the diameter of the tip portion 43, more preferably 4 to 10%, and even more preferably 5 to 9%.

[0044] [2.Joining method] Next, the bonding method of the present invention will be described. In the bonding method according to this embodiment, as shown in Figs. 4 to 6, a stacking step and a bonding step are performed.

[0045] The overlapping step is a step of overlapping a first metal member 1 and a second metal member 2. The first metal member 1 is a plate-like member made of aluminum or an aluminum alloy. The first metal member is preferably, for example, a JIS A1000 series alloy or an A6063 series alloy. The first metal member 1 has, for example, a solidus temperature of 600°C or higher and a thermal conductivity of 160 W / m·K or higher. The solidus temperature of the first metal member 1 is preferably 600°C or higher, more preferably 620°C or higher, even more preferably 640°C or higher, and particularly preferably 650°C or higher. The thermal conductivity of the first metal member 1 is preferably 160 W / m·K or more, more preferably 180 W / m·K or more, even more preferably 200 W / m·K or more, and particularly preferably 220 W / m·K or more. The plate thickness of the first metal member 1 may be set appropriately and is, for example, 1 to 5 mm.

[0046] The second metal member 2 is a plate-shaped member made of a metal having a melting point higher than that of aluminum. The second metal member includes, for example, at least one selected from the group consisting of steel, stainless steel, titanium, a titanium alloy, molybdenum, a molybdenum alloy, copper, or a copper alloy.

[0047] In the overlapping step, the rear surface 1b of the first metal member 1 and the front surface 2a of the second metal member 2 are overlapped to form an overlapping portion J1.

[0048] The joining process is a process in which a first metal member 1 and a second metal member 2 are joined by friction stirring using a rotating tool F. In the joining process, the rotated rotating tool F is inserted into the surface 1a of the first metal member 1, and the metal material of the first metal member 1 is plastically flowed by friction stirring without contacting the second metal member 2, and diffusion-bonded to the metal material of the second metal member 2, thereby joining the first metal member 1 and the second metal member 2. A plasticized region W1 is formed in the starting trajectory of the rotating tool F.

[0049] 5 , in the joining process, the insertion amount (insertion depth) is set so that the side surface 45 of the tip portion 43 comes into contact with the surface 1a of the first metal member 1 without the base portion 42 of the rotary tool F coming into contact with the first metal member 1. In other words, in the joining process, the tip portion 43 is inserted into the first metal member 1, and the base end portion 43a of the tip portion 43 on the base portion 42 side and the base portion 42 are not inserted into (do not come into contact with) the first metal member 1. In addition, the insertion depth of the tip surface portion 46 of the rotary tool F is set so that it does not come into contact with the second metal member 2, but the plasticized region W1 reaches the overlapping portion J1.

[0050] In the joining step, the distance between the surface 2a of the second metal member 2 and the lower end of the tip surface 46 may be set as appropriate, for example, to 0.05 to 0.2 mm. The distance between the surface 2a of the second metal member 2 and the lower end of the tip surface 46 is preferably 0.06 mm or more, more preferably 0.07 mm or more, even more preferably 0.08 mm or more, and is preferably 0.18 mm or less, more preferably 0.15 mm or less, even more preferably 0.12 mm or less. The insertion depth of the rotary tool F into the first metal member 1 may be set so that the distance between the surface 2a of the second metal member 2 and the lower end of the tip surface 46 of the rotary tool F falls within the above-mentioned range.

[0051] 6, in the joining process, the rotary tool F is moved linearly or curvedly in a plan view while maintaining the insertion depth, so that adjacent plasticized regions W1, W1 overlap. That is, the plasticized regions W1 of the first metal member 1 formed in adjacent joining paths are overlapped for joining. Alternatively, the first metal member 1 and the second metal member 2 may be joined so that their joining regions formed in adjacent joining paths overlap.

[0052] In the joining step, the contact length of the rotary tool F per unit plate thickness is preferably set to 50 mm or more. The contact length of the rotary tool F per unit plate thickness is more preferably 100 mm or more, further preferably 200 mm or more, and particularly preferably 300 mm or more. The contact area (mm 2 ) by the plate thickness (mm) of the first metal member 1, the contact length (mm) is calculated. 2 ) refers to the contact area between the outer shape of the cone-shaped tip portion 43 and the first metal member 1, for the truncated cone-shaped tip portion 43 having tapered side portions 45 on the side and a flat tip surface portion 46 provided on the tip side of the side portions 45, without taking into consideration the shape of the spiral groove 47, the step portion 53, and the recessed portion 54 of the tip portion 43.

[0053] The joining process (lamination technology) requires a relatively large amount of heat, and this heat can be ensured by setting the contact length of the rotating tool F per unit plate thickness to 50 mm or more. In other words, the joining process (lamination technology) does not involve contacting the rotating tool F with the second metal member 2, so the first metal member 1 and the second metal member 2 are not mixed. This is a typical solid-state joining process (temperature + plastic deformation), and joining does not occur until a predetermined temperature (relatively high) is exceeded. Therefore, a contact length of the rotating tool F per unit plate thickness of 50 mm or more is required to exceed the joining temperature (the temperature at which elements diffuse). If the plate thickness of the first metal member 1 and the insertion amount of the rotating tool F are constant, increasing the contact area between the rotating tool F and the first metal member 1 increases the contact length of the rotating tool F per unit plate thickness. In other words, increasing the contact area between the rotating tool F and the first metal member 1 increases the contact length of the rotating tool F per unit plate thickness. The contact area between the rotary tool F and the first metal member 1 can be increased by increasing the taper angle θ1 of the rotary tool F.

[0054] [3. Action and Effects] According to the joining method of this embodiment described above, the rotary tool F is inserted into the first metal member 1 while rotating, and the metal material of the first metal member 1 is plastically flowed by friction stirring without contacting the second metal member 2 with the rotary tool F, and diffusion bonded to the metal material of the second metal member 2, thereby joining the first metal member 1 and the second metal member 2.In order to perform the joining process, the rotary tool F is provided with an approximately conical tip portion 43 having a tapered side portion 45, and a spiral groove 47 is formed on the surface of the side portion 45, and the tip portion 43 is brought into contact with the first metal member 1.

[0055] As a result, the rotary tool F applies pressure to the first metal member 1 and generates frictional heat, causing plastic flow of the metal material of the first metal member 1, and the plastically flowed metal material of the first metal member 1 is rubbed against the surface 2a of the second metal member 2. The generally conical tip 43 with the tapered side 45 causes plastic flow of the metal material of the first metal member 1 over a wide area. Furthermore, the spiral groove 47 guides the metal material of the first metal member 1 toward the tip 43, thereby enhancing plastic flow toward the second metal member 2. This strengthens the rubbing action of the metal material of the first metal member 1 against the surface 2a of the second metal member 2, thereby promoting diffusion bonding between the metal materials of the first metal member 1 and the second metal member 2. In this embodiment, the truncated cone-shaped tip 43 is inserted into the first metal member 1, allowing the insertion depth to be adjusted according to the desired welding width, thereby making it easier to expand the range of welding conditions.

[0056] Furthermore, according to this embodiment, the rotary tool F does not come into contact with the second metal member 2, which is made of a metal having a higher melting point and higher hardness than aluminum, thereby reducing wear on the rotary tool F. Furthermore, according to this embodiment, the rotary tool F is attached to a normal machining center and moved while rotating, thereby joining aluminum and aluminum alloys to hard metal surfaces. According to this embodiment, partial joining is also possible, but a clad material can also be produced by planarly laminating the first metal member 1 onto the second metal member 2. In this way, a material can be obtained in which aluminum and aluminum alloys are joined (laminated) arbitrarily to a hard metal surface.

[0057] In this embodiment, the step portion 53 spirals around, with the step bottom surface 52 of the step portion 53 adjacent to the step side surface 51 of the step portion 53 located on the outer periphery of the tip portion 43, and the step side surface 51 of the step portion 53 adjacent to the step bottom surface 52 of the step portion 53 located on the inner periphery of the tip portion 43, and the step bottom surface 52 is formed with a recess 54 recessed in the direction of the rotation axis C (towards the base portion 42). In conventional rotary tools, there are some tapered tip portions in which step portions are repeatedly formed while sandwiching the tapered surfaces of the tip portion, but in such rotary tools, the tapered surfaces sandwiched between the step portions weaken the effect of plastically flowing the metal material of the first metal member 1 toward the second metal member 2. By using the rotary tool F of this embodiment, it is easier to guide the plastic flow material to the tip side of the tip portion 43 through the spiral groove 47 than when a tapered surface exists between adjacent step portions 53, making it easier to form a joint by diffusion bonding, and the tip portion 43 has a shape that makes it easier for metal to flow and less likely to become clogged.

[0058] Furthermore, the depth of spiral groove 47 is preferably 0.1 to 1.0 mm, which makes it easier to guide the plastic flow material to the tip side of tip portion 43 via spiral groove 47 and form a joint by diffusion bonding, and also makes it harder for tip portion 43 to be clogged with the plastic flow material (metal), making it easier to cause the plastic flow material to flow.

[0059] The width of the spiral groove 47 is preferably 1 to 5 mm, which makes it easier to guide the plastic flow material to the tip end portion 43 side.

[0060] Furthermore, it is preferable that the ratio of the depth H2 of the spiral groove 47 to the width R1 of the spiral groove 47 is 0.2 to 2.0, which makes it difficult for the plastic flow material (metal) to clog the tip portion 43 and makes it easier for the plastic flow material to flow.

[0061] Furthermore, the depth of recess 54 is preferably 0.1 to 0.5 mm. This makes it easier to guide the plastic flow material to the tip side of tip portion 43 via spiral groove 47 and form a joint by diffusion bonding, and also makes it harder for tip portion 43 to be clogged with the plastic flow material (metal), making it easier to cause the plastic flow material to flow.

[0062] Furthermore, it is preferable that the ratio of the depth of recess 54 to the width R1 of spiral groove 47 is 0.1 to 0.9. When the ratio of the depth of recess 54 to the width R1 of spiral groove 47 is equal to or greater than the above-mentioned lower limit, recess 54 is more likely to exhibit the effect of promoting the stirring of the metal material. When the ratio of the depth of recess 54 to the width R1 of spiral groove 47 is equal to or less than the above-mentioned upper limit, the plastic flow material (metal) is less likely to clog in recess 54 of tip 43, and tip 43 makes it easier to flow and uniformly extrude the plastic flow material.

[0063] Furthermore, the taper angle of the tip portion 43 is preferably 120 to 175°. Setting the taper angle of the tip portion 43 to 120° or more increases the contact area between the rotary tool F and the first metal member 1, increasing the amount of heat generated by friction stirring. This increases the heat input to the first metal member 1, making it easier to promote diffusion bonding between the first metal member 1 and the second metal member 2. Setting the taper angle of the tip portion 43 to the above-described lower limit or greater can enhance the plastic flow force, which is generated as the rotary tool F rotates and moves and causes the metal material of the first metal member 1 to plastically flow and press it against the second metal member 2. These actions promote diffusion bonding between the first metal member 1 and the second metal member 2 and increase the bonding strength. Setting the taper angle of the tip portion 43 to the above-described lower limit or greater can expand the range of the plasticized region W1 formed by the rotary tool F, enabling a wider region to be joined in a single joining pass, thereby improving production efficiency. When the taper angle θ1 of the tip portion 43 is equal to or less than the upper limit, the tip portion 43 of the rotary tool F acts on the first metal member 1, making it easier to induce plastic flow in the first metal member 1.

[0064] In the joining step, the distance between the surface 2a of the second metal member 2 and the lower end of the tip surface portion 46 is preferably 0.05 to 0.2 mm. By setting this distance to 0.05 mm or more, the rotary tool F does not come into contact with the second metal member 2, thereby increasing the joining strength. By setting this distance to 0.2 mm or less, frictional heat generated by friction stirring is transferred to the joining interface, thereby increasing the joining strength.

[0065] Furthermore, in the joining step, it is preferable that the tip portion 43 is inserted into the first metal member 1, and that the base end portion 43a on the base side of the tip portion 43 and the base portion 42 are not inserted into the first metal member 1. This allows the tapered tip portion 43 to firmly hold the plastic flow material without the plastic flow material spilling out.

[0066] In addition, in the joining process, the plasticized regions W1, W1 of the first metal member 1 formed in adjacent joining paths are overlapped during joining. This prevents any areas from remaining unaffected by friction stirring, increasing the joining strength. It also improves airtightness and watertightness.

[0067] Furthermore, in the joining process, the first metal member 1 and the second metal member 2 are joined by overlapping the joining regions formed in adjacent joining paths. In other words, by overlapping the joining regions that are actually joined at the overlapping portion J1, the reliability of the joining can be increased, and the joining strength can be further increased.

[0068] Furthermore, it is preferable that the thickness of the first metal member 1 is 1 to 5 mm. If the thickness of the first metal member 1 is 1 mm or more, the first metal member 1 does not deform, and a good welded member can be formed. If the thickness of the first metal member 1 is 5 mm or less, frictional heat from the rotary tool F is transmitted to the overlapping portion J1 (welding portion), and the welding strength can be increased.

[0069] Furthermore, the first metal member 1 is preferably an aluminum alloy having a solidus temperature of 600°C or higher and a thermal conductivity of 160 W / m·K or higher. When performing diffusion bonding between the first metal member 1 and the second metal member 2, inserting the rotary tool F into the first metal member 1 causes heat to be generated in the first metal member 1. This heat is then transferred to the second metal member 2, facilitating diffusion bonding at the joint. For example, the temperature at the joint between the first metal member 1 and the second metal member 2 can reach 550°C or higher. If the solidus temperature of the first metal member 1 is low, joining must be performed under joining conditions that generate relatively little heat in the first metal member 1 to avoid partial melting of the first metal member 1. In this case, it becomes difficult to promote diffusion bonding at the joint by increasing the heat generated in the first metal member 1 and transferring the heat to the second metal member 2. In this embodiment, by setting the solidus temperature of the first metal member 1 at or above the lower limit, the first metal member 1, which has been heated to a high temperature, can be pressed against the second metal member (dissimilar metal) 2, facilitating diffusion bonding. Furthermore, by having the thermal conductivity of the first metal member 1 be equal to or greater than the above numerical range, the heat input from the rotating tool F is transmitted to the first metal member 1, making it easier to further transfer heat to the second metal member (dissimilar metal) 2, thereby facilitating diffusion bonding.

[0070] In addition, in the joining step, it is preferable to set the contact length of the rotary tool F per unit plate thickness to 50 mm or more. This increases the frictional heat between the rotary tool F and the first metal member 1, thereby increasing the joining strength.

[0071] Furthermore, the first metal member 1 is preferably made of an A1000-based alloy or an A6063-based alloy, which can increase the bonding strength.

[0072] The second metal member 2 preferably contains at least one selected from the group consisting of steel, stainless steel, titanium, titanium alloy, molybdenum, molybdenum alloy, copper, and copper alloy, thereby increasing the bonding strength.

[0073] Although the embodiment of the present invention has been described above, appropriate design changes are possible within the scope of the present invention. In addition, in this embodiment, the tip portion 43 of the rotary tool F has a flat inclined surface when viewed from the side, but it may have a curved surface that is concave toward the rotation axis C, or a curved surface that is convex in the direction away from the rotation axis C. [Example]

[0074] Next, examples of the present invention will be described. In order to demonstrate the effects of the present invention, Comparative Example Test 1 and Example Tests 1 to 4 were carried out.

[0075] [Evaluation method] <Tensile test> A strip was prepared by cutting out a strip having a width of 10 mm at the center in the short direction of the joined body and a length corresponding to the entire length in the long direction of the joined body from the joined body produced by joining the first metal member 1 and the second metal member 2. Both ends of the strip specimen were set in a tensile tester and subjected to a simple tensile test to determine the breaking load.

[0076] <Simple bending test> A strip specimen was prepared by cutting out a strip from a bonded body produced by bonding a first metal member 1 and a second metal member 2. The strip had a width of 10 mm at the center of the bonded body in the short direction and a length equal to the entire length of the bonded body in the long direction. The first metal member 1 (aluminum material) side of the strip specimen was clamped in a vice, and the opposite side, the second metal member 2 (dissimilar metal material) side, was struck with a hammer to check for peeling between the first metal member 1 and the second metal member 2. Those that did not peel were rated as good, and those that peeled were rated as bad.

[0077] [Comparative Example Test 1] In Comparative Example Test 1, metal members were joined using a rotary tool G according to the comparative example, as shown in FIG. 7. The rotary tool G includes a base G1 and a stirring pin G2. The base G1 is a cylindrical portion connected to a friction stir welding device (not shown). The stirring pin G2 hangs down from the base G1 and tapers toward the tip. The tip of the stirring pin G2 has a flat surface. The diameter of the tip of the stirring pin G2 is 4 mm, and the taper angle is 40°. A spiral groove is provided in the stirring pin G2.

[0078] In Comparative Example Test 1, a laminating step and a joining step were performed. In the laminating step, the first metal member 1 and the second metal member 2 were overlapped to form an overlapping portion J1. In the joining step, a stirring pin G2 was inserted from the surface 1a of the first metal member 1, and friction stirring was performed with only the stirring pin G2 in contact with both the first metal member 1 and the second metal member 2.

[0079] The first metal member 1 was made of an aluminum alloy (JIS A5052-H34) and had a thickness of 5 mm. The second metal member 2 was made of a copper alloy (JIS C1020) and had a thickness of 5 mm. In the joining process, friction stir welding was performed while changing the insertion depth of the rotary tool G to 5.3 mm, 5.4 mm, 5.5 mm, 5.6 mm, 5.7 mm, and 5.8 mm, and the tensile strength of the joined test piece (joint) was measured.

[0080] FIG. 8 is a graph showing the relationship between the insertion depth into the first metal member 1 and the tensile strength in Comparative Example Test 1. As shown in FIG. 8, when the insertion depth was 5.3 mm, the tensile strength was 0 N / mm. In other words, when the insertion depth was 5.3 mm, the members to be joined were not joined. When the insertion depth was between 5.4 and 5.8 mm, joining was achieved, but sufficient tensile strength was not obtained. Furthermore, when the insertion depth was between 5.4 and 5.8 mm, the tensile strength decreased around the insertion depth of 5.65 mm. Thus, it can be seen that in Comparative Example Test 1, joining was not possible when the stirring pin was inserted into the second metal member 2 by 0.3 mm, but joining was possible when the insertion depth was 0.4 mm or more.

[0081] Fig. 9 is a diagram (insertion depth 1) showing the weld (welding interface) when the insertion depth was 5.4 mm in Comparative Example Test 1. Fig. 10 is a diagram (insertion depth 2) showing the weld (welding interface) when the insertion depth was 5.6 mm in Comparative Example Test 1. As shown in Figs. 9 and 10, when a first metal member 1 made of an aluminum alloy and a second metal member 2 made of a copper alloy were joined using a rotary tool G having a stirring pin G2 with a taper angle of 40°, welding was possible under the joining conditions in which the tip of the rotary tool G was inserted into the second metal member 2.

[0082] As shown in Figures 9 and 10, the rotating tool G comes into contact with the metal member 2 and stirs it, forming a plasticized region W2. In Comparative Example Test 1, gaps S1, S1 are formed at the interface between the first metal member 1 and the second metal member 2. As can be seen, the metal member 2 is joined at the location where the rotating tool G is inserted into the second metal member 2, but is not joined in the vicinity of the tool away from the tool insertion location. Furthermore, in Comparative Example Test 1, the metal member 2 is not uniformly friction-stirred, forming a non-homogeneous portion S2. This non-homogeneous portion S2 is prone to peeling, resulting in a decrease in strength.

[0083] In Comparative Example Test 1, the taper angle of the rotary tool G was small, so the contact area with the first metal member 1 was small, and when the insertion depth was 5.3 mm, there was no contact between the second metal member 2 and the rotary tool G. When there was little contact between the rotary tool G and the first metal member 1 and the second metal member 2, sufficient frictional heat and pressing force were not obtained, resulting in insufficient joining. On the other hand, when the rotary tool G was in sufficient contact with the second metal member 2, joining was possible, but depending on the conditions, a plasticized region W2 was formed, resulting in a decrease in strength. The biggest issue was tool damage, which was severe when the metal member 2 was a high-temperature, hard metal.

[0084] [Example Test 1] In Example Test 1, three types of rotary tools F1 to F3 having different taper angles at the tip 43 were used, which were the rotary tool F described with reference to Figures 1 to 3, and the above-mentioned joining method was performed by changing the material type of the second metal member 2, and the tensile strength of the joined test piece (joint) was measured.

[0085] The first metal member 1 was an aluminum alloy (JIS A1100-H14) plate with a thickness of 4 mm, a width of 80 mm, and a length of 200 mm. The second metal member 2 was a stainless steel or titanium alloy plate with a thickness of 4 mm, a width of 80 mm, and a length of 200 mm.

[0086] The first rotary tool F1 has a base 42 with a diameter of 20 mm, a tip surface 46 with a diameter of 3 mm, a tip 43 with a taper angle θ1 of 105°, and a height of 7.7 mm. The rotary tool F1 has a spiral groove 47 with a pitch of 1.5 mm and a depth H2 of 1.15 mm. The rotary tool F1 has a recess 54 with a depth of 0.3 mm and is arc-shaped. The second rotary tool F2 has a base 42 with a diameter of 20 mm, a tip surface 46 with a diameter of 3 mm, a tip 43 with a taper angle θ1 of 120°, a height of 5.8 mm, a spiral groove 47 with a pitch of 1.5 mm, and a depth H2 of 0.87 mm. The rotary tool F2 has an arc-shaped recess 54 with a depth of 0.3 mm. The third rotary tool F3 has a base 42 with a diameter of 20 mm, a tip surface 46 with a diameter of 3 mm, a tip 43 with a taper angle θ1 of 135°, a height of 4.1 mm, a spiral groove 47 with a pitch of 1.5 mm, and a depth H2 of 0.62 mm. The rotary tool F3 has an arc-shaped recess 54 with a depth of 0.3 mm.

[0087] In Example Test 1, an overlapping step and a joining step were performed. In the overlapping step, the longitudinal ends of the first metal member 1 and the second metal member 2 were overlapped over a 40 mm region to form an overlapping portion J1. In the joining step, the rotary tools F1 to F3 were inserted from the surface 1a of the first metal member 1, and their tips 43 were brought into contact with the first metal member 1 to perform friction stir welding. The tool plunge depth of the rotary tools F1 to F3 was 3.8 mm. That is, the rotary tools F1 to F3 were not in contact with the second metal member 2, and the tool tips were set 0.2 mm toward the first metal member 1 from the surface of the second metal member 2. The tool rotation speed was constant at 3000 rpm, and the joining speed was constant at 300 mm / min. Strip specimens were prepared from the joined bodies produced by joining, and tensile tests and simple bending tests were performed. In this test, all of the welds fractured due to shear.

[0088] As shown in Figure 11, the rotary tool F1 with a taper angle of 105° yielded low tensile strength for both stainless steel and titanium alloy. On the other hand, rotary tools F2 and F3 with taper angles of 120° and 135° yielded sufficient tensile strength for both stainless steel and titanium alloy. The 135° taper angle yielded higher tensile strength than the 120° taper angle.

[0089] Fig. 12 is a cross-sectional view of the structure of a weld in Example Test 1. Fig. 12 shows a weld when an aluminum alloy and stainless steel are welded using a rotary tool F3 with a taper angle of 135°. Region U1 indicates the range where the rotary tool F is inserted. Region U2 indicates the welded region (welded region). As shown in region U2, in this test specimen (welded joint), the first metal member 1 and the second metal member 2 are welded in close contact with each other.

[0090] Fig. 13 is an enlarged cross-sectional view of the joint (joint interface) in Example Test 1. Fig. 13 is an enlarged view of region V in Fig. 12. No gap is formed between the first metal member 1 and the second metal member 2, and a substantially uniform intermetallic compound (diffusion layer) is formed in a layer shape.

[0091] FIG. 14 shows elemental mapping in Example Test 1. The band on the right side of FIG. 14 shows the count amount of Fe element by elemental mapping. As shown in FIG. 14, no gap is formed between the first metal member 1 and the second metal member 2, and an intermediate layer with a thickness of about 1 μm is formed between the aluminum and SUS. From the elemental mapping, it is believed that this intermediate layer is a layered diffusion layer of an intermetallic compound of Al and Fe. It is believed that the second metal member 2 (stainless steel) diffused into the inside of the first metal member 1 (aluminum alloy), forming a diffusion layer.

[0092] In Example Test 1, the rotating tools F1 to F3 were not in contact with the second metal member 2 (stainless steel), and it was thought that solid-state welding was achieved by the aluminum material of the heated first metal member 1 (aluminum alloy) undergoing plastic deformation and rubbing strongly against the stainless steel. In addition, it is thought that as the tool angle increased to 120° and 135°, the plastic flow force of the aluminum material of the first metal member 1 generated by the tool rotation and movement increased, resulting in good welding and an increase in tensile strength.

[0093] [Example Test 2] Using the rotary tool F2, joining was performed in the same manner as in Example Test 1, except that the first metal member 1 was changed to an aluminum alloy (JIS A6063-T5). Strip specimens were prepared from the joined bodies produced by joining, and tensile tests were performed. In this test, all of the joints fractured due to shear.

[0094] In Example Test 2, the same tensile strength as in Example Test 1 was obtained, confirming that bonding was possible. The aluminum alloy (JIS A1100-H14) used in Example Test 1 has a solidus temperature of 643°C and a thermal conductivity of 220 WW / m·K. The aluminum alloy (JIS A6063-T5) used in Example Test 2 has a solidus temperature of 615°C and a thermal conductivity of 210 WW / m·K. It was confirmed that by using a material with high thermal conductivity and low high-temperature deformation resistance (high-temperature strength) as the first metal member, such as those used in Example Tests 1 and 2, it was possible to perform favorable joining.

[0095] [Example Test 3] In Example Test 3, seven types of rotary tools F11 to F17 were prepared, each of which was the rotary tool F described with reference to FIGS. 1 to 3 and had different taper angles at the tip end 43. The first metal member 1 was an aluminum alloy conforming to JIS A1050. The second metal member 2 was titanium. The first metal member 1 and the second metal member 2 were overlapped and joined by the above-described joining method.

[0096] The rotary tool F11 has the same shape as the rotary tool F1, except that the taper angle θ1 of the tip 43 is 90°, the height of the tip 43 is 10 mm, and the depth H2 of the spiral groove 47 is 1.50 mm. The rotary tool F12 has the same shape as the rotary tool F1, except that the taper angle θ1 of the tip 43 is 105°, the height of the tip 43 is 7.7 mm, and the depth H2 of the spiral groove 47 is 1.15 mm. The rotary tool F13 has the same shape as the rotary tool F1, except that the taper angle θ1 of the tip 43 is 120°, the height of the tip 43 is 5.8 mm, and the depth H2 of the spiral groove 47 is 0.87 mm. The rotary tool F14 has the same shape as the rotary tool F1, except that the taper angle θ1 of the tip 43 is 135°, the height of the tip 43 is 4.1 mm, and the depth H2 of the spiral groove 47 is 0.62 mm. The rotary tool F15 has the same shape as the rotary tool F1, except that the taper angle θ1 of the tip 43 is 150°, the height of the tip 43 is 2.7 mm, and the depth H2 of the spiral groove 47 is 0.40 mm. The rotary tool F16 has the same shape as the rotary tool F1, except that the taper angle θ1 of the tip 43 is 157.5°, the height of the tip 43 is 2.0 mm, and the depth H2 of the spiral groove 47 is 0.30 mm. The rotary tool F17 has the same shape as the rotary tool F1, except that the taper angle θ1 of the tip 43 is 160°, the height of the tip 43 is 13 mm, and the depth H2 of the spiral groove 47 is 0.20 mm.

[0097] In Example Test 3, a laminating step and a joining step were performed. In the laminating step, the first metal member 1 and the second metal member 2 were overlapped to form an overlapping portion J1. In the joining step, the rotary tools F11 to F17 were inserted from the surface 1a of the first metal member 1, and the tip portions 43 were brought into contact with the first metal member 1 to perform friction stir welding. The tool rotation speed was 3000 rpm, and the joining speed was 300 mm / min. The plate thickness of the first metal member 1 was changed to 1 mm, 2 mm, 3 mm, and 4 mm. Depending on each plate thickness, the insertion amount of the rotary tool F was set so that the distance from the tip of the rotary tools F11 to F17 to the surface 2a of the second metal member 2 was 0.1 mm, and each joining was performed. A simple bending test was performed on the test specimen (joint).

[0098] Fig. 15 is a graph showing the relationship between the thickness of the aluminum alloy in Example Test 3 and the contact area between the aluminum and the rotary tool. Fig. 16 is a graph showing the relationship between the thickness of the aluminum alloy in Example Test 3 and the contact length of the rotary tool per unit thickness. As shown in Fig. 15, the area where the rotary tool F is in contact with the first metal member 1 (contact area) was determined, and the relationship with the thickness of the first metal member 1 was plotted in a graph. When the contact area was 500 mm 2 When this occurred, the mechanical load on the equipment exceeded its limit, so the joining test was not performed.In Figures 15 and 16, the taper angle is indicated on the plots on the graphs, and the black plots indicate good results in the simple bending test, while the white plots indicate poor results in the simple bending test.

[0099] It was found that, when the taper angle is the same, the greater the thickness of the first metal member 1, i.e., the greater the insertion depth of the rotary tool F and the larger the contact area between the rotary tool F and the first metal member 1, the better the joining results. It was also confirmed that by increasing the thickness of the first metal member 1, joining can be performed under conditions of a taper angle of 120°. It was found that the larger the taper angle, the better the joining results. In particular, it was confirmed that stable joining was possible regardless of the thickness of the aluminum alloy plate when the taper angle was 150° or more.

[0100] Lines M1 and M2 were determined by approximating straight lines based on the points where the bending test results were favorable, as shown in Figures 15 and 16. As shown in Figure 16, when the relationship between the thickness of the aluminum alloy and the contact length per unit thickness, calculated by dividing the contact area by the thickness, was summarized from line M1, it was found that good joining was possible when the contact length per unit thickness was 50 mm or more.

[0101] [Example Test 4] In Example Test 4, a laminating step and a joining step were performed. Fig. 17 is a schematic plan view of Example Test 4. Fig. 18 is a schematic cross-sectional view of Example Test 4. In the laminating step, as shown in Figs. 17 and 18, the first metal member 1 and the second metal member 2 were overlapped to form an overlapping portion J1. In the joining step, a rotary tool F21 was inserted from the surface 1a of the first metal member 1, and a tip portion 43 was brought into contact with the first metal member 1 to perform friction stir welding.

[0102] The first metal member 1 was made of JIS A1050 alloy, had a thickness of 3 mm, and measured 200 mm x 300 mm. The second metal member 2 was made of titanium, had a thickness of 4 mm, and measured 200 mm x 300 mm. As shown in Figures 17 and 18, a thermocouple TC was embedded inside the second metal member 2 to measure the temperature during welding. Specifically, three elongated holes, each measuring 30 mm, 70 mm, and 110 mm in length, were formed near the surface of the second metal member 2, extending from one side of the 300 mm length toward the center. The thermocouples were positioned so that they were located at the innermost positions of the elongated holes. That is, the thermocouples TC were positioned 30 mm, 70 mm, and 110 mm from the side of the second metal member 2. A metal plate N was placed below the second metal member 2 as a base.

[0103] The rotary tool F21 had a tip 43 with a taper angle θ1 of 135° and a height of 4.1 mm, similar to the rotary tool F3. As shown in FIG. 17 , the rotary tool F21 was inserted near a corner of the surface 1a of the first metal member 1 and linearly moved parallel to the longitudinal direction to join the first metal member 1 and the second metal member 2. When the rotary tool F21 reached the edge, the joining position was moved toward the center in the lateral direction from the position where the first joining was performed. Then, the rotary tool F21 was linearly moved parallel to the longitudinal direction in the opposite direction to the first joining, to join the first metal member 1 and the second metal member 2. In this manner, the rotary tool F21 was repeatedly moved in alternating directions to join the first metal member 1 and the second metal member 2. The joining pitch between the Nth and N+1th adjacent joinings was 7 mm. The rotation speed of the rotary tool F21 was 3,000 rpm. In the joining process, the insertion depth of the rotary tool F21 into the first metal member 1 was set to 2.9 mm. That is, the insertion depth of the rotary tool F was set so that the distance between the tip of the rotary tool F21 and the surface 2a of the second metal member 2 was 0.1 mm. The movement speed (joining speed) of the rotary tool F21 was set to 300 mm / min up to 150 m from the end of the test piece, 250 mm / min from 150 mm to 100 mm, 200 mm / min from 100 mm to 60 mm, and 100 mm / min from 60 mm to 20 mm, and the effect of the joining speed was also investigated.

[0104] Figure 19 shows the results for welding speeds of 250 mm / min and 200 mm / min from 150 mm to 100 mm and from 100 mm to 60 mm, while Figure 20 shows the results for welding speeds of 100 mm / min from 60 mm to 20 mm. Both Figures 19 and 20 are graphs showing the relationship between time and temperature measured by thermocouples TC located at 30 mm, 70 mm, and 110 mm from the side. As shown in Figure 19, as the rotary tool F21 moved back and forth, the temperature measured by thermocouple TC increased as the rotary tool F21 approached and decreased as the rotary tool F21 moved away. The maximum temperature measured by thermocouple TC located 110 mm from the side was approximately 510°C, and the maximum temperature measured by thermocouple TC located 70 mm from the side was approximately 535°C. As shown in Figure 20, when the welding speed for the same test piece was 100 mm / min, the maximum temperature at the thermocouple located 30 mm from the side was 570°C.

[0105] As described above, since the temperature near the joining interface between the first metal member 1 and the second metal member 2 is 570°C, it is predicted that the surface 1a of the first metal member 1 in contact with the rotary tool F21 will be even hotter. In other words, it is necessary to avoid partial melting even at temperatures above 570°C, and an aluminum alloy with a solidus temperature of 600°C or higher is desirable. Furthermore, while the temperature of the aluminum side is important for solid-state joining, the temperature of the opposing metal is also important, and a thermal conductivity of 160 W / mK or higher is desirable for effective heat transfer from the aluminum side. [Explanation of symbols]

[0106] 1. First metal member 2. Second metal member 42 Base 43 Tip 45 Side part 46 Tip surface section 47 Spiral groove 51 Step side 52 Bottom of step 53 Step 54 Recess 55 Bottom of step 56 Overhang 57 Bottom of inner step 58 Bottom of outer step F Rotate Tool W1 Plasticization area

Claims

1. A method for friction stir welding a first metal member made of aluminum or an aluminum alloy and a second metal member made of a metal having a melting point higher than that of aluminum using a rotary tool, comprising: a superposing step of superposing the first metal member and the second metal member; a joining process of joining the first metal member and the second metal member by inserting the rotary tool into the first metal member while rotating the rotary tool, causing plastic flow of the metal material of the first metal member by friction stirring without bringing the rotary tool into contact with the second metal member, and diffusion bonding the metal material of the first metal member to the metal material of the second metal member, the rotary tool includes a base and a generally conical tip portion connected to the base; the tip portion has a tapered side surface portion on a side surface thereof centered on the rotation axis of the rotary tool, and a tip surface portion at a tip end thereof that is perpendicular to the rotation axis of the rotary tool, The tip portion has a spiral groove formed on the side surface, In the joining step, the tip portion is brought into contact with the first metal member. A joining method characterized by:

2. the spiral groove has a step portion including a step side surface extending in a direction substantially parallel to a rotation axis of the rotary tool and a step bottom surface facing in a direction substantially perpendicular to the rotation axis, the step portion is spirally wound, the step bottom surface of the step portion is adjacent to the step side surface of the step portion located on the outer periphery side of the tip portion, and the step side surface of the step portion is adjacent to the step bottom surface of the step portion located on the inner periphery side of the tip portion, and the step is repeatedly formed, The joining method according to claim 1 , wherein the bottom surface of the step is provided with a recess recessed in the direction of the rotation axis.

3. The depth of the spiral groove is 0.1 mm or more and 1.0 mm or less. The joining method according to claim 1 .

4. The width of the spiral groove is 1 mm or more and 5 mm or less. The joining method according to claim 1 .

5. a ratio of the depth of the spiral groove to the width of the spiral groove is 0.2 or more and 2.0 or less; The joining method according to claim 1 .

6. The depth of the recess is 0.1 mm or more and 0.5 mm or less. The joining method according to claim 2 .

7. a ratio of the depth of the recess to the width of the spiral groove is 0.1 or more and 0.9 or less; The joining method according to claim 2 .

8. The taper angle of the tip is 120° or more and 175° or less. The joining method according to claim 1 .

9. In the joining step, the distance of the lower end of the tip surface portion from the surface of the second metal member is 0.05 mm or more and 0.2 mm or less. The joining method according to claim 1 .

10. In the joining step, the tip portion is inserted into the first metal member, and a base end portion of the tip portion on the base portion side and the base portion are not inserted into the first metal member. The joining method according to claim 1 .

11. In the joining step, the plasticized regions of the first metal members formed in adjacent joining paths are joined in an overlapping manner. The joining method according to claim 1 .

12. In the joining step, the first metal member and the second metal member are joined in such a manner that joining regions formed in adjacent joining paths overlap each other. The joining method according to claim 1 .

13. the first metal member is an aluminum alloy having a solidus temperature of 600°C or higher and a thermal conductivity of 160 W / m·K or higher; The joining method according to claim 1 .

14. In the joining step, the contact length of the rotary tool per unit plate thickness is set to 50 mm or more. The joining method according to claim 1 .

15. The second metal member comprises at least one selected from the group consisting of steel, stainless steel, titanium, a titanium alloy, molybdenum, a molybdenum alloy, copper, and a copper alloy. The joining method according to claim 1 .

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