WO2019031145A1 - Magnesium-lithium alloy joining method and joined body - Google Patents

Magnesium-lithium alloy joining method and joined body Download PDF

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Publication number
WO2019031145A1
WO2019031145A1 PCT/JP2018/026130 JP2018026130W WO2019031145A1 WO 2019031145 A1 WO2019031145 A1 WO 2019031145A1 JP 2018026130 W JP2018026130 W JP 2018026130W WO 2019031145 A1 WO2019031145 A1 WO 2019031145A1
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joined
magnesium
friction stir
tool
stir welding
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PCT/JP2018/026130
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French (fr)
Japanese (ja)
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藤井　英俊
好昭 森貞
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国立大学法人大阪大学
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Priority to JP2019535043A priority Critical patent/JP7121402B2/en
Publication of WO2019031145A1 publication Critical patent/WO2019031145A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
    • B23K20/12—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding

Definitions

  • the present invention relates to a bonding method in which at least one material to be bonded is a magnesium-lithium alloy and a bonded body obtained by the bonding method, and more specifically, an efficient bonding method using friction stir welding. And a joined body obtained by the joining method.
  • Magnesium is high in specific strength and is attracting attention as a substitute material for conventionally used steel materials and aluminum alloys from the viewpoint of weight reduction of automobiles, trains, and aircraft.
  • magnesium alloys generally have poor formability at room temperature because they have an HCP structure.
  • Non-Patent Document 1 Microstructure and mechanical properties of Mg-lithium after TIG welding”, Transactions of Nonferrous Metals Society of China, 21.3 (2011), 477-481.
  • TIG welding Magnesium using TIG welding is used.
  • a lithium-based alloy is joined is disclosed, due to the temperature history at the time of welding, grain coarsening of the weld and softening of the heat-affected zone are inevitable.
  • the upper and lower plates are appropriately agitated and diffused by friction agitation, and bonding is performed in the solid phase state, so that a magnesium-lithium based alloy plate is obtained as in the conventional rolling bonding.
  • the surface in contact with the plate of aluminum and aluminum or its alloy is acid-washed beforehand, and a strong bond is made even without pretreatment such as polishing with a metal wire brush to remove oxide film etc. It says that product cost and manufacturing cost can be kept low compared to rolling bonding.
  • the joint strength of the obtained magnesium-lithium alloy is 84% or less of that of the base material, and the ductility is also lower than that of the base material.
  • a large amount of argon must be used to completely eliminate oxygen in the atmosphere.
  • a tool for friction stir welding is inserted from the side of the aluminum alloy plate disposed on the upper side, and the upper aluminum alloy plate and the lower magnesium A material based on lithium-based alloy is joined, and on the magnesium-lithium alloy side, almost no material flow occurs due to the action of the tool, and from the viewpoint of "frictional stirring technology", it conforms to friction stir welding of aluminum alloy. is there. That is, it can not be said that a method of obtaining a good joint of magnesium-lithium based alloy by friction stir welding has been established.
  • the present invention provides a simple and efficient friction stir welding method in which at least one bonding material is a magnesium-lithium alloy, and the stirring portion A bonding method capable of providing strength and plastic workability higher than that of a base material, and a bonded body obtained by the bonding method.
  • the present invention provides a modification method capable of imparting strength and plastic workability higher than that of a base material to an arbitrary region of a magnesium-lithium alloy, and a metal structure obtained by the modification method. Also aims.
  • the present inventor has conducted intensive studies on the material and the like of the friction stir welding tool, and as a result, the adhesion of the material to be welded (magnesium-lithium alloy) to the tool surface is suppressed.
  • the inventors have found that the present invention is extremely effective.
  • the present invention A method of friction stir welding one to-be-joined material and the other to-be-joined material At least one of the materials to be joined is a magnesium-lithium alloy, Use one of cemented carbide tools, cermet tools, ceramic tools, intermetallic compound tools and ceramic coated tools as friction stir welding tools, Inserting the friction stir welding tool into the one workpiece side;
  • the present invention provides a friction stir welding method of a metal material, characterized in that
  • Aluminum alloys and magnesium alloys can be easily friction stirred with steel tools, and there is no particular problem with tool life, so conventional friction stir welding is also made of steel (eg, from the viewpoint of tool price etc.)
  • Tools of hot tool steel: such as SKD 61) have been used.
  • any of cemented carbide tools, cermet tools, ceramic tools, intermetallic compound tools and ceramic coated tools as tools for friction stir welding can be effectively reduced by using
  • the affinity with the magnesium-lithium alloy can be reduced (a cemented carbide or cermet has a metal bonding phase, but the inorganic nonmetal phase is mainly used. Component).
  • the temperature of friction stir welding can be reduced, and it is possible to form a stirring unit having a finer and more homogeneous structure and having excellent strength and plastic workability.
  • (1) end portions of the metal plates are butted to form a bonding portion, and the rotary tool is moved while rotating along the longitudinal direction of the processed portion to move the metal plates together.
  • Bonding bonding (2) end portions of metal plates are butted to form a bonding portion, and spot bonding in which a rotary tool is rotated without moving at the bonding portion and bonded, and (3) metal plates are overlapped in the bonding portion Align, insert the rotary tool into the joint, and rotate the rotary tool without moving it at that point to join the metal plates by spot welding, (4) Overlay the metal plates at the joint, and rotate the joint to the joint Inserts the tool and moves it while rotating the rotating tool along the longitudinal direction of the joint to move it to join the metal plates together, including four aspects (1) to (4) of bonding and their combinations Friction stir Welding tool magnesium - inserted into lithium-based alloy.
  • the tool life can be shortened by inserting the tool into the magnesium-lithium alloy having a small plastic deformation resistance. It can also be improved.
  • the method of bonding a metal material according to the present invention is characterized in that a friction stir welding tool is inserted into one of the materials to be bonded (magnesium-lithium alloy side). More specifically, when one of the materials to be joined is a magnesium-lithium alloy and the other material to be joined is other than a magnesium-lithium alloy, the center of the friction stir welding tool in the butt welding (probe The center of the portion is on one side of the material to be joined with respect to the butt surface, and in overlap bonding, one material to be joined is placed on the upper side, and the friction stir welding tool is inserted from the one material side .
  • general friction stir welding conditions such as the rotational speed, moving speed, insertion amount and applied load of the tool may be appropriately set from the viewpoint of defect formation in the stirring portion and bonding efficiency.
  • the shape of the tool is not particularly limited as long as the effects of the present invention are not impaired, and various shapes of conventionally known friction stir welding tools can be used.
  • the other material to be bonded is a magnesium-lithium alloy.
  • the materials to be joined together be magnesium-lithium alloys, the importance of the friction stir action on magnesium-lithium alloys is increased, so that the effects of the method of joining metal materials of the present invention can be obtained more remarkably. Can.
  • the surface of the friction stir welding tool is not grooved. Since tool wear and tool breakage are unlikely to occur in friction stir welding of aluminum alloys and magnesium alloys, it is common to grooving such as screwing on the bottom of the shoulder and the side of the probe to increase the stirring effect of the tool. It is On the other hand, the adhesion of the magnesium-lithium alloy to the surface of the tool can be suppressed by not subjecting the groove processing to the tool. On the other hand, since the magnesium-lithium based alloy has excellent plastic workability, material flow can be sufficiently generated even with a tool without groove processing, and the stirring portion can be formed.
  • the tool for friction stir welding which is not grooved means a tool having a shoulder bottom surface and a probe side surface in a flat state.
  • the peripheral speed of the outermost periphery of the shoulder portion of the friction stir welding tool is 23.6 mm / s to 78.5 mm / s.
  • the peripheral speed range is a low speed area which is not common in friction stir welding of magnesium alloys, but when a magnesium-lithium alloy having room temperature workability is used as a material to be joined, sufficient friction stir action should be obtained. it can.
  • the peripheral speed at the outermost periphery of the probe portion of the friction stir welding tool is set to 9.5 mm / s to 31.4 mm / s.
  • the peripheral speed range is a low speed area which is not common in friction stir welding of magnesium alloys, but when a magnesium-lithium alloy having room temperature workability is used as a material to be joined, sufficient friction stir action should be obtained. it can.
  • butt joining is preferable.
  • the formation of the agitating part is more important than the superposition joining, but in the joining method of the metal material of the present invention, a favorable agitating part is obtained even when the magnesium-lithium alloy is used as a material to be joined. Since it can be formed, even if it is butt joint, jointing can be achieved efficiently.
  • Friction stir welding for the purpose of joining and friction stir process for the purpose of reforming are basically techniques based on the same principle, and the method of joining metal materials of the present invention described above is the modification of metal materials. It can also be used as a method. Specifically, friction stirring may be performed using a tool having an appropriate shape and size in consideration of the shape, size, position, and the like of a desired reformed part.
  • the present invention is It is a joined body in which one to-be-joined material and the other to-be-joined material are joined via a stirring part, At least one of the materials to be joined is a magnesium-lithium alloy,
  • the stirring portion includes recrystallized grains of the ⁇ phase of the magnesium-lithium alloy;
  • the crystal orientation of the recrystallized grain is random,
  • a zygote characterized by
  • the stirring portion since the stirring portion is formed by friction stir welding at a relatively low temperature, the stirring portion includes recrystallized grains of the ⁇ phase having the HCP structure and the ⁇ phase having the BCC structure.
  • the recrystallized grains of the ⁇ phase are clearly refined compared to the base material.
  • the crystal orientation of the ⁇ phase is randomized. Since the ⁇ phase has an HCP structure, a strong texture is generally formed after a processing process such as extrusion and rolling in which a simple shear stress is applied. On the other hand, by friction stirring under appropriate conditions using the bonding method of the present invention, it is possible to randomize the crystal orientation of the ⁇ phase, and the mechanical properties decrease and anisotropy due to the strong texture. Can be suppressed.
  • being randomized means that a strong bottom surface texture of the ⁇ phase is not formed, for example, in the orientation map of EBSD measurement, recrystallized grains of the ⁇ phase are displayed only in the same systematic color It is good without it. More specifically, in the pole figure, the Texture Intensity is preferably 1 to 10, and more preferably 1 to 5.
  • the hardness is higher than that of the base material.
  • there is no heat-affected zone at the outer edge of the agitating zone due to the temperature rise during joining there is no region where the hardness is lower than that of the base material.
  • the minimum hardness in the region of the magnesium-lithium alloy of the bonded body is 50 HV or more, and that the joint efficiency with respect to the one workpiece is 100%. Is more preferred.
  • the tensile strength of the stirring portion is preferably 1.1 times or more, more preferably 1.3 times or more of the base material tensile strength of the one material to be bonded. Most preferably 1.5 times or more.
  • the tensile strength of the stirring portion may be slightly higher than the tensile strength of the base material under bonding conditions where the heat input is relatively small.
  • the stirring portion is formed under low heat input conditions uncommon to friction stir welding of magnesium alloys, and the stirring portion is nano-organized (average crystal grain size of ⁇ phase is less than 1 ⁇ m) By doing this, the tensile strength of the stirring portion can be made 1.1 times or more the tensile strength of one of the materials to be joined.
  • the stirring portion having the nano structure is preferable also from the viewpoint of processability because it exhibits excellent superplasticity.
  • the other material to be bonded is preferably a magnesium-lithium alloy, and more preferably a butt bonded body.
  • the bonded body of the present invention can be suitably manufactured by the method of bonding the metal material of the present invention described above.
  • the present invention A metal structure including a reformed portion of a magnesium-lithium alloy, The reformed portion includes recrystallized grains of the ⁇ phase of the magnesium-lithium alloy; The crystal orientation of the recrystallized grain is random, Also provided is a metal structure characterized by The metal structure of the present invention has isotropically excellent mechanical properties and plastic workability since it has a reformed portion including recrystallized ⁇ -phase recrystallized grains.
  • the average grain size of the recrystallized grains is preferably less than 1 ⁇ m.
  • the metal structure of this invention can be suitably manufactured by the modification method of the metal material similar to the joining method of the metal material of the above-mentioned this invention.
  • the present invention is a simple and efficient friction stir welding method in which at least one of the materials to be joined is a magnesium-lithium alloy, which imparts strength and plastic workability greater than that of the base material to the stirring portion.
  • the present invention can provide a bonding method that can be used, and a bonded body obtained by the bonding method. Further, according to the present invention, there is provided a reforming method capable of imparting strength and plastic workability higher than that of a base material to an arbitrary region of a magnesium-lithium based alloy, and a metal structure obtained by the reforming method. You can also
  • Friction stir welding is called FSW (Friction Stir Welding), butt ends of two materials to be joined, which are to be joined, butt the protuberance (probe) provided on the tip of the rotating tool.
  • FSW Full Stir Welding
  • butt ends of two materials to be joined which are to be joined
  • protuberance probe
  • two metal members are joined by inserting them between the two ends and rotating and moving a rotary tool along the longitudinal direction of the ends.
  • FIG. 1 is a schematic view showing one embodiment of the method of bonding metal materials of the present invention. Inserting the to-be-joined material 2 (one to-be-joined material) and the to-be-joined material 2 ′ (the other to-be-joined material), inserting the rotated tool 4 into the desired joining area and moving along the to-be-joined line
  • the joint 6 can be obtained by
  • the bonding material 2 and the bonding material 2 ′ are both made of a magnesium-lithium alloy, basically, the butt wire is inserted so that the centers of the protruding portions (probe portions) 8 of the tool 4 coincide with each other. .
  • the protrusion (probe portion) 8 constituting the tool 4 is used in the method of bonding a metal material of the present invention. And most of the main body portion (shoulder portion) 10 abuts on the side of the workpiece 2.
  • any one of a cemented carbide tool, a cermet tool, a ceramic tool, an intermetallic compound tool, and a ceramic-coated tool can be used to make a magnesium-lithium alloy to be joined.
  • the adhesion of the alloy can be effectively reduced.
  • the surface of the tool 4 made of an inorganic nonmetal the affinity with the magnesium-lithium alloy can be reduced.
  • the temperature of friction stir welding can be reduced, and it is possible to form the stirring portion 12 having a finer and more homogeneous structure and having excellent strength and plastic workability.
  • the composition and structure of cemented carbide, cermet, ceramics and intermetallic compounds used as a tool material are not particularly limited as long as the effects of the present invention are not impaired, and various compositions and structures conventionally known may be used. Although it is possible, for cemented carbides and cermets, it is preferable to reduce the metallic bonding phase. Further, as the ceramics, for example, silicon carbide, silicon nitride, sialon, boron nitride, zirconia, alumina, titanium diboride and the like can be used, and as the intermetallic compound, for example, Ti—Al based or Ni—Al Intermetallic compounds can be used.
  • the main body of the tool 4 may be made of metal, for example, it can be made of hot tool steel (SKD 61).
  • the composition, structure, thickness and the like of the ceramic film are not particularly limited as long as the effects of the present invention are not impaired, and various compositions, structures and thicknesses conventionally known can be used. For example, they are used for cutting tools Various hard coatings can be used.
  • the above-mentioned tool material and ceramic film from the viewpoint of wettability with a magnesium-lithium based alloy, and it is preferable to make the contact angle of magnesium droplet and these materials 90 ° or more .
  • the torque applied to the tool 4 can be reduced by selecting the tool material and the ceramic coating whose contact angle is 90 ° or more.
  • FIG. 1 shows the case where a tool 4 having a cylindrical protrusion (probe portion) 8 on the bottom of a cylindrical main body (shoulder portion) 10 is used, but the shape of the tool 4 is as follows: There is no particular limitation as long as the effects of the present invention are not impaired, and various shapes of conventionally known friction stir welding tools can be used. Moreover, it is preferable not to have groove processing, such as screw processing, in the bottom face of the main-body part (shoulder part) 10 and the side surface of the projection part (probe part) 8 which contact
  • groove processing such as screw processing
  • the magnesium-lithium-based alloy used as the at least one material to be joined by the method of joining metal materials according to the present invention is mainly composed of magnesium, and an alloy to which lithium is added in order to impart plastic workability at room temperature is widely used. It is included.
  • the alloy includes an alloy to which aluminum, zinc, manganese, yttrium, lanthanoid, zirconium, silver, silicon, calcium or the like is added in order to improve strength and heat resistance.
  • lithium is preferably contained in the range of 5 to 15% by weight.
  • the content of lithium is less than 5% by weight, the plastic formability at room temperature is not improved significantly, and conversely, when the content of lithium exceeds 15% by weight, intergranular cracking (surface crack) may be caused. Also, the cost is high because lithium is expensive.
  • the other material to be joined 2 ' is also a magnesium-lithium alloy.
  • the importance of the friction stir action on magnesium-lithium alloys increases, so the effect of the joining method of the metal material of the present invention becomes more remarkable. Can be obtained.
  • General friction stir welding conditions such as rotational speed, moving speed, insertion amount and applied load of the tool 4 may be appropriately set from the viewpoint of defect formation in the stirring portion 12 and bonding efficiency.
  • the peripheral speed of the outermost periphery of the main body (shoulder portion) 10 of the tool 4 be 23.6 mm / s to 78.5 mm / s.
  • the peripheral speed range is a low speed area that is not common sense in friction stir welding of magnesium alloys, but when using a magnesium-lithium alloy having room temperature workability as the workpieces 2 and 2 ', sufficient friction stir action is required. You can get it.
  • the peripheral speed of the outermost periphery of the main body portion (shoulder portion) 10 is 23.6 mm / s or more, formation of a defect due to insufficient agitation can be suppressed, and 78.5 mm / s or less
  • the peripheral speed of the outermost periphery is approximately 23.6 mm / s by setting the rotational speed to 30 rpm, and approximately 78.5 mm by setting 100 rpm. / S.
  • the circumferential speed of the outermost periphery of the protruding portion (probe portion) 8 of the tool 4 be 9.5 mm / s to 31.4 mm / s.
  • the peripheral speed range is a low speed area that is not common sense in friction stir welding of magnesium alloys, but when using a magnesium-lithium alloy having room temperature workability as the workpieces 2 and 2 ', sufficient friction stir action is required. You can get it.
  • the circumferential speed of the outermost periphery of the protrusion (probe portion) 8 is set to 9.5 mm / s or more, formation of a defect due to insufficient stirring can be suppressed, and 31.4 mm / s or less Thus, the formation of defects due to the adhesion of the magnesium-lithium alloy to the surface of the tool 4 can be suppressed.
  • the peripheral speed of the outermost periphery is approximately 9.5 mm / s by setting the rotational speed to 30 rpm, and approximately 31.4 mm by setting 100 rpm. / S.
  • the formation of the stirring portion 12 is more important than the superposition joining, but in the joining method of the metal material of the present invention, the magnesium-lithium alloy is used as the joining members 2 and 2 '. However, since a good stirring portion 12 can be formed, bonding can be efficiently achieved by using the bonding method of the present invention.
  • FIG. 2 shows a schematic cross-sectional view in the vicinity of a bonded portion in the bonded body of the present invention.
  • a butt junction part is shown in FIG.
  • the bonded body 20 of the present invention is a bonded body in which one of the materials to be bonded 2 and the other material to be bonded 2 ′ are bonded via the stirring portion 12, and at least one material to be bonded 2 is magnesium-lithium. It is a system alloy, and is characterized in that recrystallization of the ⁇ phase is included in the region of the magnesium-lithium alloy in the stirring section 12.
  • the shape and size of the bonding members 2 and 2 ' are not particularly limited as long as the effects of the present invention are not impaired, and bonding may be performed by the bonding method of the present invention.
  • the magnesium-lithium alloy has an ⁇ phase of HCP structure and a ⁇ phase of BCC structure, but in the extruded material and the rolled material, the ⁇ phase is elongated and distributed in a streak shape.
  • the ⁇ phase is macroscopically distributed in the stirring section 12 as well, the ⁇ phase is recrystallized, and the equiaxed ⁇ phase is in a state of being gathered.
  • the magnesium-lithium-based alloy as at least one of the materials to be joined 2 contains magnesium as a main component, and widely includes an alloy to which lithium is added in order to impart plastic workability at room temperature thereto.
  • the alloy includes an alloy to which aluminum, zinc, manganese, yttrium, lanthanoid, zirconium, silver, silicon, calcium or the like is added in order to improve strength and heat resistance.
  • lithium is preferably contained in the range of 5 to 15% by weight.
  • the content of lithium is less than 5% by weight, the plastic formability at room temperature is not improved significantly, and conversely, when the content of lithium exceeds 15% by weight, intergranular cracking (surface crack) may be caused. Also, the cost is high because lithium is expensive.
  • the hardness is higher than that of the base material. Further, since there is no heat-affected zone at the outer edge of the agitating unit 12 due to the temperature rise during joining, there is no region where the hardness is lower than that of the base material.
  • the average grain size of recrystallized grains of the ⁇ phase is preferably less than 5 ⁇ m, more preferably less than 3 ⁇ m, and most preferably less than 1 ⁇ m.
  • the minimum hardness in the region of one of the bonding members 2 (magnesium-lithium-based alloy) of the bonded body 20 is preferably 50 HV or more, and one bonding member 2 of the bonded body 20 (magnesium-lithium-based alloy)
  • the joint efficiency for 100% is more preferably 100%.
  • the tensile strength of the stirring portion 12 is preferably 1.1 times or more, more preferably 1.3 times or more, and more preferably 1.5 times or more of the tensile strength of one of the materials to be joined 2. Is most preferred.
  • the tensile strength of the stirring portion may be slightly higher than the tensile strength of the base material under bonding conditions where the heat input is relatively small.
  • the stirring portion 12 is formed under low heat input conditions that are not common sense as friction stir welding of a magnesium alloy, and the stirring portion 12 is nano-organized (average crystal grain size of ⁇ phase is less than 1 ⁇ m)
  • the tensile strength of the stirring portion 12 can be made 1.1 times or more of the tensile strength of one of the bonding members 2.
  • the stirring part 12 which has the said nano structure expresses the outstanding superplasticity ability, it is preferable also from a viewpoint of processability.
  • the crystal orientation of the ⁇ phase is randomized in the recrystallization region of the stirring unit 12.
  • the crystal orientation of the ⁇ phase can be randomized, and the decrease in mechanical properties and anisotropy caused by the strong texture can be suppressed. can do.
  • the other material to be bonded 2 is also preferably a magnesium-lithium alloy, and more preferably a butt bonded body.
  • the reformed portion in the metal structure of the present invention has the same characteristics as the stirring portion in the joined body of the present invention.
  • LZ 91 magnesium alloy (9 wt% Li-1 wt% Zn-Mg Bal.) Plates having a length of 200 mm, a width of 65 mm and a thickness of 3 mm were butted together to obtain a joined body by friction stir welding.
  • the friction stir welding was performed under tool position control under the following conditions. Note that no shielding gas is used during friction stir welding, and groove processing is not performed on the bottom of the shoulder of the tool and the side of the probe.
  • Friction stir welding was performed in the same manner as in Example 1 except that the material of the tool was made of hot tool steel (SKD 61).
  • Suitable bonding conditions In order to confirm the suitable joining conditions for obtaining a good joined body, the surface and the cross section of the joint (stirred part) were observed by an optical microscope. If defects are formed in the stirring part, x, if no defects are formed, but if a large amount of burrs or surface roughness is observed, ⁇ , if defects are not formed and the surface state of the stirring part is smooth The results of the examples are shown in Table 1 with ⁇ . In addition, in the comparative example, since a defect was formed on all the conditions (evaluation of x on all the conditions), it has not shown.
  • the joint method of the present invention can provide a good joint under a wide range of joint conditions.
  • the rotational speed is higher than 150 rpm, the metallic luster on the surface of the agitating portion is lost, and the cause may be formation of oxidation or liquid phase accompanying the increase in bonding temperature.
  • the favorable stirring part surface which maintained metallic luster was able to be obtained by using argon gas as shield gas.
  • the material to be bonded adheres to the surface of the tool under all the bonding conditions, and a groove-like defect is formed in the stirring portion.
  • the material to be joined adheres to the side surface of the probe portion and the bottom surface of the shoulder portion, making it difficult to grasp the tool prototype.
  • the other tools there was a portion where coloring due to the material to be joined was present on the side surface of the probe portion and the bottom surface of the shoulder portion, but significant adhesion was not confirmed.
  • FIG. 4 shows the hardness distribution (horizontal direction of the joint at the center of the plate thickness) of the cross section of the joint obtained at a tool moving speed of 100 mm / min and a tool rotational speed of 100 to 300 rpm.
  • the hardness of all the stirring parts is higher than that of the base material, and the increase in hardness of the stirring parts is remarkable particularly at a lower tool rotation speed.
  • no softened region is observed at the outer edge of the stirring portion.
  • FIG. 5 shows the tensile properties of the joint obtained at a tool movement speed of 100 mm / min and a tool rotation speed of 30 to 100 rpm.
  • the tension test result of a base material is shown as a comparison.
  • a small tension having a parallel part of 4 mm long x 2 mm wide x 2 mm thick Also shown are the results of preparing test pieces and evaluating the bonding direction as a tensile axis at a tensile speed of 0.08 mm / min.
  • the joints obtained in the examples have the same tensile properties as the base material, and the joint efficiency is 100%. Further, the tensile properties of the stirring portion are significantly higher than that of the base material, and the tensile strength is about twice that of the base material.
  • the deformation amounts to breakage of the base material and the stirring portion were about 150% and about 1100%, respectively, and it was confirmed that the stirring portion was provided with extremely remarkable superplastic deformability.
  • An overview photograph of the test piece of the stirring unit after the evaluation is shown in FIG.
  • the parallel portion with a length of 4 mm is approximately 44 mm when broken.
  • FIGS. 7 and 8 An SEM photograph of the center of the stirring portion and an orientation map image of the ⁇ phase obtained in the base material and the example (tool movement speed 100 mm / min, tool rotation speed 100 to 300 rpm) are shown in FIGS. 7 and 8, respectively.
  • the base material is composed of an ⁇ phase and a ⁇ phase, and the ⁇ phase is distributed in a streak shape.
  • the ⁇ phase is divided to form equiaxed recrystallized grains.
  • the alpha phase of the matrix has a strong texture, but the alpha phase of the stirring section is randomly oriented.
  • the crystal grain size of the stirring portion is finer than that of the base material, and is more remarkable under the condition that the tool rotation speed is low.
  • the average crystal grain size of the ⁇ phase is less than 5 ⁇ m in the case of 300 rpm, less than 3 ⁇ m in the case of 200 rpm, and less than 1 ⁇ m in the case of 100 rpm.

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Abstract

Provided are: a joining method which makes it possible to impart strength and plastic workability which equal or exceed that of a base material to a stirred part and is a simple and efficient friction stir welding method for cases when at least one of the materials to be joined is a magnesium-lithium alloy; and a joined body obtained by using the joining method. Further provided are: a modification method which makes it possible to impart strength and plastic workability which equal or exceed that of a base material to a desired region of a magnesium-lithium alloy; and a metal structure obtained by using the modification method. Thus, a method for friction stir welding one material to be joined and another material to be joined, the method being a metal material friction stir welding method characterized in that at least one of the materials to be joined is a magnesium-lithium alloy, and in that any friction stir welding tool from among a hard metal alloy tool, a cermet tool, a ceramic tool, an intermetallic compound tool and a ceramic-covered tool is used, and said tool is inserted from the side on which the one of the materials to be joined is located.

Description

マグネシウム－リチウム系合金の接合方法及び接合体Method of joining magnesium-lithium alloy and joined body
　本発明は、少なくとも一方の被接合材をマグネシウム－リチウム系合金とする場合の接合方法及び当該接合方法によって得られる接合体に関し、より具体的には、摩擦攪拌接合を用いた効率的な接合方法及び当該接合方法によって得られる接合体に関する。 The present invention relates to a bonding method in which at least one material to be bonded is a magnesium-lithium alloy and a bonded body obtained by the bonding method, and more specifically, an efficient bonding method using friction stir welding. And a joined body obtained by the joining method.
　マグネシウムは比強度が高く、自動車、電車及び航空機等の軽量化の観点から、従来使用されてきた鉄鋼材料やアルミニウム合金の代替材料として注目されている。一方で、マグネシウム合金はＨＣＰ構造を有するため、一般的に室温での成形性に乏しい。 Magnesium is high in specific strength and is attracting attention as a substitute material for conventionally used steel materials and aluminum alloys from the viewpoint of weight reduction of automobiles, trains, and aircraft. On the other hand, magnesium alloys generally have poor formability at room temperature because they have an HCP structure.
　これに対し、Ｌｉ（リチウム）元素の添加により優れた室温成形性を発現する極めて軽量なＭｇ－Ｌｉ（マグネシウム－リチウム）系合金が提案されているが、汎用的に活用するためには接合技術の確立が必要不可欠である。 On the other hand, an extremely lightweight Mg-Li (magnesium-lithium) based alloy has been proposed which exhibits excellent room temperature formability by the addition of Li (lithium) element, but to use it widely, joining technology It is essential to establish
　しかしながら、マグネシウム－リチウム系合金は化学活性が高く、溶融溶接で良好な継手を得ることが困難である。例えば、非特許文献１（“Ｍｉｃｒｏｓｔｒｕｃｔｕｒｅ　ａｎｄ　ｍｅｃｈａｎｉｃａｌ　ｐｒｏｐｅｒｔｉｅｓ　ｏｆ　Ｍｇ－Ｌｉ　ａｌｌｏｙ　ａｆｔｅｒ　ＴＩＧ　ｗｅｌｄｉｎｇ”，Ｔｒａｎｓａｃｔｉｏｎｓ　ｏｆ　Ｎｏｎｆｅｒｒｏｕｓ　Ｍｅｔａｌｓ　Ｓｏｃｉｅｔｙ　ｏｆ　Ｃｈｉｎａ，２１．３（２０１１），４７７－４８１．）では、ＴＩＧ溶接を用いてマグネシウム－リチウム系合金を接合した例が開示されているが、溶接時の温度履歴により、溶接部の結晶粒粗大化及び熱影響部の軟化が不可避である。 However, magnesium-lithium alloys have high chemical activity, and it is difficult to obtain a good joint by melt welding. For example, in Non-Patent Document 1 (“Microstructure and mechanical properties of Mg-lithium after TIG welding”, Transactions of Nonferrous Metals Society of China, 21.3 (2011), 477-481.), Magnesium using TIG welding is used. Although an example in which a lithium-based alloy is joined is disclosed, due to the temperature history at the time of welding, grain coarsening of the weld and softening of the heat-affected zone are inevitable.
　また、特許文献１（特開２００８－２５４００３号公報）では、マグネシウム－リチウム系合金板とアルミニウムまたはその合金の板とを重ね合わせ、これを摩擦攪拌により重ね合わせ接合した後、圧延することを特徴とするクラッド材の製造方法、が開示されている。 Moreover, in patent document 1 (Unexamined-Japanese-Patent No. 2008-254003), a magnesium-lithium-type alloy plate and a plate of aluminum or its alloy are piled up, this is piled up by friction stirring, and it is characterized by rolling. And a method of manufacturing the clad material.
　上記特許文献１記載のクラッド材の製造方法においては、摩擦攪拌により上下の板材が適度に攪拌拡散され固相状態で接合が行われるので、従来の圧延接合のように、マグネシウム－リチウム系合金板とアルミニウムまたはその合金の板とが当接する面を、予め酸洗いし、金属製ワイヤーブラシで磨いて酸化皮膜などを除去する前処理をしなくても強固な接合がなされ、この点で従来の圧延接合に比べて、製品コストおよび製造コストを低く抑えることができる、としている。 In the method of producing a clad material described in Patent Document 1 above, the upper and lower plates are appropriately agitated and diffused by friction agitation, and bonding is performed in the solid phase state, so that a magnesium-lithium based alloy plate is obtained as in the conventional rolling bonding. The surface in contact with the plate of aluminum and aluminum or its alloy is acid-washed beforehand, and a strong bond is made even without pretreatment such as polishing with a metal wire brush to remove oxide film etc. It says that product cost and manufacturing cost can be kept low compared to rolling bonding.
　加えて、上記特許文献１記載のクラッド材の製造方法においては、摩擦攪拌接合により強固な接合が行われるので、摩擦攪拌接合の後に行われる圧延は、冷間（室温）で行っても接合力が維持されて低下することはなく、従来の圧延接合のように、室温での圧延の後にクラッド材を２００～３００℃程度の温度で長時間にわたり熱処理して接合力や曲げ加工性を高める必要がなく、この点でも従来の圧延接合に比べて、製品コストおよび製造コストを低く抑えることができる、としている。 In addition, in the method for producing a clad material described in Patent Document 1 above, since strong bonding is performed by friction stir welding, even if rolling performed after friction stir welding is performed cold (room temperature), bonding strength is obtained. Is not maintained, and it is necessary to heat the clad material at a temperature of about 200 to 300 ° C. for a long time after rolling at room temperature to improve bonding strength and bending workability as in conventional rolling bonding. In this respect as well, it is possible to keep the product cost and the manufacturing cost low as compared with the conventional rolling bonding.
特開２００８－２５４００３号公報JP, 2008-254003, A
　しかしながら、上記非特許文献１で開示されている溶接方法では、得られるマグネシウム－リチウム系合金の継手強度は母材の８４％以下となり、延性も母材より低下する。加えて、マグネシウム－リチウム系合金の溶融溶接では、雰囲気中の酸素を完全に排除するために大量のアルゴンを使用しなければならない。 However, according to the welding method disclosed in Non-Patent Document 1, the joint strength of the obtained magnesium-lithium alloy is 84% or less of that of the base material, and the ductility is also lower than that of the base material. In addition, in melt welding of magnesium-lithium based alloys, a large amount of argon must be used to completely eliminate oxygen in the atmosphere.
　また、上記特許文献１に開示されているクラッド材の製造方法では、上側に配置されたアルミニウム合金板側から摩擦攪拌接合用のツールを挿入して、上側のアルミニウム合金板と下側のマグネシウム－リチウム系合金板を接合するものであり、マグネシウム－リチウム合金板側ではツールの作用による材料流動が殆ど生じておらず、「摩擦攪拌技術」の観点からはアルミニウム合金の摩擦攪拌接合に準ずるものである。即ち、摩擦攪拌接合によってマグネシウム－リチウム系合金の良好な継手を得る方法は確立されているとは言い難い。 Further, in the method of manufacturing a clad material disclosed in Patent Document 1 above, a tool for friction stir welding is inserted from the side of the aluminum alloy plate disposed on the upper side, and the upper aluminum alloy plate and the lower magnesium A material based on lithium-based alloy is joined, and on the magnesium-lithium alloy side, almost no material flow occurs due to the action of the tool, and from the viewpoint of "frictional stirring technology", it conforms to friction stir welding of aluminum alloy. is there. That is, it can not be said that a method of obtaining a good joint of magnesium-lithium based alloy by friction stir welding has been established.
　以上のような従来技術における問題点に鑑み、本発明の目的は、少なくとも一方の被接合材をマグネシウム－リチウム系合金とする場合の簡便かつ効率的な摩擦攪拌接合方法であって、攪拌部に母材以上の強度及び塑性加工性を付与することができる接合方法、及び当該接合方法によって得られる接合体を提供することにある。また、本発明は、マグネシウム－リチウム系合金の任意の領域に母材以上の強度及び塑性加工性を付与することができる改質方法、及び当該改質方法によって得られる金属構造体を提供することも目的としている。 In view of the problems in the prior art as described above, it is an object of the present invention to provide a simple and efficient friction stir welding method in which at least one bonding material is a magnesium-lithium alloy, and the stirring portion A bonding method capable of providing strength and plastic workability higher than that of a base material, and a bonded body obtained by the bonding method. In addition, the present invention provides a modification method capable of imparting strength and plastic workability higher than that of a base material to an arbitrary region of a magnesium-lithium alloy, and a metal structure obtained by the modification method. Also aims.
　本発明者は上記目的を達成すべく、摩擦攪拌接合用ツールの材質等について鋭意研究を重ねた結果、ツール表面への被接合材（マグネシウム－リチウム系合金）の凝着を抑制すること等が極めて有効であることを見出し、本発明に到達した。 In order to achieve the above object, the present inventor has conducted intensive studies on the material and the like of the friction stir welding tool, and as a result, the adhesion of the material to be welded (magnesium-lithium alloy) to the tool surface is suppressed. The inventors have found that the present invention is extremely effective.
　即ち、本発明は、
　一方の被接合材と他方の被接合材とを摩擦攪拌接合する方法であって、
少なくとも前記一方の被接合材がマグネシウム－リチウム系合金であり、
摩擦攪拌接合用ツールとして、超硬合金製ツール、サーメット製ツール、セラミックス製ツール、金属間化合物製ツール及びセラミックス被覆ツールのうちのいずれかを使用し、
前記摩擦攪拌接合用ツールを前記一方の被接合材側に挿入すること、
を特徴とする金属材の摩擦攪拌接合方法、を提供する。 That is, the present invention
A method of friction stir welding one to-be-joined material and the other to-be-joined material
At least one of the materials to be joined is a magnesium-lithium alloy,
Use one of cemented carbide tools, cermet tools, ceramic tools, intermetallic compound tools and ceramic coated tools as friction stir welding tools,
Inserting the friction stir welding tool into the one workpiece side;
The present invention provides a friction stir welding method of a metal material, characterized in that
　アルミニウム合金やマグネシウム合金は鋼製のツールで容易に摩擦攪拌することができ、ツール寿命についても特段の問題が生じないため、従来の摩擦攪拌接合ではツール価格等の観点からも鋼製（例えば、熱間工具鋼：ＳＫＤ６１等）のツールが使用されてきた。 Aluminum alloys and magnesium alloys can be easily friction stirred with steel tools, and there is no particular problem with tool life, so conventional friction stir welding is also made of steel (eg, from the viewpoint of tool price etc.) Tools of hot tool steel: such as SKD 61) have been used.
　しかしながら、本発明者が工具鋼製のツールを用いた従来公知の摩擦攪拌接合方法で、マグネシウム－リチウム系合金の接合を試みたところ、軟化したマグネシウム－リチウム系合金がツール表面に凝着し、良好な攪拌部を形成させることが困難であった。 However, when the inventors attempted to join a magnesium-lithium alloy by the conventionally known friction stir welding method using a tool steel tool, the softened magnesium-lithium alloy adheres to the tool surface, It was difficult to form a good stirring part.
　これに対し、本発明の金属材の摩擦攪拌接合方法では、摩擦攪拌接合用ツールとして、超硬合金製ツール、サーメット製ツール、セラミックス製ツール、金属間化合物製ツール及びセラミックス被覆ツールのうちのいずれかを使用することで、被接合材であるマグネシウム－リチウム系合金の凝着を効果的に低減することができる。ここで、ツール表面を無機非金属製とすることで、マグネシウム－リチウム系合金との親和性を低下させることができる（超硬合金やサーメットは金属結合相を有するが、無機非金属相が主成分である）。また、その結果、摩擦攪拌接合の温度を低下させることができ、より微細かつ均質な組織を有する、強度及び塑性加工性に優れた攪拌部を形成することができる。 On the other hand, in the friction stir welding method of a metal material of the present invention, any of cemented carbide tools, cermet tools, ceramic tools, intermetallic compound tools and ceramic coated tools as tools for friction stir welding The adhesion of magnesium-lithium alloy, which is the material to be joined, can be effectively reduced by using Here, by making the tool surface made of an inorganic nonmetal, the affinity with the magnesium-lithium alloy can be reduced (a cemented carbide or cermet has a metal bonding phase, but the inorganic nonmetal phase is mainly used. Component). Moreover, as a result, the temperature of friction stir welding can be reduced, and it is possible to form a stirring unit having a finer and more homogeneous structure and having excellent strength and plastic workability.
　また、本発明の金属材の接合方法では、（１）金属板の端部同士を突き合わせて接合部とし、回転ツールをその加工部の長手方向に沿って回転させつつ移動させて金属板同士を接合する接合、（２）金属板の端部同士を突き合わせて接合部とし、回転ツールをその接合部で移動させずに回転させて接合するスポット接合、（３）金属板同士を接合部において重ね合わせ、接合部に回転ツールを挿入し、回転ツールをその箇所で移動させずに回転させて金属板同士を接合するスポット接合、（４）金属板同士を接合部において重ね合わせ、接合部に回転ツールを挿入し、回転ツールをその接合部の長手方向に沿って回転させつつ移動させて金属板同士を接合する接合の（１）～（４）の４つの態様およびこれらの組み合わせを含むが、摩擦攪拌接合用ツールはマグネシウム－リチウム系合金に挿入する。本発明の金属材の接合方法ではツール表面へのマグネシウム－リチウム系合金の凝着が抑制されることに加え、塑性変形抵抗が小さなマグネシウム－リチウム系合金にツールを挿入することで、ツール寿命を向上させることもできる。 Further, in the method of bonding metal materials according to the present invention, (1) end portions of the metal plates are butted to form a bonding portion, and the rotary tool is moved while rotating along the longitudinal direction of the processed portion to move the metal plates together. Bonding bonding, (2) end portions of metal plates are butted to form a bonding portion, and spot bonding in which a rotary tool is rotated without moving at the bonding portion and bonded, and (3) metal plates are overlapped in the bonding portion Align, insert the rotary tool into the joint, and rotate the rotary tool without moving it at that point to join the metal plates by spot welding, (4) Overlay the metal plates at the joint, and rotate the joint to the joint Inserts the tool and moves it while rotating the rotating tool along the longitudinal direction of the joint to move it to join the metal plates together, including four aspects (1) to (4) of bonding and their combinations Friction stir Welding tool magnesium - inserted into lithium-based alloy. In addition to the suppression of the adhesion of the magnesium-lithium alloy to the tool surface in the method of joining metal materials of the present invention, the tool life can be shortened by inserting the tool into the magnesium-lithium alloy having a small plastic deformation resistance. It can also be improved.
　本発明の金属材の接合方法では、摩擦攪拌接合用ツールを一方の被接合材側（マグネシウム－リチウム系合金側）に挿入すること、を特徴の一つとしている。より具体的には、一方の被接合材がマグネシウム－リチウム系合金であり、他方の被接合材がマグネシウム－リチウム系合金以外である場合、突合せ接合においては、摩擦攪拌接合用ツールの中心（プローブ部の中心）を突合せ面よりも一方の被接合材側とし、重ね合わせ接合においては、一方の被接合材を上側に配置し、当該一方の被接合材側から摩擦攪拌接合用ツールを挿入する。 The method of bonding a metal material according to the present invention is characterized in that a friction stir welding tool is inserted into one of the materials to be bonded (magnesium-lithium alloy side). More specifically, when one of the materials to be joined is a magnesium-lithium alloy and the other material to be joined is other than a magnesium-lithium alloy, the center of the friction stir welding tool in the butt welding (probe The center of the portion is on one side of the material to be joined with respect to the butt surface, and in overlap bonding, one material to be joined is placed on the upper side, and the friction stir welding tool is inserted from the one material side .
　なお、ツールの回転速度、移動速度、挿入量及び印加荷重等の一般的な摩擦攪拌接合条件は、攪拌部における欠陥形成及び接合効率等の観点から適宜設定すればよい。また、ツールの形状は本発明の効果を損なわない限りにおいて特に限定されず、従来公知の種々の摩擦攪拌接合用ツールの形状を用いることができる。 In addition, general friction stir welding conditions such as the rotational speed, moving speed, insertion amount and applied load of the tool may be appropriately set from the viewpoint of defect formation in the stirring portion and bonding efficiency. Further, the shape of the tool is not particularly limited as long as the effects of the present invention are not impaired, and various shapes of conventionally known friction stir welding tools can be used.
　また、本発明の金属材の接合方法においては、前記他方の被接合材がマグネシウム－リチウム系合金であること、が好ましい。被接合材を共にマグネシウム－リチウム系合金とすることで、マグネシウム－リチウム系合金に対する摩擦攪拌作用の重要性が増加することから、本発明の金属材の接合方法の作用効果をより顕著に得ることができる。 In the metal material bonding method of the present invention, it is preferable that the other material to be bonded is a magnesium-lithium alloy. By making the materials to be joined together be magnesium-lithium alloys, the importance of the friction stir action on magnesium-lithium alloys is increased, so that the effects of the method of joining metal materials of the present invention can be obtained more remarkably. Can.
　また、本発明の金属材の接合方法においては、前記摩擦攪拌接合用ツールの表面に溝加工が施されていないこと、が好ましい。アルミニウム合金やマグネシウム合金の摩擦攪拌接合ではツール摩耗やツール破断が生じ難いため、ツールによる攪拌効果を増大させるためにショルダ部底面やプローブ部側面に螺子加工等の溝加工が施されるのが一般的である。これに対し、それらの溝加工をツールに施さないことで、ツール表面へのマグネシウム－リチウム系合金の凝着を抑制することができる。一方で、マグネシウム－リチウム系合金は優れた塑性加工性を有していることから、溝加工を有さないツールでも十分に材料流動が生じ、攪拌部を形成させることができる。なお、溝加工が施されていない摩擦攪拌接合用ツールとは、平面状態のショルダ底面及びプローブ側面を有するツールを意味する。 Further, in the method of bonding a metal material according to the present invention, it is preferable that the surface of the friction stir welding tool is not grooved. Since tool wear and tool breakage are unlikely to occur in friction stir welding of aluminum alloys and magnesium alloys, it is common to grooving such as screwing on the bottom of the shoulder and the side of the probe to increase the stirring effect of the tool. It is On the other hand, the adhesion of the magnesium-lithium alloy to the surface of the tool can be suppressed by not subjecting the groove processing to the tool. On the other hand, since the magnesium-lithium based alloy has excellent plastic workability, material flow can be sufficiently generated even with a tool without groove processing, and the stirring portion can be formed. In addition, the tool for friction stir welding which is not grooved means a tool having a shoulder bottom surface and a probe side surface in a flat state.
　また、本発明の金属材の接合方法においては、前記摩擦攪拌接合用ツールのショルダ部最外周の周速を２３．６ｍｍ／ｓ～７８．５ｍｍ／ｓとすること、が好ましい。当該周速範囲はマグネシウム合金の摩擦攪拌接合においては常識外の低速領域であるが、室温加工性を有するマグネシウム－リチウム系合金を被接合材とする場合は、十分な摩擦攪拌作用を得ることができる。ここで、ショルダ部最外周の周速を２３．６ｍｍ／ｓ以上とすることで、攪拌不足による欠陥の形成を抑制することができ、７８．５ｍｍ／ｓ以下とすることで、ツール表面へのマグネシウム－リチウム系合金の凝着による欠陥の形成、攪拌部の表面酸化及び液相の生成を抑制することができる。 Further, in the metal material joining method of the present invention, it is preferable to set the peripheral speed of the outermost periphery of the shoulder portion of the friction stir welding tool to 23.6 mm / s to 78.5 mm / s. The peripheral speed range is a low speed area which is not common in friction stir welding of magnesium alloys, but when a magnesium-lithium alloy having room temperature workability is used as a material to be joined, sufficient friction stir action should be obtained. it can. Here, by setting the circumferential speed at the outermost periphery of the shoulder portion to 23.6 mm / s or more, formation of a defect due to insufficient stirring can be suppressed, and by setting the circumferential speed to 78.5 mm / s or less, It is possible to suppress the formation of defects due to the adhesion of a magnesium-lithium alloy, the surface oxidation of the stirring portion, and the formation of a liquid phase.
　また、本発明の金属材の接合方法においては、前記摩擦攪拌接合用ツールのプローブ部最外周の周速を９．５ｍｍ／ｓ～３１．４ｍｍ／ｓとすること、が好ましい。当該周速範囲はマグネシウム合金の摩擦攪拌接合においては常識外の低速領域であるが、室温加工性を有するマグネシウム－リチウム系合金を被接合材とする場合は、十分な摩擦攪拌作用を得ることができる。ここで、プローブ部最外周の周速を９．５ｍｍ／ｓ以上とすることで、攪拌不足による欠陥の形成を抑制することができ、３１．４ｍｍ／ｓ以下とすることで、ツール表面へのマグネシウム－リチウム系合金の凝着による欠陥の形成を抑制することができる。 Further, in the method of bonding a metal material according to the present invention, it is preferable to set the peripheral speed at the outermost periphery of the probe portion of the friction stir welding tool to 9.5 mm / s to 31.4 mm / s. The peripheral speed range is a low speed area which is not common in friction stir welding of magnesium alloys, but when a magnesium-lithium alloy having room temperature workability is used as a material to be joined, sufficient friction stir action should be obtained. it can. Here, by setting the circumferential speed at the outermost periphery of the probe portion to 9.5 mm / s or more, formation of a defect due to insufficient stirring can be suppressed, and by setting the circumferential speed to 31.4 mm / s or less, It is possible to suppress the formation of defects due to adhesion of a magnesium-lithium alloy.
　また、本発明の金属材の接合方法においては、突合せ接合とすることが好ましい。突合せ接合では重ね合わせ接合と比較して攪拌部の形成が重要になるところ、本発明の金属材の接合方法ではマグネシウム－リチウム系合金を被接合材とした場合であっても良好な攪拌部を形成させることができるため、突合せ接合であっても効率的に接合を達成することができる。 Further, in the method of the present invention for joining metal materials, butt joining is preferable. In the butt joining, the formation of the agitating part is more important than the superposition joining, but in the joining method of the metal material of the present invention, a favorable agitating part is obtained even when the magnesium-lithium alloy is used as a material to be joined. Since it can be formed, even if it is butt joint, jointing can be achieved efficiently.
　なお、接合を目的とする摩擦攪拌接合と改質を目的とする摩擦攪拌プロセスは基本的に同じ原理を用いた技術であり、上述の本発明の金属材の接合方法は、金属材の改質方法としても用いることができる。具体的には、所望する改質部の形状、大きさ及び位置等を考慮して、適当な形状及びサイズを有するツールを用いて摩擦攪拌を施せばよい。 Friction stir welding for the purpose of joining and friction stir process for the purpose of reforming are basically techniques based on the same principle, and the method of joining metal materials of the present invention described above is the modification of metal materials. It can also be used as a method. Specifically, friction stirring may be performed using a tool having an appropriate shape and size in consideration of the shape, size, position, and the like of a desired reformed part.
　また、本発明は、
　一方の被接合材と他方の被接合材とが攪拌部を介して接合された接合体であって、
　少なくとも前記一方の被接合材がマグネシウム－リチウム系合金であり、
　前記攪拌部に前記マグネシウム－リチウム系合金のα相の再結晶粒を含み、
　前記再結晶粒の結晶方位がランダム化していること、
　を特徴とする接合体、も提供する。 Also, the present invention is
It is a joined body in which one to-be-joined material and the other to-be-joined material are joined via a stirring part,
At least one of the materials to be joined is a magnesium-lithium alloy,
The stirring portion includes recrystallized grains of the α phase of the magnesium-lithium alloy;
The crystal orientation of the recrystallized grain is random,
Also provided is a zygote characterized by
　本発明の接合体では、比較的低温の摩擦攪拌接合によって攪拌部が形成されていることから、当該攪拌部にはＨＣＰ構造を有するα相及びＢＣＣ構造を有するβ相の再結晶粒が含まれており、α相の再結晶粒は母材と比較して明確に微細化されている。 In the joined body of the present invention, since the stirring portion is formed by friction stir welding at a relatively low temperature, the stirring portion includes recrystallized grains of the α phase having the HCP structure and the β phase having the BCC structure. The recrystallized grains of the α phase are clearly refined compared to the base material.
　また、攪拌部において、α相の結晶方位はランダム化されている。α相はＨＣＰ構造を有しているため、一般に、押出や圧延等、単純なせん断応力が印加される加工プロセスを経た後は、強い集合組織が形成されてしまう。これに対し、本発明の接合方法を用いて適当な条件で摩擦攪拌することにより、α相の結晶方位をランダム化することができ、強い集合組織に起因する機械的性質の低下及び異方性を抑制することができる。ここで、ランダム化されているとはα相の強い底面集合組織が形成されていないことを意味し、例えば、ＥＢＳＤ測定の方位マップにおいて、α相の再結晶粒が同一系統色のみで表示されなければよい。より具体的には、極点図において、Ｔｅｘｔｕｒｅ　Ｉｎｔｅｎｓｉｔｙが１～１０であることが好ましく、１～５であることがより好ましい。 Further, in the stirring section, the crystal orientation of the α phase is randomized. Since the α phase has an HCP structure, a strong texture is generally formed after a processing process such as extrusion and rolling in which a simple shear stress is applied. On the other hand, by friction stirring under appropriate conditions using the bonding method of the present invention, it is possible to randomize the crystal orientation of the α phase, and the mechanical properties decrease and anisotropy due to the strong texture. Can be suppressed. Here, being randomized means that a strong bottom surface texture of the α phase is not formed, for example, in the orientation map of EBSD measurement, recrystallized grains of the α phase are displayed only in the same systematic color It is good without it. More specifically, in the pole figure, the Texture Intensity is preferably 1 to 10, and more preferably 1 to 5.
　また、本発明の接合体では、攪拌部の組織が母材よりも微細化されることから、母材よりも高硬度となる。加えて、攪拌部の外縁に接合中の温度上昇に伴う熱影響部が存在しないことから、母材よりも硬度が低くなる領域が存在しない。 Further, in the joined body of the present invention, since the structure of the agitating portion is finer than the base material, the hardness is higher than that of the base material. In addition, since there is no heat-affected zone at the outer edge of the agitating zone due to the temperature rise during joining, there is no region where the hardness is lower than that of the base material.
　また、本発明の接合体では、前記接合体の前記マグネシウム－リチウム系合金の領域における最低硬度が５０ＨＶ以上であること、が好ましく、前記一方の被接合材に対する継手効率が１００％であること、がより好ましい。適当な条件で摩擦攪拌接合を施すことにより、当該機械的性質を有する接合体を得ることができる。 Further, in the bonded body of the present invention, it is preferable that the minimum hardness in the region of the magnesium-lithium alloy of the bonded body is 50 HV or more, and that the joint efficiency with respect to the one workpiece is 100%. Is more preferred. By applying friction stir welding under appropriate conditions, a bonded body having the mechanical properties can be obtained.
　また、本発明の接合体では、前記攪拌部の引張強度が前記一方の被接合材の母材引張強度の１．１倍以上であることが好ましく、１．３倍以上であることがより好ましく、１．５倍以上であることが最も好ましい。一般的な摩擦攪拌接合で形成される攪拌部に関しても、比較的入熱が小さくなる接合条件では、攪拌部の引張強度が母材の引張強度よりも若干高くなる場合がある。しかしながら、本発明の接合体では、マグネシウム合金の摩擦攪拌接合としては常識外の低入熱条件で攪拌部を形成し、当該攪拌部をナノ組織化（α相の平均結晶粒径が１μｍ未満）することで、攪拌部の引張強度を一方の被接合材の引張強度の１．１倍以上とすることができる。加えて、当該ナノ組織を有する攪拌部は優れた超塑性能を発現することから、加工性の観点からも好ましい。 Further, in the bonded body according to the present invention, the tensile strength of the stirring portion is preferably 1.1 times or more, more preferably 1.3 times or more of the base material tensile strength of the one material to be bonded. Most preferably 1.5 times or more. With regard to a stirring portion formed by general friction stir welding, the tensile strength of the stirring portion may be slightly higher than the tensile strength of the base material under bonding conditions where the heat input is relatively small. However, in the bonded body of the present invention, the stirring portion is formed under low heat input conditions uncommon to friction stir welding of magnesium alloys, and the stirring portion is nano-organized (average crystal grain size of α phase is less than 1 μm) By doing this, the tensile strength of the stirring portion can be made 1.1 times or more the tensile strength of one of the materials to be joined. In addition, the stirring portion having the nano structure is preferable also from the viewpoint of processability because it exhibits excellent superplasticity.
　更に、本発明の接合体では、前記他方の被接合材がマグネシウム－リチウム系合金であること、が好ましく、突合せ接合体であること、がより好ましい。被接合材を共にマグネシウム－リチウム系合金とし、突合せ接合体とすることで、極めて効率的に接合体の軽量化を図ることができる。 Furthermore, in the bonded body of the present invention, the other material to be bonded is preferably a magnesium-lithium alloy, and more preferably a butt bonded body. By making both materials to be joined into magnesium-lithium alloys and forming a butt joint, weight reduction of the joint can be achieved extremely efficiently.
　なお、本発明の接合体は、上述の本発明の金属材の接合方法によって好適に製造することができる。 In addition, the bonded body of the present invention can be suitably manufactured by the method of bonding the metal material of the present invention described above.
　更に、本発明は、
　マグネシウム－リチウム系合金の改質部を含む金属構造体であって、
　前記改質部に前記マグネシウム－リチウム系合金のα相の再結晶粒を含み、
　前記再結晶粒の結晶方位がランダム化していること、
　を特徴とする金属構造体、も提供する。
　本発明の金属構造体は、ランダム化したα相の再結晶粒を含む改質部を有していることから、等方的に優れた機械的性質及び塑性加工性を有している。 Furthermore, the present invention
A metal structure including a reformed portion of a magnesium-lithium alloy,
The reformed portion includes recrystallized grains of the α phase of the magnesium-lithium alloy;
The crystal orientation of the recrystallized grain is random,
Also provided is a metal structure characterized by
The metal structure of the present invention has isotropically excellent mechanical properties and plastic workability since it has a reformed portion including recrystallized α-phase recrystallized grains.
　本発明の金属構造体は、前記再結晶粒の平均粒径が１μｍ未満であること、が好ましい。再結晶粒の平均粒径を１μｍ未満とすることで、改質部をより高硬度及び高強度とすることができることに加え、優れた超塑性能を付与することができる。 In the metal structure of the present invention, the average grain size of the recrystallized grains is preferably less than 1 μm. By setting the average grain size of recrystallized grains to less than 1 μm, it is possible to impart excellent superplasticity, in addition to the fact that the modified portion can have higher hardness and high strength.
　なお、本発明の金属構造体は、上述の本発明の金属材の接合方法と同様の金属材の改質方法によって好適に製造することができる。 In addition, the metal structure of this invention can be suitably manufactured by the modification method of the metal material similar to the joining method of the metal material of the above-mentioned this invention.
　本発明によれば、少なくとも一方の被接合材をマグネシウム－リチウム系合金とする場合の簡便かつ効率的な摩擦攪拌接合方法であって、攪拌部に母材以上の強度及び塑性加工性を付与することができる接合方法、及び当該接合方法によって得られる接合体を提供することができる。また、本発明によれば、マグネシウム－リチウム系合金の任意の領域に母材以上の強度及び塑性加工性を付与することができる改質方法、及び当該改質方法によって得られる金属構造体を提供することもできる。 According to the present invention, it is a simple and efficient friction stir welding method in which at least one of the materials to be joined is a magnesium-lithium alloy, which imparts strength and plastic workability greater than that of the base material to the stirring portion. The present invention can provide a bonding method that can be used, and a bonded body obtained by the bonding method. Further, according to the present invention, there is provided a reforming method capable of imparting strength and plastic workability higher than that of a base material to an arbitrary region of a magnesium-lithium based alloy, and a metal structure obtained by the reforming method. You can also
本発明の金属材の接合方法の一態様を示す模式図である。It is a schematic diagram which shows one aspect | mode of the joining method of the metal material of this invention. 本発明の接合体における接合部近傍の概略断面図である。It is a schematic sectional drawing of the junction-part vicinity in the joined_body | zygote of this invention. 実施例で得られた接合部の断面写真である。It is a cross-sectional photograph of the junction part obtained by the Example. 実施例で得られた接合部断面の硬度分布である。It is hardness distribution of the junction-part cross section obtained by the Example. 実施例で得られた接合部の引張特性である。It is the tensile property of the junction part obtained by the Example. 塑性変形特性評価後の攪拌部試験片の概観写真である。It is a general view photograph of the stirring part test piece after plastic deformation characteristic evaluation. 母材及び実施例で得られた攪拌部中心のＳＥＭ写真である。It is a SEM photograph of a base material and the stirring center center obtained by the Example. 母材及び実施例で得られた攪拌部中心のα相の方位マップ像である。It is an azimuth | direction map image of (alpha) phase of the base material and the stirring center center obtained by the Example.
　以下、図面を参照しながら本発明の金属材の接合方法及び接合体の代表的な実施形態について詳細に説明するが、本発明はこれらのみに限定されるものではない。なお、以下の説明では、同一または相当部分には同一符号を付し、重複する説明は省略する場合がある。また、図面は、本発明を概念的に説明するためのものであるから、表された各構成要素の寸法やそれらの比は実際のものとは異なる場合もある。 Hereinafter, although the representative embodiment of the bonding method and the bonded body of the metal material of the present invention will be described in detail with reference to the drawings, the present invention is not limited thereto. In the following description, the same or corresponding parts will be denoted by the same reference symbols, and overlapping descriptions may be omitted. Further, since the drawings are for explaining the present invention conceptually, the dimensions of the components shown and their ratios may be different from the actual ones.
（１）金属材の接合方法
　本発明の金属材の接合方法では、摩擦攪拌接合を用いる。摩擦攪拌接合とは、ＦＳＷ（Ｆｒｉｃｔｉｏｎ　Ｓｔｉｒ　Ｗｅｌｄｉｎｇ）と称され、接合しようとする二つの金属材からなる被接合材それぞれの端部を突き合わせ、回転ツールの先端に設けられた突起部（プローブ）を両者の端部の間に挿入し、これら端部の長手方向に沿って回転ツールを回転させつつ移動させることによって、二つの金属部材を接合する方法である。 (1) Method of Joining Metal Material In the method of bonding a metal material of the present invention, friction stir welding is used. Friction stir welding is called FSW (Friction Stir Welding), butt ends of two materials to be joined, which are to be joined, butt the protuberance (probe) provided on the tip of the rotating tool. In this method, two metal members are joined by inserting them between the two ends and rotating and moving a rotary tool along the longitudinal direction of the ends.
　本発明における金属材の接合方法は、上述のとおり、（１）金属板の端部同士を突き合わせて接合部とし、回転ツールをその加工部の長手方向に沿って回転させつつ移動させて金属板同士を接合する接合、（２）金属板の端部同士を突き合わせて接合部とし、回転ツールをその接合部で移動させずに回転させて接合するスポット接合、（３）金属板同士を接合部において重ね合わせ、接合部に回転ツールを挿入し、回転ツールをその箇所で移動させずに回転させて金属板同士を接合するスポット接合、（４）金属板同士を接合部において重ね合わせ、接合部に回転ツールを挿入し、回転ツールをその接合部の長手方向に沿って回転させつつ移動させて金属板同士を接合する接合の（１）～（４）の４つの態様およびこれらの組み合わせを含むが、以下、代表的な態様として、「（１）金属板の端部同士を突き合わせて接合部とし、回転ツールをその加工部の長手方向に沿って回転させつつ移動させて金属板同士を接合する接合」について詳細に説明する。 As described above, in the method of bonding metal materials according to the present invention, (1) end portions of the metal plates are butted to form a bonding portion, and the rotating tool is moved while being rotated along the longitudinal direction of the processed portion. (2) spot joining in which the end portions of metal plates are butted to form a joint, and the rotary tool is rotated without being moved at the joint and joined (3) metal plates are jointed Spot welding in which metal plates are joined by inserting a rotary tool into the joint, rotating the rotary tool without moving the rotary tool at that location, and (4) superposing metal plates in the joint, joint Insert a rotating tool into the plate, move the rotating tool along the longitudinal direction of the joint while moving it to bond the metal plates together, and include four aspects (1) to (4) of bonding and combinations of these. However, hereinafter, as a representative embodiment, “(1) End portions of metal plates are butted to form a joint, and the rotary tool is moved while being rotated along the longitudinal direction of the processed portion to join the metal plates together Will be described in detail.
　図１は、本発明の金属材の接合方法の一態様を示す模式図である。被接合材２（一方の被接合材）及び被接合材２’（他方の被接合材）を突き合わせ、回転させたツール４を所望の接合領域に挿入し、被接合線に沿って移動させることで接合部６を得ることができる。ここで、被接合材２及び被接合材２’を共にマグネシウム－リチウム系合金とする場合、基本的には突合せ線とツール４の突起部（プローブ部）８の中心を一致させるように挿入する。また、被接合材２をマグネシウム－リチウム系合金とし、被接合材２’をその他の金属材とする場合、本発明の金属材の接合方法では、ツール４を構成する突起部（プローブ部）８及び本体部（ショルダ部）１０の大半が被接合材２の側に当接することになる。 FIG. 1 is a schematic view showing one embodiment of the method of bonding metal materials of the present invention. Inserting the to-be-joined material 2 (one to-be-joined material) and the to-be-joined material 2 ′ (the other to-be-joined material), inserting the rotated tool 4 into the desired joining area and moving along the to-be-joined line The joint 6 can be obtained by Here, when the bonding material 2 and the bonding material 2 ′ are both made of a magnesium-lithium alloy, basically, the butt wire is inserted so that the centers of the protruding portions (probe portions) 8 of the tool 4 coincide with each other. . Further, in the case where the bonding material 2 is a magnesium-lithium alloy and the bonding material 2 'is another metal material, the protrusion (probe portion) 8 constituting the tool 4 is used in the method of bonding a metal material of the present invention. And most of the main body portion (shoulder portion) 10 abuts on the side of the workpiece 2.
　また、ツール４としては、超硬合金製ツール、サーメット製ツール、セラミックス製ツール、金属間化合物製ツール及びセラミックス被覆ツールのうちのいずれかを使用することで、被接合材であるマグネシウム－リチウム系合金の凝着を効果的に低減することができる。ここで、ツール４の表面を無機非金属製とすることで、マグネシウム－リチウム系合金との親和性を低下させることができる。また、その結果、摩擦攪拌接合の温度を低下させることができ、より微細かつ均質な組織を有する、強度及び塑性加工性に優れた攪拌部１２を形成することができる。 In addition, as the tool 4, any one of a cemented carbide tool, a cermet tool, a ceramic tool, an intermetallic compound tool, and a ceramic-coated tool can be used to make a magnesium-lithium alloy to be joined. The adhesion of the alloy can be effectively reduced. Here, by making the surface of the tool 4 made of an inorganic nonmetal, the affinity with the magnesium-lithium alloy can be reduced. Moreover, as a result, the temperature of friction stir welding can be reduced, and it is possible to form the stirring portion 12 having a finer and more homogeneous structure and having excellent strength and plastic workability.
　ここで、ツール材質として用いる超硬合金、サーメット、セラミックス及び金属間化合物の組成及び組織は、本発明の効果を損なわない限りにおいて特に制限されず、従来公知の種々の組成及び組織とすることができるが、超硬合金及びサーメットに関しては金属結合相を低減させることが好ましい。また、セラミックスとしては、例えば、炭化ケイ素、窒化ケイ素、サイアロン、窒化ホウ素、ジルコニア、アルミナ、二ホウ化チタン等を用いることができ、金属間化合物としては、例えば、Ｔｉ－Ａｌ系やＮｉ－Ａｌ系の金属間化合物を用いることができる。 Here, the composition and structure of cemented carbide, cermet, ceramics and intermetallic compounds used as a tool material are not particularly limited as long as the effects of the present invention are not impaired, and various compositions and structures conventionally known may be used. Although it is possible, for cemented carbides and cermets, it is preferable to reduce the metallic bonding phase. Further, as the ceramics, for example, silicon carbide, silicon nitride, sialon, boron nitride, zirconia, alumina, titanium diboride and the like can be used, and as the intermetallic compound, for example, Ti—Al based or Ni—Al Intermetallic compounds can be used.
　また、セラミックス被覆する場合はツール４の本体を金属製としてもよく、例えば、熱間工具鋼（ＳＫＤ６１）製とすることができる。セラミックス被膜の組成、組織及び膜厚等については本発明の効果を損なわない限りにおいて特に制限されず、従来公知の種々の組成、組織及び膜厚とすることができ、例えば、切削工具用として使用されている種々の硬質被膜を用いることができる。 In the case of ceramic coating, the main body of the tool 4 may be made of metal, for example, it can be made of hot tool steel (SKD 61). The composition, structure, thickness and the like of the ceramic film are not particularly limited as long as the effects of the present invention are not impaired, and various compositions, structures and thicknesses conventionally known can be used. For example, they are used for cutting tools Various hard coatings can be used.
　また、上述のツール材質及びセラミックス被膜については、マグネシウム－リチウム系合金との濡れ性の観点から選定することが好ましく、マグネシウム液滴とこれらの材料との接触角を９０°以上とすることが好ましい。接触角が９０°以上となるツール材質及びセラミックス被膜を選定することで、ツール４に印加されるトルクを低減することができる。 Moreover, it is preferable to select the above-mentioned tool material and ceramic film from the viewpoint of wettability with a magnesium-lithium based alloy, and it is preferable to make the contact angle of magnesium droplet and these materials 90 ° or more . The torque applied to the tool 4 can be reduced by selecting the tool material and the ceramic coating whose contact angle is 90 ° or more.
　また、図１に示すのは、円柱状の本体部（ショルダ部）１０の底面に円柱状の突起部（プローブ部）８を有するツール４を用いた場合であるが、ツール４の形状は、本発明の効果を損なわない限りにおいて特に限定されず、従来公知の種々の摩擦攪拌接合用ツールの形状を用いることができる。また、被接合材２，２’に当接する本体部（ショルダ部）１０の底面及び突起部（プローブ部）８の側面には、螺子加工等の溝加工を有さないことが好ましい。当該溝加工をツールに施さないことで、ツール４表面へのマグネシウム－リチウム系合金の凝着を抑制することができる。一方で、マグネシウム－リチウム系合金は優れた塑性加工性を有していることから、溝加工を有さないツールでも十分に攪拌部１２を形成させることができる。 Further, FIG. 1 shows the case where a tool 4 having a cylindrical protrusion (probe portion) 8 on the bottom of a cylindrical main body (shoulder portion) 10 is used, but the shape of the tool 4 is as follows: There is no particular limitation as long as the effects of the present invention are not impaired, and various shapes of conventionally known friction stir welding tools can be used. Moreover, it is preferable not to have groove processing, such as screw processing, in the bottom face of the main-body part (shoulder part) 10 and the side surface of the projection part (probe part) 8 which contact | abuts to-be-joined materials 2 and 2 '. By not subjecting the groove processing to the tool, adhesion of the magnesium-lithium alloy to the surface of the tool 4 can be suppressed. On the other hand, since the magnesium-lithium based alloy has excellent plastic workability, the stirring portion 12 can be sufficiently formed even with a tool having no groove processing.
　本発明の金属材の接合方法で少なくとも一方の被接合材とするマグネシウム－リチウム系合金は、マグネシウムを主成分とし、これに室温での塑性加工性を付与するためにリチウムを添加した合金を広く含むものである。例えば、当該合金には、強度や耐熱性を向上させるために、アルミニウム、亜鉛、マンガン、イットリウム、ランタノイド、ジルコニウム、銀、シリコン、カルシウム等を添加されたものが含まれる。 The magnesium-lithium-based alloy used as the at least one material to be joined by the method of joining metal materials according to the present invention is mainly composed of magnesium, and an alloy to which lithium is added in order to impart plastic workability at room temperature is widely used. It is included. For example, the alloy includes an alloy to which aluminum, zinc, manganese, yttrium, lanthanoid, zirconium, silver, silicon, calcium or the like is added in order to improve strength and heat resistance.
　ここで、リチウムは５～１５重量％の範囲内で含有されるのが好ましい。リチウムの含有量が５重量％を下回ると室温での塑性加工性があまり改善されず、逆にリチウムの含有量が１５重量％を上回ると粒界割れ（表面亀裂）の原因となることがあり、またリチウムが高価であるためコスト高になる。 Here, lithium is preferably contained in the range of 5 to 15% by weight. When the content of lithium is less than 5% by weight, the plastic formability at room temperature is not improved significantly, and conversely, when the content of lithium exceeds 15% by weight, intergranular cracking (surface crack) may be caused. Also, the cost is high because lithium is expensive.
　また、他方の被接合材２’もマグネシウム－リチウム系合金であることが好ましい。被接合材２，２’を共にマグネシウム－リチウム系合金とすることで、マグネシウム－リチウム系合金に対する摩擦攪拌作用の重要性が増加することから、本発明の金属材の接合方法の効果をより顕著に得ることができる。 Further, it is preferable that the other material to be joined 2 'is also a magnesium-lithium alloy. By making both materials 2 and 2 'to be joined into magnesium-lithium alloys, the importance of the friction stir action on magnesium-lithium alloys increases, so the effect of the joining method of the metal material of the present invention becomes more remarkable. Can be obtained.
　なお、ツール４の回転速度、移動速度、挿入量及び印加荷重等の一般的な摩擦攪拌接合条件は、攪拌部１２における欠陥形成及び接合効率等の観点から適宜設定すればよい。 General friction stir welding conditions such as rotational speed, moving speed, insertion amount and applied load of the tool 4 may be appropriately set from the viewpoint of defect formation in the stirring portion 12 and bonding efficiency.
　ここで、ツール４の本体部（ショルダ部）１０の最外周の周速は２３．６ｍｍ／ｓ～７８．５ｍｍ／ｓとすること、が好ましい。当該周速範囲はマグネシウム合金の摩擦攪拌接合においては常識外の低速領域であるが、室温加工性を有するマグネシウム－リチウム系合金を被接合材２，２’とする場合は十分な摩擦攪拌作用を得ることができる。ここで、本体部（ショルダ部）１０の最外周の周速を２３．６ｍｍ／ｓ以上とすることで、攪拌不足による欠陥の形成を抑制することができ、７８．５ｍｍ／ｓ以下とすることで、ツール４の表面へのマグネシウム－リチウム系合金の凝着による欠陥の形成、攪拌部１２の表面酸化及び液相の生成を抑制することができる。なお、ツール４の本体部（ショルダ部）１０の直径が１５ｍｍの場合、最外周の周速は回転速度を３０ｒｐｍとすることで略２３．６ｍｍ／ｓとなり、１００ｒｐｍとすることで略７８．５ｍｍ／ｓとなる。 Here, it is preferable that the peripheral speed of the outermost periphery of the main body (shoulder portion) 10 of the tool 4 be 23.6 mm / s to 78.5 mm / s. The peripheral speed range is a low speed area that is not common sense in friction stir welding of magnesium alloys, but when using a magnesium-lithium alloy having room temperature workability as the workpieces 2 and 2 ', sufficient friction stir action is required. You can get it. Here, by setting the peripheral speed of the outermost periphery of the main body portion (shoulder portion) 10 to 23.6 mm / s or more, formation of a defect due to insufficient agitation can be suppressed, and 78.5 mm / s or less Thus, it is possible to suppress the formation of defects due to the adhesion of the magnesium-lithium alloy to the surface of the tool 4, the surface oxidation of the stirring portion 12 and the formation of a liquid phase. When the diameter of the body portion (shoulder portion) 10 of the tool 4 is 15 mm, the peripheral speed of the outermost periphery is approximately 23.6 mm / s by setting the rotational speed to 30 rpm, and approximately 78.5 mm by setting 100 rpm. / S.
　また、ツール４の突起部（プローブ部）８の最外周の周速は９．５ｍｍ／ｓ～３１．４ｍｍ／ｓとすること、が好ましい。当該周速範囲はマグネシウム合金の摩擦攪拌接合においては常識外の低速領域であるが、室温加工性を有するマグネシウム－リチウム系合金を被接合材２，２’とする場合は十分な摩擦攪拌作用を得ることができる。ここで、突起部（プローブ部）８の最外周の周速を９．５ｍｍ／ｓ以上とすることで、攪拌不足による欠陥の形成を抑制することができ、３１．４ｍｍ／ｓ以下とすることで、ツール４の表面へのマグネシウム－リチウム系合金の凝着による欠陥の形成を抑制することができる。なお、ツール４の突起部（プローブ部）８の直径が６ｍｍの場合、最外周の周速は回転速度を３０ｒｐｍとすることで略９．５ｍｍ／ｓとなり、１００ｒｐｍとすることで略３１．４ｍｍ／ｓとなる。 In addition, it is preferable that the circumferential speed of the outermost periphery of the protruding portion (probe portion) 8 of the tool 4 be 9.5 mm / s to 31.4 mm / s. The peripheral speed range is a low speed area that is not common sense in friction stir welding of magnesium alloys, but when using a magnesium-lithium alloy having room temperature workability as the workpieces 2 and 2 ', sufficient friction stir action is required. You can get it. Here, by setting the circumferential speed of the outermost periphery of the protrusion (probe portion) 8 to 9.5 mm / s or more, formation of a defect due to insufficient stirring can be suppressed, and 31.4 mm / s or less Thus, the formation of defects due to the adhesion of the magnesium-lithium alloy to the surface of the tool 4 can be suppressed. When the diameter of the projection (probe portion) 8 of the tool 4 is 6 mm, the peripheral speed of the outermost periphery is approximately 9.5 mm / s by setting the rotational speed to 30 rpm, and approximately 31.4 mm by setting 100 rpm. / S.
　また、突合せ接合では重ね合わせ接合と比較して攪拌部１２の形成が重要になるところ、本発明の金属材の接合方法ではマグネシウム－リチウム系合金を被接合材２，２’とした場合であっても良好な攪拌部１２を形成させることができるため、本発明の接合方法を用いることで、効率的に接合を達成することができる。 Further, in the butt joining, the formation of the stirring portion 12 is more important than the superposition joining, but in the joining method of the metal material of the present invention, the magnesium-lithium alloy is used as the joining members 2 and 2 '. However, since a good stirring portion 12 can be formed, bonding can be efficiently achieved by using the bonding method of the present invention.
（２）接合体
　図２に、本発明の接合体における接合部近傍の概略断面図を示す。なお、本発明の接合体における接合部の代表的な態様として、図２では突合せ接合部を示している。 (2) Bonded Body FIG. 2 shows a schematic cross-sectional view in the vicinity of a bonded portion in the bonded body of the present invention. In addition, as a typical aspect of the junction part in the joined object of the present invention, a butt junction part is shown in FIG.
　本発明の接合体２０は、一方の被接合材２と他方の被接合材２’とが攪拌部１２を介して接合された接合体であって、少なくとも一方の被接合材２がマグネシウム－リチウム系合金であり、攪拌部１２のマグネシウム－リチウム系合金の領域において、α相の再結晶を含むこと、を特徴としている。なお、被接合材２，２’の形状及びサイズは本発明の効果を損なわない限りにおいて特に限定されず、本発明の接合方法によって接合可能であればよい。 The bonded body 20 of the present invention is a bonded body in which one of the materials to be bonded 2 and the other material to be bonded 2 ′ are bonded via the stirring portion 12, and at least one material to be bonded 2 is magnesium-lithium. It is a system alloy, and is characterized in that recrystallization of the α phase is included in the region of the magnesium-lithium alloy in the stirring section 12. The shape and size of the bonding members 2 and 2 'are not particularly limited as long as the effects of the present invention are not impaired, and bonding may be performed by the bonding method of the present invention.
　マグネシウム－リチウム系合金はＨＣＰ構造のα相とＢＣＣ構造のβ相を有しているが、押出材や圧延材では、α相が伸長して筋状に分布している。これに対し、攪拌部１２においてもα相はマクロ的には筋状に分布しているが、α相は再結晶しており、等軸状のα相が集合した状態となっている。 The magnesium-lithium alloy has an α phase of HCP structure and a β phase of BCC structure, but in the extruded material and the rolled material, the α phase is elongated and distributed in a streak shape. On the other hand, although the α phase is macroscopically distributed in the stirring section 12 as well, the α phase is recrystallized, and the equiaxed α phase is in a state of being gathered.
　少なくとも一方の被接合材２とするマグネシウム－リチウム系合金は、マグネシウムを主成分とし、これに室温での塑性加工性を付与するためにリチウムを添加した合金を広く含むものである。例えば、当該合金には、強度や耐熱性を向上させるために、アルミニウム、亜鉛、マンガン、イットリウム、ランタノイド、ジルコニウム、銀、シリコン、カルシウム等を添加されたものが含まれる。 The magnesium-lithium-based alloy as at least one of the materials to be joined 2 contains magnesium as a main component, and widely includes an alloy to which lithium is added in order to impart plastic workability at room temperature thereto. For example, the alloy includes an alloy to which aluminum, zinc, manganese, yttrium, lanthanoid, zirconium, silver, silicon, calcium or the like is added in order to improve strength and heat resistance.
　ここで、リチウムは５～１５重量％の範囲内で含有されるのが好ましい。リチウムの含有量が５重量％を下回ると室温での塑性加工性があまり改善されず、逆にリチウムの含有量が１５重量％を上回ると粒界割れ（表面亀裂）の原因となることがあり、またリチウムが高価であるためコスト高になる。 Here, lithium is preferably contained in the range of 5 to 15% by weight. When the content of lithium is less than 5% by weight, the plastic formability at room temperature is not improved significantly, and conversely, when the content of lithium exceeds 15% by weight, intergranular cracking (surface crack) may be caused. Also, the cost is high because lithium is expensive.
　接合体２０では、攪拌部１２の組織が母材よりも微細化されることから、母材よりも高硬度となる。また、攪拌部１２の外縁に接合中の温度上昇に伴う熱影響部が存在しないことから、母材よりも硬度が低くなる領域が存在しない。なお、α相の再結晶粒の平均粒径は５μｍ未満とすることが好ましく、３μｍ未満とすることがより好ましく、１μｍ未満とすることが最も好ましい。α相の再結晶粒を微細化することで、攪拌部１２の硬度及び強度を高くすることができるだけでなく、良好な塑性変形能を付与することができる。 In the joined body 20, since the structure of the stirring portion 12 is finer than the base material, the hardness is higher than that of the base material. Further, since there is no heat-affected zone at the outer edge of the agitating unit 12 due to the temperature rise during joining, there is no region where the hardness is lower than that of the base material. The average grain size of recrystallized grains of the α phase is preferably less than 5 μm, more preferably less than 3 μm, and most preferably less than 1 μm. By refining the recrystallized grain of the α phase, it is possible not only to increase the hardness and strength of the stirring portion 12 but also to impart a good plastic deformability.
　また、接合体２０の一方の被接合材２（マグネシウム－リチウム系合金）の領域における最低硬度は５０ＨＶ以上であること、が好ましく、接合体２０の一方の被接合材２（マグネシウム－リチウム系合金）に対する継手効率は１００％であること、がより好ましい。 In addition, the minimum hardness in the region of one of the bonding members 2 (magnesium-lithium-based alloy) of the bonded body 20 is preferably 50 HV or more, and one bonding member 2 of the bonded body 20 (magnesium-lithium-based alloy) The joint efficiency for 100% is more preferably 100%.
　また、攪拌部１２の引張強度は一方の被接合材２の引張強度の１．１倍以上であることが好ましく、１．３倍以上であることがより好ましく、１．５倍以上であることが最も好ましい。一般的な摩擦攪拌接合で形成される攪拌部に関しても、比較的入熱が小さくなる接合条件では、攪拌部の引張強度が母材の引張強度よりも若干高くなる場合がある。しかしながら、接合体２０では、マグネシウム合金の摩擦攪拌接合としては常識外の低入熱条件で攪拌部１２を形成し、攪拌部１２をナノ組織化（α相の平均結晶粒径が１μｍ未満）することで、攪拌部１２の引張強度を一方の被接合材２の引張強度の１．１倍以上とすることができる。加えて、当該ナノ組織を有する攪拌部１２は優れた超塑性能を発現することから、加工性の観点からも好ましい。 In addition, the tensile strength of the stirring portion 12 is preferably 1.1 times or more, more preferably 1.3 times or more, and more preferably 1.5 times or more of the tensile strength of one of the materials to be joined 2. Is most preferred. With regard to a stirring portion formed by general friction stir welding, the tensile strength of the stirring portion may be slightly higher than the tensile strength of the base material under bonding conditions where the heat input is relatively small. However, in the joined body 20, the stirring portion 12 is formed under low heat input conditions that are not common sense as friction stir welding of a magnesium alloy, and the stirring portion 12 is nano-organized (average crystal grain size of α phase is less than 1 μm) Thus, the tensile strength of the stirring portion 12 can be made 1.1 times or more of the tensile strength of one of the bonding members 2. In addition, since the stirring part 12 which has the said nano structure expresses the outstanding superplasticity ability, it is preferable also from a viewpoint of processability.
　また、接合体２０では、攪拌部１２の再結晶領域において、α相の結晶方位がランダム化されていることが好ましい。上述の本発明の接合方法を用いて適当な条件で摩擦攪拌することにより、α相の結晶方位をランダム化することができ、強い集合組織に起因する機械的性質の低下や異方性を抑制することができる。 Moreover, in the joined body 20, it is preferable that the crystal orientation of the α phase is randomized in the recrystallization region of the stirring unit 12. By friction stirring under appropriate conditions using the above-mentioned bonding method of the present invention, the crystal orientation of the α phase can be randomized, and the decrease in mechanical properties and anisotropy caused by the strong texture can be suppressed. can do.
　更に、接合体２０では、他方の被接合材２もマグネシウム－リチウム系合金であること、が好ましく、突合せ接合体であること、がより好ましい。被接合材２，２’を共にマグネシウム－リチウム系合金とし、突合せ接合体とすることで、極めて効率的に接合体２０の軽量化を図ることができる。 Furthermore, in the bonded body 20, the other material to be bonded 2 is also preferably a magnesium-lithium alloy, and more preferably a butt bonded body. By making both the materials to be joined 2 and 2 'be magnesium-lithium alloys and forming a butt joint, the weight reduction of the joint 20 can be achieved extremely efficiently.
　以上、本発明の代表的な実施形態について説明したが、本発明はこれらのみに限定されるものではなく、種々の設計変更が可能であり、それら設計変更は全て本発明の技術的範囲に含まれる。なお、本発明の金属構造体における改質部は、本発明の接合体における攪拌部と同様の特性を有している。 As mentioned above, although the typical embodiment of the present invention was described, the present invention is not limited only to these, and various design changes are possible, and all the design changes are included in the technical scope of the present invention. Be The reformed portion in the metal structure of the present invention has the same characteristics as the stirring portion in the joined body of the present invention.
≪実施例≫
　図１に示す配置で長さ２００ｍｍ，幅６５ｍｍ，厚さ３ｍｍのＬＺ９１マグネシウム合金（９ｗｔ％Ｌｉ－１ｗｔ％Ｚｎ－Ｍｇ　Ｂａｌ．）板同士を突合せ、摩擦攪拌接合によって接合体を得た。摩擦攪拌接合用のツールにはショルダ径１５ｍｍ，プローブ径６ｍｍ，プローブ長２．８ｍｍの超硬合金製ツールを用い、ツール回転速度２５～３００ｒｐｍ，ツール移動速度２０～１００ｍｍ／ｍｉｎ，前進角３°の条件で、ツール位置制御にて摩擦攪拌接合を行った。なお、摩擦攪拌接合中にシールドガスは使用しておらず、ツールのショルダ部底部及びプローブ部側面に溝加工は施していない。 << Example >>
In the arrangement shown in FIG. 1, LZ 91 magnesium alloy (9 wt% Li-1 wt% Zn-Mg Bal.) Plates having a length of 200 mm, a width of 65 mm and a thickness of 3 mm were butted together to obtain a joined body by friction stir welding. Use a cemented carbide tool with a shoulder diameter of 15 mm, a probe diameter of 6 mm, and a probe length of 2.8 mm as the friction stir welding tool, tool rotational speed 25 to 300 rpm, tool moving speed 20 to 100 mm / min, advancing angle 3 ° The friction stir welding was performed under tool position control under the following conditions. Note that no shielding gas is used during friction stir welding, and groove processing is not performed on the bottom of the shoulder of the tool and the side of the probe.
≪比較例≫
ツールの材質を熱間工具鋼（ＳＫＤ６１）製としたこと以外は実施例１と同様にして、摩擦攪拌接合を行った。 «Comparative example»
Friction stir welding was performed in the same manner as in Example 1 except that the material of the tool was made of hot tool steel (SKD 61).
［適切接合条件］
　良好な接合体を得るための適切な接合条件を確認するため、接合部（攪拌部）の表面及び断面を光学顕微鏡によって観察した。攪拌部に欠陥が形成している場合は×、欠陥は形成していないが大量のバリや表面の荒れが認められた場合は△、欠陥が形成されず攪拌部の表面状態も滑らかな場合は○とし、実施例の結果を表１に示した。なお、比較例においては全ての条件で欠陥が形成されたため（全ての条件で×の評価）、示していない。 [Suitable bonding conditions]
In order to confirm the suitable joining conditions for obtaining a good joined body, the surface and the cross section of the joint (stirred part) were observed by an optical microscope. If defects are formed in the stirring part, x, if no defects are formed, but if a large amount of burrs or surface roughness is observed, Δ, if defects are not formed and the surface state of the stirring part is smooth The results of the examples are shown in Table 1 with ○. In addition, in the comparative example, since a defect was formed on all the conditions (evaluation of x on all the conditions), it has not shown.
　接合部の断面観察結果の一例として、実施例で得られた接合部（ツール回転速度２００ｒｐｍ，ツール移動速度１００ｍｍ／ｍｉｎ）の断面写真を図３に示す。欠陥の形成は認められず、良好な攪拌部が得られている。 As an example of the cross-sectional observation result of the joint, a cross-sectional photograph of the joint (tool rotational speed 200 rpm, tool moving speed 100 mm / min) obtained in the example is shown in FIG. No formation of defects was observed, and a good stirring section was obtained.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　実施例では２５ｒｐｍと回転速度を最も遅くした場合で攪拌部に小さな欠陥が形成されたが、それ以外の条件で欠陥の形成は認められず、攪拌部の表面も良好な状態を有していた。当該結果から、本発明の接合方法では広い接合条件で良好な継手が得られることが分かる。なお、回転速度が１５０ｒｐｍよりも高くなると攪拌部表面の金属光沢が失われており、当該原因としては、接合温度の上昇に伴う酸化や液相の生成が考えられる。なお、シールドガスとしてアルゴンガスを使用することで、金属光沢を維持した良好な攪拌部表面を得ることができた。一方で、比較例では全ての接合条件で被接合材がツール表面に凝着し、攪拌部には溝状の欠陥が形成された。 In the example, when the rotational speed was made the slowest at 25 rpm, a small defect was formed in the stirring part, but under the other conditions no defect formation was observed, and the surface of the stirring part also had a good state. . From the results, it is understood that the joint method of the present invention can provide a good joint under a wide range of joint conditions. When the rotational speed is higher than 150 rpm, the metallic luster on the surface of the agitating portion is lost, and the cause may be formation of oxidation or liquid phase accompanying the increase in bonding temperature. In addition, the favorable stirring part surface which maintained metallic luster was able to be obtained by using argon gas as shield gas. On the other hand, in the comparative example, the material to be bonded adheres to the surface of the tool under all the bonding conditions, and a groove-like defect is formed in the stirring portion.
［ツール表面への被接合材の凝着］
　ツール回転速度１００ｒｐｍ，ツール移動速度１００ｍｍ／ｍｉｎの接合条件に関して、摩擦攪拌接合後のツール表面状態を目視観察した。また、本発明に用いることができるツールとして、窒化ケイ素製ツール、炭化ケイ素製ツール、サイアロン製ツール、サーメット製ツール、工具鋼製本体部の表面にＴｉＡｌ被膜を形成させたツールに関しても同様の摩擦攪拌接合を行い、当該接合後のツール表面状態を目視観察した。 [Adhesion of bonding material to tool surface]
The tool surface condition after friction stir welding was visually observed with respect to welding conditions of a tool rotational speed of 100 rpm and a tool moving speed of 100 mm / min. Further, as a tool that can be used in the present invention, the same friction can be applied to a tool made of silicon nitride, a tool made of silicon carbide, a tool made of sialon, a tool made of cermet, and a tool having a TiAl coating formed on the surface of a tool steel main body. Stir welding was performed, and the tool surface state after the bonding was visually observed.
　比較例として用いた工具鋼製ツールでは、被接合材がプローブ部側面及びショルダ部底面に凝着し、ツール原型の把握が困難な状況であった。これに対し、それ以外のツールではプローブ部側面及びショルダ部底面に被接合材に起因する着色が認められる部分は存在するものの、顕著な凝着は確認されなかった。 In the tool steel tool used as a comparative example, the material to be joined adheres to the side surface of the probe portion and the bottom surface of the shoulder portion, making it difficult to grasp the tool prototype. On the other hand, in the other tools, there was a portion where coloring due to the material to be joined was present on the side surface of the probe portion and the bottom surface of the shoulder portion, but significant adhesion was not confirmed.
［硬度測定］
　比較例では全ての接合条件で攪拌部に溝状欠陥が形成されたため、実施例で得られた接合部の断面に対してビッカース硬度測定を行った。なお、ビッカース硬度測定は荷重：０．１ｋｇｆ、荷重負荷時間：１５ｓの条件で行った。 [Hardness measurement]
In the comparative example, since the groove-like defect was formed in the stirring portion under all the bonding conditions, the Vickers hardness measurement was performed on the cross section of the bonded portion obtained in the example. The Vickers hardness was measured under the conditions of a load of 0.1 kgf and a loading time of 15 seconds.
　図４に、ツール移動速度１００ｍｍ／ｍｉｎ，ツール回転速度１００～３００ｒｐｍで得られた接合部断面の硬度分布（板厚中心における接合部水平方向）を示す。全ての攪拌部の硬度が母材よりも高くなっており、特に、より低いツール回転速度において攪拌部の硬度上昇が顕著である。また、攪拌部の外縁に軟化領域は認められない。 FIG. 4 shows the hardness distribution (horizontal direction of the joint at the center of the plate thickness) of the cross section of the joint obtained at a tool moving speed of 100 mm / min and a tool rotational speed of 100 to 300 rpm. The hardness of all the stirring parts is higher than that of the base material, and the increase in hardness of the stirring parts is remarkable particularly at a lower tool rotation speed. In addition, no softened region is observed at the outer edge of the stirring portion.
［引張試験］
　比較例では全ての接合条件で攪拌部に溝状欠陥が形成されたため、実施例で得られた継手に対して引張特性を評価した。引張試験には、長さ５０ｍｍ×幅１２ｍｍ×厚さ２ｍｍの平行部（突合せ面を平行部中心とする）を有する引張試験片を用い、継手の板幅方向を引張軸とした。なお、引張速度は１ｍｍ／ｍｉｎとした。 [Tension test]
In the comparative example, since the groove-like defect was formed in the agitating portion under all the joining conditions, the tensile properties of the joints obtained in the examples were evaluated. For the tensile test, a tensile test piece having parallel parts (length: 50 mm × width 12 mm × thickness 2 mm) (with the butt surface at the center of the parallel part) is used, and the plate width direction of the joint is taken as a tensile axis. The tensile speed was 1 mm / min.
　図５に、ツール移動速度１００ｍｍ／ｍｉｎ，ツール回転速度３０～１００ｒｐｍで得られた継手の引張特性を示す。なお、比較として、母材の引張試験結果を示している。また、攪拌部の引張特性を評価するために、ツール移動速度１００／ｍｉｎ，ツール回転速度３０ｒｐｍで得られた攪拌部内から、長さ４ｍｍ×幅２ｍｍ×厚さ２ｍｍの平行部を有する小型の引張試験片を作製し、接合方向を引張軸として、引張速度０．０８ｍｍ／ｍｉｎで評価した結果も示す。 FIG. 5 shows the tensile properties of the joint obtained at a tool movement speed of 100 mm / min and a tool rotation speed of 30 to 100 rpm. In addition, the tension test result of a base material is shown as a comparison. In addition, in order to evaluate the tensile properties of the agitating part, from the inside of the agitating part obtained at a tool moving speed of 100 / min and a tool rotational speed of 30 rpm, a small tension having a parallel part of 4 mm long x 2 mm wide x 2 mm thick Also shown are the results of preparing test pieces and evaluating the bonding direction as a tensile axis at a tensile speed of 0.08 mm / min.
　実施例で得られた継手は母材と同等の引張特性を有しており、継手効率は１００％となっている。また、攪拌部の引張特性は母材よりも顕著に高くなっており、引張強度は母材の約２倍となっている。 The joints obtained in the examples have the same tensile properties as the base material, and the joint efficiency is 100%. Further, the tensile properties of the stirring portion are significantly higher than that of the base material, and the tensile strength is about twice that of the base material.
［塑性変形特性評価］
　母材及び、実施例のツール移動速度１００／ｍｉｎ，ツール回転速度３０ｒｐｍで得られた攪拌部内から、長さ４ｍｍ×幅２ｍｍ×厚さ２ｍｍの平行部を有する小型の引張試験片をそれぞれ作製し、２００℃，３×１０－４のひずみ速度条件下での引張変形量を評価した。 [Plastic deformation characteristic evaluation]
From the base material and from the inside of the stirring part obtained at the tool movement speed of 100 / min and the tool rotation speed of 30 rpm in the example, small tensile test pieces having parallel parts of length 4 mm × width 2 mm × thickness 2 mm were respectively prepared The tensile deformation was evaluated at 200 ° C. and a strain rate of 3 × 10 −4 .
　母材及び攪拌部の破断までの変形量はそれぞれ略１５０％及び略１１００％となり、攪拌部には極めて顕著な超塑性変形能が付与されていることが確認された。評価終了後の攪拌部試験片の概観写真を図６に示す。長さ４ｍｍの平行部が、破断時には略４４ｍｍとなっている。 The deformation amounts to breakage of the base material and the stirring portion were about 150% and about 1100%, respectively, and it was confirmed that the stirring portion was provided with extremely remarkable superplastic deformability. An overview photograph of the test piece of the stirring unit after the evaluation is shown in FIG. The parallel portion with a length of 4 mm is approximately 44 mm when broken.
［微細組織観察］
　攪拌部における結晶粒の粒径及び形状を確認するため、接合部の断面のＳＥＭ観察及びＥＢＳＤ測定を行った。なお、ＳＥＭ観察及びＥＢＳＤ測定にはＦＥ－ＳＥＭ（日本電子株式会社製ＪＳＭ－７００１ＦＡ）及びＴＳＬ社製のＯＩＭ　ｄａｔａ　Ｃｏｌｌｅｃｔｉｏｎ　ｖｅｒ５．３１を用いた。 [Fine structure observation]
In order to confirm the grain size and shape of the crystal grains in the stirring portion, SEM observation and EBSD measurement of the cross section of the bonding portion were performed. For SEM observation and EBSD measurement, FE-SEM (JSM-7001FA manufactured by Nippon Denshi Co., Ltd.) and OIM data Collection ver. 5.31 manufactured by TSL Corporation were used.
　母材及び実施例（ツール移動速度１００ｍｍ／ｍｉｎ，ツール回転速度１００～３００ｒｐｍ）で得られた攪拌部中心のＳＥＭ写真及びα相の方位マップ像を図７及び図８にそれぞれ示す。母材はα相とβ相から構成され、α相は筋状に分布している。これに対し、実施例で得られた攪拌部ではα相が分断され、等軸状の再結晶粒となっていることが分かる。加えて、母材のα相は強い集合組織を有しているが、攪拌部のα相はランダムに配向している。なお、攪拌部の結晶粒径は母材よりも微細化されており、ツール回転速度が低い条件においてより顕著である。なお、α相の平均結晶粒径は、３００ｒｐｍの場合は５μｍ未満、２００ｒｐｍの場合は３μｍ未満、１００ｒｐｍの場合は１μｍ未満となっている。 An SEM photograph of the center of the stirring portion and an orientation map image of the α phase obtained in the base material and the example (tool movement speed 100 mm / min, tool rotation speed 100 to 300 rpm) are shown in FIGS. 7 and 8, respectively. The base material is composed of an α phase and a β phase, and the α phase is distributed in a streak shape. On the other hand, it can be seen that in the stirring section obtained in the example, the α phase is divided to form equiaxed recrystallized grains. In addition, the alpha phase of the matrix has a strong texture, but the alpha phase of the stirring section is randomly oriented. The crystal grain size of the stirring portion is finer than that of the base material, and is more remarkable under the condition that the tool rotation speed is low. The average crystal grain size of the α phase is less than 5 μm in the case of 300 rpm, less than 3 μm in the case of 200 rpm, and less than 1 μm in the case of 100 rpm.
２，２’・・・被接合材、
４・・・ツール、
６・・・接合部、
８・・・突起部（プローブ部）、
１０・・・本体部（ショルダ部）、
１２・・・攪拌部、
２０・・・接合体。 2, 2 '... Bonding material,
4 ... Tool,
6 ・ ・ ・ junction,
8 ・ ・ ・ Protrusion (probe),
10 ... Main body (shoulder),
12 ··· Stirring section,
20 ... bonded body.

Claims (14)

  1. 　一方の被接合材と他方の被接合材とが攪拌部を介して接合された接合体であって、
    　少なくとも前記一方の被接合材がマグネシウム－リチウム系合金であり、
    　前記攪拌部に前記マグネシウム－リチウム系合金のα相の再結晶粒を含み、
    　前記再結晶粒の結晶方位がランダム化していること、
    　を特徴とする接合体。     It is a joined body in which one to-be-joined material and the other to-be-joined material are joined via a stirring part,
    At least one of the materials to be joined is a magnesium-lithium alloy,
    The stirring portion includes recrystallized grains of the α phase of the magnesium-lithium alloy;
    The crystal orientation of the recrystallized grain is random,
    A zygote characterized by
  2. 　前記攪拌部の外縁に母材よりも軟化した領域が存在しないこと、
    　を特徴とする請求項１に記載の接合体。     There is no area softened at the outer edge of the stirring section than the base material,
    The joined body according to claim 1, characterized by
  3. 　前記マグネシウム－リチウム系合金の領域における最低硬度が５０ＨＶ以上であること、
    　を特徴とする請求項１又は２に記載の接合体。     A minimum hardness of 50 HV or more in the region of the magnesium-lithium alloy;
    The joined body according to claim 1 or 2, characterized by
  4. 　前記攪拌部の引張強度が前記一方の被接合材の引張強度の１．１倍以上であること、
    　を特徴とする請求項１～３のうちのいずれかに記載の接合体。     The tensile strength of the stirring portion is 1.1 times or more of the tensile strength of the one material to be joined,
    The joined body according to any one of claims 1 to 3, characterized in that
  5. 　前記他方の被接合材がマグネシウム－リチウム系合金であること、
    　を特徴とする請求項１～４のうちのいずれかに記載の接合体。     The other material to be joined is a magnesium-lithium alloy;
    The joined body according to any one of claims 1 to 4, characterized by
  6. 　突合せ接合体であること、
    　を特徴とする請求項１～５のうちのいずれかに記載の接合体。     Be a butt joint,
    The bonded body according to any one of claims 1 to 5, characterized in that
  7. 　マグネシウム－リチウム系合金の改質部を含む金属構造体であって、
    　前記改質部に前記マグネシウム－リチウム系合金のα相の再結晶粒を含み、
    　前記再結晶粒の結晶方位がランダム化していること、
    　を特徴とする金属構造体。     A metal structure including a reformed portion of a magnesium-lithium alloy,
    The reformed portion includes recrystallized grains of the α phase of the magnesium-lithium alloy;
    The crystal orientation of the recrystallized grain is random,
    Metal structure characterized by
  8. 　前記再結晶粒の平均粒径が１μｍ未満であること、
    　を特徴とする請求項７に記載の金属構造体。     The average grain size of the recrystallized grains is less than 1 μm,
    The metal structure according to claim 7, characterized in that
  9. 　一方の被接合材と他方の被接合材とを摩擦攪拌接合する方法であって、
    　少なくとも前記一方の被接合材がマグネシウム－リチウム系合金であり、
    　摩擦攪拌接合用ツールとして、超硬合金製ツール、サーメット製ツール、セラミックス製ツール、金属間化合物製ツール及びセラミックス被覆ツールのうちのいずれかを使用し、
    　前記摩擦攪拌接合用ツールを前記一方の被接合材側に挿入すること、
    　を特徴とする金属材の摩擦攪拌接合方法。     A method of friction stir welding one to-be-joined material and the other to-be-joined material
    At least one of the materials to be joined is a magnesium-lithium alloy,
    Use one of cemented carbide tools, cermet tools, ceramic tools, intermetallic compound tools and ceramic coated tools as friction stir welding tools,
    Inserting the friction stir welding tool into the one workpiece side;
    The friction stir welding method of the metal material characterized by the above.
  10. 　前記他方の被接合材がマグネシウム－リチウム系合金であること、
    　を特徴とする請求項９に記載の金属材の摩擦攪拌接合方法。     The other material to be joined is a magnesium-lithium alloy;
    The friction stir welding method of the metal material of Claim 9 characterized by the above-mentioned.
  11. 　前記摩擦攪拌接合用ツールの表面に溝加工が施されていないこと、
    　を特徴とする請求項９又は１０に記載の金属材の摩擦攪拌接合方法。     The surface of the friction stir welding tool is not grooved,
    The friction stir welding method of the metal material of Claim 9 or 10 characterized by these.
  12. 　前記摩擦攪拌接合用ツールのショルダ部最外周の周速を２３．６ｍｍ／ｓ～７８．５ｍｍ／ｓとすること、
    　を特徴とする請求項９～１１のうちのいずれかに記載の金属材の摩擦攪拌接合方法。     The circumferential speed of the outermost periphery of the shoulder portion of the friction stir welding tool is 23.6 mm / s to 78.5 mm / s,
    The friction stir welding method of a metal material according to any one of claims 9 to 11, characterized in that
  13. 　前記摩擦攪拌接合用ツールのプローブ部最外周の周速を９．５ｍｍ／ｓ～３１．４ｍｍ／ｓとすること、
    　を特徴とする請求項９～１２のうちのいずれかに記載の金属材の摩擦攪拌接合方法。     The circumferential speed of the outermost periphery of the probe portion of the friction stir welding tool is set to 9.5 mm / s to 31.4 mm / s.
    The friction stir welding method of a metal material according to any one of claims 9 to 12, characterized in that
  14. 　突合せ接合であること、
    　を特徴とする請求項９～１３のうちのいずれかに記載の金属材の摩擦攪拌接合方法。
          Be butt joint,
    The friction stir welding method of a metal material according to any one of claims 9 to 13, characterized in that
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CN113502422A (en) * 2021-06-11 2021-10-15 清华大学 High-strength-toughness magnesium-lithium alloy and preparation method thereof

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JP2004209522A (en) * 2003-01-06 2004-07-29 Hyogo Prefecture Intermetallic friction stir welding method
JP2011079022A (en) * 2009-10-07 2011-04-21 Kurimoto Ltd FRICTION STIR WELDING METHOD FOR Mg AND Mg ALLOY
JP2012143811A (en) * 2010-12-24 2012-08-02 Sumitomo Electric Ind Ltd Magnesium alloy material

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2004209522A (en) * 2003-01-06 2004-07-29 Hyogo Prefecture Intermetallic friction stir welding method
JP2011079022A (en) * 2009-10-07 2011-04-21 Kurimoto Ltd FRICTION STIR WELDING METHOD FOR Mg AND Mg ALLOY
JP2012143811A (en) * 2010-12-24 2012-08-02 Sumitomo Electric Ind Ltd Magnesium alloy material

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113502422A (en) * 2021-06-11 2021-10-15 清华大学 High-strength-toughness magnesium-lithium alloy and preparation method thereof

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