WO2024034268A1

WO2024034268A1 - Friction stir welding method and friction stir welding tool

Info

Publication number: WO2024034268A1
Application number: PCT/JP2023/023046
Authority: WO
Inventors: 英俊藤井; 拓也三浦; 好昭森貞
Original assignee: 国立大学法人大阪大学
Priority date: 2022-08-08
Filing date: 2023-06-22
Publication date: 2024-02-15

Abstract

This friction stir welding method causes a friction stir welding tool to pass through a material to be welded, in the thickness direction of the material to be welded, and performs friction stir welding in a state in which a refrigerant is flowing through a through-hole provided in a rotating shaft of the friction stir welding tool.

Description

Friction stir welding method and friction stir welding tools

The present invention relates to a friction stir welding method and a friction stir welding tool.

Friction stir welding (FSW) is known as a typical solid phase joining method for metal materials. In friction stir welding, two metal materials to be joined are joined as follows. That is, the two metal materials are made to face each other at the part to be joined, and a probe provided at the tip of the rotary tool is inserted into the part to be joined. The rotary tool is rotated and moved along the interface to be joined. Two metal materials are joined by causing the metal materials to flow using frictional heat and the stirring force of a rotating tool. Friction stir welding has the characteristics that the maximum temperature reached during welding does not reach the melting point of the materials to be joined, and the decrease in strength at the joint is smaller than that of conventional fusion welding, and its practical application has rapidly progressed in recent years. There is.

However, while friction stir welding has various excellent features, it requires press-fitting a tool that is stronger than the materials to be welded, and in addition, large stress is applied to the tool. Therefore, depending on the materials to be joined, the cost and life of the tool become a major problem. Specifically, it is as follows. That is, when joining thin plates of relatively soft metal such as aluminum or magnesium, the load on the tool is small, and there are no particular problems regarding tool life and joining conditions. However, when joining high melting point metals such as steel or titanium, the tool life becomes extremely short.

On the other hand, Patent Document 1 (Japanese Patent Publication No. 2003-532543) proposes a friction stir welding tool that can friction stir weld metal matrix composite materials (MMCs), ferrous alloys, nonferrous alloys, and superalloys. There is. Specifically, the friction stir welding tool described in Patent Document 1 includes a shaft portion, a shoulder portion, and a pin, and a highly wear-resistant material disposed on at least a portion of the shoulder portion and the pin, and the shoulder portion is The shoulder is mechanically fixed to the shaft to prevent rotational movement relative to the shaft. The high wear resistant material has a first phase and a second phase, and the high wear resistant material is manufactured under extremely high temperature and pressure. Friction stir welding tools are capable of functionally friction stir welding MMCs, ferrous alloys, nonferrous alloys, and superalloys. Furthermore, Patent Document 1 discloses the use of polycrystalline boron nitride (PCBN) or polycrystalline diamond (PCD) as a highly wear-resistant material.

The friction stir welding tool described in Patent Document 1 uses materials that cannot be welded using conventional friction stir welding methods and tools, namely (i) iron alloys such as stainless steel, and (ii) iron. Friction stir welding can be applied to materials containing high melting point superalloys that contain a small amount of iron or no iron.

In addition, in general friction stir welding, the probe of the rotating tool is inserted into the part to be joined only from the surface side of the opposing metal materials. Therefore, there is also a drawback that kissing bonds, which are unbonded parts of the metal materials, are likely to occur on the back side of the metal materials.

In order to improve this drawback, for example, as disclosed in Patent Document 2 (Japanese Unexamined Patent Publication No. 2003-181654), a rotating tool called a bobbin tool is used to apply friction from both the front and back sides of the metal material. A method of performing stir welding has been proposed.

Japan Special Table No. 2003-532543 Japanese Patent Application Publication No. 2003-181654

However, since the friction stir welding tool disclosed in Patent Document 1 is manufactured under ultra-high temperature and ultra-high pressure conditions, the manufacturing cost increases significantly. The result is a tool that is unacceptably expensive for general industrial use. Also, tool manufacturing under ultra-high temperature and ultra-high pressure conditions is not suitable for mass production. Therefore, as the demand for tools increases, the price of the tools further increases.

Furthermore, when using the bobbin tool disclosed in Patent Document 2, the thin probe part moves laterally while penetrating the material to be welded, so the probe part is likely to break. Therefore, the bobbin tool disclosed in Patent Document 2 cannot be basically applied to joining high-melting point metals such as steel or titanium.

In view of the problems in the prior art as described above, an object of the present invention is to provide a friction stir welding method for inexpensively and efficiently obtaining low-defect joints made of high-melting point metals such as steel and titanium, and a method suitable for the friction stir welding. The object of the present invention is to provide a friction stir welding tool that can be used for.

In order to achieve the above object, the inventor of the present invention has conducted extensive research on friction stir welding methods and tools for friction stir welding, and as a result, has provided a through hole in the rotating shaft of the friction stir welding tool and allows a coolant to flow through the through hole. We have discovered that it is extremely effective to cool the friction stir welding tool by cooling the friction stir welding tool, and have arrived at the present invention.

That is, one aspect of the present invention is
Penetrate the friction stir welding tool in the thickness direction of the welded materials,
performing friction stir welding with a refrigerant flowing through a through hole provided in a rotating shaft of the friction stir welding tool;
A friction stir welding method is provided.

Another aspect of the present invention also provides a friction stir welding tool characterized by having a through hole in the rotating shaft.

According to the present invention, there is provided a friction stir welding method for inexpensively and efficiently obtaining a low-defect joint made of high-melting point metals such as steel and titanium, and a friction stir welding tool that can be suitably used for the friction stir welding. can do.

FIG. 1 is a schematic diagram showing one embodiment of the friction stir welding method of the present invention (when a bobbin tool is used). FIG. 1 is a schematic diagram showing one embodiment of the friction stir welding method of the present invention (in the case of reverse friction stir welding). FIG. 2 is a schematic diagram showing one embodiment of the friction stir welding method of the present invention (in a case where a friction stir welding tool is press-fitted from the surface side of the materials to be welded). FIG. 2 is a schematic diagram showing one embodiment of the friction stir welding tool of the present invention (bobbin tool, case where the through hole is thin). FIG. 1 is a schematic diagram showing one embodiment of the friction stir welding tool of the present invention (bobbin tool, case where the through hole is thick). FIG. 1 is a schematic diagram showing one embodiment of the friction stir welding tool of the present invention (inversion friction stir welding tool, case where the through hole is thin). BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing one embodiment of the friction stir welding tool of the present invention (inversion friction stir welding tool, case where the through hole is thick). 1 is a photograph of the appearance of a friction stir welded joint obtained in Example 1. 1 is an optical micrograph of a cross section of a joint part of a friction stir welded joint obtained in Example 1. 2 is a photograph of the appearance of the bobbin tool used in Example 1 before and after joining. FIG. 3 is a diagram showing the cross-sectional shape of the bobbin tool used in Example 1 before and after joining. 3 is an external photograph showing the state of reverse friction stir welding in Example 2. 2 is a photograph of the appearance of a friction stir welded joint obtained in Example 2. 2 is an optical micrograph of a cross section of a joint part of a friction stir welded joint obtained in Example 2. 2 is a photograph of the appearance of a friction stir welded joint obtained in Comparative Example 1. 3 is a photograph of the appearance of the bobbin tool used in Comparative Example 1 before and after joining. It is an external photograph showing the state immediately after stopping water cooling in Comparative Example 2. 3 is an external photograph showing changes in the tool as time passes for reverse friction stir welding in Comparative Example 2. 2 is a photograph of the appearance of a friction stir welded joint obtained in Comparative Example 2.

Hereinafter, typical embodiments of the friction stir welding method and friction stir welding tool of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these embodiments. In the following description, the same or equivalent parts are given the same reference numerals, and redundant descriptions may be omitted. Further, since the drawings are for conceptually explaining the present invention, the dimensions of each component shown and the ratios of those dimensions may differ from the actual ones.

(1) Friction stir welding method (1-1) Friction stir welding using a bobbin tool Figure 1 shows a schematic diagram of friction stir welding using a bobbin tool. In FIG. 1, the welding direction is shown by a black straight arrow, and the flow of refrigerant within the tool is shown by a thick arrow. The bobbin tool 2 used in the friction stir welding of the present invention has an upper shoulder portion 4 and a lower shoulder portion 6 connected by a probe portion 8 to form an integral body. Further, the bobbin tool 2 has a through hole 10 provided on the rotating shaft, and the through hole 10 is formed in the upper shoulder section 4 - the probe section 8 - the lower shoulder section 6.

The bobbin tool 2 rotated at high speed is inserted from the end of the welded part 14 of the welded material 12, and the welded material 12 is sandwiched between the upper shoulder part 4 and the lower shoulder part 6, thereby removing frictional heat and machining heat. Friction stir welding can be achieved by generating and friction stirring the softened materials 12 to be joined.

During friction stir welding, by circulating a coolant through the through holes 10, the temperature rise of the bobbin tool 2 is suppressed, and by keeping the bobbin tool 2 at a lower temperature than the materials 12 to be welded, the bobbin tool 2 can be lengthened. It can extend its lifespan. In addition, friction stir welding can be performed using the bobbin tool 2 made of a material whose room temperature strength is lower than that of the welded materials 12.

The type of refrigerant is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known refrigerants can be used; however, by using water, increase in process cost can be suppressed. A rust preventive agent or the like may be added to the water if necessary. As a refrigerant other than water, for example, liquid CO ₂ or liquid nitrogen can be used.

By circulating the refrigerant discharged from the through hole 10 of the lower shoulder section 6 and allowing it to flow back into the through hole 10 of the upper shoulder section 4, an increase in process costs can be suppressed. Note that when liquid CO ₂ is used as the refrigerant, the circulation mechanism is not necessary because the liquid CO ₂ is vaporized.

The flow rate and flow rate of the coolant may be adjusted as appropriate according to the material, shape, and size of the bobbin tool 2 and the material, shape, and size of the welded materials 12 so that a desired friction stir portion is formed. Here, by providing a mechanism for circulating the refrigerant through the through holes 10, the flow rate and flow rate of the refrigerant can be easily controlled. When using water as the refrigerant, for example, when the through hole is 2 mm in diameter, the flow rate (related to the flow rate) can be about 1.0 to 5.0 L/min.

Regarding friction stir welding conditions such as tool rotation speed and tool movement speed, the desired friction stir welding part is formed according to the material, shape, and size of the bobbin tool 2 and the material, shape, and size of the workpiece 12. You can adjust it accordingly.

(1-2) Reverse friction stir welding Figure 2 shows a schematic diagram of reverse friction stir welding. In FIG. 2, the welding direction is indicated by a black straight arrow, and the flow of the coolant within the tool is indicated by a thick arrow. The probe portion 8 is inserted into the welded portion 14 of the welded material 12, and the shoulder portion 20 is brought into contact with the back surface of the welded material 12. The top plate 22 is brought into contact with the surface of the workpiece 12, the workpiece 12 is sandwiched between the shoulder part 20 and the top plate 22, and the shoulder part 20 and the probe part 8 are rotated while moving along the workpiece interface. The members 12 to be welded are joined together by moving the workpieces 12 together. Note that the welding control method is not particularly limited, and various conventionally known control methods can be used, such as constant tool position control, constant load control, and constant torque control.

Here, the inverted friction stir welding tool 30 used in the friction stir welding method of the present invention has a through hole 10 provided in the rotating shaft, and the through hole 10 is formed in the probe part 8 to the shoulder part 20. ing.

The inverted friction stir welding tool 30 rotated at high speed is pulled up from the back side of the welded materials 12 and the welded materials 12 are sandwiched between the shoulder portion 20 and the top plate 22 to generate frictional heat and processing heat and soften them. Friction stir welding can be achieved by friction stirring the welded materials 12. Note that the top plate 22 is provided with an opening through which the probe section 8 can pass.

During friction stir welding, by circulating a coolant through the through holes 10, the temperature rise of the reverse friction stir welding tool 30 is suppressed, and the temperature of the reverse friction stir welding tool 30 is lower than that of the materials 12 to be welded. This makes it possible to extend the life of the inverted friction stir welding tool 30. In addition, friction stir welding can be performed using the inverted friction stir welding tool 30 that uses a material whose room temperature strength is lower than that of the materials 12 to be joined.

Here, by fixing the distance between the shoulder portion 20 and the top plate 22 to be constant, reverse friction stir welding can be performed by position control. Further, by performing friction stir welding while pulling up the shoulder portion 20 and probe portion 8, reverse friction stir welding can be performed by controlling the load. Note that reverse friction stir welding using load control can easily follow changes in plate thickness. Moreover, although FIG. 2 shows a butt joint, a lap joint may also be used. In addition, it can also be used as a processing method such as surface treatment.

Since friction stir welding is performed from the back side of the workpieces 12, for example, even if the stirring shaft (probe section 8) of the tool is not inclined (tool advance angle is 0°), a kissing bond is formed on the backside of the workpieces 12. No unbonded parts like . In addition, the stirring shaft (probe portion 8) of the tool can be tilted, and a tool advancing angle can be given during friction stir welding. Since the material flow proceeds smoothly due to the advance angle, the conditions under which welding is possible are expanded, and it becomes possible to prevent welding defects. Note that the tool advancement angle is preferably greater than 0° and less than or equal to 7°.

In addition, in the example shown in FIG. 2, a rotating member such as a bobbin tool is not brought into contact with both sides of the workpieces 12 around the joint, and the undulations of the top plate 22 are transferred to the surface of the workpieces 12. Ru. Therefore, by abutting the top plate 22 having a smooth surface, it is possible to obtain a good welding surface without creating marks after friction stir welding on the surfaces of the respective materials 12 to be welded around the welding part. Become.

Furthermore, in reverse friction stir welding, unlike the conventional friction stir welding method in which the probe of a rotating tool is inserted into the joint from only the front side of the workpieces 12 and a backing plate is brought into contact with the back side of the workpieces 12, There is no need to perform work from both the front and back sides of the material 12, and most work can be performed only from the front side of the material 12 to be joined. Therefore, as in the case of using a bobbin tool, the materials to be welded 12 can be easily joined to closed structures such as equipment and vehicle chassis by only working from the outside.

The cooling method of the inverted friction stir welding tool 30, adjustment of various friction stir welding conditions, etc. are the same as in the case of using a bobbin tool.

(1-3) Other Friction Stir Welding FIG. 3 schematically shows an example of a mode in which a friction stir welding tool 40 having a general shape is press-fitted from the surface side of the materials 12 to be welded. In FIG. 3, the welding direction is indicated by a black straight arrow, and the flow of the coolant within the tool is indicated by a thick arrow. The friction stir welding tool 40 has the shape of a conventional friction stir welding tool in which a probe portion 8 is provided at the center of a shoulder portion 20, except that a through hole 10 is formed.

The probe part 8 is inserted into the part to be joined 14 of the material to be joined 12, and the shoulder part 20 is brought into contact with the surface of the material to be joined 12. The back plate 24 is brought into contact with the back surface of the workpiece 12, the workpiece 12 is sandwiched between the shoulder part 20 and the back plate 24, and the shoulder part 20 and the probe part 8 are rotated while moving along the workpiece interface. The members 12 to be welded are joined together by moving the workpieces 12 together. Note that the welding control method is not particularly limited, and various conventionally known control methods can be used, such as constant tool position control, constant load control, and constant torque control.

Here, the friction stir welding tool 40 having a general shape used in the friction stir welding method of the present invention has a through hole 10 provided in the rotating shaft. It is formed in the section 8.

A friction stir welding tool 40 having a general shape rotated at high speed is pressed against the surface of the workpiece 12 and the workpiece 12 is sandwiched between the shoulder portion 20 and the back plate 24 to release frictional heat and processing heat. Friction stir welding can be achieved by generating and friction stirring the softened materials 12 to be joined. Note that the back plate 24 is provided with a recess or an opening through which cooling water can flow through the probe portion 8 .

By circulating a coolant through the through holes 10 during friction stir welding, the temperature rise of the friction stir welding tool 40 having a general shape is suppressed, and the temperature rise of the friction stir welding tool 40 having a general shape is suppressed. By keeping the friction stir welding tool 40 having a low temperature, it is possible to extend the life of the friction stir welding tool 40 having a general shape. In addition, friction stir welding can be performed using a friction stir welding tool 40 having a general shape and made of a material whose room temperature strength is lower than that of the materials 12 to be joined.

Here, by fixing the distance between the shoulder portion 20 and the back plate 24 to a constant value, friction stir welding can be performed by position control. Further, by performing friction stir welding while pressing the shoulder portion 20 and the probe portion 8, friction stir welding can be performed by controlling the load. Note that friction stir welding using load control can easily follow changes in plate thickness. Moreover, although FIG. 3 shows a butt joint, a lap joint may also be used.

Because friction stir welding is performed with the probe part 8 penetrating the workpiece 12 in the thickness direction, for example, even if the stirring axis of the tool (probe part 8) is not inclined (tool advancement angle 0°) , an unjoined part such as a kissing bond does not occur on the back surface of the material 12 to be joined. In addition, the stirring shaft (probe portion 8) of the tool can be tilted, and a tool advancing angle can be given during friction stir welding. Since the material flow proceeds smoothly due to the advance angle, the conditions under which welding is possible are expanded, and it becomes possible to prevent welding defects. Note that the tool advancement angle is preferably greater than 0° and less than or equal to 7°.

In addition, unlike a bobbin tool, a rotating member does not come into contact with both sides of the workpieces 12 around the joint, and the undulations of the back plate 24 are transferred to the back side of the workpieces 12, so a smooth surface can be maintained. By abutting the back plate 24 having the joints, it is possible to obtain a good joining surface without producing marks after friction stir welding on the back surfaces of each of the materials 12 to be joined around the joint portion.

The cooling method of the friction stir welding tool 40 having a general shape, adjustment of various friction stir welding conditions, etc. are the same as in the case of using a bobbin tool. In addition, it can also be used as a processing method such as surface treatment.

(2) Friction stir welding tool (2-1) Bobbin tool Figures 4 and 5 show schematic diagrams of the bobbin tool 2. In FIG. 4, the through hole 10 has a diameter of 2 mm, and in FIG. 5, the through hole 10 has a diameter of 3 mm. In FIGS. 4 and 5, the upper shoulder portion 4 and the lower shoulder portion 6 have a diameter of 12 mm, and the probe portion 8 has a diameter of 6 mm. The diameter of the through hole 10 may be adjusted as appropriate depending on the material and diameter of the bobbin tool 2, but it may be made thinner if absolute strength of the probe portion 8 is required, and thicker if a greater cooling effect is desired. preferable.

The shapes and sizes of the upper shoulder section 4, the probe section 8, and the lower shoulder section 6 are not particularly limited as long as they do not impair the effects of the present invention, and may be the shapes and sizes of various conventionally known bobbin tools. Further, by forming a coating layer of TiAlN, TiN, CrN, HfO ₂ or the like having good heat resistance and wear resistance on the surface of the tool, the life of the bobbin tool 2 can be further extended.

The material of the bobbin tool 2 is not particularly limited as long as it does not impair the effects of the present invention, but it is possible to friction stir weld steel materials with the bobbin tool 2 made of steel. As the material of the tool, for example, carbon tool steel, low alloy tool steel, cold die steel, hot die steel, high speed tool steel, etc. can be used. In addition, for example, by using the bobbin tool 2 made of a copper alloy or the like having excellent thermal conductivity, the cooling effect of the refrigerant can be maximized.

(2-2) Tool for reverse friction stir welding FIGS. 6 and 7 show schematic diagrams of the tool 30 for reverse friction stir welding. In FIG. 6, the through hole 10 has a diameter of 2 mm, and in FIG. 7, the through hole 10 has a diameter of 3 mm. In FIGS. 6 and 7, the shoulder portion 20 has a diameter of 12 mm, and the probe portion 8 has a diameter of 6 mm. The diameter of the through hole 10 may be adjusted as appropriate depending on the material and diameter of the inverted friction stir welding tool 30, but if the absolute strength of the probe part 8 is required, the diameter of the through hole 10 may be adjusted. It is preferable to make it thick.

The shape and size of the shoulder portion 20 and the probe portion 8 are not particularly limited as long as they do not impair the effects of the present invention, and may be the shape and size of various conventionally known inverted friction stir welding tools. Further, by forming a coating layer having good heat resistance, wear resistance, etc. on the surface of the tool, the life of the inverted friction stir welding tool 30 can be further extended.

The material of the inverted friction stir welding tool 30 is not particularly limited as long as it does not impair the effects of the present invention, but it is possible to friction stir weld steel materials with the inverted friction stir welding tool 30 made of steel. As the material of the tool, for example, carbon tool steel, low alloy tool steel, cold die steel, hot die steel, high speed tool steel, etc. can be used. In addition, for example, by using the inverted friction stir welding tool 30 made of a copper alloy or the like having excellent thermal conductivity, the cooling effect of the refrigerant can be maximized.

Although typical embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all such design changes are included within the technical scope of the present invention. It will be done.

≪Example 1≫
A cold-rolled steel plate (SPCC) measuring 100 mm x 50 mm x 2.0 mm was used as a test material, and butt friction stir welding was performed using a bobbin tool shown in FIG. The bobbin tool is made of tool steel (SKD61) and has a shoulder diameter of 12 mm, a probe diameter of 6 mm, and a through-hole diameter of the rotating shaft of 2 mm. Furthermore, a TiAlN film with a thickness of about 5 μm is formed on the surface of the tool.

The tool rotation speed was 400 rpm, and the joining speed was varied between 10 and 150 mm/min during joining. In addition, water was used as a refrigerant, and was allowed to flow from the upper shoulder portion of the bobbin tool to the lower shoulder portion at a rate of 2.0 L/min. The discharged water was circulated so as to flow from the upper side of the bobbin tool.

A photograph of the appearance of the obtained friction stir welded joint is shown in Figure 8. The figure shown on the upper side of FIG. 8 is an external photograph of the upper surface of the friction stir welding joint, which is the tool gripping side. The figure shown on the lower side of FIG. 8 is a photograph of the appearance of the lower surface, which is the drainage side, of the friction stir welded joint. In Example 1, butt friction stir welding was started at a welding speed of 10 mm/min in the direction of the straight arrow shown between the upper and lower figures in FIG. Then, from the position where the end point (tip) of the straight arrow on the left side connects to the starting point of another straight arrow on the right side in Figure 8, and where the vertical line is shown in the figure, the welding speed is set to 150 mm/min. Butt friction stir welding was performed by accelerating to . In FIG. 8, the direction of rotation of the tool is indicated by a curved arrow. The side on which the direction of rotation of the tool coincides with the welding direction is called AS (Advancing side), and the side on which the direction of rotation of the tool faces opposite to the welding direction is called RS (Retreating side). In the diagram shown in the upper part of FIG. 8, the upper part is the AS, and the lower part is the RS. In the diagram shown on the lower side of FIG. 8, the upper side is the RS, and the lower side is the AS.

At 400 rpm, 10 to 100 mm/min, periodic disturbances due to tool vibration were observed, but at 150 mm/min, the tool became stable, and a bond with a homogeneous and good surface quality was formed. Even when the speed was directly changed from 10 mm/min to 150 mm/min at the beginning of the welding process, a stable and homogeneous joint was similarly formed, and by selecting appropriate welding conditions (400 rpm, 150 mm/min), It has become clear that friction stir welding of steel materials is possible using a steel bobbin tool.

FIG. 9 shows the microstructure of the cross section of the joint obtained at 400 rpm and 150 mm/min. In the diagram shown in the upper part of FIG. 9, the joining direction is from the front to the back of the paper, the upper side is the upper surface, the lower side is the lower surface, the left side is the above AS, the right side is the above RS, and the stirring part is located in the center. A cross section of the joint is shown as shown. The diagram shown in the lower part of FIG. 9 shows the microstructure of the base material in cross section. The diagram shown in the middle of FIG. 9 shows, from left to right, the microstructure of the base material/stirred part (AS), the microstructure of the stirred part, and the microstructure of the stirred part/base material (RS) in the cross section. It shows.

No tunnel defects or the like were observed in the cross section, indicating that a good joint was formed. The width of the stirring section is wider than the probe diameter, slightly narrower than the shoulder diameter, and slightly wider on the top side. The base material structure was equiaxed ferrite grains of about 10 μm, but the stirred zone structure was fine equiaxed ferrite, and the formation of subgrain boundaries within the grains was observed in some parts. Since SPCC has a low carbon content and a high _A3 point, the temperature in the stirred zone during welding is in the two-phase region, and it is thought that the stirred zone is a mixture of phase-transformed ferrite and recrystallized/recovered ferrite.

The appearance and cross-sectional shape of the bobbin tool used for friction stir welding before and after welding are shown in FIGS. 10 and 11, respectively. The upper, middle, and lower diagrams in FIG. 10 show the appearance of the bobbin tool initially, after one pass, and after two passes, respectively. The diagram shown in the upper side of FIG. 11 shows the shape of the bobbin tool. The diagram shown on the lower side of FIG. 11 is a graph showing the shape of the bobbin tool at the initial stage, after one pass, and after two passes, with the horizontal axis representing the tool longitudinal position and the vertical axis representing the tool radius. In this graph, the initial shape of the bobbin tool is shown by a solid line, the shape after one pass is shown by a broken line, and the shape after two passes is shown by a chain line. In the graph, the position indicated by the arrow indicates a portion where the tool radius is 3 mm, that is, φ6 mm. No change was observed in the external appearance or cross-sectional shape before and after joining, and it can be seen that there was no change in the tool shape at a total joining length of 20 cm.

≪Example 2≫
Inverted friction stir welding was performed in the same manner as in Example 1, except that the tool for inverted friction stir welding shown in Fig. 6 was used, the tool rotation speed was 400 rpm, the tool movement speed was 10 mm/min, and the advancing angle was 3°. provided.

Figure 12 shows an external photograph showing the state of reverse friction stir welding. Figure 12 shows reverse friction stir welding performed with water cooling, with the tool feed direction being from the front to the back of the page, with the shoulder part in contact with the lower surface (back surface) of the workpieces. ing. It can be confirmed that the cooling water is discharged from the bottom of the shoulder part, and the temperature of the shoulder part hardly rises (doesn't become red hot) during bonding.

An external photograph of the obtained friction stir welded joint is shown in Fig. 13. The figure shown on the upper side of FIG. 13 is a photograph of the appearance of the upper surface, which is the fixed part side, of the friction stir welded joint. The figure shown on the lower side of FIG. 13 is a photograph of the appearance of the lower surface, which is the drainage side, of the friction stir welded joint. In FIG. 13, the butt line is shown by a dashed line. In FIG. 13, the direction of rotation of the tool is indicated by a curved arrow. In the diagram shown in the upper part of FIG. 13, the upper part is the AS, and the lower part is the RS. In the diagram shown on the lower side of FIG. 13, the upper side is the RS, and the lower side is the AS. Immediately after the start of welding, initial crack-like defects, which are also seen in normal reverse friction stir welding, are observed, but after the middle stage, the welded part has a good appearance. These results revealed that friction stir welding of steel materials is possible using a steel inverted friction stir welding tool.

FIG. 14 shows an optical micrograph of a cross section of the joint of the obtained friction stir welded joint. In the diagram shown in the upper part of FIG. 14, the joining direction is from the front to the back of the paper, the upper side is the upper surface, the lower side is the lower surface, the left side is the above AS, the right side is the above RS, and the stirring part is located in the center. A cross section of the joint is shown as shown. The figure shown on the left side of the middle part of FIG. 14 shows the microstructure of the base material in cross section, and the figure shown on the right side shows the microstructure of the heat-processed affected zone/stir zone (AS). The figure shown on the left side in the lower part of FIG. 14 shows the microstructure of the stirring zone in the cross section, and the figure shown on the right side shows the microstructure of the stirred zone/thermal processing affected zone (RS). No bonding defects were observed, indicating that a good bonded portion was formed. The base material is equiaxed ferrite with a diameter of several tens of micrometers, and a structure in which fine equiaxed ferrite is distributed in the processed ferrite is confirmed from the heat-processed zone to the stir zone.

≪Comparative example 1≫
Friction stir welding was performed in the same manner as in Example 1 except that the bobbin tool was not provided with a through hole and water cooling was not performed. The tool rotation speed was 400 rpm, and the tool movement speed was 10 mm/min.

Immediately after the start of bonding, the temperature of the tool rose to 700-800°C, and it was confirmed that it became red hot, and the tool broke from the center of the probe part about 2 minutes after the start of bonding. An external photograph of the obtained joint is shown in FIG. 15, and an external photograph of the bobbin tool before and after friction stir welding is shown in FIG. 16. The figure shown on the upper side of FIG. 15 is a photograph of the appearance of the upper surface, which is the tool gripping side, of the obtained joint. The figure shown on the lower side of FIG. 15 is a photograph of the appearance of the lower surface, which is the drainage side, of the obtained joint. In FIG. 15, the direction of rotation of the tool is indicated by a curved arrow. In the diagram shown on the upper side of FIG. 15, the upper side is AS and the lower side is RS. In the diagram shown on the lower side of FIG. 15, the upper side is the RS, and the lower side is the AS. Friction stir welding was performed at a welding speed of 10 mm/min in the direction of the straight arrow shown between the upper and lower figures in FIG. Further, the upper and lower views of FIG. 16 show the appearance of the bobbin tool before and after joining, respectively. Judging from the fracture mode of the tool, it is thought that the tool life is due to a decrease in strength due to high temperature and not due to wear. Since no through holes were provided, the tool strength was higher than the bobbin tool used in Example 1, but it was shown that friction stir welding was not possible without water cooling.

≪Comparative example 2≫
Reverse friction stir welding was performed in the same manner as in Example 2, and the cooling water was stopped approximately 6 minutes after the start of welding (corresponding to a welding length of 60 mm). During the water cooling, no red heat or the like of the tool could be observed with the naked eye, similar to the case of Example 2 shown in FIG. Figure 17 shows an external photograph showing the situation immediately after water cooling was stopped, and it can be seen that the shoulder is red hot.

Figure 18 shows the change in the appearance of the tool as the reverse friction stir welding time progresses. The diagrams shown in the upper row of FIG. 18, from left to right, show the start of bonding (-5'58'') at 4:12:91, and the time immediately before water cooling stops at 10:10:71. (-0'00'') and when the water cooling is stopped (0'00'') at 10:11:00.In addition, in the diagram shown on the left side of the upper row of FIG. The flow of cooling water is indicated by a dotted line, and the downward arrow indicates the flow of cooling water. The appearance of the tool is shown after the water cooling has stopped at 10:36:00 (0'25"), and after the water cooling has stopped at 10:41:00 (0'30"). . The diagrams shown in the lower part of FIG. 18 are, from left to right, after water cooling stops at 11:01:10 (0'50''), and at 11:06:00 when the tool breaks (0'50''). '55''), and the appearance of the tool after the tool fractured at a time of 11:36:00 (1'25'').

Five seconds after the cooling water was stopped, the entire shoulder became clearly red hot, and in about 30 seconds (equivalent to a bonding length of 5 mm), the eccentricity of the shoulder and the generation of sparks were observed, and then the probe extended, causing the shoulder to separate from the material. After 55 seconds (equivalent to a bonding length of 10 mm), it was completely broken. When water cooling was involved, the tool did not break during 100 mm long SPCC bonding twice, indicating that water cooling improves tool life by at least 20 times.

A photograph of the appearance of the obtained joint is shown in Fig. 19. The figure shown on the upper side of FIG. 19 is a photograph of the appearance of the upper surface of the obtained joint, which is the fixed part side. The figure shown on the lower side of FIG. 19 is an external photograph of the lower surface, which is the shoulder side, of the obtained joint. In the diagram shown on the upper side of FIG. 19, the upper side is AS and the lower side is RS. In the diagram shown on the lower side of FIG. 19, the upper side is the RS, and the lower side is the AS. In FIG. 19, straight arrows extending upward and downward indicate when water cooling is stopped. In addition, white straight arrows indicate tools, black diagonal straight arrows indicate burrs, and curly braces on one side indicate holes. The joint surface is relatively uniform in the water-cooled area, but large holes are formed near the tool that broke without water-cooling. The results showed that friction stir welding is impossible without water cooling.

(summary)
As described above, in one aspect of the present invention, a friction stir welding tool is passed through the welded materials in the thickness direction, and a coolant is caused to flow through the through hole provided in the rotating shaft of the friction stir welding tool. Provided is a friction stir welding method characterized by performing friction stir welding in a state in which the friction stir welding is performed.

In the friction stir welding method of one aspect of the present invention, friction stir welding is performed with a coolant flowing through a through hole provided in a rotating shaft of a friction stir welding tool, thereby reducing friction stir welding during friction stir welding. It is possible to suppress the temperature rise of the bonding tool. More specifically, by using through-holes, it is easier to increase the flow rate and flow rate of the refrigerant compared to, for example, forming a refrigerant flow path inside the friction stir welding tool. The temperature rise of the bonding tool can be extremely effectively suppressed.

In addition, in the friction stir welding method of one embodiment of the present invention, friction stir welding is performed while a coolant is flowing through a through hole provided in a rotating shaft of a friction stir welding tool, so that materials to be welded can be welded by friction. The temperature of the entire friction stir welding tool can be maintained low while ensuring the temperature rise of the outermost surface of the friction stir welding tool necessary for stirring. As a result, not only are good friction stir welding characteristics and longer life of the friction stir welding tool simultaneously achieved, but also an inexpensive friction stir welding tool made of a material whose room temperature strength is equal to or lower than that of the materials to be welded is used. be able to.

Further, the friction stir welding tool used in the friction stir welding method of one embodiment of the present invention is not particularly limited, except that a through hole is provided in the rotating shaft, as long as the effects of the present invention are not impaired. Depending on the material, shape, size, etc. of the joining material, the material, shape, and size of various conventionally known friction stir welding tools can be used.

In addition, in the friction stir welding method of one aspect of the present invention, the manner in which the friction stir welding tool penetrates the materials to be welded in the thickness direction is not particularly limited as long as the effects of the present invention are not impaired; It is preferable that the probe portion of the stirring welding tool penetrates the materials to be welded in the thickness direction. For example, the probe portion of a friction stir welding tool having a conventionally common shape may be penetrated from the back side of the materials to be welded (a recess or opening may be provided at the probe penetration position of the back plate placed on the back surface of the materials to be welded). ), reverse friction stir welding or a bobbin tool may be used.

Furthermore, in the friction stir welding method of one aspect of the present invention, it is preferable that the friction stir welding tool be a bobbin tool. Since the probe portion of the bobbin tool passes through the material to be welded in normal use, the refrigerant can easily and simply flow through the through holes. In addition, since the shoulder portion comes into contact with the front and back surfaces of the materials to be joined, it is possible to suppress the formation of kissing bonds.

Furthermore, in the friction stir welding method of one aspect of the present invention, it is preferable to use reverse friction stir welding for the friction stir welding. In reverse friction stir welding, a shoulder part is brought into contact with the back side of the materials to be welded, a probe part provided on the shoulder part is penetrated to the front side of the materials to be welded, and friction stir welding is performed while pulling up the probe part. It is a method. Since the probe portion penetrates the material to be joined, the refrigerant can be easily and simply circulated to the through hole. Furthermore, since the shoulder portion contacts the back surface of the material to be joined and the probe portion penetrates the material to be joined, it is possible to suppress the formation of a kissing bond.

Further, in the friction stir welding method of one aspect of the present invention, it is preferable to use water as the coolant. The type of refrigerant is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known refrigerants can be used; however, by using water, increase in process cost can be suppressed. A rust preventive agent or the like may be added to the water if necessary. As the refrigerant other than water, for example, liquid CO ₂ (including a mixture of gas CO ₂ and solid CO ₂ ), liquid nitrogen, etc. can be used.

Further, in the friction stir welding method according to one aspect of the present invention, it is preferable that the friction stir welding tool is made of steel, and the materials to be welded are made of steel. Conventionally, in order to friction stir weld steel materials, it was necessary to use expensive tools such as PCBN or tungsten alloy, but in the friction stir welding method of the present invention, the friction stir welding tool is efficiently cooled. , steel materials can be friction stir welded using inexpensive steel tools. Furthermore, by friction stir welding steel materials using a steel tool, the influence of contamination from the tool can be kept to a minimum. As the material of the tool, for example, carbon tool steel, low alloy tool steel, cold die steel, hot die steel, high speed tool steel, etc. can be used.

Further, in the friction stir welding method of one aspect of the present invention, it is preferable that the coolant discharged from the friction stir welding tool is circulated and allowed to flow into the friction stir welding tool. By reusing the refrigerant, it is possible to suppress an increase in process costs. Note that when liquid CO ₂ is used as the refrigerant, the circulation mechanism is not necessary because the liquid CO ₂ is vaporized.

Another aspect of the present invention also provides a friction stir welding tool characterized by having a through hole in the rotating shaft. The friction stir welding tool of the present invention can be suitably used in the friction stir welding method of the present invention. The friction stir welding tool of the present invention is not particularly limited, except that the rotating shaft is provided with a through hole, as long as the effects of the present invention are not impaired. , shape and size. Further, the hole formed in the friction stir welding tool only needs to be penetrating, and does not need to be straight, and the diameter of the hole does not need to be constant.

The friction stir welding tool according to one aspect of the present invention is preferably a bobbin tool. The bobbin tool has a relatively simple shape in which two shoulder parts are connected by a probe part and are integrated, and can easily form a through hole in the rotating shaft. Moreover, it is preferable that the friction stir welding tool of one aspect of the present invention is a reverse friction stir welding tool. Since the inverted friction stir welding tool has a configuration in which the probe portion penetrates the materials to be welded, it is easy to form a through hole in the rotating shaft.

Further, it is preferable that the friction stir welding tool according to one embodiment of the present invention is made of steel. In addition to being inexpensive, steel is easy to process in various ways, and friction stir welding tools having arbitrary shapes and sizes can be easily manufactured. As the steel material for the friction stir welding tool, for example, carbon tool steel, low alloy tool steel, cold die steel, hot die steel, high speed tool steel, etc. can be used.

2...Bobbin tool (friction stir welding tool)
4... Upper shoulder part 6... Lower shoulder part 8... Probe part 10... Through hole 12... Material to be joined 14... Part to be joined 20... Shoulder part 22...・Top plate 24...Back plate 30...Inverted friction stir welding tool 40...Friction stir welding tool having a general shape

Claims

Penetrate the friction stir welding tool in the thickness direction of the welded materials,
performing friction stir welding with a refrigerant flowing through a through hole provided in a rotating shaft of the friction stir welding tool;
A friction stir welding method characterized by:
Penetrating the probe portion of the friction stir welding tool in the thickness direction of the welded materials;
The friction stir welding method according to claim 1, characterized in that:
The friction stir welding tool is a bobbin tool;
The friction stir welding method according to claim 1 or 2, characterized in that:
using inverted friction stir welding for the friction stir welding;
The friction stir welding method according to claim 1 or 2, characterized in that:
using water as the refrigerant;
The friction stir welding method according to claim 1 or 2, characterized in that:
The friction stir welding tool is made of steel, and the material to be welded is made of steel;
The friction stir welding method according to claim 1 or 2, characterized in that:
Circulating the coolant discharged from the friction stir welding tool and causing it to flow into the friction stir welding tool;
The friction stir welding method according to claim 1 or 2, characterized in that:
having a through hole in the rotating shaft;
Friction stir welding tool featuring:
Being a bobbin tool,
The friction stir welding tool according to claim 8, characterized by:
Being a tool for inverted friction stir welding;
The friction stir welding tool according to claim 8, characterized by:
be made of steel;
The friction stir welding tool according to any one of claims 8 to 10, characterized in that: