Friction welding method

Abstract

The objective of the present invention is to provide a friction pressure welding method with which the welding temperature can be controlled accurately, the welding temperature can be lowered, and the distribution of the welding temperature at an interface to be welded can be made uniform; and to provide a welded structure obtained by this method. The present invention relates to the friction pressure welding method in which one member is abutted against another member and is made to slide in a state in which a welding pressure substantially perpendicular to the interface to be welded is applied, said friction pressure welding method being characterized in that the maximum sliding speed is no greater than 53 mm / sec, the difference in the temperature increase rate between a center portion and an outer peripheral portion at the interface to be welded is 10°C / sec or less, and the difference between the maximum attained temperature between the center portion and the outer peripheral portion at the interface to be welded is no greater than 50°C.

Description

[Technical field]

[0001] The present invention relates to a friction welding method for metallic materials, and more specifically to a friction welding method capable of accurately controlling the welding temperature and a welded structure obtained thereby. [Background technology]

[0002] In recent years, solid-state welding (friction welding) methods that utilize the phenomenon of frictional heating have been attracting attention as a joining method that can reduce the decrease in strength of the joint compared to conventional fusion welding. Representative solid-state welding methods include "friction stir welding (FSW)," in which a cylindrical tool rotating at high speed is pressed into the materials to be joined, and "friction welding," in which a rotating cylindrical material to be joined is brought into contact with a fixed material to be joined.

[0003] In particular, there are a wide variety of types and combinations of materials to be joined using tool-free friction welding, and research and development is being actively conducted on steel, a general-purpose structural material. For example, Patent Document 1 (JP Patent Publication 2001-287051 A) proposes a method for providing a friction-welded joint of high-tensile steel material in which the hardness is almost uniform in the direction of the rotation radius of the friction welding.

[0004] The friction welded joint of high tensile steel material described in the above Patent Document 1 has a fine structure with a crystal grain size of 2 μm or less and a tensile strength of 60 kgf / mm 2 In addition to the above, the friction welded joint is made of high-tensile steel with a carbon content of 0.1 wt% or less, and the carbon content of the high-tensile steel is kept low at 0.1 wt%. This low carbon content of 0.1 wt% or less suppresses structural changes and hardening in the outer periphery of the high-tensile steel during friction welding.

[0005] The present inventors have also been studying methods for lowering and controlling the joining temperature during friction welding. For example, Patent Document 2 (Publication No. 2017-022184) describes a friction joining method in which the joining surfaces of two metal workpieces are brought into contact with each other and slid against each other, in which at least one of the metal workpieces is an iron-based material, and the maximum temperature reached during joining is controlled to be equal to the A of the iron-based material. 3 Points or below or A cm The present invention proposes a friction joining method characterized in that the joining temperature is set to a temperature of not more than 100°C.

[0006] In the friction joining method described in Patent Document 2, the joining pressure applied approximately perpendicularly to the joining surfaces is set to 100 to 300 MPa, and the maximum sliding speed of the metal workpieces is set to 75 to 380 mm / sec., so that the maximum temperature reached during joining is 100 to 300 MPa, which is the same as that of the iron-based material. 3 Points or below or A cm It can be set to 0.5 points or less. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2001-287051 A [Patent Document 2] Re-tabled publication No. 2017-022184 Summary of the Invention [Problem to be solved by the invention]

[0008] One of the advantages of friction welding, a solid-state joining method, is that the joining temperature is lower than that of fusion welding. This is expected to prevent a decrease in joint strength due to softening of the heat-affected zone at the joint, and in the case of joining dissimilar materials, the formation of a brittle intermetallic compound layer.

[0009] In response to this, the above-mentioned Patent Document 1 discloses a friction welded joint made of high-tensile steel in which the hardness is almost uniform in the direction of the rotation radius of the friction weld. However, the high-tensile steel must have a carbon content of 0.1 wt% or less, and the materials to be welded are limited to an extremely narrow range.

[0010] In addition, the friction welding method disclosed in the above Patent Document 2 can effectively reduce the friction welding temperature, but does not consider the uniformity of the welding temperature at the welded interface. In friction welding, the peripheral speeds of the center and outer periphery of the welded interface are different, so non-uniformity in the temperature distribution is basically unavoidable. Non-uniform distribution of the welding temperature at the welded interface is an extremely serious problem in dissimilar material welding, in which the joint strength is greatly affected by the state of the intermetallic compound layer formed at the welded interface.

[0011] In view of the problems in the conventional techniques as described above, an object of the present invention is to provide a friction welding method which can accurately control the joining temperature, can lower the joining temperature, and can uniformly distribute the joining temperature at the joined interface, and a joined structure obtained thereby. [Means for solving the problem]

[0012] In order to achieve the above object, the present inventors have conducted extensive research into friction welding conditions and have found that by making the maximum sliding speed during friction welding smaller than a certain value, it is possible to control the temperature rise rate and temperature distribution at the center and outer periphery of the welded interface to be approximately the same, thereby arriving at the present invention.

[0013] That is, the present invention provides: A friction welding method in which one member is brought into contact with another member and slid while a welding pressure is applied substantially perpendicularly to the weld interface, The maximum sliding speed is set to 53 mm / sec or less, and the difference in the temperature rise rate between the center and the outer periphery at the joining interface is set to 10°C / sec or less, The difference in maximum temperature between the central portion and the outer periphery at the bonded interface is within 50°C. The present invention provides a friction welding method comprising the steps of:

[0014] During friction welding, the sliding speed is the highest at the outer periphery of the materials to be joined, and the heat generation at the outer periphery is greater than that at the center, which is considered to be the main cause of uneven joining temperatures. From this perspective, various friction welding conditions were examined to homogenize the temperature distribution at the joining interface during the joining process, and it was found that by setting the maximum sliding speed (the sliding speed at the outermost periphery of the materials to be joined) at 53 mm / sec or less, the difference in the temperature rise rate at the center and outer periphery at the joining interface is within 10°C / sec, and as a result, the difference in the maximum temperature reached at the center and outer periphery at the joining interface is within 50°C. Here, it is preferable that the difference in the temperature rise rate at the center and outer periphery at the joining interface is within 5°C / sec.

[0015] In the friction welding method of the present invention, the maximum sliding speed is preferably 21 mm / sec or less. By setting the maximum sliding speed to 21 mm / sec or less, the difference in the temperature rise rate between the center and the outer periphery at the bonded interface is within 10° C. / sec, and the temperature rise rate can be set to a lower value, making the temperature distribution at the bonded interface more uniform and lower. Here, the lower limit of the maximum sliding speed is not particularly limited, and it may be set to a value that suppresses the formation of defects and unbonded parts due to insufficient heat generation.

[0016] In the friction welding method of the present invention, the joining pressure is preferably more than 300 MPa and less than the yield stress at room temperature of the one member and the other member. More preferably, the joining pressure is 400 MPa or more. The joining temperature in friction welding can be lowered by increasing the joining pressure. That is, by using a high pressure of more than 300 MPa or more than 400 MPa, which is not used in general friction welding, the joining temperature can be lowered. On the other hand, by applying a high pressure at a low joining temperature, a large amount of strain is introduced near the joined interface, and a strong joint can be formed by utilizing recrystallization. The joining pressure is set to less than the yield stress of the joined materials in order to suppress buckling during the joining process.

[0017] In the friction welding method of the present invention, it is preferable that the one member and the other member have different compositions. When the materials to be welded have different compositions, the reaction between the one member and the other member at the joint interface becomes a problem. In particular, when a brittle intermetallic compound layer is formed thickly at the joint interface, the mechanical properties of the joint are significantly reduced. In contrast, in the friction welding method of the present invention, the joining temperature is controlled low and the difference in the maximum temperature reached between the center and the outer periphery of the weld interface is within 50°C, so that even if an intermetallic compound layer is formed, a uniform and thin intermetallic compound layer is formed over the entire joint interface.

[0018] In addition, in the friction welding method of the present invention, it is preferable to reduce the joining pressure when defects are formed at the welded interface, and to increase the joining pressure when an intermetallic compound layer having a thickness of 1 μm or more is formed at the welded interface and / or when a heat-affected zone having a hardness reduced by 10% or more compared to the base material is formed.

[0019] By decreasing the joining pressure, the joining temperature can be increased, and defects can be suppressed by improving the material fluidity near the joined interface. On the other hand, by increasing the joining pressure, the joining temperature can be decreased, and the formation of an intermetallic compound layer with a thickness of 1 μm or more and the formation of a heat-affected zone with a hardness 10% or more lower than that of the base material can be suppressed.

[0020] In the friction welding method of the present invention, the diameter of the interface to be welded is preferably 50 mm or less. More preferably, the diameter of the interface to be welded is 30 mm or less, and most preferably, the diameter of the interface to be welded is 10 mm or less. By setting the diameter to these values, it is possible to more reliably achieve the uniformity of the welding temperature and the suppression of defects and unwelded parts at the same time.

[0021] Furthermore, in the friction welding method of the present invention, it is preferable that the one member is a titanium alloy material and the other member is a steel material. In dissimilar material welding between a titanium alloy material and a steel material, a brittle intermetallic compound layer is easily formed at the joining interface, and it is difficult to control the film thickness of the intermetallic compound layer, but by using the friction welding method of the present invention, a defect-free joint without a mixed layer can be obtained in which an extremely thin and uniform intermetallic compound layer is formed over the entire joining interface.

[0022] The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of: A joint structure having a friction welded portion between one member and another member, the one member and the other member have different compositions; The thickness of the intermetallic compound layer formed at the joining interface of the friction welded portion is 1 μm or less, The thickness (T p ) and the thickness of the intermetallic compound in the center (T C ) and 0.8T C ≦T p ≦1.2T C And then, a mixed layer made of the one member and the other member is not formed at the joint interface; Also provided is a joint structure characterized by:

[0023] The joint structure of the present invention has a friction welded portion, and its greatest feature is that a thin and uniform intermetallic compound layer is formed over the entire joint interface of the friction welded portion. In addition, the formation of a "mixed layer," which is a serious problem in friction welding of dissimilar materials, is completely suppressed.

[0024] The thickness of the intermetallic compound at the outer periphery of the joint interface (T p ) and the thickness of the central intermetallic compound (T C ) is 0.8T C ≦T p ≦1.2T C Here, 0.9T C ≦T p ≦1.1T C It is preferable that the value is 0.95T.C ≦T p ≦1.05T C It is more preferable that:

[0025] In the bonded structure of the present invention, it is preferable that the diameter of the bonded interface is 10 to 50 mm. By having the diameter of the bonded interface be 10 to 50 mm, the intermetallic compound is 0.8T C ≦T p ≦1.2T C In addition, the formation of defects and non-bonds is significantly suppressed.

[0026] In the bonded structure of the present invention, it is preferable that the one member is a titanium alloy material and the other member is a steel material. In a dissimilar material bonded portion between a titanium alloy material and a steel material, a brittle intermetallic compound layer is easily formed at the bonded interface, and it is difficult to control the film thickness of the intermetallic compound layer, but in the bonded structure of the present invention, an extremely thin and uniform intermetallic compound layer is formed over the entire bonded interface, and a bonded portion without defects, unbonded portions, or mixed layers is formed. Effect of the Invention

[0027] According to the present invention, it is possible to provide a friction welding method that can accurately control the joining temperature, enable the joining temperature to be lowered, and also enable the joining temperature distribution at the joined interface to be made uniform, and a joined structure obtained thereby. [Brief description of the drawings]

[0028] [Figure 1] FIG. 2 is a schematic diagram showing a joining step of the friction welding of the present invention. [Diagram 2] 2 is a schematic diagram of a bonded interface 6. FIG. [Diagram 3] 1 is a graph showing the flow stress (yield stress) of carbon steel at each temperature. [Figure 4] 1 is a graph showing the tensile strength of various metals at each temperature. [Diagram 5] 1 is a schematic diagram showing a joint in a joint structure of the present invention. [Figure 6] 1 is a graph showing the effect of rotation speed (maximum sliding speed) on the maximum reached temperature and the temperature rise rate. [Figure 7] 1 is a graph showing the effect of bonding pressure on the maximum temperature reached and the temperature rise rate. [Figure 8] 1 is an SEM photograph of the center of a bonded interface obtained under practical bonding condition 2. [Figure 9] 1 is an SEM photograph of the outer periphery of a bonded interface obtained under practical bonding condition 2. [Figure 10] 1 is an SEM photograph of the center of a bonded interface obtained under bonding condition 1. [Figure 11] 1 is a SEM photograph of the outer periphery of a bonded interface obtained under practical bonding condition 1. [Figure 12] 1 is an SEM photograph of the center of a bonded interface obtained under practical bonding condition 3. [Figure 13] 1 is a SEM photograph of the outer periphery of a bonded interface obtained under practical bonding condition 3. [Figure 14] 1 is an SEM photograph of the center of a bonded interface obtained under bonding condition 4. [Figure 15] 1 is a SEM photograph of the outer periphery of a bonded interface obtained under practical bonding condition 4. [Figure 16] 1 is an SEM photograph of the center of a bonded interface obtained under practical bonding condition 5. [Figure 17] 1 is a SEM photograph of the outer periphery of a bonded interface obtained under practical bonding condition 5. [Figure 18] 1 is an SEM photograph of the center of a bonded interface obtained under comparative bonding condition 2. [Figure 19] 1 is an SEM photograph of the outer periphery of a bonding interface obtained under comparative bonding condition 2. [Figure 20] 1 shows a STEM image of the center of the bonded interface obtained under bonding condition 1 and the line analysis results perpendicular to the bonded interface. [Figure 21] 1 shows a STEM image of the outer periphery of the bonded interface obtained under bonding condition 1, and the results of line analysis perpendicular to the bonded interface. [Figure 22] 1 shows a STEM image of the center of the bonded interface obtained under bonding condition 2 and the line analysis results perpendicular to the bonded interface. [Diagram 23]1 shows a STEM image of the outer periphery of the bonded interface obtained under bonding condition 2, and the results of line analysis perpendicular to the bonded interface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Representative embodiments of the friction welding method of the present invention and the welded structure obtained thereby will be described in detail below with reference to the drawings, but the present invention is not limited to these. In the following description, the same or corresponding parts are given the same reference numerals, and duplicated descriptions may be omitted. In addition, since the drawings are intended to conceptually explain the present invention, the dimensions of each component shown and their ratios may differ from the actual ones.

[0030] (1) Friction welding method Fig. 1 is a schematic diagram showing the joining step of the friction welding of the present invention. The friction welding method of the present invention is a friction welding method in which one member 2 is brought into contact with another member 4 and rotated and slid while a load is applied substantially perpendicularly to the weld interface 6.

[0031] FIG. 2 shows a schematic diagram of a welded interface 6. In friction welding, one member 2 and / or the other member 4 are rotated, and a case where the welded interface 6 is rotating will be described. When the welded interface 6 rotates, strictly speaking, the center of the welded interface 6 does not have a sliding speed. On the other hand, since the circumferential speed increases with an increase in the rotation radius, it is the outer periphery of the welded materials that has the highest sliding speed during friction welding. In other words, the welding temperature basically increases from the center toward the outer periphery.

[0032] In the friction joining method of the present invention, the difference in the temperature rise rate between the center and the outer periphery at the joined interface 6 is set to within 5° C. / sec by setting the maximum sliding speed occurring at the outer periphery to 53 mm / sec or less. Here, the method for measuring the temperature change at the center and the outer periphery is not particularly limited as long as it does not impair the effect of the present invention, and various conventionally known temperature measuring methods can be used. For example, the temperature history can be measured by placing thermocouples at the center and the outer periphery just below the joined interface 6 on the fixed side (the other member 4 in FIG. 1). Regarding the temperature at the outer periphery, the correlation between the value obtained by the radiation thermometer and the value obtained by the thermocouple may be obtained, and the value of the radiation thermometer may be corrected and used.

[0033] By setting the difference in temperature rise rate between the center and outer periphery at the bonded interface 6 to within 10°C / sec, the difference in maximum temperature reached between the center and outer periphery at the bonded interface 6 can be set to within 50°C. A more preferable difference in temperature rise rate between the center and outer periphery at the bonded interface 6 is within 5°C / sec. More specifically, since the time during which the bonded interface 6 is held at a predetermined bonding temperature in friction welding is approximately several seconds, by setting the difference in temperature rise rate between the center and outer periphery to within 10°C / sec (more preferably within 5°C / sec), the difference in maximum temperature reached between the center and outer periphery at the bonded interface 6 can be set to within 50°C.

[0034] Furthermore, by setting the maximum sliding speed to 21 mm / sec or less, the difference in the temperature rise rate between the center and the periphery at the bonded interface 6 is within 10°C / sec, and the temperature rise rate can be set to a lower value, making the temperature distribution at the bonded interface more uniform and lower. Although it is affected by the composition and size of the bonded materials, when the maximum sliding speed is 21 mm / sec, the temperature rise rate can be reduced to about half compared to when the maximum sliding speed is 53 mm / sec. Here, there is no particular lower limit for the maximum sliding speed, and it may be set to a value that suppresses the formation of defects and unbonded parts due to insufficient heat generation.

[0035] If it is desired to further reduce the maximum temperature at the outer periphery of the bonded interface 6, it is possible to use air blowing, liquid nitrogen, or liquid CO 2In this case, from the viewpoint of cooling efficiency, it is recommended to use liquid CO 2 It is preferable to use CO 2 Since CO becomes liquid at pressures of 5 atmospheres or higher, liquid CO stored in a high-pressure tank 2 It is believed that when the mixture is sprayed onto the outer periphery of the welded interface 6, it becomes fine solid.

[0036] The joining pressure is preferably more than 300 MPa and equal to or lower than the yield stress at room temperature of the one member 2 and the other member 4. More preferably, the joining pressure is 400 MPa or higher. Although this is a principle not used in conventional general friction welding, the joining temperature in friction welding can be reduced by increasing the joining pressure.

[0037] 1, one member 2 and the other member 4 are rotated and slid on the same trajectory while a joining pressure is applied substantially perpendicularly to the joined interface 6, whereby burrs 8 are expelled from the joined interface 6. Here, the reason why burrs 8 are expelled is because the yield stress of the joined materials at the joining temperature is lower than the joining pressure, and since the temperature dependency of the yield strength is uniquely determined by the joined materials, the joining temperature can be controlled by the joining pressure.

[0038] As a specific example, the flow stress (yield stress) of carbon steel at each temperature is shown in Figure 3, and the tensile strength of various metals at each temperature is shown in Figure 4. Note that Figure 3 is a graph published in "Tetsu to Hagane, No. 11, 1981, p. 140," and Figure 4 is a graph published in "Tetsu to Hagane, No. 6, 1986, p. 55." As shown in these figures, the tensile strength and yield stress at a specific temperature are approximately constant depending on the material.

[0039] That is, when the joining pressure is set high, joined materials with higher yield strength and tensile strength can be discharged as burrs 8, and the joining temperature can be reduced. Also, as shown in Figures 3 and 4, the tensile strength and yield stress at a specific temperature are approximately constant depending on the material, so the joining temperature can be controlled extremely accurately.

[0040] The materials of the one member 2 and the other member 4 are not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known metal materials can be used, but it is preferable that the one member 2 and the other member 4 have different compositions. When the materials to be welded have different compositions, the reaction between the one member and the other member at the weld interface becomes a problem, and in particular, when a brittle intermetallic compound layer is formed thickly at the weld interface, the mechanical properties of the joint are significantly reduced. In contrast, in the friction welding method of the present invention, the welding temperature is controlled low, and the difference in the maximum temperature reached between the center and the outer periphery of the weld interface 6 is within 50°C, so that even if an intermetallic compound layer is formed, a uniform and thin intermetallic compound layer is formed over the entire area of ​​the weld interface. For example, even in the welding of a titanium alloy material and a steel material, in which it is difficult to suppress the intermetallic compound layer, a defect-free weld in which an extremely thin and uniform intermetallic compound layer is formed over the entire area of ​​the weld interface can be obtained.

[0041] In addition, the sizes of the one member 2 and the other member 4 are not particularly limited as long as they do not impair the effects of the present invention, but the diameter of the bonded interface 6 is preferably 50 mm or less, more preferably 30 mm or less, and most preferably 10 mm or less. By setting the diameter to these values, uniformity of the bonding temperature and suppression of defects and unbonded parts can be more reliably achieved.

[0042] Furthermore, if defects are formed at the bonded interface 6, it is preferable to reduce the bonding pressure applied approximately perpendicularly to the bonded interface 6, and to increase the bonding pressure if an intermetallic compound layer having a thickness of 1 μm or more is formed at the bonded interface 6 and / or if a heat-affected zone having a hardness reduced by 10% or more compared to the base material is formed.

[0043] By decreasing the joining pressure, the joining temperature can be increased, and defects can be suppressed by improving the material fluidity in the vicinity of the joined interface 6. On the other hand, by increasing the joining pressure, the joining temperature can be decreased, and it is possible to suppress the formation of an intermetallic compound layer with a thickness of 1 μm or more and the formation of a heat-affected zone in which the hardness is reduced by 10% or more compared to the base material.

[0044] Either one of the first member 2 and the second member 4 may be rotated, or both may be rotated. In addition, the first member 2 may be rotated before being brought into contact with the second member 4, or may be rotated after the welded interface 6 is formed. In either case, the maximum sliding speed is the relative speed between the first member 2 and the second member 4.

[0045] The joining parameters of the friction welding, such as the contact allowance, are not particularly limited as long as they do not impair the effects of the present invention, and may be set appropriately depending on the material, shape, size, etc. of the workpieces to be joined.

[0046] (2) Jointed structure 5 is a schematic diagram showing a joint in a joint structure of the present invention. The joint 10 is formed by friction welding, and one member 2 and another member 4 are joined via a joint interface 12. The joint structure of the present invention can be suitably produced by the friction welding method of the present invention.

[0047] The one member 2 and the other member 4 have different compositions. For example, the one member 2 may be made of a steel material and the other member 4 may be made of an aluminum material, which are completely different metal materials, or the one member 2 may be made of an alloy material having the same main metal but different compositions.

[0048] One member 2 and the other member 4 have different compositions, and as long as the effects of the present invention are not impaired, these compositions are not particularly limited, and various conventionally known metal materials can be used, but it is preferable that one member 2 is a titanium alloy material and the other member 4 is a steel material. In a dissimilar material joint between a titanium alloy material and a steel material, a brittle intermetallic compound layer is easily formed at the joint interface 12, and it is difficult to control the film thickness of the intermetallic compound layer, but in the joint 10, an extremely thin and uniform intermetallic compound layer is formed over the entire joint interface 12.

[0049] The thickness of the intermetallic compound layer formed at the bonding interface 12 is 1 μm or less, and the thickness of the intermetallic compound at the outer periphery of the bonding interface 12 (T p ) and the thickness of the central intermetallic compound (T C ) is 0.8T C ≦T p ≦1.2T C It is as follows. p and T C is 0.9T C ≦T p ≦1.1T C It is preferable that the value is 0.95T. C ≦T p ≦1.05T C It is more preferable that the thickness of the intermetallic compound layer at the bonding interface 12 is set to 1 μm or less, and in addition, the variation in thickness is reduced, so that fracture of the bonding portion from the intermetallic compound layer can be extremely effectively suppressed.

[0050] In addition, no mixed layer consisting of one member 2 and the other member 4 is formed at the joint interface 12. If a mixed layer exists at the joint interface 12, that region becomes the starting point of fracture, and the mechanical properties of the joint are significantly reduced, but the mixed layer is completely suppressed at the joint 10, and a joint structure with extremely high reliability is realized.

[0051] The diameter of the bonded interface 12 is preferably 10 to 50 mm. By setting the diameter of the bonded interface 12 to 10 to 50 mm, a good bonded interface 12 having a thin and uniform intermetallic compound layer can be formed by using the friction welding method of the present invention.

[0052] Representative embodiments of the friction welding method of the present invention and the welded structure obtained thereby have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included within the technical scope of the present invention. EXAMPLES

[0053] Example The materials to be welded were titanium alloy (Ti-6Al-4V) round bars and stainless steel (SUS316L) round bars with a diameter of 10 mm. A friction welding machine manufactured by Nitto Seiki Co., Ltd. was used as the joining device, and friction welding was performed under each of the joining conditions of Example Joining Conditions 1 to 5 shown in Table 1. The stainless steel round bar was fixed, and the titanium alloy round bar was pressed against the stainless steel round bar with the friction pressure shown in Table 1 while rotating at the speed shown in Table 1. Note that a so-called upset process was not performed, and the joining process was terminated when the approach margin reached 4 mm while the friction welding pressure shown in Table 1 was applied.

[0054] [Table 1]

[0055] Comparative Example Friction welding was performed in the same manner as in the examples, except that the joining conditions shown in Table 1 as Comparative Joining Conditions 1 and Comparative Joining Conditions 2 were used.

[0056] [evaluation] (1) Temperature history during friction welding The temperature history of the center and outer periphery of the welded interface during friction welding was measured for Example Joining Condition 3, Example Joining Condition 5, Comparative Joining Condition 1, and Comparative Joining Condition 2. Specifically, a small hole was made in the fixed stainless steel round bar, and a K-type thermocouple was placed directly under the center and outer periphery of the welded interface to measure the temperature history. The relationship between the maximum temperature reached during welding and the heating rate and the welding conditions is shown in Figure 6. The heating rate was obtained from the temperature change from 200 to 500°C.

[0057] The bonding conditions shown in Fig. 6 are the same except for the rotation speed (maximum sliding speed), and the effect of the rotation speed (maximum sliding speed) on the maximum temperature reached and the temperature rise rate can be confirmed. First, looking at the difference in the temperature rise rate at the center and outer periphery, the difference becomes smaller as the rotation speed (maximum sliding speed) decreases, and at 100 rpm (52.36 mm / s) or less, the temperature rise rate at the center and outer periphery is approximately the same.

[0058] Next, looking at the maximum temperatures reached at the center and outer periphery, the temperature difference between the center and outer periphery is 50°C or less at 100 rpm (52.36 mm / s) or less. These results indicate that the reduction in the difference in temperature rise rate between the center and outer periphery has resulted in a more uniform bonding temperature distribution over the entire bonded interface.

[0059] In addition, using a similar method, the temperature history of the center and outer periphery of the welded interface during friction welding was measured for Example Welding Conditions 1 to 3. The relationship between the maximum temperature reached during welding and the heating rate and the welding conditions is shown in Figure 7. The welding conditions shown in Figure 7 are the same except for the welding pressure, and it is possible to confirm the effect of the welding pressure on the maximum temperature reached and the heating rate.

[0060] From the results shown in Figure 7, it can be seen that the heating rate is not affected by the bonding pressure. On the other hand, the maximum temperature reached decreases as the bonding pressure increases, but the maximum temperatures reached at the center and the periphery are almost the same under all conditions. These results show that controlling the rotation speed (maximum sliding speed) is extremely important in order to homogenize the temperature distribution at the bonded interface.

[0061] (2) Cross-sectional observation of the bonded interface To confirm the condition of the bonded interface, a cross-sectional sample of the bonded portion was observed using an SEM. An FE-SEM (JSM-7001FA manufactured by JEOL Ltd.) was used for the SEM observation. The center and outer periphery of the bonded interface obtained under the implemented bonding condition 2 are shown in Figures 8 and 9, respectively. No defects or mixed layers were observed in the center and outer periphery, and a good bonded interface was obtained with an extremely thin intermetallic compound layer of approximately the same thickness.

[0062] 10 and 11 show the center and outer periphery of the bonded interface obtained under the practical bonding condition 1. The bonding temperature is high due to the low bonding pressure of 400 MPa, and as a result, there are areas where the intermetallic compound layer is thicker, but no defects or mixed layer are observed.

[0063] 12 and 13 show the center and outer periphery of the bonded interface obtained under the practical bonding condition 3. Since the bonding temperature is low due to the high bonding pressure of 500 MPa, an unbonded region is observed on the outer periphery, but no thick intermetallic compound layer or mixed layer is observed.

[0064] From the observation results of the bonded interface shown in Figures 8 to 13, it can be seen that an effective means of obtaining a good bond is to set the rotation speed (maximum sliding speed) low enough to sufficiently reduce the difference in temperature history between the center and outer periphery of the bonded interface, and then control the bonding temperature by the bonding pressure to adjust it to a temperature at which no unbonded areas are formed.

[0065] 14 and 15 show the central and peripheral parts of the bonded interface obtained under the practical bonding condition 4. As in the case of the practical bonding condition 2, no defects or mixed layers were observed in the central and peripheral parts, and a good bonded interface was obtained having an extremely thin intermetallic compound layer with approximately the same thickness.

[0066] 16 and 17 show the center and outer periphery of the welded interface obtained under practical joining condition 5. Under practical joining condition 5, the difference in sliding speed between the center and outer periphery at the welded interface is greater than under practical joining condition 2 and practical joining condition 3, and a slight mixed layer is formed on the outer periphery, but no defects or thick intermetallic compound layer are observed.

[0067] The center and outer periphery of the welded interface obtained under comparative welding condition 2 are shown in Figures 18 and 19, respectively. Under comparative welding condition 2, the rotation speed is high at 300 rpm (maximum sliding speed: 157.08 mm / s), and there is a large difference in the sliding speed and maximum temperature reached between the center and outer periphery of the welded interface, and a noticeable mixed layer is formed on the outer periphery. In addition, streak-like defects are also formed.

[0068] (3) STEM-EDS analysis of bonded interface To obtain a detailed understanding of the state of the intermetallic compound layer at the bonded interface, a STEM-EDS analysis was performed using a transmission electron microscope (JEM-2100F, manufactured by JEOL Ltd.).

[0069] STEM images of the center and outer periphery of the bonded interface obtained under practical bonding condition 1 and the results of line analysis perpendicular to the bonded interface are shown in Figures 20 and 21, respectively. STEM images of the center and outer periphery of the bonded interface obtained under practical bonding condition 2 and the results of line analysis perpendicular to the bonded interface are shown in Figures 22 and 23, respectively. The width presumed to be the intermetallic compound layer is shown by the dotted line, and it can be seen that in all cases the thickness is extremely thin at 50 nm or less, and is almost the same thickness at the center and the outer periphery.

[0070] (4) Tensile test The obtained joint was processed so that the length of the parallel part was 60 mm and the diameter was 9 mm to prepare a tensile test specimen. The diameter of the joint was 9 mm due to the removal of burrs, and although it was slightly narrower, most of the joint interface was included in the tensile test specimen. The tensile test was performed at a crosshead speed of 1 mm / min using an Autograph AG-10TB manufactured by Shimadzu Corporation. Three tensile tests were performed under each joint condition, and the average tensile strength was calculated.

[0071] The average tensile strength of the bonded bodies obtained under comparative bonding condition 2 was 150 MPa. In contrast, the average tensile strength of the bonded bodies obtained under practical bonding condition 5 was 300 MPa, which is approximately twice as high. Furthermore, the average tensile strength of the bonded bodies obtained under practical bonding condition 2, in which the bonding pressure was 450 MPa, was 500 MPa, making this a bonded body with a high strength that cannot be obtained with existing bonding methods. [Explanation of symbols]

[0072] 2...One member, 4...the other member, 6... bonded interface, 8. Bali, 10...junction, 12...Joint interface.

Claims

1. A friction welding method in which one member is brought into contact with another member and slid while a welding pressure is applied substantially perpendicularly to the weld interface, The maximum sliding speed is set to 21 mm / sec or less, and the difference in the temperature rise rate between the center portion and the outer periphery portion at the joined interface is set to 10° C. / sec or less, The difference in maximum temperature between the central portion and the outer periphery at the bonded interface is within 50° C.; A friction welding method comprising the steps of:

2. A friction welding method in which one member is brought into contact with another member and slid while a welding pressure is applied substantially perpendicularly to the weld interface, The joining pressure is set to be more than 300 MPa and equal to or less than the yield stress of the one member and the other member at room temperature, The maximum sliding speed is set to 53 mm / sec or less, and the difference in the temperature rise rate between the center and the outer periphery at the joined interface is set to 10° C. / sec or less, The difference in maximum temperature between the central portion and the outer periphery at the bonded interface is within 50° C.; A friction welding method comprising the steps of:

3. A friction welding method in which one member is brought into contact with another member and slid while a welding pressure is applied substantially perpendicularly to the weld interface, The maximum sliding speed is set to 53 mm / sec or less, and the difference in the temperature rise rate between the center and the outer periphery at the joined interface is set to 10° C. / sec or less, The difference in maximum temperature between the central portion and the outer periphery at the bonded interface is set to within 50° C., If defects are formed at the bonded interface, reducing the bonding pressure; In the case where an intermetallic compound layer having a thickness of 1 μm or more is formed at the interface to be joined and / or a heat-affected zone having a hardness reduced by 10% or more compared to that of the base material is formed, the joining pressure is increased. A friction welding method comprising the steps of:

4. the one member and the other member having different compositions; The friction welding method according to any one of claims 1 to 3, characterized in that

5. The diameter of the joined interface is 50 mm or less. The friction welding method according to any one of claims 1 to 3, characterized in that

6. The one member is made of a titanium alloy material and the other member is made of a steel material; The friction welding method according to any one of claims 1 to 3, characterized in that

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