Dissimilar material friction stir welding method and dissimilar material friction stir welding member

Abstract

To provide a different material friction stir joining method for simply and efficiently performing direct bonding of titanium or a titanium alloy material and a thermoplastic resin material, and a different material friction stir joining member having high joint strength obtained from the same.SOLUTION: A different material friction stir joining method of titanium or a titanium alloy material and a thermoplastic resin material includes: a first step of subjecting a joined region of titanium or a titanium alloy material to silane coupling treatment; a second step of bringing a thermoplastic resin material into contact with the joined region subjected to the silane coupling treatment, and forming a joined interface; and a third step of press-fitting a friction stir joining tool into the titanium or titanium alloy material, raising a temperature of the joined interface, and applying a joint pressure to the joined interface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for friction stir welding of titanium or a titanium alloy material and a thermoplastic resin material, and to a dissimilar material friction stir welded member obtained by the method. [Background technology]

[0002] There is a strong demand for weight reduction in various types of transportation equipment from the viewpoints of improving fuel efficiency and reducing the environmental load, and the use of resin materials such as carbon fiber reinforced plastics (CFRP) in aircraft and automobiles is being actively considered.

[0003] In view of this, it is essential to establish a technique for joining various metal materials to resin materials, and progress is being made in the development of techniques for joining steel, aluminum alloys, and magnesium alloys to resin materials.

[0004] Here, when fastening mechanically using bolts or the like, it is necessary to process the joined materials, and an increase in weight due to the fastening members is unavoidable. Also, when joining using an adhesive, it is not possible to provide sufficient joining strength and reliability to the joint.

[0005] In contrast, for example, Patent Document 1 (Publication No. 2017-065256) aims to provide a metal-resin bonding member and a manufacturing method thereof that can exhibit high bonding strength and the like without mainly using an anchor effect. The metal-resin bonding member includes a metal body having an iron oxide layer formed on the surface of an iron-based base material made of iron or an iron alloy, and a resin body bonded to the metal body via the iron oxide layer. The iron oxide layer has a thickness of 50 nm to 10 μm, and is composed of at least 60 to 40 at % Fe and 40 to 60 at % O on at least the outermost surface side, and is at least magnetite (Fe 3 O 4 ) has been proposed.

[0006] In the metal-resin bonding member described in Patent Document 1, the iron oxide layer formed on the surface of the iron-based base material is considered to be in an electron-deficient state and in a highly energetically active state, and therefore becomes chemically bonded to C, O, H, N, P, S, etc. present in the vicinity of the bonded surface of the resin body, resulting in a strong bond between the metal body and the resin body.

[0007] Moreover, Patent Document 2 (JP 2012-170975 A) proposes a method for joining a metal member and a resin member that can join the metal member and the resin member directly, i.e., without a resin layer between them, and a joined joint between a metal member and a resin member, the method being characterized in that the metal member and the resin member are brought into contact with each other without a resin layer between them, and a rotating rotating tool is pressed against the surface of the metal member while being inclined so that the inclination angle θ of the axis of the rotating tool with respect to the normal to the surface of the metal member satisfies the condition 0°<θ≦5°, and the metal member and the resin member are joined by frictional energy imparted to the metal member.

[0008] In the method for joining a metal member and a resin member described in the above Patent Document 2, the metal member and the resin member are brought into contact with each other without a resin layer therebetween, so that the joining can be performed inexpensively and easily because no resin layer is used, and the number of types of resin members that can be joined to the metal member increases. Furthermore, it is said that the metal member and the resin member can be joined at any position. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Re-tabled publication No. 2017-065256 [Patent Document 2] JP 2012-170975 A Summary of the Invention [Problem to be solved by the invention]

[0010] The metal-resin bonded member and the method for producing the same described in Patent Document 1 are made of magnetite (Fe 3 O 4 ) is essential, and cannot be applied to metals other than iron-based metals. Moreover, the method of joining a metal member and a resin member described in Patent Document 2 achieves joining of the metal member and the resin member via a metal oxide film formed on the surface of the metal member, and the examples only show the results of joining an aluminum alloy or magnesium alloy to a resin member. In other words, none of the patent documents show a method of joining a thermoplastic resin to a titanium or titanium alloy material, and the reality is that there is no suitable direct joining method for this combination.

[0011] Here, when the steel materials, aluminum alloys, magnesium alloys, etc. disclosed in the above Patent Documents 1 and 2 are directly bonded to a resin material such as a thermoplastic CFRP material, corrosion easily progresses on the metal material side, which is more noble than the resin material (galvanic corrosion). In contrast, titanium or titanium alloys are electrochemically stable, and no corrosion problems arise even when directly bonded to a resin material. For these reasons, titanium or titanium alloys are extremely suitable materials for use in a multi-material structure with a resin material.

[0012] In view of the problems in the conventional techniques as described above, an object of the present invention is to provide a dissimilar material friction stir welding method for simply and efficiently directly joining a titanium or titanium alloy material and a thermoplastic resin material, and a dissimilar material friction stir welded member having high joint strength obtained thereby. [Means for solving the problem]

[0013] In order to achieve the above object, the present inventors have conducted extensive research into the relationship between the surface condition of the workpieces and the friction stir welding conditions, etc., and the strength of the joint. As a result, they have discovered that in addition to treating the surface of titanium or titanium alloy material with an appropriate silane coupling agent, it is extremely effective to accurately control the temperature of the interface between the workpieces during friction stir welding, and have arrived at the present invention.

[0014] That is, the present invention provides: A method for friction stir welding a titanium or titanium alloy material and a thermoplastic resin material, comprising the steps of: A first step of subjecting a region of the titanium or titanium alloy material to a silane coupling treatment; a second step of contacting the thermoplastic resin material with the bonded region that has been subjected to the silane coupling treatment to form a bonded interface; A third step of pressing a friction stir welding tool into the titanium or titanium alloy material to heat the welded interface and apply a welding pressure to the welded interface. The present invention provides a method for friction stir welding of dissimilar materials, comprising the steps of:

[0015] In the dissimilar material friction stir welding method of the present invention, it is preferable that in the third step, the temperature of the interface to be joined is set to a melting temperature or higher and a decomposition temperature or lower of the thermoplastic resin material. By setting the temperature of the interface to be joined to a melting temperature or higher of the thermoplastic resin material, the functional group introduced into the region to be joined of the titanium or titanium alloy material by the silane coupling treatment reacts with the thermoplastic resin material, and a strong joint interface can be formed. On the other hand, by setting the temperature of the interface to be joined to a decomposition temperature or lower of the thermoplastic resin material, a decrease in strength of the joint caused by thermal decomposition of the thermoplastic resin material can be suppressed. Here, the decomposition temperature of the thermoplastic resin material is the temperature at which gasification of the thermoplastic resin material begins.

[0016] In the dissimilar material friction stir welding method of the present invention, the thermoplastic resin material is preferably a carbon fiber reinforced plastic (CFRP) material. Since the dissimilar material friction stir welding method of the present invention forms an extremely strong joint, even when a high-strength carbon fiber reinforced plastic (CFRP) material and a titanium or titanium alloy material are joined, a joint structure can be obtained that makes the most of the mechanical properties of the carbon fiber reinforced plastic (CFRP) material.

[0017] In addition, in the dissimilar material friction stir welding method of the present invention, it is preferable that the thermoplastic resin material has an amide group, and in the first step, an epoxy group is formed on the surface of the joining region of the titanium or titanium alloy material. The type of thermoplastic resin material and the functional group introduced into the joining region of the titanium or titanium alloy material by the silane coupling treatment are not particularly limited as long as they do not impair the effects of the present invention, and various conventionally known thermoplastic resin materials and functional groups can be used, but by having the thermoplastic resin material have an amide group and forming an epoxy group on the surface of the joining region of the titanium or titanium alloy material, a high-strength joining interface can be reliably obtained.

[0018] In the dissimilar material friction stir welding method of the present invention, it is preferable that in the third step, the temperature of the interface to be joined is set to 220 to 350° C. Although the melting temperature and decomposition temperature differ depending on the type and state of the thermoplastic resin material, by setting the temperature of the interface to be joined to 220 to 350° C., it is possible to cover many of the thermoplastic resin materials that are generally used as structural members by joining with metal members.

[0019] In the dissimilar material friction joining method of the present invention, the joining pressure in the third step is preferably set to 5 to 20 MPa. By setting the joining pressure to 5 MPa or more, the thermoplastic resin material and the titanium or titanium alloy material can be sufficiently adhered to each other, and by setting the joining pressure to 20 MPa or less, deterioration of the friction stir welding tool can be suppressed.

[0020] In the dissimilar material friction joining method of the present invention, it is preferable that the concentration of the silane coupling agent used in the silane coupling treatment in the first step is 2% or more. The concentration of the silane coupling agent is not particularly limited as long as it does not impair the effects of the present invention, and may be appropriately adjusted in relation to the strength of the joint of the obtained dissimilar material friction stir welded members, but by making the concentration 2% or more, a sufficient amount of functional groups that contribute to the joint strength can be introduced to the surface of the joint region of the titanium or titanium alloy material.

[0021] The present invention also provides a method for producing a semiconductor device comprising the steps of: This is a friction stir welded overlap component made of titanium or titanium alloy material and thermoplastic carbon fiber reinforced plastic (CFRP) material. The resin portion of the carbon fiber reinforced plastic (CFRP) material has an amide group, The carbon fiber reinforced plastic (CFRP) material has a crystallized region near the joint interface. The present invention also provides a dissimilar material friction stir welded member, characterized in that

[0022] In the dissimilar material friction stir welded member of the present invention, the amide groups present in the resin part of the carbon fiber reinforced plastic (CFRP) material contribute to the joining with the titanium or titanium alloy material. Although it is difficult to detect by various analyses, the amide groups react with the functional groups on the surface of the titanium or titanium alloy material to be joined, forming a strong joint interface.

[0023] In the dissimilar friction stir welded member of the present invention, it is preferable that a tensile test piece having a friction stir welded line with a length of 15 mm has a tensile shear strength of 3.0 kN or more in a direction perpendicular to the friction stir welded line. When the tensile shear strength is 3.0 kN or more, a dissimilar friction stir welded member made of titanium or a titanium alloy material and a thermoplastic carbon fiber reinforced plastic (CFRP) material can be applied to various structures. Note that since it is difficult to accurately measure the area of ​​the actual welded portion, it is specified by the load rather than the stress. Also, the tensile shear strength is a value in a state where there is no mechanical fastening or bonding area by adhesive.

[0024] Furthermore, in the dissimilar friction stir welded member of the present invention, it is preferable that the difference between the hardness of the region that breaks in a tensile shear test using the tensile test piece and the hardness of the base material of the carbon fiber reinforced plastic (CFRP) is within 5 Hv. By making the hardness of the fracture region and the hardness of the member close to each other, it is possible to obtain a good dissimilar friction stir welded member in which the welded portion does not become a singular point.

[0025] The dissimilar material friction stir welded member of the present invention can be easily obtained by the dissimilar material friction stir welding method of the present invention. Effect of the Invention

[0026] According to the present invention, it is possible to provide a dissimilar material friction stir welding method for simply and efficiently directly joining a titanium or titanium alloy material and a thermoplastic resin material, and a dissimilar material friction stir welded member having high joint strength obtained thereby. [Brief description of the drawings]

[0027] [Figure 1] 1 is a process diagram of dissimilar material friction stir welding according to the present invention. [Diagram 2] 1 is a schematic diagram of dissimilar material friction stir welding according to the present invention. FIG. [Diagram 3] 1 is a schematic cross-sectional view of a dissimilar material friction stir welded member according to one embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram of introduction of an epoxy group by silane coupling treatment. [Diagram 5] FIG. 2 is a schematic diagram showing the collection position, shape and size of a test piece. [Figure 6] 1 is a graph showing the tensile shear strength of a joint obtained by studying a silane coupling agent. [Figure 7] 1 is a photograph showing the appearance of a test piece after a tensile test on a joint obtained by studying a silane coupling agent. [Figure 8] This is the result of SEM-EDS of the pure titanium plate surface at the fracture site after a tensile test on a joint obtained by investigating a silane coupling agent. [Figure 9] 1 is a graph showing the tensile shear strength of a joint obtained by examining friction stir welding conditions. [Figure 10] 1 is a graph showing the maximum temperature reached in the vicinity of the welded interface during friction stir welding. [Figure 11] 1 is a photograph showing the appearance of a test piece after a tensile test on a joint obtained by studying friction stir welding conditions. [Figure 12] 1 is a graph showing a temperature change in the vicinity of a welded interface during friction stir welding. [Figure 13] FIG. 2 is a schematic diagram showing a bonding mechanism based on a reaction between an epoxy group and an amide group. [Figure 14] 1 is a graph showing a welding load and a welding pressure during friction stir welding. [Figure 15] 13 shows SEM photographs of the cross sections of the welded joints obtained at 100, 125, 150 and 175 rpm. [Figure 16] 13 is an optical microscope photograph of the cross section of the welded portion of joints obtained at 200 and 300 rpm. [Figure 17] 17 is an enlarged photograph of the dashed line area in FIG. 16. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Representative embodiments of the dissimilar material friction stir welding method and dissimilar material friction stir welded members obtained by the method 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 equivalent 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.

[0029] (1) Dissimilar materials friction stir welding method Fig. 1 shows a process diagram of dissimilar material friction stir welding of the present invention. The dissimilar material friction stir welding of the present invention has a first step (S01) of performing a silane coupling treatment on the region to be joined of titanium or titanium alloy material, a second step (S02) of forming a welded interface, and a third step (S03) of performing friction stir welding. Fig. 2 shows a schematic diagram of dissimilar material friction stir welding of the present invention. Each step will be described in detail below.

[0030] (1-1) First step (S01: Silane coupling treatment) The first step (S01) is a step for performing a silane coupling treatment on a joining region of the titanium or titanium alloy material 2. By performing the silane coupling treatment on the joining region of the titanium or titanium alloy material 2, it is possible to impart functional groups that contribute to bonding with a resin material to the surface of the joining region.

[0031] When a silane coupling agent is mixed with distilled water, silanol (Si-OH) is formed by hydrolysis. In addition, silanol groups show high affinity to each other, and form -Si-O-Si- bonds and several hydroxyl groups by condensation reaction. The silane coupling treatment can be performed by immersing the joining area of ​​the titanium or titanium alloy material 2 in an aqueous solution of the silane coupling agent and distilled water, then removing it and subjecting it to a heat treatment (drying treatment) at an appropriate temperature.

[0032] The silane coupling agent, which has undergone hydrolysis and condensation reactions, physically absorbs the hydroxyl groups on the surface of titanium or titanium alloy 2 through hydrogen bonds. In addition, by heating, the hydrogen bonds between the silanol and the hydroxyl groups of titanium or titanium alloy material 2 are converted to -Si-O-Ti- bonds. Through these processes, a bonded region having organic groups can be obtained.

[0033] Here, in order to form a good dissimilar material friction stir welded joint consisting of the titanium or titanium alloy material 2 and the thermoplastic resin material 4, it is necessary that the functional group of the thermoplastic resin material 4 has good reactivity with the functional group introduced by the silane coupling agent. That is, it is necessary to appropriately select an appropriate silane coupling agent depending on the thermoplastic resin material 4 that is the material to be joined.

[0034] For example, when the thermoplastic resin material 4 is "polyamide 6", since polyamide 6 has an amide group, it can react and bond with an epoxy group. That is, when joining a thermoplastic resin material 4 containing polyamide 6 and a titanium or titanium alloy material 2, a strong joining interface can be formed by using a silane coupling agent having an epoxy group.

[0035] The concentration of the silane coupling agent aqueous solution is not particularly limited as long as it does not impair the effects of the present invention, but is preferably 2% or more. By making the concentration of the silane coupling agent aqueous solution 2% or more, it is possible to introduce functional groups that provide sufficient bonding strength into the bonded region by simply immersing the titanium or titanium alloy material 2 in the silane coupling agent aqueous solution once. In addition, when the concentration of the silane coupling agent aqueous solution is low, immersion and drying may be performed multiple times.

[0036] The method for drying the aqueous solution of the silane coupling agent attached to the surface of the joining region of the titanium or titanium alloy material 2 is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known methods can be used. For example, the titanium or titanium alloy material 2 to which the aqueous solution of the silane coupling agent is attached may be held in a vacuum furnace at 100 to 140°C for about 1 hour.

[0037] (1-2) Second step (S02: Formation of bonded interface) The second step is a step for forming a joining interface by bringing the joining region of the titanium or titanium alloy material 2 that has been subjected to the silane coupling treatment in the first step (S01) into contact with the thermoplastic resin material 4.

[0038] It is not necessary that the entire area of ​​the titanium or titanium alloy material 2 that contacts the thermoplastic resin material 4 be subjected to the silane coupling treatment, but it is sufficient that the titanium or titanium alloy material 2 includes an area that has been subjected to the silane coupling treatment.

[0039] It is preferable that the titanium or titanium alloy material 2 and the thermoplastic resin material 4 are fixed to such an extent that their positions do not change during friction stir welding in the third step (S03). On the other hand, in friction stir welding, a welding pressure is applied to the welded regions by a friction stir welding tool, so there is no need to apply a separate pressing force to bring the welded surfaces into close contact with each other.

[0040] (1-3) Third process (S03: Friction stir welding) The third step (S03) is a step of performing friction stir welding on the region to be welded.

[0041] Friction stir welding, also known as FSW (Friction Stir Welding), is a method of joining two metal components by butting the ends of the two metal members to be joined, inserting a protrusion (probe) at the tip of a rotating tool between the ends, and rotating and moving the rotating tool along the longitudinal direction of the ends.

[0042] In the present invention, "friction stir welding" includes friction stir line welding in which a rotating tool is moved in the joining direction while rotating, and friction stir spot welding in which a rotating tool is not moved at the joining site while rotating, and means lap friction stir welding in which materials to be joined are overlapped and a rotating tool is inserted from the side of one of the materials to be joined. Hereinafter, friction stir line welding in which a rotating tool is moved in the joining direction while rotating will be described in detail as a representative embodiment.

[0043] The rotating friction stir welding tool 6 is pressed into the upper part of the welded region from the titanium or titanium alloy material 2 side to generate frictional heat and apply a welding pressure in a direction substantially perpendicular to the welded interface. In this state, the friction stir welding tool 6 is moved along the welded region to form a linear welded interface.

[0044] The bottom surface of the friction stir welding tool 6 may be provided with protrusions of an appropriate size and shape, but from the viewpoint of ensuring the life of the friction stir welding tool 6 and the uniformity of the temperature distribution and applied pressure at the welded interface during friction stir welding, it is preferable to have a smooth bottom shape without protrusions. The insertion amount of the friction stir welding tool 6 from the surface of the titanium or titanium alloy material 2 does not need to be larger than necessary, and it is preferable to make it small as long as the welding temperature and welding pressure at the welded interface are appropriate values. By making the insertion amount small, the life of the friction stir welding tool 6 can be extended.

[0045] The material of the friction stir welding tool 6 is not particularly limited as long as it does not impair the effects of the present invention, and may be any of various conventionally known materials used in friction stir welding tools. For example, tungsten carbide (WC), cemented carbide made of cobalt (Co) or nickel (Ni), cobalt (Co)-based alloys, tungsten (W) alloys, high melting point metals such as iridium (Ir) and alloys thereof, or Si 3 N 4 The ceramic material may be used.

[0046] The main welding parameters in friction stir welding are the rotation speed, movement speed, welding pressure and advance angle of the friction stir welding tool 6, which may be appropriately adjusted so that the temperature of the welded interface during friction stir welding is equal to or higher than the melting temperature and equal to or lower than the decomposition temperature of the thermoplastic resin material 4. In addition, it is preferable to flow an inert gas such as argon in the welded region to suppress oxidation reactions of the welded materials and the tool.

[0047] The temperature of the interface to be joined during friction stir welding is preferably 220 to 350°C. Although the melting temperature and decomposition temperature differ depending on the type and state of the thermoplastic resin material 4, by setting the temperature of the interface to be joined at 220 to 350°C, it is possible to cover many of the thermoplastic resin materials 4 that are generally used as structural members by joining with metal members. The temperature of the interface to be joined is more preferably 250 to 320°C, and most preferably 290 to 310°C.

[0048] The time for which the joining interface is held at an appropriate temperature (not less than the melting temperature and not more than the decomposition temperature of the thermoplastic resin material 4) during friction stir welding is preferably 1 second or more, more preferably 3 seconds or more, and most preferably 5 seconds or more. By holding the joining interface within an appropriate temperature range, the titanium or titanium alloy material 2 and the thermoplastic resin material 4 can be reliably joined. On the other hand, if the holding time is too long, there is a risk of the thermoplastic resin material 4 being deteriorated, so that the holding time is preferably 20 seconds or less.

[0049] Furthermore, the joining pressure applied to the interface to be joined by friction stir welding is preferably 5 to 20 MPa. By setting the joining pressure to 5 MPa or more, the thermoplastic resin material 4 and the titanium or titanium alloy material 2 can be sufficiently adhered to each other, and by setting the joining pressure to 20 MPa or less, deterioration of the friction stir welding tool 6 can be suppressed. A more preferable joining pressure is 8 to 17 MPa, and the most preferable joining pressure is 10 to 15 MPa.

[0050] The rotation direction of the friction stir welding tool 6 can be clockwise or counterclockwise, but it is preferable to set the rotation direction and the movement direction of the friction stir welding tool 6 to be opposite (retreating side) on the side where the distance from the welded region to the end of the titanium or titanium alloy material 2 is short. In friction stir welding, the welding temperature tends to be high on the side where the rotation direction and the movement direction of the friction stir welding tool 6 are the same (advancing side). In addition, when the distance from the insertion position of the friction stir welding tool 6 to the end of the titanium or titanium alloy material 2 is short, the welding temperature tends to be high due to heat storage compared to when the distance is long. From these relationships, the temperature distribution in the welded region can be made uniform by setting the side where the distance from the insertion position of the friction stir welding tool 6 to the end of the titanium or titanium alloy material 2 is short as the retreating side.

[0051] The composition of the titanium or titanium alloy material 2 is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known titanium or titanium alloys can be used. As the titanium alloy, for example, the widely used Ti-6Al-4V alloy or various highly workable titanium alloys can be used. In addition, the plate thickness of the titanium or titanium alloy material 2 is also not particularly limited as long as it does not impair the effects of the present invention, and for example, a plate material of about 1 to 5 mm can be suitably used.

[0052] The type of thermoplastic resin material 4 is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known thermoplastic resin materials can be used, but it is preferable that the thermoplastic resin material has an amide group. For example, polyamide 6 can be exemplified as a thermoplastic resin material having an amide group, and carbon fiber reinforced plastic (CFRP) having polyamide 6 as a matrix can be preferably used. Other thermoplastic resins include polypropylene resin (melting point: 170°C, thermal decomposition temperature: 328 to 410°C), nylon 66 resin (melting point: 268°C, thermal decomposition temperature: 310 to 380°C), polycarbonate resin (melting point: 150°C, thermal decomposition temperature: 420 to 620°C), nylon 6 resin (melting point: 225°C, thermal decomposition temperature: 310 to 380°C), etc.

[0053] (2) Dissimilar material friction stir welding components 3 shows a schematic cross-sectional view of a dissimilar material friction stir welded member according to one embodiment of the present invention. A dissimilar material friction stir welded member 10 is formed by overlapping a titanium or titanium alloy material 2 and a thermoplastic carbon fiber reinforced plastic (CFRP) material 12 with a friction stir welded portion 14. The resin portion of the carbon fiber reinforced plastic (CFRP) material 12 has an amide group.

[0054] A crystallized region 16 exists near the weld interface in the friction stir welded portion 14. The crystallized region 16 means that the carbon fiber reinforced plastic (CFRP) material 12 has been sufficiently softened during friction stir welding, and the surface of the titanium or titanium alloy material 2 and the surface of the carbon fiber reinforced plastic (CFRP) material 12 have been adhered closely to each other. In addition, no groove-like or void-like defects exist in the friction stir welded portion 14. This means that the temperature of the weld interface during friction stir welding was suppressed to below the thermal decomposition of the thermoplastic resin material that is the matrix of the carbon fiber reinforced plastic (CFRP) material 12.

[0055] In the dissimilar friction stir welded member 10, in a tensile test piece having a friction stir welded portion 14 (friction stir welded line) having a length of 15 mm, the tensile shear strength in the direction perpendicular to the friction stir welded portion 14 is preferably 3.0 kN or more. When the tensile shear strength is 3.0 kN or more, the dissimilar friction stir welded member 10 made of a titanium or titanium alloy material 2 and a carbon fiber reinforced plastic (CFRP) material 12 can be applied to various structures. The tensile shear strength is more preferably 3.5 kN or more, and most preferably 3.7 kN or more.

[0056] In the dissimilar friction stir welded member 10, it is preferable that the difference between the hardness of the region that breaks in a tensile shear test and the base material hardness of the carbon fiber reinforced plastic (CFRP) material 12 is within 5 Hv. When the hardness of the fracture region and the hardness of the member are close to each other, a good dissimilar friction stir welded member 10 can be obtained in which the welded portion does not become a singular point. Here, the fracture region is located near the outer edge of the friction stir welded portion 14.

[0057] Representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention.

[0058] The dissimilar material friction stir welding method and dissimilar material friction stir welded members of the present invention will be further described below in examples, but the present invention is not limited to these examples at all. EXAMPLES

[0059] In the arrangement shown in Figure 2, a commercially pure titanium (TP-340) plate with a thickness of 2 mm, width of 50 mm, and length of 150 mm and a carbon fiber reinforced plastic (polyamide 6 with 20 mass% carbon fiber added) plate with a thickness of 3 mm, width of 50 mm, and length of 150 mm were friction stir joined.

[0060] (1) Study of silane coupling agents Silane coupling treatment was performed on the surface of a pure titanium plate as a preliminary treatment for friction stir welding. In order to examine the appropriate concentration of the silane coupling agent solution used in the silane coupling treatment, the silane coupling agent was mixed with pure water to prepare aqueous solutions of the silane coupling agent with concentrations of 0%, 0.5%, 1.5%, 2.5%, and 3.5%. The silane coupling agent used was OFS-6040 (3-Glycidoxypropyl trimethoxysilane, Epoxy functional), which can introduce epoxy groups to the surface of the pure titanium plate. A schematic diagram of the introduction of epoxy groups is shown in Figure 4.

[0061] The surface of the pure titanium plate (the area to be bonded) was polished with #3000 abrasive paper, and then immersed in an aqueous solution of a silane coupling agent of various concentrations, and then dried by keeping it in a vacuum furnace at 120°C for 1 hour.

[0062] Thereafter, the surface (joint area) of the pure titanium plate and the carbon fiber reinforced plastic plate were overlapped in the manner shown in FIG. 2, and a friction stir welding tool was pressed into the pure titanium plate side to perform friction stir welding.

[0063] The friction stir welding conditions were: tool rotation speed 300 rpm, tool movement speed (welding speed) 100 mm / min, tool advance angle 3°, and friction stir welding was performed using a cylindrical carbide friction stir welding tool with a diameter of 15 mm and a smooth bottom surface without protrusions. Argon gas was flowed through the joint, and the bottom surface of the tool was inserted 0.9 mm from the surface of the pure titanium plate.

[0064] To evaluate the strength of the joint, a tensile shear test was performed on the resulting dissimilar material joint. Figure 5 shows the location, shape, and size of the test specimen. The test specimen for the tensile shear test was taken from A in Figure 5, and was 15 mm wide. The tensile speed for the tensile shear test was 0.5 mm / min, and three measurements were performed.

[0065] The obtained tensile shear strength is shown in Figure 6, a photograph of the appearance of the test piece after the tensile test is shown in Figure 7, and the SEM-EDS results of the surface of the pure titanium plate at the fractured part are shown in Figure 8. The cross-sectional sample for microstructural observation was mechanically polished with abrasive paper up to #4000 and then mirror-polished using a 1 μm diamond suspension, and a JEOL JSM-7001FA was used for SEM. The collection position, shape, and size of the sample for microstructural observation are shown as B in Figure 5.

[0066] When the silane coupling agent was not added, no joint could be obtained. When the silane coupling agent was added, a joint was formed, but under the friction stir welding conditions set, the tensile shear strength was less than 1 kN in all cases (Fig. 6), and all fractures occurred at the joint interface (Fig. 7). On the other hand, when the concentration of the silane coupling agent was 2.5% or more, carbon originating from the carbon fiber reinforced plastic plate was clearly observed on the surface of the pure titanium plate at the joint, confirming that the silane coupling agent had formed a strong joint interface (Fig. 8).

[0067] That is, a strong joint interface can be formed between a pure titanium plate and a carbon fiber reinforced plastic plate by using an appropriate silane coupling treatment and friction stir welding, but it is necessary to suppress the decrease in strength of the carbon fiber reinforced plastic plate due to friction stir welding.

[0068] (2) Study of friction stir welding conditions Friction stir welding was performed in the same manner as in (1), except that the concentration of the silane coupling agent aqueous solution was kept constant at 3.5% and the tool rotation speed was set to 50, 100, 125, 150, 175, 200, 250, and 300 rpm.

[0069] The tensile shear strength of each joint obtained in the same manner as in (1) is shown in Fig. 9. The temperature near the interface during joining was measured with a thermocouple, and the results are also shown in Fig. 9. A schematic diagram of the joining temperature measurement is shown in Fig. 10.

[0070] As shown in FIG. 9, there is a clear range of tool rotation speeds (125-175 rpm) where a high tensile shear strength of 3.0 kN or more can be obtained, and the temperature near the interface during friction stir welding is above the melting point (225°C) and below the decomposition temperature (350°C) of the carbon fiber reinforced plastic base material (polyamide 6). FIG. 11 shows an external view of the test piece after the tensile test, and all of the joints obtained at 125-175 rpm were fractured in the base material on the carbon fiber reinforced plastic plate side. In addition, when the Vickers hardness of the fracture position of these joints was measured, it was 18-20 Hv. The Vickers hardness of the carbon fiber reinforced plastic plate was also 18-20 Hv, and it can be seen that the hardness at the fracture position was hardly changed by welding.

[0071] Figure 12 shows the temperature change near the joint obtained by using a thermocouple when the tool rotation speed was 100, 125, 150, and 175 rpm. The time during which the temperature of the region was held above the melting point of polyamide 6 was 5.0 seconds at 125 rpm, 8.8 seconds at 150 rpm, and 10.3 seconds at 175 rpm, which is considered to be enough time for the epoxy group introduced by the silane coupling agent and the amide group of polyamide 6 to react sufficiently. On the other hand, in the case of 100 rpm, although the joint temperature was slightly above the melting point of polyamide 6, the time during which the temperature was held in the temperature range was extremely short at 1.3 seconds, which is considered to be the reason why a strong joint interface was not formed.

[0072] The bonding mechanism by the reaction between the epoxy groups formed on the surface of the pure titanium plate and the amide groups of polyamide 6 is shown diagrammatically in Figure 13. The epoxy groups and amide groups are bonded by insertion and addition reactions, and it is believed that the melting of the polyamide 6 near the bonded interface promotes these reactions, forming a strong bonded interface.

[0073] The welding load and welding pressure applied to the welded interface by the friction stir welding tool during friction stir welding are shown in Figure 14. As the rotation speed of the tool increases, the polyamide 6 softens and / or decomposes, so the welding load and welding pressure decrease, but it can be seen that at 125 to 175 rpm, where the welding temperature is above the melting point and below the decomposition temperature of polyamide 6, an appropriate welding pressure of 5 to 20 MPa is applied.

[0074] Figure 15 shows SEM photographs of the cross sections of the joints obtained at 100, 125, 150, and 175 rpm. At a low joining temperature of 100 rpm, gaps exist between the pure titanium plate and the carbon fiber reinforced plastic plate, and a good joint interface is not formed. In contrast, at joining temperatures of 125 to 175 rpm, which are above the melting point and below the decomposition temperature of polyamide 6, a joint interface in which the pure titanium plate and the carbon fiber reinforced plastic plate are in close contact is formed, and no defects are observed.

[0075] Optical microscope photographs of the cross sections of the welded parts of joints obtained at 200 and 300 rpm are shown in Fig. 16. Moreover, enlarged photographs of the area surrounded by the dashed line in Fig. 16 are shown in Fig. 17. It can be seen that under friction stir welding conditions where the joining temperature is equal to or higher than the decomposition temperature of polyamide 6, large grooves due to the decomposition of polyamide 6 are formed between the pure titanium plate and the carbon fiber reinforced plastic plate.

[0076] From the above results, it has been confirmed that the dissimilar material friction stir welding method of the present invention, which combines an appropriate silane coupling treatment with friction stir welding in which the joining temperature is above the melting point and below the decomposition temperature of the thermoplastic resin material, can form an extremely strong joint interface between titanium and thermoplastic resin materials, and that the dissimilar material friction stir welding member of the present invention obtained by this dissimilar material friction stir welding method has a weld formed in a tensile test piece having a friction stir weld line 15 mm long, with the tensile shear strength in the direction perpendicular to the friction stir weld line being 3.0 kN or more. [Explanation of symbols]

[0077] 2. Titanium or titanium alloy material, 4...Thermoplastic resin material, 6. Friction stir welding tools, 10....Dissimilar material friction stir welded members, 12...Carbon fiber reinforced plastic material, 14...Friction stir welding, 16...Crystallization region.

Claims

1. A method for friction stir welding a titanium or titanium alloy material and a thermoplastic resin material, comprising the steps of: A first step of subjecting a region of the titanium or titanium alloy material to a silane coupling treatment; a second step of contacting the thermoplastic resin material with the bonded region that has been subjected to the silane coupling treatment to form a bonded interface; A third step of pressing a friction stir welding tool into the titanium or titanium alloy material to heat the welded interface and apply a welding pressure to the welded interface, The friction stir welding tool is a tool having a smooth bottom surface shape without any protrusions, In the third step, a temperature of the interface to be joined is set to a melting temperature or higher and a decomposition temperature or lower of the thermoplastic resin material; A dissimilar material friction stir welding method comprising the steps of:

2. The thermoplastic resin material is a carbon fiber reinforced plastic (CFRP) material; The method for friction stir welding of dissimilar materials according to claim 1 .

3. the thermoplastic resin material has an amide group, In the first step, an epoxy group is formed on a surface of the joining region of the titanium or titanium alloy material; 3. The method for friction stir welding of dissimilar materials according to claim 1 or 2,

4. In the third step, the temperature of the interface to be joined is set to 220 to 350° C.; The method for friction stir welding of dissimilar materials according to any one of claims 1 to 3,

5. In the third step, the bonding pressure is set to 5 to 20 MPa; The method for friction stir welding of dissimilar materials according to any one of claims 1 to 4,

6. In the first step, the concentration of the silane coupling agent used in the silane coupling treatment is 2% or more; The method for friction stir welding of dissimilar materials according to any one of claims 1 to 5,

7. A lap friction stir welded member made of titanium or titanium alloy material and thermoplastic carbon fiber reinforced plastic (CFRP) material, The resin portion of the carbon fiber reinforced plastic (CFRP) material has an amide group, A crystallized region is present in the carbon fiber reinforced plastic (CFRP) material near the joint interface, In a tensile test piece having a friction stir welded line having a length of 15 mm, the tensile shear strength in a direction perpendicular to the friction stir welded line is 3.0 kN or more; A dissimilar material friction stir welded component characterized by the above.

8. the difference between the hardness of the region that breaks in a tensile shear test using the tensile test piece and the hardness of the base material of the carbon fiber reinforced plastic (CFRP) material is within 5 Hv; The dissimilar material friction stir welded member according to claim 7 .

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