JP2013121621A - Friction stir tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a friction stir tool that has high-temperature strength, is superior in wear resistance at high temperature, and has superior productivity.SOLUTION: The friction stir tool is formed of a Co-based alloy containing a γ-phase representing an Al structure and a γ'-phase representing an L12 structure precipitated in the γ-phase, and characterized in that the γ'-phase is of (Co, X)(Al, W, Z), and the Co-based alloy contains 30 to 40 at% of Ni, wherein X is mainly Ni, and Z is mainly Cr and Ta.

Description

  The present invention relates to a friction stir tool.

  A cylindrical member made of a material substantially harder than the material to be joined (hereinafter referred to as a rotary tool, a stirring tool or a friction stir tool, or simply referred to as a tool) may be rotated to the joined portion of the material to be joined. There is a friction stir welding method in which joining is performed by frictional heat generated between the rotating tool and the material to be joined by moving while rotating the rotating tool.

  In Patent Document 1, in the method of joining the workpieces (1A, 1B) in the coupling region (2), the material of the workpiece is placed on the opposite part of the workpiece on both sides of the coupling region (2) and the coupling region. Insert a harder probe (3), generate a relative circulation between the probe and the workpiece, generate frictional heat and create a plastic state in the opposite part, remove the probe (3) A friction welding method is disclosed, wherein the workpieces are joined without relative movement between the workpieces by solidifying the plastic parts and joining the workpieces together. This joining method is a method of softening the material to be joined by frictional heat between the rotary tool and the material to be joined, and utilizing a plastic flow phenomenon associated with the rotation of the rotary tool. Based on a different principle than arc welding.

  Patent Document 2 has a cylindrical rotating body and a probe protruding coaxially from a shoulder on its end face, and is generated by inserting the probe while rotating it to a joint portion where a pair of members to be joined are abutted against each other. In a friction stir welding tool that is joined by stirring while being softened by frictional heat, the probe and the rotating body are detachable, and the probe is made of cemented carbide or cobalt alloy steel (MP159). A friction stir welding tool is disclosed which is characterized by the following.

  In Patent Document 3, there is a rotary tool for friction stir welding for friction stir welding of metal-to-metal joints, which prevents adhesion of the bonding material metal to the surface of the part in contact with the metal A rotary tool characterized by forming a blocking coating is disclosed.

  In Patent Document 4, a friction stir welding tool made of a material harder than a metal workpiece is pressed and inserted while being rotated into a butting portion of a pair of metal workpieces, and the metal workpiece is friction stir welded. A stir welding tool, comprising: a central member formed of metal; and a ceramic member that covers at least a region of the central member that is in frictional contact with the metal workpiece, wherein the ceramic member is made of a nitride of Si. A friction stir welding tool is disclosed, wherein the central member is a heat-resistant alloy containing at least one of Fe, Ni, Co, and W as a main component.

  Patent Document 5 discloses a friction stir welding tool capable of friction stir welding metal matrix composite materials (MMCs), ferrous alloys, non-ferrous alloys, and superalloys, including a shaft portion, a shoulder portion, a pin, the shoulder portion, and A high wear resistant material disposed on at least a portion of the pin, wherein the shoulder is mechanically secured to the shaft to prevent rotational movement of the shoulder 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 ultra-high temperature and ultra-high pressure, and can functionally friction stir weld MMCs, ferrous alloys, non-ferrous alloys and superalloys A friction stir welding tool is disclosed.

  Patent Document 6 discloses a friction stir welding tool capable of performing friction stir welding using a metal or alloy having a high melting point of 1600 ° C. or higher as a workpiece, and at least a portion in contact with the workpiece is iridium. And a composition containing rhenium, ruthenium, molybdenum, tungsten, niobium, tantalum, zirconium, hafnium or two or more of these as subcomponents, and has a micro Vickers hardness of 200 Hv or more. A friction stir welding tool is disclosed.

  In Patent Document 7, a probe pin extended from a tip surface of a rotating rotor is press-fitted into a joint portion of a member to be joined, and the probe pin is moved along the joint portion, and the joint portion is joined at the joint portion. In the friction stir welding tool for friction stir welding of members, at least the probe pin and the rotor that are in contact with the members to be joined are composed of a WC cemented carbide containing 5 to 18% by weight of Co. A tool for friction stir welding is disclosed.

In Patent Document 8, Al: 0.1 to 10% in mass ratio, W: 3.0 to 45%, the balance is Co except for inevitable impurities, and L1 of Co3 (Al, W) in atomic ratio. _A high heat resistance and high strength Co-based alloy characterized by a metal structure in which a type ₂ intermetallic compound is precipitated is disclosed.

Japanese Patent No. 2712838 JP 2008-36664 A JP 2005-152909 A JP 2004-82144 A Japanese translation of PCT publication No. 2003-532543 JP 2006-320958 A JP 2005-199281 A International Publication No. 2007/032293

  An object of the present invention is to provide a friction stir tool having high high-temperature strength, excellent wear resistance at high temperatures, and excellent productivity.

The friction stir tool of the present invention, 'is formed of a Co-based alloy having a phase, the gamma' and gamma phase indicating an A1 structure, gamma showing an L1 ₂ structure precipitated in the gamma phase phase (Co, X ) ₃ (Al, W, Z), and the Co-based alloy contains 30-40 at% Ni. Here, X is mainly Ni and Z is mainly Cr and Ta.

According to the present invention, to reduce production costs by casting, excellent productivity, rotary tool for low friction stir of wear at high temperature can be provided. In addition, by using the above tool, it is possible to easily join difficult-to-weld materials such as Ti and Zr.

It is a side view which shows the structure of the rotary tool of the Example by this invention. It is an external appearance photograph of Co base alloy ingot which is a material of the rotary tool of the present invention. It is an electron micrograph which shows the microstructure of the Co base alloy ingot of the Example by this invention. It is an external appearance photograph which shows the junction part of SS400 material steel material produced using the Co base alloy rotary tool of this invention. It is an external appearance photograph which shows the surface part after using the rotating tool made from Co base alloy of this invention for joining. It is an external appearance photograph which shows the butt | joining junction part of Ti-15V-3Cr-3Sn-3Al material produced using the rotation tool made from Co base alloy of this invention.

  The present invention relates to a friction stir tool for joining or modifying materials by friction stir.

  The friction stir welding of low melting point metal materials such as aluminum alloys has already been put to practical use. On the other hand, it has been reported relatively early in friction stir welding of high-melting-point materials such as steel materials, but the number of research reports on friction stir welding in steel materials is considerably smaller than that of aluminum alloys.

  One of the reasons is that when a rotating tool made of tool steel, which is generally used for joining aluminum alloys, is applied to joining steel materials, the tool is thermally deformed, so joining is not easy. . The properties of the rotary tool material in friction stir welding of high melting point materials such as steel materials require high temperature strength, wear resistance, non-reactivity, and the like.

  Patent Document 5 describes a ceramic material such as PCBN (Polycrystalline Cubic Boron Nitride manufactured by MegaStir USA) as a material of a rotating tool suitable for joining steel materials and high melting point materials.

  Ceramic materials generally have high strength at high temperatures, but are difficult to cut at room temperature, so it is not easy to process them into various tool shapes. Moreover, since it is produced by sintering, there is room for improvement in terms of productivity.

  On the other hand, Co-based alloys (cobalt-based alloys) also have a relatively high high-temperature strength and are considered promising as rotating tools. The fact that Co alloy can be applied to a rotating tool is described in Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 6, Patent Document 7, and the like.

  Since a Co-based alloy has relatively good machinability at room temperature compared to a ceramic material, it can be processed relatively easily into various shapes, so that an economic advantage can be expected. However, since the strength of the material sharply decreases at a temperature exceeding 800 ° C. in the Co-based alloy, when the Co-based alloy is used as a rotating tool in joining a high melting point material such as a steel material, a tool material is used. The deterioration of the tool progresses and the tool is worn or damaged.

  Patent Document 8 describes a Co-based alloy that seems to be able to suppress a rapid strength decrease even at a high temperature around 1000 ° C. (a general joining temperature in friction stir welding of steel materials). In Patent Document 8, in γ ′ strengthened Co-4Al-26.9W (mass%) ternary alloy, the most important γ ′ solid solution is to maintain high temperature strength as the Ni content increases. It is described that the temperature is rising.

  The required characteristics of the stirring tool include wear resistance in addition to high temperature strength. On the other hand, in the Co-based alloy described in Patent Document 8, it is not clear about factors that affect the wear resistance. As the above factors, not only the γ ′ solid solution temperature but also the amount of γ ′ (volume fraction) and other precipitates are considered.

Problems of the wear resistance in the rotational tool, rotate the material of the tool, L1 ₂ structure showing the Co 3 _(Al, W) of the Co group precipitated gamma 'phase from 10% by volume fraction of up to 80% This can be solved by using an alloy.

  The reason why the volume fraction of the γ ′ phase is limited to 10% to 80% is as follows.

  When the volume fraction of the γ ′ phase was 10% or less, the high temperature strength could not be maintained, and a part of the friction stir tool was deformed, and the wear resistance was not sufficient. On the other hand, when the volume fraction of the γ ′ phase was 80% or more, the β phase having the B2 structure was excessively precipitated and the wear resistance was lowered.

  In addition to the characteristics of the Co-based alloy, a Co-based alloy in which one or more (at least one phase) selected from μ phase, Laves phase, and carbide (also referred to as carbide phase) is precipitated is rotated. It can be solved by using the tool.

  The chemical composition of the Co-based alloy capable of maintaining high temperature strength and wear resistance in the stirring temperature range of friction stirring is about 10 at% Al, about 7.5 at% W, about 3 at% Ta, about 10 at%. It is preferable to contain Cr, about 0.06 at% B, about 0.6 at% C, and about 30 at% or 40 at% Ni. Further, it is desirable that Co is contained at 25 at% or more. Here, at% is a unit that can be expressed as atomic%, and represents the number of atoms of each constituent atom with respect to the total number of atoms constituting the alloy.

  The yield strength at room temperature of the Co-based alloy having the above composition range is about 800 MPa, and it is relatively easy to cut. In addition, since the Co-based alloy can be precision cast, it can be determined that the economic effect in tool production is great.

  The friction stir tool of the present invention includes a cylindrical shank portion, a shoulder portion formed at an end portion of the shank portion, and a pin portion formed at an end portion of the shoulder portion. It is preferably an integrally molded product or a cut product cast using the Co-based alloy. The friction stir tool of the present invention is mounted and used in a friction stir welding apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
[Example 1]
FIG. 1 is an example of a tool configuration in the rotary tool of the present invention.

  The friction stir tool 101 is integrally cut from an ingot produced by precision casting. By integrally processing the friction stir tool 101, the rigidity of the tool can be improved and the manufacture of the tool can be simplified, and the cost can be greatly reduced.

  The friction stir tool 101 includes a shank portion 102 connected to the main shaft of the joining device, a shoulder portion 103 that contacts the surface of the material to be joined at the time of joining, and a pin portion 104 that is inserted into the material to be joined at the time of joining. Yes.

  As the shape of the tool 101, a shoulder portion 103 having a diameter of 15 mm was used. The pin portion 104 had a diameter of 6 mm at the pin-shoulder connection portion 105 connected to the shoulder portion 103, and 3.5 mm at the pin tip portion 106. The length of the pin part 104 was 1.8 mm. The thickness of the iron-based material that is the material to be joined was 4 mm. As the welding conditions, 250 rpm / min and 500 mm / min were used for the rotation speed and the joining speed of the tool 101, respectively.

  FIG. 2 is a photograph of the appearance of a Co-based alloy ingot produced by precision casting.

  The ingot was prepared with a composition of Co-40Ni-10Al-7.5W-3Ta-10Cr-0.06B-0.6C. The units are all at% (atomic%: the number of atoms of each constituent atom with respect to the total number of atoms constituting the alloy). The Co content is about 29%. The outer diameter of the ingot was about 30 mm, and the length was about 100 mm excluding the portion of the hot water. It is large enough to produce a rotary tool for friction stirring. Moreover, it was confirmed that the ingot can be produced in a very short time of about several minutes and is excellent in productivity. Furthermore, it was confirmed that a near net-shaped tool could be produced by precision casting.

After producing an ingot, it heat-processed at 1250 degreeC and air-cooled, and was heat-processed at 1000 degreeC after that. This is necessary to maintain high temperature strength, shows a L1 ₂ structure _{(Co, X) 3 (Al} , W, Z) in order to precipitate the gamma 'phase. Here, X is mainly Ni and Z is mainly Cr and Ta. The temperature of the heat treatment is also effective for precipitation of μ phase, Laves phase, and carbide, which is effective for wear resistance and grain boundary strengthening.

  FIG. 3 shows a microstructure photograph of the ingot.

  The ingot includes crystal grains 301, a γ ′ precipitate phase 302 finely dispersed and precipitated in the γ phase of the A1 structure in the crystal grains 301, a crystal grain boundary 303, and a precipitated phase 304 existing in the crystal grain boundary 303. It is the composition which includes. The volume fraction of the γ ′ precipitated phase 302 is about 60%. The precipitated phase 304 is one or a plurality of types of phases among a μ phase, a Laves phase, and a carbide phase. The precipitated phase 304 is a component that stabilizes the grain boundary (grain boundary stabilizing component). Here, the crystal grain 301 is a single grain surrounded by the crystal grain boundary 303 and having a large number of γ ′ precipitated phases 302 (γ ′ grains) dispersed in the Co matrix.

That is, the ingot is formed of a Co-based alloy including crystal grains containing a γ ′ precipitate phase dispersed and precipitated, and a crystal grain boundary and a precipitate phase sandwiched between adjacent crystal grains, The precipitation phase is at least one phase selected from a μ phase, a Laves phase, and a carbide phase. In particular, the γ ′ precipitate phase is Co. ₃ (Al, W) or (Co, X) ₃ It preferably has a composition of (Al, W, Z).

  Such a microstructure is effective in improving high temperature strength and wear resistance.

  Using the friction stir tool produced by processing the ingot shown in FIG. 2, joining was performed to the SS400 iron-based material.

  4 is an external view photograph showing a joint portion of an SS400 steel material (iron-based material) joined using a friction stir tool produced by processing the ingot shown in FIG. 2 into the shape of FIG.

  As shown in this figure (joint part of the SS400 material), it was confirmed that the friction stir welding of the SS400 material was possible using the friction stir tool of the present invention.

  As the welding conditions, 250 rpm / min and 500 mm / min were used for the rotation speed and the joining speed of the tool 101, respectively. The joining distance was 360 mm and the joining was repeated a plurality of times. The change in the shape of the friction stirrer with the joining distance was observed, and the performance of the friction stirrer was evaluated.

  FIG. 5 shows the external appearance of the tool surface after joining 360 mm twice and the appearance after joining 37 times. The respective total joining distances are 0.72 m and 13.32 m.

  As can be seen from this figure, no clear damage is found in the pin portion and the shoulder portion even at the junction of 13.32 m (37 times). Since the bonding material slightly adhered to the pin portion and the shoulder portion, the shape change in the tool after bonding could not be clearly measured, but it became clear that almost no wear occurred.

  As a result of performing continuous life evaluation using the above tool, it was confirmed that the tool was less worn and could be used as a tool even at a total joining distance of 45 m or more.

From the above results, it was demonstrated that the Co-based alloy tool for SS400 steel material can provide a friction stir tool with less deformation and wear.
[Examples 2 to 4]
In addition to iron-based materials, it was found that friction stir welding can be applied to pure titanium or titanium alloys using the friction stir tool 101 of FIG. The titanium materials used in this example are industrial pure Ti (Example 2), titanium alloy Ti-6Al-4V (Example 3), titanium alloy Ti-15V-3Cr-3Sn-3Al (Example 4). is there.

  As the joining conditions, the rotation speed and joining speed of the tool 101 were 200 revolutions / minute and 100 mm / minute, respectively.

  FIG. 6 is an external view photograph of a butt joint portion of a Ti-15V-3Cr-3Sn-3Al material joined using the friction stir tool 101 of FIG.

  From this figure, it can be seen that an orderly surface bead is obtained. In addition, the wear and deformation of the shoulder portion and the pin portion of the friction stir tool were not observed. In this example, it was found by the appearance inspection of the tool after joining, etc. that the reaction between the Co-based alloy rotating tool and the titanium alloy hardly occurred.

From the above results, it is clear that the friction stir tool of the present invention is also effective for friction stir welding of titanium alloys.
[Example 5]
Below, the result of the tool for friction stirring formed with the Co base alloy which has a composition of Co-30Ni-9.5Al-7.8W-2Ta-10Cr-0.06B-0.6C is shown. All units are at%. The Co content is about 40%. This tool is referred to as a tool 201. The tool 201 was produced by the same method as the tool 101. The volume fraction of the γ ′ precipitate phase in the tool 201 is about 45%.

  Table 1 shows the results of measuring the solid solution temperature of the γ 'precipitate by differential scanning calorimetry (DSC). In the table, in the case of tool 101, that is, an alloy containing 40 at% Ni, the γ ′ solid solution temperature is 1163 ° C., and in the case of tool 201, ie, an alloy containing 30 at% Ni, the γ ′ solid solution temperature is 1094 ° C.

  From the DSC results shown in Table 1, the tool 201 of this example has a solid solution temperature of γ ′ precipitate of 1094 ° C. This is because the content of Ni and Ta in the friction stir tool of the present embodiment is lower than that of the friction stir tool 101 of the first embodiment. The solid solution temperature of the γ ′ phase in the tool 101 and the tool 201 is higher than the joining temperature (1000 ° C.) in the steel material SS400, and it is considered that the γ ′ phase of the tool is stable even during joining.

  In the same manner as in Example 1, the iron-based material of SS400 was joined using the friction stir tool of this example. The friction stirrer tool of this example also has the same shape as the friction stirrer tool of Example 1. Also, the same bonding conditions as in Example 1 were used. The joining distance was 360 mm, and joining was repeated a plurality of times.

As a result, it was confirmed that the friction stir welding of the SS400 material was also possible in this example.
[Examples 6 to 12]
The results of Examples 6 to 12 are shown in Table 2 together with the results of Examples 1 to 5.

  Table 2 shows examples in which the tool 101 and the tool 201 are applied to various bonding materials.

  It was confirmed that the tool 101 and the tool 201 can be applied without problems from an aluminum alloy having a low melting point to a stainless steel, Ti alloy, or Zr alloy having a high melting point.

  The surface of the tool was observed after bonding, and the case where there was no damage to the tool, no adhesion of bonding material to the surface, and no defect in the bonded portion was evaluated as ◯.

  The joining conditions applied to Examples 6-12 are as follows.

  Example 6: N = 800 revolutions / minute, V = 200 mm / minute, Example 7: N = 200 revolutions / minute, V = 100 mm / minute, Example 8: N = 100 revolutions / minute, V = 50 mm / minute Example 9: N = 200 revolutions / minute, V = 100 mm / minute, Example 10: N = 200 revolutions / minute, V = 100 mm / minute, Example 11: N = 100 revolutions / minute, V = 50 mm / minute Minute, Example 12: N = 200 revolutions / minute, V = 100 mm / minute, N is the rotational speed of the tool, and V is the joining speed.

  Table 3 shows the γ 'volume fraction in Examples 1 to 12.

  The γ ′ volume fraction in the tool after joining was described as A: 10% or more and less than 30%, B: 30% or more and less than 50%, C: 50% or more and less than 65%, and D: 65% or more and 80% or less. Here, for example, 10% or more and less than 30% means 10% or more and less than 30%.

As can be seen from Tables 2 and 3, it is clear that the friction stir welding tool made of a Co-based alloy having a volume fraction of the γ ′ precipitation phase of 10% to 80% is effective in any joining. It is. It can also be seen that the γ ′ volume fraction in the friction stir welding tool can be changed not only by the alloy composition of the tool but also by the type of joining material and joining conditions.
[Comparative example]
Normally, when Ti alloy bonding is performed using a PCBN rotating tool, wear on the tool is severe and the surface of the bonded portion is also roughened. This is considered to be because N (nitrogen) contained in a PCBN rotating tool reacts with Ti (titanium) to form TiN (titanium nitride), and thus the tool is easily worn.

  Thus, titanium is an active metal and is often seen to react with friction stir tools during bonding. The results of active metal bonding using a PCBN tool are shown in Table 2. Since bonding was impossible due to severe tool wear, the evaluation was x.

  Further, when a ceramic rotating tool such as PCBN is repeatedly used, cracks are often generated in the shoulder portion and the pin portion, and a part of the tool is often chipped off. For this reason, the lifespan of a PCBN rotating tool cannot be predicted. This is probably because the ceramic material is vulnerable to thermal shock.

  Table 2 shows the results of joining materials such as SS400, SUS430 (AISI430), and SUS304 (AISI304) using a PCBN rotating tool. Since tool breakage suddenly occurred during use, it was evaluated as Δ2. Compared to this, since the Co-based alloy is a metal material, it is considered that sudden breakage in the tool is unlikely to occur.

  Furthermore, when a PCBN rotating tool is applied to an aluminum alloy (6N01), the bonding material (aluminum) may adhere to the tool surface and the bead surface may become rough. In Table 2, it is described as Δ1.

  It was found that when the above-mentioned friction stir tool (Co alloy stir tool) is applied to friction stir welding of the structure portion of the high melting point material, welding deformation, spatter and residual stress are reduced. The friction stir welding using the friction stir tool of the present invention can be applied to structures such as automobile panel members and pipes.

101, 201: Friction stirring tool, 102: Shank part, 103: Shoulder part, 104: Pin part, 105: Pin-shoulder connection part, 106: Pin tip part, 301: Crystal grain, 302: γ ′ precipitate phase, 303: Grain boundary, 304: Precipitation phase.

Claims (3)

A gamma phase indicating an A1 structure, the 'formed in the Co-based alloy having a phase, the gamma' gamma showing a precipitated L1 ₂ structure gamma phase phase _{(Co, X) 3 (Al} , W, Z) And
The Co-based alloy, tool friction stir, wherein 30-40At% including that of Ni.
(X is mainly Ni, Z is mainly Cr and Ta) The friction stir tool according to claim 1, wherein the Co-based alloy is formed by precision casting . A friction stir welding apparatus using the friction stir tool according to claim 1.

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