JP5629130B2 - Joining method of metal materials - Google Patents

Description

  The present invention relates to a method of joining both members to be joined using a metal material as one member to be joined and the same or different type of metal material as the other member to be joined.

  Conventionally, various methods have been employed for joining metal members. In Non-Patent Document 1, metal joining methods are roughly classified into material joining methods, chemical joining methods, and mechanical joining methods.

  In the material joining method, the members to be joined are joined firmly by metal bonding. When performed appropriately, the reliability of the joint can be increased. Specifically, it is classified into a welding method for melting and joining; a solid phase joining method such as a diffusion joining method, a friction joining method, and a pressure welding method; a liquid phase-solid phase reaction joining method such as brazing. As described above, the material bonding method realizes strong bonding by metal bonding. In particular, brazing, which is a liquid phase-solid reaction bonding method, is performed by heating the entire members to be bonded in a furnace, and therefore, multipoint bonding is possible at the same time. Brazing which makes use of such advantages is often applied to the joining of products such as automobile heat exchangers and heat sinks that have many joints and are joined at narrow intervals.

  The chemical bonding method is a bonding method using a so-called adhesive. Unlike the material joining method, there is an advantage that it is not necessary to join at a high temperature and the member to be joined itself is not deformed. However, since a strong bond such as a metal bond cannot be obtained, there is a disadvantage that the reliability and thermal conductivity of the bonded portion are inferior to those of the material bonding method.

  Examples of the mechanical joining method include rivets and bolting. Compared to material bonding methods and chemical bonding methods, bonding can be performed relatively easily. In addition, a bonding strength equal to or higher than that of the material bonding method can be obtained, and re-bonding can be easily performed depending on the method. However, there are drawbacks such as the shape of the joint being limited and being unsuitable for joining that requires hermeticity.

Conventionally, material joining methods such as a welding method, a soldering method, and a brazing method have been used for joining metal materials.
In the welding method, the joint is heated by electricity or flame to be melted and alloyed to form a joint. When the gap between the joints is large or when bonding strength is required, the filler material is simultaneously melted at the time of joining to fill the gap. Thus, since a junction part melts, reliable joining is made. On the other hand, since the joint portion is melted and joined, the shape in the vicinity of the joint portion is greatly deformed, and the metal structure is also greatly changed locally to become another structure, which may cause local weakening. In addition, since it is necessary to locally heat only the joint portion, there is a problem that it is difficult to join multiple points at the same time.

  In the soldering or brazing method, a solder or brazing material having a melting point lower than that of the member to be joined is heated by electricity or flame, so that only the solder or brazing material is melted and a gap between the joints is obtained. Is formed by filling. This is advantageous for joining point-like or line-like connecting portions, and the solder material and brazing material form a shape called a fillet at the time of solidification of the joint, thereby obtaining very high reliability in terms of strength and thermal conductivity. In addition, a strong bond can be obtained in a short time without melting the base material. Particularly in brazing of aluminum alloys, furnace brazing methods such as Nocolok brazing method and vacuum brazing method are performed, and a brazing sheet clad with a brazing material and an aluminum alloy material to be joined is used. . A heat exchanger having a complicated shape with many joints can be manufactured by pressing a brazing sheet, assembling a laminated heat exchanger having a hollow structure, and heating in a furnace. On the other hand, since the liquid phase flows in brazing or soldering, fine flow paths and the like may be filled with brazing. In addition, by using the brazing sheet, there is an advantage that the brazing sheet can be easily and uniformly supplied. On the other hand, since the manufacture of the brazing sheet is complicated, cost reduction and improvement in procurement are required. Furthermore, there is a problem that the degree of freedom of processing such as cutting on the joint surface side is impaired.

In principle, solid phase bonding methods such as diffusion bonding and friction bonding are bonding methods that do not involve melting of the members to be bonded.
In the diffusion bonding method, the base materials are brought into close contact with each other, basically pressed to the extent that the plastic deformation does not occur below the melting point of the base material, and bonding is performed using the diffusion of atoms generated between the joint surfaces. In this joining method, multi-point joining and surface joining can be performed simultaneously without deformation of the members to be joined. Therefore, it is possible to join the members to be joined having a fine shape. However, in order to utilize the diffusion phenomenon, a long time is required for joining as compared with welding or brazing. Usually, it is necessary to hold at a predetermined temperature for about 30 minutes or more. Moreover, since pressurization is required for joining, complication of joining operation and cost increase are inevitable. Furthermore, depending on the metal material, there is a case where a stable and strong oxide film is present on the surface and diffusion is inhibited thereby, making it difficult to apply solid phase diffusion bonding. In that case, a special cleaning process for removing the oxide film on the bonding surface is required, and there are problems such as requiring special processes such as argon ion bombardment, glow discharge, and application of ultrasonic waves.

  Among the friction welding methods, the friction stir welding method can be applied to various types of metal materials. Since there is no melting of the base material, there is an advantage that deformation of the member to be joined due to joining is small. On the other hand, the shape of the joint is limited to a straight line or a gentle curve, and it is difficult to join a complicated shape. In addition, since the joining tool is brought into direct contact with the joining portion, it is difficult to join the fine shapes, and it is also difficult to join multiple points at the same time. In addition, in this joining method, it is inevitable that the mark of the joining pin remains at the joining end portion. Furthermore, since the members to be joined are agitated at the joint, the joint strength may be reduced by exhibiting a structure different from that of the base material.

  As described above, when joining metal materials by a material joining method, a joining method is generally employed in which the member to be joined is not melted or only the vicinity of the joint is melted locally. This is because when the member to be joined is melted as a whole, the shape is not maintained and a desired shape cannot be obtained. However, in order to reliably perform bonding at a practical speed, a melted part is necessary, and deformation of the part could not be avoided. Therefore, there is a problem that the member must be designed and assembled in consideration of dimensional changes and strength changes after joining.

  On the other hand, the joining method which performs the whole metal member as a semi-molten state is also proposed. Patent Document 1 proposes a joining method using semi-melting of alloy powder. In this joining method, the alloy powder as a member to be joined is in a semi-molten state as a whole, so that its shape deformation is remarkable, and is not suitable for joining members that want to suppress shape deformation. Patent Document 2 proposes a method in which a nonmetallic member is press-fitted into a semi-molten alloy base material to join the nonmetallic member and the alloy base material. However, in this joining method, since the punch is pressed and joined to a predetermined mold, the shape of the product is limited.

JP 2005-30513 A JP 2003-88948 A

Welding and joining technology data book, p. 57, Welding / Joint Technology Data Book Editorial Committee (2007)

  In view of the above-described problems of the prior art, an object of the present invention is to provide a highly reliable new bonding method with good bonding properties and almost no deformation due to bonding.

  As a result of intensive studies, the present inventors have found a novel joining method using a liquid phase generated when heating a metal material that is a member to be joined, and have completed the present invention. That is, according to the present invention, the one member to be bonded and the other member to be bonded are defined in claim 1 in which the metal material is one member to be bonded, and one of the same or different types of metal materials is the other member to be bonded. And joining at a temperature at which the ratio of the mass of the liquid phase generated in the metal material to the total mass of the metal material that is the one member to be joined exceeds 0% and is 35% or less. It was set as the metal joining method characterized.

    In the second aspect of the present invention, in the metal material as the one member to be joined, the difference between the solidus temperature and the liquidus temperature is 10 ° C. or more. Further, according to the present invention, in the metal material as the one member to be joined, the dimensional change after joining with respect to before joining is 5% or less. Further, the present invention provides the metal material according to claim 4, wherein the metal material is an Al alloy, a Cu alloy, a Fe alloy, a Ni alloy, a Ti alloy, or a Mg alloy. It was assumed that this was the joining method.

  The metal material joining method according to the present invention is performed by utilizing a slight liquid phase generated inside an alloy to be joined. In the present invention, not only bonding of metal materials having the same composition but also bonding of metal materials of the same metal type having different compositions, and further, dissimilar metal materials are made possible by highly reliable metal bonding.

  Further, in the present invention, since the member to be joined itself does not flow greatly due to melting and does not use a solder material, a brazing material, a solubilizing material, or the like, a dimensional change due to joining is small, and a shape change hardly occurs. In particular, even in joining members having fine flow paths, good joining can be performed without clogging the flow paths due to inflow or deformation of the liquid phase.

  Further, since local structural change does not occur in the vicinity of the joint, strength embrittlement hardly occurs. In addition, simultaneous multi-point joining having reliability equivalent to that of the brazing method can be performed without using a brazing sheet, brazing paste, brazing sheet clad with a brazing material, or the like. Thereby, the cost of the material can be reduced without impairing the bonding performance.

Similar to the present invention, compared to diffusion bonding, in which deformation due to bonding is small and simultaneous multipoint bonding is possible, pressurization is not required, the time required for bonding can be shortened, and a metal material having a strong oxide film on the bonding surface Even for joining, a special process for cleaning the joining surface is not required.
As described above, the present invention provides a novel joining method that has not existed in the past.

It is a schematic diagram which shows the phase diagram of an Al-Si alloy as a binary eutectic alloy. It is explanatory drawing which shows the production | generation mechanism of a liquid phase in the joining method of the metal material which concerns on this invention. It is a front view which shows the observation surface position of a reverse T-shaped joining test piece and its junction part. It is a microscope picture which shows the junction part observed in FIG. It is a perspective view which shows the sample for measuring a joining rate and the deformation rate by joining. It is explanatory drawing of the measuring method of a joining rate and the deformation rate by joining.

Hereinafter, the present invention will be described in detail.
A. Combination of members to be joined In the method for joining metal materials according to the present invention, a metal material is used as one member to be joined, and either one of the same metal-based metal material or different metal material is used as the other member to be joined. The joining member and the other joined member are joined. When joining metal materials of the same metal type, those having the same alloy composition or those having different alloy compositions may be used.

B. Production of Liquid Phase In the method for joining metal materials according to the present invention, the ratio of the mass of the liquid phase produced in the metal material to the total mass of the metal material as one of the members to be joined (hereinafter referred to as “liquid phase ratio”) It is necessary to join at a temperature that exceeds 0% and not more than 35%. When the liquid phase ratio exceeds 35%, the amount of the liquid phase to be generated is too large and the metal material starts to be deformed. On the other hand, bonding is not possible unless a liquid phase is generated. When there are few liquid phases, joining may become difficult, a preferable liquid phase rate is 5-35%, and a more preferable liquid phase rate is 10-20%.

  It is extremely difficult to measure the actual liquid phase ratio during heating. Therefore, the liquid phase ratio defined in the present invention is obtained by equilibrium calculation. More specifically, the temperature is calculated from the alloy composition and the highest temperature at the time of heating by Thermo-Calc which is software for calculating the equilibrium state.

  The generation mechanism of the liquid phase will be described. FIG. 1 schematically shows a phase diagram of an Al—Si alloy, which is a typical binary eutectic alloy. When one aluminum alloy material having a Si concentration of c1 and the other member to be joined are heated, the generation of a liquid phase starts at a temperature T1 near the eutectic temperature (solidus temperature) Te. Below the eutectic temperature Te, as shown in FIG. 2A, crystal precipitates are distributed in the matrix divided by the grain boundaries. Here, when the generation of the liquid phase starts, as shown in FIG. 2B, the crystal grain boundary with a large segregation of the crystal precipitate distribution melts to become a liquid phase. Next, as shown in FIG. 2C, the periphery of the Si crystal precipitate particles and intermetallic compounds, which are the main additive element components dispersed in the matrix of the aluminum alloy, melts into a spherical shape to form a liquid phase. Further, as shown in FIG. 2 (d), this spherical liquid phase generated in the matrix is re-dissolved in the matrix with the passage of time and temperature due to the interfacial energy, and the grain boundaries and the surface are diffused by diffusion in the solid phase. Move to. Next, as shown in FIG. 1, when the temperature rises to T2, the liquid phase amount increases from the state diagram. As shown in FIG. 1, when the Si concentration of one aluminum alloy material is c2, the generation of a liquid phase starts in the vicinity of the solidus temperature Ts2 in the same manner as c1, and when the temperature rises to T3, The amount of liquid phase increases from the phase diagram. As described above, the bonding method according to the present invention uses a liquid phase generated by partial melting inside the metal material in all metal materials, not limited to aluminum alloys, and achieves both bonding and shape maintenance. Can be realized.

C. Behavior of Metal Structure in Joining The behavior of the metal structure from the occurrence of a liquid phase to joining is described with an example of joining with an aluminum alloy. As shown in FIG. 3, an inverted T-shaped joining test piece using an aluminum alloy material A that generates a liquid phase and an aluminum alloy material B to be bonded to the liquid phase is joined, and the observation surface shown in the figure is observed with a microscope. did. As described above, a very small amount of the liquid phase generated on the surface of the aluminum alloy material A during bonding fills the gap with the counterpart aluminum alloy material B in which the oxide film is destroyed by the action of flux or the like. Next, the liquid phase in the vicinity of the bonding interface between the two alloy materials moves into the aluminum alloy material B, and the solid-phase α-phase crystal grains of the aluminum alloy material A in contact with the bonding interface are aluminum alloy. Grows toward material B. On the other hand, the crystal grains of the aluminum alloy material B also grow to the aluminum alloy material A side.

  In the case where the aluminum alloy material B is an alloy that does not generate a liquid phase, as shown in FIG. 4A, the structure of the aluminum alloy material A enters the aluminum alloy material B in the vicinity of the bonding interface. Are joined. Therefore, no metal structure other than the aluminum alloy material A and the aluminum alloy material B is generated at the bonding interface. When the aluminum alloy material B is also an alloy that generates a liquid phase, as shown in FIG. 4B, both alloy materials have a completely integrated structure, and the bonding interface cannot be determined.

  On the other hand, when a brazing sheet clad with a brazing material is used as the aluminum alloy material B, as shown in FIG. 4C, a fillet is formed at the joint and a eutectic structure is observed. Thus, in FIG.4 (c), it becomes a thing different from the joining structure | tissue formed in FIG. 4 (a), (b). In the brazing method, a liquid phase braze fills the joint to form a fillet, so that a eutectic structure different from the surrounding is formed in the joint. Also, in the welding method, since the joint portion is locally melted, the metal structure is different from other portions. On the other hand, in the joining method according to the present invention, the metal structure of the joint portion is composed of only the members to be joined, or the joint structure is formed by integrating both the members to be joined. It differs from the welded joint structure.

  Due to such joining behavior, the shape change in the vicinity of the joining site hardly occurs after the joining process. That is, the shape change after joining like the bead of the welding method and the fillet in the brazing method hardly occurs in the joining method according to the present invention. In spite of this, joining by metal bonding is possible as in the welding method and the brazing method. For example, when a drone cup type laminated heat exchanger is assembled using a brazing sheet made of aluminum alloy (a brazing material clad rate is 5% on one side), the molten brazing material concentrates at the joint after brazing heating. The height of the laminated heat exchanger is reduced by 5-10%. Therefore, it is necessary to consider the decrease in product design. In the present invention, since the dimensional change after bonding is 5% or less, a highly accurate product design is possible.

D. Difference between solidus temperature and liquidus temperature In the joining method according to the present invention, it is preferable that the difference between the solidus temperature and the liquidus temperature of the metal material generating the liquid phase is 10 ° C. or more. When the solidus temperature is exceeded, liquid phase generation begins, but if the difference between the solidus temperature and the liquidus temperature is small, the temperature range in which the solid and the liquid coexist is narrowed, and the amount of the generated liquid phase is controlled. Difficult to do. Therefore, this difference is preferably set to 10 ° C. or more. For example, binary alloys having a composition satisfying this condition include Al—Si alloys, Al—Cu alloys, Cu—Zn alloys, Cu—Sn alloys, Fe—C alloys, Ti—Al Alloy, Ni—Al alloy, Mg—Zn alloy and the like. In order to satisfy this condition, the eutectic type alloy is advantageous because it has a large solid-liquid coexistence region. However, even for other alloys such as all solid solution type, peritectic type, and monotectic type, good bonding is possible by setting the difference between the solidus temperature and the liquidus temperature to 10 ° C. or more. Become. Further, the above binary alloy can contain an additive element other than the main additive element, and substantially includes a ternary alloy, a quaternary alloy, and a multi-element alloy of more than five elements.
Note that the larger the difference between the solidus temperature and the liquidus temperature, the easier it is to control the amount of liquid phase. Therefore, there is no particular upper limit for the difference between the solidus temperature and the liquidus temperature.

E. Joining Method In the joining method of the present invention, the members to be joined are usually heated in a furnace. There is no restriction | limiting in particular in the shape of a furnace, For example, the continuous furnace etc. which have conveyance mechanisms, such as a batch furnace of a 1 chamber structure, and a belt, can be used. The atmosphere in the furnace is not limited, but it is preferably performed in a vacuum, an inert gas, or a reducing gas. Moreover, it is preferable that the time when the metal material that generates the liquid phase is equal to or higher than the solidus temperature is 20 minutes or less, more preferably 15 minutes or less during the bonding heating. If it exceeds 20 minutes, deformation due to the above-mentioned grain boundary sliding may occur.

  An oxide film is formed on the surface layer of the metal material, which inhibits bonding. Therefore, it is necessary to destroy the oxide film in joining. In the joining method according to the present invention, it is preferable to apply a flux to the joining surface in order to destroy the oxide film. Moreover, in order to suppress formation of an oxide film, it is preferable to join in non-oxidizing atmosphere gas, such as nitrogen.

  Below, this invention is demonstrated in detail based on an Example and a comparative example.

(Examples 1-20 and Comparative Examples 21-25)
Table 1 shows the composition of the Al—Si alloy used for joining (containing Si in an amount of 1.5 to 4.0 mass%). Table 1 also shows the equilibrium liquid phase ratio at each temperature of 580 to 640 ° C. The equilibrium liquid phase ratio is a value calculated by Thermo-Calc. After preparing the alloy ingot shown in Table 1, a rolled plate having a thickness of 1 mm was obtained by hot rolling and cold rolling. This rolled plate was cut out and the end surfaces of which were smoothed by a milling cutter were combined to produce a joining test piece shown in FIG. An aluminum alloy plate having a composition shown in Table 1 was used for the upper and middle plates of the test piece, and a pure aluminum plate (A1070) was used for the lower plate. The upper and middle aluminum alloy plates have the same composition. These examples are joining of aluminum alloy materials having the same composition. Fluoride-based non-corrosive flux was applied to the bonding surface of this bonding test piece. As shown in FIG. 5 (a), a middle plate and an upper plate were sequentially stacked on the lower plate, and a ceramic plate jig having a plate thickness of 1 mm was arranged above and below the superposed plate. Next, as shown in FIG. 5 (b), the upper and lower stainless steel plates and the two stainless steel wires are bridged on the side surface, the ends are tied together, and the test piece consisting of the lower plate, the middle plate and the upper plate is fixed. A sample was used. In addition, the number described in FIG. 5A represents the dimension (unit: mm) of the member.

  The sample was heated to a predetermined temperature (580 to 635 ° C.) in a nitrogen atmosphere and held at that temperature for 2 minutes, and then naturally cooled at room temperature. The nitrogen atmosphere was controlled at an oxygen concentration of 100 ppm or less and a dew point of −45 ° C. or less. The heating rate was 10 ° C./min at 520 ° C. or higher.

The test piece after joining was cut so that an observation cross section shown in FIG. As shown in FIG. 6B, the upper plate and the middle plate are joined by the joint 1 and the joint 2. A partially enlarged view of the joint 1 (2) is shown in FIG. A portion where the joining interface is not seen between the upper plate and the middle plate is a joined portion, and a portion where the joining interface (horizontal line in the figure) is seen is an unjoined portion which is not joined. The joining rate is defined by the following formula (2).
Joining rate (%) = {(L1 + L2) / 2L0} × 100 (2)
Here, L1 is the length of the part joined in the joint part 1, L2 is the length of the part joined in the joint part 2, and L10 is the length to be joined in the joint part 1 and the joint part 2, respectively. That's it.

FIG. 6D shows the ceiling of the test piece. a is the length before joining the ceiling part of the test piece, a1 is the bending length after joining the upper part of the ceiling part of the test piece, and a2 is the bending length after joining the lower part of the ceiling part of the test piece. The deformation rate defined by the following formula (3) was taken as the dimensional change after joining with respect to before joining.
Deformation rate (%) = {(a1 + a2) / 2a} × 100 (3)

  A joining rate of 95% or more was judged as ◎, 90% or more and less than 95% as ○, 25% or more and less than 90% as Δ, and less than 25% as ×. Further, the deformation rate of 3% or less was evaluated as ◎, 3% and 5% or less as ◯, 5% and 8% or less as Δ, and 8% or more as ×.

  Based on the above results, for each evaluation judgment, ◎ is given 5 points, ○ is 3 points, △ is 0 points, × is -5 points, and the total score is 10 points ◎, 6 points to 9 points The following was comprehensively judged as ◯, from 1 to 5 points as Δ, and from 0 points or less as ×. In the comprehensive judgment, ◎, ○, and △ were accepted, and x was rejected. Table 2 shows the joining conditions (calculated values of temperature and equilibrium liquid phase ratio) and test results.

  In Examples 1-20, since the liquid phase rate in the aluminum alloy material at the time of joining heating was in an appropriate range, favorable joining was made and the comprehensive judgment was acceptable. In particular, in Examples 3, 8, 12, 13, 15, and 16 having a liquid phase ratio of 10 to 20%, the deformation was very small and a high bonding rate was obtained.

In Comparative Example 21, since no liquid phase was generated, bonding was not performed.
In Comparative Examples 22 to 25, since the liquid phase ratio was too high, large deformation occurred and the comprehensive judgment was rejected.

(Examples 26-40 and Comparative Examples 41-50)
Instead of the Al—Si alloy shown in Table 1, the joining rate and the deformation rate were tested in the same manner as in Examples 1-20 and Comparative Examples 21-25 using a metal material having the composition shown in Table 3. That is, also in these examples, the metal material plates of the upper plate and the middle plate have the same composition and are joining of metal materials having the same composition.

  The test piece was bonded by heating at a predetermined bonding temperature for 3 minutes in a mixed atmosphere of hydrogen and nitrogen.

  Table 4 shows joining conditions (joining temperature, calculated value of equilibrium liquid phase ratio) and test results. In addition, calculation of an equilibrium liquid phase rate, calculation of a joining rate, and a deformation rate are the same as that of Examples 1-20 and Comparative Examples 21-25.

  In Examples 26-40, since the liquid phase ratio in the metal material at the time of joining heating was in an appropriate range, favorable joining was made, and the comprehensive judgment was acceptable.

In Comparative Examples 41, 43, 45, 47, and 49, since the bonding temperature was not higher than the solidus temperature, no liquid phase was generated and bonding was not performed.
In Comparative Examples 42, 44, 46, 48, and 50, since the liquid phase to be generated was excessive, the shape of the member to be joined could not be maintained and was greatly deformed. In particular, in Comparative Example 48, the shape completely collapsed, and it was impossible to measure the joining rate.

  According to the present invention, a highly reliable joining method of a metal material with good joining properties and almost no deformation due to joining is achieved, and the industrial value is great.

a ··· length before joining the ceiling of the test piece a1 ·· curved length after joining the upper side of the ceiling of the test piece a2 ·· curving length after joining the lower side of the ceiling of the test piece c1 ·· Si Concentration c2 ·· Si concentration T ·· Temperature above T1 ·· Te Temperature higher than T2 ·· T1 Temperature above T3 ·· Ts2 Te ·· Solidus temperature Ts2 ·· Solidus temperature

Claims (4)

  In the method of joining the one member to be joined and the other member to be joined, using the metal material as one member to be joined and using either the same metal material or another metal material as the other member to be joined, Joining at a temperature at which the ratio of the mass of the liquid phase generated in the metal material to the total mass of the metal material as one of the members to be joined exceeds 0% and is 35% or less .   The metal material joining method according to claim 1, wherein a difference between the solidus temperature and the liquidus temperature is 10 ° C. or more in the metal material that is the one member to be joined.   The metal material joining method according to claim 1 or 2, wherein in the metal material as the one member to be joined, a dimensional change after joining with respect to before joining is 5% or less. The metallic material is Al alloy, Cu-based alloys, Fe-based alloys, Ni-based alloys, Ti-based alloy, an Mg-based alloy, the joining method of the metal material according to claim 1.

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