JP2018029090A - Dissimilar metal joint structure, manufacturing method thereof, and water-cooled power conversion element including the same - Google Patents

Abstract

Disclosed are a dissimilar metal joining structure capable of joining various dissimilar metals to each other while having sufficient joining strength, a method for manufacturing the same, and a water-cooled power conversion element including the same. A heat transfer plate 1 made of aluminum, a plating layer 2 formed on the heat transfer plate 1 and made of nickel, and formed between the heat transfer plate 1 and the plating layer 2, aluminum An intermetallic compound layer 5 formed by alloying nickel and nickel, and a mixed molten and solidified portion 4 formed on the plating layer 2 and mixed and melted with nickel copper are in a direction perpendicular to the heat transfer plate 1. A dissimilar metal junction structure 100 including a laminated structure 6 formed by laminating a plurality of layers is used. [Selection] Figure 3

Description

  The present invention relates to a dissimilar metal joint structure, a manufacturing method thereof, and a water-cooled power conversion element including the same.

  When different kinds of metals are joined to each other, an intermetallic compound (alloy) formed by joining different kinds of metals may be formed at the joining interface (joined portion). And when this intermetallic compound is brittle, since there is little elongation, the fall of fatigue strength and the strength fall by a crack may arise. Therefore, a technique described in Patent Document 1 is known as a technique for improving the reliability of the bonding interface between different metals.

  Patent Document 1 describes providing a power module with a high reliability of the joint. Specifically, the power module is configured by sequentially laminating an underlying conductive member formed by a thermal spraying method, a solder layer, and a semiconductor chip on a metal wiring made of a first material. Of these, the underlying conductive member is formed by injecting a particle group of the first material and a particle group of the second material having a smaller thermal expansion coefficient than the first material. In addition, since an underlying conductive member having a smaller thermal expansion coefficient than the metal wiring is interposed between the metal wiring and the solder layer, thermal stress caused by the difference in thermal expansion coefficient between the upper and lower members applied to the solder layer Is relaxed and the generation of cracks in the solder layer is suppressed.

JP 2008-300455 A

  In the technique described in Patent Document 1, an insulating resin layer made of an epoxy resin is formed between a metal wiring made of copper or the like and a heat sink made of aluminum or the like. However, usually, the bonding strength between the metal and the resin tends to be weak. Therefore, it is preferable that the structure made of, for example, copper and the structure made of, for example, aluminum are directly joined without using an epoxy resin or the like.

  However, according to the study by the present inventors, it has been found that when aluminum and copper are simply joined, an intermetallic compound composed of aluminum and copper is formed at the joining interface. And since this intermetallic compound was brittle, it turned out that a crack etc. are easy to generate | occur | produce easily in the joining interface. That is, in Patent Document 1, when a metal wiring made of copper or the like and a heat sink made of aluminum or the like are simply joined, a brittle intermetallic compound is formed at the joining interface, resulting in insufficient joining strength. I found out that Therefore, in the technique described in Patent Document 1, when different kinds of metals are joined together, the joining strength may be insufficient depending on the combination of metals to be joined.

  The present invention has been made in view of such problems, and the problem to be solved by the present invention is to dissimilar metal joints capable of joining various dissimilar metals to each other while having sufficient joint strength. The object is to provide a structure, a manufacturing method thereof, and a water-cooled power conversion element including the structure.

  In order to solve the above problems, the present inventors have conducted intensive studies. As a result, the following findings were found. That is, the dissimilar metal joining structure of the present invention includes a metal base composed of a first metal, a coating layer formed on the metal base and composed of a second metal, and the metal base. And an intermetallic compound layer formed by alloying the first metal and the second metal, and formed on the coating layer. A mixed molten and solidified portion obtained by mixing and melting three metals is provided with a stacked structure in which a plurality of layers are stacked in a direction perpendicular to the metal substrate.

  Further, in the method for producing a dissimilar metal bonded structure according to the present invention, the metal first disposing step of disposing a third metal on the metal substrate on which the coating layer composed of the second metal is formed, The third metal and the second metal are mixed and melted by irradiating the third metal with laser light from the side of the third metal arranged in the first metal arrangement step. The mixed molten and solidified part is formed, and the second metal that constitutes the coating layer and the first metal that constitutes the metal base material are alloyed by heat generated by the irradiation of the laser beam to form an intermetallic By repeating the mixed melting / alloy layer forming step of forming a compound layer and the mixed melting / alloy layer forming step a plurality of times, a plurality of the mixed molten solidified portions are stacked in a direction perpendicular to the metal substrate. Form a laminated structure A layering step of, is intended to include.

  Furthermore, the water-cooled power conversion element of the present invention includes a metal substrate composed of a first metal, a coating layer formed on the metal substrate and composed of a second metal, and the metal substrate. An intermetallic compound layer formed by alloying the first metal and the second metal formed between the coating layer, and the second metal and the third metal layer formed on the coating layer. A heterogeneous metal joining structure comprising: a laminated structure in which a plurality of mixed molten and solidified portions obtained by mixing and melting a plurality of metals are stacked in a direction perpendicular to the metal substrate; and the metal member A power conversion element that is in thermal contact, and the laminated structure is in contact with a refrigerant that cools the power conversion element.

  According to the present invention, it is possible to provide a dissimilar metal joining structure capable of joining various dissimilar metals to each other while having sufficient joining strength, a manufacturing method thereof, and a water-cooled power conversion element including the same. it can.

It is the perspective view which extracted a part of water-cooled power conversion element provided with the dissimilar metal junction structure of this embodiment. It is sectional drawing of a water-cooled power converter element provided with the dissimilar metal junction structure of this embodiment. It is the A section enlarged view of Drawing 2, and is the figure which expanded and showed the neighborhood of the layered structure in the dissimilar metal junction structure of this embodiment. It is sectional drawing after apply | coating copper powder to a heat exchanger plate. FIG. 5 is a cross-sectional view showing a state where a desired position is irradiated with laser light in the state shown in FIG. 4. It is sectional drawing which showed a mode that it irradiates each time shifting the irradiation position of a laser beam little by little, and irradiates the laser beam of the 5th time. It is sectional drawing after apply | coating the copper powder for forming the mixed melt solidification part of the 2nd layer. It is sectional drawing which shows the state which has irradiated the laser beam to the position used as the starting point for forming the mixed melt solidification part of the 2nd layer in the state shown in FIG. It is sectional drawing which shows a mode that the laser beam for forming the last mixed melt solidification part which comprises a laminated structure is irradiated after irradiating several times, shifting the irradiation position of a laser beam. It is sectional drawing of the cooling metal mold | die which is another embodiment to which the dissimilar metal joining structure of this embodiment is applied.

  Hereinafter, a form for carrying out the present invention (this embodiment) will be described with reference to the drawings as appropriate.

  FIG. 1 is a perspective view of a part of a water-cooled power conversion element 110 provided with a dissimilar metal joint structure 100 according to this embodiment. That is, FIG. 1 shows the dissimilar metal junction structure 100 and the power conversion element 10 joined thereto, which constitute the water-cooled power conversion element 110. The dissimilar metal joining structure 100 includes a heat transfer plate 1 (metal substrate), a plating layer 2 (coating layer), and water-cooled fins 11 (corresponding to the laminated structure 6 shown in FIG. 3 and the like). Is done. A power conversion element 10 (inverter) is joined to the heat transfer plate 1. The current conversion element 10 is an element that converts a direct current into an alternating current or converts an alternating current into a direct current.

  Although details will be described later with reference to FIG. 2, water 12 (see FIG. 2) is in contact with the water-cooled fins 11. Thereby, the heat generated by the current conversion by the power conversion element 10 is transferred to the heat transfer plate 1, the plating layer 2, and the water-cooled fins 11 to be dissipated to the water, thereby cooling the power conversion element 10. It is like that.

  FIG. 2 is a cross-sectional view of the water-cooled power conversion element 110 including the dissimilar metal junction structure 100 of the present embodiment. In FIG. 2, in order to simplify the illustration, some of the members such as the terminals of the current conversion element 10 are omitted. In the water-cooled power conversion element 110, a dissimilar metal joint structure 100 including the radiator plate 1, the plating layer 2, and the water-cooled fin 11 (laminated structure 6) is surrounded by an aluminum case 15 and an aluminum lid 16. And between the plating layer 2 and the aluminum lid | cover 16, the water 12 flows in the paper surface back direction.

  Also, a lap weld 13 is formed between the aluminum case 15 and the heat transfer plate 1 by laser welding in order to prevent leakage of water 12 to the current conversion element 10. Further, a butt weld 14 is also formed by laser welding at the joint between the aluminum case 15 and the aluminum lid 16 in order to prevent the water 12 from leaking to the outside. In any of the lap welds 13 and the butt welds 14, since the same metal (aluminum) is welded, sufficient joint strength is ensured.

  In this embodiment, the heat transfer plate 1 is made of aluminum (first metal), the plating layer 2 is made of nickel (second metal), and the water-cooled fins 11 are made of copper (third metal). ing. As described above, in the heat transfer plate 1 having a relatively large volume in the dissimilar metal joint structure 100, the weight reduction is achieved by using a light metal such as aluminum. In addition, since the plating layer 2 is made of nickel, the manufacturing cost is reduced because the plating layer 2 is easily formed using a plating method. Furthermore, since the water-cooled fin 11 occupies a relatively small volume in the dissimilar metal joint structure 100, heat dissipation to water can be further improved by using copper having higher heat conductivity than aluminum. Yes.

  That is, by providing the plating layer 2, it is possible to dispose the copper water-cooled fins on the aluminum heat transfer plate 1, which is difficult because the conventional technique has a problem in the bonding strength. As described above, since copper is excellent in thermal conductivity, by configuring the water-cooled power conversion element 110 in this manner, the heat dissipation of the power conversion element 10 can be enhanced as compared with the conventional case, and the durability of the power conversion element 10 is improved. Can be improved.

  Moreover, in the water-cooled power conversion element 110, aluminum and copper which are different metals are joined through the plating layer comprised with a metal, without using conventional resin etc. Therefore, the thermal conductivity between aluminum and copper is remarkably excellent as compared with the case of using a resin. Therefore, also in this respect, the heat dissipation of the power conversion element 10 can be further enhanced as compared with the conventional case, and the durability of the power conversion element 10 can be further improved.

  FIG. 3 is an enlarged view of a portion A in FIG. 2, and is an enlarged view showing the vicinity of the laminated structure 6 in the dissimilar metal bonded structure 100 of the present embodiment. As shown in FIG. 3, the laminated structure 6 (corresponding to the cooling fin 11 in FIG. 1) has a plurality of mixed molten and solidified portions 4 laminated in a direction perpendicular to the heat transfer plate 1 (hereinafter referred to as “vertical direction”). It will be. In the present embodiment, the mixed molten and solidified portion 4 is formed by laminating eight layers in the vertical direction. Therefore, when the cross section of the laminated structure 6 is observed with an electron microscope, the metal structure is not a uniform cross section (no interface is observed) in the cross section of the laminated structure 6. It can be confirmed that eight layers of metal structure are laminated (deposited).

  As described above, in the present embodiment, the plating layer 2 is made of nickel, and the laminated structure 6 is made of copper. However, details will be described later while explaining the manufacturing method of the dissimilar metal bonded structure 100, but in the laminated structure 6, the copper powder disposed on the surface of the plating layer 2 and the nickel in the plating layer 2 are mixed. It is melted. Therefore, in the laminated structure 6, the nickel content increases and the copper content decreases as the mixed molten and solidified portion 4 present in the vicinity of the plating layer 2. On the other hand, the content of nickel decreases and the content of copper increases as the mixed molten and solidified portion 4 is separated from the plating layer 2. As described above, in the laminated mixture 6, the concentrations of nickel and copper contained in the plating layer 2 gradually change as the distance from the plating layer 2 increases. That is, the content of nickel and copper has a gradient composition. Thereby, the residual stress at the time of solidification of the laminated structure 6 is reduced, and the strength of the laminated structure 6 is improved.

  Nickel constituting the plating layer 2 and copper disposed on the surface of the plating layer 2 are a combination of dissimilar metals that are simply mixed without being alloyed. As described above, some alloys (intermetallic compounds) in which different metals are alloyed are brittle. Therefore, by forming the mixed molten and solidified portion 4 that is simply mixed without being alloyed, the bonding strength between different metals can be improved. However, it does not completely exclude that an alloy in which different kinds of metals are alloyed is included in the mixed melt-solidified portion 4, and if at least a part (preferably all) of the different kinds of metals are melt-mixed. Sufficient bonding strength is maintained.

  Further, between the heat transfer plate 1 and the plating layer 2, and below the laminated structure 6, there is an intermetallic between the aluminum contained in the heat transfer plate 1 and the nickel contained in the plating layer 2. A compound layer 5 is formed. And in the part other than the downward direction of the laminated structure 6, the heat exchanger plate 1 and the plating layer 2 are directly joined. The intermetallic compound layer 5 formed between the heat transfer plate 1 and the plating layer 2 is made of an aluminum-nickel alloy. This is because the heat given by the laser beam when forming the mixed molten and solidified portion 4 is transmitted through the inside of the plating layer 2 and reaches the heat transfer plate 1. That is, this is because nickel in the plating layer 2 and aluminum in the heat transfer plate 1 react with each other at the bonding interface due to heat transmitted through the inside of the plating layer 2, and nickel and aluminum are alloyed. Therefore, the intermetallic compound layer 5 is formed below the laminated structure 6.

  In the present embodiment, the plating layer 2 that is a coating layer is formed by a plating method from the viewpoint of easy formation of a thin film having a uniform thickness, manufacturing cost, and the like. Whether or not the coating layer is formed by a plating method can be confirmed by observing a cross section of the coating layer with an electron micrograph. That is, when the coating layer is the plating layer 2 formed by the plating method, the cross section of the plating layer 2 is observed as a uniform state with no metal structure interface.

  In the present embodiment in which the coating layer is the plating layer 2, the bonding strength between the heat transfer plate 1 and the plating layer 2 is relatively low. However, the joint strength between the heat transfer plate 1 and the plating layer 2 is increased by forming the intermetallic compound layer 5 in parallel with the formation of the mixed molten and solidified portion 4. That is, the nickel-aluminum alloying causes a nickel-aluminum alloy diffusion bonding between the heat transfer plate 1 and the plating layer 2. Thereby, the heat exchanger plate 1 and the plating layer 2 will be joined metallically, and these joint strengths will improve. Therefore, sufficient bonding strength can be obtained even with the plating layer 2 formed by a plating method selected based on manufacturing cost and ease of formation.

  The nickel-aluminum alloy may become a brittle compound. However, since the intermetallic compound layer 5 is formed by the heat transferred during the formation of the mixed molten and solidified portion 4, the amount of the compound generated is not so large. Moreover, since the intermetallic compound layer 5 to be formed is also extremely thin, a decrease in bonding strength due to a brittle compound is sufficiently suppressed.

  As described above, in the present embodiment, the plating layer 2 is made of nickel (second metal), and the mixed molten solidified portion 4 and the laminated structure 6 (the plating layer 2 is disposed on the surface). Metal powder) is made of copper (third metal). However, the second metal and the third metal are not limited to these. However, it is preferable that at least one of the second metal and the third metal is a complete solid solution. Moreover, it is more preferable that both of the second metal and the third metal are a solid solution. It is because a brittle intermetallic compound is not formed by using metals of all solid solutions. Specific examples of such a total solid solution include nickel and its alloys, copper and its alloys, iron and its alloys, and the like.

  Moreover, as a combination of the second metal and the third metal, a combination of a certain metal and an alloy containing the metal is also preferable. For example, the combination of aluminum and the alloy (aluminum alloy) containing aluminum, the combination of copper and the alloy (copper alloy) containing copper, etc. are mentioned. For example, in the former case, the second metal is aluminum and the third metal is an aluminum alloy.

  Further, the metal (first metal) contained in the heat transfer plate 1 is not particularly limited. However, when the first metal reacts with the third metal to form a brittle alloy, the effect of the present invention is particularly greatly exerted. Specifically, for example, the first metal is aluminum and the third metal is copper. Therefore, the metal contained in the heat transfer plate 1 may be appropriately set according to the type of metal contained in the laminated structure 6.

  Based on these points, combinations shown in Table 1 below can be considered as combinations of metals used for the heat transfer plate 1, the plating layer 2, and the laminated structure 6. However, the combinations shown in Table 1 are examples and are not limited to the combinations shown in Table 1. The first combination is the combination used in the above embodiment.

  There are no particular restrictions on the dimensions such as the thickness of the heat transfer plate 1, the plating layer 2, and the intermetallic compound layer 5, the size of the mixed molten and solidified portion 4, and the height of the laminated structure 6. For example, the thickness of the heat transfer plate 1 can be about 3 mm. Moreover, the thickness of the plating layer 2 can be about 40 μm, for example. Furthermore, the thickness of the intermetallic compound layer 5 can be set to, for example, 5 μm or less, more specifically, for example, about 0.8 μm from the viewpoint of obtaining sufficient bonding strength.

  Next, the manufacturing method of the laminated structure 6 (namely, the manufacturing method of a dissimilar metal junction structure) is demonstrated, referring FIGS. The manufacturing method of the laminated structure 6 is a so-called powder bed method.

  FIG. 4 is a cross-sectional view after applying copper powder (third metal) to the heat transfer plate 1. In FIG. 4, the spherical copper powder 3 manufactured by the atomizing method is arranged and fixed on the surface of the aluminum (first metal) heat transfer plate 1 on which the plating layer 2 of nickel (second metal) is formed. This is shown (third metal placement step). However, the copper powder 3 does not necessarily need to be fixed to the surface of the plating layer 2 and may be disposed on the surface of the plating layer 2. The plating layer 2 can be formed by, for example, an electroplating method. Moreover, confirmation of whether the plating layer 2 is formed by the plating method can be confirmed by observing the cross section of the plating layer 2 with an electron micrograph as described above.

  The magnitude | size of the copper powder 3 arrange | positioned and fixed to the surface of the plating layer 2 can be about 20 micrometers-about 50 micrometers as a particle size, for example. In addition, the thickness of the layer in which the copper powder 3 is arranged and fixed (the layer formed on the outer side of the plating layer 2) can be about 100 μm.

  FIG. 5 is a cross-sectional view showing a state where a desired position is irradiated with laser light in the state shown in FIG. Although not shown in FIG. 5, the laser light is emitted from the front side of the paper to the back side. By irradiation with laser light, the copper powder 3 and nickel on the surface of the plating layer 2 are melted, and after these are mixed, a mixed melt solidified portion 4 is formed by heat dissipation (for example, cooling) (mixed melt / alloy). Layer forming step). In particular, during heat dissipation, although nickel and copper are sufficiently mixed, copper having a relatively high specific gravity tends to move downward, while nickel having a relatively low specific gravity tends to move upward. Therefore, in the mixed melt solidification part 4, nickel tends to exist on the upper side and copper on the lower side.

  Further, since the plating layer 2 is a metal, part of the heat used for melting the copper powder 3 and the like reaches the bonding interface between the heat transfer plate 1 and the plating layer 2 through the plating layer 2. Then, since dissimilar metals are joined at this joining interface, melting of both metals starts from that portion, and these metals are alloyed. As a result, the intermetallic compound layer 5 is formed between the heat transfer plate 1 and the plating layer 2 and below the mixed melting and solidifying portion 4 (mixed melting / alloy layer forming step).

  After the start of the formation of the intermetallic compound layer 5, the melting range of each metal expands in the upward direction in the plating layer 2 and in the downward direction in the heat transfer plate 1 while heat transfer by laser light irradiation continues. It will be. Therefore, in the intermetallic compound layer 5, the aluminum concentration and the nickel concentration are almost the same in the vicinity of the center because they are alloyed, but the nickel concentration increases and the aluminum concentration decreases as the distance from the center increases upward. become. On the other hand, the aluminum concentration increases and the nickel concentration decreases with increasing distance from the vicinity of the center. Therefore, in FIG. 5 etc., the interface between the intermetallic compound layer 5 and the heat transfer plate 1 and the plating layer 2 is clearly shown for the convenience of illustration, but in reality, these interfaces cannot often be determined. .

  Thus, in this embodiment, laser light irradiation is performed under the condition that only the surface of the plating layer 2 and the copper powder 3 are melted. As a result, a strong mixed melt-solidified portion 4 formed by mixing nickel and copper is formed, and a dissimilar metal bonded structure 100 having excellent bonding strength is obtained. Further, part of the heat used during the generation of the mixed molten and solidified portion 4 is transmitted through the plating layer 2 to form the intermetallic compound layer 5. By forming the intermetallic compound 5, the bonding strength between the heat transfer plate 1 and the plating layer 2 can be increased. As described above, the intermetallic compound layer 5 is formed in addition to the mixed melt-solidified portion 4, thereby obtaining the dissimilar metal bonded structure 100 having sufficiently higher bonding strength than the conventional structure as a whole structure. Can do.

  On the other hand, if the laser beam irradiation is strong, the plating layer 2 may penetrate and melt, and the intermetallic compound layer 5 may not be formed. In this case, the heat transfer plate 1 is also melted, and aluminum and the copper powder 3 may react to form a brittle alloy. Therefore, in this embodiment, the laser beam may be irradiated under such a weak condition that both the surface of the plating layer 2 and the copper powder 3 can be melted.

  The thickness of the intermetallic compound layer 5 can be controlled by the temperature at the bonding interface between the heat transfer plate 1 and the plating layer 2 and the irradiation time of the laser beam. Specifically, if the irradiation time of the laser beam is long or the distance from the bonding interface between the heat transfer plate 1 and the plating layer 2 to the intermetallic compound layer 5 is short, a thick intermetallic compound layer 5 is generated. There is a tendency. Therefore, the structure of the intermetallic compound 5 can be controlled by the irradiation condition of the laser beam, the coating condition of the metal powder 3, the thickness of the plating layer 2, and the like.

  For example, when the thickness of the layer composed of copper powder 3 is 100 μm and the thickness of the plating layer 2 composed of nickel is 40 μm, a continuous oscillation fiber laser device capable of irradiating laser light with a wavelength of 1070 nm is used. By moving the two reflecting mirrors to scan the two-dimensional plane, the mixed molten solidified portion 4 and the intermetallic compound layer 5 can be formed. As irradiation conditions at this time, for example, the beam diameter Φ can be set to 100 μm, the scan speed can be set to 100 m / s, and the laser output can be set to 400 W.

  Moreover, it is preferable to perform irradiation of a laser beam in inert gas (for example, argon gas) from a viewpoint of preventing the oxidation of the metal fuse | melted in the middle of formation of the mixing melt solidification part 4. FIG. Thereby, the mixed melt solidification part 4 with few impurities (for example, oxide) can be formed.

  FIG. 6 is a cross-sectional view showing a state in which the laser beam is irradiated each time while the irradiation position of the laser beam is shifted little by little and the fifth laser beam is emitted. In the state shown in FIG. 5, the laser beam is irradiated from the near side to the far side of the paper surface. In FIG. 6, the irradiation position is shifted to the right by a total of 5 times and the laser beam is irradiated. It is shown. At the time of each irradiation, the laser beam is irradiated so that the formed mixed molten and solidified portions 4 are overlapped little by little.

  In addition, the initially formed mixed molten and solidified portion 4 shown in FIG. 5 was a mixture of aluminum and nickel, but the mixed molten and solidified portion 4 formed by the second and subsequent irradiations (for example, FIG. 6). In this state, the mixed molten and solidified portion 4 includes, in addition to aluminum and nickel, the components of the mixed molten and solidified portion 4 formed at the beginning shown in Fig. 5. Therefore, the mixing formed in the left-right direction is included. Since the melt-solidified part 4 is formed of the same component, a strong mixed melt-solidified part 4 without cracks is obtained.

  A new intermetallic compound layer 5 is formed in accordance with the new formation of the mixed molten and solidified portion 4. The alloy contained in the newly formed intermetallic compound layer 5 is alloyed together with the existing alloy. Therefore, the intermetallic compound layer 5 is integrally formed with no boundary, unlike the mixed molten and solidified portion 4 simply mixed. Usually, when the size (length in the left-right direction) of the laminated structure 6 (see FIG. 3) is increased, peeling from the heat transfer plate 1 is likely to occur. However, in the present embodiment, the intermetallic compound layer 5 that improves the bonding strength between the heat transfer plate 1 and the plating layer 2 is formed in accordance with the formation of the mixed molten and solidified portion 4 constituting the laminated structure 6. Therefore, even if the size of the laminated structure 6 is increased, sufficient bonding strength can be obtained.

  FIG. 7 is a cross-sectional view after applying the copper powder 3 for forming the second layer mixed melt solidification part 4. In FIG. 7, in the state shown in FIG. 6 (the state in which five mixed molten and solidified portions 4 are formed from the front side to the back side of the paper), another copper powder 3 is made in the same manner as in the state of FIG. The arrangement is fixed. That is, FIG. 7 shows a state in which the copper powder 3 is arranged and fixed on the mixed molten and solidified portion 4 formed in FIGS. 5 and 6 (third metal arranging step, laminating step).

  FIG. 8 is a cross-sectional view showing a state in which laser light is radiated to a position serving as a starting point for forming the second layer mixed melt solidification portion 4 in the state shown in FIG. This starting point is usually the same as the laser beam irradiation position (position shown in FIG. 5) of the mixed molten and solidified portion 4 formed at the beginning of the first layer (state shown in FIG. 6). By starting the laser beam irradiation at this position, the formation of the second layer of mixed molten and solidified portion 4 is started (lamination process). The laser light irradiation can be performed in the same manner as the conditions shown in FIG.

  FIG. 9 is a cross-sectional view showing a state in which the laser beam for forming the final mixed molten solidified portion constituting the laminated structure is irradiated after the irradiation is performed a plurality of times while shifting the irradiation position of the laser beam. It is. That is, the operation shown in FIG. 5 to FIG. 7 is repeated eight times to show a state in which eight layers of the mixed molten and solidified portion 4 are formed in the vertical direction. Thus, the laminated structure 6 is obtained by laminating | stacking the some mixing melt solidification part 4 to an up-down direction (lamination process). Then, by removing the unreacted copper powder 3 remaining on the surface of the plating layer 2 from the state shown in FIG. 9, the dissimilar metal bonded structure 100 shown in FIG. 3 is obtained.

  In the laminated structure 6 in which a plurality of the mixed molten and solidified portions 4 are laminated, as described above, the nickel concentration is the highest in the vicinity of the plating layer 2, and the nickel concentration gradually decreases toward the tip (upward). On the other hand, whenever one layer of the mixed molten and solidified portion 4 is formed in the vertical direction, the copper powder 3 is applied and fixed as shown in FIG. Therefore, the copper concentration in the vicinity of the plating layer 2 is the lowest, and the copper concentration gradually increases toward the tip (upward).

  Among these, the nickel concentration particularly decreases immediately toward the tip because the amount of nickel contained in the plating layer 2 does not change. On the other hand, since the copper powder 3 is newly arranged and fixed every time the laser beam is irradiated, the concentration of copper tends to rise relatively quickly toward the tip. Therefore, although it contains nickel, the laminated structure 6 in which most of the structure is made of copper is obtained.

  In the laminated structure 6, the composition changes in a gradient manner as described above (gradient composition). The thermal expansion coefficient gradually changes due to the gradient composition. Therefore, the residual stress at the time of solidification is reduced, deformation is reduced, and a high-strength dissimilar metal bonded structure 100 without cracks is obtained.

  As described above, for example, a dissimilar metal bonded structure 100 having high bonding strength is obtained by interposing the dissimilar metals, which are difficult to bond because they form a brittle compound such as aluminum and copper, through the plating layer 2. Can be manufactured. In particular, since bonding can be performed only with metal without using a resin or the like, the bonding strength can be sufficiently increased. And since the plating layer 2 used for joining can be appropriately selected according to each metal to be joined, dissimilar metals that were conventionally difficult to join from the viewpoint of joining strength should be joined with sufficient joining strength. Can do.

FIG. 10 is a cross-sectional view of a cooling mold 120 according to another embodiment to which the dissimilar metal bonding structure 100 of the present embodiment is applied. The cooling mold 120 (dissimilar metal joint structure) is an internal flow through which a mold molding part 25 (laminated structure) for molding a molten resin and water for cooling the mold molding part 25 flows. A path 22 and a base plate 21 (metal substrate) for transferring heat from the mold molding part 25 to water are provided.
The mold molding part 25 is formed by laminating the mixed melting and solidifying part 4 in the same manner as the laminated structure 6 described above, but in FIG. 10, the mold molding part 25 is shown as being uniform for the sake of illustration. In addition, the boundary between the mold molding part 25 and the mixed melting and solidifying part 4 is clearly shown.

  On the base plate 21, the plating layer 2 is formed. An intermetallic compound 5 is formed between the base plate 21 and the plating layer 2. In addition, a mold molding part 25 is formed on the plating layer 2. A mixed molten and solidified portion 4 is formed between the plating layer 2 and the mold forming portion 25.

  In the cooling mold 120, the metal (first metal) constituting the base plate 21 is copper having high thermal conductivity in order to promote heat removal by water cooling. Moreover, the metal (2nd metal) which comprises the plating layer 2 is nickel similarly to the said water cooling power conversion element 110. FIG. And the metal (3rd metal) which comprises the metal mold | die molded part 25 is maraging steel. Maraging steel is an iron-based alloy containing nickel, cobalt, and the like. These combinations are the sixth combination in Table 1 above.

  Nickel is industrially inexpensive and does not form a brittle compound even when melted with maraging steel. And since maraging steel is high intensity | strength, since the lifetime is long as a resin molding metal mold | die, it selected as the material of the metal mold | die molding part 25. FIG.

  Here, the melting point of copper and the melting point of maraging steel are greatly different. Therefore, if the copper base plate 21 is simply joined to the die-molded portion 25 made of maraging steel, a crack occurs at the joining interface, and the joining strength is reduced. Therefore, if it is a conventional method, the mold forming part 25 cannot be directly formed on the base plate 21. Therefore, a reliable cooling mold 120 can be obtained through the plating layer 2.

  The cooling mold 120 can be manufactured basically in the same manner as the water-cooled power conversion element 110 described above. Therefore, in the following description, a method for manufacturing the cooling mold 120 will be described mainly with a point different from the method for manufacturing the water-cooled power conversion element 110 described above.

  First, a nickel plating layer 2 (thickness of about 30 μm) is formed on a base plate 21 (thickness of about 20 mm) on which the water cooling channel 22 is formed. Then, a metal powder of maraging steel (particle size of about 20 μm to 40 μm, average particle size of about 30 μm, not shown) is applied on the plating layer 2. This metal powder can be manufactured by, for example, a gas atomizing method. Thereafter, by irradiating laser light from the side of the maraging steel, the mixed molten solidified portion 4 that is a mixture of nickel and maraging steel is formed. Along with this, an intermetallic compound layer 5 composed of an alloy made of copper and nickel is formed.

  The laser light irradiation conditions can be as follows. That is, from the viewpoint of preventing metal oxidation during the melting and solidification process, the laser beam is irradiated in a nitrogen atmosphere. The beam diameter of the laser beam is 100 μm, the laser output is 200 W, and the laser scan speed can be 100 m / s. Further, a continuous wave fiber laser having a wavelength of 1070 nm can be used as the laser light.

  However, in the cooling mold 120, unlike the cooling power conversion element 110 described above, the size (height in the vertical direction) of the mold forming portion 25 that is the laminated structure 6 is not uniform. That is, as shown in FIG. 10, it is thin near the center of the mold molding part 25 and thick near both ends. Therefore, when the cooling mold 120 is manufactured, the amount and number of maraging steel applied in the vicinity of the center and the number of times of laser light irradiation are small, while these are increased in the vicinity of both ends. That is, in the manufacture of the cooling mold 120, the molding part 25 having a thickness larger than that in the vicinity of the center can be formed by repeating the application of maraging steel and laser irradiation more frequently in the vicinity of both ends. By doing in this way, the metal mold | die molded part 25 (laminated structure 6) used as a desired shape can be formed. Moreover, the die-molding part 25 of the maraging steel which hardly contains nickel can be manufactured in the upper part.

  The cooling mold 120 thus manufactured can be made into a mold having excellent strength by the mold forming part 25 made of maraging steel. On the other hand, since the copper base plate 21 is provided, the heat transfer performance by copper is excellent, and the cooling effect of the mold molding part 25 can be enhanced. In particular, the base plate 21 and the mold molding part 25 are connected only by metal. Therefore, the good heat transfer performance of copper can be exhibited to the maximum, and the cooling mold 120 excellent in cooling performance can be manufactured. Further, in the mixed melt solidification part 4 and the mold molding part 25, the composition of nickel and maraging steel is a gradient composition, like the cooling power conversion element 110 described above. Therefore, since the thermal expansion coefficient also changes in accordance with the change in composition, the residual stress due to the thermal expansion difference between different metals is reduced. Thereby, the metal mold part 25 can be joined with high strength.

  As mentioned above, although embodiment which implements this invention was described giving two specific examples, this embodiment is not limited to the said example at all.

  For example, in each of the embodiments described above, the plating layer 2 formed by the plating method is formed as the coating layer, but the coating layer may be a layer formed by a cold spray method. In the cold spray method in this case, a second metal (such as nickel) is caused to collide with the metal substrate at a melting temperature or lower to form a layer composed of the second metal. By forming the coating layer using the cold spray method, a coating layer thicker than the thickness of the plating layer 2 formed by the plating method can be formed. By forming the coating layer thickly, the distance from the position where the laser light is irradiated (that is, the position where the mixed molten and solidified portion 4 is formed) to the position where the intermetallic compound layer 5 is formed can be increased. it can. Thereby, it becomes difficult to transmit the heat by irradiation of a laser beam, and the comparatively thin intermetallic compound layer 5 can be formed.

  Whether or not the coating layer is formed by the cold spray method can be determined by observing a cross section of the coating layer with an electron microscope. That is, when the cross section is observed with an electron microscope, the second metals are deposited in a flat shape, that is, if the structure of the second metal is not uniform and the interface between the metal structures can be confirmed, It can be determined that the coating layer was formed by a cold spray method.

  Further, the coating layer can be formed by, for example, a thermal spraying method other than the plating method and the cold spray method. When forming a coating layer by a thermal spraying method, the 2nd metal which comprises a coating layer will collide with a metal base material in the molten state. The second metals after colliding tend to join. Therefore, when the cross section is observed using an electron microscope, the second metal structure can be observed, but the interface between the metal structures is slightly blurred as compared with the case where the second metal structure is formed by the cold spray method. Therefore, whether the coating layer is formed by the cold spray method or the thermal spray method can be determined from the state of the interface between the metal structures.

  Further, the coating layer may be formed using a clad material, for example. The clad material is obtained by pressing the second metal, but the state of the metal structure in the cross section observed by an electron microscope is different from the cold spray method or the thermal spray method in which the second metal collides. Therefore, in this way, it can be determined whether or not the coating layer is formed using a clad material.

  In each of the above-described embodiments, the laser beam is used to form the mixed molten and solidified portion 4, but an electron beam may be used instead of the laser beam. In addition to these, any method may be used as long as it can form the mixed melt-solidified portion 4 and the intermetallic compound layer 5.

  Further, in each of the above-described embodiments, the third metal (copper or maraging steel) is arranged and fixed every time the laser beam is irradiated, but these may be arranged and fixed each time the laser beam is irradiated. Good. That is, for example, by adjusting the focus of a laser beam or the like using a three-dimensional printer or the like, for example, it is possible to form a laminated structure 6 having an arbitrary shape in the third metal arranged only once at the beginning. it can. In this case, the third metal placement step is performed only once, and the mixed melting / alloy layer forming step is performed a plurality of times. Therefore, in this embodiment, the mixed melting / alloy layer forming step is repeatedly performed, while the third metal arranging step is performed once or a plurality of times (repeatedly).

1 Heat transfer plate (metal substrate)
2 Plating layer (coating layer)
3 Metal powder (third metal)
4 Mixed Melting and Solidifying Portion 5 Intermetallic Compound Layer 6 Laminated Structure 10 Current Conversion Element 11 Water-Cooled Fin (Laminated Structure)
12 Water (refrigerant)
13 Lap welded portion 14 Butt welded portion 15 Aluminum case 16 Aluminum lid 21 Base plate (metal base)
22 Water-cooled channel 25 Molding part (laminated structure)
100 Dissimilar metal joint structure 110 Water-cooled power conversion element (dissimilar metal joint structure)
120 Cooling mold (dissimilar metal joint structure)

Claims (11)

A metal substrate composed of a first metal;
A coating layer formed on the metal substrate and composed of a second metal;
An intermetallic compound layer formed between the metal substrate and the coating layer, wherein the first metal and the second metal are alloyed;
A laminated structure in which a plurality of mixed molten and solidified portions formed on the coating layer and mixed and melted with the second metal and the third metal are stacked in a direction perpendicular to the metal substrate. A dissimilar metal joint structure characterized by comprising:   The concentration of the second metal contained in the mixed melt-solidified portion is gradually decreased as the distance from the metal substrate is increased in the mixed melt-solidified portion. Dissimilar metal joint structure.   The dissimilar metal joint structure according to claim 1, wherein the coating layer is formed by a plating method.   The dissimilar metal bonding structure according to claim 1, wherein the coating layer is formed by a cold spray method. The intermetallic compound layer is formed between the metal substrate and the coating layer below the laminated structure,
3. The dissimilar metal bonded structure according to claim 1, wherein the metal substrate and the coating layer are in direct contact with each other at a portion other than the lower side of the laminated structure.   3. The dissimilar metal junction structure according to claim 1, wherein the second metal and the third metal are all solid solutions. 4. The first metal is aluminum;
The second metal is nickel;
The dissimilar metal bonding structure according to claim 1 or 2, wherein the third metal is copper. A third metal disposing step of disposing a third metal on the metal substrate on which the coating layer composed of the second metal is formed;
The third metal and the second metal are mixed and melted by irradiating the third metal with laser light from the third metal side arranged in the third metal arranging step. Forming a mixed melt solidified portion and alloying the second metal constituting the coating layer and the first metal constituting the metal substrate by heat generated by the irradiation of the laser beam. A mixed melting / alloy layer forming step of forming an intermetallic compound layer;
A lamination step of forming a laminated structure in which a plurality of the mixed molten and solidified portions are laminated in a direction perpendicular to the metal base by performing a third metal arranging step and the mixed melting / alloy layer forming step, respectively. The manufacturing method of the dissimilar metal joining structure characterized by including these. In the mixed melting / alloy layer forming step,
The intermetallic compound layer is formed between the metal substrate and the coating layer below the mixed melt-solidified part,
The manufacturing method for a dissimilar metal joint structure according to claim 8, wherein the metal base and the coating layer are in direct contact with each other at a portion other than the lower portion of the mixed molten and solidified portion. Method.   The method for producing a dissimilar metal junction structure according to claim 8 or 9, wherein the second metal and the third metal are all solid solutions. A metal substrate composed of a first metal;
A coating layer formed on the metal substrate and composed of a second metal;
An intermetallic compound layer formed between the metal substrate and the coating layer, wherein the first metal and the second metal are alloyed;
A laminated structure in which a plurality of mixed molten and solidified portions formed on the coating layer and mixed and melted with the second metal and the third metal are stacked in a direction perpendicular to the metal substrate. A dissimilar metal joint structure comprising:
A power conversion element in thermal contact with the metal member,
A water-cooled power conversion element, wherein the laminated structure is in contact with a refrigerant that cools the power conversion element.

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