Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
  • F28F21/081—Heat exchange elements made from metals or metal alloys
  • F28F21/084—Heat exchange elements made from metals or metal alloys from aluminium or aluminium alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
  • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering or brazing
  • B23K35/0233—Sheets or foils
  • B23K35/0238—Sheets or foils layered
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/24—Selection of soldering or welding materials proper
  • B23K35/28—Selection of soldering or welding materials proper with the principal constituent melting at less than 950°C
  • B23K35/286—Al as the principal constituent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B32—LAYERED PRODUCTS
  • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
  • B32B15/00—Layered products comprising a layer of metal
  • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
  • B32B15/016—Layered products comprising a layer of metal all layers being exclusively metallic all layers being formed of aluminium or aluminium alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/10—Alloys based on aluminium with zinc as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
  • C22C21/14—Alloys based on aluminium with copper as the next major constituent with silicon
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
  • F28F21/089—Coatings, claddings or bonding layers made from metals or metal alloys
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
  • F28F3/02—Elements or assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with recesses, with corrugations
  • F28F3/025—Elements or assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with recesses, with corrugations the means being corrugated, plate-like elements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F3/00—Plate-like or laminated elements; Assemblies of plate-like or laminated elements
  • F28F3/12—Elements constructed in the shape of a hollow panel, e.g. with channels
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W40/00—Arrangements for thermal protection or thermal control
  • H10W40/01—Manufacture or treatment
  • H10W40/03—Manufacture or treatment of arrangements for cooling
  • H10W40/037—Assembling together parts thereof
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W40/00—Arrangements for thermal protection or thermal control
  • H10W40/20—Arrangements for cooling
  • H10W40/25—Arrangements for cooling characterised by their materials
  • H10W40/258—Metallic materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10W—GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
  • H10W40/00—Arrangements for thermal protection or thermal control
  • H10W40/40—Arrangements for thermal protection or thermal control involving heat exchange by flowing fluids
  • H10W40/47—Arrangements for thermal protection or thermal control involving heat exchange by flowing fluids by flowing liquids, e.g. forced water cooling
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2275/00—Fastening; Joining
  • F28F2275/04—Fastening; Joining by brazing

Definitions

• the invention relates to a heat exchanger that is mounted in an electric automobile or a hybrid automobile, or on any of various electronic device circuits, and that cools a heat-generating device such as a semiconductor device.
• Heat exchangers that cool heat-generating devices such as semiconductor devices are mounted in electric automobiles or hybrid automobiles, or on various electronic device circuits.
• FIG. 4 This heat exchanger 100 is of a water-cooled type, in which cooling water is used as the coolant, and has: a top sheet 102, which is formed of an aluminum alloy sheet, to which to attach a cooling target such as a semiconductor device; a bottom sheet 101 of an aluminum alloy sheet, which defines a passage 104 between the bottom sheet 101 and the top sheet 102; and an inner fin 103, which is held between these aluminum alloy sheets.
• This heat exchanger 100 cools the cooling target via the top sheet 102 by heat exchange between the inner fin 103 and cooling water flowing within the passage 104.
• the top sheet 102 In order to raise the efficiency of heat exchange between the cooling water and the cooling target in this type of heat exchanger 100, the top sheet 102, to which to attach the cooling target, is configured to be sufficiently thinner than the bottom sheet 101.
• Heat exchangers of this type have also been developed in recent years in which an insulating circuit substrate (the cooling device substrate), on which the semiconductor device (cooling target) is bonded, is attached to the top sheet 102.
• This insulating circuit substrate has a metal sheet, e.g., pure aluminum, bonded on each side of a thermally conductive insulating ceramic, e.g., A1N or Si 3 N 4 , and has a function of insulating the semiconductor device from the top sheet 102 while efficiently transferring the heat produced by the semiconductor element to the top sheet 102.
• a metal sheet e.g., pure aluminum
• a thermally conductive insulating ceramic e.g., A1N or Si 3 N 4
• a clad material having a brazing filler metal layer 101S, 102S on at least the passage 104 side surface is used as the aluminum alloy sheet constituting each of the top sheet 102 and the bottom sheet 101, and the top sheet 102, bottom sheet 101, and inner fin 103 constituting the heat exchanger 100 are brazed together using the brazing filler metal layers 10 IS, 102S.
• the clad material constituting the bottom sheet 101 is also referred to as the "clad thick sheet material” and the clad material constituting the top sheet 102 is also referred to as the "clad thin sheet material".
• This type of heat exchanger 100 has the same corrosive environment as, for example, the radiator ordinarily provided for an engine, and its individual members are exposed to a corrosive environment as a result of contact between the particular member and the cooling water when the cooling water flows.
• the constituent members of the heat exchanger 100 are subjected to a severe environment, and particularly in the case of a thinned-down top sheet 102, corrosion develops in the depth direction from the passage 104 side and corrosion pitting may occur more rapidly than the designed service life. This makes it necessary in particular, in order to simultaneously achieve an improved cooling performance and a thinning down of the heat exchanger 100, to improve the corrosion resistance of the top sheet 102, i.e., the clad thin sheet material.
• a sheet material, in which a core material is clad with a Zn-doped Al-Si brazing filler metal layer or a coating material layer (sacrificial material layer) formed of an Al-Zn alloy has been proposed as a brazing sheet (clad material) with the objective of improving the corrosion resistance of the heat exchanger 100 (refer, for example, to Japanese Patent Application Publication No. 7-41895 (JP 7-41895 A)).
• a clad material having a brazing filler metal layer is used for the top sheet (clad thin sheet material) 102
• this is assembled in the heat exchanger 100 with the brazing filler metal layer 102S on the passage 104 side, and brazing is performed
• the heat treatment associated with brazing causes the Zn component present in the brazing filler metal layer 102S to diffuse into the core material, thereby forming a concentration gradient of the Zn component in the thickness direction from the surface (surface on the passage 104 side) 102a of the top sheet 102.
• the generation of this Zn concentration gradient causes the generation of a potential gradient in the thickness direction from the surface 102a of the top sheet 102 made of the clad thin sheet material. Cooling water-induced corrosion proceeds preferentially in the surface direction in a top sheet 102 in which such a potential gradient layer has been formed, and the occurrence of corrosion pitting can then be stopped due to an inhibition of corrosion in the depth direction.
• the invention provides a heat exchanger in which a corrosion-inhibiting potential gradient layer can be reliably formed in the individual clad materials that constitute the heat exchanger, thereby yielding an excellent resistance to corrosion caused by the cooling water, and in which corrosion pitting can be inhibited in the neighborhood of a joint region between individual clad materials even when a thin clad sheet material has been used.
• a heat exchanger has a clad thin sheet material; a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material; and an inner fin held between the clad thick sheet material and the clad thin sheet material, wherein joint regions of these members are joined by brazing;
• the heat exchanger is configured such that a cooling target to be attached on an opposite side of the clad thin sheet material from the passage is cooled by heat exchange with a cooling water that flows in the passage;
• the clad thick sheet material has a first core material and a first passage-side brazing filler metal layer that covers a surface of the first core material on a passage side thereof;
• the clad thin sheet material has a second core material and a second passage-side brazing filler metal layer that covers a surface of the second core material on a passage side thereof;
• a heat exchanger has a clad thin sheet material; a clad thick sheet material that is disposed so as to define a passage between the clad thick sheet material and the clad thin sheet material, and that has a sheet thickness greater than that of the clad thin sheet material; and an inner fin held between the clad thick sheet material and the clad thin sheet material, wherein joint regions of the clad thick sheet material, the clad thin sheet material, and the inner fin are joined by brazing;
• the heat exchanger is configured such that a cooling target to be attached on an opposite side of the clad thin sheet material from the passage is cooled by heat exchange with a cooling water that flows in the passage;
• the clad thick sheet material has a first core material and a passage-side brazing filler metal layer that covers a surface of the first core material on the passage side thereof;
• the first core material is formed of an aluminum alloy that contains Mn, Cu, and Si in the following contents and contains at least one selected from Fe,
• the clad thin sheet material may have an outer brazing filler metal layer that covers an opposite side of the second core material from the passage, and the outer brazing filler metal layer may be formed of an aluminum alloy brazing filler metal that contains 5.0 to 12.6 mass% of Si, with the balance being made of Al and unavoidable impurities.
• the clad thin sheet material may have an outer sacrificial material layer between the second core material and the outer brazing filler metal layer, and the outer sacrificial material layer may be formed of an aluminum alloy sacrificial material that contains Zn in the content given below and contains at least one selected from Si, Fe, Mn, Ti, and Zr in the contents given below, with the balance being made of Al and unavoidable impurities: Zn: 0.5 to 5.0 mass%, Si: 0.1 to 1.0 mass%, Fe: 0.05 to 0.5 mass%, Mn: 0.1 to 1.1 mass%, Ti: 0.05 to 0.20 mass , Zr: 0.05 to 0.15 mass%.
• the inventors have acquired the following knowledge as a result of investigations directed to improving the corrosion resistance of the heat exchanger: with regard to the corrosion resistance when brazing sheets with different sheet thicknesses are combined, not only the composition of the individual brazing sheets, but also the influence of the brazing filler metal that flows in from another brazing sheet must be considered; also, the corrosion resistance of each brazing sheet can be clearly and reliably improved, regardless of the brazing conditions, by specifying the amount of surface Zn after brazing for the individual brazing sheets.
• the heat treatment for brazing causes the diffusion of the Zn component present in each brazing filler metal layer or present in the sacrificial material layer and thus the formation of a potential gradient layer on the individual passage sides of the clad thick sheet material and the clad thin sheet material.
• an excellent anticorrosion effect is produced by the potential gradient layer when the post-brazing Zn contents Aj , A 2 , B
• the potential of the passage side surface of the clad thin sheet material is made nobler, or higher, than that of the passage side surface of the clad thick sheet material by setting the Zn content A 2 and B 2 of the passage side surface of the clad thin sheet material so that A 2 - 0.5 and B 2 - 0.5 are respectively smaller than the Zn contents A ⁇ and B i of the passage side surface of the clad thick sheet material.
• This serves to inhibit the battery effect-induced development of corrosion in the clad thin sheet material in the neighborhood of joint regions between individual clad materials and can thereby prevent the occurrence of corrosion pitting in this neighborhood to a joint region.
• the clad thick sheet material With regard to the clad thick sheet material, its sheet thickness is greater than that of the clad thin sheet material, so that Cu diffusion to the brazing filler metal surface from the core material is relatively small. At the same quantity of Zn, the potential of its surface is then baser, or lower, for the clad thick sheet material than that for the clad thin sheet material. Because of this relation, the relationships of the amounts of Zn at the brazing filler metal surfaces, that is, Ai > A 2 - 0.5 and B
• FIG. 1 is a schematic cross-sectional diagram that shows a first embodiment of a heat exchanger of the invention
• FIG. 2 is a schematic cross-sectional diagram that shows a third embodiment of a heat exchanger of the invention
• FIG. 3 is a schematic cross-sectional diagram that shows a fourth embodiment of a heat exchanger of the invention.
• FIG. 4 is a schematic cross-sectional diagram that shows a conventional heat exchanger.
• FIG. 1 is a schematic cross-sectional diagram that shows the first embodiment of a heat exchanger according to the invention.
• the heat exchanger 10 shown in FIG. 1 is constructed by stacking a clad thick sheet material 1 , which forms the bottom sheet, an inner fin 3, and a clad thin sheet material 2, which forms the top sheet, in the given sequence and, using the individual brazing filler metal layers 12, 22 disposed on the interior surfaces of the individual clad materials 1, 2, brazing the clad materials 1, 2 together at the joint regions 13, 23 and brazing the inner fin 3 to the surfaces la, 2a.
• the clad thick sheet material (bottom sheet) 1 and the clad thin sheet material (top sheet) 2 define a passage 4 through which cooling water (coolant) flows.
• the clad thick sheet material 1 has a sheet shape, and a step portion (joint region) 13, which bonds with the joint region 23 of the clad thin sheet material 2, is intermittently formed at prescribed positions therein.
• the clad thick sheet material 1 has a sheet thickness that is greater than that of the clad thin sheet material 2, which is described below, and in specific terms is formed in a thickness of about 1.0 to 4.0 mm.
• the clad thin sheet material 2 is a sheet that assumes a planar shape approximately the same as the clad thick sheet material 1 , and a height difference (joint region) 23, which bonds with the joint region 13 of the clad thick sheet material 1, is intermittently formed at prescribed locations therein.
• the clad thin sheet material 2 has a sheet thickness that is smaller than that of the clad thick sheet material 1, and in specific terms is about 0.2 to 2.0 mm.
• the clad thick sheet material 1 and the clad thin sheet material 2 are brazed to each other at their respective step portions 13, 23.
• a coolant passage 4 is defined between the clad thick sheet material 1 and the clad thin sheet material 2 and has a shape bounded by the side walls of the step portions 13, 23.
• a composite structure formed of the clad thick sheet material 1 and the clad thin sheet material 2 is adopted because the aforementioned thickness is necessary in order to secure the rigidity as a cooler (heat exchanger) through the use of the clad thick sheet material 1, while a weight reduction and an increase in the cooling performance are obtained through the use of the clad thin sheet material 2.
• the inner fin 3 has an accordion-like shape and is held within the passage 4.
• Each bend (joint region) 33 of the inner fin 3 is brazed to the surface (passage side surface) la, 2a of the clad thick sheet material 1 or the clad thin sheet material 2.
• This heat exchanger 10 is configured so that the cooling target is attached to the outside surface (opposite side from the passage 4) 2b of the clad thin sheet material 2 and can be cooled via the inner fin 3 and the clad thin sheet material 2 by coolant, e.g., cooling water, flowing within the passage 4.
• coolant e.g., cooling water
• the heat exchanger 10 is configured so that the flow direction of the coolant flowing through the passage 4 is perpendicular to the plane of the sheet on which FIG. 1 is drawn and the inflow and outflow sides of the passage 4 are connected to a coolant circulation device to circulate the coolant via the passage 4.
• a fluoride-based flux for example, a noncorrosive Nocolok flux or Zn substitution flux
• a heat treatment is then carried out in an oven having an inert atmosphere, e.g., a nitrogen gas atmosphere.
• the heat treatment temperature is about 590 to 620°C.
• the clad thick sheet material 1 has a core material 11 and a brazing filler metal layer 12 that covers the passage 4 side surface of this core material 11.
• the core material 11 is formed of an aluminum alloy that contains Mn, Cu, and Si and that contains at least one selected from Fe, Ti, and Zr, with the balance being made of Al and unavoidable impurities.
• the individual component contents are as follows: Mn: 0.4 to 1.5 mass , Cu: 0.05 to 0.8 mass%, Si: 0.05 to 1.0 mass%, Fe: 0.05 to 0.5 mass%, Ti: 0.05 to 0.20 mass%, and Zr: 0.05 to 0.15 mass%.
• Their functions are as follows.
• Mn Mn precipitates or crystallizes as an intermetallic compound and has a function of improving the post-brazing strength of the clad thick sheet material 1.
• Al-Mn-Si compound it has the effect of lowering the Si solid solubility of the aluminum matrix and raising the melting point of the matrix.
• Cu is present in a solid solution state in the matrix and has a function of raising the strength of the core material 11. This effect is not satisfactorily obtained when the Cu content is less than 0.05 mass .
• the Cu content exceeds 0.8 mass%, diffusion to the brazing filler metal surface occurs and Cu reduces the sacrificial anode effect of the potential gradient layer, resulting in a loss of its anticorrosion activity.
• the Cu content is too high, the melting point of the core material 11 is reduced and the core material 11 may then melt during brazing.
• the strength becomes too high and the press formability is reduced as a result.
• Fe precipitates or crystallizes as an intermetallic compound and has a function of increasing the post-brazing strength of the clad thick sheet material 1.
• Fe has the effect of lowering the Mn solid solubility and the Si solid solubility in the aluminum matrix and raising the melting point of the aluminum matrix.
• Ti, Zr Ti and Zr are dispersed as microscopic intermetallic compounds after brazing and have a function of improving the strength of the clad thick sheet material 1. This effect is not satisfactorily obtained when their content is less than 0.05 mass%. In addition, the processability of the core material 11 declines when the Ti content exceeds 0.20 mass or when the Zr content exceeds 0.15 mass%. The unavoidable impurity range for Ti and Zr is less than 0.05%.
• the brazing filler metal layer 12 supplies brazing filler metal that brazes the joint regions 13, 23 to each other and that brazes the surface la to the bends 33 of the inner fin 3.
• the brazing filler metal layer 12 is formed of an aluminum alloy brazing filler metal that contains Si and Zn with the balance being made of Al and unavoidable impurities.
• the Si and Zn contents are Si: 4.5 to 11.0 mass% and Zn: 0.5 to 5.0 mass%, and their functions are as follows.
• Si is melted and flows due to the heat treatment in the brazing process, and through its subsequent solidification brazes the joint regions 13, 23 to each other and brazes the surface la to the bends 33 of the inner fin 3.
• Si has a function of lowering the melting point of the brazing filler metal and a function of raising the fluidity of the brazing filler metal when the brazing filler metal is molten.
• the brazing capability is inadequate when the Si content is less than 4.5 mass%. When the Si content exceeds 11.0 mass%, eating of the brazing filler metal into the core material 11 or the bonded members 2, 3 becomes severe.
• Zn diffuses into the core material 11 due to the heat treatment accompanying the brazing process and forms a Zn concentration gradient in the thickness direction from the surface la of the clad thick sheet material 1.
• Zn has a relatively lower potential (lower ionization energy)
• the formation of such a concentration gradient produces a potential gradient in the thickness direction from the surface la of the clad thick sheet material 1.
• the brazing filler metal layer 12 of the clad thick sheet material 1 contains Zn
• the Zn component of the clad thin sheet material 2 will undergo almost no dilution even when the molten brazing filler metal therefrom flows along the surface 2a on the inner side of the clad thin sheet material 2. Due to this, a potential gradient layer with an excellent anticorrosion effect can be readily formed at the clad thin sheet material 2 side. A satisfactory potential gradient is not formed when the Zn content is less than 0.5 mass%. When the Zn content exceeds 5.0 mass , the self-corrosion rate of the potential gradient layer will be too high and the corrosion resistance and erosion resistance of the clad thick sheet material 1 cannot be improved.
• the clad thick sheet material 1 has an A
• the clad thin sheet material 2 has a core material 21 and a brazing filler metal layer 22 that covers the passage 4 side surface of this core material 21 and is configured in a manner similar to that in which the clad thick sheet material 1 is configured,, except that its thickness is less than one-half that of the clad thick sheet material 1 and A 2 , defined as the post-brazing Zn content of the passage side surface 2a (A 2 is referred to below as the "post-brazing surface Zn amount A 2 "), is specified to be 0.4 to 2.0 mass% and to be smaller than the post-brazing surface Zn amount A ⁇ of the clad thick sheet material 1.
• the clad thin sheet material 2 is thin, corrosion pitting has readily occurred in conventional structures by the development of cooling water-induced corrosion and there has thus been a risk that this will cause holes to open in the heat exchanger 10.
• the clad thin sheet material 2 in the invention has a Zn-containing brazing filler metal layer 22 on the passage 4 side, a potential gradient layer is also formed at the clad thin sheet material 2, just as in the previously described case of the clad thick sheet material 1, by the diffusion of the Zn component of the brazing filler metal layer 22 into the core material 21 due to the heat treatment that accompanies brazing. This serves to inhibit the development of corrosion in the depth direction and as a consequence the occurrence of corrosion pitting, which is a particular problematic in the clad thin sheet material 2, can be inhibited.
• the post-brazing surface Zn amounts Ai, A 2 of the respective clad materials 1, 2 must satisfy the prescribed conditions. The reasons for this will be described in the following.
• 0.5 to 3.0 mass% is specified for the post-brazing surface Zn amount A] of the clad thick sheet material 1 and 0.4 to 2.0 mass% is specified for the post-brazing surface Zn amount A 2 of the clad thin sheet material 2 so that these amounts satisfy the relation, Ai > A 2 - 0.5.
• the post-brazing surface Zn amounts A], A 2 of the clad materials 1 , 2 are the surface Zn amounts of the potential gradient layers formed by the heat treatment during brazing. Potential gradient layers that have surface Zn amounts Ai, A 2 in the indicated ranges display an excellent anticorrosion activity and can substantially improve the resistance of the clad materials 1, 2 to corrosion caused by the cooling water.
• the post-brazing surface Zn amounts Ai, A 2 of the clad thick sheet material 1 and the clad thin sheet material 2 can be adjusted into the prescribed ranges using the component compositions of the individual elements 11 , 12, 21, 22, the sheet thickness of the core materials 11, 21, the cladding ratio for the brazing filler metal layers 12, 22, the brazing conditions, and so forth.
• the inner fin 3 in this embodiment is formed of a bare aluminum alloy that contains Mn and Zn and at least one selected from Cu, Si, Fe, Ti, and Zr, with the balance being made of AI and unavoidable impurities.
• the contents of the individual components are as follows: Mn: 0.8 to 1.5 mass%, Zn: 0.5 to 3.0 mass , Cu: 0.05 to 0.3 mass%, Si: 0.05 to 1.0 mass%, Fe: 0.05 to 0.5 mass%, Ti: 0.05 to 0.20 mass%, and Zr: 0.05 to 0.20 mass%.
• Their functions are as follows.
• Mn Mn precipitates or crystallizes as an intermetallic compound and has a function of improving the post-brazing strength of the inner fin 3.
• Al-Mn-Si compound it has the effect of lowering the Si solid solubility of the matrix and raising the melting point of the matrix.
• Cu is present in a solid solution state in the matrix and has a function of raising the strength of the inner fin 3. This effect is not satisfactorily obtained when the Cu content is less than 0.05 mass%.
• Cu due to its relatively noble potential, or relatively high ionization energy, causes a decline in the sacrificial anode effect of the inner fin 3.
• the Cu content is too high, the melting point of the inner fin 3 is reduced and the inner fin 3 may then melt during brazing.
• the unavoidable impurity concentration range for Cu is less than 0.05%.
• Si is present in a solid solution state in the aluminum matrix or dispersed as an Al-Mn-Si compound and has a function of improving the strength of the inner fin 3. This effect is not satisfactorily obtained when the Si content is less than 0.05 mass%.
• Si content exceeds 1.0 mass%, the melting point of the inner fin 3 is reduced and the inner fin 3 may then melt during brazing.
• thermal conductivity is reduced and the heat exchange efficiency of the heat exchanger is then reduced.
• the unavoidable impurity concentration range for Si is less than 0.05%.
• Fe precipitates or crystallizes as an intermetallic compound and has a function of increasing the post-brazing strength of the inner fin 3.
• Fe has the effect of lowering the Mn solid solubility and the Si solid solubility in the matrix and raising the melting point of the matrix.
• Ti, Zr Ti and Zr are dispersed as microscopic intermetallic compounds after brazing and have a function of improving the strength of the inner fin 3. This effect is not satisfactorily obtained when their content is less than 0.05 mass%. In addition, the processability of the inner fin 3 declines when their content exceeds 0.20 mass%.
• the unavoidable impurity concentration range for Ti and Zr is less than 0.05%.
• a potential gradient layer having an excellent anticorrosion effect can be formed on the passage 4 sides of the clad materials 1, 2 in the heat exchanger 10 of this first embodiment as described above because Zn-containing brazing filler metal layers 12, 22 are present on the passage 4 sides of the clad thick sheet material 1 and the clad thin sheet material 2 and because the post-brazing surface Zn amounts Ai, A 2 of the clad materials 1, 2 satisfy the prescribed conditions.
• Zn-containing brazing filler metal layers 12, 22 are present on the passage 4 sides of the clad thick sheet material 1 and the clad thin sheet material 2 and because the post-brazing surface Zn amounts Ai, A 2 of the clad materials 1, 2 satisfy the prescribed conditions.
• the passage side surface 2a of the clad thin sheet material 2 takes on a nobler, or higher, potential than that of the passage side surface la of the clad thick sheet material 1 and the development of battery effect-induced corrosion of the clad thin sheet material 2 is inhibited in the neighborhood of the joint regions 13, 23 between the clad materials 1, 2 and the occurrence of the corresponding corrosion pitting can then be prevented. Accordingly, this heat exchanger 10 is resistant to the occurrence of corrosion pitting in the clad thin sheet material 2 even when cooling water flows and can simultaneously achieve a thinning down of the clad thin sheet material 2, an improved cooling performance, and an improved corrosion resistance.
• a second embodiment of the heat exchanger according to the invention will next be described. Those structures in the second embodiment that are similar to those of the previously described first embodiment will not be described in detail again.
• the heat exchanger of this second embodiment is configured in a manner similar to that in which the first embodiment is configured, except that, in the heat exchanger 10 in the preceding embodiment, the clad thin sheet material 2 has a sacrificial material layer in place of the brazing filler metal layer 22 and the inner fin 3 is a clad material that has a core material and a brazing filler metal layer that covers only the clad thin sheet material side of the core material or both sides of the core material.
• the sacrificial material layer is disposed so as to cover the surface of the passage 4 side of the core material 21.
• This sacrificial material layer is formed of an aluminum alloy that contains Zn and at least one selected from Si, Fe, Mn, Ti, and Zr, with the balance being made of Al and unavoidable impurities.
• the contents of the individual components are as follows: Zn: 0.5 to 5.0 mass%, Si: 0.1 to 1.0 mass%, Fe: 0.05 to 0.5 mass%, Mn: 0.1 to 1.1 mass%, Ti: 0.05 to 0.20 mass%, and Zr: 0.05 to 0.15 mass .
• the function of each component is as follows.
• Zn Due to the heat treatment accompanying the brazing process, Zn forms a Zn concentration gradient in the thickness direction from the surface 2a of the clad thin sheet material 2. Because Zn has a relatively lower potential when added to the aluminum matrix, the formation of such a concentration gradient produces a potential gradient in the thickness direction from the surface 2a of the clad thin sheet material 2. In the case of a clad thin sheet material 2 in which such a potential gradient layer has been formed, due to its sacrificial anode activity, cooling water-induced corrosion proceeds preferentially in the surface direction and the development of corrosion in the depth direction is inhibited. This results in an inhibition of corrosion pitting. A satisfactory potential gradient is not formed when the Zn content is less than 0.5 mass%.
• the post-brazing surface Zn amounts B i , B 2 of the clad materials 1 , 2 satisfy prescribed conditions.
• Si, Fe, Mn These components precipitate or crystallize as intermetallic compounds and have a function of improving the post-brazing strength and corrosion resistance of the clad thin sheet material 2. These effects are not satisfactorily obtained when the content of a particular component is less than the lower limit. When the content of a particular component exceeds the upper limit, the corrosion rate of the sacrificial material layer is then too high and the corrosion of the core material cannot be adequately inhibited.
• Ti, Zr These components are dispersed as microscopic intermetallic compounds after brazing and have a function of improving the strength of the clad thin sheet material 2. This effect is not satisfactorily obtained when their content is less than 0.05 mass%.
• the processability and the resistance to self-corrosion by the sacrificial material layer decline when the Ti content exceeds 0.20 mass or when the Zr content exceeds 0.15 mass%.
• 0.5 to 3.0 mass is specified for the post-brazing surface Zn amount B i of the clad thick sheet material 1 and 0.4 to 2.0 mass% is specified for the post-brazing surface Zn amount B 2 of the clad thin sheet material 2 so that these amounts satisfy the relation, B
• the clad thick sheet material 1 has a Zn-containing brazing filler metal layer 12 on its passage side and the clad thin sheet material 2 has a Zn-containing sacrificial material layer on its passage side
• the Zn component present in the brazing filler metal layer 12 and in the sacrificial material layer diffuses into the core materials 11, 21 due to the heat treatment that accompanies brazing and potential gradient layers are formed on the passage 4 sides of the clad thick sheet material 1 and the clad thin sheet material 2.
• this gradient potential layer exhibits an excellent anticorrosion effect because the post-brazing surface Zn amounts B
• this heat exchanger has a structure in which cooling water flows, corrosion of each of the clad materials 1, 2 can be reliably inhibited and the occurrence of corrosion pitting in the clad materials 1, 2 and particularly in the clad thin sheet material 2 can be effectively inhibited.
• the heat exchanger of the invention even when the cooling water flow rate is raised, the occurrence of corrosion pitting in the clad thin sheet material is inhibited, so that it is possible to simultaneously achieve a thinning down of the individual members and an increase in the cooling performance.
• FIG. 2 is a schematic cross-sectional diagram that shows a heat exchanger according to a third embodiment.
• the heat exchanger 20 in this third embodiment is configured in a manner similar to that in which the previously described first embodiment is configured, except that the clad thin sheet material 2 has a three layer structure that has a brazing filler metal layer 24 on the side opposite from the passage 4.
• the brazing filler metal layer 24 is disposed so as to cover the surface 2b of the core material 21 on the side opposite from the passage 4 side.
• This brazing filler metal layer 24 is formed of an aluminum alloy brazing filler metal that contains 5.0 to 12.6 mass% of Si with the balance being Al and unavoidable impurities.
• the clad thin sheet material 2 may have a brazing filler metal layer on the side opposite from the passage 4.
• FIG. 3 shows a heat exchanger 40 according to a fourth embodiment.
• the clad thin sheet material 2 in the heat exchanger 40 of this embodiment has the same structure as that of the clad thin sheet material 2 in the second embodiment, except that the clad thin sheet material 2 has a four layer structure that has a brazing filler metal layer 24 and a sacrificial material layer 25 on the opposite side from the passage 4.
• the brazing filler metal layer 24 in this embodiment is the same as the brazing filler metal layer 24 in the previously described third embodiment, while the sacrificial material layer 25 is the same as the sacrificial material layer in the previously described second embodiment.
• the structure of this fourth embodiment can provide the effects similar to those obtained through the heat exchanger of the second embodiment.
• cooling target attached on the clad thin sheet material on the side opposite from the passage in the heat exchanger of the invention.
• the cooling target include heat-generating devices such as semiconductor devices, composite structures provided by bonding a heat-generating device to the surface of a cooling device substrate (for example, an insulating circuit substrate provided by bonding an aluminum layer on each side of a thermally conductive ceramic, e.g., A1N or Si 3 N 4 ).
• These cooling targets may be brazed to the heat exchanger after its production or may be brazed in the same step as the brazing step for the various members constituting the heat exchanger.
• a bottom sheet was used that had the cross-sectional shape shown in FIG. 1 ; it was prepared by cladding a 3 mm-thick aluminum alloy core material having the alloy components shown in Table 1 with a 160 ⁇ -fhick brazing filler metal layer having the composition shown in Table 1 by pressure-bonding.
• a top sheet was used that had the cross-sectional shape shown in FIG. 1 ; it was prepared by cladding both the front and back sides of a 0.6 mm-thick aluminum alloy core material having the alloy components shown in Table 2 with a 70 ⁇ -fhick brazing filler metal layer having the composition shown in Table 2 by pressure-bonding.
• a 0.5 mm-thick fin with the corrugated shape shown in FIG. 1 was used; its composition is shown in Table 4.
• This bottom sheet, top sheet, and fin were assembled into the heat exchanger configuration shown in FIG. 1 and a heat exchanger was obtained by brazing by heating for 1 to 15 minutes at 580 to 615°C as shown in Table 5.
• the corrosion testing conditions are as follows. Corrosion solution: ion-exchanged water + (CP. 100 ppm, S0 4 2" : 300 ppm, Cu ++ : 50 ppm) adjusted with NaCl, Na 2 S0 4 , and CuCl 2 .
• Corrosion test repetition of a (circulation) process in which 60 liters of the corrosion solution is circulated (80°C for 8 hours) in the core and a circulation stop process at room temperature for 16 hours; different flow rates (L/min) are used. Evaluation: measurement of the depth of the largest corrosion pit feature.
• Example 1 0.42 0.79 0.05 0.05 0.05 4.5 5.5
• Example A Example 1 Example 3
• Example 5 Example 5 x 1 3
• Example 6 Example 3
• Example 8 Example 3
• Example 9 Example 1 x 3 2.9
• Example 7 Example 2 x 3 1.8
• A, A 2 leakage at joint h 3.5 10 L/min leakage NG
• top sheet brazing filler metal leakage at the top sheet (due to Si excess in the top sheet brazing filler

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