JP2012061523A - Method of brazing aluminum, and flat tube for aluminum heat exchanger manufactured by the brazing method - Google Patents

Abstract

An object of the present invention is to provide an aluminum brazing method capable of improving the jointability when a flat tube for an aluminum heat exchanger is manufactured by brazing by joining a tube material and an inner fin.
[Structure] A clad layer of an aluminum two-layer clad material having a clad layer of 5 μm or more in thickness of Al—Si based alloy containing 2 to 6% Si and the balance Al and impurities on one side of a core material of an aluminum alloy A tube formed to be an inner surface, and an aluminum inner fin material clad with an Al-Si alloy brazing material containing 7.5 to 12% Si and the balance being Al and impurities, clad of the Al-Si alloy The layers and the Al—Si alloy brazing material are assembled so as to come into contact with each other and brazed and joined.
[Selection figure] None

Description

  The present invention relates to a brazing method for aluminum, particularly a brazing method for automotive heat exchanger tubes that braze in an inert gas atmosphere using a fluoride-based flux and an Al-Si alloy brazing material. An aluminum brazing material having an Al-Si-based alloy clad layer containing a specific amount of Si is used as a brazing part, and an aluminum brazing method is obtained by the brazing method. The present invention relates to a flat tube of an aluminum heat exchanger. Aluminum includes aluminum and aluminum alloys.

  In the manufacture of aluminum alloy automotive heat exchangers such as radiators, heaters, condensers, and evaporators, in general, aluminum plates and extrusions molded into a predetermined shape are assembled into a predetermined structure, and then a fluoride-based heat exchanger is assembled. A method of brazing and joining in a heating furnace in an inert gas atmosphere using a flux is employed.

  In recent years, in heat exchangers for automobiles, the thickness of constituent materials has been reduced from the viewpoints of energy saving and resource saving, and the tube materials and fin materials of the constituent members have also become thinner. As shown in FIG. 1, when the tube member 1 and the inner fin 2 joined to the inner surface side thereof are made of an aluminum plate material, conventionally, for example, the manufacturing method is bare with the tube member clad with the brazing material on the inner surface side. This is done by brazing and joining the inner fins of the material (see, for example, Patent Document 1).

However, in this case, since the tube material is thin, the amount of brazing material to be clad is small, and when forming the inner fin, the height of the fin crest varies, and this is shown in FIG. As described above, there is a problem that a clearance d ₁ is generated between the inner surface of the tube material and the inner fin, which causes poor bonding. Bonding failure also causes a decrease in heat exchange performance, and when the tube material is thin, the pressure resistance of the tube is significantly reduced.

In order to improve the wettability between the tube material and the inner fin, the flux application amount is also increased. However, when the flux application amount is increased, as shown in FIG. When the inner fin 2 is assembled, the peak height of the inner fin 2 is lowered by the coating thickness d ₂ of the flux 3, and the clearance between the tube material and the inner fin is increased during brazing, resulting in poor bonding.

  There is also a method of assembling a tube material in which a brazing material is not clad on the inner surface side and an inner fin made of a brazing sheet having a brazing material on both surfaces and brazing and joining (see, for example, Patent Document 2). There is a problem similar to the case where the tube material clad with the brazing material on the side and the inner fin of the bare material are joined by brazing.

Attempts have been made to improve the brazing bondability by assembling a tube material clad with brazing material on the inner surface side and an inner fin made of a brazing sheet clad with brazing material on both sides. Although the bondability is good, the amount of brazing material at the joint becomes excessive, which causes melting buckling of the inner fin during brazing, and as shown in FIG. A clearance corresponding to the total thickness d ₃ of the brazing material 5 of the fin 2 is generated, resulting in poor bonding.

Japanese Examined Patent Publication No. 59-50746 (Claim 1, second page, fourth column) Japanese Patent Publication No. 62-2621 (first page, prior art)

  The present invention was made to solve the above-mentioned conventional problems in the case of manufacturing a flat tube for an aluminum heat exchanger by brazing and joining a tube material and an inner fin, and the purpose thereof is a specific amount. A method of brazing aluminum, which can eliminate brazing defects and improve bondability by using an aluminum clad material having an Al-Si-based alloy clad layer containing Si at the brazing site, and An object of the present invention is to provide a flat tube for an aluminum heat exchanger manufactured by a brazing method.

  In order to achieve the above object, the aluminum brazing method according to claim 1 is the thickness of an Al-Si alloy containing 2 to 6% Si and the balance Al and impurities on one side of the core of the aluminum alloy. A tube formed so that the clad layer of an aluminum two-layer clad material having a clad layer of 5 μm or more becomes the inner surface, and an Al—Si alloy brazing material containing Si 7.5 to 12% and the balance Al and impurities. The clad aluminum inner fin material is assembled so that the Al-Si alloy clad layer and the Al-Si alloy brazing material are in contact with each other, and brazed and joined.

  The method for brazing aluminum according to claim 2 is characterized in that, in claim 1, the Al—Si based alloy has Zn as an impurity of less than 0.5%.

  The aluminum brazing method according to claim 3 is the aluminum particle brazing method according to claim 1 or 2, wherein the maximum particle size of the Si particles dispersed in the cladding layer of the Al-Si alloy is 2/3 of the cladding layer thickness. It is characterized by being miniaturized to be as follows.

  The method of brazing aluminum according to claim 4 is the method according to any one of claims 1 to 3, wherein the Si particles dispersed in the cladding layer of the Al-Si alloy have a normal distribution of the particle size of the Si particles. When the average is μ and the standard deviation is σ, (μ + 3σ) is miniaturized so that the value is 1/3 or less of the cladding layer thickness.

  A flat tube for an aluminum heat exchanger according to claim 5 is a tube manufactured by the brazing method according to any one of claims 1 to 4, wherein Si 2 to 6% is contained on one side of a core material of an aluminum alloy. And a tube formed such that the clad layer of the aluminum bi-layer clad material having a clad layer of 5 μm or more of the Al—Si alloy composed of the remaining Al and impurities is contained on the inner surface, and contains Si of 7.5 to 12% Then, the aluminum inner fin material clad with the remaining Al and impurities Al-Si alloy brazing material is assembled so that the Al-Si alloy cladding layer and the Al-Si alloy brazing material are in contact with each other, It is characterized by being brazed.

  According to the present invention, when a flat tube for an aluminum heat exchanger is manufactured by brazing by joining a tube material and an inner fin, the Al-Si alloy clad layer containing the above-mentioned specific amount of Si. A method of brazing aluminum is provided, in which an aluminum clad material having the following characteristics is used for a brazing site to eliminate poor brazing and to improve bondability.

It is sectional drawing at the time of assembling a tube material and an inner fin. It is a partially expanded sectional view when the amount of flux application is increased when the tube material and the inner fin are assembled. When a tube material and an inner fin are assembled, it is a partially enlarged cross-sectional view when a tube material clad with a brazing material on its inner surface and a brazing sheet inner fin having a brazing material layer on both surfaces are assembled. It is a schematic side view which shows the assembly | attachment of the shape | molded brazing fin and a two-layer clad board | plate material.

  In the aluminum brazing method of the present invention, the aluminum clad material used for the brazing portion contains 2 to 6% of Si on the brazing surface side of the aluminum material, and an aluminum alloy (Al-Si consisting of the balance Al and impurities). The alloy has a clad layer, and the reason why the brazing bondability is improved by using this aluminum clad material is as follows.

  In other words, the aluminum alloy constituting the clad layer of the aluminum clad material used in the present invention only forms a small amount of liquid phase near the brazing temperature of 600 ° C., and is partially and discontinuous in the clad layer. Melting occurs. The melted portion becomes a three-dimensional reservoir in the cladding layer, and the oxide film on the surface is likely to be partially broken.

  On the other hand, an Al-7.5 to 12% Si-based alloy brazing material constituting the brazing material surface of an aluminum material (the other material, the same shall apply hereinafter) brazed and joined to the clad layer of the aluminum clad material used in the present invention, Near or near the brazing temperature of 600 ° C., most or all of the liquid phase is in a liquid phase, and when the liquid phase comes into contact with a partial melted portion in the cladding layer, the liquid phases are easily connected to each other. The liquid phase is easily connected to the partially melted part in the vicinity, and the destruction of the surrounding oxide film is promoted. As a result, the wettability is improved and the connected liquid phase immediately moves to the joint. Since the fillet is reliably formed, the bondability is improved.

  The Al—Si alloy brazing material has a flow coefficient of about 0.45 at a brazing temperature of about 600 ° C., whereas the clad layer of the aluminum clad material of the present invention has a brazing temperature of In the vicinity of 600 ° C., since the liquid phase amount is small, the flow coefficient is lowered, and the flow coefficient is significantly reduced to about 0.03 to 0.2. Therefore, during brazing, the flow of the brazing is less likely to occur, and a clearance corresponding to the thickness of the brazing material is not formed due to the loss of the brazing, so that the bondability is improved.

  The solid solubility limit of Si in Al is 1.65%. When the amount of Si is less than 1.65%, no liquid phase is generated even when the temperature is raised to about 600 ° C. of the brazing temperature, or a small amount of liquid Only a phase occurs. If the Si content is 1.65% or more, a liquid phase is generated at 777 ° C. due to the Al—Si eutectic reaction. In a hypoeutectic structure with a Si content of up to 12.6%, the amount of liquid phase generated increases with increasing Si amount, and the amount of liquid phase increases as the temperature rises above 577 ° C.

  Since the Al-Si alloy brazing material contains 7.5 to 12% of Si, most or all of the brazing material is in a liquid phase in the vicinity of 600 ° C of the brazing temperature. In the present invention, the brazing material surface is brazed. By limiting the Si amount of the clad layer to be bonded to 2 to 6%, the generation of a liquid phase near 600 ° C. is reduced, and a partially discontinuous melted part is formed in the clad layer. This promotes the destruction of the oxide film, improves fillability by ensuring the formation of fillets, and improves the bondability by reducing the flow and preventing the formation of the clearance corresponding to the thickness of the brazing filler metal due to the loss of the solder. .

  In the aluminum clad material used in the present invention, Zn contained as an impurity in the aluminum alloy constituting the clad layer is preferably limited to less than 0.5%. When the Zn content is 0.5% or more, Zn moves to the joint together with the liquid phase generated during brazing, and therefore, Zn is concentrated in the joint, and the joint is preferentially used in subsequent use. Corrosion causes separation of the joints, and tends to reduce the strength and heat exchange performance of the heat exchanger.

  The addition of Sr to the cladding layer functions to improve the fillet formation state during brazing and increase the bonding length, so 0.005 to 0.02% in the aluminum alloy constituting the cladding layer. It is preferable to make it contain in the range.

  The thickness of the cladding layer is preferably 5 μm or more. If it is less than 5 μm, Si diffuses in the direction of the core material during the temperature rising process during brazing, and at the brazing temperature, Si in the clad layer becomes less than 1.65% of the solid solubility limit, and a liquid phase is hardly generated. As a result, improvement in wettability cannot be achieved.

  In the aluminum clad material used in the present invention, Si particles are dispersed in the matrix of the Al-Si alloy constituting the clad layer so that the maximum grain size is 2/3 or less of the clad layer thickness. In addition, it is preferable that the average particle size distribution of Si particles is μ and the standard deviation is σ, so that the value of (μ + 3σ) is 1/3 or less of the cladding layer thickness. It is preferable that it is miniaturized.

  Since the Si particles are refined within the above range, the partial melting that occurs at the brazing temperature becomes uniform in the cladding layer, and the liquid phase of the Al—Si brazing material constituting the brazing material surface of the mating material. The fillet is more reliably formed and the bondability is improved.

  Al-Si alloy brazing material constituting the brazing material surface of the mating material is brazing sheet brazing material, powder material consisting of simple Si or Al-Si alloy in aluminum material alone or mixed with fluoride flux And a brazing material such as a rod-shaped or plate-shaped Al-Si alloy placed at the joint between the clad layer and the aluminum material joined thereto. Further, the counterpart material may be an aluminum alloy material containing Si 2% or more.

  Hereinafter, examples of the present invention will be described in comparison with comparative examples in the case where the brazing material of the counterpart is a brazing sheet, and the effects of the present invention will be demonstrated. These examples are one embodiment of the present invention, and the present invention is not limited thereto.

Example 1
An aluminum clad plate material having an Al—Si alloy clad layer having the composition shown in Table 1 on one surface of a 3003 alloy core material having the composition shown in Table 1 was produced according to a conventional method. Table 1 shows the thickness of each aluminum clad plate and the thickness of the clad layer. The aluminum clad plate was softened at 360 ° C. for 3 hours after the final rolling.

  About the obtained aluminum clad board | plate material (2 layer clad board | plate material) (clad material No. af), 30 arbitrary cross sections were observed, respectively, and the largest particle diameter of Si particle | grains in a clad layer was measured. In addition, since the cross-sectional shape of coarse Si particles is almost rectangular or polygonal, the longest dimension in the Si particle shape (note: for example, the dimension between opposing vertices in the case of a rectangle) is defined as the particle diameter. did.

  Further, the particle size distribution of the Si particles in the cladding layer was measured by the cross-sectional observation described above. In this case, the equivalent circle diameter was adopted as the definition of the Si particle diameter. The measured Si particle size distribution was approximated to a normal distribution using the particle size as a logarithm, and the average μ and standard deviation σ of the distribution were obtained, and (μ + 3σ) was calculated. Table 1 shows the measurement and calculation results.

  A brazing sheet fin material having a thickness of 0.07 mm in which an A3003 alloy having the composition shown in Table 2 is used as a counterpart and a brazing material having the composition shown in Table 2 is clad on both sides (the brazing material thickness clad on both sides) 7 μm each was manufactured according to a conventional method, and formed into a fin shape after the final rolling.

The two-layer clad plate was cut to a size of 20 mm × 20 mm, and 5 g / m ² of fluoride-based flux was applied to the brazed surface after solvent degreasing. The molded brazing sheet fin is cut to a size of 20 mm × 20 mm, and after solvent degreasing, as shown in FIG. 4, the two-layer clad plate material 7 is clad on each side (upper and lower surfaces) of the brazing sheet fin 6. It assembled | attached so that it might contact | abut to the brazing | wax material surface of a fin, it fixed lightly with the jig | tool made from stainless steel, and it was set as the test material of the brazing method of this invention.

  The test material was placed in a nitrogen gas atmosphere furnace, heated at an average heating rate of 30 ° C./min, and immediately cooled when the temperature reached 600 ° C. to complete brazing. In order to adjust the atmosphere during brazing heating, the flow rate of nitrogen gas flowing into the furnace was adjusted, and tests were conducted for cases where the oxygen concentration in the atmosphere was high and low.

  For the test material after brazing, observe the cross section of the fin joint, fillet formation state, joint length with the fin (note: good when exceeding 0.40 mm), fin melt buckling state and fillet breakage The occurrence situation was investigated. Moreover, about the fin junction part, the salt spray test for 4 weeks was done based on JISZ1271, and the presence or absence of the preferential corrosion of a junction part was observed. The investigation and observation results are shown in Tables 3-4.

  As seen in Tables 3-4, the test material No. In each of 1, 2, 4, 5, and 6, regardless of the oxygen concentration in the brazing heating atmosphere, the joint length is 0.40 mm or more, and a sufficient fillet is formed at the joint, so that the fin fusion seat There is no bending or fillet breakage, and the test material No. No. 6 was only slightly corroded. No preferential corrosion was observed in 1, 2, 4, and 5.

Comparative Example 1
An aluminum clad plate material having an Al—Si alloy clad layer having the composition shown in Table 5 on one surface of a 3003 alloy core material having the composition shown in Table 5 was produced according to a conventional method. Table 1 shows the thickness of each aluminum clad plate and the thickness of the clad layer. The aluminum clad plate was softened at 360 ° C. for 3 hours after the final rolling. In addition, A3003 alloy veneer was also used as a comparative material (No.k).

  About the obtained aluminum clad board | plate material (double-layer clad board | plate material) (clad material No.gj), the arbitrary cross sections of 30 places are observed, respectively, and the largest particle diameter of Si particle | grains in a clad layer by the same method as Example 1 Was measured. Further, by the cross-sectional observation, the particle size distribution of the Si particles in the cladding layer is measured by the same method as in Example 1, and the measured Si particle size distribution is approximated to a normal distribution in which the particle size is a logarithm. The average μ of the distribution and the standard deviation σ were obtained, and (μ + 3σ) was calculated. Table 5 shows the measurement and calculation results. In Table 5, in the present invention, those that deviate from the conditions of the aluminum clad material used for the brazed part are underlined.

  As in Example 1, a brazing sheet fin material having a thickness of 0.07 mm in which A3003 alloy having the composition shown in Table 2 is used as the core material and the brazing material having the composition shown in Table 2 is clad on both surfaces (both sides). The thickness of the brazing material clad in each case was 7 μm) according to a conventional method, and formed into a fin shape after the final rolling.

Next, in the same manner as in Example 1, the two-layer clad plate material was cut to a size of 20 mm × 20 mm, and 5 g / m ² of fluoride-based flux was applied to the brazed surface after solvent degreasing. Cut into 20mm x 20mm dimensions, degreased with solvent, and assembled on both sides (upper and lower surfaces) of brazing sheet fins, with each clad layer being in contact with brazing material surface of brazing sheet fins, made of stainless steel The test material was lightly fixed with a jig. An A3003 alloy single plate (No. k) was also assembled to the upper and lower surfaces of the brazing sheet fins to provide test materials.

  The test material was placed in a nitrogen gas atmosphere furnace, heated at an average heating rate of 30 ° C./min, and immediately cooled when the temperature reached 600 ° C. to complete brazing. In order to adjust the atmosphere during brazing heating, the flow rate of nitrogen gas flowing into the furnace was adjusted, and tests were conducted for cases where the oxygen concentration in the atmosphere was high and low.

  For the test material after brazing, observe the cross section of the fin joint, fillet formation state, joint length with the fin (note: good when exceeding 0.40 mm), fin melt buckling state and fillet breakage The occurrence situation was investigated. Moreover, about the fin junction part, the salt spray test for 4 weeks was done based on JISZ1271, and the presence or absence of the preferential corrosion of a junction part was observed. The investigation and observation results are shown in Tables 6-7.

  As shown in Tables 6-7, the test material No. No. 7 has a small amount of Si in the clad layer, and therefore, when the oxygen concentration in the furnace is high, a sufficient fillet is not formed at the time of brazing, resulting in poor bondability. Test material No. In No. 8, since the amount of Si in the clad layer was large, the clad layer melted at the time of brazing, and melt buckling of the fins and fillet breakage occurred as in the conventional method. Test material No. Since No. 9 has a large amount of Zn in the clad layer, brazing jointability is good, but preferential corrosion of the fillet was observed. Test material No. No. 10 has a small thickness of the cladding layer. No. 11 uses an A3003 alloy single plate, and when the oxygen concentration in the furnace is high, a sufficient fillet is not formed at the time of brazing, or a fillet is not formed, and the bondability is poor.

DESCRIPTION OF SYMBOLS 1 Tube material 2 Inner fin 3 Flux 4 Brazing material 5 Brazing material 6 Brazing fin 7 Double-layer clad board material

Claims (5)

The clad layer of an aluminum two-layer clad material that has a clad layer of 5 μm or more in thickness of an Al—Si alloy containing 2 to 6% Si and the balance Al and impurities on one side of the core of the aluminum alloy is the inner surface. The aluminum inner fin material clad with the Al—Si alloy brazing material containing 7.5 to 12% Si and the balance Al and impurities, and the Al—Si alloy clad layer and Al -A method of brazing aluminum characterized by assembling so as to abut the Si-based alloy brazing material and brazing. The aluminum brazing method according to claim 1, wherein the Al—Si alloy contains less than 0.5% of Zn as an impurity. The Si particles dispersed in the cladding layer of the Al-Si alloy are refined so that the maximum particle size is 2/3 or less of the cladding layer thickness. 3. The method for brazing aluminum according to 2. The Si particles dispersed in the cladding layer of the Al—Si alloy have a value of (μ + 3σ) when the average of the normal distribution of the particle size of the Si particles is μ and the standard deviation is σ. The aluminum brazing method according to claim 1, wherein the aluminum brazing method is refined to be 1/3 or less of the thickness. It is a tube manufactured by the brazing method according to any one of claims 1 to 4, wherein the Al-Si system comprises Si 2 to 6% on one side of an aluminum alloy core material, and the balance is Al and impurities. A tube formed such that the clad layer of an aluminum two-layer clad material having a clad layer with an alloy thickness of 5 μm or more becomes the inner surface, and an Al—Si system containing Si 7.5 to 12% and the balance being Al and impurities An aluminum inner fin material clad with an alloy brazing material is assembled so that the Al-Si alloy clad layer and the Al-Si alloy brazing material are in contact with each other, and is brazed and joined. Flat tube for heat exchanger.

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