JP2011148004A - Low-temperature brazing filler metal for joining aluminum alloy - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly corrosion-resistant low-temperature brazing filler metal for joining Al alloy. <P>SOLUTION: The low-temperature brazing filler metal for joining aluminum alloy contains ≥4.0 wt% and <8.0 wt% Si, 7.0-20.0 wt% Zn, and 10.0-35.0 wt% Cu, with the balance consisting of aluminum and inevitable impurities. Since the low-temperature brazing filler metal is superior in corrosion resistance, it stably maintains brazing strength even under a corrosive environment. Also, since brazing temperature can be set low, various problems in a high temperature brazing filler metal are all solved, such problems as deterioration in corrosion resistance of a core material caused by diffusion of Zn in a sacrificial material of a brazing sheet into the core material. Furthermore, operation time for brazing can be reduced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a low-temperature brazing material for joining an aluminum (hereinafter, abbreviated as Al as appropriate) alloy having excellent corrosion resistance.

  Conventionally, brazing of an Al alloy assembly has been performed by rolling and joining a sacrificial material (Al-Zn alloy) on one side of a core material (Al-Mn alloy) and a brazing material (Al-Si alloy) on the other side. The assembly formed using the brazing sheet is held in a furnace at a temperature near 600 ° C. exceeding the melting point (liquidus temperature) of the brazing material. This brazing method is established as an industrial method for manufacturing various products such as a heat exchanger core because a large number of locations can be brazed simultaneously. In the brazing method, Mg is added to the brazing material and heated in a vacuum furnace, and vacuum brazing is performed by destroying and brazing the oxide film on the Al surface by evaporation of Mg and getter action; There is an NB method (CAB method) in which a non-corrosive flux is used and brazing is performed in a nitrogen gas atmosphere furnace.

As shown in FIG. 1, the heat exchanger core supplies or discharges a refrigerant, a tube 1 through which the refrigerant passes, a heat-dissipating corrugated fin (hereinafter referred to as a fin) 2 brazed between the tubes 1. For example, the header pipe 3 or the pipe 4 and the end cap 5 for closing the top and bottom of the header pipe 3 and the side plate 6 for fixing between the two header pipes 3 are configured. And the said brazing sheet is used for the tube 1, and the tube 1 and the fin 2 are brazed.

JP-A-8-206875

  However, the brazing method using the Al—Si alloy brazing material has the following problems because the brazing temperature is as high as about 600 ° C. That is, (1) Zn in the sacrificial material (Al—Zn alloy) constituting the aluminum brazing sheet during brazing diffuses into the core material (Al—Mn alloy), and the corrosion resistance of the core material decreases. (2) Mn precipitates in the core material are re-dissolved during brazing, the thermal conductivity of the core material is lowered, and the thermal characteristics of the heat exchanger are impaired. (3) Cu and Mg alloy elements effective for improving the strength cannot be added to the core material because the solidus temperature is lowered below the brazing temperature. Furthermore, Mg diffuses on the surface of the brazing sheet during brazing and lowers the function of the flux. (4) Since the aluminum heat exchanger recycled material contains 2 to 5 wt% Si and lowers the solidus temperature below the brazing temperature, it cannot be used as a core material.

  Thus, there are various problems with the current high-temperature brazing filler metal, and these problems can be solved by lowering the melting point of the brazing filler metal. In particular, if the brazing temperature can be lowered to around 520 ° C., the melting of the brazing material and the formation of fillets can be made rapidly, and the brazing operation time can be shortened. For this reason, a low-temperature brazing material made of an Al—Si—Zn—Cu alloy has been proposed (Japanese Patent Laid-Open No. 3-57588), but there is a problem that sufficient corrosion resistance cannot be obtained. Therefore, the present inventors examined the reason why sufficient corrosion resistance cannot be obtained with the low-temperature brazing material, and as a result, the brazing material contains a large amount of Cu that increases the natural potential and improves the corrosion resistance. It was discovered that the compound was formed with Si (8.0 wt% or more) to inhibit the effect of Cu, and further studies were made to complete the present invention. An object of this invention is to provide the low-temperature brazing material for Al alloy joining excellent in corrosion resistance.

  The invention according to claim 1 contains Si in a range of 4.0 wt% to less than 8.0 wt%, Zn in a range of 7.0 wt% to 20.0 wt%, Cu in a range of 10.0 wt% to 35.0 wt%, and the balance Is a low-temperature brazing material for joining aluminum alloys comprising aluminum and inevitable impurities.

  As described above, the low temperature brazing material of the present invention contains an appropriate amount of Cu that increases the natural potential with respect to Zn that lowers the natural potential, and the content of Si that inhibits the effect of Cu is 8%. Since it is suppressed to less than 0.0 wt%, it has excellent corrosion resistance, and good brazing properties can be stably obtained even in a corrosive environment. In addition, since the brazing temperature can be lowered, all the problems in the high temperature brazing material such as the diffusion of Zn in the sacrificial material of the brazing sheet to the core material and lowering the corrosion resistance of the core material are eliminated, and the brazing work time is further reduced. Can be shortened. Therefore, there is an industrially significant effect.

It is a perspective view of a heat exchanger core. It is a perspective explanatory view of a brazing member for brazing test using the brazing material of the present invention. It is an isometric view explanatory drawing of the brazing article for salt spray tests using the brazing material of this invention. It is a longitudinal cross-sectional explanatory drawing of the tension test method of the brazing article after a salt spray test.

  The low-temperature brazing material for joining an Al alloy of the present invention is obtained by reducing the melting point of the brazing material by adding an appropriate amount of Si, Zn and Cu to the Al base material, and reducing the natural potential (decrease in corrosion resistance) due to the Zn. In addition, an appropriate amount of Cu for increasing the natural potential is suppressed, and the Si content that inhibits the above effect of Cu is suppressed to less than 8.0 wt%.

In the present invention, the reason why the Si content is specified to be 4.0 wt% or more and less than 8.0 wt% is that the melting point of the brazing material is not sufficiently lowered if the content is less than 4.0 wt%, and the natural content of Cu is not less than 8.0 wt%. This is because the effect of increasing the potential is hindered and sufficient corrosion resistance cannot be obtained. The reason for prescribing the Zn content to 7.0 to 20.0 wt% is that the melting point of the brazing material is not sufficiently lowered when the content is less than 7.0 wt%, and the natural potential is significantly reduced when the content exceeds 20.0 wt%. This is because it is difficult to restore the natural potential even when Cu is contained. The reason why the Cu content is specified to be 10.0 to 35.0 wt% is that if it is less than 10.0 wt%, the melting point of the brazing material is not sufficiently lowered, and the decrease of the natural potential due to Zn cannot be sufficiently suppressed. This is because when the content exceeds 0 wt%, an intermetallic compound is generated in the brazing material and the joint becomes brittle.

Hereinafter, the present invention will be described in detail with reference to examples.
As shown in FIG. 2, a sacrificial material (Al—Zn-based JIS7072 alloy) 8 is rolled and bonded to one surface of a core material (Al—Mn-based JIS3003 alloy) 7 at a thickness ratio of 10%, and the present invention is applied to the other surface. A brazing sheet 10 is prepared by mixing a low temperature brazing material 9 powder (atomized powder having an average particle size of 35 μm) having a prescribed composition with an organic binder in a layer form, and a JIS 3003 alloy is formed on the low temperature brazing material 9 layer of the brazing sheet 10. The plate 11 is vertically contacted, Cs flux is applied to the contact portion, and this is held in a nitrogen gas atmosphere furnace at a temperature 5 ° C. higher than the liquidus temperature for 10 minutes to hold the brazing sheet 10 and the JIS 3003 alloy plate 11. Brazed.

(Comparative Example 1)
A brazing sheet and a JIS 3003 alloy plate were brazed by the same method as in Example 1 except that the composition of the brazing material powder was not defined in the present invention.

(Comparative Example 2)
A brazing sheet is prepared by rolling and pressing a sacrificial material (JIS7072 alloy) on one side of the core material (JIS3003 alloy) and a brazing material (JIS4343 alloy) on the other side. A non-corrosive KF-AlF ₃ system flux was applied to the contact part, and the brazing sheet and the JIS 3003 alloy plate were brazed by holding it in a nitrogen gas atmosphere furnace at 597 ° C. for 3 minutes. .

About each brazing member obtained in Example 1 and Comparative Examples 1 and 2, the fillet shape and the gap filling length of the brazing material (indicating the fluidity of the brazing material) were examined. Further, the diffusion distance of Zn in the sacrificial material to the core material in the brazing sheet was measured by EPMA.

  A composite plate (thickness: 0.25 mm) in which a sacrificial material (JIS7072 alloy) is rolled and joined to one side of a core material (JIS3003 alloy) at a thickness ratio of 10% is electro-sewn with the core material as the front side, and the length is 150 mm As a tube material, a brazing material powder of the present invention composition is mixed on the surface of the tube material and coated with an organic binder to form a tube, which is arranged in parallel as shown in FIG. A corrugated fin (JIS3003 alloy + 1 wt% Zn) 13 having a thickness of 70 μm is sandwiched, the whole is fixed with a jig, and held in a nitrogen gas atmosphere furnace at a temperature 5 ° C. higher than the liquidus temperature for 10 minutes. The fin 13 was brazed.

  (Comparative Example 3) The tube and the fin were brazed by the same method as in Example 2 except that the composition of the brazing powder was outside the scope of the present invention.

(Comparative Example 4) A conventional brazing sheet in which a sacrificial material (JIS7072 alloy) is rolled and joined on one side of a core material (JIS3003 alloy) and a brazing material (JIS4343 alloy) on the other side is used as a brazing sheet. The tube and the fin were brazed in the same manner as in Example 2 except that a corrosive KF-AlF ₃ system flux was used and maintained in a 597 ° C. nitrogen gas atmosphere furnace for 3 minutes.

  With respect to each tube and fin brazed product obtained in Example 2 and Comparative Examples 3 and 4, a salt spray test was performed for 100 hours based on JISZ2371, and the brazed product after the test was subjected to a tensile test. As shown in FIG. 4, in the tensile test, three iron pins 14 are passed between each of the fins 13 on the tube 12 side (three-pin set), and the iron pins are inserted between the fins 13 on the tube 15 side. Each of the four 14 pins (four pins) was fixed, the three pins were fixed, and the four pins were pulled downward. It was judged that the corrosion resistance of the brazed part was good when it broke at 2 parts of the fin, and the corrosion resistance of the brazed part was bad when it broke at the brazed part. Further, the corrosion resistance of the tube after the salt spray test was determined by the presence or absence of pinholes. The results of Examples 1 and 2 and Comparative Examples 1 to 4 are shown in Table 1. Table 1 shows the composition of the brazing filler metal powder and the liquidus temperature and the solidus temperature determined by thermal analysis.

  As is apparent from Table 1, the brazing filler metal of the present invention (Nos. 1 to 5) has a good fillet shape and a long gap filling length of the brazing filler metal. The flowability is good and the diffusion distance of Zn in the sacrificial material to the core material is short. In addition, the tensile test after the salt spray test was broken at the fins, indicating that the corrosion resistance of the brazing material was good. Further, since the diffusion of Zn into the core material is small, the tube has excellent corrosion resistance. In contrast, No. of the comparative example. No. 6 has less Cu. No. 7 had a large amount of Si, so that the effect of increasing the natural potential of Cu was not sufficiently obtained. In either case, the brazed part was corroded and fractured at the brazed part. No. 8 (conventional material) has a high brazing temperature (melting point of the brazing material), so that a large amount of Zn in the sacrificial material diffuses into the core material, reducing the corrosion resistance of the core material and pinholes in the tube after the salt spray test. Occurred.

Comparing the time required for brazing (in-furnace holding time including temperature rising and cooling time), when the brazing material of the present invention was used (Example 2), the brazing temperature was around 520 ° C. It was about 1 hour. On the other hand, in the conventional method (Comparative Example 4), the brazing temperature was as high as 600 ° C., and therefore the time required for brazing was about 1.3 hours per cycle. Thus, since the brazing material of the present invention has a low melting point, the brazing temperature can be suppressed to around 520 ° C., and the brazing operation time can be shortened.

In the present invention, since the brazing temperature is suppressed to around 520 ° C., Mn re-dissolves during brazing and the thermal conductivity of the core material is reduced, or Mg diffuses to the surface and functions as a flux. There is no decline. Furthermore, even if Cu or Mg is added to the core material to improve the strength or Si is mixed by using a recycled material, the solidus temperature of the core material does not drop below 530 ° C. It is possible to improve the strength or use recycled materials for the core material.

DESCRIPTION OF SYMBOLS 1 Tube 2 Corrugated fin 3 Header pipe 4 Pipe 5 End cap 6 Side plate 7 Core material 8 Sacrificial material 9 Low temperature brazing material 10 Brazing sheet 11 JIS3003 alloy plate 12 Tube 13 Corrugated fin 14 Iron pin 15 Tube

Claims (1)

Aluminum containing 4.0 wt% or more and less than 8.0 wt% of Si, 7.0 wt% or more and 20.0 wt% or less of Zn, 10.0 wt% or more and 35.0 wt% or less of Cu, with the balance being aluminum and inevitable impurities Low temperature brazing material for alloy joining.

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