JP2013193128A - Brazing method of aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brazing method which has excellent and stable soldering property and is industrially applicable, in the brazing method not using flux utilizing destructive action of an oxide film by Mg.SOLUTION: In a brazing method of an aluminum alloy, the brazing part of an aluminum object to be brazed is disposed in an enclosed closed space; the supply source of Mg is installed inside the closed space, and heating is performed in an inert gas atmosphere without using flux. In the brazing method of the aluminum alloy, the volume X(cm) inside the closed space, the surface area Y(cm) of the Mg supply source inside the closed space, and the surface Mg concentration C(mass%) of the Mg supply source inside the closed space at a brazing temperature satisfy the relational expression of 0.1<Y×C/X<7.

Description

  The present invention relates to a method for brazing aluminum that does not use a flux, and more particularly to a brazing method suitable for manufacturing a heat exchanger.

  Aluminum materials are frequently used in heat exchangers including those mounted on automobiles because of their high thermal conductivity and light weight. A heat exchanger that circulates water, oil, or the like inside to exchange heat is composed of members such as tanks, tubes, fins, etc., and each member is metallically joined by brazing.

  As an aluminum material constituting a heat exchanger manufactured by brazing, a brazing sheet in which a brazing material or the like is clad on one side or both sides of an aluminum alloy plate as a core material is often used. Generally, an aluminum alloy having a melting temperature of 600 ° C. or higher is used as the core material alloy of the brazing sheet, and an Al—Si alloy having a melting temperature of 600 ° C. or lower is used as the brazing material alloy to be clad. A heat exchanger member is produced by combining the brazing sheet with the brazing sheet and heated to a temperature of about 600 ° C., thereby melting only the brazing alloy of the brazing sheet and brazing the other member. Can be produced. That is, by using a brazing sheet, a large number of members constituting the heat exchanger can be brazed at a time, and therefore the brazing sheet is widely used as a heat exchanger material.

  Brazing methods that are mainly put to practical use include vacuum brazing and noclock brazing. In the vacuum brazing method, a brazing material made of an Al-Si-Mg alloy is used. When heated in vacuum, Mg in the brazing material evaporates from the material, and at that time, the oxide film on the surface of the material is destroyed. It is possible to braze. However, the vacuum brazing method has a drawback of requiring an expensive vacuum heating device. On the other hand, the Nocolok brazing method uses a brazing material made of an Al-Si alloy, and after applying the flux, heats it in an inert gas to break the oxide film on the material surface with the flux and enable brazing. Is. However, if there is uneven coating in flux application, it causes brazing failure, and it is necessary to apply the flux uniformly to the required locations.

On the other hand, a method that enables brazing by heating in an inert gas without using an expensive vacuum heating apparatus or flux has been proposed. Patent Document 1 describes a method of brazing without using a flux using a brazing material made of an Al-Si-Mg-based alloy when brazing a turbulent flow insert piece into a flat pipe. . However, it is necessary to braze the outside of the flat pipe by a noclock brazing method in which a flux is applied, and it is not possible to braze all brazing sites without flux. Patent Document 2 describes a method in which a brazed product containing Mg is covered with a carbonaceous cover and heated, and brazed in an inert gas without using a flux. In this method, oxygen present in the carbonaceous cover reacts with carbon in the carbonaceous cover, and brazing is possible by reducing the oxygen concentration in the carbonaceous cover. However, since carbon monoxide and carbon dioxide produced by the reaction of oxygen and carbon are oxidizing gases for aluminum, even if covered with a carbonaceous cover, it does not become a sufficient non-oxidizing atmosphere, so it is stable. It was difficult to obtain brazability.
JP-A-9-206980 JP 2007-44713 A

  An object of the present invention is to provide a brazing method that has a better and stable brazing property and is industrially applicable in a brazing method that does not use a flux that utilizes the destruction action of an oxide film by Mg. To do.

  As a result of intensive studies in view of the above problems, the inventors of the present invention enclose the periphery of the brazed part, and install a prescribed amount of Mg supply source therein, so that the brazed part is It has been found that good brazing properties can be achieved by supplying moderate Mg to the enclosed space surrounding the periphery.

Claim 1 of the present invention is arranged in a closed space in which the brazing part of the brazing object made of aluminum is surrounded, and an Mg supply source is installed inside the closed space, without using a flux, In the brazing method of an aluminum alloy heated in an inert gas atmosphere, the volume X (cm ³ ) inside the closed space, the surface area Y (cm ² ) of the Mg supply source inside the closed space, the inside of the closed space at the brazing temperature The aluminum alloy brazing method is characterized in that the surface Mg concentration C (mass%) of the Mg supply source satisfies the following relational expression.
0.1 <Y × C / X <7

  Claim 2 of the present invention is that the Mg supply source according to claim 1 is a brazing sheet in which an aluminum alloy containing Mg is used as a core material, and one or both surfaces of the core material are clad with an Al-Si alloy brazing material. This is a brazing method characterized by the following.

  Claim 3 of the present invention is a brazing sheet in which the Mg supply source according to claim 1 or claim 2 is made of an aluminum alloy as a core material, and one or both surfaces of the core material are clad with an Al-Si-Mg alloy brazing material. It is a brazing method characterized by being.

  A fourth aspect of the present invention is a brazing method characterized in that the Mg supply source according to any one of the first to third aspects is a brazing sheet constituting a brazed object.

  According to a fifth aspect of the present invention, there is provided a brazing method characterized in that the Mg supply source according to any one of the first to third aspects is a material surrounding the object to be brazed and is an aluminum alloy containing Mg.

  By the brazing method of the present invention, it is possible to obtain good brazing properties without using flux by utilizing the oxide film destruction action of Mg. This brazing method gives stable brazing properties. It is also suitably applied industrially.

Front view showing a state before brazing, which is a gap filling test piece for brazing evaluation Front view showing a state after brazing, which is a gap filling test piece for brazing evaluation

  The present invention is described in detail below.

Although the surface of the aluminum material is covered with an oxide, it is necessary to destroy the oxide on the surface to expose the metal surface of the aluminum in order to enable brazing. In the brazing method of the present invention, the oxide on the aluminum surface is destroyed by using Mg, which is easier to oxidize than aluminum. That is, the aluminum metal surface is exposed by the reaction of Al ₂ O ₃ + Mg → Al + MgO on the aluminum surface. Furthermore, the exposed aluminum metal surface comes into contact with the atmospheric gas, but when the amount of oxygen in the atmosphere is large, the aluminum metal surface is oxidized again. In order to enable brazing, it is desirable that the oxygen concentration in the atmosphere is low. At least around the object to be brazed, the oxygen concentration needs to be sufficiently low. In the present invention, oxygen remaining in a trace amount in an inert gas atmosphere is reacted with Mg to generate a low oxygen atmosphere, preventing oxidation of the aluminum metal surface and enabling brazing.

  In order to achieve destruction of the oxide film on the surface of the aluminum material due to Mg as described above and low oxygen concentration of the atmosphere gas, the brazed portion of the brazing object made of aluminum is arranged in a closed space surrounded by the surroundings. It is necessary to install an Mg supply source inside the closed space. Normally, brazing is carried out in a heating furnace filled with an inert gas. However, if a brazing object is installed in the heating furnace as it is, the brazing object is always used because of the air flow generated in the heating furnace. Contact with trace amounts of oxygen in the inert gas. In order to make the whole furnace into a low oxygen atmosphere with Mg, a large amount of Mg supply source is required, which is practically difficult. Therefore, by installing a closed space surrounding the brazed portion and installing an Mg supply source inside, a small volume of the closed space is efficiently made into a low oxygen atmosphere by Mg.

As a result of examining the amount of Mg installed in the closed space, the volume X (cm ³ ) in the closed space, the surface area Y (cm ² ) of the Mg supply source, and the surface of the Mg supply source in the closed space at the brazing temperature It has been found that the brazing property is affected by the Mg concentration C (mass%). And it turned out that favorable brazing property is obtained when the relational expression of 0.1 <Y × C / X <7 is satisfied. This relational expression can be brazed with a small amount of Mg supply when the volume of the closed space is small, but when the volume of the closed space is large, the area of the Mg supply source is increased or an Mg supply source with a high surface Mg concentration is used. It means that it needs to be installed. When Y × C / X is 0.1 or less, the amount of Mg supplied is small, so the inside of the closed space cannot be maintained in a low oxygen atmosphere, and the brazing property is lowered. On the other hand, if Y × C / X is 7 or more, the effect of Mg in a low oxygen atmosphere is saturated, and the amount of Mg supplied in the closed space becomes excessive, and Mg is deposited on the surface of the brazed object. Will decline. A more preferable range is 2 <Y × C / X <6.

  As the Mg supply source, a Mg-containing aluminum alloy such as 5000 series or Mg alone can be installed in the closed space. In this case, since the Mg concentration on the surface hardly changes before and after the brazing heat, the surface Mg concentration C (mass%) of the Mg supply source in the closed space at the brazing temperature is the Mg content before the brazing heat. Can be substituted. Although the shape is not limited, a plate-like one is preferable in order to clarify the surface area of the Mg supply source.

  Further, as the Mg supply source, a brazing sheet in which an aluminum alloy containing Mg is used as a core and an Al—Si alloy brazing material is clad on one side or both sides of the core can be used. If the brazing sheet is composed of the brazing sheet and its Mg supply amount is sufficient, it is not necessary to install a separate Mg supply source in the closed space. Since Mg of the core material diffuses on the surface of the brazing material during the heat of brazing, the Mg concentration on the surface changes before and after the brazing heat. Therefore, the surface Mg concentration after the brazing heat is applied as the surface Mg concentration C (mass%) of the Mg supply source inside the closed space at the brazing temperature. Here, the Mg content of the core material is preferably 0.15 to 2.5 mass% (hereinafter simply referred to as%). If it is less than 0.15%, the amount of Mg diffusing into the brazing material of the brazing sheet during brazing addition heat decreases, and a sufficient amount of Mg cannot be obtained, resulting in reduced brazing properties. On the other hand, if it exceeds 2.5%, an excessive amount of Mg diffuses from the core material to the brazing material during the brazing heat, and the brazing property is lowered by increasing the thickness of the MgO oxide film as described above.

  Furthermore, as an Mg supply source, a brazing sheet in which an aluminum alloy is used as a core and an Al—Si—Mg alloy brazing material is clad on one or both sides of the core can be used. Also in this case, the brazing material Mg diffuses to the core material side due to the brazing addition heat, and the Mg concentration on the surface changes before and after the brazing addition heat, so the surface Mg concentration C (mass) of the Mg supply source inside the closed space at the brazing temperature %), The surface Mg concentration after the brazing heat is applied. The Mg content of the brazing material is preferably 0.5 to 2.0%. If it is less than 0.5%, a sufficient amount of Mg that can exhibit an effective oxide film breaking action cannot be obtained, and brazing properties are reduced. If it exceeds 2.0%, an excessive amount of Mg diffuses on the surface of the brazing material during the brazing heat, and a large amount of Mg remains without being evaporated from the surface of the brazing material. As a result, an oxide film of MgO is formed, which becomes thicker and lowers the brazing property.

  Moreover, it is also possible to use the aluminum alloy containing Mg of both the core material and the brazing material as the brazing sheet. In this case, the Mg content in the brazing material is preferably 0.1 to 1.8%, and the Mg content in the core material is preferably 0.15 to 1.2%. Furthermore, a material in which an aluminum alloy not containing Mg for preventing oxidation is clad on the opposite side of the surface of the brazing material in contact with the core material is also applicable as the Mg supply source.

  As long as it does not melt at the brazing temperature, an element other than Mg may be added to the core material from the viewpoint of the strength and corrosion resistance of the material. Examples of such elements include Si, Fe, Mn, Ni, Cu and the like for improving the strength of the material amount, and Zn for imparting a sacrificial anticorrosive effect to the brazing sheet and improving the corrosion resistance. , Sn, Si and the like. Moreover, you may contain the well-known element contained in a brazing material as additive elements other than Mg in a brazing material. As the brazing material containing such an element, an Al—Si based aluminum alloy containing 4.0 to 13.0% Si is preferably used. In addition to Si, a brazing material to which elements such as Zn and Cu are added in order to adjust the melting point and potential of the brazing sheet can also be used.

  In addition, an aluminum alloy containing Mg can be used using a material surrounding the brazed object as an Mg supply source. In this case, Mg is supplied into the closed space from the inner surface of the material to be enclosed. When the amount of Mg to be supplied is insufficient with only the brazing object, it becomes an effective means as an Mg supply source.

  As conditions for the brazing method according to the present invention, general conditions can be used. The time required to reach the melting temperature of the brazing material is 10 to 30 minutes. The brazing temperature is a temperature equal to or higher than the melting temperature of the brazing material, and is usually 590 to 610 ° C., although it varies depending on the alloy composition of the brazing material. The holding time is usually 3 to 10 minutes.

  Next, the present invention will be described based on examples and comparative examples.

  An alloy having the composition shown in Table 1 was cast. A1 to A5 were homogenized at 520 ° C., and then both surfaces were chamfered to a thickness of 40 mm to obtain a core material for a brazing sheet. Alloys B1 to B4 for brazing material were hot rolled to a thickness of 5 mm. The produced core material and brazing material are combined in the order of “brazing material / core material / brazing material” in the order of the brazing sheet in Table 2 and heated to 500 ° C. to perform clad rolling, and further cold-rolled to a thickness of 1 After annealing to 0.0 mm, annealing was performed to produce a brazing sheet of double-sided brazing material. The clad thickness of the brazing material is 0.1 mm per side (clad rate 10%).

Using the brazing sheet produced as described above, a gap filling test piece shown in FIG. 1 was produced. The brazing sheet was cut into 60 × 20 mm to obtain a vertical plate (1). In addition, a JISA3003 having a plate thickness of 1.0 mm was obtained by cutting a bare material into 70 × 20 mm as a horizontal plate (2). The vertical plate (1) stands upright with respect to the horizontal plate (2). Spacer (3) for forming a gap between stainless steel wires of φ2.5 mm, 60 mm along the long side direction of horizontal plate (2) from the position of contact portion (6) between horizontal plate (2) and vertical plate (1) It installed along the short side direction of the horizontal board (2) in the separated position. In this way, a gap filling test piece was produced. Since the core material or brazing material of each brazing sheet contains Mg, the surface of the brazing sheet serves as a supply source of Mg during brazing addition heat. Therefore, the surface area using the brazing sheet as the supply source of Mg is 24 cm ² for both areas of the brazing sheet.

On the other hand, as the enclosure material, C1 to C5 in Table 1 were annealed after the thickness was set to 1.0 mm by hot rolling and cold rolling. The enclosure material was bent to produce an enclosure for the above-mentioned gap-weighted test piece. There were two types of enclosures, one with an upper surface of 80 × 25 mm and a height of 25 mm, and one with an upper surface of 80 × 40 mm and a height of 40 mm, both of which had an open bottom surface. Volume of space formed by the enclosure material of the former is 50 cm ^3, the latter is 128 cm ^3. In the case of an enclosure made of an alloy containing Mg, the inner surface of the enclosure becomes a source of Mg during brazing heat. Therefore, the surface area using the enclosure material as the supply source of Mg is the inner area of the enclosure material, the former being 72.5 cm ² and the latter being 128 cm ² .

  A gap filling test piece was placed on the stainless steel plate, and an enclosure was placed so as to cover the gap filling test piece, and the gap filling test piece was brazed without applying flux. Nitrogen gas was introduced into the furnace as an inert gas and heated in an atmosphere in which the oxygen concentration was adjusted to 10 ppm or less. Measure the temperature of the gap filling test piece in the enclosure, heat it under the temperature rising condition so that the time until the temperature reaches 600 ° C. is about 15 minutes, hold it at 600 ° C. for 5 minutes, and then cool it. Was taken out of the furnace.

As shown in FIG. 2, for the gap filling test piece after brazing, the length of the fillet (4) formed from the contact point of the horizontal plate (2) and the vertical plate (1) was measured, and the gap filling length ( 5). Table 2 shows the measured gap filling length. The gap filling length was evaluated according to the following criteria.
A: The gap filling length is 30 mm or more. O: The gap filling length is 20 or more and less than 30 mm. X: The gap filling length is less than 30 mm.
◎ and ○ were accepted, and x was rejected.

  Further, a part of the brazing sheet after brazing was cut out, and the Mg concentration on the surface of the brazing material was measured. For the measurement of Mg concentration, EPMA was used to analyze the surface of the brazing material, and compared with a calibration curve prepared in advance, the Mg concentration on the surface of the brazing material was used. The measurement results of the surface Mg concentration are shown in Table 2.

  Since there was almost no fluctuation in the surface Mg concentration before and after brazing, the surface analysis after brazing was not performed. The surface Mg concentration of the supply source using the enclosure material as the supply source of Mg is the amount of Mg contained in the material, and is shown in Table 2.

Y × C / X was calculated from the surface area Y (cm ² ), the surface Mg concentration C (%), and the space volume X (cm ³ ) serving as the Mg supply source for each gap filling test piece and listed in Table 2. When the Mg supply source is both the brazing sheet and the enclosure, the total value of Y × C is divided by the space volume X to obtain a value of Y × C / X.

  In Examples 1 to 24 of the present invention, the gap filling length was 20 mm or more, and good brazing properties were exhibited. In Comparative Example 1 and Comparative Examples 3 to 6, since the value of Y × C / X was smaller than the range of the present invention, the brazing property was unacceptable. In Comparative Example 2, since the value of Y × C / X was larger than the range of the present invention, the brazing property was unacceptable.

  By applying the brazing method of the present invention and utilizing the Mg oxide film breaking action and heating in an inert gas without using a flux, excellent brazing properties can be achieved. In addition, stable and reliable brazing is possible, and industrial applicability is excellent.

DESCRIPTION OF SYMBOLS 1 Vertical material 2 Horizontal material 3 Spacer 4 Fillet 5 Crevice filling length 6 Contact part

Claims (5)

Aluminum that is brazed with aluminum brazing material is placed in a closed space surrounded by aluminum, an Mg supply source is installed inside the closed space, and aluminum is heated in an inert gas atmosphere without using a flux. In the brazing method of the alloy, the volume X (cm ³ ) inside the closed space, the surface area Y (cm ² ) of the Mg source inside the closed space, the surface Mg concentration C ( mass%) satisfy | fills the following relational expression, The brazing method of the aluminum alloy characterized by the above-mentioned.
0.1 <Y × C / X <7   The brazing method according to claim 1, wherein the Mg supply source is a brazing sheet in which an aluminum alloy containing Mg is used as a core, and one or both surfaces of the core are clad with an Al—Si alloy brazing material.   The brazing sheet characterized in that the Mg supply source according to claim 1 or 2 is a brazing sheet in which an aluminum alloy is used as a core material, and one or both surfaces of the core material are clad with an Al-Si-Mg alloy brazing material. Method.   The brazing method characterized by the Mg supply source of Claims 1-3 being a brazing sheet which comprises the brazing object.   4. The brazing method according to claim 1, wherein the Mg supply source is a material surrounding the brazing object and is an aluminum alloy containing Mg.

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