JP2013086103A - Aluminum alloy brazing sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy brazing sheet used for brazing in an inert gas atmosphere without using flux.SOLUTION: A hypereutectic Al-Si-based brazing filler metal including 13-20% of Si and the balance aluminum with unavoidable impurities and a hypoeutectic Al-Si-based brazing filler metal including 4-11% of Si and the balance aluminum with unavoidable impurities are superposed and cladded on one face or both faces of a core made of an aluminum alloy so that the hypereutectic Al-Si-based brazing filler metal becomes a surface layer. Either one or both of the hypoeutectic Al-Si-based brazing filler metal and the core include Mg. The Mg content of the hypoeutectic Al-Si-based brazing filler metal is 0.2-1.0% and the Mg content of the core is 0.4-1.2%.

Description

  The present invention relates to an aluminum alloy brazing sheet used for brazing in an inert gas atmosphere without using a flux.

  As a method of brazing and joining a member such as a heat exchanger made of an aluminum alloy brazing sheet clad with an Al—Si brazing material, a fluoride flux is interposed in the member and heated to about 600 ° C. in a nitrogen gas furnace. Then, there are a flux brazing method in which a joint is formed by molten Al—Si brazing and a vacuum brazing method in which heating is performed at about 600 ° C. in a vacuum furnace using an Al—Si brazing material containing Mg. Commonly used.

  In the flux brazing method, JIS-BA4045 alloy containing 9 to 11% Si and JIS-BA 4343 alloy containing 6.8 to 8.2% Si are used as the Al-Si brazing material, In the vacuum brazing method, Bi: 0.02 to 0.20% is further added to JIS-BA4004 alloy and JIS-BA4004 alloy containing Si: 9 to 10.5% and Mg: 1.0 to 2.0%. Including JIS-BA 4104 alloy is used as the Al—Si brazing material, and an Al—Si brazing material having a hypoeutectic composition is applied to all of them.

  The reason for the application of Al-Si brazing material with hypoeutectic composition is that, in brazing such as heat exchangers that heat and heat in a short time, the rate of temperature increase for thin fins and thick plates However, when a brazing material with a eutectic composition (Si: 12.6%) is used, the brazing part of the part exceeding the eutectic temperature flows locally and violently. This is because the solder may melt the base material or the thin part of the plate may melt, so that excessive solder flow is suppressed, and poor bonding is less likely to occur. In addition, an Al-Si brazing material having a hypoeutectic composition that gradually melts as the temperature rises is used.

In addition, in order to braze and join aluminum materials, it is necessary to destroy a dense and strong oxide film. For this reason, as described above, a brazing method using a fluoride flux or heating in a vacuum furnace is required. The vacuum brazing method is applied. However, the vacuum brazing method has a cost problem, and in the brazing method using a fluoride-based flux, a flux of 3 g / m ² or more is applied in order to destroy the oxide film and obtain a good joint. Since the applied flux remains as a residue on the product surface even after brazing, if the refrigerant passage has a very fine structure, the flux residue fills the microstructure and heat exchange There are problems such as performance degradation.

  Furthermore, since the flux is extremely reactive, there is a problem that the jig for conveying the furnace wall material of the brazing heating furnace and the article to be brazed significantly deteriorates. In addition, expensive and highly resistant materials were used, and maintenance costs were high. Since the flux itself is expensive, the cost is increased, and a technique capable of brazing and joining without using the flux has been desired.

  As a method of brazing and joining without using flux, an aluminum alloy brazing sheet in which 0.2 to 1.0% Mg is added to the core material and a small amount of Mg is also added to the brazing material is used, and the oxygen concentration is adjusted. A method of heating by brazing in a non-oxidizing gas atmosphere kept extremely low (Patent Document 1) or adding 0.1 to 5.0% Mg to a brazing material of aluminum clad material, A method (Patent Document 2) in which the amount of Si particles is increased and the brazing target member is brought into close contact with the brazing target has been proposed (Patent Document 2). Since it cannot be taken, it takes time in the process of assembling the heat exchanger.

  On the other hand, an Al—Si brazing material having a hypereutectic composition containing Si exceeding the eutectic composition (Si: 12.6%) used in torch brazing is formed of aluminum on the surface of the Si particles present in the brazing material. Since it is difficult to produce an oxide film, the amount of aluminum oxide film formed on the surface can be reduced, and therefore the amount of flux applied to destroy the oxide film and obtain good bonding can be reduced. However, when a hypereutectic Al-Si brazing material containing Si exceeding 13% is used, excess Si melts the base material, making it difficult to ensure sound joint quality. The problem arises.

JP 2011-025276 A Japanese Patent No. 4547032

  In order to obtain an aluminum alloy brazing sheet that can be used for brazing in an inert gas atmosphere without using a flux, the inventors conducted various tests and examinations based on the prior art. As a brazing material clad on the core material, a hypoeutectic Al-Si brazing material and a hypereutectic Al-Si brazing material are clad with each other so that the hypereutectic Al-Si brazing material becomes a surface layer. In this case, problems with the hypereutectic brazing material such as excessive flow of the brazing and occurrence of defects due to excessive melting can be prevented, and the advantages of the Al-Si brazing material having the hypereutectic composition can be utilized. Furthermore, it has been found that by adding Mg to a hypoeutectic Al—Si brazing material or a core material, brazing can be performed in an inert gas atmosphere without using a flux.

  The present invention has been made on the basis of the above-mentioned findings, and the object thereof is to achieve brazing in an inert gas atmosphere without using a flux and to achieve excellent brazing properties. An object of the present invention is to provide an aluminum alloy brazing sheet that can be used.

  In order to achieve the above object, an aluminum alloy brazing sheet according to claim 1 is an aluminum alloy brazing sheet used for brazing in an inert gas atmosphere without using a flux, and comprises an aluminum alloy. One side or both sides of the core material includes Si: 13 to 20% (mass%, the same shall apply hereinafter), the hypereutectic Al-Si brazing material composed of the balance aluminum and inevitable impurities, and Si: 4 to 11% Then, the hypoeutectic Al-Si brazing material composed of the remaining aluminum and inevitable impurities is clad so that the hypereutectic Al-Si brazing material becomes a surface layer, and the hypoeutectic Al-Si brazing material is clad. Either or both of the material and core material contain Mg, the Mg content of the hypoeutectic Al-Si brazing material is 0.2 to 1.0%, and the Mg content of the core material Characterized in that it is a 0.4 to 1.2%.

  An aluminum alloy brazing sheet according to claim 2 is characterized in that, in claim 1, Sr: 20 to 500 ppm is added to one or both of the hypereutectic Al-Si brazing material and the hypoeutectic Al-Si brazing material. It is characterized by containing.

  The aluminum alloy brazing sheet according to claim 3 is the aluminum alloy brazing sheet according to claim 1 or 2, wherein the hypereutectic Al-Si brazing material is further Zn: 0.1-3.0%, Cu: 0.1-0.6. %, And the hypoeutectic Al—Si brazing material further contains Zn: 0.5-4.0%, Cu: 0.1-0.8% It contains 1 type or 2 types, It is characterized by the above-mentioned.

  According to the present invention, it is possible to braze in an inert gas atmosphere without using a flux, and there are problems in a hypereutectic brazing material such as excessive flow of wax and occurrence of defects due to excessive dissolution. An aluminum alloy brazing sheet is provided that makes it possible to achieve excellent brazing properties.

It is a figure which shows the gap filling test piece used in an Example.

  The aluminum alloy brazing sheet of the present invention includes a hypoeutectic Al—Si alloy brazing material (hereinafter, hypoeutectic brazing material) and a hypereutectic Al—Si alloy brazing material (hereinafter, hypereutectic alloy brazing material). The hypereutectic brazing material becomes a surface layer, and the characteristics of the hypereutectic brazing material will be described. Si is 12.6. In the eutectic Al—Si alloy brazing material containing 1%, the α phase in which Si is dissolved in Al and the Si phase have a eutectic structure crystallized in a dendrite shape. The hypoeutectic brazing filler metal having a Si content of less than 12.6% has a structure in which the α phase and the Al—Si eutectic structure are mixed, and the Si content exceeds 12.6%. The brazing material has a structure in which an Al—Si eutectic structure and Si grains are mixed.

When coarse Si particles existing in the hypereutectic brazing material are exposed on the surface of the brazing material, an aluminum oxide film (Al ₂ O ₃ ) hardly forms on the surface of the Si particles, Since the thermal expansion coefficient and the thermal expansion coefficient of the α phase are different, the aluminum oxide film formed on the surface of the α phase of the brazing material is likely to crack near the Si particles due to thermal expansion during brazing heating.

  On the surface of the Si grains, the oxide film is more easily crushed than the oxide film formed on the surface of the Al—Si eutectic structure, so that the wettability is improved and the molten brazing begins to form fillets at the joint. Since it becomes easy to push up its own oxide film, fillet forming ability is also improved. The improvement of wettability and the improvement of fillet forming ability enable brazing and joining. The present invention has been made based on the finding that the above-described characteristics of the hypereutectic brazing material can be utilized by using the hypereutectic brazing material as a surface layer.

  Further, when heating is performed at a temperature equal to or higher than the eutectic temperature (577 ° C.) of Al—Si in a state where the hypereutectic brazing material and the aluminum material having a low Si concentration are in contact, the excess Si and the aluminum material are melted to approach the eutectic composition. For this reason, a material in which a hypereutectic brazing material and an aluminum alloy core material are clad causes a problem that the core material melts. The Al—Si brazing material close to the eutectic composition has a small difference between the solidus temperature and the liquidus temperature, so that the brazing rapidly melts in brazing heating, and the molten brazing becomes easy to flow. Causes excessive dissolution at the flow site. This has been the reason why the hypereutectic brazing material has not been put into practical use.

  In the present invention, a hypoeutectic brazing material is disposed inside the hypereutectic brazing material in order to solve the above problems. Since the hypereutectic braze is metallically bonded to the hypoeutectic braze by clad rolling, the hypereutectic braze reacts with the hypoeutectic braze before reacting with the base metal, and the hypoeutectic braze. Since the brazing material begins to melt simultaneously with the hypereutectic brazing material (at the Al-Si eutectic temperature of 577 ° C.), the brazing filler metal resulting from the hypereutectic brazing material immediately fuses with the hypoeutectic brazing material. To do. For example, if a hypereutectic brazing material containing 14% Si and a hypoeutectic brazing material containing 6% Si are metal-bonded in equal amounts, substantially the same properties as the brazing material of Si 10% are exhibited. According to the present invention, the problem can be overcome without losing the above-mentioned characteristics of the hypereutectic brazing material, and by including Mg in one or both of the hypoeutectic brazing material and the core material, It is possible to braze without using a flux in an inert gas atmosphere.

The significance of each component element of the hypereutectic brazing filler metal and the hypoeutectic brazing filler metal and the reason for the limitation will be described.
(Hypereutectic brazing material)
Si: 13-20%
When the amount of Si particles in the brazing material increases, the area of the Si particles on the brazing material surface increases, and an aluminum oxide film (Al ₂ O ₃ ) formed on the brazing material surface during material production and brazing heating hardly occurs. Become. Also, cracks are likely to occur in the aluminum oxide film due to the difference in thermal expansion between the Si particles and the aluminum matrix during brazing heating. The preferable content of Si is in the range of 13 to 20%. When the content is less than 13%, the effect is small. When the content exceeds 20%, it becomes difficult to produce a brazing material and a plate material clad with the brazing material.

Sr: 20 to 500 ppm
Sr functions to refine the Si particles in the brazing material. The preferable content of Sr is in the range of 20 to 500 ppm. If the content is less than 20 ppm, the effect is small, and even if the content exceeds 500 ppm, the effect is saturated and is not efficient.

Zn: 0.5-3.0%
Zn functions to lower the melting point of the brazing material. The preferable content of Zn is in the range of 0.5 to 3.0%. If the content is less than 0.5%, the effect is small. If the content exceeds 3.0%, the fillet potential becomes too low, and in some cases, bonding Penetration corrosion occurs in the part, and the joint strength decreases. A more preferable content range of Zn is 1.5 to 3.0%.

Cu: 0.05 to 0.6%
Cu functions to lower the melting point of the brazing material. The preferable content of Cu is in the range of 0.05 to 0.6%, and if it is less than 0.05%, the effect is small, and if it exceeds 0.6%, it acts as a cathode when exposed to a corrosive environment. Corrosion is likely to occur in other parts. A more preferable content range of Cu is 0.3 to 0.6%.

(Hypoeutectic brazing material)
Si: 4-11%
The hypoeutectic brazing material, like the hypereutectic brazing material, forms a molten brazing during brazing heating to form a joint fillet. When there is no hypoeutectic brazing filler metal, the amount of Si in the hypereutectic brazing filler metal is large. Therefore, a part of the core material is melted with the melting of the brazing filler to form a eutectic composition. The hypoeutectic brazing material functions to reduce the Si content of the hypereutectic brazing material and not to melt the core material. When the amount of Si in the hypereutectic brazing filler metal is large and the thickness of the hypereutectic brazing filler metal layer is large, it is effective to reduce the amount of Si in the hypoeutectic brazing filler metal. The preferable content of Si in the hypoeutectic brazing filler metal is in the range of 4 to 11%. If it is less than 4%, it is difficult to form a brazing filler. If it exceeds 11%, the Si content of the hypereutectic brazing filler metal is reduced. There is a risk that a part of the core material is melted.

Sr: 20 to 500 ppm
Sr functions to refine the Si particles in the brazing material. The preferable content of Sr is in the range of 20 to 500 ppm. If the content is less than 20 ppm, the effect is small, and even if the content exceeds 500 ppm, the effect is saturated and is not efficient.

Mg: 0.2-1.0%
After the hypereutectic brazing filler metal and the hypoeutectic brazing filler metal are melted, Mg in the hypoeutectic brazing filler metal diffuses to the surface, reacts with the oxide film (Al ₂ O ₂ ) on the surface, and spinel type compound ( By forming (Al ₂ MgO ₄ ), the effect of destroying the oxide film is exhibited. When Mg is contained in the hypereutectic brazing material, MgO is likely to be formed during the production of the material and during the temperature rise of the brazing heating, and the destruction of the oxide film is inhibited. It is preferable to add to the hypoeutectic brazing filler metal. The preferable content of Mg is in the range of 0.2 to 1.0%. If it is less than 0.2%, the effect of destroying the oxide film is poor, and if it exceeds 1.0%, the amount of MgO formed increases. Brazing property decreases.

Zn: 0.5-4.0%
Zn functions to lower the melting point of the brazing material. The preferable content of Zn is in the range of 0.5 to 4.0%. When the content is less than 0.5%, the effect is small. When the content exceeds 4.0%, the potential of the fillet becomes too low. Penetration corrosion occurs in the part, and the joint strength decreases. A more preferable content range of Zn is 2.5 to 4.0%.

Cu: 0.05 to 0.8%
Cu functions to lower the melting point of the brazing material. The preferable content of Cu is in the range of 0.05 to 0.8%, and if it is less than 0.05%, the effect is small, and if it exceeds 0.8%, it acts as a cathode when exposed to a corrosive environment. Corrosion is likely to occur in other parts. A more preferable content range of Cu is 0.4 to 0.7%.

(Heartwood)
Mg: 0.4-1.2%
After the hypereutectic brazing filler metal and hypoeutectic brazing filler metal are melted, Mg in the core material diffuses to the surface, reacts with the oxide film (Al ₂ O ₃ ) on the surface, and spinel type compound (Al ₂ MgO ₄ ) Is effective in destroying the oxide film. In order for the hypoeutectic brazing material to suppress the diffusion of Mg, it is necessary to increase the amount of Mg in the hypoeutectic brazing material. The preferable Mg content in the core material is in the range of 0.4 to 1.2%. If the content is less than 0.4%, the effect of destroying the oxide film is poor. Penetration into the braze decreases. A more preferable content range of Mg is 0.6 to 1.0%.

  The core material of the brazing sheet of the present invention is not particularly limited as long as it is usually used as a material for a heat exchanger, and is not particularly limited except for containing Mg, but in order to improve the strength, Mn, Cu, Si , Fe can be contained, and elements such as Cr, Ti and Zr can be added to control the structure. Moreover, when using as a member which gave the sacrificial anode effect, elements, such as Zn, In, and Sn, can also be added.

(Layer thickness and clad rate of hypereutectic brazing filler metal and hypoeutectic brazing filler metal)
The layer thickness and clad rate of the hypereutectic brazing material and hypoeutectic brazing material to be clad can be appropriately set. The average Si concentration of the hypereutectic brazing material and hypoeutectic brazing material is preferably 6 to 11%, and the total cladding ratio of the hypereutectic brazing material and hypoeutectic brazing material is preferably 5 to 25%.

(Average Si concentration)
The average Si concentration is: (Si concentration of hypereutectic brazing filler metal layer thickness of hypereutectic brazing filler metal + Si concentration of hypoeutectic brazing filler metal layer thickness of hypoeutectic brazing filler metal) / (hypereutectic brazing filler metal) (The thickness of the layer + the layer thickness of the hypoeutectic brazing material).

  In the present invention, when a hypoeutectic brazing material and a hypereutectic brazing material are clad on one side of a core material made of an aluminum alloy, a general Al-Si alloy brazing material, a sacrificial anode is formed on the opposite surface of the core material. A known skin material such as a material or pure aluminum can be clad, and an intermediate material can also be clad between the core material and the skin material.

  The brazing sheet of the present invention can be manufactured using a known technique. That is, the brazing sheet is manufactured by ingoting a hypereutectic brazing material and a hypoeutectic brazing material having a predetermined composition, a core material, and, if necessary, a skin material and an intermediate material by continuous casting, and cutting the resulting slab. Then, it is adjusted to a predetermined thickness and overlapped, or homogenized if necessary, hot rolled and overlapped, clad rolled by hot rolling, then cold rolled, and intermediated as necessary This is done by adding annealing.

  Examples of the present invention will be described below in comparison with comparative examples to demonstrate the effects of the present invention. In addition, these Examples show one embodiment of this invention, and this invention is not limited to these.

Example 1 and Comparative Example 1
Hypereutectic brazing material (hereinafter referred to as first layer brazing material) (A1 to A10, A11 to A14) having the composition shown in Table 1, hypoeutectic brazing material (hereinafter referred to as second layer) having the composition shown in Table 2 (Referred to brazing material) (B1 to B10, B11 to B15), core materials (C1 to C2, C11) having the compositions shown in Table 3 are combined as shown in Table 4, and a single-side brazing sheet (thickness 0) .4 mm) 1-20, 21-35. In Tables 1 to 3, those outside the conditions of the present invention are underlined.

  The layer thicknesses of the first layer brazing material and the second layer brazing material were 0.012 mm and 0.028 mm, respectively, and the total thickness of the brazing material was 0.04 mm (cladding rate 10%). The brazing sheets 20 to 25 are obtained by cladding only the first layer brazing material on one side of the core material with a thickness of 0.04 mm. These brazing sheets 1 to 35 were subjected to a gap filling test and a corrosion resistance test by the following methods.

Gap filling test: As shown in FIG. 1, a brazing sheet that has been degreased and partially coated with a flux (fluoride-based flux containing KF and AlF ₃ as a basic composition) is used as a horizontal material, and a 3003 alloy plate (thickness) 1 mm) was assembled as a vertical member to form a gap filling test piece. Using a nitrogen gas furnace consisting of a two-chamber furnace with a preheating chamber and a brazing chamber with an internal volume of 0.4 m ³ , the gap-filled test piece was charged into the brazing chamber and brazed at an ultimate temperature of 595 ° C. did. As brazing conditions, 20 m ³ / h of nitrogen gas was fed into each chamber of the nitrogen gas furnace, and the temperature was raised from 450 ° C. to 595 ° C. in about 4 minutes. The oxygen concentration in the brazing chamber at the end of heating was 16 to 24 ppm. When the temperature of the gap filling test piece reached 595 ° C. in the brazing chamber, the gap filling test piece was transferred to the preheating chamber, cooled to 550 ° C. in the preheating chamber, and then taken out and cooled in the atmosphere. The gap filling length was measured from the gap filling specimen after cooling to evaluate the fillet forming ability. Those having a gap filling length of 25 mm or more were evaluated as having good fillet forming ability. The evaluation results are shown in Tables 4-5.

  Corrosion resistance test: As with the gap filling test piece, a reverse T-shaped test piece was prepared using the brazing sheet as the horizontal material and the 3003 alloy plate as the vertical material, and the SWAAT test was conducted for one month based on ASTM G85, and the fillet corrosion status The corrosion resistance was evaluated by observing. The case where the horizontal material and the vertical material were separated due to the corrosion of the fillet was evaluated as poor corrosion resistance (x). The evaluation results are shown in Tables 4-5.

  As seen in Table 4, all the brazing sheets 1 to 20 according to the present invention were clad with a conventional brazing sheet (for example, Al-10% Si brazing material on one side of the core material C1 without applying flux). In the gap filling test, a fillet having a gap filling length of 25 mm or more was formed in the gap filling test, as in the case where the flux was applied using a brazing sheet). Also in the corrosion test, the joint state of the fillet was good and showed good corrosion resistance.

In addition, when the cross section of the joining part was observed, the joining part of the brazing sheets 1 to 20 according to the present invention is, for example, a conventional brazing sheet in which an Al-10% Si brazing material is clad with a thickness of 40 μm on one side of the core material C1. (Thickness: 0.4 mm), and a good bonding structure similar to the bonding portion when a gap filling test was performed by applying flux at a coating amount of 5 g / m ² , and a base material made of brazing material The dissolution amount of was almost the same.

On the other hand, when the gap filling test was performed on the brazing sheet 21 just clad with the first layer brazing material A1 without applying the flux, the fillet was hardly formed and a part of the core material was melted. did. The brazing sheet 22 only clad with the first layer brazing material A11 does not form any fillet in the gap filling test without flux application, and the fillet formation is slight when the flux application amount is 1 g / m ² (brazing sheet 23). Yes, a good bonding state was obtained for the first time when the flux application amount was 3 g / m ² (brazing sheet 24) and the flux application amount was 5 g / m ² (brazing sheet 25).

  In the first layer brazing material, it was difficult to produce the brazing sheet 26 having a high Si content. The brazing sheet 27 with a high Zn content and the brazing sheet 28 with a high Cu content were both poor in corrosion resistance.

  In the brazing sheet 29 having a low Si content in the second layer brazing material, a sufficient fillet was not formed in the gap filling test when no flux was applied. The brazing sheet 30 having a large Si content excessively dissolved the vertical member in the gap filling test. In the brazing sheet 31 having a high Mg content, a sufficient fillet was not formed in the gap filling test when no flux was applied. The brazing sheet 32 with a high Zn content and the brazing sheet 33 with a high Cu content were both poor in corrosion resistance.

  In the core material, the brazing sheet 34 having a high Mg content penetrates the grain boundary of the core material, and when the flux is not applied, a sufficient fillet is not formed in the gap filling test. In the brazing sheet 35 in which neither the core material nor the second layer brazing material contains Mg, a sufficient fillet was not formed.

Claims (3)

An aluminum alloy brazing sheet used for brazing in an inert gas atmosphere without using a flux, and Si: 13 to 20% (mass%, below) on one or both sides of a core material made of an aluminum alloy And a hypereutectic Al—Si based brazing material comprising the balance aluminum and unavoidable impurities and Si: 4 to 11%, and a hypoeutectic Al—Si brazing material comprising the balance aluminum and unavoidable impurities And the hypereutectic Al-Si brazing material is overlapped and clad so that it becomes a surface layer, and either or both of the hypoeutectic Al-Si brazing material and the core material contain Mg, and the hypoeutectic crystal An aluminum alloy brazing sheet, wherein the Al-Si brazing material has a Mg content of 0.2 to 1.0% and the core material has a Mg content of 0.4 to 1.2%. 2. The aluminum alloy brazing according to claim 1, wherein one or both of the hypereutectic Al—Si brazing material and the hypoeutectic Al—Si brazing material contains Sr: 20 to 500 ppm. Sheet. The hypereutectic Al—Si brazing material further contains one or two of Zn: 0.1 to 3.0% and Cu: 0.1 to 0.6%, and the hypoeutectic 2. The Al—Si brazing material further contains one or two of Zn: 0.5 to 4.0% and Cu: 0.1 to 0.8%. 2. The aluminum alloy brazing sheet according to 2.

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