JP5675092B2 - Aluminum alloy tube for heat exchanger excellent in corrosion resistance and heat exchanger using the same - Google Patents

Description

  The present invention relates to an aluminum alloy tube for a heat exchanger excellent in corrosion resistance, which suppresses corrosion of a sacrificial anode layer provided on the surface and has excellent corrosion resistance life, and a heat exchanger using the same.

Brazing sheets clad with an Al-Si alloy brazing material have been widely used so far in aluminum alloy heat exchangers made of brazing by using tubes, fins and header pipes as main components. Even if it is not used, a product can be manufactured at low cost by applying a brazing filler metal composition made of a mixture of an Al-Si alloy powder and Si powder as a flux and a binder to the surface of an extruded tube (hereinafter referred to as a tube). It has become to.
However, when the brazing filler metal composition is used, Si diffuses from the tube surface to the inside due to heating during brazing, so that the Si concentration is high on the surface and low inside, and the tube has a high surface potential and internal. A low potential gradient is formed. For this reason, there arises a problem that corrosion occurs in the tube and pitting corrosion occurs, causing refrigerant leakage and strength reduction.
Therefore, by mixing and applying Zn-containing flux together with powder such as Si to form a Zn diffusion layer on the tube surface, the tube surface potential was low and a high potential gradient was formed inside, thereby improving pitting corrosion resistance. A structure has been proposed.

The present inventors have, in Patent Document 1, Si on the outer surface of the tube the fins are joined, the coated amount of Si powder coating weight of 1 to 5 g ^/ m 2, Zn-containing flux as 5 to 20 g / ^{m 2} A tube for heat exchanger in which a coating film for brazing containing powder and Zn-containing flux was formed was proposed.
According to this proposal, since the Si powder and the Zn-containing flux are mixed, the Si powder is melted at the time of brazing to become a brazing liquid, and the Zn in the flux is uniformly diffused in the brazing liquid, and the tube surface is spread. Spread evenly. Since the diffusion rate of Zn in a liquid phase such as a brazing liquid is significantly larger than the diffusion rate in a solid phase, the Zn concentration on the tube surface can be made substantially uniform, and thereby a uniform sacrificial anode layer on the tube surface. The corrosion resistance of the heat exchanger tube can be improved.

JP 2004-330233 A

However, according to further studies by the present inventors, even if the Zn concentration on the outer surface of the tube to which the fins are joined can be made uniform, the potential gradient generated in the tube is different from the potential near the outer surface of the tube and the anticorrosion. Since the potential difference from the site to be made (for example, the side surface of the tube where the Zn diffusion layer does not exist) becomes very large, the corrosion rate increases, the sacrificial anode layer is consumed early, and the corrosion resistance life may be shortened. .
In view of these backgrounds, the present invention has a high bonding rate between the fins and the tube, and even if the tube is corroded, the corrosion rate can be minimized and the corrosion resistance can be extended. It aims at providing the tube for exchangers, and a heat exchanger provided with the same.

The aluminum alloy tube for heat exchanger excellent in corrosion resistance according to the present invention is an aluminum alloy tube for heat exchanger in which fins are brazed to the surface, and brazing a coating film for brazing containing Si and Zn applied on the surface. A thickness of 30 to 150 μm formed by diffusing Si and Zn from the Al—Si liquid phase brazing material containing Zn that is sometimes melted and generated in the surface direction and depth direction of the tube surface, Is characterized in that a sacrificial anode layer having a region lower than the potential of the tube itself and having a constant potential in the range of ± 10 mV in the depth direction of the tube is formed.
The aluminum alloy tube for heat exchangers excellent in corrosion resistance according to the present invention is characterized in that the potential of the sacrificial anode layer is 10 to 50 mV lower than the potential inside the tube.
Above aluminum alloy tube excellent in corrosion resistance of the present invention, the surface before brazing, Si powder 1 to 5 g ^/ m 2, Zn-containing flux 3 to 10 g / ^{m 2,} binder 0.5～3.5G / A coating film for brazing made of m ² is formed, and the sacrificial anode layer is formed by diffusion of Si and Zn by heating accompanying brazing.

The aluminum alloy tube for heat exchangers excellent in corrosion resistance of the present invention is characterized in that the maximum particle size (D99) of the Si powder is 20 μm or less and the average particle size (D50) is 1 to 10 μm.
The aluminum alloy tube for a heat exchanger having excellent corrosion resistance according to the present invention is composed of Si: 0.1 to 0.6% by mass, Fe: 0.1 to 0.6% by mass, and Mn: 0.1 to 0.6% by mass. , Ti: 0.005 to 0.2% by mass, Cu: less than 0.1% by mass, and a balance Al.
A heat exchanger according to the present invention includes the aluminum alloy tube for a heat exchanger having excellent corrosion resistance according to any one of claims 1 to 5.

Since a sacrificial anode layer having a thickness of 30 to 150 μm having a constant potential in the range of ± 10 mV in the depth direction of the tube is provided on the surface of the tube where the fins are brazed, the sacrificial anode layer is formed on the outer surface of the tube. The potential difference between the region where the sacrificial anode layer is not formed and the region where the sacrificial anode layer is not formed is reduced, and the corrosion rate of the sacrificial anode layer can be reduced. Can be lengthened. If the sacrificial anode layer is too thin or too thick, corrosion resistance superior to that of the prior art cannot be obtained.
The potential of the sacrificial anode layer is preferably about 10-50 mV lower than the potential of the inside of the tube, in other words, the tube itself. By providing this potential difference, the sacrificial anticorrosive effect of the sacrificial anode layer is satisfactorily exhibited and the corrosion resistance of the tube is improved. improves.

The sacrificial anode layer is formed by diffusing the components of the coating film for brazing provided on the surface of the tube by heating at the time of brazing. The component of the coating film for brazing is 1 to 5 g / m ^{2 of} Si powder. , Zn-containing flux 3 to 10 g / ^{m 2,} it is preferable that a binder 0.5~3.5g / ^{m 2,} it is possible to obtain the sacrificial anode layer of constant potential purposes by this component. Moreover, it is preferable that Si powder provided in the coating film for brazing has a maximum particle size (D99) of 20 μm or less and an average particle size (D50) of 1 to 10 μm.
The composition of the tube is as follows: Si: 0.1 to 0.6% by mass, Fe: 0.1 to 0.6% by mass, Mn: 0.1 to 0.6% by mass, Ti: 0.005 to 0.005%. It is preferable that 2% by mass, Cu: less than 0.1% by mass, and the balance Al. By applying the brazing coating to a tube having this composition and brazing, a target sacrificial anode layer can be produced. it can.
If it is a heat exchanger provided with the tube of this invention, the heat exchanger excellent in the corrosion-resistant lifetime can be provided by the anticorrosion effect which a sacrificial anode layer provides with respect to a tube.

It is a front view which shows one structural example of the heat exchanger provided with the aluminum alloy tube which concerns on this invention. It is the elements on larger scale which show the state which assembled the header pipe, the tube, and the fin in the heat exchanger which concerns on this invention, Comprising: The state before brazing is shown. It is a partial expanded sectional view which shows the heat exchanger of the state which assembled and brazed the header pipe, the tube, and the fin in the heat exchanger which concerns on this invention. It is a figure which shows an example of the cross-sectional shape of the aluminum alloy tube which concerns on this invention. It is explanatory drawing which shows an example of the electrical potential gradient from the surface to the inside about the aluminum alloy tube which concerns on this invention, and the conventional tube. It is explanatory drawing which shows the state in which Si powder and Zn containing flux powder of the coating film for brazing exist on the surface of an aluminum alloy tube. It is explanatory drawing which shows the state which heated from the state in which the brazing coating film exists on the surface of the aluminum alloy tube to the brazing temperature, the Zn flux melted, the oxide film was removed, and Zn and Si began to diffuse. is there. It is explanatory drawing which shows the state which heated to the brazing temperature from the state which the brazing coating film exists on the surface of an aluminum alloy tube, and the liquid brazing of the Al-Si alloy began to form with Si diffused in aluminum. . It is explanatory drawing which shows the state which heated from the state in which the brazing coating film exists on the surface of an aluminum alloy tube to brazing temperature, and Zn and Si were diffused and the sacrificial anode layer was produced | generated.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 shows an example of a heat exchanger provided with an aluminum alloy tube according to the present invention. A heat exchanger 100 of this embodiment includes header pipes 1 and 2 arranged in parallel to be separated from each other on the left and right. A plurality of flat tubes 3 which are joined in parallel with each other between the header pipes 1 and 2 at a right angle to the header pipes 1 and 2 and brazed to each tube 3. The corrugated fin 4 is mainly used. The header pipes 1 and 2, the tubes 3 and the fins 4 are made of an aluminum alloy which will be described later.
More specifically, a plurality of slits 6 shown in FIG. 2 or FIG. 3 are formed at regular intervals in the length direction of each pipe on the opposite side surfaces of the header pipes 1 and 2. The tube 3 is installed between the header pipes 1 and 2 by inserting the end of the tube 3 through the slit 6. Further, fins 4 are arranged on the upper and lower surfaces of a plurality of tubes 3 that are installed between the header pipes 1 and 2 at a predetermined interval, and these fins 4 are brazed to the upper surface or the lower surface of the tubes 3. That is, as shown in FIG. 3, a fillet 8 is formed of a brazing material at a portion where the end of the tube 3 is inserted into the slit 6 of the header pipes 1 and 2, and the tube 3 is brazed to the header pipes 1 and 2. It is attached. Further, in the corrugated fin 4, the wave apex portion is opposed to the surface of the adjacent tube 3, and a fillet 9 is formed by a brazing material in the portion between them, and the corrugated fin 4 is brazed on the surface of the tube 3. Has been.

The heat exchanger 100 of this embodiment is shown in FIG. 2 by assembling the header pipes 1 and 2 and a plurality of tubes 3 and a plurality of fins 4 installed between them, as will be described in detail in a manufacturing method described later. The heat exchanger assembly 101 constructed as described above is manufactured by brazing.
In the tube 3 before brazing, Si powder: 1 to 5 g / m ² , Zn-containing fluoride-based flux (KZnF ₃ ): _{3 to} 10 g / m ^2, and a binder ( For example, the surface on which the coating film for brazing (brazing material coating film) 7 having a composition of 0.5 to 3.5 g / m ² is joined to the fins of the tube 3 as shown in FIG. It is formed so as to cover (so that the coating film covers the surface excluding the corner portion). Although not shown, the coating film may be formed on the entire outer peripheral surface.

As shown in FIG. 4, the tube 3 of this embodiment has a plurality of passages 3C formed therein, and includes a flat upper surface 3A and a lower surface 3B, and a side surface 3D adjacent to the upper surface 3A and the lower surface 3B. 4 is configured as a flat multi-hole tube as shown in the cross section of FIG.
As an example, on the upper surface 3A and the lower surface 3B of the tube 3 before brazing, the uncoated portions are slightly left with a predetermined width at both ends in the width direction in the direction orthogonal to the length direction of the tube 3 for brazing. A coating film 7 is formed.

  The tube 3 having a cross-sectional shape shown in FIG. 4 is applied, the tube 3 is formed from an aluminum alloy having a composition described later, the fin 4 is formed from an aluminum alloy having a composition described later, and the coating film 7 for brazing is formed using a composition described later. In the case of the structure, in the structure composed of the tube 3 and the fin 4 joined to the tube 3 by the fillet 9, the side surface 3D side of the tube not provided with the brazing coating film 7 is a cathode portion that is anticorrosive. The fins 4 and the fillets 9 are the anode parts that are preferentially (sacrificed) eroded. Further, on the surface portion of the tube 3 after brazing, the sacrificial anode layer 3a containing Si and Zn is formed as a result of diffusion of Si and Zn contained in the brazing coating film 7 at the brazing temperature. Yes.

Hereinafter, the composition which comprises the said coating film 7 for brazing is demonstrated.
<Si powder>
The Si powder reacts with Al constituting the tube 3 to form a braze that joins the fin 4 and the tube 3. At the time of brazing, the Zn-containing flux and the Si powder melt to form a brazing liquid. Zn in the flux is uniformly diffused in the brazing solution and spreads uniformly on the surface of the tube 3. Since the diffusion rate of Zn in the brazing liquid which is a liquid phase is significantly larger than the diffusion rate in the solid phase, uniform Zn diffusion is achieved, and the Zn concentration in the surface direction of the tube 3 surface becomes substantially uniform. Further, when the diffusion from the surface of the tube 3 in the depth direction is observed, Si and Zn spread uniformly on the surface by the brazing material containing Zn formed on the tube surface are diffused in the depth direction, and a predetermined thickness is obtained. The sacrificial anode layer 3a is formed. In the sacrificial anode layer 3a, the potential is constant (constant in a range of ± 10 mV). The formation of the sacrificial anode layer 3a can improve the corrosion resistance of the tube 3.

<Si powder coating amount: 1 to 5 g / m ² >
If the coating amount of the Si powder is less than 1 g / m ² , the brazing will be insufficient and a uniform sacrificial anode layer will not be formed. On the other hand, if the coating amount exceeds 5 g / m ² , the surface of the sacrificial anode layer will be precious. A cathode layer containing a large amount of Si is formed, and the effect of the sacrificial anode layer is shortened. For this reason, content of Si powder in a coating film shall be 1-5 g / m < ² >.
<Si powder particle size: Maximum particle size: (D99): 20 μm or less>
<Si powder particle size: average particle size: (D50): 1 to 10 μm>
If the particle size of the Si powder is 20 μm or less in (D99), a uniform sacrificial anode layer can be formed. On the other hand, if it exceeds 20 μm, deep erosion is locally generated, and the uniform sacrificial anode layer is formed. It cannot be formed. For this reason, the particle size of the Si powder is preferably 20 μm or less at the maximum particle size (D99).
A uniform sacrificial anode layer can be formed if the particle size of the Si powder is in the range of 1 to 10 μm in the average particle size (D50). However, if the thickness is less than 1 μm, the formation of the solder becomes insufficient, and a uniform sacrificial anode layer is not formed. On the other hand, when the thickness exceeds 10 μm, brazing is scattered and a uniform sacrificial anode layer is not formed. For this reason, it is preferable that the particle size of Si powder shall be 1-10 micrometers in (D50).
In addition, (D99) is a particle size of particles that accumulate from small particles in a volume ratio and become 99% of the whole. Moreover, (D50) is the particle diameter of the grains that are accumulated from small grains by volume ratio and become 50% of the whole. Any of these values can be measured by a laser light scattering method.

<Zn-containing fluoride flux>
The Zn-containing fluoride-based flux has an effect of forming a sacrificial anode layer 3a in which Zn is diffused on the surface of the tube 3 so that the potential of the sacrificial anode layer is appropriately base at the time of brazing. Moreover, it has the effect | action which removes the oxide of the surface of the tube 3 at the time of brazing, improves the brazing property by accelerating | stimulating the spreading | diffusion and wetting of brazing.
<Flux application amount: 3 to 10 g / m ² >
When the coating amount of the Zn-containing fluoride-based flux is less than 3 g / m ² , the potential difference becomes less than 10 mV, and the sacrifice effect is not exhibited. Moreover, since the destruction and removal of the surface oxide film of the brazing material (tube 3) is insufficient, a brazing failure is caused. On the other hand, when the coating amount exceeds 10 g / m ² , the potential difference exceeds 50 mV, the corrosion rate increases, and the anticorrosion effect due to the presence of the sacrificial anode layer 3a is shortened. For this reason, it is preferable that the application quantity of Zn containing fluoride system flux shall be 3-10 g / m < ² >.
KZnF ₃ can be used as the Zn-containing fluoride-based flux. The particle size of the flux is preferably in the range of 1 to 6 μm in (D50).

<Binder>
The coated material contains a binder in addition to Si powder and Zn-containing fluoride flux. An example of the binder is preferably an acrylic resin.
The binder has the effect of fixing the Si powder and Zn-containing flux necessary for the formation of the sacrificial anode layer 3a to the surface of the tube 3, but if the coating amount of the binder is less than 0.5 g / m ² , At the time of brazing, Si powder and Zn flux fall off from the tube 3, and the uniform sacrificial anode layer 3a is not formed. On the other hand, when the coating amount of the binder exceeds 3.5 g / m ² , the brazing property is lowered due to the binder residue, and the uniform sacrificial anode layer 3a is not formed. For this reason, the coating amount of the binder is set to 0.5 to 3.5 g / m ² . The binder usually evaporates by heating during brazing.

  The method for applying the brazing composition comprising the Si powder, the flux and the binder is not particularly limited in the present invention. The spray method, the shower method, the flow coater method, the roll coater method, the brush coating method, the dipping method, the static method. It can be performed by an appropriate method such as an electrocoating method. Further, the application area of the brazing composition may be the entire surface of the tube 3 or may be a part of the surface of the tube 3. In short, at least the tube necessary for brazing the fins 4 is used. 3 may be applied to the surface area. Depending on the coating method, when a brazing composition is applied to the upper surface or the like, a part of the brazing composition may be formed on the side surface as a result.

Tube 3 is Si: 0.1-0.6%, Fe: 0.1-0.6% by mass, Mn: 0.1-0.6% by mass, Ti: 0.005-0.2% by mass Cu: Less than 0.1% by mass, produced by extruding an aluminum alloy consisting of aluminum and inevitable impurities.
Hereinafter, the reasons for limiting the constituent elements of the aluminum alloy constituting the tube 3 will be described.
<Si: 0.1 to 0.6% by mass>
The Si content is important in order to moderate the Si diffusion gradient and form a uniform sacrificial anode layer. When the Si content is less than 0.1% by mass, the Si diffusion gradient increases and a uniform sacrificial anode layer is not formed. On the other hand, when Si exceeds 0.6 mass%, the melting point of the alloy constituting the tube is lowered and the extrudability is lowered. Therefore, the Si content in the present invention is 0.1 to 0.6 mass%. A more preferable Si content is 0.2 to 0.5 mass%.
<Fe: 0.1 to 0.6% by mass>
Fe is effective for forming an intermetallic compound with diffusion Si and generating a uniform sacrificial anode layer. When the Fe content is less than 0.1% by mass, the Si diffusion gradient increases, and a uniform sacrificial anode layer is not generated. If the Fe content exceeds 0.6% by mass, the intermetallic compounds in the aluminum alloy constituting the tube increase, and the extrudability (die life) tends to decrease. A more preferable Fe content is 0.15 to 0.5 mass%.
<Mn: 0.1 to 0.6% by mass>
Mn is an effective element for forming a uniform sacrificial anode layer by forming an intermetallic compound with diffusion Si. Further, Mn is an element that is effective in improving the corrosion resistance of the tube 3, improving the mechanical strength, and improving the extrudability during extrusion molding.
If the Mn content is less than 0.1% by mass, the Si diffusion gradient becomes large and a uniform sacrificial anode layer is not formed. If the Mn content exceeds 0.6% by mass, the extrudability increases due to an increase in extrusion pressure. descend. Therefore, the Mn content in the present invention is 0.1 to 0.6% by mass. A more preferable Mn content is 0.15 to 0.5% by mass.
<Ti: 0.005 to 0.2% by mass>
Ti forms a fine intermetallic compound that does not inhibit the corrosion resistance, and contributes to improving the strength of the tube 3. When the amount is less than 0.005% by mass, the effect of addition is not observed. When the amount exceeds 0.2% by mass, the extrusion pressure of the tube alloy increases and the extrudability decreases. A more preferable Ti content is 0.005 to 0.1% by mass.
<Cu: less than 0.1% by mass>
Cu is effective for increasing the potential of the tube and maintaining the sacrificial anode layer effect for a long time. However, when the addition amount exceeds 0.1 mass%, the corrosion rate increases and the effect of the sacrificial anode layer is reversed. In a short time. The addition amount of Cu is preferably less than 0.05% by mass.

Next, the fin 4 will be described.
For the fins 4 to be joined to the tube 3, an alloy mainly composed of a JIS 3003 series aluminum alloy can be applied. Alternatively, the fins 4 may be formed from an aluminum alloy obtained by adding about 2% by mass of Zn to a JIS 3003 series aluminum alloy.
The fin 4 is formed into a corrugated shape by melting an aluminum alloy having the above composition by a conventional method, and passing through a hot rolling process, a cold rolling process, and the like. In addition, the manufacturing method of the fin 4 is not specifically limited as this invention, A well-known manufacturing method can be employ | adopted suitably.

Next, the header pipe 1 will be described.
2 and 3, the header pipe 1 includes a core material layer 11, a sacrificial material layer 12 provided on the outer peripheral side of the core material, and a brazing material layer 13 provided on the inner peripheral side of the core material. A three-layer structure consisting of
By providing the sacrificial material layer 12 on the outer peripheral side of the core material layer 11, in addition to the anticorrosion effect by the fins 4, the anticorrosion effect by the header pipe 1 can also be obtained, so the sacrificial anticorrosion effect of the tube 3 in the vicinity of the header pipe 1 is further enhanced. be able to.

The core material layer 11 is preferably an alloy based on an Al—Mn system.
For example, it is preferable to contain Mn: 0.05 to 1.50%, and as other elements, Cu: 0.05 to 0.8%, Zr: 0.05 to 0.15% may be contained. it can.
The sacrificial material layer 12 provided on the outer peripheral side of the core material layer 11 is composed of an aluminum alloy composed of Zn: 0.60 to 1.20%, the balance Al and inevitable impurities. The sacrificial material layer 12 is integrated with the core material layer 11 by clad rolling.

Next, the manufacturing method of the heat exchanger 100 which uses the header pipe 1, 2 tube 3, and the fin 4 demonstrated above as main components is demonstrated.
FIG. 2 shows a part of the heat exchanger assembly 101 that shows a state in which the header pipes 1, 2, the tubes 3, and the fins 4 are assembled using the tubes 3 in which the brazing material layer 13 is applied to the joint surfaces with the fins 4. It is an enlarged view and shows the state before heat brazing. In the heat exchanger assembly 101 shown in FIG. 2, the tube 3 is attached by inserting one end of the tube 3 into a slit 6 provided in the header pipe 1.
When the heat exchanger assembly 101 composed of the header pipes 1, 2, tubes 3 and fins 4 assembled as shown in FIG. 2 is heated to a temperature equal to or higher than the melting point of the brazing material, as shown in FIG. The coating film 7 and the brazing filler metal layer 13 are melted to join the header pipe 1 and the tube 3, and the tube 3 and the fin 4. Thus, the heat exchanger 100 having the structure shown in FIGS. 1 and 3 is obtained. At this time, the brazing filler metal layer 13 on the inner peripheral surface of the header pipe 1 is melted and flows in the vicinity of the slit 6 to form the fillet 8 and the header pipe 1 and the tube 3 are joined. Also, the brazing coating 7 on the surface of the tube 3 melts and flows in the vicinity of the fin 4 by capillary force, forms a fillet 9, and the tube 3 and the fin 4 are joined.

At the time of brazing, the coating film 7 for brazing and the brazing material layer 13 are dissolved by heating to an appropriate temperature in an appropriate atmosphere such as an inert atmosphere. Then, the activity of the flux increases, and Zn in the flux precipitates on the surface of the brazing material (tube 3) and diffuses in the thickness direction of the brazing material and the surfaces of both the brazing material and the brazing material. The oxide film is destroyed to promote the wetting between the brazing material and the brazing material.
As described above, the heating temperature for brazing is not lower than the melting point of the brazing material, but in the case of the brazing material having the above-described composition, it is heated to 580 to 615 ° C. and held for about 1 to 10 minutes.

At the time of brazing, a part of the aluminum alloy matrix constituting the tube 3 reacts with the composition of the coating film 7 for brazing applied to the tube 3 to braze the tube 3 and the fin 4. The On the surface of the tube 3, Zn in the flux diffuses by brazing and becomes lower than the inside of the tube 3.
More specifically, when the Si powder 20, the Zn-containing flux powder 21 and the binder (not shown) are applied to the surface of the tube 3 as shown in FIG. 6, when the whole is heated, the binder is first decomposed and evaporated, and then The Zn-containing flux melts and becomes a melt 22 as shown in FIG. 7 and spreads on the surface of the tube 3, and Zn and Si start to diffuse on the surface of the tube 3 as indicated by an arrow 13.
Thereafter, by maintaining a brazing temperature of 580 to 615 ° C. for a predetermined time, an Al—Si liquid phase brazing material containing Si having a eutectic composition with Al as shown by an arrow 25 in FIG. 8 is produced. After that, this region extends over the entire area of the tube 3.

As shown in FIG. 5 (B), the surface of the tube 3 is shown in FIG. 5 (B) in contrast to the conventional state shown in FIG. 5 (A) by the production of the Al—Si liquid phase brazing material containing Zn generated by the heating during the brazing. A region a having a substantially constant potential is generated with a small potential difference with respect to the potential on the side surface or inside of the tube 3 as in the state. That is, when the sacrificial layer is formed on the tube 3 by simply performing only Zn diffusion, the potential difference between the side surface and the inside of the tube 3 and the sacrificial anode layer is large as shown in FIG. Since the potential gradient changes greatly depending on the depth from the surface, the corrosion rate is increased.
On the other hand, as shown in FIG. 5B, if the potential gradient is such that a region a having a small potential difference with respect to the potential on the side surface or the inside of the tube 3 is generated, the corrosion rate of the region a having a small potential difference is Since it is slow, a structure excellent in corrosion resistance can be provided.

In the brazing structure of the present embodiment, Si is an element that raises the potential of Al, and Zn is an element that lowers the potential of Al. Therefore, the potential in the tube 3 increases as the amount of Si added increases, and Zn Increasing the amount decreases. Further, the weight and particle size of the Si powder contained in the brazing coating film 17 and the weight of the Zn flux and the composition of the aluminum alloy constituting the tube 3 all affect the potential gradient.
That is, the potential in the depth direction in the tube 3 is determined by the distribution state of Si and Zn contained in the depth direction of the tube 3 after brazing, and the thickness of the sacrificial anode layer 3a is in a state where the potential is balanced. It increases when these elements diffuse deeper. Therefore, the thickness of the sacrificial anode layer 3a can be controlled by the length of the brazing time, and can be increased by increasing the brazing time. The potential difference of the sacrificial anode layer 3a (the potential difference between the inside of the tube 3 and the sacrificial anode layer 3a) can be increased when the sacrificial anode layer 3a is made lower. Therefore, the potential difference between the outermost surface portion of the tube having the highest Zn concentration and the sacrificial anode layer 3a can be adjusted by the Zn concentration.
Furthermore, since Fe and Mn contained in the tube 3 combine with Si that diffuses at the time of brazing to produce an intermetallic compound, the production of this intermetallic compound acts to counteract the effect of increasing the potential inherent in Si. . Therefore, when the amount of Fe or Mn contained in the tube 3 is large, the effect of increasing the potential of the sacrificial anode layer 3a by the diffusion of Si is negated.
And, in order to generate the potential constant region a in the above-mentioned range after brazing, it is preferable to employ the above-mentioned coating amount, Si powder maximum particle size (D99), average particle size (D50), and composition range. The grain size is also important for the uniform and reliable generation of the sacrificial anode layer 3a. For example, if the Si powder contains a large particle size, large erosion (erosion) occurs due to Si diffusion during brazing in the region where the coarse Si powder is present, and an excessive liquid phase brazing is formed. Therefore, a uniform sacrificial anode layer is not formed, and the corrosion resistance cannot be improved.
In addition to the Si powder supply amount, the Zn-containing flux supply amount, and the binder supply amount, the particle size of the Si powder and the composition of the aluminum alloy tube are adjusted and brazed to have a substantially constant potential as shown in FIG. It is important in the present embodiment to generate the region a.

According to the structure of the present embodiment, when brazing, there is no residue of Si powder, good brazing is performed, and a sufficiently large fillet 9 is formed between the tube 3 and the fin 4. A sacrificial anode layer 3a is formed.
According to the heat exchanger 100 obtained as described above, the sacrificial anode layer 3a is formed on the surface of the tube 3 so as to generate the region a having a substantially constant potential of 30 to 150 μm in thickness. The region a where the potential difference between the sacrificial anode layer 3a and the inside of the tube is small from the surface of the tube 3 to the inside of the tube 3 both in the depth direction and the surface direction of the tube 3, resulting in a slow corrosion rate of the region a. The sacrificial anode layer 3a of the tube 3 is not consumed at an early stage, and the corrosion resistance life of the tube 3 can be extended.

Therefore, since the sacrificial anode layer 3a having a constant potential of 30 to 150 μm is provided on the surface of the tube 3 of the present embodiment where the fins 4 are brazed, the corrosion rate of the sacrificial anode layer 3a is reduced because the potential difference is small. As a result, the premature consumption of the sacrificial anode layer 3a can be suppressed, and the corrosion resistance life can be extended. If the sacrificial anode layer 3a is too thin or too thick, corrosion resistance superior to that of the prior art cannot be obtained.
The potential of the sacrificial anode layer 3a is desirably about 10 to 50 mV lower than the potential of the inside of the tube 3 (inside of the tube 3 where Zn diffusion is not performed), in other words, the tube 3 itself. Early consumption of the sacrificial anode layer 3a can be suppressed, and the sacrificial anticorrosive effect can be sufficiently exhibited for a long period of time to improve the corrosion resistance life of the tube 3.

The aluminum alloy for fins (JIS3003 + 2 mass% Zn) of the composition shown in Table 1 was subjected to homogeneous heat treatment, followed by hot rolling and cold rolling to obtain a plate material having a thickness of 0.1 mm. A test bare fin was manufactured by corrugating the plate material.
Aluminum alloys for tubes having the compositions shown in Tables 2 and 3 were melted. This aluminum alloy for tubes is subjected to a homogeneous heat treatment, and is then subjected to hot extrusion to have a cross-sectional shape (thickness 0.26 mm × width 17.0 mm × total thickness 1.5 mm) as shown in FIG. An aluminum alloy tube was produced.

Next, the brazing material composition was roll-coated on the surface of the flat aluminum alloy tube for a heat exchanger and dried.
The brazing filler metal composition includes Si powder ((D50) particle size (average particle size) and (D99) particle size (maximum particle size)), flux (KZnF ₃ : (D50) particle size 2.0 μm), and acrylic resin (solvent). 3methoxy-3methyl-1-butanol, and a mixture of isopropyl alcohol and water), and the mixing amount of each element so that the coating amount of each element becomes the value shown in Table 2 and Table 3 below. And provided for testing.

Next, the tubes and fins were assembled into 4 stages of tubes and 3 stages of fins as in the structure of the heat exchanger shown in FIG. No. 1-4 of the different combinations shown in Tables 2 and 3 for the Si powder, Zn flux powder amount, binder amount, Si powder particle size ((D99) and (D50)) and tube composition in the brazing material coating film A test specimen was prepared.
Next, brazing was performed under the condition that these specimens were held in a furnace in a nitrogen atmosphere at 600 ° C. for 3 minutes. By this brazing, a sacrificial anode layer was formed and fins were brazed on the surface of the tube on which the brazing coating had been formed, and these were used as heat exchanger specimens.
The SWAAT 20-day corrosion resistance test was performed using the heat exchanger specimen obtained by this brazing process.
Moreover, about the heat exchanger test body after a corrosion resistance test, after removing a corrosion product, the depth of the corrosion which arose on the tube surface in which the sacrificial anode layer was formed was measured, and corrosion resistance was evaluated. The sacrificial anode layer constituting the constant potential region where the potential is in a substantially constant range (± 10 mV) repeats chemical etching from the tube surface, and the potential is measured each time, thereby the potential distribution in the tube depth direction. And the potential difference between the sacrificial anode layer thickness and the inside of the tube was confirmed from the distribution state. The test results are shown in Table 2 and Table 3.

From the results shown in Tables 2 and 3, it was found that a brazing coating consisting of Si powder, Zn-containing flux (KZnF ₃ ), and a binder was applied to the surface of the tube, and this was applied to a heat exchanger specimen that was brazed together with fins. Thus, it has been found that a sacrificial anode layer having a predetermined thickness can be obtained with a constant potential difference from the potential of the tube itself. Further, according to the results in Tables 2 and 3, a constant potential sacrificial anode layer having a thickness in the range of 30 to 140 μm can be obtained, and a constant potential sacrificial anode layer having a potential difference in the range of 5 to 55 mV can be obtained. It was.

Furthermore, according to the test results of No. 40 and No. 41 specimens shown in Table 2 and Table 3, the thickness of the constant potential sacrificial anode layer is 20 μm, too thin, or 170 μm. Corrosion depth increased. Further, considering the results of the corrosion depths of No. 1 to 39 specimens, it can be determined that the thickness of the constant potential sacrificial anode layer is preferably 30 to 150 μm.
Next, the corrosion depths of the No. 8 test body having a Si powder content of 0.4 g / m ^{2 and} the No. 11 test body having a content of 5.5 g / m ^{2 in} the brazing coating film. Considering that it is slightly deeper than other specimens, it can be determined that the coating amount of Si powder is more preferably in the range of 1 to 5 g / m ² .
Next, the corrosion depth of the No. 4 specimen with a Zn-containing flux content of 2 g / m ^{2 and} the No. 7 specimen with a content of 11 g / m ^{2 in} the brazing coating is another test. Considering that it is slightly deeper than the body, it can be determined that the coating amount of the Zn-containing flux is more preferably in the range of 3 to 10 g / m ² .
Next, the corrosion depths of the No. 12 specimen having a binder content of 0.3 g / m ^{2 and} the No. 15 specimen having a content of 4.5 g / m ^{2 in} the brazing coating are different. In view of the fact that it is slightly deeper than the test specimen, it can be determined that the binder coating amount is more preferably in the range of 0.5 to 3.5 g / m ² .

Next, with respect to the Si powder particle size, the No. 16 specimen having a maximum particle diameter (D99) value of 25 μm and the corrosion depth of the specimen having an average particle diameter (D50) of 0.4 μm or 12 μm are different from each other. In consideration of the fact that it is slightly deeper, the maximum particle size (D99) is preferably 20 μm or less and the average particle size (D50) is preferably in the range of 1 to 10 μm.
Next, when the Fe content is increased with respect to the composition of the tube, a decrease in extrudability is observed (No. 29), and a decrease in extrudability is also observed when the Mn content is large (No. 33). When it increases, the extrudability decreases (No. 37). Further, a test specimen (No. 22) having a Si content of 0.05% by mass and a low content (No. 22), a test specimen having a Si content of 0.7% by mass (No. 25), and a Fe content of 0.8%. Specimen with a low mass of 05 mass% (No. 26), a specimen with a high Fe content of 0.7 mass% (No. 29), and a test with a small Mn content of 0.05 mass% Body (No. 30), test body (No. 33) having a high Mn content of 0.7% by mass, test body (No. 37) having a high Ti content of 0.25% by mass, Cu In the test specimen (No. 38) having a high content of 0.11% by mass, the extrudability starts to decrease or the corrosion depth starts to decrease slightly. In addition, the No. 34 specimen having a Ti content of 0.002% by mass is difficult to obtain the effect of improving the tube strength.

  Considering these results, the composition ratio of the aluminum alloy constituting the tube according to the present invention is as follows: Si: 0.1 to 0.6 mass%, Fe: 0.1 to 0.6 mass%, Mn: 0.00. It is preferable that they are 1-0.6 mass%, Ti: 0.005-0.2 mass%, Cu: less than 0.1 mass%, and remainder Al. Moreover, from these results, the composition ratio of the aluminum alloy constituting the tube is as follows: Si: 0.2 to 0.5 mass%, Fe: 0.15 to 0.5 mass%, Mn: 0.15 to 0.005. More preferably, it is 5 mass%, Ti: 0.005-0.1 mass%, Cu: less than 0.05 mass%, and the balance Al.

  DESCRIPTION OF SYMBOLS 100 ... Heat exchanger, 101 ... Heat exchanger assembly, 1, 2 ... Header pipe, 3 ... Tube, 3A ... Upper surface, 3a ... Sacrificial anode layer, 3B ... Lower surface, 3C ... Passage, 3D ... Side surface, 4 ... Fin , 6 ... slit, 7 ... brazing coating (brazing material coating), 8, 9 ... fillet, 11 ... core material layer, 12 ... sacrificial material layer, 13 ... brazing material layer, 20 ... Si powder, 21 ... Zn-containing flux, 22 ... melt. .

Claims (6)

An aluminum alloy tube for heat exchanger with fins brazed on the surface, and a brazing coating film containing Si and Zn applied on the surface is melted during brazing and generated in the surface direction and depth direction of the tube surface 30 to 150 μm in thickness formed by diffusing Si and Zn from the Al—Si liquid brazing material containing Zn into the tube, and the potential is lower than the potential of the tube itself. An aluminum alloy tube for a heat exchanger excellent in corrosion resistance, characterized in that a sacrificial anode layer having a constant region in the range of ± 10 mV in the depth direction is formed.   The aluminum alloy tube for heat exchangers with excellent corrosion resistance according to claim 1, wherein the potential of the sacrificial anode layer is 10 to 50 mV lower than the potential inside the tube. Before brazing surface, Si powder 1 to 5 g ^/ m 2, Zn-containing flux 3 to 10 g / ^{m 2,} brazing coating film comprising a binder 0.5~3.5g / ^{m 2} is formed, brazed The aluminum alloy tube for heat exchangers with excellent corrosion resistance according to claim 1, wherein the sacrificial anode layer is formed by diffusion of Si and Zn by heating by heating.   The aluminum alloy tube for heat exchangers with excellent corrosion resistance according to claim 3, wherein the maximum particle size (D99) of the Si powder is 20 µm or less and the average particle size (D50) is 1 to 10 µm.   Si: 0.1-0.6 mass%, Fe: 0.1-0.6 mass%, Mn: 0.1-0.6 mass%, Ti: 0.005-0.2 mass%, Cu: The aluminum alloy tube for heat exchangers having excellent corrosion resistance according to any one of claims 1 to 4, wherein the aluminum alloy tube is made of an aluminum alloy composed of less than 0.1% by mass and the balance Al.   A heat exchanger comprising the aluminum alloy tube for a heat exchanger excellent in corrosion resistance according to any one of claims 1 to 5.

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