CN104246417A - Heat exchange tube attached with aluminum alloy inner groove - Google Patents

Abstract

Provided is a hairpin that has good bending workability, is less prone to breakage of a heat sink, and has a heat transfer tube with good corrosion resistance. A heat pipe made of aluminum alloy with grooves on the inner surface, characterized in that: two or more ridge-shaped heat sinks are formed on the inner surface; Mn is contained: 0.8 to 1.8% by mass (hereinafter, mass% is represented by %) , Cu: 0.3-0.8%, and Si: 0.02-0.2%, and the rest are unavoidable impurities and Al, and the average crystal grain size of the formed product is 150 μm or less.

Description

Aluminum alloy heat pipe with grooves on the inner surface

technical field

The present invention relates to an aluminum alloy with grooves on the inner surface used as a heat transfer tube of a cross-fin type heat exchanger in a home air conditioner, a business air conditioner, a heat pump water heater, etc. Heat pipes.

Background technique

In a general cross-fin type (alias "fin-and-tube type") heat exchanger (Figure 1), a heat transfer tube is inserted into the insertion hole opened in the aluminum heat sink, and then the heat transfer tube is inserted into the heat transfer tube. A mandrel for tube expansion with an outer diameter larger than the inner diameter is pressed inside to expand the diameter of the heat transfer tube so that the outer peripheral surface of the heat transfer tube and the insertion hole of the aluminum heat sink are tightly fitted (expanding process, Figure 2). Afterwards, the heat conduction tube formed integrally with the aluminum heat sink is bent into a hairpin (Hairpin) shape, and the other heat conduction tube (U-shaped tube) bent into a U shape is connected by flame brazing to obtain a finished product (non-patent literature 1).

As for the heat transfer tube used in the cross-fin heat exchanger, since the refrigerant HFC etc. flows in the tube to perform heat exchange, the inner surface of the tube has a heat transfer tube with a trapezoidal or triangular cross-sectional shape such as ridge fins ( Hereinafter referred to as "heat transfer tubes with grooves on the inner surface") are used, so that the high efficiency and energy saving of heat exchangers can be developed. Someone has disclosed a heat pipe with grooves on the inner surface, and has fins of various shapes, and in terms of these shapes, it is stipulated: the depth of the groove between the protruding fins as shown in Figure 4, the thickness of the bottom ( The wall thickness of the base of the protruding heat sink), the shape of the heat sink (vertex angle, etc.), or the lead angle of the protruding heat sink as shown in Figure 5 (Lead angle, that is, the arrangement of the heat sink relative to the length of the tube Angle). (eg, Patent Document 1). The heat transfer performance of the heat transfer tube with grooves on the inner surface is excellent because the surface area of the inner surface of the tube is larger than that of a smooth tube without fins, and a uniform refrigerant liquid film is conceived in the tube through the groove (Non-Patent Document 2) .

The inner surface of the heat pipe with grooves on the inner surface is generally processed by rolling the tube blank (that is, the unprocessed tube, here refers to the smooth tube) to form continuously arranged spirally protruding fins. As for the rolling processing method, it is known that a plug with a groove that rotates freely is inserted into the tube, and a roll that rotates freely outside the tube is squeezed to make it rotate planetary, and the roll that pulls out the tube is known. (roll rolling) manufacturing method (as shown in Figure 3), or the ball rolling manufacturing method (non-patent document 1, patent document 2) of extruding ball (ball) without rolling.

Copper materials such as copper or copper alloys are currently mainly used on heat pipes with grooves on the inner surface. However, in order to meet the requirements of reducing material costs and light weight, some people consider using aluminum materials such as aluminum or aluminum alloys (hereinafter referred to as aluminum alloys) .

However, aluminum alloys have poor corrosion resistance compared to copper materials. Patent Documents 3 and 4 disclose a heat transfer tube with grooves on the inner surface, wherein the heat transfer tube has a two-layer structure, and Al - Mn alloy clad with a sacrificial anti-corrosion layer of Al-Zn alloy on the outer layer.

On the other hand, in addition to the problem of corrosion resistance, when the heat transfer tubes made of aluminum alloy with grooves on the inner surface are processed by tube expansion, the top of the protruding fins on the inner surface of the tube is damaged, which is called "fin breakage", or Insufficient expansion of the tube and insufficient bonding with the aluminum heat sink lead to the problem that the expected thermal conductivity cannot be obtained. The reason for these problems is that the material strength of aluminum or aluminum alloy heat pipes with grooves on the inner surface is lower than that of copper.

In addition, there was another problem that the bent portion was broken when the above-mentioned heat transfer pipe made of aluminum with grooves on the inner surface was subjected to hairpin bending.

In addition, in Patent Document 5, it is considered that adding a Zn alloy as a skin material to JIS3003 improves pipe expandability.

【Background technical literature】

【Patent Literature】

[Patent Document 1] Japanese Patent Laid-Open No. 2003-287383

[Patent Document 2] Japanese Patent Application Publication No. 4-262818

[Patent Document 3] Japanese Patent Laid-Open No. 2000-121270

[Patent Document 4] Japanese Patent Laid-Open No. 2009-250562

[Patent Document 5] Japanese Patent Laid-Open No. 2008-267714

【Non-patent literature】

[Non-Patent Document 1] Masaki Ito: Thermal Conduction, 42, 174(2003), 3

[Non-Patent Document 2] Akio Isozaki and others: R&D Kobe Steel Technical Bulletin 50, 3(2000), 66

Contents of the invention

【Problems to be solved by the invention】

However, the prior art described in the above documents still has room for improvement in the following points.

In Patent Document 1, Patent Document 2, and Non-Patent Documents 1 and 2, the problem of cracking during the hairpin bending process and the problem of damage to the heat sink are not solved. In Patent Document 3, it is described that the purpose is to improve the corrosion resistance of the aluminum alloy heat transfer tube, but the problems of cracking during hairpin bending and damage to the heat sink have not been solved. Patent Document 4 is characterized in that in order to improve corrosion resistance, the outer surface is coated with a skin material having a potential lower than that of the core material, but there is no description about the problem of cracking during hairpin bending and the problem of heat sink damage.

In addition, in order to improve the corrosion resistance, when the Al-Zn alloy is coated on the heat transfer tube, since the surface is soft, microscopic flaws are generated on the surface when the blank tube before rolling is manufactured. When those tubes are used for rolling processing, the minute flaws are cracks (cracks) that grow to several hundreds of micrometers. The resulting problem is that these cracks will become the starting point for cracking when the hairpin is bent.

In addition, in the method of Patent Document 5, the problem of cracking during hairpin bending is not improved. In addition, since Cu and Fe are added to the skin material, the corrosion resistance of the skin material is poor, and the expected sacrificial anti-corrosion effect may not be obtained. In addition, since the core material is used, and the core material is composed of an alloy equivalent to JIS3003, the problem of breakage of the heat sink is not solved.

In view of the above circumstances, an object of the present invention is to provide a heat transfer pipe made of aluminum alloy having grooves on the inner surface excellent in hairpin bending workability. Another object of the present invention is to provide an aluminum alloy heat transfer pipe with grooves on the inner surface having excellent corrosion resistance. Another object of the present invention is to provide a heat transfer pipe made of aluminum alloy with grooves on the inner surface, in which the damage of the heat radiation fin hardly occurs.

【Means to solve the problem】

The inventors of the present invention have conducted various studies on aluminum alloy heat transfer pipes with grooves on their inner surfaces, and found that it is possible to provide a material that is characterized in that the core material alloy contains a specific type and content, so that the Hairpin bendability is excellent, and heat sink breakage is less likely to occur.

Furthermore, there is provided a material characterized in that the distribution of Zn in the sacrificial anti-corrosion layer is limited to a specific range, so that the bending workability of the hairpin is excellent, the breakage of the heat sink is less likely to occur, and the material is excellent in corrosion resistance.

The first invention described in claim 1 is an aluminum alloy heat transfer tube with grooves on the inner surface, characterized in that two or more grooves are formed on the inner surface (the range of "A or more", including A itself) The heat transfer tube of the ridge fin is an aluminum alloy heat transfer tube, and its composition is to contain Mn: 0.8-1.8% by mass (hereinafter only expressed as % by mass), Cu: 0.3-0.8%, Si: 0.02-0.2%, The remainder is unavoidable impurities and Al; and, the average crystal grain size of the cross-section of the heat pipe is 150 μm or less.

The second invention described in claim 2 is an aluminum alloy heat transfer pipe having grooves on its inner surface, wherein the surface of the heat transfer pipe described in claim 1 has a surface Zn concentration of 0.5% or more, And the average surface Zn concentration is 1 ~ 12%, and the concentration of any surface is within ± 50% of the average surface Zn concentration, and has a Zn diffusion layer, wherein, the Zn diffusion depth from the surface (hereinafter referred to as "Zn diffusion layer") Thickness") is 100 to 300 μm.

The third invention described in claim 3 is a heat transfer tube made of aluminum alloy with grooves on its inner surface, characterized in that the heat transfer tube described in claim 2 is a heat transfer tube made of aluminum alloy, and its composition is to contain Mn: 0.8 to 1.8%, Cu: 0.3 to 0.8%, Si: 0.02 to 0.2%, and the rest are unavoidable impurities and Al; and a heat pipe made of aluminum alloy is used as the core material, and the heat pipe made of aluminum alloy is characterized in that the heat conduction The cross-sectional average grain size of the tube is 150 μm or less; the outer surface of the tube is coated with Al-Zn alloy as a skin material; and Zn diffusion heat treatment is performed.

A fourth invention described in claim 4 is an aluminum alloy heat transfer tube having grooves on its inner surface, wherein in the heat transfer tube described in claim 3, the core after the Zn diffusion heat treatment is The hardness difference between the material and the above-mentioned skin material is 15Hv or less.

A fifth invention described in claim 5 is an aluminum alloy heat transfer tube having grooves on its inner surface, wherein in the heat transfer tube described in claim 3 or claim 4, the skin material contains Zn : 1.0 to 7.0%, and Mn: 0.3 to 1.5%, and the rest are unavoidable impurities and Al.

The 6th invention described in claim 6 is an aluminum alloy heat conduction pipe with grooves on the inner surface, characterized in that: the heat conduction pipe as described in claim 2 is an aluminum alloy heat conduction pipe, and its composition is to contain Mn: 0.8 to 1.8%, Cu: 0.3 to 0.8%, and Si: 0.02 to 0.2%, and the rest are unavoidable impurities and Al; and the aluminum alloy heat pipe is characterized in that the cross-sectional average crystal grain size of the above heat pipe is 150 μm Next: Zn is sprayed on the outer surface of the above-mentioned aluminum alloy heat transfer tube, and Zn diffusion heat treatment is performed.

The seventh invention described in claim 7 is an aluminum alloy heat transfer tube having a groove on its inner surface, wherein, in the heat transfer tube described in claim 6 , the heat transfer tube that is sprayed with Zn is The outer surface, the coverage rate is more than 90%.

The eighth invention described in claim 8 is a method of manufacturing an aluminum alloy heat transfer pipe with grooves on its inner surface as described in claim 6 and claim 7, wherein spraying is carried out on the heat transfer pipe. During plating, the geometric center of the cross-section of the heat pipe is connected to the centers of more than two (including 2) Zn spraying guns, and adjacent lines form an angle with the geometric center, and the angle is less than 120°.

【Effect of invention】

The aluminum alloy heat transfer pipe with grooves on the inner surface of the present invention has the effect of suppressing the occurrence of cracks during hairpin bending. In addition, it has the effect that it has good corrosion resistance and is less likely to cause damage to the heat sink.

Description of drawings

[Simple description of drawings]

FIG. 1 is an example of an enlarged view of a part of a cross-fin heat exchanger.

Fig. 2 shows an example of a mandrel pipe expansion method.

Figure 3 shows an example of a rolling device.

FIG. 4 is a schematic diagram showing an example of a cross-section of a heat transfer pipe with grooves on its inner surface.

Figure 5 is a schematic diagram showing the lead angle of the inner ridge fin.

Detailed ways

【Best Mode of Invention】

Embodiments of the present invention will be described in detail below.

The heat conduction pipe conceived in this embodiment is, for example, a heat conduction pipe used in a heat exchanger for an air conditioner in an ordinary household, and its size is, for example, an outer diameter of φ4.0 to φ9.54mm, and a thickness of 0.3 to 0.6 Small-diameter thin-walled tubes of about mm. Therefore, among various aluminum alloys, the alloy (for example, Al -Mn's A3003 alloy (Al-1.0～1.5%Mn-0.05～0.20%Cu alloy)) as the base (base), by adjusting the addition of elements, the refinement and strength of crystal grains are improved, so that an aluminum alloy can be obtained , The feature of this aluminum alloy is to prevent cracking during hairpin bending and damage to heat sinks.

Composition of the heat pipe

Next, the reasons for limiting the components of the heat transfer pipe in this embodiment will be described.

Mn is the main additive element for improving the strength in the 3000 alloy. It is dissolved in aluminum and partially precipitated to impart strength. If the added amount is less than 0.8%, the strength of the heat pipe will be insufficient. On the other hand, if the addition amount is more than 1.8%, the effect of improving the strength will be saturated, the amount of coarse intermetallic compounds will increase, and problems such as cracks will easily occur in the pipe manufacturing process. Therefore, the amount of Mn added is in the range of 0.8 to 1.8%. A more preferable range is 1.0 to 1.5%.

Cu dissolves in aluminum and has the effect of further improving the strength without hindering workability. Moreover, Cu increases the pitting corrosion potential, and the pitting corrosion potential difference between the Zn diffusion layer and the central part of the tube without Zn diffusion is large, which can improve the sacrificial corrosion protection effect. When the added amount is less than 0.3%, the strength is insufficient to prevent groove damage caused by mechanical tube expansion, and the degree of raising the pitting potential is insufficient, and the sacrificial corrosion protection effect is low. More than 0.8%, extrudability, stretchability, and corrosion resistance are poor. Therefore, the amount of Cu added is in the range of 0.3 to 0.8%. A more preferable range is 0.4 to 0.6%.

If Si is contained in the Al-Mn-Cu alloy, it forms an Al-Mn-Si or Al-Mn-Si-Cu intermetallic compound, which has the effect of increasing the strength. On the other hand, these intermetallic compounds inhibit recrystallization during hot extrusion, and when the added amount exceeds 0.2%, the average crystal grain size becomes 150 μm or more, which causes surface roughness and fracture during hairpin bending. On the other hand, the presence of Si in the aluminum alloy is unavoidable, and it is difficult to limit it to 0.02% or less from a practical point of view. Therefore, the added amount of Si is 0.02 to 0.2%. A more preferable range is 0.02 to 0.1%.

Fe, Mg, Zn, etc. are impurities, and when Fe is 0.6% or less, Mg is 0.2% or less, and Zn is 0.3% or less, they do not hinder the effect of the present invention.

In addition, Ti, Cr, and Zr can be contained because they have the effect of uniformly refining the structure of the ingot, but if it exceeds 0.2%, a huge intermetallic compound will be formed or the extrudability will decrease, so the content is preferably 0.2% or less. If it is within this range, the effect of the heat pipe in this embodiment will not be hindered. In addition, its content may be 0 to 0.1%, or 0 to 0.05%.

In addition, the amounts of various components used in the heat pipe or the sacrificial anti-corrosion layer in this embodiment can be the values described in Examples S1-S11, K1-K8 below, and can be within the range of these values.

About Coated Sacrificial Corrosion Protection

Next, the reason for limiting the distribution state of Zn in the sacrificial anticorrosion layer of the clad pipe in this embodiment will be described.

In the aluminum alloy clad pipe according to the embodiment of the present invention, the Zn diffusion layer is formed by performing Zn diffusion heat treatment after coating with Al—Zn alloy as the skin material and stretching. The above-mentioned Zn diffusion layer has a lower pitting corrosion potential than a part of the pipe in which Zn is not diffused, so the corrosion resistance of the pipe is made by sacrificing the anti-corrosion effect, and the durable life of the pipe is extended.

In the aluminum alloy clad pipe according to the embodiment of the present invention, the conditions of the diffusion heat treatment are adjusted so that the surface Zn concentration after the Zn diffusion heat treatment is 0.5 to 12%. The surface Zn concentration means the Zn concentration measured at an arbitrary point on the surface with an analysis device such as an EPMA (X-ray microanalyzer). If the surface Zn concentration is lower than 0.5%, the sacrificial anti-corrosion effect is insufficient, and deep corrosion occurs at an early stage. On the other hand, when the surface Zn concentration is higher than 12%, the corrosion rate increases. Therefore, the surface Zn concentration is 0.5 to 12%. A more preferable range is 0.5 to 10.0%, and an even more preferable range is 3.0 to 5.0%.

In the embodiment of the present invention, the thickness of the Zn diffusion layer of the aluminum alloy clad pipe is 100-300 μm. The thickness of the Zn diffusion layer means the depth at which Zn diffuses from the surface in the thickness direction of the sheet through the Zn diffusion treatment. In the embodiment of the present invention, the thickness of the Zn diffusion layer is: the distance (thickness) from the pipe surface to the Zn concentration of 0.05%. As far as the Zn diffusion layer is concerned, it functions as a sacrificial anti-corrosion layer for the whole tube. If the Zn diffusion layer is too thin, the sacrificial anti-corrosion layer will be lost in the early stage; if the Zn diffusion layer is too thick, the Zn gradient will gradually slow down, and the sacrificial anti-corrosion The corrosion effect is insufficient. Therefore, the thickness of the Zn diffusion layer is 100 to 300 μm. The thickness of the Zn diffusion layer may also be 150 to 250 μm.

Next, the rationale for limiting the components of the skin material of the clad pipe according to the present embodiment will be described.

Zn lowers the potential of the skin material, functions as a sacrificial anode, and improves the corrosion resistance of the heat transfer tube. When the added amount is less than 1.0%, the potential difference with the core material is insufficient, and a sufficient sacrificial anti-corrosion effect cannot be obtained, and when it exceeds 7.0%, the corrosion resistance decreases. Therefore, the added amount of Zn is in the range of 1.0 to 7.0%. A more preferable range is 4.0 to 5.5%.

Mn is a main added element for improving strength, and if the added amount is less than 0.3%, the strength is insufficient and the strength difference with the core material becomes large. As a result, minute cracks (cracks) on the surface are generated during the production of the blank tube, which causes cracks during the hairpin bending process. On the other hand, when the added amount is more than 1.5%, the electric potential of the skin material becomes high, so it becomes difficult to ensure the electric potential difference with the core material. Therefore, the added amount of Mn is in the range of 0.3 to 1.5%. A more preferable range is 0.6 to 1.0%.

Impurities such as Si, Fe, Cu, etc. of the skin material of the clad pipe do not hinder the effect of the present invention if the content of Si is 0.5% or less, Fe is 0.6% or less, and Cu is 0.2% or less.

In addition, Ti, Cr, and Zr can be contained because they have the effect of uniformly refining the structure of the ingot, but if it exceeds 0.2%, a huge intermetallic compound will be formed or the extrudability will decrease, and the content is preferably 0.2% or less. Within this range, the effect of the heat pipe in this embodiment will not be hindered. In addition, the content may be 0 to 0.1%, or 0 to 0.05%.

The thickness of the skin material of these covering pipes is not particularly limited, but is preferably 5 to 30% of the total wall thickness. When the thickness of the skin material is less than 5% of the total wall thickness, the validity period of the sacrificial anti-corrosion layer of the heat exchanger is not enough, and if it exceeds 30%, the strength of the heat transfer pipe decreases. A more preferable range is 6 to 15%.

In addition, when the strength difference between the core material and the skin material is large, because of the difference in the deformation resistance of the core material and the skin material, tiny cracks occur on the surface during the manufacture of the tube blank, which becomes the cause of the crack during the hairpin bending process. Therefore, the hardness difference between the core material and the skin material is 15 Hv or less. More preferably, it is 10 Hv or less.

About the sacrificial anti-corrosion layer of Zn spraying

Next, the reason for limiting the distribution state of Zn in the sacrificial anticorrosion layer of the thermal spraying tube, that is, the Zn diffusion layer in this embodiment will be described.

In the aluminum alloy sprayed tube according to the embodiment of the present invention, a Zn diffused layer is formed by performing Zn diffusion heat treatment after Zn sprayed on the outer surface. The above-mentioned Zn diffusion layer has a lower pitting corrosion potential than the part of the pipe where Zn is not diffused, so the pipe corrosion is prevented by sacrificing anti-corrosion effect, and the durable life of the pipe is improved.

After spraying pure Zn or the Zn component of Zn-Al alloy on the aluminum alloy spraying tube, it is better to carry out Zn diffusion heat treatment at 400-550°C for 30 minutes to 10 hours. The amount of Zn sprayed is 5-28g/m ² . If the amount of Zn sprayed is too small, it is difficult to uniformly adhere Zn to the surface of the pipe. If the amount of Zn sprayed is too large, the amount of Zn after Zn diffusion heat treatment is too large, resulting in an increase in corrosion rate. Therefore, the amount of Zn sprayed is 5 to 28 g/m ² . More preferably, the amount of Zn spraying is 5 to 25 g/m ² , still more preferably 8 to 20 g/m ² .

In the aluminum alloy tube in the embodiment of the present invention, the surface Zn concentration after the Zn diffusion heat treatment is 0.5 to 15%. The surface Zn concentration means the concentration of Zn when an arbitrary point on the surface is measured with an analytical device such as EPMA. If the surface Zn concentration is too low, the sacrificial anti-corrosion effect will be insufficient, and deep corrosion will occur in some of them at an early stage; if the surface Zn concentration is too high, the corrosion rate will increase, and the wall thickness of some of them will be extremely reduced.

In the aluminum alloy tube according to the embodiment of the present invention, the average surface Zn concentration after the Zn diffusion heat treatment is 1 to 12%, and the thickness of the Zn diffusion layer is 100 to 300 μm. The average surface Zn concentration refers to an average value obtained by measuring at least four arbitrary points on the surface that are separated from each other by 5 mm or more. The so-called Zn diffusion layer thickness refers to the depth of Zn diffusion from the surface to the plate thickness direction through Zn diffusion treatment. In the embodiment of the present invention, the Zn diffusion layer thickness is the distance from the pipe surface to the Zn concentration of 0.05%. The average Zn concentration and the thickness of the Zn diffusion layer indicate the amount of the sacrificial anticorrosion layer in the entire tube. If the average Zn concentration and the thickness of the Zn diffusion layer are too small, the sacrificial anticorrosion layer will be lost at an early stage. In addition, if the average Zn concentration is too high, the corrosion rate will increase; if the Zn diffusion layer is too thick, the Zn gradient will be slowed down, and the sacrificial anti-corrosion effect will be insufficient. Therefore, the average surface Zn concentration is 1 to 12%, a more preferable range is 0.5 to 10.0%, and a more preferable range is 3.0 to 5.0%. In addition, the thickness of the Zn diffusion layer may be 100 to 300 μm, or may be 150 to 250 μm.

In the aluminum alloy tube according to the embodiment of the present invention, the Zn concentration on any surface after the Zn diffusion heat treatment is within ±50% of the average surface Zn concentration. When the surface Zn concentration is too high relative to the average surface Zn concentration, only this part is preferentially corroded, and the wall thickness is extremely reduced. To avoid this, the Zn concentration at any surface needs to be within ±50% of the average surface Zn concentration. Preferably within ±30%.

The so-called Zn coverage of thermal spraying: 0% when Zn is not attached at all, and 100% Z when Zn is attached to the entire surface. When the Zn coverage is high, the Zn distribution becomes uniform and the corrosion resistance improves. In the present invention, the coverage rate of Zn is more than 90%. More preferably 95% or more for me.

Formation method of sacrificial anticorrosion layer

Next, an example of an embodiment of a method for forming a sacrificial anticorrosion layer will be described.

In this embodiment, on the outer side of the Al-Mn-Cu alloy cylindrical billet (Billet) of the heat pipe, the sacrificial anti-corrosion alloy plate is bent into a cylindrical shape and covered on the outer side to make a combined billet , heated to 350-600°C in a heating furnace for homogenization. Afterwards, the body was extruded with an indirect extruder to obtain a two-layer coated extruded tube. Next, the above-mentioned extruded tube was stretched to obtain a predetermined outer diameter and wall thickness to obtain a double-coated blank tube (smooth tube). For the stretching process, it is preferable to use a block-drawing type continuous stretching machine with high productivity.

In addition, the blank of the cylindrical sacrificial anti-corrosion material is heated to 350-600°C, and the cylindrical core material hollow blank is shrink-fitted (or translated as "shrink fit") on its inner side. The obtained two-layer hollow body is extruded, and then stretched in the same manner to obtain a two-layer-coated blank tube (smooth tube).

In addition, it is also possible to roll a clad sacrificial anti-corrosion material sheet on one side of an aluminum alloy core material sheet (sheet) to obtain a two-layer "clad sheet", roll the sheet into a tubular shape, and then Welding of the sheet butt joints as a 2-layer clad electric resistance welded tube.

Diffusion heat treatment is performed on the two-layer clad pipe manufactured as described above to obtain a Zn diffusion layer, that is, a sacrificial anticorrosion layer.

In terms of the formation method of the sacrificial anti-corrosion layer other than the above, it is also possible to spray Zn or Al-Zn alloy on the extruded (hot extruded or conformal (conform) extruded), or stretched heat pipe , Diffusion heat treatment is carried out to form a Zn diffusion layer, that is, a sacrificial anti-corrosion layer. In order to attach a required amount of Zn on the entire surface of the circular pipe in the circumferential direction, when the center of the circumferential section of the pipe is linked with the Zn spray coating gun, the angle formed between the lines at the center of the circumferential section is preferably 120°. the following. Furthermore, the angle formed between the lines at the centers of the circumferential cross-sections is preferably 90° or less. In terms of specific methods, examples that can be cited include: increasing the number of Zn spraying guns generally used in flat tubes from 2 to more than 3; rotating the tube after spraying, and spraying several times. A method of plating; a method of rotating a tube or a coating gun; and the like. The Zn thermal spraying may be performed after rolling processing for forming grooves on the inner surface of the heat transfer tube.

In addition, according to the above method, for the tube blank (smooth tube) on which the sacrificial anti-corrosion layer is formed, in order to facilitate the rolling process in the next step, it is better to perform annealing and softening treatment in advance. In this case, it is industrially preferable that the annealing temperature is 300 to 400° C. and the time is 2 to 8 hours.

Method for manufacturing heat pipe with grooves on inner surface

Next, roll processing is performed on the smooth tube by a rolling method, a ball rolling method, etc., to manufacture a heat transfer tube having ridge-shaped fins and grooves on the inner surface (FIG. 3).

As for the heat conduction tube with grooves on the inner surface of this embodiment, various sizes can be manufactured according to the application of the heat exchanger. When used in a household air conditioner, considering the productivity of manufacturing the tube, it is preferable that the outer diameter φ4.0mm or more ; In consideration of miniaturization and weight reduction of the heat exchanger, it is preferable that the outer diameter φ9.54mm or less.

In addition, the bottom thickness t (see FIG. 4 ) is preferably 0.3 mm or more in consideration of the compressive strength, and 0.6 mm or less in consideration of the miniaturization and weight reduction of the heat exchanger.

In addition, it is preferable that the height H of the ridge-shaped fins on the inner surface is 0.1-0.4 mm, the diagonal angle of the ridge-shaped fins on the inner surface is α10-40°, and the number of ridge-shaped fins on the inner surface is 40 or more. The stroke angle β (the angle formed by the inner ridge-shaped fins and the tube length direction, see FIG. 5 ) is 20° or more.

After rolling, an annealing softening treatment may be performed. Its purpose is to remove the processing deformation caused by rolling and make hairpin bending processing (serpentine bending processing) easier. Annealing may be performed at 300 to 400° C. for about 2 to 8 hours.

The heat transfer tube with grooves on the inner surface of this embodiment manufactured as described above was adhered to the insertion hole of the aluminum heat sink through tube expansion processing ( FIG. 2 ). In order to obtain good bonding, it is appropriate to carry out the following steps: set the gap between the insertion hole and the heat pipe so that the tube expansion rate (outer diameter growth rate) is about 4-6%. In addition, in terms of pipe expansion, production efficiency can be improved by using a hydraulic pipe expansion method that applies internal pressure to the pipe with oil pressure or water pressure instead of the mechanical pipe expansion method of the mandrel.

As mentioned above, although embodiment of this invention was described, these are only the example of this invention, and various structures other than the above-mentioned can also be employ|adopted.

【Example】

<Example 1>

Next, the present invention will be described in further detail based on examples.

The alloys shown in Table 1 were cast by continuous casting, and an extruded tube with an outer diameter of φ47 mm and a wall thickness of 3.5 mm was obtained by indirect extrusion. The extruded tube was stretched with a block-drawing type continuous stretching machine to obtain a stretched tube with an outer diameter of φ10 mm and a wall thickness of 0.45 mm.

【Table 1】

After annealing and softening at 360°C for 2 hours on the stretched tube manufactured as described above, insert a plug (the plug is a floating plug, a rod, a plug with a groove). ) as a whole), through the floating die (Floating dice), the processing head (Processing head), and the forming die (Forming dice) to process the grooves on the inner surface, the heat conduction tube with grooves on the inner surface is made as follows: Diameter: φ7mm, bottom thickness: 0.35mm, ridge fin height H: 0.22mm, number of ridge fins: 50, apex angle α: 15°, lead angle β: 35°. And finally, an annealing and softening treatment was performed at 360° C. for 2 hours to complete the heat transfer pipe with grooves on the inner surface.

The following tests were conducted on the characteristics of the heat transfer tubes of the examples of the present invention and the comparative examples prepared as above with grooves on their inner surfaces. Table 2 shows the results obtained.

(a) Tensile test

In order to measure the strength of heat pipes with grooves on the inner surface, a tensile test is performed according to JIS Z2241.

(b) Average crystal grain size

A test piece for microstructure observation was cut out from the obtained heat transfer tube with grooves on the inner surface, and the average crystal grain size was measured. Specifically, the measurement of the average crystal grain size was carried out in two directions, the tube thickness direction and the circumferential direction, by the intersection method, and the average value was obtained.

(c) Pipe expandability

Using a steel mandrel, the above-mentioned heat transfer tube having an outer diameter of φ7mm with grooves on the inner surface was expanded to increase the outer diameter by 5%. Afterwards, the section of the tube was observed, and the decrease in height H of the ridge fin was measured to evaluate the amount of fin damage. In order to obtain the thermal conductivity of the heat exchanger, the amount of damage to the fins is preferably 0.02 mm or less.

(d) Hairpin bending workability

Bending a φ7mm pipe with grooves on the inner surface, and performing hairpin bending with a pitch of 16mm. The surface after the bending process was visually observed to check whether cracks occurred on the surface. At this time, 10 pipes with grooves on the inner surface were prepared for each of S1 to S17, and evaluated according to the following criteria.

○: 10 No cracking occurred in all.

△: Only 1 to 9 pieces did not break.

×: All 10 cracked.

【Table 2】

The evaluation results shown in Table 2 will be described. Examples S1 to S11 are products within the scope of the present invention, and their mechanical properties, heat sink damage, average crystal grain size, and whether cracks occur during hairpin bending are all excellent. However, Comparative Examples S12 and S15 failed to obtain desired thermal conductivity characteristics due to their low strength and large amount of damage to the heat sink. In addition, S13 and S14 were not produced due to tensile fracture during stretching. In addition, S16 was cracked during hairpin bending because the average grain size exceeded 150 μm. In addition, the crystal grains of S17 are small, and although it does not break during the hairpin bending process, the problem of high manufacturing cost is high because of the extremely low Si content.

<Example 2>

Through continuous casting, the alloys for skin materials shown in Table 3 are cast, and the core material alloys shown in Table 1 and the combinations in Table 4 are extruded by indirect extrusion with an outer diameter of φ47mm and a wall thickness of 3.5mm. Extruded tube with 10% coverage. The extruded tube was stretched with a block-drawing type continuous stretching machine to obtain a stretched tube with an outer diameter of φ10 mm and a wall thickness of 0.45 mm. Zn diffusion heat treatment is further performed.

【table 3】

【Table 4】

After annealing and softening treatment at 360°C for 2 hours on the stretched tube prepared according to the above-mentioned steps, insert a plug (the plug is a floating plug, a rod, a plug with a groove) (plug) as a whole), through the floating die (Floating dice), processing head (Processing head), forming die (Forming dice) to process the inner surface with grooves, the following heat conduction with grooves on the inner surface is obtained. Tube: Outer diameter: φ7mm, Bottom thickness: 0.35mm, Ridged fin height H: 0.22mm, The number of ridged fins is 50, Apex angle α: 15°, Lead angle β: 35° . And finally, an annealing and softening treatment was performed at 360° C. for 2 hours to complete the heat transfer pipe with grooves on the inner surface.

The characteristics of the thus-produced heat exchanger tubes with grooves on their inner surfaces were tested as follows. Table 5 shows the results obtained.

(a) Tensile test

In order to measure the strength of the heat pipe with grooves on the inner surface, a tensile test was performed according to JIS Z2241.

(b) Cross section hardness

The hardness of the core material and the skin material of the above-mentioned heat conduction tube with an outer diameter of φ7 mm and grooves on the inner surface was measured. In addition, the measurement procedure of the hardness is as follows: Fill the cross section of the pipe with the groove with resin, grind it, and measure it under the condition of a load of 50 g using a Micro Vickers hardness tester (manufactured by Akashi Seisakusho).

(c) Hairpin bending workability

Bending a φ7mm pipe with grooves on the inner surface, and performing hairpin bending with a pitch of 16mm. The surface after the bending process was visually observed to check whether cracks occurred on the surface. At this time, 10 pipes with inner grooves were prepared for each of C1 to C12, and the evaluation was performed according to the following criteria.

○: 10 No cracking occurred in all.

△: Only 2 to 9 pieces did not break.

×: 9 to 10 cracks occurred.

(d) Corrosion resistance

In order to evaluate the external corrosion resistance, a 1500-hour CASS test was performed in accordance with JISZ8681 for each of the heat transfer pipes with grooves on the inner surface. After the test, remove the corrosion product on the surface of the pipe used for the test, observe the corrosion condition of the pipe, and evaluate the external corrosion resistance according to whether there is a perforation. At this time, 10 heat transfer tubes with grooves on the inner surface were prepared for C1 to C12, respectively, and evaluated according to the following criteria.

◯: None of the 10 pieces were perforated.

△: Only 2 to 9 pieces were not perforated.

×: 9 to 10 of them had perforation.

【table 5】

The evaluation results shown in Table 5 will be described. For C1-C8, the hardness difference between the core material and the skin material was small, and no cracks occurred during the hairpin bending process. Moreover, corrosion resistance is also favorable. On the other hand, C9, which has a low Mn content, has a large difference in hardness between the core material and the skin material, and microscopic scratches occur on the surface during drawing, which becomes the starting point of cracking during hairpin bending. C10 with a large Mn content has a small potential difference between the core material and the skin material, resulting in perforation in the corrosion resistance test. In addition, C11 having a large Zn content was poor in corrosion resistance, and as a result, perforation occurred in the corrosion resistance test. On the other hand, C12 with less Zn content cannot fail to obtain sufficient sacrificial anti-corrosion effect, and perforation occurred in the anti-corrosion test.

<Example 3>

Through continuous casting, the S10 alloy in Table 1 was cast, and an extruded tube with an outer diameter of φ47 mm and a wall thickness of 3.5 mm was obtained by indirect extrusion. The extruded tube was stretched with a block-drawing type continuous stretching machine to obtain a stretched tube with an outer diameter of φ10 mm and a wall thickness of 0.45 mm.

After annealing and softening at 360°C for 2 hours on the stretched tube manufactured as described above, insert a plug (the plug is a floating plug, a rod, a plug with a groove). ) as a whole), through the floating die (Floating dice), the processing head (Processing head), and the forming die (Forming dice) to process the grooves on the inner surface, the heat conduction tube with grooves on the inner surface is made as follows: Diameter: φ7mm, bottom thickness: 0.35mm, ridge fin height H: 0.22mm, number of ridge fins: 50, apex angle α: 15°, lead angle β: 35°. And finally, an annealing and softening treatment was performed at 360° C. for 2 hours to complete the heat transfer pipe with grooves on the inner surface.

Shot blasting, Zn spraying, and Zn diffusion heat treatment are performed on the thus-produced heat conduction tube with grooves on the inner surface to complete the heat conduction tube with grooves on the inner surface having a Zn diffusion layer. The conditions of Zn spraying and Zn diffusion heat treatment are shown in Table 6.

【Table 6】

To evaluate the properties of the thus-produced heat transfer tube with grooves on its inner surface, the following tests were conducted. Table 7 shows the results obtained.

(a) Zn distribution

EPMA was performed to detect the surface Zn concentration and the Zn diffusion distance after the Zn diffusion heat treatment. The detection method is as follows: for each sample, 10 points are detected, and the distance between these points is more than 5mm.

(b) Zn coverage

To examine the Zn coverage after Zn diffusion heat treatment, the COMPO images of SEM were used. If covered by Zn, a white image is obtained; if the substrate Al is exposed, a black image is obtained. The image was analyzed to calculate the Zn coverage.

(c) Corrosion resistance

In order to evaluate the external corrosion resistance, a 1500-hour CASS test was carried out in accordance with JIS Z8681 for each heat pipe with grooves on the inner surface. After the test, remove the corrosion product on the surface of the pipe used for the test, observe the corrosion condition of the pipe, and evaluate the external corrosion resistance according to whether there is a perforation. At this time, 10 heat transfer tubes with grooves on the inner surface were prepared for each of Y10 to Y21, and the evaluation was performed based on the following criteria.

○: None of the 10 pieces were perforated.

△: Only 2 to 9 pieces were not perforated.

×: 9 to 10 of them had perforation.

【Table 7】

The evaluation results shown in Table 7 will be described. In Y1 to Y9, no penetrating corrosion occurred, and good corrosion resistance was exhibited. In Y10 and 12, because the lower limit of the surface Zn concentration was not reached, and in Y14, because the lower limit of the average surface Zn concentration was not reached, sacrificial corrosion protection did not function effectively, resulting in early breakthrough. Because the upper limit of the surface Zn concentration is exceeded in Y11 and 13, and the upper limit of the average surface Zn concentration is exceeded in Y15, the sacrificial layer is consumed quickly and breakthrough is achieved early. In Y16 and 17, since the upper limit of the Zn concentration difference was exceeded, the corrosion was concentrated, resulting in early penetration. In Y18, since the lower limit of the Zn diffusion distance was not reached, the amount of the sacrificial layer was small, resulting in early penetration. In Y19, because the upper limit of the Zn diffusion distance was exceeded, the Zn gradient slowed down, and sacrificial corrosion protection did not work effectively, resulting in early penetration. In Y20 and 21, because the Zn coverage rate did not reach the lower limit, the corrosion was concentrated, resulting in early penetration.

The present invention has been described above with examples. This embodiment is just an example, and various modification examples are possible, and these modification examples also belong to the scope of the present invention, which is understood by those skilled in the art.

【Description of symbols】

1 aluminum heat sink

2 heat pipes (heat pipes with grooves on the inner surface)

3 Transom (Louver)

4 Expansion plug (mandrel)

5 tube blank (smooth tube)

6 Rolled plug (Rolled plug)

7Rotating roll

8 heat pipe with spiral grooves on the inner surface

9 ridge fins

10 sacrificial anti-corrosion layer

Claims (8)

1. A heat pipe made of aluminum alloy with grooves on the inner surface, characterized in that: The heat transfer tube having two or more ridge-shaped fins formed on the inner surface is a heat transfer tube made of aluminum alloy, containing Mn: 0.8 to 1.8% by mass (hereinafter only expressed as % by mass), Cu: 0.3 to 0.8%, and Si: 0.02-0.2%, the rest is composed of unavoidable impurities and Al; and, the cross-sectional average crystal grain size of the above-mentioned heat pipe is 150 μm or less. 2. The heat pipe made of aluminum alloy with grooves on the inner surface as claimed in claim 1, wherein, On the surface of the above-mentioned heat transfer pipe, the surface Zn concentration is 0.5% or more, and the average surface Zn concentration is 1 to 12%, and the concentration on any surface is within ±50% of the average surface Zn concentration, and has, from A Zn diffusion layer in which the Zn diffusion depth from the surface is 100 to 300 μm. 3. The heat pipe made of aluminum alloy with grooves on the inner surface as claimed in claim 2, characterized in that: Contains Mn: 0.8-1.8%, Cu: 0.3-0.8%, and Si: 0.02-0.2%, and the rest is composed of unavoidable impurities and Al; The characteristic is that the cross-sectional average grain size of the above-mentioned heat pipe is less than 150 μm, and its outer surface is covered with a skin material of Al-Zn alloy, and then subjected to Zn diffusion heat treatment. 4. The heat pipe made of aluminum alloy with grooves on the inner surface as claimed in claim 3, characterized in that: The difference in hardness between the core material and the skin material after the Zn diffusion heat treatment is 15 Hv or less. 5. The aluminum alloy heat pipe with grooves on the inner surface as claimed in claim 3 or 4, characterized in that: The above-mentioned skin material contains Zn: 1.0-7.0%, Mn: 0.3-1.5%, and the remainder is unavoidable impurities and Al. 6. The heat pipe made of aluminum alloy with grooves on the inner surface as claimed in claim 2, characterized in that: Contains Mn: 0.8-1.8%, Cu: 0.3-0.8%, and Si: 0.02-0.2%, and the remainder is unavoidable impurities and Al, In addition, the average grain size of the cross-section of the heat pipe is 150 μm or less; Zn was sprayed on the outer surface of the aluminum alloy heat pipe, and Zn diffusion heat treatment was performed. 7. The heat pipe made of aluminum alloy with grooves on the inner surface as claimed in claim 6, characterized in that: With respect to the outer surface of the heat pipe, the coverage of the sprayed Zn is 90% or more. 8. The method of manufacturing an aluminum alloy heat pipe with grooves on its inner surface as claimed in claim 6 or 7, characterized in that: When spraying on the above-mentioned heat-conducting tube, the geometric center of the section of the above-mentioned heat-conducting tube is connected to the centers of more than two (including two) Zn spraying guns, and the angle formed by the adjacent connecting lines at the above-mentioned geometric center is 120° or less.