JP2010085065A - Aluminum alloy extrusion tube for fin tube type air conditioner heat exchanger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy extrusion tube having superior workability and strength as a tube of a heat exchanger for an air conditioner. <P>SOLUTION: This aluminum alloy extrusion tube for the fin tube type air conditioner heat exchanger, including 0.1-1.6 mass% of Mn, and Al and unavoidable impurities as remaining parts, and having superior formability and strength, further includes one or more of 0.1-1.0 mass% of Si and 0.01-1.0 mass% of Cu, and may include 0.1-1.0 mass% of Fe. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a heat transfer tube incorporated in a heat exchanger, and more particularly to an aluminum alloy extruded tube for a fin tube type air conditioner heat exchanger that is excellent in formability and strength and is preferably incorporated in a heat exchanger for an air conditioner. .

  In recent years, heat exchangers such as home and commercial air conditioners have been widely used, and have become indispensable for realizing comfort in daily life. These heat exchangers use copper or copper alloy piping materials with excellent thermal conductivity and workability, and fins in which a plurality of aluminum alloy thin fin materials are arranged in parallel around the copper pipe A tube heat exchanger is used (for example, Patent Document 1). Based on FIG. 1, FIG. 2, the schematic structure of a fin tube type heat exchanger is demonstrated.

  As shown in FIG. 1 (a), the fin tube type heat exchanger produces a U-shaped hairpin tube 2 by bending a heat transfer tube (tube) made of copper or a copper alloy into a hairpin shape at the center thereof. After inserting the hairpin tube 2 through the fin material 1 made of aluminum or aluminum alloy arranged in parallel at a predetermined interval, the two are closely attached to each other by expanding the tube and bent in advance to the tube end of the adjacent hairpin tube 2 A plurality of hairpin tubes 2 are connected to the U-bend tube 3 by fitting the processed U-bend tube 3 and brazing the hairpin tube 2 and the U-bend tube 3.

JP 2002-147981 A

As the tubes constituting the hairpin tube 2 and the U-bend tube 3, copper tubes that are excellent in thermal conductivity, corrosion resistance, workability, strength, etc. are widely used. In addition, as the fin material 1, aluminum or an aluminum alloy is widely used from the viewpoint of being excellent in lightness, workability, and thermal conductivity. The fin material 1 is made thinner and higher in strength, and surface treatment is performed to improve the hydrophilicity and corrosion resistance of the surface.
However, in recent years, heat exchangers are required to be designed not only with high performance and high functionality, but also with consideration for environmental aspects such as low resources, low energy, and low space. Furthermore, as the price of copper soars, the demand for cost reduction through the use of inexpensive members is also increasing. Therefore, in the future, in addition to higher performance and higher quality, further cost reduction, lighter weight, and improved recyclability are indispensable for heat exchangers.
In order to improve the performance of heat exchangers for air conditioners, and to obtain heat exchangers that combine cost reduction, weight reduction, and recyclability, the tubes should be made of aluminum alloy extruded tubes that are lightweight and less expensive than copper. Becomes effective.
However, since aluminum has a lower material strength than copper, there is a problem that local deformation occurs during hairpin processing or tube expansion, and molding defects or cracks are likely to occur. In addition, the tube is required to have high strength in order to ensure structural strength and durability as a heat exchanger. Furthermore, since the hairpin tube 2 and the U-bend tube 3 are joined by brazing, an alloy capable of brazing must be selected. Moreover, since aluminum tends to cause pitting corrosion and is inferior to copper in corrosion resistance, it is necessary to select an alloy having excellent pitting corrosion resistance.
This invention is made | formed in view of the said situation, and it aims at providing the extruded tube made from an aluminum alloy which is excellent in workability and intensity | strength as a tube of the heat exchanger for air conditioners.

At the time of manufacturing the heat exchanger, the tube is expanded by inserting a tube expansion rod slightly larger than the inner diameter of the tube into the tube, allowing it to pass through, and then expanding the tube from the inside so that there is no gap between the fins. However, if the tube strength is too low, aluminum adheres to the tube expansion rod, and the pressure at the time of insertion increases remarkably, and it becomes necessary to remove the aluminum piece each time after tube expansion, which causes a decrease in productivity. . Also, if the tube strength is too high and the elongation is low, local deformation such as thinning occurs in part during tube expansion, causing cracking. Furthermore, the occurrence of cracks and thinning of the metal at the time of molding also becomes a problem in the bent portion of the hairpin processing and the flared portion that becomes the joint portion with the U bend.
As described above, the air conditioner tube needs to optimize the aluminum alloy components constituting the tube in order to improve formability and tube expansion. In addition, it is necessary to improve the workability by controlling the crystal grain size and optimizing the mechanical properties and tempering.
Further, in order to ensure the structural strength as a heat exchanger and the durability strength when used as a heat exchanger, it is necessary to improve the strength as an aluminum alloy constituting the tube. Although it is possible to ensure strength by increasing the wall thickness, an alloy having as high a strength as possible is required because tube expandability and formability deteriorate. Since general pure aluminum has insufficient strength, it is necessary to improve the strength of an aluminum alloy containing an additive element.

  Considering the case of manufacturing an extruded tube having a complicated shape, it is necessary to have an alloy composition for ensuring sufficient extrudability. In addition, it is necessary to select an alloy that provides an appropriate potential gradient when the corrosion resistance of the tube alone is improved or a Zn diffusion layer is provided on the outer surface of the tube.

In order to solve the above problems as an aluminum alloy extruded tube for a fin tube type air conditioner heat exchanger, the present inventors include Mn: 0.1 to 1.6% by mass, and the balance is made of Al and inevitable impurities. It has been found that the tube is excellent in moldability and strength and suitable for an air conditioner heat exchanger.
The present invention further contains Mn: 0.1 to 1.6% by mass, Si: 0.1 to 1.0% by mass, and Cu: 0.01 to 1.0% by mass, or one or two of them. An aluminum alloy extruded tube for a fin tube type air conditioner heat exchanger having excellent formability and strength, characterized in that the balance is made of Al and inevitable impurities.
Furthermore, the present invention can contain Fe: 0.1 to 1.0% by mass in the above composition.

  The extruded aluminum alloy tube for fin tube type air conditioner heat exchanger of the present invention has excellent formability and strength. By using this tube, reduction of material cost, weight reduction, improvement of recyclability, etc. Can do. Moreover, since it is possible to produce a heat exchanger with the same production equipment as the current copper pipe, there is no need for new equipment investment, and there is a remarkable industrial effect.

The present invention is characterized by the composition of an aluminum alloy extruded tube (hereinafter simply referred to as a tube) for a fin tube type air conditioner heat exchanger, and the reason for limitation of the composition defined in the present invention will be described below.
<Mn: 0.1 to 1.6% by mass>
Mn is dissolved in the aluminum matrix or precipitated as an Al—Mn intermetallic compound depending on the amount added, and improves the strength. In addition, the Al—Mn intermetallic compound serves as a starting point for recrystallization, and has the effect of reducing the crystal grain size and improving the formability. Furthermore, since the Al—Mn-based intermetallic compound is the starting point of corrosion, the occurrence of corrosion is dispersed, and there is an effect of suppressing the occurrence of deep pitting corrosion. In order to obtain these effects, the present invention contains 0.1% by mass or more of Mn. However, when the content increases, a large number of coarse Al—Mn intermetallic compounds are produced, and the extrudability is remarkably lowered. A coarse Al—Mn intermetallic compound becomes a starting point of cracking during flare processing. Therefore, the present invention sets the Mn content to 1.6 mass% or less. A preferable Mn content is 0.3 to 1.2% by mass.

<Si: 0.1 to 1.0% by mass>
Si dissolves in the aluminum matrix according to the amount added, and improves the strength. Moreover, when added simultaneously with Mn, it precipitates finely as an Al-Mn-Si type intermetallic compound, and remarkably improves strength and workability. Furthermore, since there exists an effect | action which refines | miniaturizes an Al-Mn type intermetallic compound, the deformation resistance at the time of extrusion is made small, and extrudability is improved. Furthermore, the Al—Si-based intermetallic compound serves as a starting point for recrystallization, and has the effect of reducing the crystal grain size and improving the formability. In order to acquire this effect, this invention contains 0.1 mass% or more of Si. However, if the content is increased, the extrudability and the corrosion resistance are lowered. Therefore, the present invention sets the Si content to 1.0 mass% or less. A preferable Si content is 0.3 to 0.7% by mass.

<Cu: 0.01 to 1.0% by mass>
Cu is dissolved in the aluminum matrix to improve the strength. In order to acquire this effect, this invention contains 0.01 mass% or more of Cu. However, if the content increases, the corrosion rate of the tube increases and the growth of pitting corrosion is promoted, so that through holes are easily generated. Therefore, the present invention sets the Cu content to 1.0 mass% or less. The preferable Cu content is 0.05 to 0.5% by mass.

<Fe: 0.1 to 1.0% by mass>
Fe produces an Al—Fe-based or Al—Mn—Fe-based intermetallic compound and improves the strength. Further, since Fe-based crystallized substances are finely present in the material, they serve as a source of pitting corrosion and have an effect of suppressing the generation of deep pitting corrosion. In order to acquire this effect, this invention contains 0.1 mass% or more of Fe. However, when the content is increased, an Al—Mn—Fe-based giant intermetallic compound is generated, which deteriorates castability and extrudability. Therefore, the present invention sets the Fe content to 1.0 mass% or less. A preferable Fe content is 0.2 to 0.5% by mass.

  In addition, the effect of the tube of this invention is not impaired even if 1.0% or less of Zn is contained in addition to the above elements. Furthermore, 0.3% or less of Zr, Ti, Cr, V, Sr, Bi can be added as trace elements for improving strength, formability, and corrosion resistance.

  What is necessary is just to follow the manufacturing method of the tube of this invention in a conventional method. That is, an aluminum alloy billet is produced by a semi-continuous casting method and is subjected to hot extrusion. In order to improve the extrudability, it is preferable to perform a homogenization treatment of the billet. In addition, it can be considered that the process of heating a billet before hot extrusion serves as a homogenization process.

  The tube of the present invention does not affect the corrosion resistance in any shape. Specifically, a tube having a groove on the inner surface is usually used to improve heat exchange performance, but the inner surface shape is not limited. The outer diameter (diameter) of the tube is appropriately selected from the range of 5 to 12 mm. In order to enhance the corrosion resistance of the tube, the present invention allows the surface of the tube outer surface to be subjected to a surface treatment such as a Zn diffusion layer.

<Heat exchanger>
The heat exchanger for an air conditioner using the tube of the present invention is manufactured in substantially the same process as when a copper tube is used as the tube.
That is, the tube is bent into a hairpin shape at the center to produce a U-shaped hairpin tube 2, and the hairpin tube 2 is attached to the fin material 1 made of aluminum or aluminum alloy arranged in parallel at a predetermined interval. Is inserted. After that, the two are closely fixed by expanding the tube, and an aluminum alloy U-bend tube 3 that has been bent in advance is fitted to the end of the adjacent hairpin tube 2, and the hairpin tube 2 and the U-bend tube 3 are connected to each other. A plurality of hairpin tubes 2 are connected to the U-bend tube 3 by brazing using an aluminum alloy brazing material to form a heat exchanger.

A billet prepared using an aluminum alloy having the composition shown in Table 1 was homogenized under the conditions of 595 ° C. × 12 hr, then heated at 500 ° C., and then hot-extruded, and outer diameter 7 mm, inner diameter 6 mm, wall thickness A 0.5 mm round tube was produced.
Using the hot-extruded tube, hairpin bending, tube expansion test, and flare processing for joining with the U-bend portion were performed, and the tube shape change and cracking were evaluated. The results are shown in Table 2. The conditions for hairpin bending, tube expansion test and flare processing are as follows.
Hairpin bending: Hairpin bending (curvature radius 8mm) is performed using the above-mentioned aluminum tube with a pipebender for hairpin bending using the same manufacturing method as copper tube Tube expansion test: Tube expansion rate (change in tube outer diameter) is constant at 10% Expand the tube by changing the size of the tube expansion rod so that the flare is processed. Flare processing: Perform processing with a flare processing dimension of 9 mm and observe whether cracks occur in the U-bend pipe insertion part.

  Next, using the created hairpin tube, a heat exchanger was manufactured in combination with a JIS 1050 alloy and a fin material made of aluminum alloy having a plate thickness of 0.1 mm, and a pressure resistance test was performed. The results are shown in Table 2.

Table 2 shows the following.
(1) When Mn is included within the scope of the present invention, both the moldability of the tube and the breaking pressure during the pressure test are excellent, whereas when Mn is less or greater than the scope of the present invention, Problems occur during flare processing (No. 1-8).
(2) When one or two of Si and Cu are added, the breaking pressure during the pressure resistance test is improved. However, when too much is added, the moldability of the tube is lowered (No. 9 to 24). Compared with Si and Cu, Cu has a higher strength improvement effect.
(3) Fe also contributes to strength improvement, but if too much, too, the formability of the tube is lowered (No. 25-31).

(A) is a side view which shows the structure of a fin tube type heat exchanger, (b) is the perspective view which looked at the fin tube type heat exchanger shown to Fig.1 (a) from the hairpin tube side. (A) is the perspective view which looked at the fin tube type heat exchanger from the U bend pipe side, (b) is the partially expanded view of (a).

Explanation of symbols

  1 ... Fin material, 2 ... Hairpin tube, 3 ... U-bend tube

Claims (3)

Mn: 0.1 to 1.6% by mass,
An aluminum alloy extruded tube for a fin tube type air conditioner heat exchanger excellent in formability and strength, characterized in that the balance is made of Al and inevitable impurities. Mn: 0.1 to 1.6% by mass,
Furthermore, Si: 0.1-1.0% by mass and Cu: 0.01-1.0% by mass of 1 type or 2 types,
An aluminum alloy extruded tube for a fin tube type air conditioner heat exchanger excellent in formability and strength, characterized in that the balance is made of Al and inevitable impurities.   Furthermore, the aluminum alloy extrusion tube for fin tube type air conditioner heat exchangers which is excellent in the moldability and intensity | strength of Claim 1 or 2 which contains Fe: 0.1-1.0 mass%, and remainder consists of Al and an unavoidable impurity.

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