JPH11100628A - Heat exchanger made of aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat exchanger made of an aluminum alloy which is suitable as a heat exchanger for automobile, etc., and has an excellent fatigue characteristic. SOLUTION: The tubes 2 of the heat exchanger consisting of the plural tubes 2 constituting refrigerant passages, fins disposed between the tubes 2 and a header for feeding and discharging the refrigerant for the tubes 2 as main components consist of aluminum alloy brazing sheets of a three-layered structure formed by joining a sacrificial anode material 7, a core material 8 and a brazing filler metal 9 in this order. The recrystal grain size (d) in the thickness direction of the sacrificial anode material 7 at the cross section of the tubes 2 is below the thickness (t) of the sacrificial anode material. The grain fracture of the sacrificial anode material 7 which is the start point of fatigue fracture is dispersed into the many grain boundaries and the progression thereof is suppressed and the fatigue life is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat exchanger made of an aluminum alloy having excellent fatigue characteristics and used for a heat exchanger for an automobile.

[0002]

2. Description of the Related Art For example, as shown in FIG. 1, an automobile heat exchanger 1 includes a plurality of tubes 2 serving as refrigerant passages, fins 3 arranged between the plurality of tubes 2 and contributing to heat radiation, and a plurality of tubes. A resin tank 6 is attached to a core 5 formed by assembling a header 4 serving as a refrigerant supply / discharge pipe of the tube 2 and brazing. The tube 2 and the header 4
In general, a brazing sheet is formed into a flat cylindrical shape by an electric sewing process or the like. The tube 2 and the header 4 are assembled with the fins 3 and brazed to form the core 5. By this heating at the time of brazing, the tube 2, the header 4, the fins 3 and the like have a recrystallized structure.
The brazing sheet is a plate material having a three-layer structure in which a sacrificial anode material, a core material, and a brazing material are joined in this order, and the sacrificial anode material includes an Al-Zn-based alloy (such as JIS-7072 alloy),
The core material is an Al-Mn alloy (such as JIS-3003 alloy), and the brazing material is an Al-Si alloy (JIS-4045).
Alloys) are mainly used.

In recent years, there has been a demand for a thinner material and a corresponding increase in material strength in order to reduce the weight and cost of automobiles. For tubes and headers, Al-Al is used as a sacrificial anode material of a brazing sheet, which is a constituent material thereof. 1.5-3wt% M
with g-1-5 wt% Zn alloy, a method of strengthening the Si of 0.5 wt% about contained in Mg and the core material of the sacrificial anode material in during brazing to precipitate Mg ₂ Si by diffusion reaction such Is adopted. By the way, the cooling of the engine mounted on the automobile is performed by circulating the refrigerant cooled by the heat exchanger by the pump through the engine portion. At this time, the inside of the tube or the header is usually 0.09 MPa, and the maximum is 0.18 MPa.
There is a problem that the tube and the header will eventually be fatigue-ruptured when the internal pressure is applied to the extent and the internal pressure is repeatedly applied.

[0004]

For this reason, the present inventors have studied methods for improving the fatigue characteristics of tubes and headers. Sacrificial anode material (Al-Mg-Z)
The origin of the fatigue fracture is caused by the fact that the sacrificial anode material 7 forming the tube 2 or the header 4 has a large recrystallized grain size, as shown in FIG. The inventors of the present invention have conducted further research and have completed the present invention. In FIG. 3, 8 is a core material and 9 is a brazing material. An object of the present invention is to provide an aluminum alloy heat exchanger that improves the fatigue characteristics of aluminum alloy tubes or headers used in automobile heat exchangers and the like and that can be used safely for a long time.

[0005]

According to the first aspect of the present invention,
In a heat exchanger mainly including a plurality of tubes serving as refrigerant passages, fins arranged between the tubes, and a header serving as a supply / discharge tube for the plurality of tubes, the tubes may include a sacrificial anode material and a core. 3 where the brazing material and brazing material were joined in this order
It is made of an aluminum alloy brazing sheet having a layer structure, and has excellent fatigue characteristics characterized in that the recrystallized grain size in the thickness direction of the sacrificial anode material in the cross section of the tube is less than the thickness of the sacrificial anode material. It is an aluminum alloy heat exchanger.

According to a second aspect of the present invention, a plurality of tubes serving as refrigerant passages and fins arranged between the tubes are provided.
In a heat exchanger mainly including a header serving as a supply / discharge pipe for the plurality of tubes, the header is formed of a three-layer aluminum alloy brazing sheet in which a sacrificial anode material, a core material, and a brazing material are joined in this order. A heat exchanger made of an aluminum alloy having excellent fatigue characteristics, wherein a recrystallized grain size in a thickness direction of the sacrificial anode material in a cross section of the header is smaller than a thickness of the sacrificial anode material. It is.

[0007]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, as shown in FIG.
The sacrificial anode material 7, the core material 8, and the brazing material 9 were joined in this order 3
The aluminum alloy brazing sheet 10 having a layer structure is formed in a cylindrical shape with the sacrificial anode material 7 inside, and the recrystallized grain size in the thickness direction in the cross section of the sacrificial anode material 7 of the tube 2 is 7 is an aluminum alloy heat exchanger having a thickness of less than t. In the present invention, the recrystallized grain size of the sacrificial anode material 7 is an average value of n = 20 or more of the length d in the thickness direction of the recrystallized grains of the sacrificial anode material 7 in the cross section of the tube 2.

According to the first aspect of the present invention, the recrystallized grain size of the sacrificial anode material of the brazing sheet forming the tube is
The reason for making the thickness smaller than the thickness of the sacrificial anode material is that, when the recrystallized grain size of the sacrificial anode material reaches the thickness of the sacrificial anode material, fatigue failure caused by repeated application of the refrigerant pressure rapidly progresses. That is, the tube expands due to the refrigerant pressure, and its side surface curves outward, and tension is applied to the innermost sacrificial anode material of the tube. Due to this tension, a starting point of the fatigue fracture is generated at the crystal grain boundary, and the fracture proceeds along the grain boundary. If the recrystallization grain size is small, the grain boundary fracture or fatigue fracture is dispersed in many crystal grain boundaries and the progress thereof is suppressed. Fatigue failure progresses rapidly when the thickness reaches the thickness.

In the present invention, a method for reducing the recrystallized grain size of the sacrificial anode material constituting the tube is as follows.
Examples of such methods include adding elements that reduce the crystal grain size, such as n, Cr, and Zr, increasing the ingot homogenization treatment temperature, increasing the cold rolling reduction, and performing brazing at a low temperature in a short time. Can be In particular, use of a low-temperature brazing material is effective in lowering the brazing temperature (Japanese Patent Laid-Open No. 7-8867).
8). In addition, there is a method in which Si is added to the sacrificial anode material to increase the amount of Mg ₂ Si deposited in the sacrificial anode material to suppress the growth of recrystallized grains during brazing. According to this method, fatigue fracture is suppressed from the viewpoint of improving strength.

The second aspect of the present invention specifies the crystal grain size of the sacrificial anode material of the header constituting the heat exchanger, for the same reason as in the case of the tube. In general, the header is larger in size than the tube, and is less susceptible to fatigue failure than the tube, but when the recrystallized grain size in the thickness direction of the sacrificial anode material in the cross section of the header reaches the thickness of the sacrificial anode material, The present invention is also useful for headers because of the rapid progress of fatigue failure.

[0011]

The present invention will be described below in detail with reference to examples. (Example 1) Al-Si alloy ingot for brazing material, Al-Mn alloy ingot for core material, Al-2wt% for sacrificial anode material
An Mg-4wt% Zn alloy ingot is cast by an ordinary method, and the brazing material ingot and the core material ingot are subjected to a predetermined homogenization treatment. The homogenization treatment conditions were variously changed in order to change. Next, after shaving these ingots to a predetermined thickness, the sacrificial anode material was 10 mm,
The core material was hot-rolled to 50 mm, and the brazing material was hot-rolled to 8 mm. Then, the sacrificial anode material, the core material, and the brazing material were stacked in this order and hot-rolled and joined to form a clad material having a thickness of 5 mm. Next, the clad material was subjected to cold rolling and intermediate annealing to produce a brazing sheet having a thickness of 0.25 mm. Here, the thickness of the sacrificial anode material was 37 μm.
Two kinds of brazing materials having a brazing temperature of 600 ° C. and 580 ° C. were used. As the brazing material having a brazing temperature of 580 ° C., a brazing material to which Cu and Zn are added, which is disclosed in JP-A-7-88678, was used. A small amount of Zr was added to some of the sacrificial anode materials in order to reduce the recrystallized grain size.

After heating the obtained brazing sheet at a brazing temperature for a predetermined time, the brazing sheet is repeatedly subjected to plane bending such that tensile stress is applied to the sacrificial anode material side, and the number of bending times until the fracture is caused (fatigue failure). Fatigue life) was measured.

(Example 2) The brazing sheet obtained in Example 1 was processed into a tube by electric resistance sewing, and this tube was assembled with a separately prepared header and fins (Al-Mn alloy). The attached body was brazed to produce a radiator core, and a resin tank was attached to the core to produce a radiator.

A refrigerant (water) was repeatedly pumped at a pressure of 0.2 MPa into the tube of the obtained radiator, and the number of times of pumping (fatigue life) until the tube was broken was measured.
Table 1 shows the fatigue test results of Examples 1 and 2. In Table 1,
The main manufacturing conditions and the recrystallized grain size of the sacrificial anode material of the brazing sheet (tube) before the fatigue test are also shown. The recrystallized grain size of the sacrificial anode material was obtained by measuring the length of the crystal grains of the sacrificial anode material in the cross section of the tube in the thickness direction for 20 crystal grains and averaging the measured values.

[0015]

[Table 1]

As is apparent from Table 1, N of the product of the present invention was
In all of o.1 to 10, the fatigue life of the brazing sheet and the heat exchanger was long. This is because the recrystallized grain size of the sacrificial anode material is smaller than the thickness of the sacrificial anode material and the number of crystal grain boundaries is large, so that grain boundary destruction is dispersed in many crystal grain boundaries, and the progress thereof is suppressed. This is clear from the fact that the fatigue life is almost inversely proportional to the recrystallized grain size. Zr for sacrificial anode material
Is added, compared to those manufactured under the same conditions,
Recrystallized grain size is small and fatigue life is improved. On the other hand, the comparative examples No. 11 to 15 all had a short fatigue life. This is because the recrystallized grain size has reached the thickness of the sacrificial anode material. In the second embodiment, a 5 mm thick clad material produced in the same manner as in the first embodiment was cold-rolled and subjected to intermediate annealing to form a 1.2 mm thick brazing sheet on the header by press molding. What was done was used. The thickness of the sacrificial anode material of this header is 100
μm, and the crystal grain size was less than 100 μm. Therefore, the header did not break.

The tube of the radiator for an automobile has been described above. However, the present invention can obtain the same effect on other heat exchangers such as a heater core and an evaporator other than the radiator and also on the header. Things.

[0018]

As described above, the heat exchanger tube or header of the present invention is formed of a brazing sheet, and the recrystallized grain size of the sacrificial anode material in the cross section of the tube or header is smaller than that of the sacrificial anode material. Since the thickness is less than the thickness, the intergranular fracture of the sacrificial anode material, which is the starting point of the fatigue fracture, is dispersed in many grain boundaries and the progress thereof is suppressed, and the fatigue life is improved. Therefore, an industrially remarkable effect is achieved.

[Brief description of the drawings]

FIG. 1 is a front view of a radiator.

FIG. 2 is an explanatory view of a recrystallized structure of a sacrificial anode material in a cross section of the tube of the present invention.

FIG. 3 is an explanatory view of a recrystallized structure of a sacrificial anode material in a cross section of a conventional tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat exchanger 2 Tube 3 Fin 4 Header 5 Core 6 Resin tank 7 Sacrificial anode material 8 Core material 9 Brazing material 10 Brazing sheet t Thickness of sacrificial anode material d Length of sacrificial anode material in the thickness direction of recrystallized grains

Claims (2)

[Claims] 1. A heat exchanger mainly including a plurality of tubes serving as refrigerant passages, fins arranged between the tubes, and a header serving as a supply / discharge tube for the plurality of tubes, wherein the tubes are: A sacrificial anode material, a core material, and a brazing material are joined in this order to form a three-layer aluminum alloy brazing sheet. An aluminum alloy heat exchanger excellent in fatigue characteristics, characterized in that the thickness is less than the thickness. 2. A heat exchanger mainly comprising a plurality of tubes serving as refrigerant passages, fins arranged between the tubes, and a header serving as a supply / discharge tube for the plurality of tubes, wherein the header is: A sacrificial anode material, a core material, and a brazing material are joined in this order to form a three-layer aluminum alloy brazing sheet, and the recrystallized grain size in the thickness direction of the sacrificial anode material in the cross section of the header is equal to An aluminum alloy heat exchanger excellent in fatigue characteristics, characterized in that the thickness is less than the thickness.