JPH0741919A - Manufacture of heat exchanger tube material for noncorrosive flux brazing - Google Patents

Abstract

PURPOSE:To obtain a tube material which is excellent in tube-making property as the tube material especially for a radiator, etc., for automotive use, has a high strength after brazing and excellent in brazing property and internal corrosion resistance. CONSTITUTION:In a manufacturing method of the brazing sheet which takes an aluminum alloy which contains, by wt.%, 0.6-1.8% Mn, 0.5-1.5% Si, <=0.3% Cu, 0.1-0.7% Fe and 0.01-0.20% Ti and in which Mg is controlled to be <=0.2% as a core material, Al-Si base allay brazing filler metal is cladded on one side of the core material and an aluminum allay sacrificial anode surface material which contains 1.0-3.0% Zn, 0.5-2.5% Mg, 0.05-0.5% Si and 0.05-0.5% Fe and also in which Cu is controlled to be <=0.1% is cladded on the other side, the ingot of the core material, brazing filler metal and surface material are hot- cladding-rolled at <=550 deg.C and cold rolling is executed to a prescribed thickness that the final rolling rate becomes 20-60%. The desired thickness is made by cold rolling at a draft of 20-60% after intermediate annealing and the final local annealing is executed at 200-450 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a pipe material for an aluminum heat exchanger which is brazed by a non-corrosive flux, and more specifically, it has excellent pipe-forming property as a pipe material for a radiator of an automobile, Moreover, the present invention relates to a method for producing a pipe material having high strength after brazing, excellent brazing property, and excellent internal corrosion resistance.

[0002]

2. Description of the Related Art An aluminum heat exchanger such as an automobile radiator or heater core in which a water-based heat medium is circulated has a plurality of flat tubes 2 sandwiching corrugated fins 1 like the radiator shown in FIG. The header plate 3 and the tank 4 are arranged at both ends of the heating medium to form a heat medium passage, and the flat pipe 3 and the fins 2 exchange heat between the high temperature heat medium and the low temperature air.

The aluminum heat exchanger as described above is manufactured by heating a flat tube made of a brazing sheet having a brazing material clad on the outer surface thereof, a header plate and corrugated fins, and heating to 600 ° C. or higher.
This is performed by a so-called brazing method in which a brazing material is melted and each member is joined. As the brazing method, in-furnace brazing method using a non-corrosive flux of potassium aluminum fluoride which is excellent in brazing property and does not require post-treatment is often adopted.

In the flat tube 2 for heat medium passage as described above, however, the material plate 11 is arcuately or circularly shaped by a forming roll as shown on the left side of FIG. The outer surface is cut smoothly to form a circular tube 13, which is gradually formed into an elliptical tube 14 or an oval tube 15 and then a flat tube 2 which is sequentially formed into a pipe-forming roll.

As a brazing sheet for a pipe of a heat exchanger in which an aqueous heat medium circulates, an Al-Mn alloy such as 3003 having a certain strength after brazing is used as a core material, and 4045 or the like is provided on one side thereof. The Al-Si alloy brazing filler metal of No. 3 is usually a three-layer material in which an Al-Zn alloy sacrificial anode skin material such as 7072 is clad on one side that is always in contact with an aqueous heat medium that is corrosive to aluminum. It is used. The manufacturing method of such a brazing sheet is such that the core ingot, the brazing material and the skin material are clad rolled in a hot state, and then cold rolled,
It is a general method to perform semi-hardening by cold rolling after intermediate annealing.

However, in recent years, with the progress of miniaturization and weight saving of heat exchangers, there has been an increasing demand for reducing the thickness of the pipe material. However, if the above-mentioned brazing sheet that has been conventionally used is thinned as it is, there arises a problem that the strength after brazing becomes insufficient or the internal corrosion resistance to the water-based heat medium cannot be satisfied, and therefore the conventional Al-
Various studies have been conducted to increase the strength after brazing of a brazing sheet having an Mn-based alloy as a core material and to improve internal corrosion resistance. For example, JP-A-63-11804.
4. Si, Cu or further Mg added to the core material as disclosed in JP-A-2-50934, or JP-A-2-175
093 and Japanese Patent Application Laid-Open No. 4-371368 propose a material in which Mg is added to an Al—Zn alloy sacrificial anode skin material.

[0007]

In the prior art as described above, addition of Si, Cu, etc. to the Al-Mn alloy core material and Al
-Adding Mg to the Zn-based alloy skin material is effective for thinning the pipe material because it increases the strength of the brazing sheet after brazing, but on the other hand, the strength before pipe making becomes too high and the plate thickness It is thin and dusty, which causes misalignment during roll forming during pipe making, and the phenomenon of wavy edges and buckling between the molding rolls, resulting in a normal electric resistance welded joint. It has become clear that the problem of not being obtained arises. Further, in order to enhance this pipe forming property, it is conceivable to reduce the final cold rolling rate by the conventional manufacturing method to reduce the strength before pipe forming, but this is because the release of the processing strain is delayed when the brazing heat is added, This is not preferable because another problem that the erosion of the core material by the brazing increases and the brazing property deteriorates occurs.

[0008] Furthermore, in order to increase the strength by adding Cu to the core material, when the amount of addition is large, the diffusion of Cu from the core material that occurs during brazing reaches the surface of the skin material when the material for pipes is thinned, and Al- There is a possibility that the sacrificial anode effect of the Zn-based alloy may be significantly reduced. It is known that the addition of Mg to the core material significantly hinders the brazing property even when a small amount of Mg is added by brazing using a non-corrosive aluminum potassium fluoride type flux.

[0009]

SUMMARY OF THE INVENTION The present invention has been studied in view of the above-mentioned circumstances, and as a result, has been indispensable as a material for a high-strength and highly corrosion-resistant pipe of a heat exchanger made of aluminum for a water-based heat medium that is small and lightweight. It was confirmed that the steel has the same pipe forming and brazing properties as the conventional material. Therefore, the present inventors first conducted various experiments on the pipe-forming property of the thin-walled high-strength and high-corrosion-resistant pipe material using a pipe forming equipment for radiator tubes, and found that the tensile strength before pipe forming was 200 N / mm ² or less. If so, it was confirmed that a good electric resistance welded pipe could be manufactured relatively easily by adjusting the forming roll of roll forming, and the tensile strength before pipe making was 20 without lowering the brazing property and internal corrosion resistance.
The present invention succeeds in obtaining a manufacturing method of 0 N / mm ² or less, and is as follows.

(1) wt%, Mn: 0.6-1.8
%, Si: 0.5 to 1.5%, Cu: 0.3% or less, F
e: 0.1 to 0.7%, Ti: 0.01 to 0.20%, M
An aluminum alloy whose g was restricted to 0.2% or less was used as a core material, an Al—Si alloy brazing material was used on one surface of the core material, and a Zn: was used on the other surface.
1.0-3.0%, Mg: 0.5-2.5%, Si: 0.05-0.5%
%, Fe: 0.05 to 0.5%, and a brazing sheet clad with an aluminum alloy sacrificial anode skin material in which Cu is regulated to 0.1% or less. And the skin material is hot clad rolled at a temperature of 550 ° C. or lower, and cold rolled to a predetermined plate thickness at which the final rolling ratio becomes 20 to 60%, and the reduction ratio after intermediate annealing is 20 to 60%.
The method for producing a material for a heat exchanger tube for non-corrosive flux brazing, comprising: performing a final partial annealing at 200 to 450 ° C. to a target plate thickness by cold rolling.

[0011]

The reason for limiting the alloy composition of the core material constituting the present invention as described above is as follows. Mn: 0.6 to 1.8% Mn is an element effective in forming a fine second phase compound together with Si and Fe and improving the strength of the core material after brazing. In addition, the pitting corrosion potential of the core material is made more noble than the natural potential to make pitting corrosion less likely to occur. If the addition amount is less than 0.6%, these effects are small, while if it exceeds 1.8%, huge crystallized substances are generated during casting and workability is deteriorated, which is not preferable.

Si: 0.5-1.5% Si forms a fine second-phase compound together with Mn and Fe in a solid solution state, and further, Mg, which diffuses from the skin material during brazing.
Generates Mg ₂ Si compound and significantly increases the strength after brazing. If the added amount is less than 0.5%, its effect is poor, and it is 1.5%.
If it exceeds, the melting start temperature is lowered, which is not preferable.

Cu: 0.3% or less Cu is an element effective in improving the strength of the core material after brazing in a solid solution state, but if the content exceeds 0.3%, the skin material during brazing is formed. It diffuses on the surface and hinders the sacrificial anode effect. Therefore, the upper limit is 0.3%.

Fe: 0.1 to 0.7% Fe forms a fine second-phase compound together with Si and Mn, and improves the strength of the core material after brazing. If the addition amount is less than 0.1%, the effect is small, and if it exceeds 0.7%, the effect is saturated and the pitting corrosion resistance decreases, so the content is made 0.1 to 0.7%.

Ti: 0.01 to 0.20% Ti refines the cast structure and causes coring, which inhibits the progress of pitting corrosion in the sheet thickness direction after brazing and improves pitting corrosion resistance. It also suppresses the cathodic reaction of the core material and reduces the corrosiveness of the material. If it is less than 0.01%, these effects are small, and if it exceeds 0.20%, large crystallized substances are generated during casting and the workability is deteriorated.
It was set to 0%.

Mg: 0.2% or less Mg enhances the strength after brazing even with a small amount, but when brazing with a non-corrosive flux of potassium aluminum fluoride, the flux components F and Mg react. Therefore, the effect of the flux is reduced, and the brazing property is significantly reduced.
Therefore, the amount is regulated to 0.2% or less, preferably 0.1% or less.

In addition to the above, the core material is 0.3 in each case.
The presence of Cr and Zr up to 10% is acceptable because it has little influence on the properties of the alloy of the present invention.

Next, as the brazing material, JIS-4045, 4
Al-Si alloy such as 343 or JIS-4N45, 4N
Al-Si-Zn alloys such as 43 can be used.

Further, the composition of the skin material is as follows. Zn: 1.0 to 3.0% Zn is an essential element for providing the skin material with a sacrificial anode effect and protecting the core material from corrosion by the aqueous heating medium. If the addition amount is less than 1.0%, the effect is small, and if it exceeds 3.0%, the amount of self-corrosion increases and the life of the skin material is shortened, which is not preferable. Therefore, it is set to 1.0 to 3.0%.

Mg: 0.5-2.5% Mg suppresses the evaporation of Zn from the surface of the skin material that occurs during brazing and shifts the skin material potential to the base to enhance the sacrificial anode effect. Also, when brazing, it diffuses into the core material and the Si and Mg ₂ Si
It also has the effect of forming a compound and improving the strength after brazing. If the added amount is less than 0.5%, the effect is small, and 2.5%
If it exceeds, the melting start temperature is lowered, which is not preferable.

Si: 0.05 to 0.5% Si forms a Mg ₂ Si compound together with Mg and improves the strength of the skin material after brazing. If the addition amount is less than 0.05%, its effect is small, and if it exceeds 0.5%, Al-having a noble potential is formed.
Since Fe-Si compound is generated in large quantity and the sacrificial anode effect of the skin material is reduced, it is set to 0.05 to 0.5%.

Fe: 0.05-0.5% Fe forms a fine Al-Fe-Si compound together with Si,
Improve the strength of brazing material after brazing. Addition amount is 0.05%
If it is less than 0.5%, the effect is small, and if it exceeds 0.5%, the effect is saturated and the pitting corrosion resistance is deteriorated.
It was set to 5%.

Cu: Regulated to 0.1% or less Cu, when present in a very small amount, significantly impairs the sacrificial anode effect of the skin material. Therefore, it is necessary to regulate it to 0.1% or less.

Explaining the manufacturing process in the present invention, first, the core material according to the present invention is melted and then formed into an ingot by a normal semi-continuous casting method. On the other hand, the brazing material and the sacrificial anode skin material are obtained by melting after being melted by a normal semi-continuous casting method and then hot-rolled to a predetermined plate thickness.

A brazing material is laminated on one surface of the core ingot and a skin material is laminated on the other surface, and hot clad rolling is carried out at a temperature of 550 ° C. or lower to obtain a three-layer clad material. Before the hot clad rolling, the core material may be homogenized in order to improve the rolling workability, but the temperature is preferably 550 ° C or lower. Here, the temperature of hot clad rolling is set to 550 ° C. or lower because the brazing filler metal may melt at a temperature higher than this temperature.

Next, the hot-rolled sheet is cold-rolled for several passes to a predetermined sheet thickness so that the final rolling rate is 20 to 60%, and is completely softened by intermediate annealing, and then cold rolled with a reduction rate of 20 to 60%. The target plate thickness is obtained by hot rolling. If it is difficult to perform cold rolling from a hot rolled sheet to a predetermined sheet thickness, intermediate annealing may be performed during the pass. The rolling reduction of the subsequent cold rolling is regulated to 20 to 60%. When the rolling reduction is less than 20%, the work strain is small, so that the recrystallization of the core material is delayed at the time of the brazing heat applied after the final partial annealing described later. Because. That is, when the recrystallization of the core material is delayed, the molten brazing material violently erodes the core material through the sub-grain boundaries remaining in the crystal grains of the core material. On the other hand, if the rolling reduction exceeds 60%, the recrystallized grains of the core material generated by the additional heat of the brazing after the final partial annealing become fine, and the corrosion of the molten brazing material along the crystal grain boundaries of the core material becomes large. When such erosion of the molten brazing material to the core material occurs, not only the strength of the core material lowers but also the amount of the molten brazing material used for joining the fins to flow decreases and the brazing property lowers, which is preferable. Absent.

At the end of the process, partial annealing is performed at 200 to 450 ° C. By this partial annealing, the brazing sheet for a pipe material according to the present invention is tempered to a strength suitable for subsequent pipe making. The annealing time is preferably 3 hours or less from the viewpoint of cost and productivity, but is not limited to this unless the core material is completely softened. If the core material is completely recrystallized, a slight strain applied to the pipe material during pipe forming causes corrosion of the core material by the brazing during brazing, and as a result, the brazing property is deteriorated, which is not preferable. The reason why the annealing temperature is 200 to 450 ° C. here is that if the temperature is less than 200 ° C., the strength is less decreased and the pipe forming property is not sufficiently improved even if the annealing time is lengthened.
On the other hand, if the annealing temperature exceeds 450 ° C., the Zn added to the skin material diffuses into the core material so much that the sacrificial anode effect of the skin material is reduced, which is not preferable.

The clad ratio of the brazing material is preferably 5 to 12% from the brazing property, and the clad ratio of the skin material is preferably 7 to 14% from the strength after brazing and the internal corrosion resistance.

[0029]

EXAMPLES Some of the concrete examples of the present invention are shown below together with comparative examples and conventional examples as appropriate.

Example 1 After the aluminum alloy core material, the brazing material and the sacrificial anode skin material having the compositions shown in Table 1 below were separately cast, the brazing material and the skin material were 48
It was hot rolled at 0 ° C. to produce a thick plate for cladding. Then, a brazing material was laminated on one surface of the core material, and a skin material was laminated on the other surface, and the core material was held at 480 ° C. for 2 hours, and then hot clad rolling was performed. The clad ratios of the brazing material and the skin material are 10% for the brazing material and 12% for the skin material.

[0031]

[Table 1]

Next, the hot-rolled sheet was cold-rolled to the sheet thickness shown in the following Table 2, then completely softened by intermediate annealing at 340 ° C. for 2 hours, and cold-rolled to the sheet thickness of 0.25 mm. Then, partial annealing was performed under the temperature and time conditions shown in Table 2 to obtain a brazing sheet for pipe material.

[0033]

[Table 2]

With respect to each of the plates obtained as described above, the strength before pipe making, the pipe making property, the strength after brazing, the brazing property, the erosion depth of the brazing core material, and the internal corrosion resistance were evaluated. The results are shown in Table 3 below.

[0035]

[Table 3]

The pipe forming properties shown in Table 3 above were evaluated by observing the appearance and cross section of the electric-welded portion of a flat pipe formed into a size of 18.5 × 2.5 mm using a pipe forming equipment for radiator tubes. . In addition, the brazing property and the erosion depth of the core material were evaluated by cutting a flat tube made into a pipe to a length of 100 mm, combining it with a corrugated plate having a thickness of 0.10 mm and a width of 21 mm, 3N03 fin, and degreasing after solvent removal. Cross-section observation of a test piece which was brazed at 600 ° C for 5 minutes in a nitrogen gas atmosphere with a dew point of -30 ° C was applied by applying a flux of a mixed composition of KAlF ₄ and K ₃ AlF ₆ at about 2 g / m ^2. It was done by doing. The strength after brazing was measured by subjecting a plate material before pipe making to heat treatment at 600 ° C. for 5 minutes on the assumption that the plate was to be brazed, cutting out a JIS-13B tensile test piece and performing a tensile test. The internal corrosion resistance evaluation test is performed in a nitrogen gas atmosphere under the assumption that the plate material before pipe making is brazed.
After heat treatment at 0 ℃ for 5 minutes, seal the brazing filler metal side and end with resin, Cl ion 500ppm, SO ₄ ion 500pp
m, Cu ion 10ppm was immersed in a corrosive solution adjusted to pH 3 with hydrochloric acid, and a beaker test was repeated 28 times with 88 ° C × 8 hours → 35 ° C × 16 hours as one cycle to confirm that pitting corrosion occurred on the skin side. Depth was measured by the microscope depth of focus method.

That is, in all of the production examples of the present invention, the tensile strength before pipe forming was 200 N / mm ² or less, and pipes could be produced without problems, and the tensile strength after brazing was 154 N / mm ² or more. Yes,
Since the core material is less eroded by brazing, the brazing property is good,
Even in the internal corrosion resistance evaluation test, only shallow corrosion with a maximum of 52 μm or less occurred. On the other hand, Comparative Example 14 and Conventional Example 1
No. 6 has a poor pipe forming property because the tensile strength before pipe forming exceeds 200 N / mm ^2, and the pipes having Comparative Examples 9 to 13 have a large corrosion of the core material due to the brazing, resulting in poor joining. There is. Further, it is apparent that the sample according to Comparative Example 15 is not preferable in this respect even if it is preferable in pipe forming property and brazing property because deep pitting corrosion of 126 μm occurred in the internal corrosion resistance evaluation test.

Example 2 Each aluminum alloy core material, sacrificial anode skin material and 4045 brazing material having the compositions shown in the following Table 4 were separately semi-continuously cast, and the brazing material and the skin material were hot rolled at 480 ° C. A thick plate for clad was produced. Then, a brazing material was laminated on one surface of the core material, and a skin material was laminated on the other surface, and the core material was held at 480 ° C. for 1 hour, and then hot clad rolling was performed. The clad ratio of brazing material and skin material is 10 for brazing material.
%, The skin material is 12%.

[0039]

[Table 4]

Next, the above hot-rolled sheet was cold-rolled to a sheet thickness of 0.38 mm, then completely softened by intermediate annealing at 340 ° C. for 2 hours, and cold-rolled to a sheet thickness of 0.25 mm. The rolling reduction at this time is 34%. Then, partial annealing was performed at 340 ° C. for 1 hour to obtain a test brazing sheet. With respect to these test plates, the strength before and after brazing, brazing property, and corrosion resistance on the skin material side were evaluated in the same manner as in Example 1. In addition, the test piece for brazability evaluation was performed by using a test plate cut into a length of 100 mm and a width of 20 mm instead of the flat tube used in Example 1. The results of each evaluation test are shown in Table 5 below.

[0041]

[Table 5]

That is, the brazing sheets having the composition according to the present invention have a tensile strength before brazing of 200 N / mm ² or less, which does not cause a problem in pipe forming property, and a tensile strength after brazing is 144.
N / mm ² or more, good brazing property, and internal corrosion resistance evaluation test shows only shallow corrosion of 78 μm or less at maximum, whereas brazing sheets according to Comparative Examples 9, 10, 14 and Conventional Composition Example 15 are brazed. Tensile strength after attachment is 138
N / mm ² or less. In addition, the brazing sheets according to Comparative Examples 11 to 13 have sufficient tensile strength after brazing, but No. 12 is defective in joining because Mg is added to the core material. In the internal corrosion resistance evaluation test, deep pitting of 116 μm or more occurred.

[0043]

As described above, according to the production method of the present invention, a high-strength, high-corrosion-resistant pipe material for brazing of a non-corrosive flux having good pipe-forming properties can be obtained, and a thin and lightweight heat exchanger can be obtained. It is an invention that has a large effect industrially because it is properly achieved.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an example of an automobile radiator.

FIG. 2 is an explanatory view showing a manufacturing process of the flat tube for the heat medium passage shown in FIG.

[Explanation of symbols]

 1 Corrugated fin 2 Flat tube 3 Header plate 4 Tank 11 Material plate 12 Welding 13 Round tube 14 Elliptical tube 15 Oval tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunichi Ushino 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Nipparu Giken Co., Ltd. No. 1 within Nikkei Giken Co., Ltd. (72) Inventor Tatsuyuki Kobayashi 1-34-1 Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture

Claims (1)

[Claims] 1. Wt%, Mn: 0.6-1.8%, Si:
0.5 to 1.5%, Cu: 0.3% or less, Fe: 0.1 to 0.7
%, Ti: 0.01 to 0.20%, and an aluminum alloy whose Mg content is restricted to 0.2% or less is used as a core material, and one side of the core material is
Al-Si alloy brazing material, Zn: 1.0-3.0%, Mg:
0.5-2.5%, Si: 0.05-0.5%, Fe: 0.05-0.5%
%, And in the brazing sheet clad with the aluminum alloy sacrificial anode skin material in which Cu is regulated to 0.1% or less, the core ingot, the brazing material and the skin material are heated at a temperature of 550 ° C. or less. Clad rolling, cold rolling to a predetermined plate thickness that gives a final rolling rate of 20 to 60%, cold rolling with a reduction rate of 20 to 60% after intermediate annealing to obtain the target sheet thickness, and final rolling at 200 to 450 ° C. A method for producing a heat exchanger tube material for non-corrosive flux brazing, characterized by performing partial annealing.