JPS62176672A - Brazing method for aluminum made heat exchanger having excellent corrosion resistance - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance by brazing the liquid passing tube for heat exchanger consisting of the Al alloy containing Cu and Mn in the specified quantity and the fin consisting of Al of Al alloy by using KAlF4- KF group flux. CONSTITUTION:The composition of the liquid tube 2 for heat exchanger is of the Al alloy containing 0.4-1.0wt% Cu and 0.2-0.8% Mn if necessary and the balance being composed of Al with impurities. The liquid tube is subjected to corrosion protection by the anode action of the fin which makes the electrode potential of the liquid tube 2 high and has lower electrode potential than that of the liquid tube 2 by this composition. In case of brazing, what is of the mixing proportion containing 80-99% KAlF4 and 20-0.2% KF is used for the flux. The liquid tube 2 and fin 3 are joined by brazing by melting a brazing filler metal with their drying and heating after flux coating. By said brazing the corrosion resistance of the liquid tube is improved and the heat exchanger in perfect junction state can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for brazing aluminum heat exchangers with excellent corrosion resistance.

Conventional technology and problems Conventionally, when manufacturing aluminum heat exchangers such as automobile radiators, car cooler evaporators, or condensers using flux brazing specifications, chloride-based fluxes containing zinc chloride, etc. were used. 2. Description of the Related Art A method is known in which a liquid passage pipe and a fin, which are structural members for a heat exchanger, are joined together by brazing. At the same time as each member is joined by brazing, zinc is precipitated on the surface of the component member by heat added to the brazing and diffused into the member, and the sacrificial anode effect of the zinc diffusion layer improves the corrosion resistance of the heat exchanger. This is because we hope that this will also improve the results.

However, in this method, since the flux used is essentially water-soluble and has strong hygroscopic properties, it is necessary to wash and remove flux residue immediately after brazing. This method has the drawbacks of high equipment costs, complicated processes, and a heavy workload.

And of course, if the removal of flux residue was incomplete, there was a risk of corrosion.

On the other hand, as a brazing method that does not require flux cleaning as described above, a non-corrosive fluoride-based flux whose composition is a fluoroaluminum complex salt (K3ArlF6 and KAQF4) to which zinc or zinc fluoride is added is used. A method of brazing has also been proposed (for example, JP-A-56
-160869), but since such brazing is usually carried out in a non-oxidizing atmosphere such as an inert gas atmosphere, it is possible to perform brazing with a reduced amount of flux; The absolute amount was so small that it became difficult to form a sufficient diffusion layer, and therefore it was not possible to exhibit a sufficient anticorrosive effect. Moreover, when the above-mentioned flux is actually produced industrially, ApF3 and KF are generally used as starting materials, and the starting materials are mixed with KAΩF4, which is a eutectic mixture thereof, and 3AQF6 in a predetermined manner. Mix in a dry state in an appropriate ratio such that
Since the mixture is once melted and the molten mixture is cooled and solidified, there is a problem that the number of manufacturing steps is large and adjustment is troublesome.

This invention was made in view of the above-mentioned matters, and aims to make it possible to manufacture an aluminum heat exchanger with excellent corrosion resistance with as simple and low-cost operation as possible. .

Means for Solving the Problems For this purpose, as a result of various experiments and research, the inventors found that the electrodes of the liquid passage tubes were formed by forming the liquid passage tubes, which are the constituent members of the heat exchanger, from an AQ-Cu alloy. By making the potential more noble than that of the fins and improving the corrosion resistance of the liquid passage pipe through sacrificial corrosion protection, and by brazing using the newly developed non-corrosive KAQFa-KF flux as the flux, The company succeeded in manufacturing an aluminum heat exchanger with excellent corrosion resistance.

That is, in this invention, Cu: 0. 4-1. 0wt
% and further Mn as necessary: 0.2 to 0°8wt%
A liquid passage tube for a heat exchanger formed of an aluminum alloy containing aluminum and the remainder consisting of aluminum and unavoidable impurities, and a fin formed of aluminum or an aluminum alloy whose electrode potential is less noble than that of the liquid passage tube are used.
4:80-99.8wt%, KF: 20-0. 2
The gist of the present invention is a method for brazing an aluminum heat exchanger with excellent corrosion resistance, which is characterized by brazing using a flux consisting of a mixture of % by weight.

First, in the AI2 alloy that is the constituent material of the liquid passage pipe, Cu
As mentioned above, is added to make the electrode potential of the liquid passage tube sufficiently noble.

Moreover, Cu also contributes to improving the strength of the liquid passage pipe. However, if the content is less than 0.4 wt%, these effects will be poor, and on the other hand, if the content exceeds 1.0 wt%,
It is true that the electrode potential of the liquid passage tube becomes nobler and the strength improves, but
On the other hand, corrosion resistance decreases, and plastic workability also decreases. Therefore, the content ratio of CU is defined in the range of 0.4 to 1.0 wt%.

Furthermore, in the alloy composition of the liquid passage tube, in addition to the above-mentioned essential component Cu, if necessary, Mn: 0.2 to 0.
A content of 8 wt% is allowed.

Mn also enriches the electrode potential of the liquid passage tube and contributes to the strength improvement effect, but if it is less than 0°2 νt%, these effects are poor, and conversely if it is contained in an amount exceeding 0°8wt%. This is not preferable because it not only reduces plastic workability but also increases susceptibility to intergranular corrosion. In addition to Cu and Mn, the alloy components of the liquid passage tube also contain unavoidable impurities such as Fe and St.
etc. are allowed.

On the other hand, the present invention requires that the fins joined to the liquid passage tube be formed of aluminum or an aluminum alloy having an electrode potential less noble than that of the liquid passage tube. This is because the sacrificial anode action of the fins causes the fins to selectively corrode, thereby protecting the liquid passage pipe from corrosion. Examples of such aluminum or aluminum alloys for fins include AQ-Mn alloys such as JISA3003 alloys, pure A
Ω etc. can be mentioned.

The liquid passage pipe and the fin as described above are joined by brazing. In this invention, during brazing, KApF4:80-99
．． A mixture of KF: 20 to 0.8 wt% and KF: 20 to 0.2 wt% shall be used as the flux. By selecting the above blending ratio of KAρF4 and KF in the flux, it is possible to lower the melting point and allow the flux to act effectively during brazing heating.
If it is less than the allowable lower limit, the effect will be poor, and conversely, if too much is mixed above the allowable upper limit, the complete melting temperature (liquidus temperature) will rise, making it difficult to achieve good brazing. In addition, there is a risk that the reaction temperature of the flux will exceed the melting point of the liquid passage pipe or fin material used as the bonding member, and the brazing material itself may become impossible. This flux adjustment is performed by mixing KAΩF4 and KF at the above ratio, but since both KAΩF4 and KF are traded as commercial products and are easily available, ApF3 is generally used for ease of adjustment. It is extremely advantageous compared to conventional NI3AQF6-KAρF4 fluxes produced using KF and KF as starting materials.

Furthermore, the flux used in the present invention has a non-corrosive residue, and does not affect the corrosion resistance of the product even if no defluxing treatment is performed after brazing.

When performing brazing, the above-mentioned flux is used by suspending it in the form of a slurry in a liquid such as water, and this suspension is uniformly applied to at least one of the joining members. In order to facilitate suspension and application in this liquid and improve brazing properties, the powder particle size of the flux component is preferably approximately 200 μm or less. Although spraying or brushing can be used as the above-mentioned application method, it is recommended to use a dipping method as a uniform application method suitable for mass production.

The liquid passage pipe and fins, which are the bonding members, are dried after being coated with the above-mentioned flux, and then heated in a heating furnace or the like in a non-oxidizing atmosphere such as an inert gas atmosphere to a temperature lower than the melting point of the bonding member and the melting point of the flux. Approximately 580-620℃ higher than
By heating to , the brazing material is melted and a brazing phase bonding is achieved. For example, the brazing filler metal has a Si content of about 4.
5-13. Approximately 5 wt% of A, 12-Si based alloy is used. From the viewpoint of workability, it is desirable that the brazing filler metal be used by cladding at least one of the liquid passage pipes or fins to be joined.

Effects of the Invention According to the implementation of the present invention as described above, by using an Aρ-Cu alloy as the material for the liquid passage pipe, it is possible to make the electrode potential of the liquid passage pipe sufficiently sensitive to the fins. Due to its sacrificial anti-corrosion effect, the corrosion resistance of the liquid pipe can be significantly improved. Furthermore, by adding Cu or Mn, the strength of the liquid passage pipe can also be improved. Moreover, KF-KA used in this invention
βF4-based flux has the effect of destroying oxides on the surface of the joint,
It exhibits an excellent flux effect in promoting the spread of brazing filler metal, making it possible to form sufficiently strong brazed joints, and the residue after brazing is non-corrosive, making it easier to use than conventional chlorides. As in the case of using a system flux,
There is no need to wash and remove flux residue after brazing. Therefore, while simplifying a series of brazing work steps, it is possible to manufacture a heat exchanger in a completely bonded state with less risk of corrosion and extremely excellent corrosion resistance. In addition, since both KAQF4 and KF are available individually as commercial products, the flux used in this invention can be easily adjusted by mixing them as starting materials. Therefore, AgF2 and KF are used as starting materials. Conventional 3 Af
It does not require a complicated adjustment process like the lFe-KIF4 flux, and has the advantage of being able to be easily adjusted.

Example Next, examples of this invention will be shown.

(Example 1) Using alloys having various compositions shown in Table 1 below, four-hole extruded sections having a thickness Q of 7 mm as shown in FIG. 2 were produced.

Table 1 On the other hand, a 0.11 mm thick plate was prepared by cladding a core material made of An-1,1 wt% Mn-0,05 wt% In alloy with brazing filler metal made of kQ-8 wt% Si at a cladding ratio of 1296. processing sheet into a corrugated shape. Then, the extruded section (1) was bent into a meandering shape to form a liquid passage pipe, and a corrugated plating sheet was interposed between adjacent parts of the liquid passage pipe to assemble it into a serpentine heat exchanger.

Then, KAfl F4: 88 wt%, KF: 12
Add water to the flux consisting of a mixture of wt% to obtain a concentration of 7.
% suspension, and the heat exchanger assembly was immersed in this suspension and dried. Incidentally, the powder particle size of each flux component was 100 μm or less.

After that, each of the above assemblies was placed in a furnace with N2 gas atmosphere for 61 hours.
Brazing is performed by heating at 0°C for 5 minutes, and as shown in Figure 1, the liquid passage pipe (2) and the fin (3) are joined, and then the union (4) (4) is brazed at the specified location. Heat exchanger (
Capacitor) (5) was obtained.

In order to examine the corrosion resistance of each heat exchanger obtained above, a CASS test of 80G hours based on JIS-H8681 was conducted.
A test was conducted to examine the depth of pitting corrosion that occurred in the liquid pipe. The results are shown in Table 2.

Table 2 (Example 2) As shown in FIG. 3, Ap-10w
A brazing material (2b) made of a t%St alloy was clad on one side, then rolled and electric resistance welded to produce a flat liquid passage pipe (2') with a thickness of 0.4 mm. Note that the cladding ratio of the brazing filler metal was 10%.

Next, a corrugated fin made of an alloy of An-1, lvt% Mn-1, and 3vt% Zn was prepared. As shown in Fig. 4, a plurality of the liquid passage pipes (2゛) are arranged at intervals, and side plates (
6) (6) is arranged, and the corrugated fin (3') is interposed between the liquid passage pipes (2'') and between the liquid passage pipe (2') and the side plate (6), and header brake) (7) (7) and header tank (8) (8)
were placed in place and temporarily assembled into the heat exchanger assembly.

After that, each of the above assemblies was heated and brazed using the same flux suspension and under the same conditions as in Example 1, and then the input vibrator (9) and the outlet vibrator (lO) were placed in the predetermined locations. A heat exchanger (radiator) (5") was obtained by brazing.

In order to examine the corrosion resistance of each of the heat exchangers obtained above, a CASS test was conducted for 800 hours in the same manner as in Example 1, and the depth of pitting corrosion that occurred in the liquid passage tubes was examined. The results are shown in Table 3.

As is clear from the results in Tables 2 and 3, it has been confirmed that the present invention can produce a heat exchanger with extremely excellent corrosion resistance.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 show an embodiment of this invention.
Fig. 1 is a front view of the heat exchanger, Fig. 2 is a perspective view of an extruded section for forming liquid passage pipes of the heat exchanger shown in Fig. 1, and Figs. 3 and 4 show other embodiments. 3 is a perspective view of the liquid passage pipe, and FIG. 4 is a front view of the heat exchanger. (2)(2”)...Liquid pipe, (3)(3-)...Fin, (5)(!M)...Heat exchanger.

Claims (1)

[Claims] A liquid flow pipe for a heat exchanger formed of an aluminum alloy containing Cu: 0.4 to 1.0 wt% and, if necessary, Mn: 0.2 to 0.8 wt%, the balance being aluminum and inevitable impurities. , KAlF_4: 80 to 99.8 wt.
%, KF: A method for brazing an aluminum heat exchanger with excellent corrosion resistance, characterized by brazing using a flux consisting of a mixture of 20 to 0.2 wt%.