JPS6234827B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a water-resistant, high-strength brazing sheet for vacuum brazing and a heat exchanger using the same, and in detail, in addition to specifying the alloy composition of the core material, between the core material and the brazing material layer, A water-resistant brazing sheet for brazing that has improved water and corrosion resistance in a water-corrosive environment by interposing an Al alloy with adjusted thickness and electrochemical properties as an intermediate layer, and this brazing sheet can be used as a partition wall between a heat medium and This relates to heat exchangers. Brazing sheets for vacuum brazing made of Al alloy (hereinafter abbreviated as Al alloy BS) are widely used, for example, as materials for heat exchangers such as condensers and evaporators of automobile air conditioners. However, as a component for heat exchangers that use water-based coolant,
There are few examples using Al alloy BS. The reason is,
This is because conventional Al alloy BSs have insufficient water corrosion resistance, so if the quality of the coolant water is poor, penetrating corrosion is likely to occur even after short-term use, which is a fatal defect as a heat exchanger. Therefore, for Al alloy BS applied to this type of use,
There is a strong demand for improved water corrosion resistance. In view of the above situation, the present inventors have been conducting research to develop an Al alloy BS for vacuum brazing that has excellent water resistance and corrosion resistance. As a result, the chemical composition of the Al alloy core material can be specified, and if a brazing filler metal is placed on one or both sides of the core material with an Al alloy having an appropriate thickness and electrochemical properties interposed as an intermediate layer, the above results can be achieved. The present invention has now been completed by learning that it is possible to obtain a BS made of Al alloy that meets the purpose of the invention. That is, the Al alloy BS for vacuum brazing according to the present invention essentially contains Cu: 0.2 to 2.0%, and further contains Mn: 0.05 to 0.5%, Cr: 0.05 to 0.5%, Zr: 0.05 to 0.5%. Contains one or more elements selected from the group consisting of seeds, with the remainder consisting of Al and unavoidable impurities
Al alloy is used as a core material, and a cladding ratio of 3 is applied to one or both sides of the core material.
~15% thicker and 20~20% thicker than the core material
The gist is that the brazing material layer is formed through an intermediate layer made of an Al alloy having a base potential difference of 100 mV. Moreover, the heat exchanger according to the present invention is characterized in that the partition wall on the side that comes into contact with the heat medium is constituted by the brazing sheet described above. The reasons for determining the chemical components, etc. of each constituent material in the present invention will be explained in detail below. First, the reason for limiting the content of the Al alloy that constitutes the core material is that Cu is an essential element for increasing the mechanical strength and potential of the Al alloy, and if it is less than 0.2%, these effects will not be effectively exhibited. Furthermore, Cu is
Although Cu is an element that significantly reduces the corrosion resistance of Al alloys, the corrosion resistance inhibiting effect of Cu is significantly reduced after heating for brazing, so it can be effectively used as an element to improve strength and potential. However, if the Cu content exceeds 2.0%, it is impossible to prevent corrosion resistance from decreasing even if the thickness and electrochemical properties of the intermediate layer are appropriately adjusted as described in detail below. Mn, Cr, and Zr are all elements that strengthen subgrains, suppress recrystallization, and improve brazability.
Each element must be contained in an amount of 0.05% or more. However, too much Mn increases susceptibility to intergranular corrosion, and too much Cr and Zr generates giant intermetallic compounds and reduces workability.
All elements must be kept below 0.5%. Next, the above core material and brazing material (generally used as brazing material)
(Al--Si alloy or Al--Si--Mg alloy is used).This is an intermediate layer that is interposed between the layers (Al-Si alloy or Al-Si-Mg alloy is used), but it prevents the surface diffusion of Cu from the core material toward the brazing material layer, and also It functions as a barrier layer to prevent Si from diffusing toward the core material and maintain both the mechanical strength of the core material and the brazing properties of the brazing material at a high level, and furthermore, The concentration gradient of Cu acts as a sacrificial anode and prevents corrosion of the core material. In order to effectively utilize these effects,
The thickness of the intermediate layer must be at least 3% of the thickness of the BS, and if it is less than this, the effect as a blocking layer and the sacrificial anode function will not be effectively exhibited. However, these effects are saturated at a thickness of 15%, and if the thickness exceeds 15%, the strength of the Al alloy BS as a whole decreases, and selective corrosion of the intermediate layer becomes more likely to occur, especially at the brazed part, resulting in a decrease in corrosion resistance. It gets lower. In addition, in the present invention, the potential difference between the core material and the intermediate layer is also extremely important in relation to the purpose of effectively exerting the sacrificial anode effect, and it is difficult to avoid the fact that the potential of the intermediate layer is simply base with respect to the core material. In addition, effective sacrificial anode action cannot be obtained unless there is a potential difference of 20 mV or more. However, when the potential difference exceeds 100 mV, only the intermediate layer is selectively dissolved, and the corrosion resistance of the Al alloy BS as a whole deteriorates. Therefore, it is necessary for the Al alloy used as the intermediate layer to appropriately control the potential difference without impairing its own corrosion resistance, taking into consideration the relationship with the chemical components of the core material. Here, when combined with an Al alloy core material with a Cu content of about 0.5%, commercially pure Al can provide sufficient corrosion protection as an intermediate layer, but depending on the electrochemical properties of the core material used, , which constitutes the middle tier
It is desirable to control the potential difference by adding an appropriate amount (approximately 0.05 to 0.5%) of Mn, Cr, or Zr to the Al alloy. That is, these elements have the property of slightly shifting the potential of Al to a higher level, so they are extremely useful as potential difference adjustment elements, and in addition, they also have the effect of increasing the bonding strength with the core material. However, if the content of these alloying elements is higher than that of the core material, there will be a problem in the direction from the core material to the intermediate layer during brazing.
Due to the diffusion of Cu, the potential difference becomes too small and the sacrificial anode effect of the intermediate layer may deteriorate.
The blending amount should be kept lower than the same content of the core material. Other elements that can be added to the Al alloy for the intermediate layer include Cu, Mg, and Zn, each of which has the following effects. That is, Cu is effective for controlling the potential of the intermediate layer, and its effect is effectively exhibited when it is added in an amount of 0.05% or more. However, if it is contained in an amount exceeding 0.5%, the potential of the intermediate layer shifts to a higher value, resulting in a decrease in the anticorrosion effect. Additionally, Mg has the effect of promoting the diffusion of Cu from the core material to the intermediate layer during brazing and suppressing selective corrosion of the intermediate layer, and this effect is effectively exhibited by containing 0.05% or more. . but
If it exceeds 0.5%, the diffusion of Cu and Si in the brazing material becomes excessive, resulting in a decrease in the corrosion resistance of the intermediate layer as a whole. Zn has the effect of lowering the potential of the intermediate layer,
Necessary when the Cu content in the core material is low. However, if the amount of Zn is less than 0.1%, no potential lowering effect can be expected, while if the amount of Zn exceeds 1.0%, evaporation and scattering during brazing will become significant and may contaminate the furnace. Moreover, in combination with the core material made of the above chemical components, since the core material originally has a potential above a certain level, Zn
There is almost no need to lower the potential to the extent that it is necessary to add . As detailed above, the Al alloy BS according to the present invention
By forming a brazing material layer on one or both sides of a core material whose chemical composition has been specified, through an intermediate layer whose thickness and electrochemical properties are adjusted, the core material and wax material contained in the intermediate layer are separated. Since the shielding effect of the material layer and the sacrificial anode effect on the core material are effectively utilized,
Demonstrates outstanding water and corrosion resistance as a whole. In addition, the mechanical strength has been increased by specifying the alloy components of the core material, so it can meet the recent demands for thinner walls and lighter weights. Therefore, this Al alloy BS fully demonstrates its excellent performance when used as a brazing material for heat exchangers. In particular, as explained at the beginning, Al alloy BS is widely used as a brazing material for heat exchangers, and the Al alloy BS of the present invention is used as a partition wall between the heat transfer medium and the heat exchanger.
If used, corrosion caused by heat media (especially water) will be drastically reduced, and its lifespan will be significantly extended. Next, experimental examples will be given to further clarify the structure and effects of the present invention. Experimental example 1 Using the Al alloy for the core material shown in Table 1, the Al alloy for the intermediate layer shown in Table 2, and the brazing filler metal of Al-10%Si-1.5%Mg, these were shown in Tables 3 and 4. A BS with a plate thickness of 1 mm was prepared by combining as shown. The potential difference between the core material and the intermediate layer (difference in natural potential in a 3.5% NaCl aqueous solution) of each BS obtained is also listed in Tables 3 and 4.
Furthermore, the following corrosion tests were conducted using each of the obtained BSs. The results are shown in Tables 3 and 4. [Corrosion test] Using each BS, the test was carried out as shown in Fig. 1 (enlarged cross-sectional view of main parts: 1 is the core material, 2 is the intermediate layer, 3 is the brazing metal layer, A is the flat part, and B is the fillet part. The corrosion test specimen shown in (shown) is prepared by vacuum brazing.
The brazed side of each specimen obtained was used as the test surface,
It is immersed in a corrosive solution containing 3000 ppm of Cl ions and 10 ppm of Cu ions, and subjected to a repeated temperature cycle of 80°C x 8 hours ← → room temperature x 16 hours for 3 months, and then the erosion depth is measured using cross-sectional micrographs. The corrosion resistance values shown in Tables 3 and 4 represent the maximum erosion depths obtained in this test.

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[Table] From these experimental results, the following can be considered. (1) Nos. 1 to 44 are all examples that satisfy all the specified requirements of the present invention, and it was confirmed that they exhibited excellent corrosion resistance and also had extremely good strength. (2) Nos. 45, 46, 53, and 56 are comparative examples in which the potential difference between the core material and the intermediate layer is too small, and the sacrificial anode action is not exhibited, resulting in extremely poor corrosion resistance. In particular, No. 56 has a negative potential difference (the potential of the core material is more base than the potential of the intermediate layer), so penetrating corrosion occurs. (3) Nos. 47, 48, 49, 52, and 58 are comparative examples in which the potential difference between the core material and the intermediate layer is excessive, and the selective corrosion of the intermediate layer is significant, resulting in poor corrosion resistance of the entire BS. (4) Nos. 50 and 51 are comparative examples in which the cladding ratio of the middle class is too small or too large, and when it is too small (No. 50)
If the sacrificial anode effect is not fully exerted, corrosion resistance is poor, while if it is too large (No. 51), selective corrosion of the intermediate layer at the brazed part tends to progress, resulting in decreased corrosion resistance and low strength. It was confirmed that (5) Nos. 52 to 55 are comparative examples in which the alloy composition of the core material exceeds the specified requirements, and either the strength or corrosion resistance is extremely poor and cannot be put to practical use.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of the main part of the specimen used in the corrosion resistance test. 1... Core material, 2... Intermediate layer, 3... Brazing material, A
... flat part, B... fillet part.

Claims (1)

[Claims] 1 Cu 0.2 to 2.0% (wt% unless otherwise specified)
In addition, it contains one or more elements selected from the group consisting of three types: Mn: 0.05-0.5% Cr: 0.05-0.5% Zr: 0.05-0.5%, with the remainder being Al and unavoidable elements. consists of impurities
Al alloy is used as the core material, and a cladding ratio of 3 to 15 is applied to one or both sides of the core material.
% thickness and a potential difference 20 to 100 mV less base than the core material, through an intermediate layer made of an Al alloy,
A water-resistant, high-strength bracing sheet for vacuum brazing, characterized by forming a brazing metal layer. 2 In claim 1, the intermediate layer is
Pure aluminum or selected from the group consisting of six types: Mn: 0.05-0.5% Cr: 0.05-0.5% Zr: 0.05-0.5% Cu: 0.05-0.5% Mg: 0.05-0.5% Zn: 0.1-1.0% A bracing sheet that is an Al alloy containing one or more elements, with the remainder consisting of Al and impurities. 3 In addition to containing 0.2 to 2.0% Cu, it contains one or more elements selected from the group consisting of Mn: 0.05 to 0.5%, Cr: 0.05 to 0.5%, Zr: 0.05 to 0.5%, and the balance is Consists of Al and inevitable impurities
Al alloy is used as the core material, and the cladding rate is 3 to 15% on one or both sides of the core material.
A brazing sheet is formed by forming a brazing metal layer through an intermediate layer made of an Al alloy having a thickness of A vacuum brazed heat exchanger characterized by being composed of a brazing sheet. 4 In claim 3, the intermediate layer is
Pure aluminum or selected from the group consisting of six types: Mn: 0.05-0.5% Cr: 0.05-0.5% Zr: 0.05-0.5% Cu: 0.05-0.5% Mg: 0.05-0.5% Zn: 0.1-1.0% A heat exchanger that is an Al alloy containing one or more elements, with the remainder consisting of Al and impurities.