JPS6248743B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to tubes for aluminum heat exchangers, and more specifically, to improve corrosion resistance, which is important in tubes for heat exchangers that use water as a heat exchange medium, such as automobile radiators or heater cores. The present invention relates to a significantly improved aluminum heat exchanger tube. [Prior Art] Generally, in automotive heat exchangers, air conditioning heat exchangers or air-cooled oil cooling heat exchangers use air as the heat exchanger medium on the outside, Freon gas on the inside, and oil on the inside. Aluminum or aluminum alloys are used because they are used in a relatively mild corrosive environment. However, radiators, heater cores, etc. use air as a heat exchange medium on the outside, which is the same environment as the heat exchanger described above, but the inside uses water (cold water and hot water during operation), which is a very harsh corrosive environment. Therefore, the use of aluminum or aluminum alloys poses problems in terms of corrosion resistance. However, although aluminum or aluminum alloy (hereinafter referred to as aluminum) has been widely used as a material with good corrosion resistance, for example, when used as a brazed structure such as a heat exchanger, In this case, the brazing filler metal acts cathodically on the aluminum base material, electrically accelerating the corrosion of the aluminum base material. Furthermore, there is a risk that Si in the brazing filler metal will diffuse into the aluminum base material at grain boundaries, causing intergranular corrosion in the aluminum base material using this Si as a core. Furthermore, the corrosion resistance of the aluminum base material decreases due to high temperature heating during brazing, and although the corrosion accelerating effect of the brazing material is alleviated in an environment where water is used, the corrosion resistance is insufficient. Therefore, as a method for preventing corrosion of aluminum materials under the various environments explained above, (1) the brazing filler metal contains specific elements such as Zn, Sn,
A method in which the brazing filler metal itself acts as an anode by containing In. (2) The fins and corrosion-resistant slat layer in the heat exchanger contain the above-mentioned specific element that acts as an anode,
A method of corrosion-protecting the main components having other heat exchanger functions by its anode action. (3) A method to improve and strengthen the grain boundary expansion resistance of the aluminum base material against Si. (4) A method in which a third component is contained in the aluminum base material so that the aluminum base material acts as a cathode in contrast to the brazing metal. etc. have been proposed. However, in the various methods mentioned above, using an element that acts as an anode, using Zn as the element can provide some effect in terms of improving corrosion resistance, but in the vacuum brazing method, Since the vapor pressure of Zn is high, during brazing,
In particular, there is a problem that the corrosion prevention effect is considerably lost due to evaporation and scattering, as well as contamination of the furnace.
The method of using Sn or In instead of Zn does not have the problem of evaporation and scattering as with Zn, but it has the disadvantage that the desired corrosion prevention effect cannot be achieved sufficiently and workability is reduced. In addition, (3) and (4) above.
For example, Cu, Fe,
Although Zr has been incorporated or heat treatment conditions such as soaking have been changed, sufficiently satisfactory results have not yet been obtained. The JIS3003 material mentioned above contains Mn as the main alloying element to improve strength, and has good general corrosion resistance, but after brazing, that is, after high-temperature heating, it is significantly susceptible to intergranular corrosion. There is a problem that damage accidents due to corrosion will occur in a short period of time. In addition, tube materials for heat exchangers generally include:
A composite material consisting of a brazing filler metal layer and a sacrificial anode layer is often used as a cladding material.Extrusion is the tube manufacturing method, but billet manufacturing becomes complicated and manufacturing costs are high.Therefore, as a tube manufacturing method, strip material is The most suitable method is to mold it from scratch and perform high-frequency resistance or high-frequency induction welding. [Problems to be Solved by the Invention] The present invention has been made in view of the various drawbacks and problems of the conventional tubes for heat exchangers as explained above, and is mainly aimed at tubes for automobile radiators and heater cores. The present invention provides a tube for an aluminum heat exchanger that has excellent corrosion resistance even after vacuum brazing. [Means for Solving the Problems] The aluminum heat exchanger tube according to the present invention has a core made of an Al alloy containing 0.2 to 2.0% Cu, the balance being Al and impurities, and a sacrificial anode on the inner surface. The first invention is an aluminum heat exchanger tube characterized by being clad with pure Al, Al-Mg-Si alloy, or Al-Mn alloy containing less than 0.2% Cu; ~2.0%, and one or more of Zr0.01~0.5%, Mn0.05~0.5%, Cr0.05~0.5%, and the balance consists of Al and impurities. The second aluminum heat exchanger tube is characterized by having a core material and an inner surface clad with pure Al, Al-Mg-Si alloy, or Al-Mn alloy containing less than 0.2% Cu as a sacrificial anode. This invention consists of two inventions. Note that the outer surface of the aluminum heat exchanger tube can be clad with a brazing material. Further, the tube for an aluminum heat exchanger according to the present invention has a core material in the form of a plate or strip with a sacrificial anode layer clad on one side, or a sacrificial anode layer clad on one side and a brazing filler metal on the other side. The core material can be formed into an aluminum heat exchanger tube by butt seam welding. Tube for aluminum heat exchanger according to the present invention (hereinafter sometimes referred to as tube according to the present invention)
will be explained in detail. First, the material used as the core material in the tube according to the present invention contains Cu 0.2-2.0% as an essential component, Zr 0.01-0.5%, Mn 0.05-0.5%,
It is an Al alloy containing one or more of 0.05 to 0.5% of Cr, or an impurity with the balance Al not containing it, and the material used as a sacrificial anode contains less than 0.2% of Cu. Al (JIS1××
×) series, Al-Mn (JIS3×××) series alloy, Al-Mg
-Si (JIS6×××) alloy. Here, the above (JIS6×××) is, for example, 6000 like JIS6001.
It means the alloy of the series. Therefore, in the tube according to the present invention, the excellent effects of the tube according to the present invention are exhibited by combining the core material and the sacrificial anode with the above-mentioned ingredients and component ratios. Unless the conditions are met, the intended purpose of the tube according to the present invention cannot be achieved. In other words, Cu is well known as a component that improves the strength of Al and shifts the potential to a nobler state, but since Cu content significantly inhibits the general corrosion resistance of Al, it is not used as a corrosion-resistant Al alloy. The limit for use is that the Cu content is at most 0.4% or less. However, when assembling Al alloy by flux or vacuum brazing,
570℃~610℃ for melting Al-Si brazing filler metal
When subjected to this high temperature heating, the contained Cu component is used to improve strength and potential without significantly reducing corrosion resistance. The inventor has confirmed that this is possible. Therefore, the Cu content ratio in the tube according to the present invention was determined based on the above confirmation, and if the Cu content is less than 0.2%, the potential of the base material cannot be made sufficiently noble. The strength is also insufficient for the intended purpose, and the Cu content is 2.0%.
When the potential increases beyond this value, the potential becomes nobler and the strength of the base material improves, but on the contrary, the corrosion resistance tends to decrease. Therefore, the Cu content is set to 0.2 to 2.0% as a suitable range for improving strength and potential without reducing corrosion resistance. Next, as a component other than Cu, one or more of Zr, Mn, and Cr may be included as necessary. Zr forms an intermetallic compound of Al, Al ₃ Zr, and is finely distributed in the base metal, strengthening subgrains and suppressing recrystallization, so the metal structure becomes fiber during rolling and extrusion processing. Even after high-temperature heating during brazing, the crystals do not become equiaxed crystals, but instead become oblate grains elongated in the processing direction.As a result, grain boundary diffusion of Si during brazing is suppressed, and susceptibility to intergranular corrosion increases. prevent. When the Zr content is less than 0.01%, this effect is insufficient, and when the Zr content increases beyond 0.5%, this effect is saturated and the formation of giant crystals occurs. etc., resulting in a decrease in workability. Therefore, the Zr content is set to 0.01 to 0.5%. Mn and Cr strengthen subgrains like Zr,
It has the effect of suppressing recrystallization and is also effective in improving the drawing workability of the base material. However, this effect is insufficient when the Mn and Cr contents are less than 0.05%.
Furthermore, the intergranular corrosion susceptibility of the base metal tends to increase when the amount exceeds 0.5%. Then,
Mn and Cr content shall be 0.05 to 0.5%. Next, in the sacrificial anode of the tube according to the present invention, the Cu content is set to less than 0.2% in order to prevent the potential from becoming noble.
It is desirable that the difference in Cu content is 0.2% or more. In addition, the materials used for the sacrificial anode include:
Pure than its own corrosion resistance, brazability and strength
Al, Al-Mn alloys, and Al-Mg-Si alloys are preferred. In addition, since Al-Cu (JIS2×××) alloys have a noble potential, sufficient anodic corrosion protection cannot be obtained, and Al-Si (JIS×××) alloys do not tolerate high-temperature heating during brazing. Al-Mg (JIS5×××) alloys, Al-Zn
(JIS7×××) type alloys have the problem that their constituent Mg and Zn components evaporate and scatter during vacuum brazing, resulting in contamination of the furnace, so they are not preferred as sacrificial anodes. As described above, by selecting the components and proportions of the core material and sacrificial anode of the tube according to the present invention, the corrosion resistance of the tube for an aluminum heat exchanger can be significantly improved. Furthermore, under heating during brazing, Cu contained in the core material diffuses into the sacrificial anode.
This diffusion creates a concentration gradient in which the Cu content gradually decreases from the core material to the surface of the sacrificial anode, and the potential difference follows the same trend, making the effect of the sacrificial anode more pronounced. The cladding ratio for the core material of such a sacrificial anode naturally varies depending on the thickness of the core material used, but for example, for a 0.4t thick material expected to be used as a radiator tube material, about 10% is good. Also, since the tube is usually brazed to the fin, brazing material is not necessary on the tube side if a brazing sheet with brazing material on the fin side is used, but if there is no brazing material on the fin side, It is sufficient to provide a brazing material on the outside of the tube. The components of this brazing material differ depending on the brazing method, but for vacuum brazing,
Al-Si-Mg alloys such as AA4004 and 4104, Al-Si-
Mg-Bi alloys, Al-Si alloys such as A4343 and A4047 are used for flux brazing, and Al-Si alloys containing other elements are used for other atmosphere brazing methods. be done. As for the manufacturing method of tubes, the method of extrusion → drawing is difficult to produce billets and is very expensive, and is insufficient for mass production.The method of forming from plates or strips and seam welding is more efficient than extrusion → drawing. You can obtain something equivalent to that, and
This is a good method because it is inexpensive. In addition, typical seam welding methods include high frequency resistance welding and high frequency induction welding.
Any method may be used; in short, butt welding may be used. [Example] Next, an example of the tube for an aluminum heat exchanger according to the present invention will be described together with a comparative example. Example 1 Table 1 shows the components and component ratios of the core material, sacrificial anode, and brazing material of the tube according to the present invention.
In addition, in Table 1, core material-1 and core material 2
Si, Fe, Zn, and Ti are impurities. Note that in Table 3 to be described later, Si, Fe, Zn, and Ti are impurities as well. A flat tube was made from this material by high frequency induction welding. Plate thickness: 0.4t Temperature: H14 Clad ratio: Both sacrificial anode and filler metal are 10% of the total plate thickness Tube dimensions: See Figure 3 This tube was subjected to a pressure breakdown test using a hydraulic pump, and the results were reported. It is shown in Table 2.

【table】

[Table] From this, it can be seen that one or two of the three tubes broke at the non-welded part, and the other two tubes that broke at the welded part had approximately the same fracture pressure as the tubes that broke at the non-welded part. It has sufficient performance in terms of strength. Example 2 Using materials with the components and component ratios shown in Table 3, test materials having the configurations and shapes shown in Table 4 were prepared. After heating this sample material under a vacuum of 7×10 ^-5 Torr to a temperature equivalent to brazing, a tap water running test was conducted using the apparatus shown in FIG. That is, in Figure 1, PH7.23, Cu0.01ppm, Cl17.5ppm,
Tap water with an electrical conductivity of 131.0 μv/cm is supplied through a 15φCu tube (1 m) 2 installed at the bottom of the tank 1. The test piece S was placed in a 13φ x 500L glass tube 3, and tap water was poured into it. In this case, the test was conducted at a tap water flow rate of 0.2 m/sec and a room temperature of 15 to 20°C for 30 days. A cross-sectional microscopic investigation of the corrosion situation was conducted through this test. That is, FIG. 2 shows a microscopic photograph of the cross-sectional microstructure after the corrosion test. The micrographs in Figures 2a and 2b are cross-sectional microstructures of the material of the tube according to the present invention, and corrosion has stopped at the sacrificial anode, whereas the micrographs in Figures 2c and d of comparative materials 3, 4, and 5 are , e, it is clear that corrosion has progressed to the core material. Note that FIG. 2a corresponds to 1. Present invention in Table 4, and FIG. 2 b corresponds to 2. Present invention in Table 4. Table 5 also shows the calculated corrosion rate (MDD) from weight loss. Corrosion rate (MDD) was calculated as explained below. (1) Calculate the surface area of the test piece from the weight and dimension measurements of the sample before the corrosion test. (2) Tap water running water test After 30 days have passed, remove the test piece, remove the corrosion products on the surface with the following solution, and then measure the weight of the sample. Liquid: 20 g of CrO ₃ per ₁₁ g _of distilled water 35 c.c. From the values measured and calculated from 2), calculate the corrosion rate (MDD) using the following formula. Corrosion rate {MDD (mg/day・dm ² )} = {Weight before corrosion test (mg) - Weight after corrosion test (mg)} / {Number of test days (days) × Sample surface area (dm ² )} Corrosion rate It can be seen that the tube material according to the present invention has the smallest (MDD), which is slightly better than Comparative Material 4 (3SC), rather than being approximately the same, and exhibits excellent corrosion resistance.

【table】

【table】

[Table] Example 3 Table 6 shows the components and content ratios of the core material, and Table 7 shows the content and content ratio of the core material.
The table shows the components and content ratios of the sacrificial anode material coated on the tube. For the core materials (No. 1 to No. 7) in Table 6,
10% (0.04mm) of No.11 and No.12 to No.15 on both sides
(thickness) and produced a clad material with a thickness of 0.4 mm,
These clad materials are heated under vacuum (10 ^-4 to ^{10 -5} Torr).
Heat to a temperature equivalent to brazing at 595℃ x 3 minutes,
This material was used as a specimen material for the clad tube corrosion test. These test materials were mixed with 3% NaCl + 0.1% H ₂ O ₂ at pH 3.
The test was carried out by immersing it in a liquid at a temperature of 30°C for 7 days. After the test, the maximum corrosion depth (mm) and corrosion morphology of the core material of these test materials were investigated using a cross-sectional microscope. Table 8 shows the results.

【table】

【table】

【table】

[Table] From Table 8, the following explanation is clear. Tube for aluminum heat exchanger according to the present invention (core material No. 1 to No. 6, cladding material No. 11, No. 12 and
For those coated with No. 13), corrosion was stopped by the clad material, whereas for those whose core material No. 7 was coated with a clad material of any alloy, corrosion penetrated all the way to the core. Occurrence of intergranular corrosion is unavoidable. Note that cladding with coating material No. 14 protects the core material, but during vacuum brazing assembly, the material in the alloy
Zn evaporates and scatters, causing contamination of the vacuum heating furnace, so it is not preferred as a cladding material for the inner sacrificial anode of the tube. In addition, some of the materials coated with clad material No. 15 have corrosion that progresses to the core material and penetrates through it.
If the potential of the core material does not become more noble than that of the cladding material, it means that erosion cannot be prevented. On the other hand, the aluminum heat exchanger tube according to the present invention has cladding materials No. 11, No. 12 and
No. 13 has a sacrificial anode effect on any of the core materials No. 1 to No. 6. [Effects of the Invention] As explained above, since the aluminum heat exchanger tube according to the present invention has the configuration shown above, the sacrificial anode is provided even under severe conditions when water is used. Therefore, it exhibits extremely excellent corrosion resistance, and further has the effect of being excellent in corrosion resistance even after brazing.

[Brief explanation of the drawing]

Fig. 1 is a schematic explanatory diagram of the equipment used for the corrosion test, Fig. 2 is a micrograph of the tube material for an aluminum heat exchanger according to the present invention and a comparative material after the corrosion test, and Fig. 3 is the dimensions of the tube of Example 1. FIG. 1 - tank, 2, 3, 4 - pipe, S - test piece.

Claims (1)

[Claims] 1. An Al alloy containing 0.2 to 2.0% Cu, with the balance consisting of Al and impurities as a core material, and a sacrificial anode on the inner surface of pure Al, Al-Mg-Si system containing less than 0.2% Cu. An aluminum heat exchanger tube characterized by being clad with an alloy or an Al-Mn alloy. 2. The tube for an aluminum heat exchanger according to claim 1, wherein the outer surface of the tube for an aluminum heat exchanger is clad with a brazing material. 3 Contains Cu0.2-2.0%, and one or more of Zr0.01-0.5%, Mn0.05-0.5%, Cr0.05-0.5%, and the remainder is Al and impurities. For aluminum heat exchangers, the core material is an Al alloy consisting of the Tube. 4. The tube for an aluminum heat exchanger according to claim 3, wherein the outer surface of the tube for an aluminum heat exchanger is clad with a brazing material.