JPH0473080B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention provides high strength and strength not only when the wall thickness of the cooling water pipe is normal, but also when the wall thickness is thin.
This invention relates to a cooling water pipe for a water-cooled Al alloy heat exchanger that has excellent brazing properties and excellent pitting corrosion resistance against cooling water circulating inside, and can therefore be made thinner than usual. [Prior Art] Some of the applicants previously filed an application for an Al alloy brazing sheet that has excellent pitting corrosion resistance and high strength and is used as a tube material or fin material for a heat exchanger (Japanese Patent Application Laid-Open No. (See Publication No. 57-5840). This Al alloy brazing sheet is made of a high-strength Al alloy with a core material consisting of Mn: 0.3-2.0%, Mg: 0.10-0.80%, Cu: 0.05-0.50%, Al and unavoidable impurities: the remainder. and the skin material clad on one side of the core material is composed of a sacrificial anodic Al alloy having a composition of Mg: 0.1 to 2.5%, Zn: 0.3 to 2.0%, Al and unavoidable impurities: the remainder, Furthermore, the skin material clad on the other side of the core material has a composition consisting of Si: 7.0 to 15.0%, Mg: 0.3 to 2.5%, and if necessary, Bi: 0.01 to 0.30% Al and unavoidable impurities: the remainder. It is characterized in that it is constructed of an Al alloy brazing material having a weight percentage of (the above weight %). [Problems to be solved by the invention] The Al alloy brazing sheet described above has a thickness of 1.2 mm after heat treatment equivalent to vacuum brazing treatment (maintained at 600°C for 3 minutes in a vacuum of approximately 10 ^-4 torr). It has a tensile strength of approximately 16-18.5Kg/ ^mm2 at a thickness of
It had relatively high strength and also had excellent pitting corrosion resistance. However, attempts are currently being made to make cooling water pipes thinner in order to reduce the weight of heat exchangers.
Subsequent tests revealed that when the Al alloy brazing sheet was made thinner and made into a tube, the following problems occurred. That is, (a) the strength (usage strength) after vacuum brazing treatment, which is a process for manufacturing heat exchangers, is not sufficient. (b) During vacuum brazing, the high-temperature strength of the brazing sheet itself is not sufficient, and as the heat treatment time increases, the high-temperature strength further decreases due to the intrusion of brazing metal, causing plastic deformation of the brazing sheet and causing the shape to deteriorate. During vacuum brazing, if the heat treatment temperature is high or the heat treatment time is long, the filler metal may penetrate into the core material, and even if it is thin, a small amount of filler metal may (c) Pitting corrosion resistance is insufficient. Therefore, an object of the present invention is to provide high strength, excellent brazing properties, and excellent resistance to cooling water circulating inside, not only when the wall thickness of the cooling water pipe is normal, but also when the wall thickness is thin. It is an object of the present invention to provide a cooling water pipe for a water-cooled Al alloy heat exchanger that has pitting corrosion and can therefore be made thinner than a normal thickness. [Means for Solving the Problems] As a result of various tests and studies, the present inventors have found that the above-mentioned Al alloy brazing sheet with V added to the core material is used as a heat exchanger tube material. The cooling water pipe of the water-cooled Al alloy heat exchanger is
It has been found that the above object can be achieved by creating an electric resistance welded pipe made of a three-layer clad material, each consisting of an inner skin material, a V-added core material, and an outer brazing material, each having a specific composition. This invention was invented based on the above knowledge, and in a cooling water pipe of a water-cooled Al alloy heat exchanger,
It consists of an electric resistance welded pipe made of a three-layer clad material consisting of an inner skin material, a core material, and an outer brazing material, and the inner skin material contains Mg: 0.1 to 1.5%, Zn: 0.5 to 2.0%, and the remaining is composed of an Al alloy having a composition consisting of Al and inevitable impurities, and the core material contains Mn: 0.5 to 1.5%, Mg: 0.1 to 0.5%, Cu: 0.1 to 0.5%, and V: 0.01 to 0.2%. The outer brazing filler metal contains Si: 6 to 12%, Mg: 0.05 to 2.0%, and if necessary, Bi: 0.03 to 0.15. %, with the remainder consisting of Al and unavoidable impurities (all compositions are weight %)
It is characterized by being made of Al alloy. The configuration of this invention will be explained below. () Inner skin material (a) Mg The Mg component itself has a corrosion inhibiting effect, and by coexisting with Zn, it can provide a significant pitting corrosion inhibiting effect. If the Mg content is less than 0.1%, the above effects will not be sufficient, while if it exceeds 1.5%, not only will there be no further improvement effect, but the work hardening of the skin material will increase, and the core material and skin Differences in the workability of the three-layer clad materials will cause problems with the workability of the three-layer clad materials, so the content should be reduced.
It was set at 0.1-1.5%. (b) Zn The Zn component is contained in Al and has the effect of making it electrochemically less noble and contributing to improving pitting corrosion resistance. Such an effect can be achieved even with a trace amount of Zn, but since Zn has a high vapor pressure, it evaporates from the material surface during vacuum brazing, which is a later process for manufacturing a heat exchanger, and also enters the core material. After diffusion and brazing, the residual amount is required to be 0.5% or more, since when the cooling water is circulated and used, the residual amount will be reduced to a fraction of what it is. on the other hand,
If it exceeds 2.0%, the amount of Zn evaporated during brazing will increase significantly, contaminating the furnace and reducing brazability, so the content is set at 0.5 to 2.0%. () Core material (a) Mn When the Mn component is contained in Al, it forms an Al-Mn compound, and this compound improves corrosion resistance by incorporating unavoidable impurities such as Fe and Si. Furthermore, the Al--Mn compound formed by adding the Mn component exists relatively stably even at high temperatures, and has the effect of preventing deformation during high-temperature heating during brazing. Mn
If the amount is less than 0.5%, the above effects will not be sufficient,
On the other hand, if it exceeds 1.5%, not only will there be no further improvement effect, but the processability of the material will be impaired, so the content should be reduced to 0.5 to 1.5%.
%. (b) Mg When the Mg component is contained in the Al alloy, it has the effect of improving the working strength, which is the strength after brazing, depending on its content. The amount of Mg
If it is less than 0.1%, the effect is not sufficient;
If it exceeds 0.5%, work hardening during the manufacture of the three-layer clad material will increase, causing problems in its workability, and the recrystallized grains formed during the subsequent brazing process will become finer, causing the filler metal to form at the grain boundaries. The content is set at 0.1 to 0.5% because it becomes more likely to penetrate, lowering high-temperature strength (resistance to plastic deformation during high-temperature heating), and deteriorating brazing properties and corrosion resistance. (c) Cu Similar to the Mg component, when contained in an Al alloy, the Cu component has the effect of improving the strength in use (strength after brazing) depending on its content. If the amount of Cu is less than 0.1%, the effect will not be sufficient, while if it exceeds 0.5%, grain boundary precipitation will occur during cooling after brazing, resulting in intergranular corrosion. Its content was set at 0.1-0.5%. (d) V When V component is included in Al, it forms a fine compound with Al, increases the recrystallization temperature during brazing, and adjusts the recrystallized grains formed (the crystal grains are adjusted in the thickness direction). This reduces the grain boundary area and suppresses the intrusion of solder, and the reduction in the grain boundary area and the inhibition of solder intrusion combine to improve high-temperature strength ( In addition to improving the resistance to plastic deformation during high-temperature heating, the recrystallized grains also contribute to improved strength in use, and improve brazability by suppressing the penetration of solder into the core material. It has the effect of improving corrosion resistance by making it more noble. If the amount of V is less than 0.01%, the effect will not be sufficient, while if it exceeds 0.2%, not only will there be no further improvement effect, but also coarse crystallized substances (compounds consisting of V and Al) will be formed when the core material is cast. )
as it forms and deteriorates the workability of the material.
Its content was set at 0.01-0.2%. () Outer brazing filler metal (a) Si The Si component is contained in Al and lowers its melting point, giving the Al alloy properties as a brazing filler metal. If the Si content is less than 6%, the above effects will not be sufficient, while if it exceeds 12%, corrosion of the core material by wax during high temperature heating during electric resistance welding or vacuum brazing will become a problem. The content was set at 6-12%. (b) Mg When Mg is contained in an Al-Si brazing filler metal, it not only evaporates during brazing and acts as a getter for moisture, oxygen, etc. that are harmful to brazing, but also destroys the oxide film of the brazing filler metal. , has the effect of improving fluidity and brazing properties. If the amount of Mg is less than 0.05%, the above effects will not be sufficient, while if it exceeds 2.0%, not only will further improvement effects not be achieved, but the amount of evaporation of Mg during brazing will increase significantly, contaminating the furnace. Therefore, its content was set at 0.05 to 2.0%. (c) Bi The Bi component is contained in the Al-Si brazing filler metal and has the effect of improving its fluidity and brazing properties. Mixed as necessary. If the amount of Bi is less than 0.03%, the above effect will not be sufficient. On the other hand, if it exceeds 0.15%, corrosion of the brazing material into the core material during brazing will become a problem, so the content is set at 0.03 to 0.15%. Ta. [Example] The structure and effects of the present invention will be explained below by giving examples together with comparative examples. Examples Al alloys 1' to 7' for the core material of the present invention, Al alloys A to B for the inner skin material of the present invention, and Al alloys A to B for the outer brazing material of the present invention having the final component compositions shown in Table 1 by a conventional method. Al alloys X to Y and Al alloy a for comparative core material not containing V as an alloy component were melted and cast into ingots, and subjected to homogenization heat treatment.
All of these Al alloys contain unavoidable impurities such as Fe: 0.4% or less, Cr: 0.02% or less, and Zr:
0.01% or less, and in addition, for the core material of the present invention
The Al alloy and comparative Al alloy for core material contain unavoidable impurities such as Si: 0.15% or less, Zn: 0.01% or less, Bi:
Si: 0.14% or less, Cu: 0.01% or less,
Mn: 0.01% or less, Bi: 0.01% or less, and Cu:
It contained 0.03% or less, Mn: 0.01% or less, and Zn: 0.01% or less. Next, the core material ingot is 8
The ingots for the inner skin material and the ingots for the outer brazing material are both hot-rolled to a thickness of 5 mm, and then the hot-rolled plates for the inner skin material and the hot-rolled plates for the outer brazing material are respectively cooled. Both were rolled to a thickness of 1 mm. In this state, the hot-rolled plate for the core material, the cold-rolled plate for the inner skin material, and the cold-rolled plate for the outer brazing material are stacked on both sides in the combinations shown in Table 2, and then hot-rolled. By cladding and then repeated cold rolling with intermediate annealing, the final plate thickness is
3 for manufacturing an ERW welded pipe of 0.4 mm (core material 0.32 mm, outer brazing material and inner skin material both 0.04 mm)
A layered cladding material was produced. Corrosion test specimens were made from this three-layer clad material at 50×
A piece of paper for the sagging resistance test was cut out to a size of 30 x 140 mm. In addition, a tensile test piece with a gauge part of 10 x 50 mm was also prepared. Both the corrosion test paper pieces and the tensile test pieces were tested at 620°C in a vacuum of 10 ^-5 torr, which corresponds to a vacuum brazing process.
Heat treatment was performed for 10 minutes. After this heat treatment, the brazing metal side of the corrosion test paper strips was painted and insulated and exposed to tap water with Cu ²⁺ addition (1 ppm) at 40℃ and Cu ²⁺ plus Cl ^- , HCO ₃ ^- , SO ₄ ^{2- at} 40℃. (Cu ²⁺ : 10ppm, Cl ^- , HCO ₃ ^- and SO ₄ ^2- are each
Corrosion tests were conducted by immersing each material in an aqueous solution (100 ppm) for 30 days. Data regarding pitting corrosion resulting from the tests are shown in Table 2. The mechanical properties of the heat treated tensile test specimens are also shown in Table 2. The drooping resistance test was performed by holding a 30 x 40 mm piece of paper horizontally and subjecting it to the above heat treatment, which corresponds to vacuum brazing, and then measuring the drooping distance at the tip of the test piece. The degree of penetration into the core material was evaluated by microscopic observation of the cross section of the material. These results are shown in Table 2. [Effects of the Invention] Table 2 shows that the comparative three-layer cladding material had poor corrosion resistance in the tap water test and solution test, with deep pitting corrosion occurring through or close to penetrating, whereas the three-layer cladding material of the present invention had poor corrosion resistance in the tap water test and solution test. So, we also conducted a tap water test (40℃, 30 days) with Cu ²⁺ addition, and a solution test (40℃, 30 days).
However, it shows good pitting corrosion resistance with almost no occurrence of pitting corrosion, and the 3-layer cladding material is as thin as 0.4mm, and it can withstand the harsh conditions used in this test.

【table】

【table】

[Table] It is clear that it can withstand use even in corrosive environments. Further, while the comparative three-layer clad material has poor mechanical properties, the three-layer clad material of the present invention has excellent mechanical properties even though it is thin. This seems to be because the strength of the core material in the three-layer clad material of the present invention is sufficient, and there is almost no penetration of wax into the core material during heat treatment. Furthermore, in the comparative three-layer clad material, the brazing filler metal penetrates deeply into the core material during brazing, whereas in the case of the present invention 3
It is clear that the layered clad material exhibits excellent brazing properties because the solder hardly penetrates into the core material and most of it contributes to the bonding, and also has good sagging resistance. As mentioned above, the cooling water pipe manufactured by electric resistance welding from the three-layer clad material of the present invention has excellent brazing properties even though it is thin, and also has excellent mechanical properties and pitting corrosion resistance after brazing. This makes it possible to reduce weight by making the wall thinner. Furthermore, it is expected to improve durability and productivity, so it is extremely useful in practice.

Claims (1)

[Scope of Claims] 1. A cooling water pipe for a water-cooled Al alloy heat exchanger, comprising an electric resistance welded pipe of a three-layer cladding material consisting of an inner skin material, a core material, and an outer brazing material; The material is composed of an Al alloy having a composition containing Mg: 0.1 to 1.5%, Zn: 0.5 to 2.0%, and the remainder consists of Al and inevitable impurities, and the core material contains Mn: 0.5 to 1.5%, Mg 0.1~0.5%, Cu: 0.1~0.5%, V: 0.01~0.2%, and the remainder is Al and inevitable impurities; ~12%, Mg: 0.05~2.0%, with the remainder consisting of Al and unavoidable impurities (all compositions above are weight %)
Water-cooled Al, characterized by being composed of Al alloy
Alloy heat exchanger cooling water pipe. 2. The cooling water pipe of a water-cooled Al alloy heat exchanger consists of an electric resistance welded pipe made of a three-layer clad material consisting of an inner skin material, a core material, and an outer brazing material, and the inner skin material has Mg of 0.1 to 0.1. 1.5%, Zn: 0.5 to 2.0%, and the remainder is Al and inevitable impurities, and the core material is Mn: 0.5 to 1.5%, Mg: 0.1 to 0.5%, It is composed of an Al alloy having a composition containing Cu: 0.1 to 0.5%, V: 0.01 to 0.2%, and the remainder consisting of Al and inevitable impurities, and furthermore, the outer brazing filler metal contains Si: 6 to 12%, Mg: 0.05 to 2.0%, Bi: 0.03 to 0.15%, and the remainder consists of Al and unavoidable impurities (all compositions are weight %)
Water-cooled Al, characterized by being composed of Al alloy
Alloy heat exchanger cooling water pipe.