JPH029098B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat exchanger structural member with excellent pitting corrosion resistance. Conventionally, in general, for example, automobile radiators,
Al alloy heat exchangers, which are widely used in air conditioning equipment, are made of aluminum alloy tubes, fins,
Furthermore, it is manufactured by vacuum brazing or flux brazing after assembling structural members such as header plate material and cover material. However, for example, Al-Mn represented by JIS3003
Tube materials made of alloy veneer material undergo a thermal history of high-temperature heating and slow cooling during the brazing process in the heat exchanger manufacturing process, and this thermal history causes significant intergranular corrosion during practical use. Localized corrosion often occurs, which develops into through-holes and shortens the life of the heat exchanger, as well as corrosion products (white powder).
There was also the problem of air pollution. In addition, this Al-Mn alloy is used as a core material in place of the Al-Mn alloy veneer material described above. is electrochemically base, resulting in a sacrificial anode effect on the core material.
Attempts have also been made to construct heat exchanger structural members using composite materials made by cladding Al-Zn alloy skin materials typified by JIS7072, but with the Al-Zn alloy skin material,
Corrosion rate is relatively high under severe corrosive environments.
Moreover, local corrosion often occurs, so
It was not possible to sufficiently suppress intergranular corrosion in the core material of the Al--Mn alloy. Therefore, from the above-mentioned viewpoint, the present inventors have developed a heat exchanger that will not cause local corrosion during practical use even if subjected to brazing treatment that involves high-temperature heating and slow cooling during the manufacturing process of the heat exchanger. In other words, as a result of research to develop heat exchanger structural members with excellent pitting corrosion resistance, we found that in weight percent (hereinafter % indicates weight percent), Mn: 0.1 to 0.6%, Si: 0.1 to 0.6%, Cu: 0.1~
Mg: 0.1-1.2%, Zn: 0.1-1.5%, Mg: 0.1-1.2%, Zn: 0.1-1.5%, A composite material made by cladding a skin material of an Al alloy with a composition containing Al and the remainder consisting of Al and unavoidable impurities, or a composite material made of a skin material of an Al alloy on one side of the core material and an Al-Si alloy on the other side. When a heat exchanger structural member is composed of a brazing sheet made of brazing filler metal, it is possible to
In conventional Al-Mn alloy core materials containing Mn, this
When kept at a high temperature, most of the Mn contained becomes a solid solution in the matrix, while at temperatures sufficiently lower than this, only a small amount of Mn can be dissolved in the matrix. The Mn required to form this compound is replenished by the solid solution Mn near the grain boundaries, so a phase with a lower amount of solid solution (Mn As a result, the interior of the grain with a high amount of solid solution of Mn becomes electrochemically noble compared to the Mn-deficient phase, which leads to corrosion and damage to the core material. When dissolution occurs, the Mn-deficient phase preferentially dissolves, resulting in intergranular corrosion.In contrast, the above core material has a Mn content of 0.1 to 0.6%, which is lower than that of conventional Al-Mn alloy core materials. In addition, the amount of change due to solid solution and precipitation of Mn is kept extremely low due to the inclusion of Si, so the occurrence of local corrosion is significantly suppressed, and the above-mentioned skin material has excellent pitting corrosion resistance. In addition, since it is electrochemically less noble than the core material, the sacrificial anode effect on the core material provides good corrosion protection, which prevents the occurrence of localized corrosion such as intergranular corrosion during practical use. As a result, they found that the heat exchanger can be used for a long period of time. This invention has been made based on the above knowledge, and the reason why the component compositions of the core material and skin material in the composite material and plating sheet constituting the heat exchanger structural member are limited as described above is explained below. explain. A Core material (a) Mn The Mn component interacts with Fe, which is unavoidably contained in the core material and reduces corrosion resistance.
By making this an insoluble Al-Mn-Fe-based compound, we not only reduce the deterioration of corrosion resistance caused by Fe, but also improve the high-temperature strength of the core material, which significantly suppresses thermal deformation during the brazing process during heat exchanger manufacturing. Furthermore, it has the effect of making the core material electrochemically more noble than the skin material, and as a result, the core material becomes corrosion-proof due to the sacrificial anode effect of the skin material, but its content If the content is less than 0.1%, the desired effect cannot be obtained, while if the content exceeds 0.6%,
When brazing treatment is performed as described above, a phase with a lower amount of Mn solid solution than inside the grains (Mn-deficient phase) appears in the vicinity of the grain boundaries, promoting intergranular corrosion. Therefore, the content was set at 0.1 to 0.6%. (b) Si The Si component contains Al−Mn−Si combined with Mn.
This compound is thermally stable and not only improves high-temperature strength but also resists heat treatment that requires high temperatures.
It has the effect of significantly suppressing the solid solution of Mn into the crystal grains and its precipitation, and further enriching the core material electrochemically, but its content is 0.1
If the content is less than 0.6%, the desired effect cannot be obtained, while if the content exceeds 0.6%, the corrosion resistance will deteriorate. Therefore, the content was set at 0.1 to 0.6%. (c) Cu and Zr Both of these components have the effect of improving the strength of the core material, and Cu in particular has the effect of improving the strength of the core material.
It has the effect of electrochemically ennobling the core material and further promoting the sacrificial anode effect of the skin material.Also, Zr has the effect of precipitating fine Al-Zr compounds to form Al, which constitutes the core material. By increasing the recrystallization temperature of the alloy, the recrystallized grains formed thereby become coarser, so when used as a plating sheet, for example,
It has the effect of significantly suppressing the penetration of the brazing filler metal into the core material, but if the content is less than 0.1% Cu and 0.02% Zr, the desired effect of improving the above effect cannot be obtained; If the content exceeds Cu: 0.5% and Zr: 0.20%, the corrosion resistance will tend to decrease, so the content should be adjusted accordingly.
Cu: 0.1 to 0.5%, Zr: 0.02 to 0.20%. B Skin material (a) Zn The Zn component makes the skin material electrochemically less noble than the core material, makes the corrosion mode completely soluble, and has an excellent sacrificial anode effect on the core material. It has the effect of imparting excellent pitting corrosion resistance, but if its content is less than 0.1%, the desired effect cannot be obtained;
If the content exceeds less than 0.1%, not only will the sacrificial anode effect deteriorate, but the corrosion will become a localized dissolution type, leading to deterioration of pitting corrosion resistance.
It was set at 1.5%. (b) Mg The Mg component has the effect brought about by Zn when it coexists with Zn, that is, the effect of further improving the sacrificial anode effect and pitting corrosion resistance, but if its content is less than 0.1%, the The desired effect of improving the action cannot be obtained, and on the other hand,
If the content exceeds 1.2%, processability deteriorates and it becomes difficult to manufacture composite materials, so the content was set at 0.1 to 1.2%. Next, the heat exchanger structural member of the present invention will be specifically explained using examples. Example Al alloy A for core material of the present invention having the component compositions shown in Table 1 by ordinary melting and casting method.
~H, conventional Al alloys for core materials, Al alloys a and b for skin materials of the present invention, conventional Al alloys for skin materials c, and Al alloys for brazing materials were melted and cast into ingots.

[Table] Although these ingots are not shown in Table 1, they all contain Mn: 0.01 as an unavoidable impurity.
% or less, Mg: 0.01% or less, Cu: 0.04% or less,
Zn: 0.02% or less, Fe: 0.35% or less, and Cr:
It contained 0.01% or less. Next, the various Al alloy ingots obtained as a result are hot rolled, and the Al alloy for the core material has a plate thickness of 8.
mm, plate thickness for Al alloy for skin material and Al alloy for brazing material: 3
The hot-rolled sheets of Al alloy for skin material and Al alloy for brazing material were cold-worked to have a thickness of 1 mm. Next, a part of the above hot-rolled Al alloy plate for the core material with a thickness of 8 mm and a cold-rolled plate of the Al alloy for the skin material with the plate thickness of 1 mm were combined as shown in Table 2. The heat exchanger structural member composite plate of the present invention (hereinafter referred to as the structural member composite plate of the present invention) is then assembled, clad on both sides by hot rolling, and then cold rolled to a thickness of 0.5 mm. 1 to 8 (hereinafter referred to as conventional structural member composite materials) and conventional heat exchanger structural member composite materials (hereinafter referred to as conventional structural member composite materials) were manufactured. Similarly, a part of the hot-rolled Al alloy plate for the core material with a thickness of 8 mm was added to the above plate for the skin material with a thickness of 1 mm.
Cold-rolled sheets of Al alloy and Al alloy for brazing metal are stacked together in the combinations shown in Table 2, cladded by hot rolling, and then cold-rolled to a thickness of:
By adjusting the thickness to 0.5 mm, heat exchanger structural member brazing sheets of the present invention (hereinafter referred to as the present invention structural member brazing sheets) 1 to 8 and conventional heat exchanger structural member brazing sheets (hereinafter referred to as conventional structural member brazing sheets) were manufactured, respectively. did. Next, from the various structural component composite materials and structural component brazing sheets obtained as a result, 50 mm
Cut out a test piece with dimensions of x80mm x 0.5mm,
Using this test piece, conditions equivalent to brazing treatment in the heat exchanger manufacturing process, namely pressure:
In a vacuum of 10 ^-4 torr or in a nitrogen gas atmosphere of 10 ^-1 torr, heat treated at 600°C for 3 minutes and air cooling, containing 10 ppm Cu ²⁺ ions at temperature: 40 °C in tap water, and respectively
with 100 ppm Cl ^- , So ₄ ^2- and HCO ₃ ^- ions;

【table】

[Table] A tap water immersion test and a solution immersion test were conducted for 30 days in an aqueous solution containing 10 ppm Cu ²⁺ ions at a temperature of 40°C, and the number of pitting corrosion and maximum pitting depth were measured. Note that the structural member plating sheet was subjected to the test with the brazing material side insulated with paint. These results are shown in Table 2. From the results shown in Table 2, it can be seen that the structural member composite materials 1 to 8 of the present invention and the structural member plating sheets 1 to 8 of the present invention did not cause local corrosion even in extremely corrosive environments. It is clear that while the conventional structural member composite material and the conventional structural member plating sheet exhibit pitting corrosion resistance, the occurrence of localized corrosion is significant. As mentioned above, in the heat exchanger structural member of the present invention, the composite material and brazing sheet that constitute it have extremely excellent pitting corrosion resistance, so a heat exchanger manufactured using the same has excellent pitting corrosion resistance. Even when exposed to extremely harsh corrosive environments, there is no pitting corrosion or intergranular corrosion in the structural members that make up the product, making it possible to use it for an extremely long period of time, making it an industrially useful property. It has.

Claims (1)

[Claims] 1 Mn: 0.1 to 0.6%, Si: 0.1 to 0.6%, Cu: 0.1
~0.5%, Zr: 0.02~0.2%, and the rest consisting of Al and unavoidable impurities. A heat exchanger with excellent pitting corrosion resistance, characterized in that it is made of a composite material made of a clad Al alloy skin material having a composition (by weight %) containing: , and the remainder consisting of Al and unavoidable impurities. Structural members. 2 Mn: 0.1-0.6%, Si: 0.1-0.6%, Cu: 0.1
Mg: 0.1-1.2%, Zn: 0.1-1.5%, on one side of an Al alloy core material with a composition of ~0.5%, Zr: 0.02-0.2%, and the rest consisting of Al and unavoidable impurities. It consists of a brazing sheet made of an Al alloy skin material with a composition (by weight %) of Al and unavoidable impurities, and a brazing sheet made of an Al-Si alloy brazing material on one side. A heat exchanger structural member with excellent pitting corrosion resistance.