JPH0375263B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for brazing aluminum alloy structures with good ability to form brazed joints. Normally, when brazing assembled structures made of aluminum alloy as a base material, such as heat exchangers, using the fluxless brazing method, the assembled structures are placed in a vacuum furnace or in an inert gas atmosphere such as _N2 using brazing sheets. This is done by placing the structure in a furnace and uniformly heating the entire structure to the brazing temperature. Therefore, as the scale of the structure increases, the time required for the above-mentioned heating will inevitably increase; however, in general, the thermal conductivity of a structure varies considerably from part to part, and parts with high thermal conductivity take a long time to heat. As a result of being exposed to high brazing temperatures for a long time, for example, in the plate fin type heat exchanger shown in FIG. The amount of the brazing filler metal 2 that should be supplied to the joint portion of the fin material 3 is reduced, resulting in a defect that an appropriate joint width L, which becomes a narrow joint width L, is not formed. For this reason, there is a limit to the size of aluminum alloy structures that can be manufactured using conventional brazing methods. In view of the actual situation, the inventors of the present invention have repeatedly conducted various experiments and research to prevent the above-mentioned defects. Assembled structures made from aluminum alloy plates that have been heated at a temperature of 200 to 350°C for more than 1 hour during the parts stage before assembly will not hold joints even if exposed to long-term brazing heat during brazing. The molten brazing filler metal does not spread more than necessary, forming an appropriate joint width L,
It has been found that the soldering material is retained and the diffusion and penetration of the brazing material into the base material is also suppressed, and the above-mentioned conventional defects do not occur at all. The following may be considered as the reason why the brazing property is improved by the above heat treatment. By heating at a lower temperature than the normal heat treatment temperature (approximately 360°C), the relationship between recrystallization and precipitation differs. In other words, in the temperature range of 200 to 350°C, it is generally considered that precipitation tends to occur before recrystallization, so it is important to analyze the recrystallized structure, grain boundary structure, and quantity ratio of precipitates compared to ordinary heat-treated materials. This is thought to be the reason for the differences in wettability, diffusion and penetration of solder, etc. due to the influence on the properties and underlying structure of the alloy surface. The present invention is based on the above knowledge, and when brazing an aluminum alloy structure, the aluminum alloy plate, which is the material of the structure, is used at the material stage before being formed into a structural member of the structure, or After the above components are formed and processed, they must be preheated at a temperature of 200 to 350°C for at least 1 hour (preferably at a temperature of 230 to 300°C for at least 3 hours) at the component stage before assembly. The gist of this paper is a brazing method for aluminum alloy structures characterized by the following. In the present invention, the heating temperature of the aluminum alloy plate is limited to a range of 200°C or more and 350°C or less because
This is because if the temperature is below 200℃, the mechanical performance necessary to form the aluminum alloy plate into the desired structure shape cannot be obtained, and if it is above 350℃, it becomes the same as normal heating and there is no heat treatment effect. be. This effect is noticeable in the temperature range of 230-380°C. In addition, the holding time at the heating temperature was limited to 1 hour or more because if the holding time is less than 1 hour, the mechanical performance necessary for forming aluminum alloy plates cannot be obtained, and the wax will not spread when the solder is heated. This is because the effect of suppressing the diffusion and penetration of the brazing filler metal component into the inside of the base material does not appear sufficiently. This effect becomes even more remarkable when heated for 3 hours or more. Furthermore, the reason why aluminum alloy plates are heated at the material or component stage is that when they are heated after being assembled into a structure, the temperature at the periphery and center of each member differs due to the thickness and size of each member. This is because each part cannot be heated uniformly. The heating atmosphere in the present invention may be air, vacuum, gases such as nitrogen and Ar at atmospheric pressure, carrier gas under reduced pressure, or the like. Further, the heating rate up to the heating temperature and the cooling rate after heating may be selected in any manner. That is, any combination of rapid and slow heating and cooling may be used. Further, the heating temperature does not necessarily need to be kept constant as long as it is within the range of 200 to 350°C. Next, examples and effects of the present invention will be described. Three types of aluminum alloy plates of JIS standards 3003 and 3004 and AA standard 6951 were processed at 200°C for 3 hours at 300°C in accordance with the method of the present invention.
After heating at 350°C for 168 hours for 24 hours, it was processed into the fin material 3 of the plate-fin heat exchanger shown in Figure 1 (plate thickness 0.5 mm, number of fins 17/inch), and waxed on both sides. Plate 1 clad with material 2
(4004/3003, 1.6mmt), vacuum brazing and _N2 gas atmosphere brazing were performed. As a comparative example, three types of aluminum alloy plates similar to those described above were heated at 360°C x 1, which is outside the range of the present invention at the material stage.
After heating under the same conditions as above, it was processed into a fin material similar to the above, and combined with a plate similar to the above and subjected to vacuum brazing and _N2 gas atmosphere brazing. In addition,
Vacuum brazing was carried out at a heating temperature of 590° C., a heating time of 120 minutes, and a furnace pressure adjusted to 5×10 ^-5 Torr and 10 Torr. As shown in Table 1, the plate-fin type heat exchanger brazed according to the method of the present invention requires a certain degree of wetting and spreading of the brazing material in both vacuum brazing and _N2 gas atmosphere brazing. The minimum value is ◎ or ○, and an improvement of 25% to 91% in brazed joint width has been achieved compared to the comparative example. Especially in _N2 gas atmosphere brazing when the furnace pressure is adjusted to 0.1 Torr, the brazed joint width is 52 mm compared to the comparative example.
% to 91%, and was found to have a remarkable effect.

[Table] In the above example, the fin material 3 of the heat exchanger was subjected to the heat treatment according to the method of the present invention, but even if the plate material 1, that is, the core material of the brazing sheet, was heat treated according to the method of the present invention, Needless to say, similar effects can be obtained. Further, the heat treatment according to the present invention can be applied not only to plate materials for heat exchangers, but also to plate materials of all aluminum alloy structures to be brazed, and produces the same effects as described above. In addition, in the above embodiment, vacuum brazing and _N2 gas atmosphere brazing (so-called fluxless brazing) were used as the brazing method, but the method is not limited to these, and so-called flux brazing such as immersion brazing and furnace brazing is also used. The same effect as above can be obtained even if the attachment is adopted. As explained above, according to the present invention, even if an aluminum alloy structure is exposed to brazing temperature for a long time, the wetting and spreading of the brazing material is prevented to the necessary minimum, and an appropriate brazing material joint width is formed. Since it is held, it becomes possible to manufacture large aluminum alloy structures that were previously impossible to manufacture. Further, effects such as the ability to use No. 1000 series, No. 8000 series, and No. 6000 series materials as the fin material of the plate fin type heat exchanger can be obtained.

[Brief explanation of drawings]

FIG. 1 is a partial cross-sectional view and an enlarged cross-sectional view of a main part, illustrating a brazed portion of a plate-fin type heat exchanger. 1: Plate, 2: Brazing material, 3: Fin material,
L, l: Brazed joint width.

Claims (1)

[Claims] 1 When brazing an aluminum alloy structure, the aluminum alloy plate, which is the material of the structure, is used at the material stage before being formed into the structural member of the structure, or after it is formed into the above-mentioned structural member. 200~ at the parts stage before assembly.
A method for brazing aluminum alloy structures, which is characterized by heating at a temperature of 350°C for one hour or more.