JPS6328706B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum soldered structure, and more particularly, an aluminum soldered structure that is made by brazing, has good corrosion resistance, and can be made thinner in applications where airtightness is required. This relates to attached structures. In general, aluminum and aluminum alloys are widely used as materials that are lightweight and have good corrosion resistance. However, for example, when used as a brazed structure such as an automobile heat exchanger, the Si in the brazing filler metal diffuses into the aluminum base material (including alloy) and uses this Si as a core. As a result, a local battery is formed between the aluminum base material and the
There is a risk of causing intergranular corrosion, and even if there is no effect of Si diffusion as described above, high temperature heating during brazing increases the susceptibility of the material itself to intergranular corrosion, and if it is not subjected to normal heating. Corrosion resistance deteriorates significantly in comparison. For this reason, conventional techniques have been used to improve the corrosion resistance of the brazing filler metal, to protect other components by making some of the constituent materials act as an anode, and to improve the corrosion resistance of the aluminum base material (including alloys) itself. Improvements were being made. However, for brazing materials, for example,
The effect of adding Zn or Sn to the brazing material to act as an anode is particularly pronounced in Zn-added materials and is widely used in ordinary applications, but it is mainly used as an aluminum brazing method. The current vacuum brazing method has the problem that the vapor pressure of Zn is high and it evaporates and scatters during brazing, resulting in a drastic reduction in the anodic action and contamination of the furnace. Although there is no problem of evaporation and scattering like with Zn, Zn
There is a problem in that it lacks stability comparable to that of steel and has poor workability, making rolling difficult and impractical. In addition, using materials that act as an anode for some of the constituent materials has the same problems as when adding Zn and Sn, and furthermore, depending on the constituent materials, all of the It must be said that it is extremely unstable as the components cannot be protected. Next, improvement of the corrosion resistance of the aluminum base material itself is necessary, for example, for aluminum materials commonly used as brazing sheet core materials (e.g.
Adding Cu, Fe, Cr, Zr, etc. to JIS3003 materials,
Alternatively, attempts have been made to change the heat treatment conditions such as soaking, but satisfactorily results have not yet been achieved. The present invention is an aluminum brazed structure that solves the deficiencies and problems of conventional techniques regarding corrosion in brazed structures made of aluminum materials (including alloys) and improves the corrosion resistance of brazed structures made of aluminum materials. . Although the following description mainly concerns the heat exchanger, it goes without saying that the same applies to other brazed structures. In the aluminum brazed structure according to the present invention, especially in the aluminum brazed heat exchanger, the biggest problem is corrosion penetration that occurs in the material constituting the heat exchange medium passage, and the above-mentioned measures to prevent this are However, in the aluminum brazed structure according to the present invention, the corrosion progress is mainly controlled by suppressing the progress in the plate thickness direction. , the progress of corrosion is dispersed (progresses in layers) in the width and length directions of the plate. However, in general, corrosion of brazing materials is dominated by intergranular corrosion that progresses along grain boundaries.
The progress of corrosion is greatly influenced by the properties and shape of the grain boundaries. Therefore, it is necessary to suppress intergranular corrosion by controlling the state of precipitation at the grain boundaries and the potential relationship with the intragranular matrix. Therefore, it is possible to suppress intergranular corrosion by controlling the grain shape. In the aluminum brazed structure according to the present invention, for example, a heat exchanger having an airtight passage, penetration due to progression of corrosion in the thickness direction is fatal, so the progression of corrosion in the thickness direction is fatal. Suppressing this will immediately lead to improving the life of the heat exchanger. Therefore, by controlling the crystal grain shape, the progress of corrosion is dispersed in the width and length directions of the plate, thereby suppressing the progress of corrosion in the thickness direction. The aluminum brazed structure according to the present invention is characterized in that the crystal grains of the aluminum plate constituting the structure are The length of the crystal grains in the thickness direction) is 3 or more, and the length of the crystal grains in the thickness direction is 50 μm or less. In the aluminum brazed structure according to the present invention, after brazing, the width of the grain-shaped plate in the plate thickness direction, the flat shape extending in the length direction,
Or, it is controlled so that it has a fibrous structure, and as explained in Fig. 1, the width or
The grain length ratio (elongation) between the length direction and the plate thickness S direction, and the grain length (a) in the thickness direction, are as follows: Grain length ratio (elongation, b/a): 3 or more Plate thickness Grain length in direction (a): 50μ or less. In the aluminum brazed structure according to the present invention, the following conditions are effective for controlling the crystal grain shape, particularly controlling the crystal grains to be flat or fibrous. Adjust by combining them. That is, (1) Aluminum material (alloy-containing) is made to contain transition elements such as Mn, Cr, and Zr. (2) Casting increases the cooling rate and the degree of supersaturation. (3) Soaking and hot rolling should be performed at a low temperature to increase the amount of precipitation and make it finer. (4) The processing rate of cold rolling should be high. (5) The annealing temperature should be low. (6) The material before brazing shall be completely annealed material. It is. Under these conditions, (grain length in the plate surface direction/crystal grain length in the plate thickness direction) should be 3 or more, and the crystal grain length in the plate thickness direction should be 50μ or less. In particular, if the grain length ratio (elongation degree) is less than 3, or if the grain length in the thickness direction exceeds 50μ, it will not be possible to disperse the progress of corrosion, and the effect of suppressing corrosion in the thickness direction will not be achieved. It will disappear. In addition, the material used for the aluminum brazed structure according to the present invention is Al-Mn based material.
3203, 3003, Al―Mg―Si series 6951, Al―Mn―
There are Mg-based materials such as 3004, 3005, and 3105, but any other materials that can be used for brazing are also eligible. Next, examples of aluminum brazed structures according to the present invention will be described together with comparative materials. Example (1) Test material Core material A3003 (Al-1.1% Mn-0.15C%) was
It was finished into a 30mm ^T material using the steps shown in the table.

[Table] On the other hand, brazing filler metal AA4004 (Al-10%Si-1.5%
Mg) is ingot-formed using a 50mm ^t air-cooled cast iron mold,
After grinding 2.5mm ^t on each side, it was soaked at 510℃ for 6 hours and hot rolled to 6.4mm ^t . Next, in order to clad the brazing filler metal on both sides of the core material, it is heated at 480°C for 0.5 hours and then hot rolled.
After finishing to 3.5 mm ^t , the present invention material and comparative material 2 were cold rolled to 0.6 mm ^t , and then annealed at 380°C for 3 hours. Comparative material 3 was hot-worked to 0.6 mm ^t , annealed at 380°C for 3 hours, and then hot-worked again to 0.48 mm ^t . (2) Test method The test material was heated at 595℃ in a vacuum of 5×10 ^-5 Torr.
Heated at a heating temperature of 2 min. Thereafter, an accelerated anodic electrolysis test was performed at room temperature using a corrosive medium of 0.1 N NaCl, a counter electrode of SUS304, and electrolytic conditions of 0.5) mA/cm ² ×16 hrs. The results of a microscopic examination of the corrosion state in the cross section in the plate thickness direction are shown in the micrographs in FIGS. 2, 3, and 4 and in Table 2. Fig. 2 shows the material according to the present invention, Fig. 3 shows comparative material 2, and Fig. 4 shows comparative material 3, where a shows the grain structure and b shows the corrosion state. In addition, the material of the present invention shown in FIG. 2 has an elongation degree of 5 and a grain length in the thickness direction of 25 μm, and comparative material 2 in FIG. is expansion degree 2.5,
The grain length in the thickness direction is 80μ. Next, Table 2 shows the degree of elongation, grain length in the thickness direction, and corrosion depth in the thickness direction of the present invention and comparative materials.

[Table] Furthermore, electrolytic polishing and electrolytic etching were performed under the following conditions to investigate the grain structure. (1) Electrolytic polishing Phosphoric acid 700ml Sulfuric acid 200ml Chromic anhydride 100ml Water 75ml (2) Electrolytic etching Methyl alcohol 49ml Hydrofluoric acid 49ml Water 2ml Then, Keller's solution was used to examine the corrosion situation. As a result of the above tests, the material according to the present invention having flat grains (elongation rate: 5, grain length in the thickness direction: 25 μm) showed less progress in corrosion in the thickness direction, and was excellent in preventing through-thickness penetration. It can be seen that it has a suppressive effect. On the other hand, the comparative materials that have approximately the same grain length in the thickness direction and the same grain length in the width or length direction have the same degree of elongation as the material according to the present invention. This is below the range, and no effect on suppressing corrosion in the thickness direction is observed.

[Brief explanation of the drawing]

FIG. 1 is an explanatory cross-sectional view of crystal grains of an aluminum brazed structure according to the present invention, and FIGS. 2 to 4 are microscopic photographs showing the grain structure and corrosion state. 1... Crystal grain, 2... Plate thickness cross section, S... Plate thickness.

Claims (1)

[Claims] 1 It is an aluminum brazed structure, and the crystal grains of the aluminum plate constituting the structure have a ratio of (crystal grain length in the plate surface direction/crystal grain length in the plate thickness direction) of 3 or more. An aluminum brazed structure characterized in that the length of crystal grains in the plate thickness direction is 50μ or less.