JPH0156146B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of increasing the surface area of an Al alloy thin plate, and more particularly to a method of increasing the surface area of an Al alloy fin material for a heat exchanger in order to impart excellent corrosion resistance and drainage properties. In general, Al alloys have excellent thermal conductivity, plastic (rolling) workability, moldability, and corrosion resistance, so they are widely used in the production of heat exchanger fin materials that require these properties. In a heat exchanger that includes a tube material through which a medium passes and a fin material that primarily plays the role of heat exchange, corrosion resistance of the tube material is particularly important, so the fin material is made of a material that is less electrochemically base than the tube material. It is widely practiced to prevent corrosion of pipe materials by the so-called sacrificial anode effect of the fin material. The magnitude of this sacrificial anode effect depends on the relationship between the fin material on the corrosion-protecting side and the pipe material on the corrosion-protected side.
It depends on the area ratio of the surface in contact with water, and the larger the ratio, that is, the larger the surface area of the fin material, the more pronounced the effect can be.Therefore, a method of expanding the surface area of the fin material has been desired. Ta. In addition, since the surface of the Al alloy fin material has poor drainage properties, condensed water that adheres to the surface of the fin material when a heat exchanger is used turns into water droplets, grows further, and reaches adjacent fin members, causing gaps between the fin members. As water droplets completely fill a wide area, the circulation of air, which acts as a heat exchange medium in the atmosphere, deteriorates, and the water obstructs heat transfer, reducing heat exchange performance. will decrease significantly. The reason why the Al alloy fin material has poor drainage properties is that the surface of the Al alloy thin plate after cold rolling is an extremely smooth and glossy surface. Water tends to form large droplets due to its large surface tension, and therefore, the surface where the condensed water that adheres to it is easily washed away before it becomes large droplets.
That is, a fin material having a surface with excellent drainage properties has been desired. Therefore, the above-mentioned characteristics of excellent corrosion resistance and water drainage can be obtained by forming a surface of the fin material that is rich in irregularities and has an expanded surface area, but it is possible to obtain the characteristics of excellent corrosion resistance and water drainage by simply immersing it in an acid or alkaline solution. Chemical etching, which only involves etching, does not produce a microscopically fine uneven surface even if some unevenness is obtained.On the other hand, electrolytic methods (electrolytic etching) require special electrolytic equipment and require complex and delicate electrolytic conditions. In addition to having to configure the settings, the processing time is significantly longer.
There were practical difficulties in terms of both cost and operation. From the above-mentioned point of view, the present inventors have conducted various studies to form fine irregularities on the surface of an Al alloy thin plate by chemical etching without using electrolytic methods, and have found that Sn: at least 0.05 to 0.3. After applying solution treatment to an Al alloy thin plate containing % by weight at a temperature within the range of 500 to 630°C, chemical etching was performed by immersion in an acidic aqueous solution with a pH of 3.5 or less for 1 to 60 minutes to form an Al alloy. When fine irregularities are formed on the entire surface of the thin sheet, and then the etching solution is removed by neutralizing water washing, fine irregularities are formed on the surface of the Al alloy thin sheet, and its surface area is significantly expanded. When used as a fin material,
They discovered that it exhibits excellent corrosion resistance and drainage properties. Therefore, this invention has been made based on the above knowledge, and is based on the above-mentioned findings.
Al alloy thin plate containing 0.3% by weight, heated to 500~630℃
An Al alloy thin plate characterized by being subjected to solution treatment at a temperature within the range of , followed by chemical etching under the conditions of immersion in an acidic aqueous solution with a pH of 3.5 or less for 1 to 60 minutes, and then subjected to a neutralizing water washing treatment. The present invention provides a method for enlarging the surface area of. The above acidic aqueous solution used as the etching solution in this invention is preferably an aqueous solution of various metal chlorides, such as an aqueous aluminum chloride solution, but other acidic aqueous solutions conventionally used in this field, such as an aqueous aluminum sulfate solution, may also be used. You can also. Next, in this invention, the Sn of the Al alloy thin plate is
The reason why the content, solution treatment temperature, and etching conditions were limited as described above will be described. (a) Sn content of Al alloy thin plate Ordinary Al alloy thin plate dissolves extremely slowly in a neutral aqueous solution because it is covered with a relatively strong oxide film that is naturally formed on its surface. Although the dissolution rate increases in an acidic aqueous solution, the dissolution proceeds with uniform dissolution over the entire surface, resulting in a relatively smooth surface after chemical etching. On the contrary,
When Sn is incorporated as a solid solution into an Al alloy thin plate, the oxide film on the surface becomes weaker and it dissolves slowly even in a neutral aqueous solution, but the dissolution rate increases even more rapidly in an acidic aqueous solution. As it melts, the melting process does not occur smoothly, but instead forms fine irregularities on the surface of the thin plate.
The surface area becomes significantly enlarged. However, if the Sn content in the thin plate is less than 0.05% by weight,
Even if an appropriate solution treatment is performed, the above effects cannot be obtained, and on the other hand, even if the Sn content exceeds 0.3% by weight, no further improvement effect can be seen due to the above action, so the Sn content is increased from 0.05 to 0.3% by weight. It was determined as weight%. (b) Solution treatment temperature The effect described in (a) can only be obtained not only by incorporating Sn into the Al alloy thin plate but also by subjecting the Sn-containing Al alloy thin plate to solution treatment. Generally, the solid solubility of Sn in Al alloys is at most 0.1% by weight.
It is extremely small and hardly becomes a solid solution at room temperature. The solid solubility of Sn in Al alloy increases above 500℃ and reaches its maximum around 600℃.
If it is less than
Solution treatment at temperatures exceeding 630°C not only does not improve the effect, but also causes significant softening, and there is a risk that some thin plates may melt, so the solution treatment temperature was set at 500 to 630°C. . (c) Chemical etching conditions As mentioned in (a), an Al alloy thin plate containing Sn as a solid solution dissolves quickly and forms fine irregularities only in an acidic aqueous solution, but the pH of the solution exceeds 3.5. The pH of the etching solution was determined to be 3.5 or less because the progress of dissolution becomes slow and clear unevenness is not formed. Furthermore, if the etching time is less than 1 minute, the dissolution will not proceed to the extent that sufficient unevenness is formed, and if the etching time is immersed for more than 60 minutes, the dissolution rate will rapidly increase due to the effect of increasing the surface area, and the loss due to dissolution will increase. Therefore, the immersion time was determined to be 1 to 60 minutes. Next, the method of the present invention will be specifically explained using examples. Example Molten metals having the final component compositions shown in Table 1 were prepared using the usual melting method, cast into ingots, and then homogenized at a temperature of 580°C for 15 hours. After applying and facing, hot rolling under normal conditions and cold rolling with intermediate annealing were performed to obtain thin sheets with thicknesses of 0.15 mm and 0.5 mm, respectively. Similarly, the first
Solution treatment (forced air cooling) was performed under the conditions shown in the table, and among the thin plates after solution treatment, those with a thickness of 0.5 mm were cold rolled to a thickness of 0.15 mm. Subsequently, the resulting thin plate was treated with a 1N AlCl ₃ aqueous solution at a temperature of 40°C and a pH of 2.5, and a 1N Al ₂ (SO ₄ ) solution at a temperature of 40°C and a pH of 3.0 as chemical etching solutions. _3Aqueous solution or liquid temperature: 40℃, PH: 6.0
Methods 1 to 19 of the present invention and comparative methods 1 to 1 were obtained by chemically etching using a 1N NaCl aqueous solution of 7 were carried out respectively. Comparative methods 1 to 7 are conditions in which any one of the Sn content of the Al alloy thin plate, solution treatment, and chemical etching (marked with * in Table 1) is outside the scope of this invention. This was carried out in In addition, all of the above Al alloy ingots are
Although not shown in the table, as an unavoidable impurity,
Fe: 0.25% or less, Si: 0.13% or less, Cu: 0.09% or less, Mn: 0.1% or less, Ti: 0.1% or less, Cr: 0.1%
Below, Mg: 0.1% or less, Zr: 0.05% or less, and
Zn: It contained 0.05% or less. Next, methods 1 to 19 of the present invention and comparative methods 1 to 19
Natural potential (Ecorr) using a calomel electrode as a reference electrode: Anode current (positive current) obtained when the Al alloy thin plate treated by 7 is held at a constant potential from approximately -1350 mV to 100 mV.
was measured, and this value was compared with the anode current measured immediately before chemical etching.The anode current value immediately before chemical etching was set as 100, and the increase rate of the surface area was evaluated based on the increase rate with respect to this value. These results are also shown in Table 1. From the results shown in Table 1, methods 1 to 19 of the present invention
In the Al alloy thin plate treated by

【table】

[Table] It is clear that while the surface areas of the Al alloy thin sheets treated by Comparative Methods 1 to 7 are significantly increased, no significant increase in surface area can be expected. As mentioned above, according to the method of this invention, Al
The surface area of the alloy thin plate can be significantly expanded,
Therefore, when used as a fin material in a heat exchanger, for example, it exhibits excellent corrosion resistance (sacrificial anode effect) and water removal properties, making it possible to use the heat exchanger for an extremely long period of time. It brings about useful effects.

Claims (1)

[Claims] 1 Contains at least Sn: 0.05 to 0.3% by weight
After solution-treating the Al alloy thin plate at a temperature within the range of 500 to 630°C, chemical etching is performed by immersing it in an acidic aqueous solution with a pH of 3.5 or less for 1 to 60 minutes,
It is characterized in that it is then subjected to a neutralizing water washing treatment.
Method for expanding surface area of Al alloy thin plate.