JPS6246633B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a surface treatment method for imparting excellent drainage properties to the surface of an Al alloy fin material for a heat exchanger. In general, Al alloys have excellent thermal conductivity, plastic (rolling) workability, moldability, and corrosion resistance, so they are widely used to manufacture fin materials for heat exchangers that require these properties. However, another characteristic that the fin material should have is water drainage. Normally, condensed water that occurs when a heat exchanger is used adheres to the surface of the fin material, but in the case of Al alloy fin materials, the surface has poor drainage properties, so the condensed water becomes water droplets, which grow and grow on the surface of the fin material. As the water droplets reach the fin members of the fins and completely fill the space between the fin members over a wide area, the circulation of air, which acts as a heat exchange medium in the atmosphere, deteriorates. , the heat exchange performance was significantly reduced. The reason for the poor drainage performance of Al alloy fin material is that after cold rolling,
The surface of an Al alloy thin plate is an extremely smooth and shiny surface, and water on such a surface forms water droplets due to relatively large surface tension. Therefore, in order to improve the drainage properties of the surface of the Al alloy fin material, surface treatments such as anodizing treatment, boehmite treatment, and chromate treatment are performed on the fin material. These surface treatment methods have significantly improved drainage properties, but all of these surface treatment methods require significantly longer processing times, and these surface treatment processes account for a very large proportion of the fin material manufacturing process, which is a major factor in the manufacturing process. This has a large impact on cost, and some of the surface films formed by these surface treatment methods have extremely poor thermal conductivity. It was something that could not be avoided. From the above-mentioned viewpoints, the present inventors have developed a sacrificial anode containing at least 0.1 to 0.5% by weight of Zn and having excellent thermal conductivity, molding workability, plastic (rolling) workability, pitting corrosion resistance, and sacrificial anode. Focusing on the heat exchanger fin material made from Al alloy, which has both excellent effects, we aimed to impart excellent water removal properties to the surface of this fin material in an extremely short processing time and without forming a surface film. As a result of research, it was found that the above-mentioned Al containing at least 0.1 to 0.5% by weight of Zn
Before or after forming the fin material for an alloy heat exchanger, the surface is etched in a 3-20% aqueous solution of caustic soda at a temperature of room temperature to 80°C for 1 second to 10 minutes. The inventors have found that the surface has excellent drainage properties. Therefore, this invention has been made based on the above knowledge, and in the surface treatment method of this invention, first, the target Al alloy is treated with at least
The Al alloy containing 0.1 to 0.5% by weight of Zn was made from Al
When an alloy contains Zn, it has excellent properties as described above, and when etched with a caustic soda aqueous solution, erosion occurs preferentially at boundaries such as grain boundaries and around impurity compounds, resulting in surface damage. This is because the coarser the condition and the finer the crystal grain size, the better the rough surface condition and the better the drainage properties. On the other hand, Al alloys that do not contain Zn not only cannot ensure the above properties, but also undergo almost complete dissolution on the surface during etching treatment with aqueous caustic soda solution, resulting in Although the glossy surface is lost, the surface roughness does not increase significantly, so no significant improvement in water removal performance is observed. Therefore, Al
If the Zn content in the alloy is less than 0.1% by weight, the desired water removal properties and the above properties cannot be guaranteed, while if it exceeds 0.5% by weight, the etching morphology becomes semi-microscopically non-uniform. In addition to the deterioration of drainage properties, the above characteristics,
In particular, as pitting corrosion resistance deteriorates,
The Zn content in the Al alloy was determined to be 0.1 to 0.5% by weight. In addition, the temperature and concentration of the caustic soda aqueous solution in the surface treatment method of this invention, as well as the treatment time, were determined empirically. When the processing time is set to 1 second to 10 minutes, it is possible to ensure an etched surface with extremely good drainage properties. At the treatment time, it was not possible to ensure the desired excellent drainage properties, and on the other hand, when the aqueous solution temperature exceeded 80°C, the 20%
If the concentration of the aqueous solution exceeds 1,000 or more, and the treatment time exceeds 10 minutes, surface erosion due to full-scale melting will occur, resulting in a significant decrease in the thickness of the fin material, which will have a negative impact on the heat exchange performance and strength of the fin material. It will become. Typically 10% heated to around 50℃ as standard
Etching treatment is performed by immersion in a concentrated caustic soda aqueous solution for 10 seconds to 1 minute. Next, the method of the present invention will be explained using examples. Example 1 Invention Al alloys 1 to 8 and comparative Al alloys having the final component compositions shown in Table 1 were prepared by a conventional melting method.
Alloys 1 to 5 are melted and cast into ingots, and then subjected to homogenization heat treatment, followed by hot rolling, intermediate annealing, and cold rolling under normal conditions. Plate thickness: 0.2mm plate material. Next, measure the dimensions of 50mm x 30mm from the above board material.

【table】

[Table] Each test piece was cut out, and these test pieces were sequentially annealed at a temperature of 300°C for 1 hour, and degreased by immersion in acetone for 3 minutes.
Etching treatment by immersion in a 10% caustic soda aqueous solution held at a temperature of 50°C for 10 seconds and 1 minute, followed by neutralization treatment by immersion in a 30% nitric acid aqueous solution at a temperature of 20°C for 1 minute. After that, it was washed with water, dried, and stored in a desiccator for 24 hours. Regarding the test piece subjected to surface treatment in this way,
Ion-exchanged water of 6 μm was dropped onto the surface, and the contact angle of the water droplet with the plate-like surface was measured to evaluate water removal properties. The measurement results are also shown in Table 1. For the purpose of comparison, Table 1 also shows the measurement results of the contact angle on the surface of the test piece after the above degreasing treatment under the same conditions. As shown in Table 1, the etching treatment with a caustic soda aqueous solution significantly improves the water removal property, but this improvement effect on the water removal property is due to the fact that the etching treatment with aqueous caustic soda solution significantly improves the water removal property. invention
Al Alloys 1 to 8 are better than Comparative Al Alloys 3 to 5, which do not contain Zn, and Comparative Al Alloys 1 and 2, which contain Zn but whose content is higher than the range of the present invention. It is clear that this is even more remarkable. Example 2 The present invention alloy 4 shown in Table 1 was subjected to etching treatment using a caustic soda aqueous solution.

[Table] Methods 1 to 4 of the present invention and comparative methods 1 to 5 were carried out under the same conditions as in Example 1 above, except that the conditions shown in Table 2 were used, and the contact angles were measured in the same manner. The measurement results are also shown in Table 2. As is clear from the results shown in Table 2, when etching treatment with caustic soda is carried out under conditions within the scope of the present invention, excellent water removal properties can be ensured, whereas under the above conditions, If any of them is outside the scope of the present invention, it will be difficult to provide desired water removal properties. As mentioned above, according to the surface treatment method of the present invention, Al for heat exchangers can be treated in a very short time and without forming a surface film that causes a decrease in thermal conductivity.
This makes it possible to impart extremely excellent drainage properties to the surface of the alloy fin material.

Claims (1)

[Claims] 1 Al containing at least 0.1 to 0.5% by weight of Zn
When forming a heat exchanger fin material from a thin alloy plate, the temperature:
For use in a heat exchanger, the surface of which is etched in a 3-20% aqueous solution of caustic soda at room temperature to 80°C for 1 second to 10 minutes to provide excellent drainage properties. Surface treatment method for Al alloy fin material.