The corrosion properties and the mechanical properties of brazing alloy and brazed butt joints are equally important problems that have to be made clear.
In brazing, the joints are jointed with different metals to a base metal. Consequently, the corrosion properties of a brazed joint become a very important thing.
It is said that the corrosion properties of copper-phosphorus brazed joints are good. However, very little is definitely known about these properties through reasearch.
In this study, the corrosion properties of a copper-phosphorus brazing alloy and a brazed joint with the same alloys are examined both in a normal chemical solution and in an ammonium sulfid gas atomosphere.
The results obtained are as follows:
1) The corrosion in copper-hosphorus brazing alloys increases in proportion to the amount of phosphorus added to the brazing alloys. (in roome temperature)
When oxygen (30cc/min.) is added to the corrosion atmosphere ((NH
4)
2S-Gas), the corrosion rate increased ten times. Also when the temperature of the test chamber is increased to 70°C the corrosion rate becomes five or seven times greater than the room temperature. Two cylindrical copper brazed butt joints, joined together by a copper-phsphorus brazing alloy, were placed in a test chamber atmosphere filled with (NH
4)
2S gas. The brazed joints were attached to the wall of the chamber and a weight (3Kg/mm
2) was hung from the free side of the brazed joint. This lasted for a period of 100 days. At the end of the 100 days, it was found that the outlayer surfaces of the two cylindrical copper brazed butt joints, attached directly to the phosphorus brazing alloy, were beginning to corrode.
2) The corrosion rate of a copper-phosphours brazing alloy in a chemical solution of HNO
3 is the fastest. After this solution the following chemical solutions in this order have the fastest corrosion rate, namely chemical solution of NH
4OH; (NH
4)
2S; HCl and H
2SO
4. Aside from the corrosion effect of HCl and H
2SO
4 solution s an pitting corrosion was also observed on the brazing alloy surface.
This pitting corrosion was found to be in the α-phase.
3) Two cylindrical copper brazed butt joints, joined together as above by a phosphorus brazing alloy, were placed in separate chemical solutions of HCI, NHO
3 and NH
4OH for 30 days. After 30 days the cylindrical joints were taken out of each of these solutions and the strength of each was tested by a tension test. It was found that the cylindrical brazed joint in the chemical solution of NH
4OH was the weakest followed by joints in HCI and NHO
3 chemical solutions respectively. The brazed joint was 1/3 dgree weaker than it was prior to placing in that solution.
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