ろう付部ミクロ組織が銅合金ろう付部の耐食性に及ぼす影響

抄録

Copper alloys with excellent machinability and thermal conductivity are widely used as piping materials, and brazing is used as the connection method. Exposure to running water containing sulfate ions and ammonium ions may cause corrosion damage such as pitting corrosion near the brazed joint of the pipe, leading to leakage of the refrigerant. Therefore, it is necessary to evaluate not only the piping but also the corrosion resistance of the joints of the piping.

In this study, the corrosion resistance of brazed joint to acidic, neutral, and alkaline solutions was measured by an electrochemical method. In addition, the cross–sectional structure was observed to investigate the corrosive behavior of the brazed joint. Using C3604 as a base metal, a single lap shaped brazed specimen was prepared. Phosphorus copper filler metal and silver filler metal were used for brazing. The area was controlled with Kapton tape, and the corrosion resistance of the base metal, brazing filler metal, and brazed specimen was evaluated by the three–electrode method. Furthermore, the cross–sectional structure of the brazed joint was observed using an optical microscope.

From the polarization curve, in the case of fresh water and 0.05 mol NH₃, the current densities of both specimens increased monotonically. In the case of 0.05 mol H₂SO₄, it was found that the brazed specimen was greatly affected by the base metal. From in–situ observation, it was found that Cu and Cu–Zn were preferentially corroded in the brazed specimen. Due to the preferential corrosion of Cu and Cu–Zn, it was considered that the brazing filler metal, base metal, and brazed specimen showed similar corrosion behavior in fresh water and 0.05 mol NH₃.