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We aimed to understand the corrosion behavior of Pb-free Cu alloys (Japan Industrial Standards (JIS) CAC411 and CAC901) and the substances (Cu2S and Bi, respectively), which are in the alloys as particles, in a 3.0 mass% NaCl aqueous solution. The corrosion behavior of the Pb-free Cu alloys and the substances were compared with those of a Cu alloy (JIS CAC406), which Pb detected as crystallized particles in it, and a Cu alloy (JIS CAC403) without any crystallized substances. Cu2S specimens were produced by sintering Cu2S powders. Bi specimens were produced by Bi electro-plating on Cu plates. The measured corrosion potentials of CAC411, CAC901, and CAC403 were close to that of Sn instead of Cu. The anodic polarization curves of all the Cu alloy specimens showed that the anodic current density increased rapidly at a potential above −0.20 V vs. Ag/AgCl, and the rapid increase in the current density was similar to that of Cu. Therefore, it was concluded that the increase in the current density of the Cu alloys results from the dissolution of Cu in a matrix. Cu2S was converted into CuS during the anodic reaction. However, the corrosion potential of Cu2S was higher than those of Cu and CAC411. Therefore, it was concluded that the Cu2S particles in CAC411 act as cathodic sites and remain stable during the natural corrosion. The corrosion potential of Bi was higher than that of CAC901 and slightly lower than that of Cu. At the potentials below −0.10 V vs. Ag/AgCl, Bi was thought to be covered with a passive Bi2O3 lm and the passive lm was expected to protect Bi from corrosion. Therefore, it was concluded that the Bi particles in CAC901 hardly suffer severe corrosion. The corrosion potential of Pb was lower than those of the Cu and Cu alloys, expect for CAC406. In addition, Pb exhibited a large anodic current density and dissolved actively around the corrosion potential of Cu. Therefore, it was concluded that the Pb particles dissolved preferentially during the corrosion of CAC406 owing to galvanic corrosion. Finally, it was concluded that the Cu2S and the Bi particles in CAC411 and CAC901, respectively, hardly suffer severe corrosion compared with the Pb particles in CAC406 in chloride-containing aqueous solutions such as sea water. [doi:10.2320/jinstmet.J2018034]

Corrosion Behavior of Lead-Free Copper Alloy Castings and Their Crystallized Substances of Cu<sub>2</sub>S and Bi