Effect of Cr on the corrosion resistance of Cu-6Ni-4Sn alloys

The corrosion characteristics of Cu-6% Ni-4% Sn-x% Cr alloys in an acid-chloride solution (0.1 M H₂SO₄ + 0.0056 M NaCl) at pH 1.2, were studied as a function of the chromium content. Three kinds of Cu-6% Ni-4% Sn-x% Cr alloys were prepared by melting and casting, followed by thermomechanical treatments. The corrosion behavior of the Cu-6% Ni-4% Sn-x% Cr alloys was investigated using electrochemical corrosion test and surface analyses (optical microscopy, electron probe microanalysis and scanning electron microscopy). The addition of Cr was found to prevent the localized corrosion behavior, which is caused by the decreased Sn-rich precipitates in Cu-6% Ni-4% Sn-x% Cr alloys. These precipitates induced galvanic corrosion due to the difference of the chemical composition.