Microstructure and corrosion resistance of Cd coating electroplated from a cyanide-free 5,5-dimethyl-hydantoin bath
[Introduction]The microstructure and properties of cadmium coating electroplated from a cyanide-free bath using 5,5-dimethylhydantoin(DMH)as complexing agent needs to be studied,providing experimental data to broaden its application.[Method]Cadmium electroplating was conducted in an alkaline DMH bath.The microstructure of Cd coating was analyzed by scanning electron microscopy and X-ray diffraction.The corrosion resistance and corrosion behavior of Cd coating were studied by electrochemical measurement,neutral salt spray test,and long-term immersion test.[Result]The Cd coating electroplated in DMH bath was brightly white,featured hexagonal prismatic grains slightly larger in size but more compact in microstructure as compared with the Cd coating electroplated in a cyanide bath,and exhibited a highly preferred orientation in(002)crystal plane with a texture coefficient up to 99.834%.The corrosion current density of the Cd coating electroplated in DMH bath was about 40%of the one electroplated in cyanide bath in 3.5%NaCl solution,and it withstood the corrosion of neutral salt spray for 876 hours.After being passivated with hexavalent chromium,the Cd coating electroplated in DMH bath could endure neutral salt spray test for 2 384 hours without any red rust.During the long-term immersion corrosion process,the corrosion control step and corrosion rate of DMH cadmium-electroplated specimen would change with the generation and destruction of corrosion products.[Conclusion]The corrosion resistance of Cd coating electroplated in alkaline DMH bath is comparable to that electroplated in cyanide bath,and it is expected to be applied to the protection of structural steel components used in aviation industry.
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