Effect of current density and electrolyte pH on microstructure of Mn-Cu electroplated coatings

In the present study 304 stainless steel (SS) was electrochemically plated with nanocrystalline Mn-Cu alloy coatings from a bath containing ammonium sulfate. The electrochemical investigation of Mn-Cu electrodeposited films was managed by potentiodynamic scans and galvanostatic experiments. The effect of pH and current density on the microstructure, cathodic efficiency, crystallographic structure, and chemical composition of the deposits were characterized by means of scanning electron microscopy (SEM), weight gain measurements, X-ray diffraction (XRD), and energy dispersive X-ray spectrometry (EDS), respectively. The results showed that Mn-Cu coatings obtained at low current density contain a large amount of Cu and a heterogeneous microstructure, while at high current density uniform, compact, and amorphous coatings with a small amount of Cu was obtained. The XRD and SEM analyses of the films showed that the deposition of Mn-Cu alloy is more affected by the current density than electrolyte pH. However, the results did not show any specific changes in the grain size of the coatings with variation of current densities. The results indicated that Cu co-deposition delayed the phase transformation of as-deposited ductile γ-Mn to the brittle and hard α-Mn.