Preparation and characterization of Cr–P coatings by electrodeposition from trivalent chromium electrolytes using malonic acid as complex

Cr–P coatings were prepared by electrodeposition from trivalent chromium plating bath using malonic acid as complex. The influences of bath composition on the trivalent chromium electrodeposition process and deposited coating properties were studied. The effects of plating parameters such as current density, bath pH and plating time on structure and morphology of deposited coatings were investigated in detail. XRD, SEM, EDAX and XPS techniques were used to characterize the Cr–P deposited coatings. Results show that the composition, microstructure and surface morphology of the Cr–P coatings depend on bath composition and plating conditions including bath pH, current density, plating time, etc. Results of EDAX and XPS indicate that the deposited coatings contain Cr(s), Cr(III), phosphorus, oxygen and carbon. The optimum bath composition was obtained using malonic acid as complex and the mechanism of Cr–P electrodeposition was analyzed. The optimum plating parameters for good-quality chromium deposited coating are pH 2–3, current density 3–12 dm2, temperature 35 °C and Ti/IrO2 as anode. These results may be of great practical and theoretical significance for further improvement of trivalent chromium plating process.