Influence of ammonium selenate and thiourea mixture on mechanical properties and morphology of Zn–Mn alloy coatings electrodeposited from sulphate–citrate bath

Abstract The influence of thiourea (TU, 0·5 g L−1) and additive mixture of ammonium selenate and thiourea (AS–TU, 0·5 g L−1) on electrodeposition of Zn–Mn alloy coatings from sulphate–citrate bath (SCB) has been studied. Investigations of alloy composition were carried out by atomic absorption spectroscopy and inductively coupled plasma. A profile of the relative concentration of sulphur was obtained using glow discharge spectroscopy. The morphology of the coatings was studied by scanning electron microscopy. The crystal structure was investigated by X-ray diffraction. Two phases (metastable ϵ and β) were detected in coatings electrodeposited from SCB with TU and mixture of AS–TU at j c≥10 A dm−2 (≥50%Mn). Zn–Mn alloy coatings, electrodeposited from an SCB with 0·5 g L−1 TU were harder than coatings electrodeposited from SCB with AS alone, and a mixture of AS–TU. Coatings electrodeposited from SCB with a mixture of AS–TU had the lowest tensile stress.