Electrodeposition, structure and composition of ternary Zn–Ni–P alloys

The presented work reports on conditions of electrodeposition of ternary Zn–Ni–P alloys on low carbon steel substrates, using a chloride–sulfate electrolyte containing beta(β)-alanine, NaH2PO2·H2O and H3PO2. The chemical and phase compositions of the alloy are determined via scanning electron microscopy (SEM), coupled with an Energy-dispersive X-ray (EDAX) device and X-ray diffraction (XRD) analysis. At pH values of the electrolyte 2–3 and current densities of 1–2 A dm−2, the electrodeposited alloys contain an amorphous phase and they are essentially Ni–Zn–P alloys with different phosphorous content. The increase of pH up to 4 and higher current densities (5 A dm−2) lead to the deposition of Zn–Ni–P alloys with traces of phosphorous, i.e. practically Zn–Ni alloys are obtained. These alloys however differ substantially both in the surface morphology and phase composition as to the usual Zn–Ni alloys, electrodeposited from phosphorous-free electrolytes. The paper reports also results from cyclic voltammetry (CVA) studies on the electrodeposition process of the Zn–Ni–P alloys. Discussion on fundamental aspects of electrodeposition of ternary alloys is made. -- Highlights: ► The electrolytic bath for Zn–Ni–P alloys contains β-alanine, NaH2PO2·H2O and H3PO2. ► Zn does not co-deposit with P if Ni2+ ions do not present in the electrolytic bath. ► The presence of P itself alters the overall characteristics of the obtained alloys. ► The P content depends on Ni percentage in the alloy which dependence is not linear.