Evaluation of properties of the Zn-Ni alloy coating on the surface of low carbon steel specimens by plasma electrolyte saturation

The purpose of this work is formation of the Zn-Ni alloy coating on the st12 low carbon steel specimens by plasma electrolyte saturation method in order to improve surface and corrosion properties. Electrolyte bath consisted of sulphate aqueous solution and magnesium sulphate by 35-65 ratios. Working specimens was connected to the high voltage source with direct current and and pulsed direct then was immersed in corresponding electrolyte. The morphology and composition of the coated surface was investigated by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that NiZn8 alloy coating has been formed on the specimen’s surface with unique morphology. Results show Coatings generated by pulse current are thinner than Coatings generated by direct current and have more regular morphology. This phenomenon is due to the higher solubility and the absence of coating formation in the cutout time. The results of roughness showed coating of the pulsed, lower roughness compared to coating generated by direct current, and the pulse frequency of 100 to 1000 Hz with increasing roughness increases.Corrosion behavior of the coating was investigated by linear polarization tests in %3.5 Wt NaCl solution. The results showed that corrosion behavior improved due to surface composition changes. Because of the existence of magnesium in Ni-Zn Alloy coating, the coating potential was lower than pure zinc coating potential, therefore alloy coating protect steel surface through galvanic corrosion.