Microstructure and Corrosion Resistance of Cold-Sprayed Zinc-Nickel Alloy Coatings

Zn-Ni alloy powder with different Ni contents was prepared by mechanical alloying.Resultant Zn-Ni powder was then cold-sprayed onto the surface of Q235 steel to afford Zn-Ni alloy coatings.The corrosion resistance of Zn-Ni alloy coatings in seawater was evaluated by potentiodynamic polarization test.The morphology and microstructure of as-prepared Zn-Ni alloy powder and coatings as well as the corroded surface morphology and corroded product composition of the coatings were analyzed by means of scanning electron microscopy and X-ray diffraction.It was found that mechanical alloying led to partial alloying of Zn-Ni powder,and cold-spraying helped to promote the alloying of the Zn-Ni powder.When the Zn-Ni alloy coatings were immersed in seawater,Zn was preferentially dissolved to form a compact top layer while a Ni-rich layer was formed at the sub-surface thereby retarding the corrosion process of the alloy coatings.Incorporated Ni was able to increase the stabilization potential and reduce the corrosion rate of the alloy coatings.However,excessive incorporation of Ni led to micro-cell corrosion of the alloy coatings,and the Zn-Ni alloy coating with 15% Ni(mass fraction) possessed the best corrosion resistance.More over,Ni was able to stabilize Zn(OH)2 and retard its transformation into ZnO,thereby resulting in more uniform and compact corroded surfaces of the alloy coatings.