Corrosion behavior of cold sprayed pure zinc coating on magnesium

Abstract

As protective coatings or transition layers, pure Zn coatings were deposited on AZ31b substrate by cold spraying. Processing parameters and mechanical properties were evaluated by scanning electron microscopy, microhardness, and adhesion strength test. The corrosion properties and protective mechanism of the coatings were investigated by potentiodynamic polarization testing and electrochemical impedance spectroscopy (EIS) measurements. The results indicated that the dense, low-porosity Zn coatings were successfully deposited on AZ31b magnesium with good mechanical properties. The cold sprayed pure Zn coatings exhibited higher corrosion resistance than that of the substrate, and the open circuit potential and corrosion potential of cold sprayed Zn coatings were close to those of bulk Zn. A change involving the diffusion of reactants and production of corrosion products in EIS equivalent circuit was observed during immersion for 10 d. The corrosion behavior was related to the unique morphology of cold sprayed Zn coating, and a “corrosion tunnel” was observed in the cross-section of the coatings after immersion, corresponding to the evolutionary mechanism of the particle–particle interface microstructure.