Microstructure and corrosion behavior of electrodeposited nano-crystalline nickel coating on AZ91 Mg alloy

In order to enhance the corrosion resistance, nickel coating was electrodeposited onto AZ91 Mg alloy. Activation, zincating, and Cu electrodeposition used as pretreatment processes for better adhesion and corrosion performance of the nickel over layer. The corrosion properties of the AZ91 Mg alloy, nickel electroplated AZ91 Mg alloy, and pure nickel was assessed via polarization and electrochemical impedance spectroscopy (EIS) methods in 3.5 wt% NaCl solution. Moreover, the structure of the coating was investigated by means of X-ray diffraction, whereas specimen's morphology and elemental composition were analyzed using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). Measurements revealed that the coating has a nano-crystalline structure with the grain size of 95 nm. Corrosion results showed superior corrosion resistance for the coated AZ91 Mg alloy as the corrosion current density decreased from 2.5 x 10(-4) A cm(-2), for the uncoated sample, to 1.5 x 10(-5) A cm(-2), for coated specimen and the corrosion potential increased from -1.55 V to -0.98 V (vs. Ag/AgCl) at the same condition. (C) 2014 Elsevier B.V. All rights reserved.