Pulse plated Zn transition layer in electroplating Sn-Ni alloy coatings on magnesium alloys

An environmentally friendly Zn transition layer was electrodeposited on the AZ31 magnesium alloy substrate aimed to improve its corrosion resistance during the process of electroplating Sn-Ni alloy coating. Direct current (DC) and pulse current (PC) electroplated Zn layers with different thicknesses were compared. Scanning electron microscopy and X-ray diffraction were employed to investigate the surface morphology and microstructure. The corrosion resistance of the Zn transition layers was analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in Sn-Ni plating solution. The results showed that the Zn transition layer was essential for subsequent electroplating Sn-Ni alloy coating on magnesium alloy. For the same thickness, the application of the PC plating mode was more favorable to prepare compact, smooth, non-porous, and fine Zn transition layer. Moreover, the corrosion resistance of PC plated Zn transition layer was enhanced compared to the DC plated layers. Most importantly, a Sn-Ni alloy coating could be successfully electrodeposited on magnesium alloy by using PC plated Zn transition layer.