Corrosion resistance of Ni/Cu/Ni-P triple-layered coating on Mg-Li alloy

In the present paper, a protective Ni/Cu/Ni-P triple-layered coating was successfully prepared on Mg-Li alloy. The Ni, Cu and Ni-P layers served as the outmost, middle and transition layers with the thickness of similar to 0 mu m, -20 mu m and -5 mu m, respectively. The Ni/Cu/Ni-P coating showed superior corrosion resistance in 3.5 wt% NaCl solution with the corrosion current density of 4.04 mu A cm(-2) compared to 12,878.2 mu A cm(-2) of the Mg-Li substrate. No corrosion was macroscopically observed after the coating was immersed in 3.5 wt.% NaCl solution for 360 h. The corrosion mechanism was systematically discussed based on cyclic voltammetry. It was revealed that the outmost Ni layer significantly improved the pitting potential. The Cu middle layer was galvanically protected. We believe that the coated Mg-Li alloy exhibiting superior corrosion resistance will find a wide range of applications in aeronautic, astronautic, electronic and automotive industries. (C) 2014 Elsevier B.V. All rights reserved.