Zn/Ni composite coating modified by reduced graphene oxide and layered double hydroxide with synergistic effect for superior corrosion protection of Mg alloys

In this work, layered double hydroxide (LDH) and reduced graphene oxide (rGO) were incorporated into Zn/Ni matrix coating by cold-spraying on the surface of Mg alloys. Inside the resulting GLG@Zn/Ni coating, LDH/rGO are homogeneously dispersed and inner-connected to a protective network. Compared with other coatings without LDH or rGO nanosheets, the GLG@Zn/Ni coating shows the best corrosion resistance, with a high self-corrosion potential at - 1.174 V (vs. - 1.471 V for Mg), a decent self-corrosion current density of 344.7 mu A center dot cm(-2) (vs. 878.3 mu A center dot cm(-2) for Mg), and the longest available protection (>720 h) against corrosion. Electrochemical and morphological characterizations reveal a synergistic effect of the coating compositions in enhancing corrosion resistance. In detail, the LDH/rGO network inside the coating restricts the penetration of the corrosive medium, particularly for LDH, which has the capacity to capture corrosive Cl- ions. Meanwhile, Ni promotes the conversion of Zn into passivation layers, which then spread to fill the corrosion pores and interphase cracks. This transformation ultimately leads the GLG@Zn/Ni coating to become a unified whole, providing excellent corrosion resistance.