Robust corrosion protection of Ni-thiolate coordination polymer/Mg(OH)2 coating on magnesium alloy AZ31

Abstract

Although magnesium alloys have been effectively used in industry, they have weak corrosion resistance. Herein, robust Ni-thiolate coordination polymer Mg(OH)2 coatings were prepared by an oxidation-hydrolysis-coordination (OHC) strategy to make AZ31 magnesium alloy highly resistant to corrosion in 3.5 wt% NaCl solution. The OHC process includes three steps: I) oxidation of AZ31 to produce AZ31@MgO; II) hydrolysis of MgO to produce Mg(OH)2, cation exchange between Mg(OH)2 and Ni(II) to produce Mg–Ni LDH; III) coordination of Ni(OH)2 from Mg–Ni LDH by the 1,4-Benzenedithiol (BDT) ligand to produce LDH-BDT coatings. Potentiodynamic polarization, EIS, and in situ SRET in 3.5 wt% NaCl solution were used to assess the hybrid coating's anti-corrosion performance. Surprisingly, LDH-BDT coating achieves excellent corrosion inhibition performance (99.9999%) with the icorr of 1.926 × 10−10 A cm−2, which is six orders of magnitude lower than that of AZ31 substrate, this is due to the cooperative effect, such as the physical protection provided by thick LDH-BDT coatings and the hydrophobic properties of Ni(II)-BDT coordination polymers. This study provides fresh insight into the fabrication of Mg(OH)2-based coatings modified with Ni-thiolate complex to significantly improve Mg alloys' resistance to corrosion.