Development of mechanically robust and anticorrosion slippery PEO coating with metal-organic framework (MOF) of magnesium alloy

A novel anticorrosion and mechanically robust coating system was discovered via plasma electrolytic oxidation (PEO), in-situ MOFs growth strategy, and lubricant-infusion to produce slippery surface of AZ31 magnesium alloy. The PEO coating acts as a transition layer and provides a moderate corrosion barrier to Mg alloy. The homogenous and uniform ZIF-8 film on the PEO coating surface was successfully constructed by a practical and simple in-situ method. The incorporation of ZIF-8 particles plays a vital role to strengthen the corrosion resistance of PEO coating while increasing superhydrophobicity. Furthermore, the ZIF-8 film provides the anchoring site for storing infused lubricants to create a slippery surface. The prepared PEO-MOF-SLIPS showed six orders of magnitude lower icorr value than bare Mg alloy, indicating substantially improved corrosion resistance with an effective barrier performance. In addition, PEO-MOF-SLIPS demonstrates superior corrosion potential of -0.21 V/Ag/AgCl, after 2 days of immersion in 3.5 wt.% NaCl solution. The potentiodynamic polarization test (PDS) results proved that the slippery surface has superior water-repellence to other coatings, indicating higher endurance of SLIPS in 3.5 wt.% NaCl solution. Moreover, the PEO-MOF-SLIPS maintained its hydrophobicity for a longer time in 3.5 wt.% NaCl solution compared to PEO-MOF-SHS. EIS test results also proved that the PEOMOF-SLIPS has a better resistance than that of PEO-MOF-SHS in prolonged immersion in a corrosive solution. According to the abrasion test, the PEO-MOF-SHS maintained its superhydrophobicity up to 100 cm under 100 g load and 80 cm under 200 g load. On the other hand, the PEO-MOF-SLIPS maintained its contact angle stable under both abrasion loadings. The as-prepared slippery surface showed durable water-repellent against the corrosive solution and higher mechanical robustness. The results demonstrate that the MOFs modified PEO coatings system provides a new pathway to the construction of the slippery surface of Mg alloy. It also proves that water-stable MOFs are efficient corrosion-resistant materials and can be used for various anticorrosion applications.