Preparation and Corrosion Resistance of Hydrothermal Coatings on LZ91 Mg–Li Alloy

A corrosion-resistant coating was fabricated on the surface of LZ91 Mg–Li alloy via a one-step hydrothermal method under varying reaction temperatures (70, 90, 110, and 130 °C). This involved immersing bare Mg–Li alloy substrates in a 10 wt.% Na2CO3 aqueous solution for 3 h. The microstructure, elemental distribution, and phase composition of the as-prepared coatings were systematically characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The corrosion resistance was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization measurements. The results revealed that the hydrothermal treatment led to the formation of a dense nanostructured coating composed of fine nanosheets, with their morphology and population density being highly dependent on the reaction temperature. Phase analysis confirmed that the coating primarily consisted of Mg(OH)2, MgCO3, and Li2CO3. The electrochemical tests demonstrated that the coatings substantially enhanced the corrosion resistance of the alloy. Additionally, the corrosion resistance decreased in the following order: 130 °C > 110 °C > 90 °C > 70 °C > bare LZ91 substrate.