It is an advanced surface treatment technology by in-situ synthesis of Mg-Al Layered double hydroxide (LDH), which can improve surface properties without changing the matrix material, such as corrosion resistance, wear resistance, hydrophobic performance and other properties. Due to the active chemical properties of the magnesium alloy matrix and their low standard potential and poor corrosion resistance, which seriously limits its wide application and development. How to improve anticorrosion of magnesium alloys have attracted considerable attention. This article studies the corrosion resistance and wear corrosion of LDH coatings on surface of LA43M Mg-Li alloy． The LA43M Mg-Li alloy was divided into 25 mm×25 mm×3 mm thin slices as substrate.At room temperature (25 ℃), 0.05 mol/L Al (NO3)3·9H2O (AR) was prepared in 40 mL deionized water, and 0.01 mol/L NaOH (AR) was added to adjust the pH of the solution, keep it in the range of 12-13. The cleaned substrate samples and the mixed solution were transferred to a hydrothermal reactor and heated with an electric drying oven(101-0BS) at 90 ℃, and the hydrothermal time is 12, 18 and 30 h, respectively. After cooling to room temperature, the sample was removed and cleaned with alcohol and deionized water. The surface morphology, composition and phase of the coating were characterized by SEM, EDS and XRD respectively. The corrosion resistance and wear resistance of LDH coated samples were evaluated by immersion test, hydrogen evolution test, potentiodynamic polarization cures and friction and wear test. A well-formed LDH coating, which is uniform, strong adhesive to the substrate, was successfully prepared on the surface of LA43M Mg-Li alloy via a in-situ hydrothermal treatment. SEM results showed that after the hydrothermal reaction, fine sheet structures are formed on the surface of the alloy, and with the increase of hydrothermal time, their size and quantity increase, and their distribution become more densely. Meanwhile, the lamellar LDH nanosheet is well bonded with the substrate and its thickness gradually increased with an increase in the hydrothermal time. XRD result demonstrated that the Mg-Al LDH coating is mainly composed of LDH and Mg(OH)2 nanosheets. The experiments of immersion and hydrogen analysis showed that the corrosion resistance of LDH coatings rank as LDH-30 h＞LDH-18 h＞LDH-12 h＞LA43M. After 8 days corrosion in simulated seawater 3.5wt.% NaCl solution, LA43M substrate were corroded into holes, with cracks and pitting corrosion. However, LDH coated samples had light corrosion, only some of them had pitting corrosion and microcracks. The potentiodynamic polarization cures of the film coated at 30 h exhibited excellent corrosion resistance. Compared with the substrate, its self-corrosion potential increased by 143.7 mV, and its corrosion current density decreased by about two orders of magnitude. The friction and wear test results showed that the substrate has the largest friction coefficient and the wear marks were deep and wide, and its wear mechanism is typical abrasive wear. while the friction coefficients of LDH coating were obviously smaller than the substrate, and the wear marks were shallow and narrow. The Mg-Al LDH coating exhibited an improved corrosion resistance, even after immersion in 3.5wt.% NaCl solution for 8 days, showing good corrosion resistance and durability. Furthermore, anti-corrosion and anti-wear protection mechanism of Mg-Al LDH layer was investigated and proposed. The corrosion protection ability of LDH coatings may be due to barrier protection, ion-exchange, competitive adsorption for chloride and self-healing property. Besides, LDH coating is strong adhesive to the substrate and stable chemical properties are also an important reason for improving corrosion resistance. On the other hand, LDH could significantly reduce the friction coefficient and wear of Mg-Li alloy substrate. The anti-wear mechanism of LDH could be described as follows: It contains a large number of active groups (such as hydroxyl, etc.), can effectively cover the rubbing pair, shear slip occurs between layers, thereby reducing the friction coefficient. In addition, micron-nano particles acted as lubricant to reduce the coefficient of friction and wear. All in all, this method is effective to improve the corrosion resistance and wear resistance of Mg-Li alloys, which is simple, cost-effective and eco-friend. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.
