Anticorrosion Performance of LDH Coating Prepared by CO₂ Pressurization Method

Abstract

Many surface treatment methods are used to improve the corrosion resistance of magnesium alloys. LDH (layered double hydroxides) conversion coatings are currently found in the most environmentally friendly and pollution-free coatings of magnesium alloy. In this study, the CO2 pressurization method was applied to the preparation of LDH coating on magnesium alloy for the first time. The effect of CO2 pressurization on the formation and corrosion resistance of LDH coating on AZ91D alloy was investigated. The hardness and adhesion were significantly higher on LDH coating in the case of CO2 pressurization than it is in atmospheric pressure. The surface and cross-sectional morphologies show that LDH coating is more compact in the case of CO2 pressurization than with atmospheric pressure. The results of the polarization curve, hydrogen evolution, and immersion tests indicate that the corrosion resistance of the LDH coating prepared by the CO2 pressurization method was significantly improved.

Effect of Temperature on Corrosion Resistance of Layered Double Hydroxides Conversion Coatings on Magnesium Alloys Based on a Closed-Cycle System

“…From the sample electrochemical test results, the E corr (1.36V ± 0.034) of the LDH conversion coating at 50 • C was higher than that of the AZ91D magnesium alloy (−1.41V ± 0.059) and tends to be more positive at 50 • C. The i corr (8.92 ± 1.37 µA•cm −2 ) of the LDHs conversion coating prepared at 50 • C was nearly one order of magnitude lower than that of the AZ91D magnesium alloy (83.62 ± 1.63 µA•cm −2 ). The E corr and i corr of samples with LDH conversion coating have a certain error but agree well with the published values [53][54][55].…”

“…The icorr (8.92 ± 1.37 μA•cm −2 ) of the LDHs conversion coating prepared at 50 °C was nearly one order of magnitude lower than that of the AZ91D magnesium alloy (83.62 ± 1.63 μA•cm −2 ). The Ecorr and icorr of samples with LDH conversion coating have a certain error but agree well with the published values [53][54][55]. The results indicate that the LDH conversion coating prepared at 50 °C can effectively enhance the corrosion resistance of the AZ91D magnesium alloy matrix.…”

“…The treatment solution can be recycled without affecting the formation effect. So, the author proposed a CO 2 pressurization method for the first time, and the effect of CO 2 pressure and treatment time on the corrosion resistance of LDH conversion coating was studied, and the formation mechanism of the micro-galvanic regions with different β-phase morphology on the magnesium alloy was proposed [53][54][55]. The author found that temperature is also an important factor under the closed-cycle system, and the microstructures of LDH conversion coatings are quite different at low and high temperatures.…”