Corrosion of AZ31 with LDH conversion coatings loaded with inorganic inhibitors.

Layered Double Hydroxides (LDHs) coatings were developed for corrosion protection of AZ31 Mg alloy. LDH coatings were fabricated under co-precipitation conditions and applied under hydrothermal conditions. Two different systems Zn-Al LDH and Li-Al LDH were studied. Specimens were post-treated via immersion for 2 h at 45 ºC in Na2WO4·H2O or LiNO3 baths respectively, to produce Zn-Al LDH(W) and Li-Al LDH(Li). The characterization of the coatings was carried out by field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The corrosion process was studied by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). Surface was also evaluated by water drop contact angle and paint adhesion test by using an epoxy primer. The characterization of the coating revealed two-layered coatings with a denser inner layer and a flaky outer layer. Both coatings improved the corrosion resistance of the AZ31 alloy. Loading with inhibitor further increased the corrosion resistance by one order of magnitude (Bare substrate, Z10mHz ⁓ 102 Ω cm2; LDH, Z10mHz ⁓ 103-4 Ω cm2; LDH-inhibitor, Z10mHz ⁓ 105 Ω cm2)