One-Step Fabrication and Localized Electrochemical Characterization of Continuous Al-Alloyed Intermetallic Surface Layer on Magnesium Alloy

Abstract

A continuous intermetallic compound coating was fabricated on AZ91D magnesium alloy via heat treatment at 400 • C in AlCl 3-NaCl molten salts for 10 h. The microstructure and composition of the coating were characterized by scanning electron microscope and energy dispersive X-ray spectrometry. The results showed that the coating has a two-layer structure (the outer Mg 2 Al 3 phase layer and the inner Mg 17 Al 12 phase layer) up to 37 µm thick with compact and planar interfaces between the layers and the substrate. The corrosion property of the coating was investigated using electrochemical impedance spectroscopy (EIS) and two localized electrochemical techniques, i.e., localized electrochemical impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET). The charge transfer resistance (R ct) of the Al-alloyed coating was 2119 Ω cm 2. The localized impedance and current density maps obtained through LEIS and SVET indicate not only significantly improved corrosion resistance (the impedance modulus increased by one order of magnitude and the current density decreased to approximately 3.8%, compared with the substrate) but also defect-free surface condition.

Improvement of AZ91 Alloy Corrosion Properties by Duplex NI-P Coating Deposition

“…The resulting R p value is the sum of R 2 and R 3 according to Equation (5). The EC model (Figure 7b) representing the electrochemical corrosion behavior of uncoated AZ91 alloy in 0.1 M NaCl solution after 5 min includes the elements such as R 1 , which is the solution resistance [41]. High-frequency loop characterizing damaged Mg(OH) 2 layer is observed-elements Q 2 and R 2 (Figure 7b).…”

A Zinc-Rich Coating Fabricated on a Magnesium Alloy by Oxide Reduction

“…Coatings are fabricated on the surface to enhance the corrosion resistance of magnesium alloys [7][8][9][10][11][12][13][14][15][16][17][18][19]. Among which, the zinc coating is an effective one.…”

Corrosion Behavior of Fe/Zr Composite Coating on ZK60 Mg Alloy by Ion Implantation and Deposition

“…to reduce the corrosion rate of Mg-based alloys [8][9][10][11]. Metallic coatings have been proved to exhibit high corrosion resistance, excellent mechanical property, good biocompatibility and favorable electric conductivity, which can simultaneously enhance the corrosion resistance and surface strength without deteriorating the electric conductivity [12][13][14][15][16]. Jin et al [13] deposited Ta-containing coating on the ZK60 Mg alloy surface by reactive magnetron sputtering and the corrosion resistance and biocompatibility were improved by the modified surface composed of Ta 2 O 5 , Ta suboxide and Ta.…”

“…In addition, composite metallic coatings have been prepared to further modify Mg alloys to obtain desirable corrosion rate. Fu et al reported that the corrosion rate of AZ91D Mg alloy was obviously reduced by the Al-Mg intermetallic compound coating fabricated by heat treatment in AlCl 3 -NaCl molten salts, which was attributed to the gradient microstructure of outer Mg 2 Al 3 and inner Mg 17 Al 12 phases formed on the surface [16].…”