Continuous intermetallic compounds coatings on AZ91D Mg alloy fabricated by diffusion reaction of Mg–Al couples

Continuous intermetallic compounds coatings were fabricated on AZ91D Mg alloy by diffusion reaction of Mg-Al couples at relatively low temperature of 300 °C to improve its wear and corrosion resistance. SEM/EDXS and XRD analysis showed the coatings consisted of β-phase (Mg17Al12) layer and γ-phase (Mg2Al3) layer. The thickness range of the coatings was 16–110 μm, depending on the treatment time. The mechanical properties were evaluated by Vickers micro-hardness test and indentation test, and the corrosion performance was studied by immersion test and electrochemical measurement. The results indicated that the hardness and the corrosion resistance of the AZ91D Mg alloy were greatly improved due to the formation of the continuous intermetallic compounds layers. Furthermore, the continuous intermetallic compounds layers exhibited passive behavior and no appreciable hydrogen evolved during immersion in 3.5% NaCl solution for 72 h.