Lower temperature fabrication of continuous intermetallic coatings on AZ91D magnesium alloy in molten salts

Abstract

A continuous Mg–Al intermetallic coating was fabricated on an AZ91D Mg alloy in molten salts in the lower temperature range from 300 °C up to 400 °C. The coating consists of a single Mg 17Al 12 intermetallic layer or both Mg 17Al 12 and Mg 2Al 3 intermetallic layers, depending on the treatment temperature. In contrast to the conventional powder pack cementation process, active Al atoms can be formed at a lower temperature in molten salts, which contributes to the lower temperature formation of continuous intermetallic layers. The intermetallic layer markedly improves the hardness as well as the corrosion resistance of the AZ91D Mg alloy. Furthermore, the continuous intermetallic layer exhibits passive behaviour in 3.5 wt.% NaCl solution, which is attributed to the homogenously distributed intermetallic phases.