Influence of microstructure on corrosion properties of multilayer Mg–Al intermetallic compound coating

A multilayer Mg–Al intermetallic coating was fabricated on the Mg alloy in molten salts at 400 °C with treatment time range from 2 to 8 h. The coating consists of a single Al12Mg17 intermetallic layer or Al12Mg17, Al0.58Mg0.42 and Al3Mg2 intermetallic layers. The corrosion resistance of the coating which is obtained at 400 °C for 2 h is the best. When the treatment time is higher than 2 h, some cracks developed in the layers. The cracks were resulted from the thermal stress due to the different thermal expansion coefficient of the substrate and the intermetallic layer during the rapid cooling process.

Research highlights
► A multilayered coating is fabricated on magnesium alloy with molten salt bath surface treatment method.
► The coating consists of δ (Mg), α (Al) solid-solution and Al12Mg17, Al0.58Mg0.42, Al3Mg2 Mg-Al intermetallic compound layers.
► The structural defects in the microstructure of a surface alloyed Al coating influence its corrosion behavior.