Intermetallic-Rich Layer Formation for Improving Corrosion Resistance of Magnesium Alloys

The present work examines the formation of a corrosion protective coating containing intermetallic phases on magnesium alloy substrates. The protective coating was formed on the surfaces of commercially pure magnesium (cp Mg) and AZ31B magnesium alloy by vacuum thermal evaporation of commercially pure aluminium (cp Al) and a subsequent heat treatment of the sample. This coating was continuous, homogenous and its microstructure was a eutectic phase composed by clusters of α-Mg surrounded by β phase (Mg17Al12). This eutectic-type coating provided 168 and 504 h of protection inside the salt spray chamber for the cp Mg and AZ31 alloy samples, respectively. To achieve this, it was required to deposit at least 5.5 µm of cp Al and then perform a combined thermal treatment involving heating the samples to 583 K for 60 min and then raising the temperature to 693 K for 5 min.