Influence of Si and Sb additions on the corrosion behavior of AZ91 magnesium alloy

Small amount of silicon and antimony additions (individual and combined) have been carried out on AZ91 alloy and its effect on electrochemical corrosion behavior is investigated. Immersion test, potentiodynamic polarization and electrochemical impedance measurements have been used to estimate the corrosion rate and the behavior. Individual addition of Si and Sb forms massive Chinese script Mg2Si and needle shaped Mg3Sb2 intermetallics, respectively. Addition of Sb to AZ91 + Si alloy is found to modify the Chinese script Mg2Si intermetallic into a fine polygonal shape besides distributing them evenly along the grain boundaries. Improved corrosion behavior is noticed with Si addition, whereas Sb addition is found to reduce the corrosion resistance of AZ91 alloy. However, combined addition of Si and Sb shows highest corrosion resistance. The Mg2Si intermetallic when present as a fine polygonal shape and distributed evenly along the boundary inhibit the corrosion more effectively compared to the bulk Chinese script. On the other hand, Mg3Sb2 intermetallic in the Sb added alloy, acts as an effective cathode to the α-Mg matrix and thereby increase the corrosion rate.