Corrosion behavior of Mg,AZ31, and AZ91 alloys in dilute NaCl solutions

Corrosion behavior of extruded Mg, extruded AZ31 alloy, and cast AZ91 alloy was investigated by electrochemical measurements in dilute NaCl solutions. Corrosion products and passivation films were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. All specimens exhibit the corrosion and passivation zones in dilute NaCl solutions. The aluminum content and alloy microstructure influence the corrosion and passivation processes. AZ91 alloy shows the broadest passivation zone followed by AZ31 alloy and Mg. AZ91 alloy reveals a highest corrosion resistance, and preferential attack is located at the primary Mg phase. Its relatively fine β-phase (Mg₁₇Al₁₂) network and Al₂O₃/Al(OH)₃ compounds produced on the passivation film are the main factors which limit the corrosion progress as compared with AZ31 alloy and Mg. The thick passivation product on AZ31 alloy is the key factor which restricts the corrosion attack in dilute solutions.