Corrosion Behavior of Die-Cast and Friction Stir-Processed AZ91 Magnesium Alloys in 5% NaCl

Abstract

Corrosion resistance and microstructure by optical microscopy of commercially available die-cast, friction stir-processed (without aluminum powder) and friction stir-processed (with aluminum powder) AZ91 magnesium (Mg) alloys (three conditions) were investigated. For corrosion study, salt spray and immersion tests in 5% NaCl solution were carried out. Corrosion behavior was analyzed by scanning electron microscopy for investigation of pits available after 48 h in specimens of all three conditions. This SEM investigation proved that AZ91 Mg alloy that is friction stir-processed with aluminum powder has the lowest pit size compared to the friction stir-processed AZ91 Mg alloy and commercially available die-cast AZ91 Mg alloy. This is because of more solubility of aluminum in α-phase and high fraction of β-phase (Mg17Al12) which improves corrosion resistance of friction stir-processed AZ91 Mg alloy with aluminum powder.