A study on Mg and AlN composite in microstructural and electrochemical characterizations of extruded aluminum alloy

A combination of composites and metallic materials has been shown to be an effective way to modify the microstructure and thus enhance the corrosion properties. This study focuses on the development of a new aluminum alloy using Mg and AlN composite and the hot extrusion processing. The microstructures and electrochemical properties have been characterized using the advanced surface analysis and electrochemical techniques in a naturally-aerated 0.1 M chloride solution. Open circuit potential and potentiodynamic polarization results indicate that Mg and AlN composite additions could improve corrosion and pitting potentials as well as passive film quality formed on the alloy surface. Electrochemical impedance spectroscopy has confirmed that the addition of Mg and AlN composite also increases the passive film and charge transfer resistances, resulting in an improvement of passive film stability and pitting resistance. X-ray photoelectron spectroscopy suggests that Mg and AlN composite addition promotes the stable passive film formed on the aluminum alloy surfaces due to the existence of Mg oxides/hydroxides and AlN incorporating with Al oxides/hydroxides. The improved pitting resistance could be attributed to the reduction in the grain sizes and defects in the alloy matrix that are observed by electron backscatter diffraction and could directly relate to the alloy dissolution and passive film formation.