INFLUENCE OF MODIFICATION ON MICROSTRUCTURE DEGRADATION OF AlSi12 ALLOY EXPOSED TO THE CORROSION ENVIRONMENT

Abstract

The corrosion resistance of aluminum-silicon (Al-Si) foundry alloys is a result of microstructure development influenced by melt treatment and solidification. As a part of the main eutectic (αAl + βSi), βSi particles are cathodic with respect to the αAl matrix enabling micro-galvanic couple formation and localized corrosion. Despite its high polarization and low current density, increase in the eutectic (αAl + βSi) will contribute to the microstructure degradation of an alloy in corrosive environment. The research was performed in order to estimate the influence of eutectic βSi particles size on the microstructure degradation of AlSi12 alloy with mixed morphology of eutectic (αAl + βSi). The results of light microscopy indicated preferred initiation and progress of cavities involving modified eutectic (αAl + βSi) with eutectic βSi particles of smaller average particle size. The unmodified eutectic (αAl + βSi) with lamellar morphology and dendrites of primary αAl phase were not visually affected by degradation. The average cavity size and pH value of the solution increase with the increasing exposure time, while microstructure degradation rate decreases.