Pressureless infiltration of Al-Mg based alloys into Al₂O₃ preforms: mechanisms and phenomenology

Abstract

Al-Mg based alloys have been infiltrated into Al₂O₃ preforms by pressureless infiltration in nitrogen atmosphere at and above 800°C. The study revealed the twin role of Mg in initiation and in continuation of infiltration. Mg reduces the alumina layer on the Al-alloy surface thereby bringing about the contact between the melt and the preform, which marks the initiation of infiltration. It has been determined that the premature termination of infiltration is related to localised depletion at the infiltration front of Mg, which getters the residual oxygen in the nitrogen thereby making the front free of passivating alumina or spinel. Evaporation of Mg from the front and reaction of Mg with the reinforcement are the principal causes for depletion. Two methods have been devised to avoid/delay termination thereby making it possible to fabricate useful section thicknesses with minimal Mg in the alloy.