Characterization of some types of oxide inclusions in aluminum alloy castings

摘要

Some aspects of molten aluminum oxidation during turbulent handling operation are discussed. Melt transference and mold pouring have been considered the most critical operations, since a large quantity of melt surface is exposed and in contact with the air. Amorphous alumina film is presented as the product of direct oxidation of melt. Its instability and the dependence of resultant alumina inclusion type with the formation age are presented. Turbulent mold pouring is associated with the formation of amorphous alumina film inclusions ("young film"). Turbulent melting operation and metal transference to ladles or to holding, furnaces are associated with generation of crystalline γ-Al{sub}2O{sub}3, films ("old film"). Accumulation ofγ-Al{sub}2O{sub}3 films at the crucible walls is presented as the main cause of' the transformation of γ-Al{sub}2O{sub}3 toα-Al{sub}2O{sub}3 that constitutes the "hard spots" inclusions. The most important characteristics of each type of alumina inclusion are described and their aspects are presented as observed in the optical and scanning electron microscope.