ON THE ORIGIN OF STAINS IN ALUMINUM ALLOY SHEETS

Abstract

Brownished shadows on the surface of twin-roll casting strips origin is explained by the use of semi-empirical alloy theory fundamentals, when applied to non-metallic elements disolved in liquid metals. SEM microstructural features and X-ray line profile of elements and EDAX point analysis are evidences to  support the proposed mechanism formation. Faceted idiomorphs containing Si and Al and also maltese-cross morphologies where B, Cl, Na, K, and Al are second phase particles observed in 6 mm strip thickness in commercial aluminum alloys. Solvent-solute electron donnor-acceptor interaction characteristics in the liquid system show favorable tendencies to Al-Si clusters bonding instead Al-C clusters. However, these Al-C clusters, which are the main cause of the idiomorphic stability, is helped when promotion of high surfactance effects by dissolved halide salt additions lead to their evelopment. During solidification the undissolved immiscible halide salts produce dendritic morphologies that react with humid ambient atmosphere to generate the brownished shadows seen on the strip surface.