Generation of dislocations and subgrains in semisolid al-6.2wt%Si alloy

Abstract

Generation of large amount of tangled dislocations and subsequent formation of subgrains by the pile-up of the dislocations in the stircast Al-6.2wt%Si alloy has been observed through a detailed transmission electron microscopy. The misorientations between the subgrains were measured by selected area diffraction patterns and convergent beam electron diffraction (CBED) patterns. The density and the degree of entanglement of dislocations increased with the increase of solid fraction, shear stress and shear rate. Longer isothermal stirring time gave rise to higher dislocation density and smaller subgrain size. The melt-off of high-angle boundaries which was suggested by Vogel-Doherty-Cantor’s grain boundary melting model is supported by the observation of the subgrains within the primary solid particles due to the generation and subsequent pile-up of the extremely large amount of dislocations during semi-solid stirring.