Comparison of flow behaviour and microstructure and texture development of aluminium alloy A356 in semisolid state submitted to two different thermomechanical treatments

摘要

In the present work, an ingot of a commercial aluminium alloy, A356 (Al-7Si-0.3Mg), was deformed by rolling; a second ingot was extruded; and a third was cast in such a way as to obtain fine sized dendrites. All specimens were partially remelted in a salt bath, and water quenched. Microstructural examination indicated that the particle growth rate was reasonably similar for all specimens; however, while rolling gave an almost ideal microstructure of equiaxed particles, extrusion produced microstructural heterogeneities that led to abnormal grain growth and liquid segregation. Texture studies indicated that the rolled specimen recrystallised during heating to the semisolid state, while the extruded specimen recrystallised immediately after deformation. Simple compression experiments (parallel plates) showed that for high solid fractions (0.80) the extruded material exhibited the highest deformation response among specimens, but when the solid fraction was lower (0.60) the deformation behaviour of as cast, extruded, and rolled specimens was similar. Skeleton formation and liquid segregation were found to be associated with both non-spherical morphologies and high solid fractions.