Thixocasting Of An A356 Alloy Overview: Tensile Strenght, Porosity And Fatigue Behaviour

Abstract

Near-equiaxed microstructure was obtained in an A356 by the following raw material conditioning processes: (i) deformation-recrystallization thermomechanical treatment (TTM), (ii) magnetic stirring (MHD) and (iii) low pouring temperature (LPT). Specimens for porosity assessment and microstructural studies, for tensile and fatigue tests were obtained from a specially designed thixocast part. Microstructure was described by quantitative features such as particle average radius, interparticle spacing, shape factor and entrapped liquid volume fraction. Results showed a relative uniformity both of microstructure and tensile behaviour, with the MHD and TTM specimens exhibiting a slight advantage. Porosity was found to be minimal, with the LPT material exhibiting the highest level among the three semi-solid specimens. Finally, low cycle isothermal and thermomechanical fatigue tests were performed on the TTM-conditioned material; fatigue life was much longer than that of the permanent mould cast material, a behaviour attributed to its globular microstructure and lower porosity level.