The microstructural evolution during semi-solid processing
and thixoformability of a 7075 alloy prepared by conventional and new modified strain induced melt activation
(SIMA) processes were comparatively investigated in this
paper. The semi-solid slurries were thixoformed at 600 8C,
at which temperature the solid fraction was estimated to be
0.8. The coarsening process of the semi-solid samples was
described using Lifshitz–Slyozov–Wagner theory and the
effect of pre-deformation on the coarsening kinetics of the
solid particles was discussed. The coarsening rate constant
of the new modified SIMA sample showed a remarkable
decrease compared to that of the conventional SIMA sample. Microstructural and mechanical investigations indicated that the sample with a near-equiaxed microstructure
deforms through the plastic deformation of solid grains
mechanism. However, the sliding of solid grains and flow
of liquid incorporating solid grains mechanisms were dominant in the sample with a globular microstructure. Also, it
was observed that the yield and ultimate strengths and hardness of the sample prepared by the new modified SIMA
process after thixoforming and T6 heat treatment increased
by about 15%, 10% and 25% respectively, compared to
those of the conventional SIMA sample.