Semisolid microstructural evolution of (CNTs + Sip)/AZ91D powder compacts prepared from powders by cold pressing and remelting

The evolution of semisolid microstructure during partial remelting of (CNTs + Si-p)/AZ91D powder compacts prepared by cold pressing was studied. The results indicate that rapid grain coarsening is driven by the dissolution of eutectic beta phase material during the initial heating period of 0-10 min, so the AZ91D powders with fine equiaxed grains surrounded by intergranular eutectic phases evolve into compact particles. As the heating time proceeds, alpha-Mg particles were gradually separated by liquid due to the phase transformations of alpha-Mg + beta -> L and alpha-Mg -> L. The primary particles coarsened rather slowly and the as-received Mg powder evolved into nearly spheroidal particles surrounded by liquid phase after partial remelting. The in situ synthesized Mg2Sip were distributed homogeneously around the CNTs with maintained structural integrity during partial remelting. Moreover, this microstructural evolution was accompanied by densification through pore filling. An ideal semisolid ingot suitable for thixoforming can therefore be obtained by partially remelting a (CNTs + Si-p)/Mg powder compact.