Process Optimization of Controlled Diffusion Solidification with Simultaneous Mixing via Orthogonal Method

The effects of four processing parameters related to the mixing equipment of controlled diffusion solidification (CDS) with simultaneous mixing on the Al–8Si casting microstructure were first investigated by orthogonal test method, taking pure Al and Al–12Si as precursor alloy 1 and precursor alloy 2 respectively. The result indicated that the influence degree decreased in the sequence of mixing crucible diameter, pouring height, mixing rate and pouring distance, due to the reduced variation magnitudes of flow field and vorticity field intensities in the mixed melt revealed by using subsequent one-factor variation method. Specially, a set of optimal parameters was obtained, at which a better mixing effect was achieved than those from all the previous investigations. The final experiment showed that the resulted CDS casting had a quite ideal nondendritic microstructure with primary grain size of 38.56 μm and shape factor of 1.28. More importantly, the casting had good tensile properties, and the yield strength, ultimate tensile strength and fracture elongation were 18.9, 28.6 and 165.5% higher than those of the traditional casting counterpart, respectively, attributing to the significant decrease and even elimination of shrinkage porosities, as well as the refinement of eutectic Si phases.