Efficient fabrication of semisolid nondendritic Al alloy slurry with high quality

Subjecting a normal mechanical vibration to a cooling slope plate,is a proposed method for preparing semisolid nondendritic slurry,named shear-vibration coupling sub-rapid solidification(SCS).Taking Al-8Si alloy as model material,the temperature field and distribution field of solid or liquid phase during SCS were simulated using COMSOL Multiphysics software to primarily choose the optimal processing parameters.Subsequently,the slurries were prepared with the parameters selected according to the simulation results and the microstructures of the slurries were experimentally investigated.Results indicate that the simulation results could provide a basis for roughly choosing the processing parameters,although the calculated solid fractions are always higher than the experimental ones.The processing parameters affect the primary grain size,shape factor and solid fraction mainly through altering the contact duration of melt on the plate,and thus affecting the cooling effect on the melt,nucleation rate,and grain dissociation and proliferation.Experiments with optimized processing parameters show that the primary grains in the slurry have an average size of about 32μm and shape factor of 1.38,and are quite uniform,even at the highest pouring rate of 2.81 kg·s^(-1),the size and shape factor are about 46μm and 1.7,respectively,which implies that the proposed SCS is a promising technology for efficient fabrication of high-quality Al slurry available for engineering applications.

Effect of mixing temperature on microstructure of an Al-Si alloy prepared by controlled diffusion solidification

The effects of mixing temperature,i.e.,the temperatures of two precursor melts(pure Al and Al-12Si),on the temperature and solute fields of resultant mixture,the nucleation and growth,and the size and morphology of primary grains during controlled diffusion solidification(CDS) of Al-8Si alloy were investigated by using simulation and calculation.The results indicate that a lower mixing temperature is helpful for achieving more supercooled microscale Al-rich pockets in the mixture,and increasing the width and supercooling degree of supercooling zone in the Al-rich pockets,and thus,the nucleation rate.The nuclei grow up in nondendritic mode,resulting in spheroidal,at least,nondendritic grains.In a successful CDS,the superheat degrees of the two precursor melts should be limited within several degrees,and it is not necessary to extra stipulate the superheat degree of target alloy melt(Al-8Si) when the requirement about Gibbs energies of the three melts is matched.Subsequent observation on casting microstructures shows that the employed simulation and calculation processes are reasonable and the achieved results are reliable.