Research on Semi-Solid Microstructural Evolution of SiCP/2024pComposite Prepared by Powder Thixoforming

Abstract:

A new technology, powder thixoforming, has been proposed in this paper. Microstructural evolution during partial remelting of the SiC_p/2024 aluminum composite prepared by cold pressing of alloy powders has been investigated. The effects of heating temperature and SiC_p volume fractions (0%~20%) on semisolid microstructure have also been discussed. The results indicate that the microstructural evolution of the 5%SiC_p/2024 composite can be divided into three stages, the initial rapid coarsening of the fine grains within 2024 powders, the formation of continuous liquid layer on the primary particle surface and finally formed the slurry needed by thixoforming with the small and spheroidal solid particles through the spheroidization during heating at 635℃ (0~60 min), which are attributed to the phase transformations of θ→α, θ + α→L and α→L, and α→L, respectively. Proper rising the partial remelting temperature is beneficial for obtaining ideal semisolid microstructure available for thixoforming. The microstructural evolution rate of the composites is slower than that of the matrix alloy. The coarsening rate of the primary particles is quite slow, one powder evolves into one primary particle with a continuous liquid layer surface.

Key words:powder thixoforming; phase transformation; microstructural evolution rate; cold pressing