Microstructure evolution of semisolid billet of nano-sized SiCp/7075 aluminum matrix composite during partial remelting process

Microstructure evolution of the nano-sized SiCp/7075 composite during partial remelting process was investigated. The results show the microstructure of the semisolid billet fabricated by rheoforming the semisolid slurry consisted of fine near spheroids and equiaxed grains. Existence and uniform distribution of nano-sized SiC particles have been illustrated by using X-ray diffraction, high resolution scanning electron microscopy and transmission electron microscopy. Grain size of the semisolid billet during the partial remelting process firstly increases and then is followed by a decrease with increasing remelting temperature. Average grain sizes of the semisolid billet upon remelting temperatures of 580 degrees C, 590 degrees C, 600 degrees C and 610 degrees C are 32.4 mu m, 36.3 mu m, 37.5 mu m and 35.3 mu m, respectively. A coarsening trend of solid grain upon soaking for different time at 600 degrees C was found in the microstructure. When the soaking time increases from 0 min to 25 min, the average grain size increases from 25 mu m to 41.7 mu m. Coarsening tends to occur via Ostwald ripening and coalescence. A lower coarsening rate constant of 40.5 mu m(3) . s(-1) is achieved due to hindering action of nano-sized SiC particles to coarsening of solid grains. (C) 2016 Elsevier Ltd. All rights reserved.