Microstructures and hardness of A356-SiC composites produced by the mechanical stir casting

The present research was aimed to investigate the carbide distribution and hardness in A356-SiC composite produced by stir casting. The particle size of reinforcingphase was 37 mu m silicon carbide with loading content of 5, 10, 15 and 20 percent by weight. In the casting process, molten composite was stirred by the rotor blades with a stirring speed of 300 rpm. Molten A356 was continuously stirred during cooling from superheated liquid state to a semi-solidtemperature of 615 degrees C. During stirring the SiC powder was slowly added into the melt and continuouslystirred for another 15 min. The melt was then poured into a stainless moldat the pouring temperature of 680 degrees C. The results showed that silicon carbide was uniformly distributed in the A356 in all conditions. SEM micrographs showed that the interface between the matrix and reinforced particles of 5, 10 and 15percent SiC exhibited well bonding. However, at a composition of 20 percent SiCby weight, small cracks were found at the interface between a reinforced phase and the matrix phase. Hardness values of composite material of 5, 10, 15 and 20 percent were 69.87, 71.09, 74.05 and 71.01 HB, respectively. (C) 2017 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of The 10th Thailand International Metallurgy Conference.