Study of the Microstructure Semi Solid Al-Si-Mg Casting

Semi-solid metal processing involves processing metallic alloys between the solidity and the liquidity. The microstructure must be non-dendritic and consist of spheroids of solid in a liquid matrix. In this work two potential routes are used: First, The superheated Al-Si-Mg alloy was continuously cooled down to various temperatures above its liquidity (620,630,640) o C . When the desired temperature of the melt has been reached, then mechanical stirring with rotational speed of (800)rpm for (30)sec. was started. The resultant slurry was bottom poured into a stainless steel mold placed below the crucible. The solidified samples were reheated to the semi-solid metal processing temperature, held there for (10) min, and rapidly quenched in into water tank to retain the semi solid microstructures. In the second set of experiments , the superheated melt was continuously cooled down to various temperature in semi solid range (610,600,595,590,580)o C, then mechanically stirred at rotating speed(800)rpm for (30)sec. the resultant slurry was bottom poured into a stainless steel mold placed below the crucible. The metallic mold is then rapidly quenched in water to room temperature. Metallographic examinations indicate that the mixing method leads to highly globular semi-solid slurries of fine particle size. The particle sizes of slurry quenched at various temperatures within the semi solid metal range are much smaller when compared to the reheated structures. The particle size gradually increases as the slurry temperature decrease.