Macrosegregation in indirectly squeeze cast Al-0.9wt%Si

Cylindrical, compact components of the Al-0.9wt%Si alloy have been indirectly squeeze cast to study pressure induced macrosegregation. The influence of different process parameters such as pressure, die temperature, melt temperature and grain refinement has been investigated. With the grain refined Al-0.9wt%Si alloy, a significant region of macrosegregation was observed to be located around the centerline of the casting, and a smaller region of segregation was located in the vicinity of the hot spot of the biscuit. The typical centerline segregation started above the gate as a cylinder enveloping unsegregated material, gradually converging to centerline segregation. The biscuit segregation formed as either a concentrated pocket in the hot spot or as strings radiating into the hot spot. The segregation pattern varied little when changing the casting parameters; only the amount of segregation was affected. The non-grain-refined Al-0.9wt%Si alloy contained macrosegregation located around the centerline, but not as significant as in the grain refined squeeze castings. More segregation was, however, located at the hot spot of the biscuit. A critical pressure had to be exceeded to obtain dense castings. gs with a long biscuit contained less segregation than castings with a short biscuit.