2014 Volume 55 Issue 11 Pages 1727-1732
Semi-solid forging of a high strength Al alloy was carried out to investigate the macro-segregation characteristics in regard to the evolution of solidification microstructures. The evolution of segregation was closely affected by the feeding behavior of semi-solid slurries. Two types of macro-segregation were found in semi-solid forging: one is composed of fine dendritic α-Al particles caused by liquid segregation and the other is the residual eutectic segregation. The formation of these segregations was strongly affected by the quality of semi-solid slurries, such as the shape and the size of the primary α-Al particles. In the case of coarse dendritic microstructures, α-Al particles are easily interlocked with each other, resulting in the formation of macro-segregation. In the case of fine and uniform globular microstructures, primary globular α-Al particles can be readily filled into a die cavity during forging, leading to uniform microstructures without the formation of macro-segregation. Optimization of process parameters was carried out both for semi-solid slurry making and for semi-solid forging. The T6 heat treatment was carried out, and hardness distribution on the semi-solid forging specimens was also evaluated to investigate the effect of macro-segregation on mechanical properties.