Microstructure and rheological behavior of grain refined and modified semi-solid A356 Al–Si slurries

Abstract A comprehensive study was carried out to establish the effect of melt treatment using Ti–B grain refiner and Sr modifier additions on the microstructural evolution and rheological properties of A356 aluminum alloy in the semisolid state. Rheocast billets of 75 mm in diameter and ∼140 mm in length, prepared by the SEED process, were deformed and several parameters were investigated to characterize the flow behavior of the billets in a compression test. Strain–time graphs were used to calculate the viscosity and liquid segregation was monitored to identify the optimum conditions for melt treatment. It is shown that non-treated alloy has the highest apparent viscosity. Refined semisolid billets have smaller particle size and more globularity of primary α-Al particles and as a result deform and flow more easily. It is postulated that modifier addition reduces the liquid surface tension and leads to improved deformability.