<p>  The microstructure of AC4CH (Al-7%Si-0.45%Mg) alloy castings with different semi-solid die casting conditions (Sleeve filling ratio: SFR and Shot time lag: STL) was investigated to determine the generation mechanism of very-fine globular α-Al phases (diameter: under 15μm). In the case of SFR of 10% with STL of 10 seconds, a larger number of very-fine globular α-Al phases were observed between the globular α-Al (under 50μm) phases at the product surface compared to SFR of 30% and 50% with STL of 10 seconds. The size of the very-fine globular α-Al phases was about 5μm on the product surface and under 15μm at the product center. The very-fine globular α-Al phases at the product surface were coarser in the case of SFR of 10% with STL of 0 seconds than those of STL of 10 seconds, and their size was under 15μm. These results suggest that there exist conditions for promoting the generation of very-fine globular α-Al phases in the melt at the stage of reaching the eutectic temperature in case of the low sleeve filling ratio.</p>