A356-series Al-Si-Mg alloys are subjected to SiO 2 sand erosion when they are used as the molding die in automatic molding to prepare sand mold for casting. In the current investigation, SiO 2 sand erosion of the as-cast and T6-treated A356.2 alloy was studied. To simulate the erosion during the sand-filling process in automatic molding, two test conditions of about 36 and 66 m s - 1 average particle velocities were chosen. The results show typical ductile erosion behavior with maximum erosion rate at oblique impact, although brittle cracking of eutectic Si particles occurs. An ultrafine-grained surface layer which is mixed with fine SiO 2 particles can be observed on top of the strain-hardened dislocation cell region. Erosion of the T6 specimens leads to dissolution of the Mg 2 Si precipitates. Owing to this softening effect, the T6 treatment does not improve the erosion resistance.