Effect of eutectic Si on surface nanocrystallization of Al-Si alloys by surface mechanical attrition treatment

► During surface mechanical attrition (SMAT) process of Al-Si alloy, unlike Al matrix, the eutectic Si is refined through direct breakage. ► The refined Si particles, in turn, promote grain refining of the Al matrix. Thus, the nanocrystalline grains in the A356 alloy are much smaller. ► Under the present SMAT conditions, for a particular alloy the grains within the top nanocrystalline region cannot be refined indefinitely. ► The minimum grain size not only depends on the nature of the alloys, but also relies on the strain rate applied to the alloy.