The effects of eutectic silicon on grain refinement in an Al-Si alloy processed by accumulative continuous extrusion forming

Grains of Al-1Si(wt%) alloy were refined by accumulative continuous extrusion forming (ACEF). Electron backscatter diffraction and transmission electron microscopy were used to analyze the microstructure evolution of the Al-1Si(wt%) alloy. The grain size of the alloy decreased from 54.36 to 2.59 mu m after four passes of ACEF. The grain refinement was attributed to continuous dynamic recrystallization (CDRX). The enhanced effect of nanosized precipitates on CDRX was pronounced. Nanosized eutectic Si precipitates retained a high density of dislocations in the alloy by promoting their generation and pile-up, resulting in an increase in the driving force for CDRX and a consequent promotion of grain refinement. After 4 ACEF passes, the tensile yield strength of the alloy at room temperature increased from 102 MPa to 117 MPa. Further, the elongation of the alloy at room temperature decreased from 38 to 17 % after 3 ACEF passes and subsequently increased to 23 % after 4 ACEF passes.