Efficient microstructure refinement of Al-Si-Mg alloy manipulated by nanocrystals formed by in-situ crystallization in melt

Al-Si-Mg alloys manipulated by in-situ synthesized nanoparticles have been prepared by casting method in this work. The addition of different contents of refiners promoted the obvious grain refinement of the Al-Si-Mg alloys. It was found that 0.10 wt% refiners addition caused a significant and efficient refinement on a-Al (from 1675 mu m to 199 mu m) and Mg2Si in the inoculated Al-Si-Mg alloys. The morphology of the eutectic Si in the inoculated Al-Si-Mg alloys transformed from needle-like structure to a fibrous one, and the mean size sharply decreased (from 26.56 mu m to 11.89 mu m) and increased a little with the increase of FeBSi amorphous refiners content. Tensile property tests showed that both strength and ductility of the alloys were improved by the addition of FeBSi amorphous refiners. The yield strength, tensile strength, fracture strain and elongation of the alloy inoculated with 0.10 wt% FeBSi amorphous refiners for 20 min were 226 MPa, 343 MPa, 18.4% and 16.7%, compared to those of the uninoculated alloy (170 MPa, 289 MPa, 13.7% and 12.2%), respectively. It was found that the Fe2B and Fe3Si nano-sized particles which were crystallized from FeBSi amorphous refiner contributed to the grain refinement of alpha-Al, resulting in higher strength. Moreover, grain refinement shortened the atomic diffusion distance and refines Mg2Si. The grain refinement and spheroidization of eutectic Si enhance uniform deformation during tension, and reduce the possibility of crack initiation and expansion, thus improving the plasticity.