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Abstract 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 α-Al (from 1675 µm to 199 µm) and Mg 2 Si 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 µm to 11.89 µm) 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 Fe 2 B and Fe 3 Si nano-sized particles which were crystallized from FeBSi amorphous refiner contributed to the grain refinement of α-Al, resulting in higher strength. Moreover, grain refinement shortened the atomic diffusion distance and refines Mg 2 Si. 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. Graphical abstract fx1 Highlights • The inoculated Al–7Si–0.3Mg alloy appeared as 199 µm fine grains. • The inoculated alloy reached 226 MPa, 343 MPa, 18.4%(δ) and 16.7%(ε f). • This work achieved the refinement of α-Al and Mg 2 Si and the spheroidization of eutectic Si. • The Fe 2 B, Fe 3 Si had better lattice mismatch with α-Al and eutectic Si. [ABSTRACT FROM AUTHOR]

The overall microstructure-manipulated Al-13Si-5Cu-0.6 Mg alloy was successfully fabricated via introducing 0.1 wt% Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator with short time of 60 s, to determine its suitability for applications at room and higher temperatures. The microstructure manipulation mechanism, mechanical properties and strengthening mechanism in manipulated Al-13Si-5Cu-0.6 Mg alloy were discussed. The Zr 55 Cu 30 Al 10 Ni 5 amorphous alloy manipulator provides more nucleation sites in the formation of primary Si, Al Si eutectic and Al 2 Cu. As a result, the optimal microstructure is composed of finer α-Al grains, Al 2 Cu and more rounded primary and eutectic Si, with sizes decreased to ∼52%, 13%, 73% and 42%, respectively. The yield strength, tensile strength, elongation and fracture strain of manipulated Al-13Si-5Cu-0.6 Mg alloy are improved by 22.9%, 16.8%, 58.2% and 47.7% at room temperature than those of the unmanipulated Al-13Si-5Cu-0.6 Mg alloy, respectively. The improved tensile properties at room temperature are attributed to the significant strengthening effect of smaller precipitates and grain refinement while the excellent plasticity is derived from finer α-Al grain, round-corner primary Si and eutectic Si spheroidization. The yield strength and tensile strength are increased by 28.1% and 15.3% at 250 °C, and 28.3% and 10.8% at 300 °C, respectively. The strengthening mechanism at high temperature is mainly the second phase strengthening and the effect of finer eutectic Si on the pinning grain boundary. The overall microstructure manipulation in this work provides better comprehensive mechanical properties and a practicable method to fabricate the Al-Si-Cu-Mg alloy with superior strength and ductility, especially for die-casting alloy with short-time and high-efficiency. [Display omitted] • Fully microstructure-manipulated alloy was made via adding trace nanoparticles. • Nanosized ZrCu(B2) and Zr 2 Cu have ideal lattice mismatch with Si, α-Al and Al 2 Cu. • The sizes of primary Si, α-Al, eutectic Si and Al 2 Cu decreased simultaneously. • The tensile strength and elongation of manipulated alloy are greatly improved. [ABSTRACT FROM AUTHOR]

A new design method of Al-Si-Mg alloy manipulated by in situ nanosized crystals was proposed. Starting from source design of the microstructure manipulation agent with a high crystallographic matching relationship with the α-Al, eutectic Si and Mg 2 Si phases in Al-Si-Mg alloy, the interatomic misfit (f r) between NiTi(B2) and α-Al or Mg 2 Si is 5.0% or 5.3%, respectively, and that between NiTi(B2) and Si is 9.9%, corresponding to good crystallographic matching. Based on calculations, in situ nanosized crystals could be considered as heterogeneous nucleation sites of α-Al, eutectic Si and Mg 2 Si, thus, uniformly fine α-Al grains, near-spherical eutectic Si and fine precipitated Mg 2 Si were obtained. The solidification behavior analysis also highly corresponded to the E2EM calculations. In the alloy manipulated by 0.05 wt% NiNbTi manipulation agent, the average sizes of α-Al, eutectic Si and Mg 2 Si were greatly decreased by nearly 8, 2 and 20 times, respectively, thus achieving comprehensive multiscale manipulation of the microstructure of the alloy in one step. Specially, the huge energy stemmed from the B2 to B19' phase transformation will generate a large number of crystal defects, which provides nucleation sites and driving force for the formation of Mg 2 Si and greatly refines the Mg 2 Si.Moreover, the yield stress, tensile stress and fracture strain of the manipulated alloy were simultaneously improved by 34.1%, 20.4% and 35.0%, respectively. The excellent strength and plasticity could be ascribed to grain-refinement strengthening, Orowan strengthening and eutectic Si refinement and spheroidization, which reduced the stress concentration during deformation. The comprehensive microstructure manipulation of Al-Si-Mg alloy using nanosized crystals formed by in situ physical crystallization, especially the manipulation of the precipitated phase, is an innovative work that not only avoids the "poisoning" effect between multiple manipulation agents but also realizes comprehensive manipulation of the overall microstructure, consequently broadening further industrial applications. • The low fr shows good mismatch between Al, Si, Mg 2 Si and NiTi. • The new method achieves multiscale manipulation of the alloy in one step. • The mean sizes of α-Al, eutectic Si and Mg 2 Si were decreased by nearly 8, 2 and 20 times. • The yield strength and plasticity were simultaneously improved by 34.1% and 35.0%. [ABSTRACT FROM AUTHOR]