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In this study, different contents (0.0, 0.1, 0.2, and 0.4 wt.%) of Zr55Cu30Al10Ni5 amorphous alloys (Zr-AA) are used to manipulate hypereutectic Al-Si alloys. The edge-to-edge model shows that there is a perfect lattice matching between the crystallized phases and α-Al and Si phases. The thermal analysis of solidification behavior of hypereutectic Al-Si alloys unmanipulated and manipulated by Zr-AA, indicates that the addition of Zr-AA greatly promotes the nucleation of primary Si and significantly accelerates the process of eutectic reaction. When manipulated by the optimal content of 0.2 wt.% Zr-AA, the sizes of α-Al dendrites and primary Si decrease from 212.46 μm and 19.24 μm to 143.39 μm and 16.47 μm, respectively. The eutectic Si changes from needle-like to rod-like and exhibits a mean size decrease from 20.21 μm to 11.69 μm. Meanwhile, alloys exhibit ultimate tensile strength of 362 MPa and fraction strain of 2.21% after 0.2 wt.% Zr-AA manipulation, which are 23% and 37% higher than those of the unmanipulated alloy (295 MPa and 1.61%). The strengthening mechanisms of hypereutectic Al-Si alloys manipulated by in situ nanocrystals crystallized in the melt are mainly attributed to the fine grain strengthening effect and precipitation strengthening effect. The increase in plasticity is due to the refinement and morphology improvement of Si phases.

In this study, the thermal stability of Ni–Nb–Ti metallic glasses was investigated under isothermal and non-isothermal conditions. The effectiveness of NiTi phases, one of the nanosized crystallized phases, as grain refiners for Al–Cu alloys was also investigated from a crystallographic point of view using the edge-to-edge matching (E2EM) model. Thermal analysis showed that NiTi phases promote solidification of α-Al, and these nanocrystalline phases also promote an Al–Cu eutectic reaction and inhibit the growth of eutectic phases. A significant refining effect of α-Al grains from 402.7 μm to 69.1 μm was achieved with 0.05 wt.% nanocrystalline phases. Simultaneously, values for yield strength, ultimate tensile strength and fracture strain of inoculated Al–Cu alloys were increased by 18%, 13% and 78% to 363.2 MPa, 534.3 MPa and 11.92%, respectively, when compared with those of uninoculated Al–Cu alloys. Strengthening mechanisms of Al–Cu alloys manipulated by the nanocrystalline phases are grain boundary strengthening and precipitation strengthening.

This experiment aimed to design a method to alter the multi-microstructure of Al-13Si-5Cu-0.6Mg alloys by in situ nano-intermetallics crystallized from Fe-B-Si metallic glasses. The results showed that for alloys manipulated by Fe2B and Fe3Si nano-intermetallics, the sizes of α-Al dendrites and eutectic Si were refined. In addition, the precipitates of β-Mg2Si and θ' phases were significantly refined and were evenly distributed in the matrix. The average sizes of the α-Al dendrites, the eutectic Si structure, and the θ' and β-Mg2Si precipitates were greatly reduced by 63.6 %, 50.0 %, 30.1 % and 80.6 %, respectively. In the refinement mechanism, the Fe2B and Fe3Si phases, which had excellent lattice mismatch with α-Al and Si, can be used as heterogeneous nucleation sites. Furthermore, the alloy manipulated by nano-intermetallics showed excellent strength and fracture strain at room and high temperatures, respectively. In particular, the treated alloy achieved an ultimate tensile strength (UTS) of 238 MPa at 250 °C, which is similar to the effect of Ni addition on high-temperature tensile properties. With this design, nano-intermetallics as refiners provide a new method for developing high-temperature lightweight alloys with high efficiency and low cost.

This experiment aimed to design a method to alter the multi-microstructure of Al-13Si-5Cu-0.6Mg alloys by in situ nano-intermetallics crystallized from Fe-B-Si metallic glasses. The results showed that for alloys inoculated by Fe2B and Fe3Si nano-intermetallics, the sizes of α-Al dendrites and eutectic Si were refined. In addition, the precipitates of β-Mg2Si and θ' phases were significantly refined and were evenly distributed in the matrix. The average sizes of the α-Al dendrites, the eutectic Si structure, and the θ' and β-Mg2Si precipitates were greatly reduced by 63.6%, 50.0%, 30.1% and 80.6%, respectively. In the refinement mechanism, the Fe2B and Fe3Si phases, which had excellent lattice mismatch with α-Al and Si, can be used as heterogeneous nucleation sites. Furthermore, the alloy inoculated by nano-intermetallics showed excellent strength and fracture strain at room and high temperatures, respectively. In particular, the treated alloy achieved an ultimate tensile strength (UTS) of 238 MPa at 250 °C, which is similar to the effect of Ni addition on high-temperature tensile properties. With this design, nano-intermetallics as refiners provide a new method for developing high-temperature lightweight alloys with high efficiency and low cost.

AlCu alloys inoculated by in-situ nano-sized particles crystallized from Ni-Nb-Ti amorphous alloys were prepared by casting method in this work. Different compositions of Ni-Nb-Ti amorphous alloys significantly enhanced heterogeneous nucleation for α-Al and promoted obvious grain refinement of the AlCu alloys. It was found that 0.05 wt% Ni-Nb-Ti amorphous alloys addition caused a significant and efficient refinement on α-Al (from 200 μm to 39 μm) and θ′ phase (from 146.4 nm to 37.6 nm). The strength and ductility of the inoculated alloy were improved significantly at high temperature. The tensile strength and fracture strain of the alloy inoculated by 0.05 wt% Ni-Nb-Ti amorphous alloy for 20 min at 533 K under the strain rates of 10−1 s−1 were increased by 32.63% and 90.35% respectively, compared to those of the uninoculated alloy. The nano-sized NiTi particles contributed to the grain refinement of α-Al, and grain refinement shortened the solute atomic diffusion distance and refined θ′ phase during heat treatment, resulting in higher strength and plasticity at high temperature. The model developed for this new type AlCu alloy is found to be efficient in predicting the stress at 453 K–533 K under the strain rates of 10−4 s−1 to 10−1 s−1. Keywords: In-situ nanocrystals, Amorphous alloys, Microstructure refinement, Mechanical properties, Precipitates, Stress prediction model