Search

Trace in situ nanocrystals crystallized from metallic glasses as innovative microstructure manipulation agents were proposed to manipulate the multilevel microstructure configuration of eutectic Al–Si13.0–Cu5.0–Mg0.6 alloy. And the manipulation effect by nanocrystals for different times was compared with Sr, nanocrystals + Sr and Ni alloying. The calculations indicated that NiTi nanocrystals had an ideal mismatch with α-Al and silicon; thus, nanocrystals can stimulate their nucleation and hinder their growth. Sr and Ni alloying were found to only refine the silicon phases, but nanocrystals refined both α-Al and silicon phases. Moreover, the inhibition of nanocrystals and Sr was verified. After the manipulation by nanocrystals for 20 min, the optimum microstructure configuration and mechanical properties were realized. The results showed that the size of α-Al was reduced by 86.7%, and the size and aspect ratio of eutectic silicon were decreased by 27.7% and 50.0% compared with that of the unmanipulated alloy. Primary silicon was distributed more evenly and reduced in number. In addition, the size of Al2Cu and Mg2Si was decreased by 57.7% and 90.6%. Accordingly, a prominent microstructure configuration comprised of refined α-Al, silicon phases and precipitations was established successfully via nanocrystals. Moreover, the ultimate tensile strength (UTS) and fracture strain (FS) were increased by 17.8% and 73.3% compared with that of the unmanipulated alloy at ambient temperature, and the yield strength (σ0.2) and UTS were increased by 21.5% and 14.4% at 250 °C. The specific strengthening mechanisms were revealed, as well. Therefore, in situ nanocrystals have great application potential and developmental value.

Based on the principle of bionics, the lightweight and high-strength the Neptune’s shell was chosen as a bionic model for this study due to its light weight and high strength. Micro-nano mixed-scale dual-phase reinforced aluminum matrix composites were prepared by one-step densification of combustion synthesis combined with hot pressing. We aimed to control the particle size of the ceramic and the ratio of the soft and hard phases by controlling the composition of the composite, and to study the mechanical properties of the biomimetic structure of the composite at normal and high temperatures. The results showed that as the aluminum content in the composite decreased, the ceramic particle size increased and the ceramic particles became evenly distributed in the matrix. Compression testing showed that as the ceramic volume fraction increased the ultimate compressive strength (σUCS) and fracture strain (εf) first increased and then decreased, both at room temperature and at 473 K and 523 K. (TiB2-TiCx)/Al-Cu-Mg composites of 40 vol.% exhibited optimal compressive properties at room temperature and at high temperatures. The increase in the size of the ceramic particles caused an increase in the spacing between the particles, which also weakened the bonding strength between the ceramic particles and the aluminum matrix. Therefore, when the ceramic volume fraction exceeded 40% by volume, the compression properties of the composite tended to decrease. The coupling effect of the layered structure and the soft-hardened structure played a key role in the stability of the biomimetic composite.

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.

An experimental investigation was carried out to study the effects of solid solution treatment and aging treatment on the microstructures and mechanical properties of an Al-13Si-5Cu-2Ni alloy. The results show that the size of eutectic silicon decreased with solid solution treatment temperature increasing until 510 °C. Subsequently, the eutectic silicon size continued to increase as the temperature increased to 520 °C. Initially, the acicular eutectic silicon of the as-cast alloy was 10.1 μm in size. After the solid solution treatment at 510 °C, the eutectic silicon size was reduced to 6.5 μm. The θ′ phase is the main strengthening phase in the alloy, therefore, the effect of aging treatment on θ′ phases was explored. As the aging time increased, the diameter, length, and fraction volume of the θ′ phases were found to increase. The main reason for the improved performance of this alloy following heat treatment is the passivation spheroidization of the silicon phase and Orowan strengthening due to the θ′ phases. The optimal tensile strength of an Al-13Si-5Cu-2Ni alloy was obtained after solid solution treatment at 510 °C for 8 h followed by an aging treatment at 165 °C for 8 h. Therefore, this work has great significance for promoting the application of Al alloys at high temperatures.