Hongkui Mao

The microstructural evolution and mechanical properties of a dual-phase Mg-9Li-4Al-1.5Zn-0.2Ca alloy subjected to 30 d of natural aging followed by solution treatment at 350 °C were systematically investigated. After natural aging, the alloy exhibited pronounced interphase partitioning of Al, multiscale second-phase particles, and a high density of deformation-induced defects. After solution treatment at 350 °C х 0.5 h, the Al-Zn-rich particles were partially dissolved, promoting solute redistribution, while MgLi2Al-type nanoprecipitates, Al2Ca particles, and dislocation structures were largely retained. Consequently, the ultimate tensile strength increased from 288 to 372 MPa, while a high elongation of 14.8% was maintained. With increasing holding time, Al progressively evolved toward a more homogeneous distribution between the two matrix phases. Distinct precipitation behaviors were observed within the β-Li grains and at the α-Mg/β-Li interfaces, accompanied by dislocation rearrangement and phase coarsening, resulting in non-monotonic variations in strength and ductility. These results demonstrate that the strengthening response during solution treatment after prolonged natural aging is governed by the synergistic effects of second-phase dissolution, solute redistribution, spatially heterogeneous precipitation, and defect-structure evolution.

First-principles calculation is widely used to study solid-solid interfaces, which provides insights into the atomic and electronic structure of an interface including the interfacial stability and adhesion strength. In general, the interface of the Fe/Al₂O₃ composite material is hardly wetted, and the aluminum oxide layer is firm and thin. It is difficult to observe the interface via an electron microscope. Thus, the changes at the interface were studied by first-principles calculations. Interfacial stability, energy of the Fe (111) surface, the Al₂O₃ (0001) surface, and Fe (111)/Al₂O₃ (0001) interfaces were studied using the first-principles calculation method. The work of adhesion (W_ad), interface energy (γ_int), and the electronic structure of Fe (111)/Al₂O₃ (0001) interfaces were studied. The results indicated that W_ad of the O-terminated interface was significantly larger than that of the Al-terminated interface. The O-terminated interface was the most stable interface. Furthermore, the O-terminated interface consisted of strong polar covalent bonds and weak metallic bonds, while the Al-terminated interface primarily consisted of covalent and metallic bonds. Furthermore, the segregation of Al atoms at the interface enhanced the stability of the interface structure, and interfacial bonding ability was increased with the increase in aluminum atoms. Only aluminum atoms diffused through the initial oxide layer forming intermetallic compounds on the iron side. The inclusion of Al₂O₃ significantly impacts the mechanical properties of steel, such as toughness and fatigue, underscoring that it is important to predict and control the inclusions in steel to obtain desired mechanical properties. The insights obtained from the study described here provide fundamental insights and guidelines into tailoring the steel/aluminum composite interface.