Zhongping Que

Commercial aluminum (Al) metals contain unavoidable impurities, such as iron (Fe) and silicon (Si). Due to its low solubility and high chemical affinity to Al, Fe exists in the form of Fe-containing intermetallic compounds (Fe-IMCs), which are crucial in solidification processes, determining the micro-structure and consequently the mechanical performance of the cast parts. Meanwhile, Si, as an impurity or addition, may join the binary Fe-IMCs. Here, we investigate the Si stabilization effects on the frequently observed Al-rich Fe-IMCs in a comprehensive and systematic way using a first-principles density-functional theory (DFT) approach. The study reveals different Si stabilization effects on the cubic α- and hexagonal α’-phase, as well as other binaries: Al₁₂Fe, η-Al₆Fe, τ₄-, β-, and θ-phases. The enhancement of stability for the α-phase is moderate, while it is strong for the α’-phase. For the stability series (from higher to lower) is θ-Al₁₃Fe₄ > η-Al₆Fe > α-Al₄.₇₅Fe in the binary system, while it becomes τ₄-(Al,Si)₅Fe > β-Al₄.₅SiFe > α’-(Al,Si)₄.₁₇₄Fe for the ternary Fe-IMCs. The information obtained here helps understand the formation of Fe-IMCs particles during casting of Al-Si alloys, and the design of novel Al alloys of fine micro-structures and desired mechanical performances of the products from the primary Al and the scraps and wastes.

Commercial aluminum (Al) metals contain unavoidably iron (Fe) and silicon (Si) as impurities. Due to its low solubility and high chemical affinity to Al, Fe exists in the form of Fe-containing intermetallic compounds (Fe-IMCs) which act crucially in solidification processes, determining the micro-structure and consequently the mechanical performance of the cast parts. Meanwhile, Si as impurity or addition may join the binary Fe-IMCs. Here, we investigate the Si stabilization effects on the frequently observed Al-rich Fe-IMCs in a comprehensive and systematical way using a first-principles density-functional theory (DFT) approach. The study revealed different Si stabilization effects on the cubic α- and hexagonal αʹ-phase, as well as other binaries: Al₁₂Fe, η-Al₆Fe, τ₄-, β- and θ-phases. The enhancement of stability for the α-phase is moderate while it is strong for the αʹ-phase. For the stability series (from higher to lower) is θ-Al₁₃Fe4 > η-Al₆Fe >α-Al_4.75Fe in the binary system, while it becomes τ₄-(Al,Si)₅Fe>β-Al_4.5SiFe >αʹ-(Al,Si)_4.174Fe for the ternary Fe-IMCs. The information obtained here helps understand the formation of Fe-IMCs particles during casting of Al-Si alloys, and design of novel Al alloys of fine micro-structures and desired mechanical performances of the products from the primary Al and the scraps and wastes.

The seismic design of aluminum alloy structures requires specific attention due to the material’s distinct mechanical properties compared to steel, which renders direct application of steel joint design methods inappropriate. This study investigates the seismic behavior of T-shaped aluminum alloy beam–column bolted connections, which consist of 6061-T6 aluminum alloy beams and columns connected by S304 stainless steel connectors via high-strength bolts. A finite element model, incorporating a mixed hardening constitutive model for accurate cyclic response, is established and validated against low-cycle cyclic loading tests. Parametric analyses evaluated the influence of L-shaped connector dimensions on hysteresis response, skeleton curves, stiffness degradation, energy dissipation, and ductility. Results demonstrate that increasing the thickness of the short leg of the L-shaped connector between the beam flange and column flange significantly enhances the ultimate bending moment, with an increase of up to 36.7% per 2 mm increment, alongside improved energy dissipation and ductility. Stiffness degradation follows a natural exponential decay, with residual stiffness between 23.85% and 32.57% at ultimate deformation. An efficiency analysis identifies the most cost-effective measures for seismic design. The primary novelty of this work lies in the successful application and validation of a mixed hardening model for simulating the complex cyclic behavior of T-shaped aluminum alloy connections, coupled with a systematic efficiency-oriented parametric study. The findings offer practical, quantitative guidelines for designing aluminum alloy bolted connections in seismic-prone regions.

Al–Ti–B-based grain refiners have been successfully used in the aluminium industry for more than six decades. Recent advancements have demonstrated that manipulating the nucleation potency of substrates through interfacial segregation can enhance the heterogeneous nucleation of both single-phase and intermetallic compounds by providing structural and compositional templating. However, the segregation of Fe and Si, two of the most common alloying elements or impurities in Al alloys, on TiB₂ surface and its subsequent effects are not fully understood. In this work, TiB₂ particles were synthesized in an Al–3.7Ti–1.5B alloy melt containing 0.43 wt pct excess free Ti, followed by isothermal treatment to promote Fe and Si segregation on the TiB₂ surface. The segregation behaviour of Fe and Si on different terminated surfaces of the TiB₂ particles was investigated using scanning transmission electron microscopy (STEM). The experimental results show that Fe and Si exhibit distinct segregation behaviours depending on the atomic configuration of TiB₂ surfaces, leading to the formation of two-dimensional compounds (2DCs) at the Al/TiB₂ interfaces. The formation of interfacial segregation layers has been shown to profoundly affect subsequent solidification, particularly nucleation and growth processes of intermetallic compounds (IMCs) in the alloys, resulting in significant refinement of these phases and the final solidification microstructure. In part 1, this research focuses on investigating the nature of interfacial segregation of Fe and Si on TiB₂ particles. Experimental results concerning the segregation and the characterization of the structure and chemistry of the resulting interfacial layers are presented. In the subsequent Part II, the investigation will address the effects of Fe and Si interfacial segregation on the solidification behaviour of Al alloys, with particular emphasis on the heterogeneous nucleation and refinement of primary Fe-bearing intermetallic compounds and the primary Si phase in Al–Fe–Si and Al–Si alloys. Graphical Abstract