High temperature tensile properties and long-term thermal stability play an important role in practical applications of Al-Zn-Mg-Cu alloys. In order to evaluate the effect of Er addition on the properties of an Al-Zn-Mg-Cu alloy as potential high temperature structural materials, the heat resistance properties of an Al-Zn-Mg-Cu alloy were investigated at various temperatures. After high temperature tensile testing and long periods of heat exposure testing, the microstructures of Al-Zn-Cu-Mg alloys with and without small Er addition is intentionally investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and quantitative transmission electron microscopy (TEM) characterization to explore the potential effect of Er on the tensile properties. The experimental results reveal that the heat resistance of T76-tempered Al-Zn-Cu-Mg alloy is obviously improved by adding trace Er. The Al₈Cu₄Er phase is found to segregate at the localized regions along grain boundaries and strengthens the grain boundaries at elevated temperatures. The η′ and η precipitation is obviously promoted by adding trace Er, and dispersed nano-sized Al₃(Er, Zr) precipitates were formed in the Er-containing alloys after homogenization, thereby enhancing the strength of Al-Zn-Mg-Cu. In addition, precipitates in both alloys gradually coarsen with the increase in thermal exposure temperature and the extension of thermal exposure time. The influence of precipitates on mechanical properties of the investigatived alloy after thermal exposure is also discussed.

Fluorinated carboxylate ester solvents are promising electrolyte components for lithium metal batteries because they can improve oxidative stability and promote LiF-rich solid electrolyte interphase (SEI) formation. However, how fluorination position and degree regulate their intrinsic decomposition behavior on lithium metal remains unclear. Herein, density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations were employed to systematically investigate six pure fluorinated ethyl acetate solvents on the Li(001) surface, including α-fluorinated ethyl fluoroacetate (EFA), ethyl difluoroacetate (EDFA), and ethyl trifluoroacetate (ETFA), as well as β-fluorinated 2-fluoroethyl acetate (FEA), 2,2-difluoroethyl acetate (DFEA), and 2,2,2-trifluoroethyl acetate (TFEA). Electronic-structure analysis shows that although the lowest unoccupied molecular orbitals (LUMOs) of all six solvents are mainly distributed around the carbonyl and adjacent regions, the dominant electron-accepting center strongly depends on the fluorination position. In α-fluorinated solvents, the LUMO is highly localized on the α-C atom directly bonded to fluorine, whereas in β-fluorinated solvents, it remains concentrated around the carbonyl C atom. Real-time Bader charge and bond-evolution analyses reveal that fluorination position is the primary factor governing the initial decomposition pathway. The α-fluorinated series preferentially undergoes C-F bond cleavage, and increasing fluorination degree induces deeper cascade decomposition; fully fluorinated ETFA even exhibits C=O double bond cleavage. In contrast, β-fluorinated solvents preferentially undergo carbonyl-side C-O bond cleavage, while C-F bond cleavage occurs only in subsequent steps or is completely suppressed. Notably, β-fluorinated solvents retain high chemical stability even with α-H atoms because the LUMO electron density on α-H is negligible. Meanwhile, limited deep decomposition can still provide F⁻ species for SEI formation. These findings establish an atomic-level structure–reactivity relationship for fluorinated carboxylate ester solvents and provide theoretical guidance for designing stable electrolyte solvents for lithium metal batteries.