Abstract: Hypervelocity impact phenomena are commonly observed in various fields, including spacecraft shielding against space debris, military armor damage assessment, and the formation of astrophysical craters. However, the dynamic response of finite-thickness metal plates under hypervelocity impact still necessitates further exploration. In particular, the propagation of shock waves within materials and the resulting interface-evolution mechanisms require in-depth study to quantitatively inform the design of protective structures. To this end, this study investigates the hypervelocity impact of a stainless-steel sphere on an aluminum plate by numerical simulation. A two-dimensional axisymmetric model simulating the hypervelocity impact of a stainless-steel sphere on a finite-thickness aluminum plate is developed based on a numerical method for multi-material elastic-plastic flow under the Eulerian framework. The developed model employs a hyperelastic constitutive relation to describe large deformations and a plasticity model that accounts for strain hardening and thermal softening, enabling accurate capture of material deformation and wave propagation during the impact process. In this way, this study reveals the effects of waves on interface evolution by closely examining both material deformation and wave propagation during impact. Furthermore, particular focus is given to the effects of the initial impact velocity of the stainless-steel sphere  U_\textP and the initial thickness of the aluminum plate H_\textT0 on the impact behavior. Two typical flow modes are identified as “penetrated mode” and the “unpenetrated mode”. A flow-mode phase diagram is then confirmed in the parameter space defined by  U_\textP and H_\textT0 . The results demonstrate that increasing  U_\textP significantly enhances the strength of the initial shock wave, while decreasing H_\textT0 intensifies the rarefaction wave reflected from the rear surface of the aluminum plate. The enhancement of either the initial shock wave or the reflected rarefaction wave induces stronger subsequent shock and rarefaction waves within the materials, causing the aluminum plate to experience higher-intensity impacts. Consequently, as  U_\textP increases or H_\textT0 decreases, the flow mode transitions from the unpenetrated mode to the penetrated mode.