Pb plays an important role in determining the morphologies and mechanical properties of the Mg₂Si phase in Mg-2.5Si-xPb alloys. As the amount of Pb increases from 0.4 wt.% to 1 wt.%, the primary Mg₂Si phase is refined during solidification. Its morphologies transform from equiaxed-dendrite to polygonal and finally to roughly circular. The key reason for morphology evolution is the preferential adsorption of Pb atoms on Mg₂Si {100} surfaces to suppress the growth rate along the ⟨100⟩ directions, which is demonstrated by the adsorption model based on first principles. In addition, the hardness of the Mg₂Si phase decreases with the increasing solution content of Pb according to the results of the nanoindentation. With the addition of Pb at 1 wt.%, Pb content in the primary Mg₂Si phase reaches a maximum of 0.4 wt.%, and the hardness of the primary Mg₂Si phase reaches a minimum of 3.64 GPa. This reduction in hardness is attributed to the augmented ionic bond ratio resulting from the solution of Pb, which concurrently enhances the toughness of the Mg₂Si phase.

A highly sensitive and recyclable surface-enhanced Raman scattering (SERS) substrate was successfully fabricated through in situ reduction of bimetallic gold-silver nanoparticles (Au-Ag NPs) on vertically aligned titanium dioxide nanorods (TiO ₂ NRs) grown on porous silicon (PS). The as-prepared Au-Ag/TiO ₂ /PS substrate demonstrated exceptional SERS performance for the detection of crystal violet (CV), reaching a low detection limit (LOD) of 10 ^− 11 M and a high enhancement factor (EF) of 1.74×10 ⁷ . This superior performance can be attributed to the synergistic effect of the appropriately sized Au-Ag NPs with nanoscale interparticle gaps that generate intense localized surface plasmon resonance (LSPR), as well as the large surface area of PS, which facilitates analyte enrichment. Moreover, the substrate exhibited excellent photocatalytic self-cleaning capability under UV irradiation. The rapid generation of non-equilibrium carriers within the TiO ₂ NRs, the directional transfer and efficient charge separation at the Au-Ag/TiO ₂ Schottky junction, together with the abundant active sites on PS, collectively contribute to the effective degradation of adsorbed CV molecules. Notably, the substrate maintains excellent recyclability and stability even after five consecutive cycles. These findings offer valuable insights for the design of multifunctional SERS platforms for the detection and degradation of organic pollutants.