**2. Computed Methods**

All calculations in this work were performed in Vienna ab initio Simulation Package (VASP) [34] with the 5.4.4 version, which adopts the framework of density functional theory (DFT) [35] calculations to solve the Kohn–Sham equation and obtain the total energy from different models. In the calculated processing of VASP, to relax all models to their most stable ground state, the electron–core interaction was described by the projector augmented wave (PAW) [36] method. The optimal choice of exchange–correlation functional was considered using the generalized gradient approximation (GGA) with the Perdew–Burke– Ernzerh (PBE) version [31]. A 10 × 10 × 10 k-point sampling grid with the Gammacentered Monkhorst–Pack method [37] in the first Brillouin zone was selected via strict convergence testing (see Figure 1) for bulk properties calculation. A cut off energy of the plane-wave basis of 500 eV was chosen for the whole calculated process. The energy and force tolerance were set to 10−<sup>7</sup> eV and 0.01 eV/Å, respectively, by using conjugate gradient (CG) minimization and Broyden–Fletcher–Goldfarb–Shannon (BFGS) schemes [38].

**Figure 1.** The total energy of Al3Sc as a function of k-point sampling grids.

Here, based on the slab model, we investigated three low-index surfaces, containing (100), (110) and (111) surfaces of Al and L12-Al3TM, which adopted 14, 14 and 16 layers, respectively [24,39]. All interfaces of (100), (110) and (111) surfaces of Al/L12–Al3TM are calculated by using the 18 layers interface model. A 10 × 10 × 1 k–mesh grid for both cases was tested to be suitable for this work. To simulate diffusion behavior, we constructed a 3 × 3 × 3 supercell with 4 × 4 × 4 k–mesh grids to obtain the diffusion barriers of the solute diffusion of TMs in the Al matrix based on the climbing-image nudged elastic band (CI-NEB) [40] method. Meanwhile, a spring force constant of 5 eV/Å was considered to keep all the images separated, and these CI-NEB iterations were continued until the forces on each atom were less than 0.05 eV/Å.

### **3. Conclusion Description**
