Fig. 1. Microstructural characterizations on the as-received 2024Al-T4 alloy. (a)-(c) Inverse pole figure (IPF) maps. Inset of (b): kernel average misorientation (KAM) map. EBSD scan step size: 4.73 m. (d)-(f) Backscattered electron images. White areas refer to precipitates. RD: rolling direction; TD: transverse direction; ND: normal direction.

Fig. 2. (a) Schematic setup for ballistic impact experiments. 1: target chamber; 2: gun barrel; 3: aluminum sabot; 4: spherical projectile; 5: electromagnetic induction velocimeter; 6: steel block; 7: 2024Al-T4 alloy target; 8: target holder; 9: polycarbonate windows; 10: high-speed camera; 11: light. (b) Definition of experimental parameters. dp: projectile diameter; dc: crater diameter; Dc: crater depth; Vc: crater volume.

Fig. 3. Geometry and meshing of the 2024Al-T4 alloy target and stainless steel projectile. Dimensions are in millimeters.

Fig. 4. Snapshots of a steel projectile impacting on a 2024Al-T4 alloy target (sample 1) at ~400 m s-1.

Fig. 5. (a) Optical images of the postmortem samples impacted along the ND for 1-5 times (samples 1-5). (b)-(c) 3D laser scanning reconstruction of the impact craters viewed from different perspectives.

Fig. 6. Cross-sectional profiles of the craters after 1-5 impacts (samples 1-5). The original plane refers to the target surface prior to impact.

Fig. 7. (a) Depth (Dc), diameter (dc), shape coefficient (Dc/dc) and (b) volume (Vc) of craters as a function of the number of impact. Symbols: experimental data; lines: fitting to data with a power function.

Fig. 8. Microhardness distributions along the two lines marked in Fig. 2b for samples 1, 3, and 5. Hv0.2 refers to the Vickers hardness under a load of 0.2 kg. Dashed lines: the as-received sample.

Fig. 9. EBSD characterizations of the postmortem samples. (a)-(d) IPF maps for samples 1 and 3. The centers of maps (a) and (b) lie on the line AB (Fig. 2b), and are 4 mm away from point A (crater bottom). The centers of maps (c) and (d) lie on the line CD (Fig. 2b), and are 4 mm and 1 mm away from point C (crater sidewall center), respectively. (e)-(h) KAM maps corresponding to maps (a)-(d). EBSD scan step size: 4.73 m.

Fig. 10. Local misorientation distributions of the as-received and postmortem samples (samples 1 and 3) at different positions.

Fig. 11. (a)-(d) EBSD characterizations of the impact-recovered samples. Unindexed areas and grain boundaries with misorientation greater than 10° are marked in black. EBSD scan step size: 0.5 m. (e)-(h) {110} and {111} pole figures corresponding to the regions indicated by white rectangles in (a)-(d). (i)-(l) Grain boundary orientation distribution corresponding to (a)-(d). Insets of (i)-(l) display the positions of EBSD characterizations (red dots) for (a)-(d). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 12. Crater depth (Dc) and diameter (dc) as a function of the number of impacts obtained from FEM simulations and experiments.

Fig. 13. FEM simulations: snapshots of instantaneous velocity fields of the 2024Al-T4 alloy targets after (a) the 1st impact and (b) 3rd impact.

Fig. 14. Snapshots of instantaneous (a) effective plastic strain ($\varepsilon _{\text{eff}}^{\text{p}}$) fields and (b) shear strain (${{\varepsilon }_{\text{s}}}$) fields of the 2024Al-T4 alloy targets after the 1st to 5th impact. The black dots in figure (b) mark locations for EBSD characterization in Fig. 11a-d.