Fig. 1. Secondary electron image showing the morphology of the pre-alloyed powder (a), XRD patterns for the powder and L-PBF samples (b).

Fig. 2. The aging response of the L-PBF-processed Al-Mg-Sc-Zr alloy at 300, 325, 350, and 400°C (air cooling), the peak-aged condition (325°C/4 h) was marked as the red circle.

Fig. 3. One of the acquired DIC images (a), the geometry of the DIC specimen (b), the Gatan micro-tension tester (c), and the geometry of the in-situ tensile specimen (d), the tensile axis is parallel to the building direction, the unit of the dimensions in the tensile drawings is mm.

Fig. 4. Backscattered electron (BSE)-SEM images showing the heterogeneous microstructure (a, b); EBSD maps showing the heterogeneous grain structure (c), and {100} pole figures for the CG (d) and FG regions (d); grain size distribution of the equiaxed grains (e), and width distribution of the columnar grains (f). Building direction (BD) is indicated as the inset yellow arrow. The sample frame of reference for the pole figures is shown in (b), and Z is parallel to the BD.

Fig. 5. STEM-EDS mapping results showing the distributions of Al, Mg, Mn, Sc, Zr, Fe, and Si elements in the FG (a) and CG (b) regions.

Fig. 6. BF-TEM image (a), SAD pattern (b), and HAADF-STEM image (c) taken along [001] zone axis in the CG region; BF-TEM image (d), SAD pattern (e), and HAADF-STEM image (f) taken along [001] zone axis in the FG region; the 001-type superlattice reflections marked by the red/purple arrows showing the secondary Al3(Sc,Zr) phase with L12 ordered structure; particle-size distributions for the secondary Al3(Sc,Zr) in the CG (g) and FG (h) regions.

Fig. 7. Engineering stress-strain curves (a) and the comparison between tensile properties of the L-PBF-processed Al-Mg(Mn)-Sc-Zr alloys and those of traditionally-made Al-Mg-Sc alloys, such as casting, CR, RS/PM, and those of 2 × × × and 7 × × × wrought Al alloys (b); the discontinuous yielding behavior with the definitions of ${{\sigma }_{\text{U}}}$, YS, Lüders elongation or YPE, and ${{\varepsilon }_{\text{L}}}$ (c); the $\text{ln}{{\sigma }_{\text{t}}}-\text{ln}{{\varepsilon }_{\text{t}}}$ curves and the fitting curves (d); the K, n in Holloman equation and the Lüders true stress (${{\sigma }_{\text{t}-\text{L}}}$) (e); the θ against the net flow stress ${{\sigma }_{\text{t}}}-{{\sigma }_{\text{t}-\text{L}}}$ curves (f).

Fig. 8. Evolution of the full-field local strain during the tensile test of the as-built (a) and direct-aged (b) samples; the evolution of the maximum local strain (c) and the Lüders elongation stages were marked as the black/red rectangular boxes; the evolution of the normalized maximum local strain (d). The tensile axis is parallel to the building direction.

Fig. 9. Simulated temperature field (a); temperature-time dependency for the marked points located at the centerline of the molten pool (b), the historical characteristics of cooling rate during the solidification interval of the primary Al3Sc phase are presented as the inset figures; equilibrium phase diagram for Al-3.3Mg-0.48Mn-xSc (wt.%) alloy system calculated via Thermo-Calc software (c), the solidification temperature interval of primary Al3Sc is marked as the dotted line; the predicted critical condition for suppressing the nucleation of primary Al3Sc phase, and the correlated grain structure evolution paths (d).

Fig. 10. Microhardness maps showing the mechanical heterogeneity in the as-built (a) and direct-aged (c) samples; BSE images showing the typical indentations located in the FG and CG regions in the as-built (b) and direct-aged (d) samples. The building direction is indicated as the yellow arrows.

Fig. 11. Optical micrograph showing the Lüders bands after tensile straining to 2% of an as-built tensile specimen (a), BF-TEM images showing the dislocation configurations in the FG and CG regions for the swept (b, d) and unswept (c, e) regions in the tensile specimen; the TEM images of columnar grains are taken near the <011> axis. The dislocations lines are indicated with the yellow arrows.

Fig. 12. Evolution of steady-state subgrain size (w) with true stress (σt), ${{w}_{\text{YS}}}$ is the estimated subgrain size with the σt corresponding to YS of the as-built sample.

Fig. 13. BSE images showing the deformed CG and FG regions with different load-line strains, and the load against load-line displacement curves for the as-built (a) and direct-aged samples (b); schematic illustrating the relationship between displacement and strain components (c); strain partitioning behavior between the CG and FG regions in the as-built (d) and direct-aged (e) samples during the in-situ tensile testing.

Fig. 14. (a) True stress-strain curves obtained via LUR tensile test; (b) the close-up view of the typical hysteresis loops taken from a part of (a), and the unloading/reloading yield point is defined as the point which has a 10% reduction in slope from the effective elastic modulus; (c) HDI stress versus true strain derived from the LUR hysteresis loops; (d) Ratio of HDI stress to true stress versus applied true strain.

Fig. 15. 3D reconstructions of the surface morphology for the in-situ tensile specimens, which show the features of deformation at the macroscale and molten-pool scale in the as-built (a-c) and direct-aged (d-f) specimens, the inset BSE image in (e) showing the planar slip characteristic in the direct-aged specimen.