Fig. 1. Secondary electron image showing the morphology of the Zr-2024Al alloy powders (a), the particle size distribution of the powders (b).

Fig. 2. DSC curve of the SLM-processed Zr-2024Al alloy at heating rate of 20 °C/min.

Fig. 3. Backscattered electron (BSE) images showing the microstructure of the as-fabricated sample (a), and the solution-treated samples after solution times of 1, 3, 5, 7 and 9 h (b-f), respectively.

Fig. 4. Variation of hardness with aging time for solution treated sample aged at 195 °C (a), for as-fabricated sample aged at 310, 340, 370, and 400 °C (b).

Fig. 5. EBSD map and corresponding grain size distribution in the as-fabricated sample (a); TEM-BF images taken from the ultrafine grains region and selected area diffraction pattern (SADP) of the Al3Zr-L12 particle within Al grain (b); TEM-BF images for the in-situ precipitated second phases during SLM and corresponding HRTEM images taken along [001]Al revealing the secondary Al2CuMg precipitates within the α-Al matrix in the as-fabricated sample (c).

Fig. 6. The equilibrium phase diagram for 2024Al-xZr (wt.%) alloy system (Zr content shown by red dotted line) (a), the variation of precipitated phase content vs. temperature, (b) calculated by Thermal-Calc® software with TTAL7 database. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 7. Backscattered electron (BSE) image (a), EBSD map (b), the grain size distributions of the UFG (c) and the CG (d) regions in the STA sample.

Fig. 8. TEM-EDS mapping results showing the distributions of Cu, Mg, Mn, Zr, Fe, and Si elements in the CG (a) and UFG (b) regions in the STA sample.

Fig. 9. TEM-BF image showing the precipitates during after solution treatment and aging (a); HRTEM image taken along [001] revealing the secondary Al3Zr and S′ precipitates within the α-Al matrix (b); TEM-EDS mapping results of the Cu, Mg, Mn, and Zr for the second phase particle marked by the yellow arrows (c). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 10. Backscattered electron (BSE) image (a), EBSD map (b), the grain size distributions of the UFG (c) and the CG (d) regions in the DA sample.

Fig. 11. TEM-EDS mapping results showing the distributions of Cu, Mg, Mn, Zr, Fe, and Si elements in the UFG (a) and CG (b) regions in the DA sample.

Fig. 12. TEM characterizations at equiaxed region of the DA sample. (a) TEM-DF image viewed along the [001]Al zone axis; (b) Atomic resolution HAADF-STEM image of the area in (a); (c) TEM-DF image of the small spherical phase; (d) The selected area diffraction pattern of (c).

Fig. 13. Engineering stress-strain curves (a) and the comparison between tensile properties of the additive manufactured Al-Cu-Mg alloys and those of wrought Al-Cu-Mg alloys (b); lnσ-lnε curves and the fitting curves (c); work-hardening exponent and elastic modulus of the samples (d).

Fig. 14. HAADF-STEM image taken along [001]Al axis in the STA sample showing precipitation of intragranular Al3Zr-L12 type precipitates with planar faults.

Fig. 15. BF-TEM image (a) in the STA sample; HRTEM image taken along [001] showing the Al3Zr-D023 type and Al2CuMg-S precipitates located at grain boundaries (b); HRTEM image taken from the marked area with blue rectangle revealing the D023-Al3Zr precipitates with planar faults (c); BF-TEM image around grain boundary showing a precipitate-free zone surrounding the grain boundary (d).

Fig. 16. Fracture morphologies and cross-section near fracture surface for the T6-treated (a) and DA-treated samples (b) after tensile test.