Fig. 1. Powder particle size distribution and XRD results. (a) Particle size distribution of AZ91D powder; (b) XRD results of powder and formed sample

Fig. 2. Schematics of forming. (a) Sample arrangement and cross section characterization; (b) block; (c) LPBF forming parameters and strategy for tensile test bar

Fig. 3. Diagram of imaging system

Fig. 4. Typical optical micrographs of vertical sections of LPBF formed samples at T=200 ℃. (a) h=0.06 mm; (b) h=0.08 mm

Fig. 5. Relative density versus scanning speed at T=200 ℃ under different laser powers. (a) h=0.06 mm; (b) h=0.08 mm

Fig. 6. Relative density versus input volumetric energy density at T=200 ℃ under different parameters. (a) h=0.06 mm; (b) h=0.08 mm

Fig. 7. Relative density versus scanning speed at T=25 ℃ under different laser powers. (a) h=0.06 mm; (b) h=0.08 mm

Fig. 8. RRN‑aver_{of defect areas of formed samples under different parameters at T=200 ℃. (a) h=0.06 mm; (b) h=0.08 mm}

Fig. 9. Pore fraction curves when h=0.06 mm and T=200 ℃. (a) Pore fraction versus scanning speed when P is 150 W and 200 W; (b) pore fraction versus laser power when V=300 mm·s^-1

Fig. 10. Molten pool sizes under different scanning speeds when P=200 W and h=0.06 mm

Fig. 11. Schematics of defect formation. (a) Distribution of keyhole defects; (b) keyhole formation process; (c) morphology of pores; (d) incorporation of pores

Fig. 12. Schematics of lack of fusion defects formation. (a) h=0.06 mm; (b) h=0.08 mm

Fig. 13. Morphologies of lack of fusion defect areas when h=0.08 mm and P=200 W. (a) V=500 mm·s^-1; (b) V=600 mm·s^-1

Fig. 14. Visualized images about element evaporation during LPBF process

Fig. 15. Microstructures of LPBF formed specimens at h=0.06 mm. (a) P=200 W, V=300 mm·s^-1, T=200 ℃; (b) P=200 W, V=600 mm·s^-1, T=200 ℃; (c) P=75 W, V=300 mm·s^-1, T= 200 ℃; (d) P=200 W, V=300 mm·s^-1, T=25 ℃

Fig. 16. LPBF formed specimens without preheating. (a) Typical crack morphology; (b) SEM micrograph and elemental distributions

Fig. 17. Stress-strain curves of LPBF formed magnesium alloy test bars when P=200 W, V=300 mm·s^-1, h=0.06 mm, and T=200 ℃

Fig. 18. Microscopic images of tensile fracture of AZ91D high-density specimen formed by LPBF