Laser powder bed fusion of Al–Mg–Zr alloy: Microstructure, mechanical properties and dynamic precipitation

A Sc-free and high-plasticity Al-4.8Mg-1.6Zr aluminum alloy was densified via laser powder bed fusion. The microstructure features a typical bimodal grain structure, with abundant L1 2 -Al 3 Zr particles about 100 nm distributed. The yield strength (YS) of 449 ± 4 MPa, ultimate tensile strength (UTS) of 449 ± 5 MPa, and the elongation to failure (EL) of 15.1 ± 1.9% are obtained after peak aging. In addition to solid solution strengthening, grain boundary strengthening and nanoparticle strengthening, the long-range stacked ordered 9R phase associated with high content Mg and Zr also contributes to strengthening. Besides, the difference in strain distribution between coarse and fine grain zones causes deformation-induced hardening. Low-temperature dynamic precipitation is observed in this Al–Mg–Zr alloy for the first time. The deformation-induced hardening and dynamic precipitation improve the strain-hardening capability, consequently delaying necking instability. After peak aging treatment, the number of Al 3 Zr particles with strong high-temperature stability increases, inhibiting grain coarsening and enhancing the precipitation strengthening effect. The excellent strength-ductility trade-off of the printed Al–Mg–Zr without expensive Sc element gives it a broad application prospect in economical and large-scale additive manufacturing. • The LPBF-fabricated sample is crack-free with a relative density of 99.47% and porosity of 0.55% when it is printed at a VED of 80 J/mm 3 . • The yield strength (YS) of 449 ± 4 MPa, ultimate tensile strength (UTS) of 449 ± 5 MPa, and the elongation to failure (EL) of 15.1 ± 1.9% of Al–Mg–Zr alloy are obtained in as-built condition. • High content of Mg and Zr elements leads to low stacking fault energy, and the introduced 9R phase contributes to strengthening. • HDI hardening and low-temperature dynamic precipitation that first found in Al–Mg–Zr alloy, improves the strain-hardening capability.