The evolution and characterizations of Al₃(Sc_xZr_1-x) phase in Al–Mg-based alloys proceeded by SLM

The addition of Sc and Zr endows selective laser melted Al–Mg-based alloys with exceptional properties, which are predominately related to the Al₃(Sc_xZr_1-x) precipitates. The Al₃(Sc_xZr_1-x) precipitates formed in different stage of processing are identified as primary- Al₃(Sc_xZr_1-x) and aged- Al₃(Sc_xZr_1-x) according to different crystallographic characteristics. The experimental results show most of primary Al₃(Sc_xZr_1-x) particles located in the grain boundaries with incoherent interface and irregular shape, which is seldom reported in conventional casting. In contrast, the subsequent aging brings out more spherical Al₃(Sc_xZr_1-x) with coherent interface emerged in the grains. Combined the first-principle calculations with pseudo binary-diagram, we search the possible structures of Al₃(Sc_xZr_1-x) based on their formation enthalpy and binding energy, whose space group should be altered as Sc enters the Al₃Zr (DO₂₃) dispersoids. The most possible structure of primary Al₃(Sc_xZr_1-x) phase is evaluated as Al₁₂Sc₃Zr, and the calculated crystallo-graphic parameters are consistent with the experimental results. As the primary Al₃(Sc_xZr_1-x) is hard to act as nucleation particle, it can be inferred that the grain refinement resulting from the modification and hindrance of these particles during grain growth. A corresponding ultimate tensile strength and ductility is separately about 521.26 ± 12.30 MPa and 15.83 ± 0.94% after aging at 325 °C for 4 h. The results demonstrate the difference between the primary Al₃(Sc_xZr_1-x) and the aged Al₃(Sc_xZr_1-x) as well as the formation of primary Al₃(Sc_xZr_1-x), which offer a new idea to design new alloy for additive manufacturing.