Micro-modification of AlMgScZr alloy for additive manufacturing: new insights on the evolution of interphase interface and mechanical properties of complex phase reinforcement

The introduction of low-cost Si elements into AlMgScZr alloy to form complex phase reinforcement is a potential cost reduction micro-modification method, but the interface behavior of complex phase reinforcement and its effect on mechanical properties are still unclear. In this study, TEM, EBSD, and other characterization methods were used to systematically study the relationship between the microstructure characteristics of Mg₅Si₆, Al₃Sc, and other enhanced particles and the interfacial orientation. The results show that the average grain size of Al is 7.3 μm in the columnar region and 4.0 μm in the fine equiaxed region. There is an orientation relationship of [001]Al//[01–1]Al₃Sc//[010]Mg₅Si₆, with a planar relationships of (200)Al//(200)Al₃Sc and (220)Al//(802)Mg₅Si₆. Al serves as an interfacial transition layer that effectively promotes the connection between Al₃Sc and Mg₅Si₆. The ultimate tensile strength of 446 MPa and yield strength of 370 MPa were obtained in this study. Fracture analysis showed that Mg₅Si₆ and Al₃Sc precipitated phases increased the stress concentration and interface separation while increasing the strength, resulting in local brittle fracture. Therefore, these synergies and porosity lead to the characteristics of high strength and low plasticity of the material, which is essentially the multi-scale brittle phase coupling effect induced by LPBF process.