Microstructure and mechanical properties of a novel Al–Mg–Er–Zr-Sc alloy fabricated by selective laser melting

In this work, Er–Zr-Sc modified Al–Mg alloy, manufactured by selective laser melting, offers excellent mechanical properties, due to the formation of a desirable microstructure and the synergistic effects of multiple strengthening mechanisms. The microstructure in as-built and aged alloys have been characterized by scanning electron microscopy and transmission electron microscopy. The results show that the microstructure of alloy is composed of equiaxed grains (∼0.7 μm in diameter) along the boundary of molten pool and columnar grains (∼1.46 μm in width) inside the molten pool. Al3(Sc,Zr) particles serve as nucleation sites to promote the nucleation of equiaxed grains, and Al3(Er,M) eutectic phases and other compounds at the grain boundaries inhibit grain growth, both of which greatly refine the grains and bring significant grain boundary strengthening and Orowan strengthening effect. During the aging process, coherent Al3(Er,Zr,Sc) nano-precipitates are dispersedly precipitated from the Al matrix, which plays a key role in improving the mechanical properties of the aged alloy, and then the alloy reaches a yield strength of 530 MPa, a tensile strength of up to 542 MPa, and an elongation of over 12 %. Under the combined addition of Er, Sc, and Zr, and the influence of multi-element interaction, the alloy has high-density secondary phases and extremely fine grains, which are the main sources of reinforcement.