Microstructure and mechanical properties of Al-Mg-Zr alloys processed by selective laser melting

By J. Croteau, S. Griffiths, Marta D. Rossell, Christian Leinenbach, C. Kenel, V. Jansen, David N. Seidman, D. Dunand, Nhon Q. Vo. Acta Materialia, 2018

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Abstract Gas-atomized powders of two ternary alloys, Al-3.60Mg-1.18Zr and Al-3.66Mg-1.57Zr (wt.%), were densified via laser powder bed fusion. At energy densities ranging from 123 to 247 J/mm3, as-fabricated components are near-fully densified (relative density 99.2–99.9%) as verified by X-ray tomography. While Mg acts a solid-solution strengthener, Zr creates two types of metastable L12 Al3Zr precipitates, each playing dual roles: (a) sub-micrometer Al3Zr particles form in the melt upon solidification and act as grain refining agents, nucleating fine aluminum grains, which (i) prevent hot-tearing during the rapid solidification inherent to laser melting and (ii) enhance tensile strength (Hall-Petch strengthening) and ductility (influence a heterogenous grain structure) after fabrication; (b) Al3Zr nano-precipitates form in the solid alloy during subsequent aging, which (i) precipitation-strengthen the alloy leading to an increase of >40% in strength over the as-fabricated value, and (ii) promote thermal stability of the fine grain size (and the associated Hall-Petch strengthening) after exposure to high temperature due to the slow kinetics of Al3Zr coarsening (from the sluggish diffusivity of Zr in solid Al-Mg). While the Zr-richer alloy shows higher yield and ultimate tensile strength in the as-fabricated state, both alloys have identical mechanical properties after peak aging. Interconnected bands of fine (∼0.8 μm), equiaxed, isotropic grains and coarser (∼1 × 10 μm), columnar, textured grains – both containing oxide particles and Al3Zr precipitates - provide a combination of high yield strength and high ductility (e.g., ∼354 MPa, and ∼20%, respectively) with isotropic values in both as-fabricated and peak-aged samples, unlike Al-Si alloys processed via laser fusion of commercial Al-Si-based powders. The pre-alloyed, gas-atomized Al-Mg-Zr powders do not contain expensive alloying elements such as Sc, nor do they require blending with a second powder to nucleate fine grains, making them excellent candidates for economical, large-scale additive manufacturing applications.

Subfields: Aerospace Engineering, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/c7f20b40f02358d94e7e6e6111c53a4809ead143

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Citations in the corpus

A review of Laser Powder Bed Fusion Additive Manufacturing of aluminium alloys: Microstructure and properties (2021, background): “ductility, and improve overall processability [56, 69, 120, 146-149].”
Coarsening- and creep resistance of precipitation-strengthened Al–Mg–Zr alloys processed by selective laser melting (2020, methodology): “The use of Mn for solid solution strengthening, instead of Mg, would minimize the disadvantages associated with Mg such as: (i) Mg suffers from significant in-process (SLM) evaporation [15] and (ii.”
3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting (2019, background): “It is worth noting that the Zr-modified alloy was characterised by higher ductility than the Sc-modified alloys [197].”