From macro-, through meso- to micro-scale: Densification behavior, deformation response and microstructural evolution of selective laser melted Mg-RE alloy

Abstract

To clarify the densification behavior, deformation response and strengthening mechanisms of selective laser melted (SLM) Mg-RE alloys, this study systematically investigates a representative WE43 alloy via advanced material characterization techniques. A suitable laser output mode fell into the transition mode, allowing for the fabrication of nearly full-density samples (porosity = 0.85 ± 0.021 %) with favorable mechanical properties (yield strength=351 MPa, ultimate tensile strength = 417 MPa, the elongation at break = 6.5 % and microhardness = 137.9 ± 6.15 HV_0.1) using optimal processing parameters (P = 80 W, v = 250 mm/s and d = 50 µm). Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal <a> and prismatic <a> slips. Starting from a random texture before deformation (maximum multiple of ultimate density, Max. MUD = 3.95), plastic stretching led the grains to align with the Z-axis, finally resulting in a {0001}<$10\overline{1}0$$10\overline{1}0$> texture orientation after fracture (Max. MUD = 8.755). Main phases of the SLM state are mainly composed of α-Mg, Mg₂₄Y₅ and β’-Mg₄₁Nd₅, with an average grain size of only 4.27 µm (about a quarter of that in the extruded state), resulting in a favorable strength-toughness ratio. Except for the nano-β’ phase and semi-coherent Mg₂₄Y₅ phase (mismatch = 16.12 %) around the grain boundaries, a small amount of nano-ZrO₂ and Y₂O₃ particles also play a role in dispersion strengthening. The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening (44.41 %), solid solution strengthening (34.06 %) and grain boundary strengthening (21.53 %), with precipitation hardening being predominantly driven by dislocation strengthening (67.77 %). High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024, receiving favorable attention. This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.