Friction stir processing (FSP) was applied to wire-arc additively manufactured (WAAM) Mg-9.54Gd-1.82Y-0.44Zr (GW92K) alloy to address coarse microstructure and porosity defects inherent to layer-by-layer deposition. FSP induced complete dissolution of the coarse Mg₅(Gd,Y) eutectic network (initial size: 3.3 ± 0.5 µm) and triggered dynamic recrystallization, achieving a 69.5% grain refinement from 16.4 µm (WAAMed) to 5.0 µm (FSPed). This microstructural transformation enhanced ultimate tensile strength (UTS) by 32% (217 ± 3 MPa → 286 ± 2 MPa), yield strength (YS) by 46% (124 ± 2 MPa → 182 ± 7 MPa), and elongation (EL) by 35% (9.7 ± 1.1% → 13.1 ± 1.4%). Quantitative analysis via Hall-Petch relationship confirmed that grain refinement contributed ~50 MPa (79%) of the total YS increment, while nano-precipitation (β′′/β′ phases <20 nm) effects accounted for the remaining ~13 MPa. The simultaneous strength-ductility enhancement originates from FSP-induced defect elimination (porosity reduction: 1.75% → 0.18%) and dual-phase grain boundary pinning by Zr particles and β-Mg₅(Gd,Y) precipitates. These findings establish FSP as a viable post-treatment for overcoming WAAM limitations in high-performance Mg-RE alloy fabrication.

Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices. The essential magnetic properties of Nd-Fe-B magnets, particularly coercivity and remanent magnetization, are significantly influenced by the phase characteristics and microstructure. In this work, Nd-Fe-B magnets were manufactured using vacuum induction melting (VIM), laser directed energy deposition (LDED) and laser powder bed fusion (LPBF) technologies. The microstructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail. The results indicated that the solidification velocity (V) and cooling rate (R) are key factors in the phase selection. In terms of the VIM-casting Nd-Fe-B magnet, a large volume fraction of the α-Fe soft magnetic phase (39.7 vol.%) and Nd₂Fe₁₇B_x metastable phase (34.7 vol.%) are formed due to the low R (2.3 × 10⁻¹ ℃ s⁻¹), whereas only a minor fraction of the Nd₂Fe₁₄B hard magnetic phase (5.15 vol.%) is presented. For the LDED-processed Nd-Fe-B deposit, although the Nd₂Fe₁₄B hard magnetic phase also had a low value (3.4 vol.%) as the values of V (<10⁻² m s⁻¹) and R (5.06 × 10³ ℃ s⁻¹) increased, part of the α-Fe soft magnetic phase (31.7 vol.%) is suppressed, and a higher volume of Nd₂Fe₁₇B_x metastable phases (47.5 vol.%) are formed. As a result, both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties. In contrast, employing the high values of V (>10⁻² m s⁻¹) and R (1.45 × 10⁶ ℃ s⁻¹) in the LPBF process resulted in the substantial formation of the Nd₂Fe₁₄B hard magnetic phase (55.8 vol.%) directly from the liquid, while the α-Fe soft magnetic phase and Nd₂Fe₁₇B_x metastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet. Additionally, crystallographic texture analysis reveals that the LPBF-processed Nd-Fe-B magnets exhibit isotropic magnetic characteristics. Consequently, the LPBF-processed Nd-Fe-B deposit, exhibiting a coercivity of 656 kA m⁻¹, remanence of 0.79 T and maximum energy product of 71.5 kJ m⁻³, achieved an acceptable magnetic performance, comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP (Nd-lean) Nd-Fe-B powder.