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<p>Driven by rare-earth supply risks and cost pressure, the L1<sub>0</sub>-<i>τ</i> (MnAl) phase is an attractive rare-earth-free permanent-magnet candidate. However, <i>τ</i>-MnAl is metastable and readily decomposes during annealing, while transformation-related defects further limit coercivity. In this work, Mn<sub>54</sub>Al<sub>46</sub>Gd<sub><i>x</i></sub> ingot alloys (<i>x</i> = 0.00–0.70) were fabricated by arc melting followed by a two-step heat treatment. The effect of minor Gd additions on the <i>ε</i> → <i>τ</i> transformation, <i>τ</i>-phase stability, and magnetic performance was investigated. An orthogonal design (wheel speed/annealing temperature/holding time) was employed to establish the heat-treatment processing window. The ingots exhibited a non-monotonic dependence on Gd content, with the optimum at <i>x</i> = 0.20 [<i>M</i>(2T) = 95.14 A·m<sup>2</sup>/kg, <i>H</i><sub>c</sub> = 43.8 kA/m]. This enhancement was associated with microstructural refinement and the appearance of bright secondary particles near grain boundaries. Meanwhile, Gd addition promoted <i>τ</i>-phase formation under non-equilibrium solidification and suppressed the precipitation of competing phases. For melt-spun ribbons, Gd further promoted direct <i>τ</i>-phase formation during rapid quenching; after annealing at 500 °C for 10 min, the coercivity of the ribbon sample spun at 25 m/s reached 160.7 kA/m. Orthogonal analysis identified annealing temperature as the dominant parameter governing <i>τ</i>-phase evolution and magnetic properties, followed by wheel speed, while holding time has a comparatively minor effect. These results provide practical guidance for the synergistic optimization of microalloying and the design of the processing window to improve the performance in Mn-Al-based permanent magnets.</p>

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Effects of minor Gd addition and heat treatment on the L10 τ-MnAl phase

  • 期刊论文

  • 发表日期：

    2026年5月12日

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  • Gengsheng Mao,
  • Lei Ma,
  • Mufen He,
  • Jiwang Liu,
  • Lin Li,
  • Xuehong Cui,
  • Yuying Meng

摘要

Driven by rare-earth supply risks and cost pressure, the L10-τ (MnAl) phase is an attractive rare-earth-free permanent-magnet candidate. However, τ-MnAl is metastable and readily decomposes during annealing, while transformation-related defects further limit coercivity. In this work, Mn54Al46Gdx ingot alloys (x = 0.00–0.70) were fabricated by arc melting followed by a two-step heat treatment. The effect of minor Gd additions on the ε → τ transformation, τ-phase stability, and magnetic performance was investigated. An orthogonal design (wheel speed/annealing temperature/holding time) was employed to establish the heat-treatment processing window. The ingots exhibited a non-monotonic dependence on Gd content, with the optimum at x = 0.20 [M(2T) = 95.14 A·m2/kg, Hc = 43.8 kA/m]. This enhancement was associated with microstructural refinement and the appearance of bright secondary particles near grain boundaries. Meanwhile, Gd addition promoted τ-phase formation under non-equilibrium solidification and suppressed the precipitation of competing phases. For melt-spun ribbons, Gd further promoted direct τ-phase formation during rapid quenching; after annealing at 500 °C for 10 min, the coercivity of the ribbon sample spun at 25 m/s reached 160.7 kA/m. Orthogonal analysis identified annealing temperature as the dominant parameter governing τ-phase evolution and magnetic properties, followed by wheel speed, while holding time has a comparatively minor effect. These results provide practical guidance for the synergistic optimization of microalloying and the design of the processing window to improve the performance in Mn-Al-based permanent magnets.