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<p>High temperature oxidation as a primary degradation mode in magnesium alloys with calcium incorporation shown to improve oxidation resistance at elevated temperatures. The oxidation behaviors of Mg-12Al-<i>x</i>Ca alloys (<i>x</i> = 4, 5, 6, and 7) were carried out at 400, 450, 500, and 550&#xa0;°C. Microstructural analysis revealed that the second phase evolved from discrete distribution <i>β</i>-Mg<sub>17</sub>Al<sub>12</sub>, Al<sub>2</sub>Ca, and (Mg, Al)<sub>2</sub>Ca, to a dendritic network-like composed of Al<sub>2</sub>Ca and (Mg, Al)<sub>2</sub>Ca, which eventually transformed into a coarsened Al<sub>2</sub>Ca + (Mg, Al)<sub>2</sub>Ca structure as the Ca content increased. At a Ca content of 6 wt.%, no rapid oxidation was detected after 96&#xa0;h at 400&#xa0;°C, with the parabolic rate constant remaining only 0.007&#xa0;mg·cm<sup>−2</sup>·h<sup>−1</sup>. With increasing temperature to 450, 500, and 550&#xa0;°C, the oxidation rate constants before oxidation failure rose moderately to 0.015, 0.025, and 0.19&#xa0;mg·cm<sup>−2</sup>·h<sup>−1</sup>, respectively, indicating superior oxidation resistance of the alloy. The morphology and thickness of the oxide film varied across different phases: Fine oxide particles with relatively thick films were observed on Al<sub>2</sub>Ca and (Mg, Al)<sub>2</sub>Ca phases, whereas coarse oxide particles with comparatively thin films were formed on the <i>α</i>-Mg matrix. The uniformly distributed fine reticular Al<sub>2</sub>Ca structure promotes the formation of a continuous and dense oxide film, thereby enhancing oxidation resistance. At elevated temperatures, higher Ca promotes a compact oxide film and a protective Al<sub>2</sub>Ca/(Mg, Al)<sub>2</sub>Ca interfacial layer, thereby enhancing oxidation resistance. Moreover, integrating Gibbs free energy thermodynamics and first-principles calculations identifies the relative oxidation order of second phases and their surface oxygen affinity.</p>

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Achieving a high oxidation-resistant Mg-Al-Ca alloys by coordinating oxidation of α-Mg matrix and intermetallic phases

  • 期刊论文

  • 发表日期：

    2025年12月16日

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  • Bo Yin,
  • Yicheng Feng,
  • Shouwei Zhang,
  • Ning Zhang,
  • Dongrong Liu,
  • Lei Wang,
  • Erjun Guo

摘要

High temperature oxidation as a primary degradation mode in magnesium alloys with calcium incorporation shown to improve oxidation resistance at elevated temperatures. The oxidation behaviors of Mg-12Al-xCa alloys (x = 4, 5, 6, and 7) were carried out at 400, 450, 500, and 550 °C. Microstructural analysis revealed that the second phase evolved from discrete distribution β-Mg17Al12, Al2Ca, and (Mg, Al)2Ca, to a dendritic network-like composed of Al2Ca and (Mg, Al)2Ca, which eventually transformed into a coarsened Al2Ca + (Mg, Al)2Ca structure as the Ca content increased. At a Ca content of 6 wt.%, no rapid oxidation was detected after 96 h at 400 °C, with the parabolic rate constant remaining only 0.007 mg·cm−2·h−1. With increasing temperature to 450, 500, and 550 °C, the oxidation rate constants before oxidation failure rose moderately to 0.015, 0.025, and 0.19 mg·cm−2·h−1, respectively, indicating superior oxidation resistance of the alloy. The morphology and thickness of the oxide film varied across different phases: Fine oxide particles with relatively thick films were observed on Al2Ca and (Mg, Al)2Ca phases, whereas coarse oxide particles with comparatively thin films were formed on the α-Mg matrix. The uniformly distributed fine reticular Al2Ca structure promotes the formation of a continuous and dense oxide film, thereby enhancing oxidation resistance. At elevated temperatures, higher Ca promotes a compact oxide film and a protective Al2Ca/(Mg, Al)2Ca interfacial layer, thereby enhancing oxidation resistance. Moreover, integrating Gibbs free energy thermodynamics and first-principles calculations identifies the relative oxidation order of second phases and their surface oxygen affinity.