镁合金孪晶界阻尼的作用规律及机理研究

Enhancing damping capacity without losing the mechanical property is of great importance for a wider usage of magnesium alloys. However, the current research of high damping magnesium alloys is carried out on the basis of dislocation/matrix interactions, which is not capable of solving the above mentioned problems. In the present research, a novel concept of “high damping magnesium alloy of twin type” is proposed for the first time. This is based on the fact that boundaries of tensile twin in magnesium alloys are movable and they can shrink and grow even at extremely low stress. Magnesium alloys with high damping capacity are achieved via introducing high density of tensile twin boundaries through pre-deformation and optimizing the twin boundary mobility by a subsequent heat treatment yet without sacrificing the mechanical properties. 7 binary magnesium alloys are used in the present research. By combination of characterizations on both twin boundary microstructure and performance of the resultant alloys, the twin damping mechanism was analyzed from the relationships between damping capacity and twin boundary characteristics such microstructure, stress distribution, and mobility. This result would provide both experimental and theoretical basis for developing magnesium alloy with both high strength and high damping capacity. Three key scientific issues will be solved in this research: (1) characterizing the twin boundary microstructure, stress distribution across twin boundary, and twin boundary mobility via using intrinsic parameters; (2) establishment of quantitative relationship between damping capacity and twin boundary coherence degree, precipitation degree, stress distribution, mobility, twin boundary characteristic; (3) establishment of theory for twin damping in magnesium alloys.

如何在保持镁合金优异力学性能的同时，大幅改善其阻尼性能是关系到镁合金更广阔应用的重要课题。目前阻尼镁合金研究多以位错阻尼理论为基础，强调位错/合金状态关联，难以彻底解决这一问题。本项目基于镁合金孪晶在微小应力作用下，可扩张和收缩从而吸收外部能量的特性，首次提出孪晶阻尼镁合金这一概念，通过预变形导入高密度孪晶界，后续短时时效增强孪晶界可动性，实现镁合金阻尼性能大幅提高。本课题拟以7种典型二元镁合金为对象，结合合金元素、微结构、微塑性变形、阻尼，围绕孪晶界共格度、应力状态、偏析度及可动性与阻尼的关系，揭示孪晶型镁合金的阻尼机理，为开发高强高阻尼镁合金提供科学依据和理论方法。主要解决3个关键科学问题:(1)设定合适的本征参数表征孪晶界共格度、应力状态、偏析度及可动性;(2)构建合金元素、孪晶界密度、共格度、应力状态、偏析度、可动性与阻尼系数的数学模型;(3)建立镁合金孪晶阻尼的可控性理论。

如何在保持镁合金优异力学性能的同时，大幅改善其阻尼性能是关系到镁合金更广阔应用的重要课题。目前阻尼镁合金研究多以位错阻尼理论为基础，强调位错/合金状态关联，难以彻底解决这一问题。本项目基于镁合金孪晶在微小应力作用下，可扩张和收缩从而吸收外部能量的特性，首次提出孪晶阻尼镁合金这一概念，通过预变形导入高密度孪晶界，后续短时时效增强孪晶界可动性，实现镁合金阻尼性能大幅提高。本项目针对 Mg, Mg-Al, Mg-Zn, Mg-Li, Mg-Gd 等合金，对孪晶形成及退孪晶等孪晶可动性现象进行了系统的研究，提出基于孪晶变形-热处理的高阻尼镁合金开发理论，高强Mg-Al合金开发理论及Mg-Zn合金的孪晶-退孪晶行为及机理。主要得到以下研究成果：分析得出孪晶界可动性与合金成分，预变形量，热处理的定量定性关系,获得提高镁合金孪晶界可动性或阻尼性能的关键参数。2. 提出了判断镁合金变形机制的 ST-MLRA 理论，对镁合金甚至其它HCP 结构金属的变形机制判断提供更加先进手段。3. 分析得出基于孪晶界强化的变形-热处理协同作用机制，为高强高加工硬 化率镁合金开发提供新理论与新技术。4. 首次提出在不牺牲力学性能的前提下，利用孪晶界移动来大幅提高镁合 金的阻尼性能，建立镁合金基于孪晶界的阻尼理论，对丰富和完善镁合金阻尼 理论有重要意义。发表高水平学术论文8篇，其中Acta Mater1篇，Scripta Mater1 篇，Journal of Magnesium and Alloys2 篇，Journal of Alloy and Compounds3篇; 培养硕士生5名，博士生3名；参加国内外学术会议6次，做会议报告5次。