异质颗粒对镁合金动态再结晶与析出行为的调控机理研究

Owing to the uncompleted dynamic recrystallization (DRX) for Mg alloy deformed at low temperature, it is hard to achieve good matching between strength and plasticity. To overcome this problem, the microstructure of Mg alloy deformed at low temperature was controlled in this project by micron heterogeneous particles, for which can promote the nucleation of DRX. Then, the refinement of DRXed grains and improvement of DRX ratio will be realized in the same time, which will result in the increment of the Mg alloy’s mechanical properties. Through investigating the formation mechanism of particle deformed zone (PDZ) and analyzing the influence of the PDZ’s size and distance on the nucleation and growth of DRXed grains, the DRX behavior effected by heterogeneous particles will be revealed. The kinetics for precipitation will be researched by constructing the relationship among the size, volume fraction and hot deformation parameters of precipitate in Mg alloy deformed at low temperature. The influence of heterogeneous particles on the dynamic precipitation behavior of Mg alloy will be revealed. Based on above research and analysis, the regulating mechanism of microstructure and mechanical properties of Mg alloy controlled by heterogeneous particles will be clarified. The cooperative strengthening mechanism between heterogeneous particles and precipitates will be revealed based on the investigation on their influence on dislocation, twinning, grain boundary, initiation and propagation of crack, etc. The realization of grain refinement in Mg alloy controlled by heterogeneous particles will provide a new way for the design and development of Mg alloy with high strength and better ductility in this project, which will have important theoretical significance and application value in the future.

低温变形镁合金由于动态再结晶（DRX）不完全，无法实现强度和塑性的良好匹配。为此，本项目基于微米级异质颗粒能够促进DRX形核的思想，对低温变形镁合金显微组织进行调控，同时实现镁合金DRX晶粒细化和DRX率提高，达到提升其综合力学性能的目的。通过研究异质颗粒周围变形区（PDZ）的形成机理，分析PDZ尺寸和间距对镁合金DRX晶粒形核和长大的影响规律，阐明异质颗粒对DRX行为的影响机制；建立低温变形镁合金析出相尺寸、体积分数与热变形条件之间的关系，研究其析出动力学，揭示异质颗粒对镁合金动态析出行为的影响机制；在此基础上，阐明异质颗粒对低温变形镁合金显微组织和力学性能的调控机制；分析异质颗粒与析出相在室温变形过程中同位错、孪晶、晶界、裂纹萌生与扩展等作用规律，揭示其协同强化机制。项目基于异质颗粒调控实现镁合金晶粒细化的思想，为高强韧镁合金的设计与开发提供了一条新途径，具有重要的理论意义和应用价值。

降低变形温度是实现镁合金晶粒细化的重要途径。镁合金经低温挤压后，动态再结晶（DRX）晶粒尺寸减小，但因含大量的未动态再结晶组织，强度虽高，塑性较差。为此，本项目提出了采用微米级异质颗粒促进DRX形核的思想，通过研究异质颗粒对DRX行为的影响机制、异质颗粒对镁合金动态析出行为的影响规律、微量SiCp调控Mg-5Zn的高温变形机理及热加工行为、低温变形SiCp/Mg-5Zn材料组织与性能控制、以及异质颗粒调控镁合金的协同强化机理等，实现低温变形镁合金DRX晶粒细化和DRX率的同时提高，达到提升其综合力学性能的目的。研究结果表明，微米颗粒附近能够形成具有高密度位错和较大取向差梯度区域（PDZ），微量PDZ的形成可以显著降低DRX临界应变，加速DRX速率，随PDZ尺寸增加，DRX临界应变增大但DRX速率减缓；PDZ对DRX形核的影响与变形量有关：在变形初期，Mg基体以晶界“弓出”形核为主，随着变形量增大，PDZ对DRX形核促进作用逐渐凸显，且随PDZ尺寸增大而增强；PDZ能够同时促进Mg-Zn相的形核与长大，随PDZ尺寸增大，DRX率降低，Mg-Zn相尺寸和体积分数均有所减小；PDZ不会改变Mg基体的织构类型，却降低了基面织构强度，随着PDZ尺寸的增大，基面织构强度增加；微量PDZ可降低Mg合金的变形激活能，拓宽Mg合金的热加工区间，改善其成形性能；PDZ能够显著提升Mg合金的力学性能，随PDZ尺寸增大，强度降低但伸长率提高；Zn元素和SiCp对Mg基体屈服强度的贡献包括：细晶强化、析出强化、位错强化机制和载荷传递作用，其中细晶强化机制和析出强化机制贡献最大；SiCp的添加导致Mg-5Zn合金在拉伸变形过程中的加工硬化现象减弱，与Mg-Zn析出相相比，晶粒细化对Mg基体软化作用更强，致使拉伸变形过程中SiCp/Mg-5Zn材料的软化作用大于Mg-5Zn合金。项目的开展对航空、航天、民用汽车等领域用轻质、高强韧镁基材料的设计与开发，具有重要的理论指导意义。