预制孪晶与第二相耦合增强ECAP制备超细晶Mg-Gd-Y合金的机理研究

超细晶结构稀土镁合金材料展现出优越的力学性能，应用前景广泛。受变形条件限制，等通道转角挤压技术（ECAP）很难获得超细晶结构稀土镁合金材料。为进一步细化微观组织，提高材料的力学性能，本项目拟以Mg-Gd-Y系镁合金为研究对象，通过固溶处理、预压缩变形、时效处理的方法制备高密度预制孪晶与稳定析出第二相的耦合结构，提高ECAP对稀土镁合金材料微观组织细化的效率与程度，改善材料力学性能。利用SEM-EBSD、TKD、TEM等表征与分析技术，系统研究耦合结构中预制孪晶体积分数及第二相尺寸、形貌、分布与加工后材料的动态再结晶晶粒体积分数、晶粒尺寸、高角度晶界比例、织构强度之间的关系，深入分析耦合结构引入的界面与位错运动的交互作用，阐明在ECAP过程中耦合结构对材料晶内和晶界处塑性变形机制的影响，建立耦合结构调控动态再结晶实现组织细化的理论模型。该项目研究成果为制备高强韧超细晶稀土镁合金提供理论依据。

Ultra-Fine Grain (UFG) structured Magnesium-rare earth (Mg-RE) alloys become attracting materials due to their excellent mechanical properties. Due to the limitation of the deformation conditions, it is difficult to obtain UFG structured Mg-RE alloys by the Equal Channel Angular Pressing (ECAP). In order to produce Mg-RE alloys with smaller grain size, the solid solution treated Mg-Gd-Y based alloys are used as the experimental material. The effect of ECAP on the microstructure refinement and homogenization of the Mg-RE alloys is improved via the coupled structure of the high-density tensile twins and the stable second-phase particles, which is produced by pre-compression and peak aging treatment. The SEM-EBSD, TKD and TEM techniques are performed to systematically investigate the effect of volume fraction of twins, the size of second-phase particles as well as the morphology and distribution, the volume fraction of the dynamic recrystallization and recovery grains and the texture of the produced Mg alloys. The interaction between the dislocations and the introduced interfaces via the fabrication of the coupled structure will be analyzed, as well as the effect of coupled structure on the deformation mechanism of the materials within the grains and at the grain boundaries during ECAP. The model for realizing grain refinement via coupled structure based dynamic recrystallization will be established, thus building a theoretical basis for producing Mg-Re alloys of high performance.