细晶Mg-Gd-Ag合金中位错诱导高效沉淀析出调控与强化机理研究

沉淀硬化是轻质镁合金主要强化方式，但目前其强化作用远不及在铝合金中有效，针对于此，本项目提出“细晶组织位错结构构建—位错诱导低温析出调控—析出相高效沉淀强化”新思路。选取高沉淀硬化潜力Mg-Gd-Ag合金体系，调控热挤压+低温预轧+低温时效工艺，在细晶合金中构建不同位错结构，利用位错诱导析出实现高效沉淀硬化，制备超高强镁合金。着重利用透射电镜双束、HAADF-STEM技术，解析位错结构（类型、密度）和析出相数密度与特征（尺寸、形态、分布等），阐明位错结构对柱面和基面析出相形核、生长的影响规律和作用机理，揭示位错结构与析出相数密度和特征的定性和定量关系，构建位错诱导时效析出动力学模型；解析力学测试中不同数密度/特征析出相与位错运动的交互作用关系，建立以析出相高数密度和优化特征为核心的镁合金强化机制。研究成果将丰富和发展镁合金析出相变及强化基础理论，同时为制备超高强镁合金材料提供关键技术基础。

Precipitation hardening is the main strengthening mechanism of lightweight magnesium alloys, but it is far less effective in magnesium alloys than in aluminum alloys at present. In view of it, this project puts forward a new idea of "dislocation structure construction in fine grains-dislocation induced precipitation regulation at low temperature-highly effective precipitation strengthening". It is proposed to select Mg-Gd-Ag alloy system with high precipitation hardening potential and regulate hot-extrusion + low temperature pre-rolling + low temperature aging processes. Consequently, different dislocation structures in fine-grained alloys can be constructed and highly effective precipitation hardening would be achieved by dislocation-induced precipitation, which contribute to preparation of ultra-high strength magnesium alloy materials. The TEM two-beam diffraction and HAADF-STEM technologies are especially used to analyze dislocation structure (type and density) and precipitated phase number density and characteristics (size, morphology, distribution, etc.), so as to clarify the influence law and mechanism of dislocation structure on the precipitate nucleation and growth formed on prismatic plane and basal plane, reveal the qualitative and quantitative relationship between dislocation structure and precipitated phase number density and characteristics, and construct the kinetic model of dislocation-induced aging precipitation. The interaction between different number density/characteristic precipitates and dislocation motion in mechanical property tests is analyzed, so as to establish a strengthening mechanism for magnesium alloy focusing on precipitated phase with high number density and optimized characteristics. The research results will enrich and develop the basic theory of phase transformation and strengthening for precipitation-hardened magnesium alloys, and also provide the key technical basis for the preparation of ultra-high strength magnesium alloy materials.