基于短流程复合成形新工艺的稀土镁合金环件近终精确成形微观组织调控

A new composite forming process is called liquid forging & isothermal rolling is proposed for manufacturing RE-modified magnesium alloy ring with complex cross section. Based on the novel short process, the project explores the macro and micro cooperative control method for manufacturing magnesium rings. The theoretical system of as-cast microstructure evolution through isothermal incremental deformation will be developed. The internal relations between microstructure evolution and macroscopic mechanical properties will be revealed. Moreover, we attempt to associate macroscopic mechanical properties with microscopic parameters such as material system , phase composition , grain size and so on. Then a systematic study on main process parameters of liquid forging and homogenizing annealing will be performed. Afterwards, by the analysis of deformation behavior of as-cast microstructure during isothermal heat rolling, a constitutive equation for the isothermal deformation and then the thermal processing map will be established. A detailed investigation on the necessary conditions of microstructures evolution from as-cast to forged and the microstructures completely modified in near-net-shape will be revealed. Finally, the comprehensive performance of magnesium rings made by three typical ring rolling processes will be determined through the comparative study on microstructure and mechanical properties. This work will provide theoretical as well as experimental insights into developing microstructure control technical of RE-modified magnesium alloy ring with superior properties.

本课题基于申请人提出的“复杂截面环件液态模锻后等温轧制”的全纤维复合成形新工艺，旨在探寻高强度镁合金全纤维大锻环短流程制备宏微观协同控制策略，发展稀土镁合金铸态锭坯在有限连续增量变形过程充分锻态改性的理论体系和方法，揭示稀土镁合金微观组织演化与宏观力学性能之间的内在联系，力图将短流程制备的稀土镁合金锻环最终宏观力学性能与材料体系、物相组成、晶粒度等微观参数定量地联系起来。针对液态模锻工艺制备Yb改性ZK60镁合金铸坯，详细考察合金的成分、加工条件和热处理对合金的微观组织、析出行为和力学性能的影响；针对铸态组织向锻态组织的转变条件和机理，开展液锻铸态组织的等温增量变形和改性研究，探讨近终复杂截面环坯完全锻透的必要条件；针对典型环坯制备工艺，开展环件综合性能的对比，解析不同工艺链对组织和性能的影响机理。本项目为新型高性能镁合金复杂截面环件短流程制备的组织性能调控技术提供理论和实验依据。

本项目以稀土镁合金环件增量热变过程微观组织演化为研究对象，旨在探索新型高强度稀土镁合金铸态锭坯在连续增量热变形过程充分锻态改性的理论体系和控制方法，揭示稀土镁合金微观组织演化与宏观力学性能之间的内在联系。首先考察稀土元素含量和加工条件对合金晶粒尺寸，形貌，第二相形态和分布的影响，通过对比研究探讨获得晶粒均匀细小，组织致密无缺陷的铸态锭坯的控制策略。其次，研究试验合金在不同变形温度和应变速率下的热变形响应，构建本构方程和热加工图，并与其他稀土改性镁合金进行对比分析。然后，拟合试验合金的再结晶动力学模型，系统考察Zener-Hollomon参数对合金动态再结晶特征参数的影响；提出再结晶敏感性指数考察再结晶程度对变形条件变化的敏感性；绘制再结晶分数等高线图，解析再结晶程度随变形条件和程度的演化历程；通过与不添加稀土的基体合金的对比分析，从理论上阐明其对再结晶动力学的影响规律。最后，基于理论解析总结高性能稀土镁合金全纤维大锻环短流程制备强塑性协同控制策略。通过本项目的研究，可提升稀土镁合金增量热变形过程中微观组织演化和力学性能影响的认识水平，为新型高性能镁合金环件短流程制备的组织调控技术提供理论和实验依据。