等温模压变形镁合金板材强韧化细化机理及工艺优化研究

Poor room-temperature ductility, absolute strength and formability of magnesium alloys greatly limit their industrial application. Groove pressing has significant advantages in grain refinement and property improvement of sheet metals while no reasonable explanation of its deformation mechanism is available until now. Aiming at these problems, choosing AZ31 magnesium alloy sheets as object of study, strengthening-toughening and refinement mechanism of magnesium alloys during isothermal groove pressing and process optimization methods are investigated in this work. First of all, an experimental system and a coupled thermo-mechanical finite element model for isothermal groove pressing are established, and the fracture behavior and its prediction methods of magnesium alloy sheets during groove pressing are studied. Then, the influence of die structure and process condition on flow law, microstructure and mechanical properties and deformation homogeneity of magnesium alloy sheets during groove pressing are systematically investigated, and the influence mechanism of deformation temperature and path is emphasized. The multi-objective optimization of die structure and process parameters is achieved. Finally, the deformation mechanism of magnesium alloys during isothermal groove pressing is revealed, and bulk ultra-fine grained magnesium alloy sheets with superior comprehensive properties are fabricated. This work can enrich and develop the basic plastic deformation theory of magnesium alloys, and speed up the development of preparation technology of high performance magnesium alloys, and lay a theoretical foundation for application and promotion of the new severe plastic deformation process.

室温塑性差、绝对强度低、成形性能差等问题严重制约了镁合金的工业应用。模压变形在金属板材晶粒细化与性能改善方面优势明显，但目前有关其变形机理的解释尚不成熟。针对上述问题，本项目以AZ31镁合金板材为研究对象，研究等温模压变形镁合金的强韧化细化机理及工艺优化设计方法。首先，构建等温模压变形实验系统及热力耦合的有限元模型，研究镁合金板材在模压变形过程中的断裂行为及其预测方法。然后，系统研究模具结构和工艺条件对模压变形镁合金板材的流动规律、组织结构与力学性能、变形均匀性等的影响，着重阐明变形温度和路径的影响机理，并实现模具结构参数和工艺参数的多目标优化。最后，揭示等温模压变形镁合金的变形机理，制备出综合性能优异的大体积超细晶镁合金板材。项目的开展将丰富和发展镁合金的塑性变形基础理论，加快高性能镁合金制备技术的开发进程，为剧烈塑性变形新工艺的应用和推广奠定理论基础。

镁合金是目前工程应用中最轻的金属结构材料，但是室温塑性变形能力差、绝对强度偏低、耐腐蚀性能差等问题严重制约着镁合金的应用与推广。模压变形是一种极具工业应用潜力的新型剧烈塑性变形方法，尤其适用于金属板材的微观组织调控与性能改善。本项目围绕镁合金板材的等温模压变形过程所涉及的关键科学问题，结合理论分析、数值模拟和工艺实验等方法，开展了相关的研究工作。项目构建了等温模压变形实验系统并实现了镁合金板材的模压变形过程，制备出性能优异的大体积超细晶AZ31和LA81镁合金板材，证实了模压变形在镁合金改性方面的适用性；建立了热力耦合的镁合金板材多道次等温模压变形有限元模型，分析了镁合金板材在模压变形过程中的塑性变形行为与机理，实现了模压变形工艺过程与模具结构的优化设计；研究了等温模压变形对镁合金板材微观组织与性能的影响，分析了模压变形镁合金板材的温热变形行为与热稳定性，探讨了模压变形镁合金板材的超声喷丸表面改性效果，揭示了等温模压变形镁合金板材的微观组织演化与性能改善机理。项目的开展，有助于模压变形方法的工业应用与推广，并将推动镁合金制备与加工技术的发展及高性能轻质合金的工程应用。研究结果在Materials Science and Engineering A、International Journal of Advanced Manufacturing Technology、Metals、塑性工程学报、锻压技术等塑性成形领域权威期刊发表学术论文8篇，授权实用新型专利1项，申请发明专利1项。