基于侧向应变挤压一体化实现镁合金织构可控制备及其机理研究

Mg alloys sheets usually give rise to a strong texture during primary processing such as hot-extrusion and hot-rolling processing, which resulted in the poor room temperature ductility and strong anisotropy, and then further limited the applications of Mg alloy sheets. In this work, the thin and thick sheets of Mg alloy were intended to prepare by the novel integrated extrusion equipped with the side direction strain to achieve grain refinement and weak texture. The dynamic recrystallization and texture softening behavior of the side direction strain zone were studied, and the influence of the original grain orientation and the side direction strain gradient geometry on the recrystallization behavior was elucidated. The plastic deformation mechanism of the lateral strain zone was explored. The effects of lateral deformation geometry, side direction strain and hot extrusion process parameters on grain orientation and grain size were analyzed. The relationship between the different gradient of lateral strain and the texture components and grain size were set up. The work aims to reveal the microstructural evolution of the extruded Mg alloy sheets under lateral strain and the qualitative relationship with the lateral deformation factors. High performance and tailoring texture of Mg alloy sheet are expected to introduce by a single processing step of strain paths associated with the novel integrated extrusion processing, which will expand the application of magnesium alloy to provide theoretical and experimental basis.

镁合金板材在挤压或者轧制过程中易产生强基面织构，这种的织构形成导致了各向异性强和成形性能差等问题，进而限制镁合金板材的应用。因此，如何在制备加工过程中实现镁合金板材织构改性一直是热门的研究课题。本项目拟通过在热挤压过程中耦合侧向应变一体化，在板材侧部形成梯度应变场，实现晶粒细化和织构可控的镁合金薄、厚板的一次成形制备。研究侧向应变几何约束因素、侧向应变量和挤压工艺对晶粒取向和尺寸的影响；分析侧向应变挤压过程中动态再结晶及其诱发的织构软化行为，阐明原始晶粒取向和侧向应变梯度几何特性对再结晶行为的影响，探索应力-应变场作用下侧向应变区塑性变形机制；构建不同梯度侧向应变量与织构组分和晶粒尺寸的关系，揭示基于侧向应变下镁合金挤压板材微观结构演变规律以及与侧向应变因素的关系，实现挤压织构可控和高性能板材一体化的制备，为改善镁合金挤压薄、厚板成形性能和扩大镁合金应用领域提供理论基础和实验依据。

镁合金因独立滑移系少、非基面滑移临界剪切应力高，导致板材室温成形性能差且各向异性强，晶粒取向和织构改性是解决该问题的有效途径。镁合金板材在轧制或者挤压加工过程易产生强基面织构及强度低等问题，本项目采用热挤压耦合侧向应变一次成形制备不同尺寸镁合金板材，研究侧向应变区特征参数对板材组织均匀性、晶粒大小和动态再结晶行为的影响。基于侧向应变诱发动态再结晶调控织构为主要目标，以晶粒转动和微观取向演变为晶体学物理模型，构建不同侧向应变区横向及法向应变梯度，揭示微观结构、晶粒取向、变形参数和挤压工艺对织构调控的影响规律。研究侧向形变热挤压过程中动态再结晶及其诱发的织构软化行为，探索侧向应变区塑性变形机制；分析侧向形变几何约束因素、侧向应变量和热挤压工艺参数对晶粒取向和晶粒尺寸影响，得出合理的侧向应变调控板材基面织构机制。. 本项目旨在揭示基于侧向应变下镁合金挤压板材微观结构演变规律以及与侧向形变因素的定性关系，阐明原始晶粒取向和侧向应变梯度几何特性对再结晶行为的影响，实现基面织构弱化，提高杯突值，降低各向异性系数r值，为改善镁合金挤压薄、厚板成形性能和扩大镁合金应用领域提供理论基础和实验依据。设计了渐进式非对称挤压、大应变挤压、变截面挤压等三种非对称剪切挤压模具，其力学性能得到显著改善，抗拉强度由332MPa提高到358MPa，屈服强度由161MPa提高到171MPa，延伸率由15.4%提高到21.9%。相关研究有助于进一步完善细晶弱织构镁合金制备技术设计及控制理论，并为侧向应变热挤压一体化制备高性能镁合金板材及其应用提供重要的技术保障和理论支撑。