连续剪切正挤压镁合金的组织调控、强韧性能与拉深变形机理

Now, severe plastic deformation methods of Mg alloy usually possess complicated processes, repeated multiple steps, low efficiency and high cost. Furthermore, they can only prepare the material with a small volume and unable to realize the continuous and mass-production of Mg alloy. These disadvantages limit their application scope. Based on the problems, this project proposed one new severe plastic deformation method, namely continuous shear extrusion, by combining the characteristic of the metal which is under great three-dimensional compressive stress in deformation zone during extrusion. This method realizes a combination of multiple deformation modes during one extrusion process, can effectively refine the grain microstructure and weaken the base texture. Furthermore, this method is simple and it can produce large-scale Mg alloy sheet. This project will study the evolution law and stability of microstructure to reveal the grain refinement mechanism and texture weakening mechanism. Based on texture control, microstructure evolution of Mg alloy under different stress state during deep drawing will be studied to reveal the influence mechanism of texture on the drawing deformation. This project will produce Mg alloy sheet with high strength-ductility properties and high formability. The research results have important theoretical value and practical application significance to preparing of large-scale Mg alloy sheet with high strength-ductility properties and high formability, and will show a new way for expanding application of Mg alloy. In addition, This project will get through the barrier between the texture control and deep drawing of Mg alloy , and provide a new way and theoretical basis from microscopic mechanism to prediction and control of forming defects during deep drawing.

目前，镁合金剧烈塑性变形方法较复杂，需反复多个步骤，效率低、成本高，且只能制备小体积材料，无法连续、规模化生产，这限制了其应用范围。基于此，本项目结合金属在挤压过程中变形区承受三向压应力的特点，提出连续剪切正挤压剧烈塑性变形新方法，实现了一次挤压过程多种变形模式的组合，可有效细化镁合金晶粒组织、调控基面织构，且简单易行，可连续制备大尺寸镁合金板材。本项目将研究连续剪切正挤压镁合金的组织演变规律、组织稳定性，揭示晶粒细化机理及织构调控机制；基于织构调控，研究镁合金板材在拉深变形过程中不同应力状态下的组织演变规律，揭示织构影响拉深变形的微观机制；获得高强韧性、高成形性能镁合金板材。研究成果对制备大尺寸高强韧性、高成形性能镁合金板材具有重要的理论价值与实际应用意义，为扩展镁合金应用展示一条新途径；同时将打通织构调控与拉深成形之间的壁垒，从微观机制方面为预测与控制拉深成形缺陷提供新思路和理论基础。

针对镁合金常用剧烈塑性变形方法较复杂，需反复多个步骤，效率低、成本高，且只能制备小体积材料等问题，本项目结合金属在挤压过程中变形区承受三向压应力的特点，开发了连续剪切正挤压剧烈塑性变形新方法，实现了一次挤压过程多种变形模式的组合，有效细化了镁合金晶粒组织、调控了基面织构，且简单易行，相对于其它大塑性变形方法如等径角挤压、高压扭转、往复挤压等，可制备尺寸较大的镁合金板材。首先，本项目根据连续剪切正挤压工艺建立有限元模拟模型，模拟分析挤压变形过程中镁合金所受应力应变分布等，通过理论计算获得了连续剪切正挤压过程中的等效应变，优化了连续剪切正挤压工艺。其次，研究了不同变形条件下连续剪切正挤压镁合金在不同挤压变形阶段的微观组织变化，获得了连续剪切正挤压过程中的组织演变规律。第三，研究了连续剪切正挤压过程中再结晶晶粒形核区域的组织特征，揭示了连续剪切正挤压镁合金板材的晶粒细化机理及织构调控机制。第四，研究了不同织构镁合金拉深杯形件不同区域的组织演变规律，揭示了织构对镁合金板材拉深变形影响的微观机制。研究成果对制备大尺寸高强韧性、高成形性能镁合金板材具有重要的理论价值与实际应用意义，为扩展镁合金应用展示了一条新途径；同时打通了织构调控与拉深成形之间的壁垒，从微观机制方面为预测与控制拉深成形缺陷提供新思路和理论基础。