高强Mg-Zn-Zr系变形镁合金轧制板材塑性成形性能的织构依赖性研究

The large-scale application of wrought magnesium alloy sheets in industrial fields has been impeded by the poor sheet formability at room temperature. Basal texture weakening is the most effective way to enhance the formability. However, the texture effect as well as its mechanism on formability of magnesium alloys is still unclear. We have studied the texture influence on plastic deformation under a uniaxial tensile state for Mg-6.6wt.%Zn-0.5wt.%Zr alloy sheets, and achieved an exponential relationship between uniform strain and strain hardening, which is strongly correlated with texture. In this study, magnesium alloys sheets with various texture patterns will be prepared by combining extrusion, differential speed rolling and addition of rare-earth element Y. The plastic deformation mechanisms and the hardening behavior under the uniaxial tensile state will be analyzed systematically with texture variation using a crystal plasticity model. The contributions of slip systems and twinning to the plastic strain will be quantified simultaneously. A more reasonable dependence of texture on formability under the uniaxial tensile state will be constructed. Subsequently, this process will be extended to plane strain state and biaxial stretching state, and also to reveal the texture effect on microscopic deformation mechanism. Finally, a modified forming limit diagram (FLD) considering the texture effect will be trying to establish. This makes a lot of sense to develop new fabricating techniques for wrought magnesium alloy sheets with high formability, and also to new forming techniques for wrought magnesium sheets at lower temperature, and maybe successfully at room temperature.

变形镁合金轧制板材较差的室温成形性制约着其在工业领域的规模化应用。织构弱化是改善镁合金塑性最有效的方法，但织构对塑性的影响规律及其作用机理尚不清晰。目前，我们已研究了单向拉伸状态下板材织构对Mg-6.6wt.%Zn-0.5wt.%Zr变形镁合金塑性的影响，并得到了均匀应变与织构相关硬化曲线斜率的指数依赖关系。本研究将通过挤压-异步轧制复合工艺及微量稀土Y元素添加，获得织构可控的镁合金板材，并借助晶体塑性模型，系统分析单向拉伸状态织构对塑性变形机制及硬化行为的影响，量化滑移、孪生等微观变形机制对塑性应变的贡献，构建完善的塑性织构依赖关系，随后将其扩展至平面应变、双等拉伸等多向应力状态，揭示多向应力状态下织构影响的微观变形机理，最后建立包含织构影响的较为完备的成形极限图。这对基于织构优化设计开发新型高成形性镁合金板材制备技术以及发展轻质变形镁合金板材中低温甚至室温成形技术都具有极为重要的意义。

结构轻量化是航空航天、汽车、电子等众多工业领域发展的重要目标和方向。实现镁合金轻体结构的冲压成形，可充分发挥其轻质特性，助推深加工产业发展。然而，镁合金轧制板材较差的室温成形性严重制约着应用。前期研究表明织构弱化是改善镁合金塑性最有效的方法，但受制于织构状态难以调控的现状，织构对镁合金塑性的影响规律及其作用机理尚不清晰，很难为板材制备及后续冲压成形领域的织构优化设计提供切实可行的理论指导。为此本项目拟以板材基面织构弱化为切入点，研发基于稀土微合金化与塑变加工工艺的板材基面织构弱化控制工艺，并系统研究了板材织构对镁合金板材塑性成形性能的影响。.主要研究内容为：（1）以高强Mg-Zn-Zr（ZK61）镁合金为研究对象，通过稀土元素Y添加和挤压/轧制工艺控制，研究铸造/挤压/轧制/热处理等多过程组织性能关系，探求有效的板材基面织构控制工艺，完成弱织构板材制备；（2）基于板材组织性能研究与晶体塑性模型，研究单向拉伸状态下织构对塑性变形机制及硬化行为的影响，量化各微观变形机制开动程度及对应变量的贡献值，确立单向拉伸状态下利于塑性发挥的微观变形模式及织构状态；（3）研究拓展至多向应力状态（平面应变和双等拉伸）下，揭示多向应力状态下织构影响下的微观变形机理，建立并验证含织构影响的成形极限图（FLD），确定基于模拟的成形性改善的织构优化设计原则。.研究结果揭示了稀土元素Y和挤压/轧制工艺对板材基面织构弱化的基本影响规律；建立了包含熔铸/挤压/轧制/热处理全过程的镁合金板材基面织构弱化控制工艺，从工程化角度上实现了对板材基面织构状态的连续可控，获得具有不同织构状态的镁合金板材；揭示了冲压成形工艺三种典型状态（单向拉伸、平面应变和双等拉伸）下织构对板材塑性成形性影响机理，建立了包含织构影响的成形极限图，为变形镁合金板材塑性成形性改善的织构优化设计方法提供依据，也为高成形性镁合金板材制备及冲压成形技术的开发开拓了思路。