多级连续剪切-弯曲变形镁合金板材的晶粒细化与织构控制

Severe plastic deformation is one of the effective ways to prepare high-performance wrought magnesium alloy. Nowadays it has become a hot research topic. Equal channel angular rolling (ECAR) is a process which is a combination of rolling and shearing process. However, the relationship between the grain refinement and the control of the texture of the magnesium alloy sheet during the ECAR is hard to be coordinated due to the repeated rolling and heating. Thus, how to solve the problem is crucial to further improve the room temperature ductility of the magnesium alloy sheet. In the project, a new processing, so-called multi-pass continuous shearing-bending (MP-CSB) processing, this is a combination of normal rolling, multi-pass shearing and bending process, is proposed. With the aim of the grain refinement and texture control of the magnesium alloy sheet, via the combination of numerical simulation and measurements, the deformation behaviors and the evolving principles of the grain size, deformation twins and texture of the sheet, during the MP-CSB procedure are investigated systematically. In addition, the contributions of the deformation twining, dislocation slipping and recrystallization behavior to the grain refinement and texture control of the sheet are studied, respectively. The characteristics and mechanisms of dynamic recrystallization of the sheet during the MP-CSB are explored. So the influence laws and mechanisms of the combination of rolling, shearing and bending processes and the alternation of shearing and bending processes on the grain refinement and texture control of the sheet can be revealed, respectively. Thereby, the studies in the project will enrich the plastic deformation theory of magnesium alloy, and lay the theoretical and technical foundation for the industrial production of wrought magnesium alloy sheet with excellent integrate performance.

大塑性变形技术是研制高性能变形镁合金的有效方法之一，已成为当今材料领域的研究热点。其中，等径角轧制是一种将轧制与剪切变形相结合的工艺。但是其自身的特点（反复轧制和保温）使镁合金板材难以实现晶粒细化和织构控制的相互协调。因此，如何解决以上问题是进一步提高镁合金板材室温塑性的关键。本项目率先提出一种将轧制与连续多次剪切、弯曲变形相结合的新工艺，即多级连续剪切-弯曲工艺（简称MP-CSB）。以晶粒细化和织构控制为目标，以数值模拟和实验相结合为手段，系统研究MP-CSB变形过程中镁合金板材的变形行为及晶粒组织、孪晶、织构的演变规律；变形孪生、位错滑移、再结晶行为等对MP-CSB板材晶粒细化与织构演变的贡献。探究MP-CSB过程中的动态再结晶特点与机理；揭示轧制、剪切、弯曲复合作用以及剪切、弯曲交替作用对板材晶粒细化和织构控制的影响规律和机理；为高性能变形镁合金板材的工业化生产奠定理论和技术基础。

大塑性变形技术是研制高性能变形镁合金的有效方法之一，已成为当今材料领域的研究热点。其中，等径角轧制是一种将轧制与剪切变形相结合的工艺。但是其自身的特点（反复轧制和保温）使镁合金板材难以实现晶粒细化和织构控制的相互协调。因此，如何解决以上问题是进一步提高镁合金板材室温塑性的关键。本项目率先提出一种将轧制与连续多次剪切、弯曲变形相结合的新技术，即多级连续剪切-弯曲变形（简称MP-CSB）。以晶粒细化和织构控制为目标，以数值模拟和实验相结合为手段，系统研究MP-CSB变形过程中AZ31镁合金板材的变形行为及晶粒组织、孪晶、织构的演变规律；变形孪生、位错滑移、再结晶行为等对MP-CSB板材晶粒细化与织构演变的贡献。探究MP-CSB过程中的动态再结晶特点与机理；揭示轧制、剪切、弯曲复合作用以及剪切、弯曲交替作用对板材晶粒细化和织构控制的影响规律和机理。主要获得以下研究结果：（1）开发了两种调控镁合金板材组织与织构的MP-CSB工艺，即1次剪切-1次或多次弯曲复合和多次剪切-弯曲交替，并利用有限元技术优化了模具结构，其中剪切圆角半径、模具通道间隙对MP-CSB板材的变形行为（应变状态和变形模式（剪切或弯曲变形））和表面质量等影响显著；（2）MP-CSB镁合金板材中高密度的孪晶是分割原始晶粒并诱导动态再结晶细化晶粒的主要原因。相比多次剪切-弯曲交替，1次剪切-1次或多次弯曲复合对AZ31镁合金板材织构的调控更为显著。在该变形过程中，首先在剪切应力作用下非基面取向的动态再结晶晶粒以及拉伸孪晶形成，使其部分晶粒分别向RD转动45°和90°；其次，在拉、压应力作用下大量拉伸孪晶形核、长大并逐渐“吞噬”原始变形晶粒，使其大量晶粒向RD方向旋转90°，导致基面织构进一步弱化。退火后，该板材获得了非常特殊的织构特征，使其室温IE高达7.4mm，这与变形过程中产生的高密度<c+a>非基面位错和孪晶有关。综上所述，MP-CSB可以实现镁合金板材晶粒细化与织构控制的相互协调，这为高性能变形镁合金板材的工业化生产奠定理论和技术基础。