弱基面织构镁合金板材复合变形机制演变规律的定量研究

The poor formability of magnesium alloy sheet has restrained its wide use for light-weight applications. Fortunately, the development of advanced magnesium alloy sheet with weak basal texture makes it possible to handle this issue. However, the evolution of the deformation mechanisms, including dislocation slip, twinning and grain boundary sliding, during plastic deformation has not been fully investigated, which reduces its capability. The project aims on Mg-2Zn-0.1Ca sheets with various material features (texture and grain size). For different processing conditions (Temperature：25~300℃，strain rate ：1E-4~1E-2 s-1), to study the evolution of the activated slip systems according to slip trace analysis firstly; Then, to calculate the strain distribution based on Green-Lagrange strain tensor and von Mises strain; Thirdly, to study the change of the shear in each activated slip system based on the analysis of slip system activities and strain distribution; Furthermore, to analyze the evolution of twinning and grain boundary sliding; Eventually, to quantitatively investigate the correlation between the evolution of deformation mechanisms and material features and processing conditions, respectively. This work can contribute to a better understanding of the effects of these two key factors on formability, and provide theoretical fundamentals to enhance the formability of magnesium alloy sheet.

镁合金板材有限的成形性能极大地限制了其在轻量化领域的广泛应用。而新型弱基面织构镁合金板材的开发使这一问题的解决成为可能，但是其塑性变形机制（位错滑移、孪生和晶界滑动）的演变规律尚未得到深入研究，使其优势未能得到充分挖掘。本项目拟以Mg-2Zn-0.1Ca合金板材为研究对象，在不同变形工艺条件下（温度：25~300℃和应变速率：1E-4~1E-2 s-1），针对具有不同材料特征参量（织构和晶粒尺寸）的板材，通过滑移迹线分析变形过程中滑移系激活规律的演变；并运用网格法计算局部应变（Green-Lagrange应变张量和von Mises应变）；再基于滑移系激活规律和局部应变研究各滑移系切应变的变化，同时研究孪生和晶界滑动的演变；最终阐明材料特征参量和变形工艺参数与镁合金板材复合变形机制演变规律的关系，深入理解上述两个关键因素对成形性能的影响机理，为镁合金板材成形性能的提升提供理论基础。

镁合金板材有限的成形性能极大地限制了其在轻量化领域的广泛应用。而新型弱基面织构镁合金板材的开发使这一问题的解决成为可能，但是其塑性变形机制（位错滑移和孪生）的演变规律尚未得到深入研究。本项目以Mg-2Zn-0.1Ca合金板材为研究对象，通过滑移迹线分析和高分辨数字图像相关技术（High resolution digital image correlation, HRDIC）分析了局部应变，定量研究了材料特征参量（织构和晶粒尺寸）和变形工艺参数（温度和应变速率）对Mg-2Zn-0.1Ca板材在不同应变阶段变形机制的演变规律，并以此为基础阐明了材料特征参量和变形工艺参数对其成形性能的影响机理，为镁合金板材成形性能的提升提供了理论基础。主要结果如下：1）Mg-2Zn-0.1Ca板材具有双峰织构，该织构使其在变形过程中变形机制（位错滑移和孪生）的演变具有显著的各向异性，进而导致其力学性能和加工硬化率也具有明显的各向异性；2）变形温度对变形机制有显著影响。与室温变形相比，高温变形过程中有更多的非基面滑移被激活；3）应变速率对力学性能和变形机制的激活规律有显著影响，与低应变速率相比，高应变速率会激活更多的非基面滑移，尤其是柱面滑移，使强度提升；4）晶粒尺寸对变形机制和力学性能亦有显著影响。晶粒细化不仅使强度提高，还可以使变形过程中的应变分布更加均匀。在细晶样品中，我们发现有更多的非基面滑移被激活，使其具有更好的塑性。