利用复合孪晶结构调控镁合金力学性能机制研究

The hot-rolled AZ31 Mg alloy plate with a basal texture is used in current project. A cross compression pre-straining is employed to prepare a composite twin structure containing the primary extension twins and the secondary extension twins. The composite twin structure is used to strengthen the pre-strained sample along RD, TD and ND at the same time,meanwhile improve the tension-compression yield asymmetry. Using the TEM,in-situ EBSD and XRD, the quantified relationship between the content of the composite twin structure and the pre-straining parameters is systematically investigated. The deformation mechanism of the pre-strained sample subjected to loading along different dirctions is also fully addressed to disclose the role of different microstructures in the plstic deformation. At last, the strengthening mechanism and the corresponding strengthening model along different directions are built, too. In addition, the nature for the influence of composite twin structure on the tension-compression yield assymetry is revealed.The results of this project provide a novel method for strengthening and toughening treatment of Mg alloys and form the principles to tailor the microstructure and the mechanical properties of Mg alloys by deformation twins. This study also contributes to the techniques and the theory of strengthening and toughening of Mg alloys.

本申请选择具有基面织构的AZ31镁合金热轧厚板为试验材料，利用侧面交叉压缩预变形制备一次拉伸孪晶-二次拉伸孪晶的复合孪晶结构，实现材料沿轧向、法向和横向的三维同步强化，并改善板材的拉伸-压缩屈服不对称性。综合利用TEM、原位EBSD和XRD等先进的表征与分析技术，系统研究预变形参数与复合孪晶结构的组成（孪晶类型、孪晶体积分数和片层间距）及织构演化之间的定量关系，深入分析沿不同方向加载时复合孪晶结构中各类组织的微观变形机制，揭示复合孪晶结构中各类组织及其结构因数（尺寸和体积分数）在塑性变形中的作用与地位，阐明复合孪晶结构沿三个方向的强化机制并建立相应的强化模型，同时揭示复合孪晶结构影响板材拉伸-压缩屈服不对称的本质。通过本项目的研究，提供了一种新型的镁合金强韧化方法，建立利用形变孪晶调控镁合金组织和力学性能的理论，丰富镁合金强韧化的技术和理论体系。

孪晶细化晶粒是强化金属的重要方法，本项目针对镁合金中一次孪晶只能强化特定方向的问题，利用一次孪晶+二次孪晶的复合孪晶结构实现块体材料三维方向上的同时强韧化，并改善板材的拉伸-压缩屈服不对称。.主要开展了以下几个方面的研究：（1）变形参数与孪晶结构因数之间的定量关系；（2）复合孪晶结构沿不同方向拉伸和压缩的力学行为和变形机制（3）位错及溶质原子与孪晶界面相互作用及对力学行为的影响；（4）复合孪晶结构影响拉压屈服不对称的规律和机制。. 重要的研究发现包括：（1）建立了高效强化复合孪晶结构的制备准则，即小应变+大应变的交叉压缩变形，可获得三维方向上同时强韧化；（2）孪晶构成和加载条件均显著影响复合孪晶结构的变形机制，孪晶周围组织改变可使变形机制由退孪生转变为孪生形核，此种结构具有更高的强化效果；（3）复合孪晶结构可以显著降低三个方向的拉-压屈服不对称，其主要机制是使拉伸或压缩变形中同时启动几种不同的变形机制；（4）晶界和孪晶界细化晶粒可以产生显著不同强化作用：晶界可以更好的强化位错滑移变形，孪晶界可以更好强化孪生变形，使得孪晶界可以更好的降低拉压屈服不对称性。. 本项目发表SCI论文23篇，包括Acta Materialia 1篇、Scripta Materialia 1篇、Scientific Reports 2篇。项目培养了博士1名，硕士4名，在本领域重要学术会议做特邀报告11次。