耦合孪生变形与时效调控镁合金析出相晶体学的机理研究

The major phase in most precipitation-hardening Mg alloys is plate-shaped or lath-rod-shaped and is often parallel to the basal plane of the matrix phase. This largely affects its hardening effect. However, currently it is very difficult to alter the original orientation relationship (OR) of the precipitates. It is known that twinning can rotate grain orientation and promote aging precipitation. It is also found that twinning will not rotate the precipitates, but just bent them elastically. Based on these facts, we propose to tailor the OR of the precipitates in Mg alloys by combining pre-twinning and aging. Two typical low-cost Mg alloys AZ80 and ZK60 will be used as the model materials. HRTEM, 3D-AP and HAADF techniques will be employed to study the effect of pre-twinning on aging precipitation and its underline mechanism. The crystallography of the precipitates formed at twin boundaries and its mechanism will be analyzed in-depth. The evolution of the OR and the phase interface during twinning deformation and aging will be revealed. The processing window for controlling the crystallography of the precipitates will be determined. Then the interaction between the precipitates and dislocation or twinning will be understood. These achievements will provide theoretical guideline for developing new strengthening methods for precipitation-hardening Mg alloys.

大部分沉淀硬化型镁合金中的主要析出相多以基面片状板条出现，严重影响了镁合金的强度，然而想要改变析出相特有的位向关系目前还很困难。针对镁合金中孪生变形可以改变晶粒取向，并促进时效析出的特点，以及被孪晶界扫过的析出相仅仅发生弹性弯折的实验现象，项目提出耦合孪生变形与时效调控镁合金析出相位向关系的新思路。拟选用AZ80和ZK60两种典型的低成本镁合金作为模型材料，利用HRTEM、3D-AP、HAADF等微观分析手段，系统研究预孪生变形对镁合金时效析出的影响规律及微观机制，深入分析孪晶界上析出相的晶体学特征及形成机理，阐明析出相位向关系及相界面在孪生变形与时效过程的演变规律，明确调控镁合金析出相晶体学的工艺窗口，阐明析出相与位错和孪生的交互作用，从而为发展适用于沉淀硬化型镁合金的新型强韧化方法提供理论支撑和技术原型。

大部分沉淀硬化型镁合金中的主要析出相多以基面片状板条出现，严重影响了镁合金的强度，然而想要改变析出相与镁基体特有的位向关系目前还很困难。针对镁合金中孪生变形可以改变晶粒取向，并促进时效析出的特点，以及被孪晶界扫过的析出相只发生弹性弯折的实验现象，本项目提出通过耦合时效处理和孪生变形调控镁合金中析出相与镁基体的位向关系，系统研究析出相的晶体学特征及其与孪生的交互作用，研究结果有助于发展适用于镁合金材料的新型强韧化方法和理论。. 在项目的实施过程，申请人选用AZ80和ZK60两种典型的低成本镁合金作为模型材料，在镁铝合金中发现了四种新的析出相与镁基体之间的取向关系，通过研究预孪生变形对镁合金时效析出的影响，创造性地设计了孪生-时效-退孪生工艺，实现了对镁合金中基面析出相取向的调控，显著提高了镁合金的析出强化效果，为开发高性能镁合金提供了一种全新的思路。项目深入研究了拉伸、压缩及二次孪晶界上析出相的晶体学特征，明确了孪晶界析出相的取向关系、界面特征及变体选择规律，揭示了孪晶界对析出行为的影响规律。. 项目发展了预测孪生调控析出相与镁基体取向关系的晶体学算法，并在Mg-Al合金中得到验证，所提出的通过孪生调控析出相取向的新思路有望在其它各类可沉淀强化镁合金中得到广泛应用。项目研究结果有望为发展高效的低成本的镁合金材料制备加工技术提供重要的理论指导。