脉冲电流条件下纳米晶金属箔材超塑性微成形机理与尺寸效应

Aim at the problems of poor formability and inhomogeneous deformation of metal foil during superplastic micro forming, the electro superplastic and Joule effect of pulse current are employed to improve the superplastic formability and uniformity of nano-crystalline metal foil.To disclosure the mechanism of superplastic micro forming by the pulse current, the responses of the alloys with the different microstructure and the cavities under these technological conditions are researched. Moreover, to illuminate size effect of the formability and establish the constitutive quations, the superplastic mechanical properties of the metal foil with different sizes under the state of uniaxial and biaxial stress by the action of the pulse current are studied, and the theory model of the relationship of pulse current, microstructure, superplastic formability and size effect is established. Through the theory model, the superplastic forming ability of the metal foil under the condition of high strain rate is explored,and the special technology and equipment of the nano-crystalline metal foil superplastic micro forming by pulse current are studied, and the mould and equipment are designed, and the parameters and the process of the technology are optimized. The micro forming with the characteristic of high accuracy, high efficiency and large strain is achieved finally.This study would lay a foundation of the pulse current auxiliary superplastic micro forming technology.

针对金属箔材在微成形时存在成形能力差、变形不均匀等问题，利用脉冲电流的"电致超塑性效应"及"焦耳热效应"，提升纳米晶金属箔材的超塑性微成形性能与变形均匀性。通过研究脉冲电流条件下纳米晶金属箔材超塑性微成形过程中的微观组织演变及空洞行为，揭示其超塑性微成形机理；通过研究脉冲电流参数、晶粒大小及试样特征尺寸对纳米晶金属箔材单向及双向应力状态下超塑性力学性能的影响规律，构建材料的本构方程，描述脉冲电流作用下材料微成形性能的尺寸效应，并建立脉冲电流参数、材料微观组织、超塑性力学性能及其尺寸效应间相关性的理论模型。以该模型为依据发掘材料在高应变速率区的超塑性微成形能力，制定脉冲电流条件下纳米晶金属箔材超塑性微成形的工艺流程，设计相应的工装模具，优化工艺参数，最终实现纳米晶金属箔材的高精度、高效率、大变形量的超塑性微成形。该项目研究将为脉冲电流辅助超塑性微成形工艺奠定基础。

为提高纳米晶金属箔材的微成形性能，实现其大应变量的微成形，提出了一种脉冲电流辅助塑性及超塑性微成形方法。通过正交试验优化了纳米晶Ni箔材的电沉积制备工艺，获得了具有不同晶粒尺寸及性能的纳米晶箔材；系统研究了纳米晶金属箔在脉冲电流条件下的塑性及超塑性微成形性能，揭示了脉冲电流对其微成形行为的影响规律，明晰了其作用机理；利用人工神经网络构建了脉冲电流条件下纳米晶箔材微塑性流动的本构模型，结果表明该模型具有较高的预测精度；描述了脉冲电流条件下纳米晶金属箔材流动应力的尺寸效应，并研究了脉冲电流对其尺寸效应的影响规律；设计并实施了脉冲电流条件下纳米晶箔材的应力松弛试验，其试验结果进一步证实了脉冲电流在纳米晶金属箔材微成形过程中的增塑与致塑作用，并从机理上对这一现象进行了阐述；设计了脉冲电流辅助纳米晶金属箔材超塑性微成形装置，进行了工艺试验，成形出了尺寸微小的薄壁半球形试验件，为实现纳米晶金属箔材的低成本、高效率微成形奠定了理论与技术基础。