Economical High Strain Rate Superplastic Forming via Friction Stir Processing

超塑性成形用于生产复杂形状的部件和单元结构。搅拌摩擦成形在克服传统超塑性成形的两大缺点方面显示出很大的潜力：(A)超塑性成形速度慢，(B)超塑性原料成本高。建议的研究将集中在与重叠方案和较大刀具几何形状的基本显微组织-性能形成关联上。这项研究对于推动基于搅拌摩擦加工的超塑性技术的发展具有重要意义。搅拌摩擦加工增强超塑性的基本概念是基于固态搅拌摩擦过程中形成的非常精细的微观组织。这项新的加工技术将作为一种手段，实现三步近净成形制造路线：板材铸造+搅拌摩擦加工+高应变速率超塑性成形。为了成功地开发增强超塑性的搅拌摩擦工艺，需要了解的关键问题包括：(I)搅拌摩擦工艺参数和工具对组织发展的影响；(Ii)搅拌摩擦加工过程中重叠道次对显微组织的影响；(Iii)异常晶粒长大的机理及其抑制/避免的方法；以及(Iv)多道次搅拌摩擦加工材料的组织-超塑性性能关系。这些问题将在可热处理(7475Al)和铸造Al-Zn-Mg-Sc合金中进行研究。这项拟议的研究涉及大学(UMR)和行业(罗克韦尔科学公司和苏佩尔公司)的理想结合。这项拟议研究的更广泛影响包括为本科生课程带来创新想法，如金属变形处理和金属结构-性能实验室。在工业方面，苏佩尔是世界领先的超塑成型部件制造商，如果这一概念能够成功开发，他们的参与将导致技术转让和实施。超塑性成形是一种节能、环保的技术，将其应用于更多的产品将有助于推动环境友好型制造。

Superplastic forming is used to produce complex shaped components and unitized structures. Friction stir processing has demonstrated a strong potential to overcome two major drawbacks of conventional superplastic forming: (a) slow superplastic forming rates, and (b) high cost of starting material for superplasticity. The proposed research will focus on the fundamental microstructure-property-forming correlations with overlapping scheme and larger tool geometry. Such study is crucial to promote the initial concept and develop breakthrough enabling superplastic technologies based on friction stir processing.The basic concept of friction stir processing for enhanced superplasticity is based on the very fine microstructure that develops during solid-state friction stirring. This new processing technique will be used as a means to achieve a three-step-near-net-shape manufacturing route: casting of sheet + friction stir processing + high strain rate superplastic forming. The critical issues that need to be understood for successful development of friction stir processing for enhanced superplasticity include: (i) influence of friction stir processing parameters and tools on the microstructural development; (ii) the effect on microstructure of overlapping passes during friction stir processing; (iii) the mechanism of abnormal grain growth and ways to suppress/avoid it; and (iv) microstructure-superplastic property correlations in multi-pass friction stir processed materials. These issues will be investigated in heat treatable (7475 Al) and cast Al-Zn-Mg-Sc alloys. The proposed research involves an ideal combination of university (UMR) and industries (Rockwell Scientific and Superform). The broader impact of the proposed study includes bringing innovative ideas to undergraduate courses such as metal deformation processing and metals structure-property laboratories. On the industrial front, Superform is the world's leading manufacturer of superplastically formed components and their involvement will result in technology transfer and implementation if this concept can be successfully developed. Superplastic forming is an energy-efficient and environmentally friendly technology, and expansion of its applicability to a wider range of products will help in promoting environmentally benign manufacturing.