Economical High Strain Rate Superplastic Forming via Friction Stir Processing

超塑性成形是一种近净成形技术，可用于生产复杂形状的零件和航空航天应用的组合结构。尽管超塑性成形具有许多吸引人的特征，但在航空航天领域之外的广泛商业应用受到两个主要缺点的阻碍：（a）超塑性成形速率慢，和（B）超塑性起始材料的高成本。细晶粒尺寸是材料表现出超塑性行为的关键要求，即，拉伸延展性为200%。 传统的轧制热机械加工方法制备具有超塑性的铝合金通常需要六个步骤，本研究的目的是开发一种创新的一步热机械加工技术，即搅拌摩擦加工（FSP）。FSP（摩擦搅拌焊的一种改进）用于增强超塑性的基本概念是基于在固态摩擦搅拌期间形成的非常精细的显微组织。FSP的成功开发将为开发新概念提供机会，这些新概念包括：（a）选择性超塑性成形;（B）厚板的超塑性成形;以及（c）从铸造板或热压粉末冶金板一步超塑性加工。 该项目将重点发展对关键微观组织问题的理解，例如：（1）FSP参数对微观组织发展的影响;（2）FSP过程中重叠道次对微观组织的影响;（3）细化微观组织对高温暴露的响应;以及（4）摩擦搅拌加工材料中的微观组织-超塑性性能相关性。该研究涉及大学（UMR）和行业（罗克韦尔科学中心和波音幻影工厂）的积极合作。工业界的直接参与将导致更快的技术过渡，总体影响可能非常显著。

Superplastic forming has emerged as an attractive near net shape forming technique for production of complex shaped components and unitized structures for aerospace applications. In spite of many attractive features, the widespread commercial use of superplastic forming outside aerospace sector is hampered by two major drawbacks: (a) slow superplastic forming rates, and (b) high cost of starting material for superplasticity. Fine grain size is a key requirement for materials to exhibit superplastic behavior, i.e., tensile ductility of 200%. The conventional rolling-based thermo-mechanical processing methods for producing aluminum alloys having superplastic properties typically require six steps.The goal of this research is to develop an innovative one-step thermo-mechanical processing technique for grain refinement, Friction Stir Processing (FSP). The basic concept of FSP (an adaptation of friction stir welding) for enhanced superplasticity is based on the very fine microstructure that develops during solid-state friction stirring. Successful development of FSP would provide opportunities to develop new concepts, that include: (a) selective superplastic forming; (b) superplastic forming of thick sheets; and (c) one-step processing for superplasticity from cast sheet or hot-pressed powder metallurgy sheet. This project will focus on developing an understanding of critical microstructural issues, such as: (1) influence of FSP parameters on the microstructural development; (2) the effect on microstructure of overlapping passes during FSP; (3) the response of refined microstructure to elevated temperature exposure; and (4) microstructure-superplastic property correlations in friction stir processed materials. The research involves active collaboration of university (UMR) and industries (the Rockwell Science Center and the Boeing Phantom Works). The direct industrial participation will result in faster technology transition and the overall impact is likely to be very significant.