Economical High Strain Rate Superplastic Forming via Friction Stir Processing

Missouri University Of Science And Technology, Rolla MO

Investigators

Abstract

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.