High Strain Rate, Thick Section Superplasticity Created Via Friction Stir Processing


This work demonstrates friction stir processing as a thermomechanical process to create a fine grain microstructure in 7050 T7651 Al resulting in high strain rate (>10-3), thick section (>5mm) superplasticity. Elements of process control and microstructural evolution are characterized. Superplastic behavior is illustrated as a function of test conditions of temperature, accumulated strain, and strain rate. High strain rate and thick section superplasticity are two material properties never before demonstrated on a practical scale. For example, high uniform elongation (>500%) is achieved for strain rates >1x103s-1 at temperatures less than 460°C. Further, friction stir processing produces a relatively uniform fine grain size through the sheet thickness. This allows fine grain microstructures to be created in a section thickness >5mm, i.e., a thickness considerably greater than attainable by conventional thermomechanical processing. It will be shown that high levels of elongation, even at the highest strain rates, remain uniform, i.e., no diffuse necking. This offers the potential to form complex shaped parts at a higher rate and in section thickness never before possible.


Materials Science and Engineering

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Article - Conference proceedings

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Publication Date

01 Dec 2001

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