Papers by Author: Rajiv S. Mishra

Abstract: The use of friction stir processing (FSP) on marine grade aluminum sheet has been investigated with the objective of locally enhancing the material properties. This can potentially allow low cost commercial grade aluminum to be used in superplastic forming applications or further enhance the formability to allow more complex geometries to be formed. FSP has been demonstrated to enable superplasticity (uniform elongations >250%) in 5083-H116 over a range of friction stir processing conditions.

Abstract: This paper brings together and compares data of various ultrafine grained (UFG) Al alloys processed through different routes. In general, the trend of decreasing ductility with increasing strength was observed for the UFG alloys. As compared to the coarse grained (CG) alloys, the UFG alloys show a lower ductility, a lower extent of work-hardening and a lower uniform elongation. Unlike the CG alloys, which show a large fraction of uniform to total elongation, in UFG alloys this fraction varies with processing technique. It is shown here that aging of some UFG Al alloys improves ductility. Further, it is shown that increasing the equivalent strain of pre-deformation increases ductility. From this it was inferred that high angle grain boundaries have an important influence on ductility. The variation of ductility with strain rate sensitivity has been found to match both the analytical prediction as well as data of various materials.