Book Synopsis Flow Behavior and Microstructural Evolution During Superplastic Deformation of AA8090 Aluminum-lithium Alloy by :
Download or read book Flow Behavior and Microstructural Evolution During Superplastic Deformation of AA8090 Aluminum-lithium Alloy written by and published by . This book was released on 1906 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Superplasticity in AA8090 Al-Li alloy has been a subject of extensive studies, due to its potential for commercial applications since last decade. However, the anisotropy and microstructural gradient existing in this material introduce additional complication in understanding the mechanisms for superplastic deformation and has resulted in a debate about the role of dislocation activity. This has necessitated a more detailed microstructural study, especially texture, than that is commonly required to understand the deformation mechanism in other superplastic materials. Attempt has been made in this investigation to achieve this by means of microstructural characterization of specimens deformed in ten ion by using optical microscopy, TEM, SEM and orientation imaging microscopy (OIM). The microstructural characterization of the as-received material showed that there were three distinct layers in the cross-section of the sheet. Pancake grains in the center layer of about 1/3 thickness with brass-type texture, and nearly equiaxed grains on either side of it of about 1/3 thickness with copper texture. Tensile tests were conducted over a temperature range of $25{-}570\sp\circ$C and a strain rate range of $\rm 1 \times 10\sp{-4}{-}1 \times 10\sp{-2}/s.$ Optimum superplastic conditions were found in a temperature range of 500-530$\sp\circ$C and in a strain rate range of $\rm 1 \times 10\sp{-4}{-}1 \times 10\sp{-3}/s.$ These deformation conditions yielded the maximum value of strain rate sensitivity index $\rm(m \approx 0.5)$ and the minimum value of instability parameter (I). During superplastic deformation, there occurred grain growth, texture weakening and change in grain shape. The disappearance of initial microstructural gradient occurred at a strain of about 1.0. The relationship between grain size (d) and strain $(\varepsilon)$ could be expressed as $\rm d\propto\varepsilon\sp{q}, $ with the value of exponent q ranging from 0.21-0.44 depending on the test temperature. T.
