Superplastic Deformation Behavior of Friction Stir Processed 7075Al Alloy
Commercial 7075Al rolled plates were subjected to friction stir processing (FSP) with different processing parameters, resulting in two fine-grained 7075Al alloys with a grain size of 3.8 and 7.5 μm. Heat treatment at 490 °C for 1 h showed that the fine grain microstructures were stable at high temperatures. Superplastic investigations in the temperature range of 420-530 °C and strain rate range of 1×10−3-1×10−1 s−1 demonstrated that a decrease in grain size resulted in significantly enhanced superplasticity and a shift to higher optimum strain rate and lower optimum deformation temperature. For the 3.8 μm 7075Al alloy, superplastic elongations of >1250% were obtained at 480 °C in the strain rate range of 3×10−3-3×10−2 s−1, whereas the 7.5 μm 7075Al alloy exhibited a maximum ductility of 1042% at 500 °C and 3×10−3 s−1. The analyses of the superplastic data for the two alloys revealed a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy close to that for grain boundary self-diffusion. This indicates that grain boundary sliding is the main deformation mechanism for the FSP 7075Al. This was verified by SEM examinations on the surfaces of deformed specimens.
Z. Y. Ma et al., "Superplastic Deformation Behavior of Friction Stir Processed 7075Al Alloy," Acta Materialia, Elsevier, Oct 2002.
The definitive version is available at http://dx.doi.org/10.1016/S1359-6454(02)00278-1
Materials Science and Engineering
National Science Foundation (U.S.)
United States. Office of Naval Research
Keywords and Phrases
Friction Stir Processing; Aluminum alloys; Superplasticity
Article - Journal
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