2002 Volume 43 Issue 10 Pages 2449-2454
The deformation behavior near room temperature in Zn-22 mass%Al alloy including nanocrystalline structure produced with Thermo Mechanical Controlling Process (TMCP) technology has been characterized over a wide range of strain rates from 10−6 to 10−1 s−1 at temperatures from 273 to 473 K . The microstructure of TMCP produced Zn-22 mass%Al alloy had both a random distribution of equiaxed Al-rich and Zn-rich phases with grain size of 1.3 \\micron and many nanocrystalline Zn particles in Al-rich phases. Since the flow stress in the deformation near room temperature was much larger than that in superplastic deformation and a maximum m value is only 0.3 (n=3) at low strain rates below 10−5 s−1, the pure superplastic behavior may not be observed near room temperature. However it is noted that the large elongation of ∼ 200% was observed at 10−5 s−1. From microstructural observations of the specimens tested in the condition with the m value of 0.3 near room temperature, furthermore, it is considered that grain boundary sliding (GBS) is the dominant deformation process, and the specimen may be fractured by cavitation as well as the conventional superplastic materials. Therefore, it seems that the various factors contribute to the deformation flow at room temperature.
