No abstract

The superplastic deformation behavior of quasi-single phase Zn-0.3 wt.%Al was investigated. A series of load relaxation and tensile tests was conducted at various temperatures ranging from RT (20 o C) to 200 o C. The recently proposed internal variable theory of structural superplasticity was applied. The flow curves obtained from load relaxation tests were shown to consist of contributions from interface sliding (IS) and accommodating plastic deformation. In the case of quasi-single phase Zn-0.3 wt.% Al alloy with an average grain size of 1 μm, the IS behavior could be described as a viscous flow process characterized by a power index of M g =0.5. A large elongation of about 1400 % was obtained at room temperature and the strain rate sensitivity parameter was about 0.4. Although relatively large-grained (10 μm) single phase alloy showed a high value of strain rate sensitivity comparable to that of fine-grained alloy at very low strain rate range, IS was not expected from the analysis based on the internal variable theory of structural superplasticity at room temperature. As the temperature increased above 100 o C, however, the contribution from IS was observed at a very low strain rate range. A high elongation of ~400 % was obtained in a specimen of 10-μm-grain-size at 200 o C under a strain rate of 2×10 -4 /sec.

The superplastic deformation behavior of a quasi-single phase Zn-0.3 wt.% Al and a microduplex Zn-22 wt.% Al eutectoid alloy has been investigated in this study within the framework of the internal variable theory of structural superplasticity (SSP). Load relaxation and tensile tests were conducted at room temperature for quasi-single phase alloy and at 200°C for eutectoid alloy. The flow curves obtained from load relaxation tests on superplastic Zn-Al alloys were shown to consist of the contributions from interface sliding (IS) and the accommodating plastic deformation due to dislocation activities. The IS behavior could be described as a viscous flow characterized by the power index value of Mg = 0.5. In the case of quasi-single phase Zn-0.3 wt.% Al alloy with the average grain size of 1 µm, a large elongation of about 1400 % was obtained at room temperature. In a relatively large-grained (10 µm) single-phase alloy, however, grain boundary sliding (GBS) was not expected from the analysis based on the internal variable theory of SSP.