Abstract
Zn–22Al alloy was processed using a well-designed two-step equal channel angular extrusion/pressing (ECAE/P), and ultrafine-grained (UFG) microstructure with 200 nm grain size was achieved. UFG Zn-22Al was subjected to long-term (up to 60 days) aging at room temperature (RT) and it was seen that natural aging caused limited grain growth in the microstructure. Grain sizes of about 300 nm, 350 nm and 350 nm were measured after 15, 30 and 60 days aging, which mean that UFG Zn-22Al alloy has a good microstructural stability at RT up to 60 days. ECAPed Zn-22Al alloy showed a maximum elongation of about 400% at a high strain rate of 5x10-2 s-1 and maximum elongation decreased with increasing grain size. Elongation to failures of ~375% and ~350% were obtained with the samples having 300 nm and 350 nm grain sizes, respectively. In addition, natural aging slightly decreased the strain rate at which superplastic region formed. While the maximum elongation occurred at the strain rate of 5x10-2 s-1 in ECAPed UFG alloy, it took place at lower strain rate of 1x10-2 s-1 after aging for all time periods. Also, flow stress of the alloy increased with increasing grain size during natural aging.
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