Effect of grain refinement and phase composition on room temperature superplasticity and damping capacity of dual-phase
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dri C. Atli Department of Mechanical Engineering, Anadolu University, Eskisehir 26555, Turkey
Harun Yanar and Gencaga Purceka) Department of Mechanical Engineering, Karadeniz Technical University, Trabzon 61080, Turkey (Received 22 November 2017; accepted 15 February 2018)
The effects of grain refinement and phase composition on superplasticity and damping capacity of eutectic Zn–5Al and eutectoid Zn–22Al alloys were investigated. For grain refinement, equal-channel angular pressing (ECAP) was applied to these alloys. ECAP completely eliminated the as-cast lamellar microstructures of both alloys and resulted in ultrafine-grained structures along with room temperature superplasticity. Furthermore, these microstructural changes with ECAP increased the damping capacity of both alloys in the dynamic hysteresis region, where damping arises from viscous sliding of phase/grain boundaries. Dynamic recrystallization at the surface and thermally activated viscous motion of grain/phase boundaries at the subsurface of the samples of both alloys were proposed as the damping mechanisms in the region where the alloys showed combined aspects of static/dynamic hysteresis damping behavior. Although the grain size is larger in Zn–5Al compared to Zn–22Al, it showed higher damping capacity due to the different sliding characteristics of its phase boundaries.
I. INTRODUCTION
Superplasticity is known as the high tensile elongation (higher than 400%) achieved in some polycrystalline materials prior to failure.1 Although superplasticity is generally observed at high temperatures (.0.5Tm, where Tm is the absolute melting point of the material) and low strain rates (between 10 5 and 10 3 s 1), recent studies showed that it is possible to achieve superplasticity for some alloys at high strain rate (HSR) and low temperature [even at room temperature (RT)] by formation of ultrafine-grained (UFG) microstructures.2–11 However, such superplastic behavior can be observed in limited alloy systems such as Sn–Bi,12 Pb–Tl,13 Pb–Sn,14 and Zn–Al6–11 due to the their low melting points and suitable microstructures for superplasticity. Among them, binary Zn–Al alloy system is the most commonly studied one, and it was shown that RT superplasticity could be observed in a wide range of phase composition of this system. Eutectoid Zn–22Al with duplex phase structure is well known for exhibiting excellent superplastic ductility in Zn–Al alloys and many studies have been performed on RT superplasticity of this alloy.6–8 RT superplasticity was also achieved in eutectic Zn–5Al alloys and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.46
quasi-single phase Zn–Al alloys having Al content up to 1.1% in weight. However, limited studies are available in the open literature on the RT superplastic behavior of those alloys.9,11 Besides having RT superplastic behavior, Zn–Al alloys have also high plastic deformation- and elastic deformation-induced damping capacity. Limited studies have been performed on the plastic deformation
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