Room Temperature Deformation Behavior of Zn-22 mass%Al Alloy with Nanocrystalline Structure

Abstract

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 µm 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.

Superplasticity at Room Temperature in Zn-22Al Alloy Processed by Equal-Channel-Angular Extrusion

“…4, which also includes comparative data taken from Ref. (7,24,25,28). The region exhibiting large elongations was roughly in good agreement with the region where high m-values were achieved.…”

“…2, which includes the results of earlier reports, 7,20,[24][25][26] as well. The strain rate sensitivity exponent (m-value) is defined in the equation (d ln =d ln _ " ") where is the flow stress and _ " " is the strain rate.…”

“…3, which also includes the results of earlier reports. 7,10,20,24,25) The grain size exponent, p-value, which is estimated from the slope of the line, was found to be 2 at lower strain rates. Several experimental results on superplasticity at high temperature in Zn-22Al alloys have also indicated p ¼ 2.…”

“…4,5) Such discoveries have enormous practical significance; for instance, it was reported recently that the ultrafine grained Zn-Al alloy could be applied as a seismic damper for high-rise buildings by attaining high strain rate superplasticity at room temperature. [6][7][8][9][10][11] Recently, severe plastic deformation (SePD) techniques such as equal-channel-angular extrusion (ECAE) or torsion straining (TS) have been seen as methods for producing bulk materials with ultrafine-grains. 12,13) The principle behind these techniques is to produce a very large strain in the sample; the rearrangement of the dislocations introduced by straining leads to a substantial grain refinement down to the submicrometer or even the nanometer scale.…”

Post-characteristics of Formed Zn-22 mass%Al Alloy to Seismic Damper for General Residence

“…[3][4][5][6] Especially, the melting point of superplastic Zn-22 mass%Al alloy is comparatively low (693 K), and it has been reported that superplasticity was expressed even at room temperature. [7][8][9][10][11] Recently, it was also demonstrated that superplastic Zn-22 mass%Al alloy could possibly be applied to seismic damping devices, showing higher performance in comparison with that using a low-yield-point steel. 12,13) The seismic damping device formed by machining Zn-22 mass%Al alloy has already been put into actual use in a high-rise building.…”