Deformation behavior of superplastic Zn-Al alloy

Abstract

The deformation behavior of superplastic Zn-Al alloy of eutectoid composition (40.6 at.% Al) has been investigated by metallography, X-ray diffraction, and creep deformation. Metallographic examination of specimens deformed at 250°C showed that the phases maintained their approximately equiaxed shape. No preferred orientation of the phase was found in the X-ray diffraction patterns of specimens deformed at 250°C. Steady state creep measurements show that the process of deformation is thermally activated. The values of the activation energies, Q, are 35.3 ± 1.0 kcal/g-atom and 21.0± 1.0 kcal/g-atom for temperatures of deformation above 200°C and below 175°C respectively. The strain rate, {greater-than with dot}3, could be related to the applied stress, σ, at a temperature, T, by an equation of the form σ = α{greater-than with dot}3a + β{greater-than with dot}3c in which a = 017-020, c = 046-050, α = B exp (aQ/RT), and β = C exp (cQ/RT); B and C are functions only of the particle size. It is shown that the rate-controlling mechanism can be described by the motion of dislocations in an internal stress field. © 1967.