Frequency and temperature dependence on the creep characteristics of Al-5 wt.% Zn alloy

Samples prepared from highly pure Al and Zn were homogenized for 50 h then swaged into wire of diameter 0.7 mm. The samples were solution treated at 773 K for 2 h then quenched in water to room temperature, and immediately, the specimens were aged for 2 h at different temperatures. Creep tests were carried out under constant stress of 27 MPa, constant shear strain amplitude of 5.16 x 10(-4) and low frequencies from 0.0 to 3.9 Hz superimposed on the static stress during creep test. Both the transient parameters beta and n increased with increasing temperature. Increasing frequency decreased beta and increased n due to a certain degree of fatigue hardening. The observed decrease of beta and steady stat rate, (epsilon)over dot(s) after the peak values may be attributed to the coarsening of Al-rich phase particles, which reduces their inhibiting effect on grain boundary. The higher values of beta obtained at higher temperatures, were attributed to the reduced crack initiation life associating the existing large grain size. The high average value of gamma(= delta ln beta/delta ln (epsilon)over dot(s)), 0.77, was explained in view of the so-called, substeady state creep. (C) 2012 Elsevier B.V. All rights reserved.