A. F. Abd El-Rehim

Effect of superimposed oscillations on creep behaviour of Al – 2 4·.5Cu and Al – 2 4·5Cu – 2 0·1In (wt-%) alloys containing θ′ precipitates

Abstract The behaviour of both transient and steady state creep of Al – 4·5Cu and Al – 4·5Cu – 0·1In (wt-%) alloys was investigated using a constant stress where torsional oscillations of different frequencies and shear strain amplitudes were operated at various working temperatures. An augment in both transient and steady state creep rates was observed by increasing both frequency and shear strain amplitude of the applied oscillations. The mean values of the activation energy of both alloys for both creep stages were found to be equal to that quoted for dislocation intersection mechanism.

Examination of breakdown stress in creep by viscous glide in Al-5·5 at.-%Mg solid solution alloy at high stress levels

Abstract Creep tests on Al–5·5 at.-%Mg solid solution alloy show that the stress exponent n increases with increasing stress from 3·1 to 5·5. It is demonstrated that the transition to n≈5·5 is not consistent either with normal power law breakdown or with a transition to a region of viscous glide controlled by pipe diffusion, but the results are in good agreement with a breakdown of the dislocations from their solute atmospheres. The activation energies for creep at low and high stresses are 136 and 170 kJ mol−1 respectively.

Effect of cyclic stress reduction on high temperature creep characteristics of solid solution Al−2·9 wt-%Mg alloy

Abstract Creep characteristics of solid solution Al−2·9 wt-%Mg alloy have been investigated under the effect of cyclic stress reduction of different amplitudes (12·47−26·18 MPa) and frequencies (0·20−0·44 Hz) at different working temperatures ranging from 533 to 593 K. It was found that increasing both amplitude and frequency of cyclic stress reduction resulted in an increase in both transient and steady state creep stages. The enhancement of creep rate was observed above either a threshold stress or a threshold frequency. The activation energy values of the mechanisms operating in both transient and steady state creep stages were found to be 130 and 171 kJ mol−1 respectively.