Some Activation Parameters in Steady-State Creep of Aluminium–Magnesium Alloys at High Temperatures

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Abstract
The internal stress, σi , and the effective-stress exponent of dislocation velocity, m*, have been studied during steady-state creep tests on aluminium and Al–Mg alloys containing 0·5–7 at.-% Mg at temperatures between 523 and 723K under an applied stress of 3·9–98 N/mm2. Stress-transient dip-tests showed that σi had an appreciable value almost independent of composition and thus cannot be neglected in discussing creep processes in these materials. Values of m* determined from analyses of relaxation curves immediately after creep were close to unity in alloys containing 2 at.-% or more of magnesium. The same result was obtained from stress-increment tests on an Al–5·5 at.-% Mg alloy. It is concluded that high-temperature creep of Al–Mg alloys under the conditions of this work is controlled by solute-atmosphere dragging. An explanation has also been given for the fact that the applied-stress exponent of steady-state creep rate, n, is nearly 3 when m* = 1 and σi is at a significant level.