EFFECT OF PHASE-TRANSFORMATION AND PREDEFORMATION ON CREEP CHARACTERISTICS OF AL-40 WT-PERCENT ZN ALLOY

The change in the steady state creep rate of Al-40 wt% Zn alloy is stu died under constant stresses ranging from 42 to 50.3 MPa and at differ ent temperatures ranging from 503 to 623 K. The study is extended to s amples given different degrees of torsional predeformation in the same investigated temperature range. The stress sensitivity parameter m' i s found to decrease from 5 to 2.3 by increasing the working temperatur e. The energy activating the steady state creep is found to be 78 kJ/m ol in the temperature range from 513 to 533 K and 128.5 kJ/mol in the temperature range from 603 to 623 K characterizing a grain boundary di ffusion mechanism of Zn in beta-phase and of Al in a-phase, respective ly. The activation energy 105.7 kJ/mol obtained in the temperature ran ge from 573 to 593 K may characterize volume self-diffusion of Zn. The se values decrease by increasing the degree of predeformation which is associated with creep strain rates. The analysis of the microstructur al variations confirms that the above-mentioned mechanisms are expecte d to take place during the investigated steady state creep stage.