Effect of multi directional forging on impression creep behavior of Zn-24Al-2Cu alloy

Abstract

Multi directional forging (MDF) of Zn-24Al-2Cu alloy were carried at 100�C and 200�C with total equivalent strain of 0.6 and 1.2 respectively. The average grain size was reduced from 30 to 1 ?m after MDF processing. Impression creep behavior of MDF processed samples was studied at 2 kg and 2.5 kg load with temperatures 30, 50, 100 and 150�C. Microstructural characterizations were carried out using optical microscope, transmission electron microscope and X-Ray diffractometer. Steady state creep rate values were recorded in the range of 1.2x10-5 to 5.2x10-7. The four phase transformation occurred in the structure after MDF process and during the impression creep test. Initial stress exponent (n) values are in the range of 2.5 to greater than 5. High values of 'n' showed due to the existence of threshold stress. The true activation energy values calculated are in the range of 22-129 kJ/mol. Changes in creep properties of MDF processed samples seem to be more sensitive to change in temperature compared to microstructural differences. Lattice diffusion controlled by dislocation climb is the dominant creep mechanism. � 2018 Elsevier Ltd. All rights reserved.