Creep characteristics and cavitation mechanisms of AA2017

Abstract

In this work, the creep behavior of AA2017 and the governing cavitation processes were investigated at intermediate temperatures. Initially, the examined alloy was subjected to solution treatment at 495 °C and then over-aged at 210 °C. Afterward, the creep tests were performed over a temperature range of 120 °C to 210 °C and applied stress in the 120 MPa to 310 MPa range. The obtained results facilitated the analysis of the predominant creep mechanism and the impact of second-phase precipitations on cavitation nucleation and growth kinetics. Moreover, the morphology and the distribution of cavities were studied and the volume fraction of cavities was defined using optical metallography and scanning electron microscopy. The physical models of cavity growth were also utilized to justify the observed phenomena. It was found that the stress exponent varied between 3.4 and 9.8 at temperatures between 120 and 210 °C while the activation energy for creep was computed as 151.3 kJ/mol at the stress of 230 MPa. However, as the stress decreased to 180 MPa, the activation energy increased to about 194 kJ/mol. This suggests that dislocation climb is the dominant creep mechanism at lower temperatures while solute drag dominates the creep process at 210 °C. The examined alloy is susceptible to cavitation during creep testing. At the same time, the coalescence was observed at the high applied stress, particularly at the stress of 290 MPa at creep strains higher than 0.015.