Creep behavior of heat resistant Al–Cu–Mn alloys strengthened by fine (θ′) and coarse (Al20Cu2Mn3) second phase particles

Abstract

In this work, creep behaviors of two Al–Cu–Mn alloys (Alloy-A: Al-1.7 wt%Cu-0.3 wt%Mn, Alloy-B: Al-2.2 wt%Cu-0.8 wt%Mn) were investigated at temperature 448 K–523 K under applied stress of 30–50 MPa for Alloy-A and 40–70 MPa for Alloy-B, respectively. Alloy-A contains small amount of fine (θʹ, <500 nm) precipitates and Alloy-B contains a great amount of coarse (T-Al20Cu2Mn3, 500nm-1μm) particles. Alloy-B exhibits much slower creep rates (as compared to Alloy-A) at every temperature up to an applied stress of 60 MPa. Creep mechanisms are discussed in terms of stress exponent and activation energy. It is observed that fine particles (θʹ) strengthened alloy exhibits an increased value of stress exponent with temperature while the coarse (T-Al20Cu2Mn3) particles strengthened alloy exhibits decreased values. Also, both the alloys show two regimes of creep mechanisms in the selected stress and temperature range, 498 K being the transition temperature. The fine particles (θʹ) strengthened alloy shows a transition from dislocations interaction process (due to small amount of particles) to dislocation climb mechanism with an activation energy of 110 kJmol-1 (at 50 MPa). While, the coarse particles (T-Al20Cu2Mn3) strengthened alloy shows a transition from grain boundary pipe diffusion mechanism to boundary sliding with 51 kJmol-1 of activation energy (at 65 MPa). Furthermore, the creep activation energy of the coarse particles strengthened alloy is decreased with the applied stress. The constructed constitutive equations show a good agreement between the experimental and simulated steady state creep rates, with an error less than 10% for Alloy-A and Alloy-B.