Abstract
Strain time measurements for Al-3 wt.%Si, Al-3 wt.%Si-1 wt.%Ag and Al-3 wt.%Si-1 wt.%Sn alloys were performed under static peak stress (sigma(s)= 83.2 MPa), cyclic stress reduction sigma(cy) (0-3.48 MPa) and frequency nu (0-0.38 Hz) at different working temperatures T-w from 413 to 493 K. The creep curves were obtained under both static stress, sigma(s) (with nu = sigma(cy) = 0), and then with superimposed cyclic stress at either: constant frequency (nu = 0.38 Hz) and different sigma(cy) values (hereafter specified as a-state), or at constant value of cyclic stress reduction (sigma(cy) = 3.48 MPa) and different frequency values (here after, b-state). The observed improved tensile ductility and softening with Ag addition, was due to the partial precipitation of Si attaching to the reticulate boundaries of the Ag phases. The improved mechanical properties with Sn addition were rendered to the spheroidization of Sn phases around Si particles forming the peritectic-type island structure. The high value of gamma ratio relating beta and epsilon(st) may point to a single mechanism operating in both creep stages. (c) 2012 Elsevier B.V. All rights reserved.