Effect of cyclic stress reduction on the creep parameters of Al–Si alloy with Ag and Sn additions

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 (σs = 83.2 MPa), cyclic stress reduction σcy (0–3.48 MPa) and frequency υ (0–0.38 Hz) at different working temperatures Tw from 413 to 493 K. The creep curves were obtained under both static stress, σs (with υ = σcy = 0), and then with superimposed cyclic stress at either: constant frequency (υ = 0.38 Hz) and different σcy values (hereafter specified as a-state), or at constant value of cyclic stress reduction (σcy = 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 γ ratio relating β and ε ˙ st may point to a single mechanism operating in both creep stages.