Transient Creep Characteristics Near the Transformation Temperatures of Al-5wt%Zn and Al-15wt%Zn Alloys

Al-Zn alloys are stronger than most aluminum based alloys. They provide materials which combine the high wear resistance, heat resistance and strength with the castability needed for many industrial applications. Constantstress creep tests were conducted for Al-5wt%Zn and Al-15wt%Zn alloys under various stresses ranging from 114.6 to 129.8 MPa for Al-5wt%Zn alloy and from 129.8 to 150 MPa for the second alloy. The transient creep parameters n and β were determined for each alloy in the temperature range around their transformation temperatures. The results for both alloys revealed two different transient deformation regions around their transition points which existed at 393 and 473 K for the two alloys, respectively. The temperature dependence for each of the transient creep parameters n and β attained peak values at the transition points for all the applied stresses. The transient creep was activated with (31.5 ± 0.5) and (29.9 ± 0.4) kJ/mol in the low deformation regions for the two alloys of 5wt%Zn and 15wt%Zn, respectively. These values characterize a dislocation mechanism involving grain sliding or grain migration. The best fitting equation, obtained by the least squares method of the relation between the steady state creep strain rate ε • st and the transient creep parameter β, was used to correlate the transient and steady state creep stages for each alloy.