Work‐hardening rates during the steady‐state creep of aluminum and alloys determined from stress‐change tests

Work‐hardening rates of aluminum and selected aluminum alloys during steady‐state creep at 300 °C are determined from the instantaneous strains on sudden stress changes (increments and decrements). Alloys examined included Al‐0.4% Li, Al‐0.3% Li (in three different irradiated conditions), Al‐2.73 at% Mg and Al‐4.2 at% Mg. Work hardening rates, h, varied from about 0.1 to about 1 times Young's modulus, E. h/E decreases with increasing creep stress, σ. At a given value of σ, h/E is the lowest for polycrystalline aluminum and highest for the irradiated Al‐0.3% Li alloys. Although the values for h/E are comparable to previously determined values for the creep of f.c.c., b.c.c. and h.c.p. metals, they are higher than strain‐hardening rates determined from tensile tests. These differences are rationalized in terms of the dependence of work (strain) hardening on the strain rate