Under the nominal steady-state creep, the stress exponent
is equal to one regardless of initial state of specimens.
However, the nominal steady-state creep rate for water
quenched 5N Al is one order less than that for quenched
specimens located in air within one year due to work (cold)
hardening. The hardness for 5N Al after quenching was about
18 HV, whereas it is about 13HV for the specimens located
in air within one year. With increase in stress, creep
strengthening (the creep rate progressively decreasing in
subsequent segments) was observed, which is due to different
hardening remains because changing-stress creep experiment
was conducted in the transient creep stage. Those phenomena
of work hardening provided evidences of creep controlled by
recovery and hardening mechanism.