The annealing spectra of precipitating Al‐Li alloys are isochronally tested in the temperature range 25 to 400°C by observing the associated changes in internal friction and resistivity. A second order precipitation kinetics characterizes the first observed annealing band activated by 0.63 eV. As the annealing is proceeded, the β‐phase (AlLi) starts to precipitate according to a first order reaction of energy 0.6 eV, and a second band correspondingly appears. Pre‐annealing enhances both the previous bands but shifts only the second one to higher temperatures. Recrystallization starts at temperatures above 200°C and proceeds in a similar way as previously observed in dilute Al‐Li alloys. Further heating at higher temperatures dissolves the (Al Li) β‐phase and allows the lithium atoms to disperse by diffusion through the matrix. This expresses itself as a peak in Q−1 associated with a drop in resistivity.
Two annealing bands are found in the recovery of cold‐worked pure Al and three dilute AlLi alloys (0.25, 2.5, and 4.5 at% Li) in the temperature range 25 to 200 °C. A third one occurring at higher temperatures is detected only in Al–2.5 at% Li and Al–4.5 at% Li. The first annealing band is characterized by the annealing out of relatively free dislocations. The Li solute atoms, acting as impurity‐pinning points, retarded the dislocation mobility and, consequently, the recovery process. The second annealing stage, attributed to recrystallization, is found to be activated by an energy in the range 1.2 to 1.4 eV which is found to increase with increasing solute concentration. The binding energy between the Li solute atoms and dislocations is about 0.16 eV. At higher temperatures, a third stage of annealing characterized by a high activation energy (1.46 eV), is assumed to originate from the tendency of solute lithium atoms to form clusters in the matrix.
The transient creep of Cu–10 wt% Zn and Cu–30 wt% Zn solid solution alloys is investigated in the temperature range of 200 to 325°C and in the stress range of 150 to 400 MPa. The behaviour of the transient creep reveals that these alloys behave as class II “normal” at low stresses and as class I “inverse” at high stresses. The stress exponent m't, associated with the transient creep, is found to be 2.7 ± 0.3 at low stresses and greater than 4 at high stresses. The transition takes place at a stress σc which depends on both, temperature and the concentration of Zn‐solute atoms in the matrix. At low stress region the apparent activation energy Qt of the transient creep is found to be (0.3 ± 0.01) eV for the Cu–10 wt% Zn alloy and (0.6 ± 0.03) eV for the Cu–30 wt% Zn alloy. In the high stress region, Qt amounts to (0.9 ± 0.01) eV for both the alloys. These values of Qt are used to find the expected values of the apparent activation energy associated with the steady state creep. Also the investigation of the effect of pre‐coldwork on the transient creep shows that the processes controlling the creep mechanism in the different transient stages are independent of the dislocation density in the matrix and only depend on the concentation of Zn‐solute atoms in the Cu‐matrix.
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