日本金属学会誌

J. Japan Inst. Metals, Vol. 56, No. 7 (1992),
pp. 757-763

Behaviour of Fe Atoms and Age-Softening in Al-Fe Alloy

Satoru Yamamoto1, Atsushi Kirihata1 and Masataka Mizuno1

1Department of Metallurgy, Faculty of Engineering, Kyoto University, Kyoto

Abstract:

The aim of this investigation is the clarification of the mechanism of age-softening and the influence of pre-treatments on this phenomenon in Al-Fe alloys. The main results are as follows. The combination of treatments: soaking at 673 K, hot-rolling at 673 K and annealing at 673 K as pre-treatments results in age-softening in Al-Fe alloys. It has been cleared by the measurement of specific resistivity that the amount of Fe dissolved into matrix is always limited below 0.01 mass%Fe in the age-softened specimens. Electron microscopic observation has clarified fine precipitates smaller than 1 μm and recrystallized structures in the age-softened specimens but no such precipitates nor recrystallized structures in the work-hardened specimens.
Further, the lowering of recrystallization temperature has been confirmed by the experiments of isochronal annealing of specimens. Thus, the mechanism of age-softening in Al-Fe alloys is as follows: The pre-treatments are necessary for the complete precipitation of dissolved Fe which results in the lowering of recrystallization temperature. The age-softening occurs due to the recovery and recrystallization of the worked specimens at room temperature. The preexisting second phase (Al3Fe) in the as-cast state accelerates the precipitation of dissolved Fe. The physical meanings of each step of pre-treatments are as follows:
673 K: the temperature suitable for the complete precipitation of dissolved Fe in Al.
soaking: homogenizing of structure of segregated cast alloys which results in the easiness of following hot-rolling.
hot-rolling: acceleration of precipitation of dissolved Fe.
annealing: complete precipitation of remaining dissolved Fe.


(Received 1991/11/12)

Keywords:

age-softening, work-softening, aluminum-iron alloys, specific resistivity, recovery, recrystallization


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