Torsional fatigue experiments were performed with Al-7.27% Ag alloy in the quenched state. The △E-N curves were determined under various torsion strains and metallographie observations were made on the specimen surface after various numbers of stress cycles.Experimental results showed that, when the torsion strain is small, △E was found to decrease with the increase of stress cycle N. The change of the △E-N curves is similar to those previously reported for Al-Cu and Al-Mg alloys under lower torsion strains. However, when the torsion strain is large, AE decreases slightly at the beginning, increases subsequently to some higher value, and drops again until the specimen is fractured. The shape of the △E-N curves is very different from those of Al-Cu and Al-Mg alloys at same strains. The metallographie change of the specimen surface during cyclic deformation was found to be divided into two distinct stages. In the initial period of fatigue loading, fine straight slip lines are homogeneously distributed within certain grains. However, some of them suddenly become highly concentrated and prominent after a certain number of cycles. With increasing fatigue cycles, newly generated localized slip bands occur successively between the existing ones. This observation is markedly different from that observed on pure aluminiun and the quenched Al-Mg alloys, where only the existing slip regions appeared to become broader with the increase of cyclic straning. In addition, fatigue cracks were frequently observed to initiate and propagate along grain boundaries.The results obtained was discussed in terms of the electrical interaction of silver atoms with dislocation and the cutting effect of the to-and-fro moving dislocations though spherical clusters of silver solute atoms.
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