The behavior of internal friction during strain ageing and amplitude-dependent effect behaved in high purity aluminium were studied. After specimen is twisted to a certain degree, internal friction exhibits anomalously amplitude dependent effect. This can be observed in a large temperature region but does not appear in completely annealed or elongated specimens. The way of twisting deformation of specimen can affect amplitude-dependent effect. As the purity is lower, the anomalously amplitude-dependent effect is not so easy to be observed. It is considered that the appearance of anomalously amplitude-dependent effect is attributed to the reason that deformation leads to high enough dislocation density and much smaller region allowed for the movement of dislocations. The increase of nternal friction during strain ageing at room temperature is suggested to be due to the dislocation slip aided by vacancy produced through deformation.
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