Relations among load fluctuation, geometrical shape and propagation behavior of a deformation band were examined for an inhomogeneous plastic deformation generated at relatively low temperature. The geometrical shape and propagation behavior of the deformation band were evaluated by strain gauges and surface roughness of specimen. Quantitative analysis of the load fluctuation was also carried out by fast Fourier transform method. The following results were obtained. A wavy load fluctuation was observed in two-deformation regions; i.e., one of which was a yield deformation region and the other was a serration one. The geometrical shape and the tilt of the deformation band in each deformation region were similar, while the number of cycles, the velocity of propagation and the amount of increasing strain were different each other. However, it was clearly shown that the wavy load fluctuation generated in each deformation region resulted from a continuous propagation of the deformation band.

Fast Fourier Transform FFT method was applied in order to evaluate a repeated load drop serration observed in the load-time curves in the tensile test. 5083 aluminum alloy plates were tested in tension at temperatures between 203 K and 333 K using an Instron type tensile test machine. Changes in repeated load drops with the deformation temperature were characterized by a conventional method mean amplitude DL m and number N of load drops and FFT method maximum amplitude C max and peak frequency f p derived from the Fourier spectrum . C max and f p were compared with DL m and N, respectively. The comparison showed the reasonable agreement between f p and N, as well as that of C max and DL m . In evaluation of the serration using FFT method, there was no artificial reading error and reliable analysis could be carried out in a short time. Therefore it suggests that FFT method is suitable for the investigation of the serration.

The eŠects of solution treatment temperature on the serration in 6061 aluminum alloy sheets were investigated by tensile test carried out at 303 K. In order to examine the microstructure change with solution treatment temperature, measurements of the electrical resistivity and grain size were performed. Serrations were quantitatively evaluated using the critical strain, mean amplitude and frequency of stress drops. The amplitude of stress drops increased with higher solution treatment temperature due to the increase of solute atoms, whereas the amplitude and the frequency of stress drops vanished rapidly at coarsening of grain size. The critical strain of A type serration decreased slightly with the rise of solution treatment temperature, whereas it of B type increased markedly due to the increase of solute atoms. Grain size had, furthermore, no eŠect on the critical strain for each serration.

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