The ultrasonic attenuation was studied, and it was found to be different to that in pure Al. It could not be explained in terms of the point defect cloud model. The attenuation depended strongly upon the loop length of the dislocation segment which was pinned between 2 point defects, and the variation in attenuation over a cycle was therefore attributed to the bowing out and returning of free dislocation segments. During unloading, dislocations returned from the bowed state at first and then bowed out in the opposite direction. When the applied stress was sufficiently high, the dislocation which experienced the largest repulsive force de-pinned and slipped until it met a dislocation wall. As the applied stress was further increased, the other dislocations moved in this way one-by-one until the strain reached its limit.

G.K.Kuang, Z.G.Zhu: Physica Status Solidi A, 1994, 142[2], 357-63