アルミニウム合金の高温降伏現象の機構

Abstract

A new type yield point phenomenon observed when some binary aluminium alloys such as Al-Mg or Al-Cu are deformed at high temperatures above about 350°C has been reported in the previous paper. The present paper is devoted to a detailed explanation of the mechanism which controls the high temperature yield point phenomenon. The proposed theory in this report concerns the viscous motion of dislocations dragging the Cottrell atmospheres around them and the state equation of deformation derived theoretically explains quite well the phenomena observed at high temperatures. In the viscous motion of a dislocation, a fairly larger stress is needed to increase the dislocation velocity. This means that a remarkable yield drop must occur due to the dislocation multiplication during deformation. Comparing the theoretical state equations deduced from the analysis of Cottrell and Jaswan with the experimental stress-strain curves, the increasing process of the dislocation density was calculated. The results have been shown to be quite reasonable.The stress-strain curves obtained by a rapid change of the tensile speed agree with the theoretical predictions from the strain rate dependence of the dislocation density. Further the theoretical prediction of the critical temperature above which the viscous motion of dislocations dragging solute atmospheres controls the deformation is in good agreement with the critical temperature for the yield point phenomenon determined experimentally, which shows that the approximation of the theory is highly reasonable.