Relation between strain aging and Portevin-LeChatelier effect in Al-1at%Mg alloys

Abstract

The relation between strain aging and Portevin-LeChatelier effect (dynamic strain aging) was studied for clarifying the mechanism of P-L effect.Experiments for strain aging were conducted on Al-1at.%Mg alloy which had been stretched by 2%at-60°-20°C, and then, aged at the deformation temperature under interrupted load.The strain aging process was divided into two stages. The 1st stage of less than 7sec. in aging time approximately conformed to the time law of t2/3 and the activation energy was found to be 0.21eV. The time law in the 2nd stage, more than 10sec. in aging time, was approximately to t1/3 and the value of activation energy was 0.45eV. The activation energy in the 2nd stage was interpreted as the migration energy of pairs of Mg atom-single vacancy. The activation energy of 0.60eV previcusly found in the process of P-L effect of this alloy was assumed to be the migration energy of Mg atom-single vacancy pairs, part of which move by cutting the binding between the Mg atom and the vacancy, becuase P-L effect occurred at higher temperature than that for strain aging.It was noted that the vacancies induced by strain played an important role in appearance of yield point due to strain aging form the results of experiments for eliminating the vacancies which had existed before the occurrence of strain aging. As the results of above studies, it may be concluded that P-L effect is the phenomenon in which strain aging occurs during plastic deformation.