JERKY FLOW BEHAVIOR IN A RAPID SOLIDIFICATION PROCESSED AL-LI ALLOY

The specific jerky flow behavior in a rapid solidification processed ( RSP) AI-Li alloy has been studied systematically. The results show tha t stress-strain curves of the as-quenched RSP AI-Li alloy tensioned wi th a moderate strain rate (6.9 x 10(-4) s(-1)) show a typical plateau step feature with obvious physical yielding; the width of each plateau (except for the yield plateau) increases linearly with increasing tot al strain, while the height of the steps is almost the same for one sp ecimen. Small and regular serrations usually begin to appear beyond th e third plateau of transverse specimens, and the size of serrations in each plateau is equal, while that on the latter plateau is larger tha n that on the former. The specific jerky flow behavior of the RSP Al-L i alloy is suggested to be formed by initiation and propagation of a l ocal deformation band during the tensile deformation process, which is caused by the combined effects of static and dynamic strain aging of Li and Mg atoms. The yield plateau is thought to be related to the sta tic strain aging that occurred in the time period between aging treatm ent and tensile tests. Other plateaus are suggested to be caused by th e first stage of dynamic strain aging (DSA I), while small and regular serrations on plateaus are attributed to the second stage of dynamic strain aging (DSA II). High Li content, high volume fraction of delta' phase and very fine grains in the RSP AI-Li alloy are major causes le ading to the specific jerky flow behavior. The plateau step characteri stic in stress-strain curves of longitudinal specimens is not so typic al as that of transverse specimens. The influence of artificial aging and tensile strain rates on the jerky flow behavior is also discussed. (C) 1998 Elsevier Science S.A. All rights reserved.