STUDY ON TWO CRITICAL MECHANISMS OF PLC EFFECT OF 5456 Al-BASED ALLOY

Abstract

The normal critical behavior at low temperature and inverse critical behavior at high temperature of 5456 Al-based alloy were observed via tension tests at different temperatures.By comparing the stress-strain curves at different temperatures,the lower and upper envelope curves were identified.Before the critical strain,the stress followed the lower envelope curve at low temperature while followed the upper envelope curve at high temperature.The subsequent serrations,which were upward at low temperature but downward at high temperature,waved between the two envelope curves. Furthermore,in relation with stress and dislocation motion,two types of dislocation motion for stable plasticity corresponding to the upper and lower envelope curves were presented,respectively.The lower envelope curve implied few dislocations were pinned by solute,while the upper envelope curve implied some dislocations were pinned by solute prior to escape.Finally,two critical mechanisms were proposed that the critical strain depended on the first pinning process in normal behavior and on the first unpinning process in inverse behavior.