THE EFFECT OF STRECH UPON S-PHASE DISTRIBUTION AND DYNAMIC RECOVERY BEHAVIOUR OF AN Al-Li-Cu-Mg ALLOY

Abstract
A TEM study has been made of the effect of varying the magnitude of the applied stretch upon the distribution of S-phase after subsequent ageing of an 8090 Al-Li-Cu-Mg-Zr alloy. The S-phase has also been varied without stretching by means of a duplex ageing treatment. A comparison has been made of the yield stress and initial work hardening rates in tensile tests at temperatures between 21°C and 277 °C of each of the microstructures produced. Dynamic recovery occurs at the lowest temperature in material subjected to the highest degree of prior stretch, and at the highest temperature in unstretched material. It is concluded that the dislocation substructure introduced during the stretch acts as an effective dislocation sink during high temperature deformation of the aged alloys. The duplex-aged material thus exhibits a high resistance to dynamic recovery. The work-hardening rates observed at the highest temperatures appear to be dependent upon the size and amount of the S-phase present.