MECHANICAL BEHAVIOUR OF ULTRAFINE GRAINEI Al ALLOYS PRODUCED BY CRYOROLLING

Abstract

The mechanical properties and microstructural evolution of Al 6063 alloy subjected to cryorolling and warm rolling have been investigated in the present work. The Al 6063 alloy was subjected to thickness reduction of 70% by cryorolling followed by thickness reduction of 20% by warm rolling. The cryorolled+ warmrolled (CR+WR) samples were characterized by EBSD, DSC, XRD and 'TENT to substantiate the role of deformation strain and temperature on their microstructural features and compared with cryorolled (CR) samples. The CR+WR samples showed a significant improvement in tensile strength (310 MPa) and improvement in ductility (10 %) as measured from tensile testing. It is mainly due'to the combined effect of partial grain refinement, solid solution strengthening, dislocation hardening, dynamic recovery, and dynamic ageing during cryorolling and warm rolling. The effect of ageing on CR+WR samples was investigated and the optimum ageing condition was found to be 24 hours at 125 °C, which gives improved tensile strength of (335 MPa) and good tensile ductility (15%). During peak ageing treatment, the strength has been retained by pinning of dislocations through nanosized precipitates generated during warm rolling and it has been improved further by precipitation of the remnant dissolved second phase in the matrix. However, the observed ductility of CR±PA sample was 13 % more than CR+WR+PA sample due to extremely low dislocation density after ageing.