MECHANICAL BEHAVIOUR OF ULTRAFINE GRAINED AL ALLOYS

Abstract

Aluminum-Magnesium-silicon (Al 6082) alloy was subjected to cryo-rolling (CR) and cryo forging to produce ultra fine grain. Cryorolled sample were followed by the annealing at different temperature starting from the 150°C to 400°C (For 1 hour) to investigate the changes in mechanical behavior, microstructure evolution and thermal stability was carried out with the help of hardness measurement, tensile test, X-ray diffraction (XRD), differential scanning calorimetry(DSC), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM). The solution treated 6082 Al alloy was subjected to cryo-rolling to produce ultra fine grained and followed by annealing to check its thermal stability. The cryo rolled sample shows thermal stability up to 350°C in the persentwork.After annealing at 150°C for 1 hour recrystalisation of the grain started and completed at 250°C.with in the annealing temperature range 250-350°C small size precipitate and A1Mn6despersoids pinned the grain boundry by zener drag effect which give thermal stability at higher temperature. The size of the precipitate with in the temperature range 150-325°C was <1tm observed. Strength and ductility both increased of cryo rolled followed by annealing at 150°C for 1 hour. Further annealing with in the temperature range 150-350°C there was decrease in the strength and ductility increased. Further increased in the annealing temperature with in the range 350-400°C strength and ductility both remain constant. Cryo-forging immerged as new technique to produce ultra fine grained. Sample after solution treatment goes for multi axial cryo-forging, total true strain applied to sample was 2 which was less than true strain applied in cryo rolled samplei.e 2.6, for 90% deformation.Transmission electron microscopy (TEM) image of annealed sample at 200°C showing the ultra fine grain with in 200-300 nm size.X-ray diffraction (XRD) of annealed sample confirm the evolution of precipitate which gives strength to the material.Strength and ductility obtained after cryo-forging were similar to the after 90% cryo-rolled sample.