Investigating the Microstructural Evolution and Homogeneity in Al 6061 Alloy Processed through Multi-directional Forging at Cryogenic Temperature

In the present analysis, Multi-directional forging (MDF) at cryogenic temperature (−196 °C)\of Al 6061 alloy in supersaturated solid solution state showed evolution of micro-shear bands microstructure with increasing strain (true strain- 1.8, 3.6 and 6). The density of micro-shear bands has increased with increasing deformation strain. EBSD analysis showed the center (core of the forged sample) of the sample exhibits homogeneously structured dislocation free Ultrafine grains with grain orientation spread less than one after 10 MDF cycles. The average grain size of 400-600 nm with sharp boundaries (Grains with HAGBs) after 10 MDF cycles has been observed. Microstructural homogeneity has been investigated by microstructure evolution and Vickers hardness along different sample locations from center to the edge processed after 3, 6 and 10 MDF cycles was investigated. The average hardness has increased with MDF cycles, however due to inhomogeneity the hardness varies moving from center to edge in the sample. The structural inhomogeneity observed in MDF samples is due to orientation difference in grains after non-uniform distribution of strain owing to the friction between sample and forging hammer.