Microstructures and mechanical properties of HPT processed 6063 Al alloy

6063 Al alloy is subjected to severe plastic deformation through high-pressure torsion (HPT) using disk
samples. The values of the Vickers microhardness and equivalent strain were recorded along diameters
in each disk. The microhardness of 6063 Al alloys increases strongly and continuously with increasing
equivalent strain but levels off and enters into a steady-state where the hardness remains unchanged
with further straining. It is confirmed that the yield and ultimate tensile strength also follows the same
single role of the equivalent strain as the hardness. Transmission electron microscopy showed that a
subgrain structure develops at an initial stage of straining with individual grains containing disloca-
tions. When increasing the straining, the subgrain size decreases whereas the misorientation angle
increases and more dislocations are formed within the grains. In the steady-state range, some
recrystallized grains formed which are free from dislocations. The mechanism for the grain refinement
is discussed in terms of dislocation mobility.