Microstructural changes in aluminum under reversing strains

99.9 Aluminum hot worked at 400°C-500°C and strain rates ([Special characters omitted.] ) of 0.004-0.1 s -1 , under reversing strains (f) of 0.5 to 0.2 or 0.5 to 0 and also advancing from 0.5 to 1 or 0.5 to 5. Under similar test conditions for different parts of the strain paths, the average measured flow stresses are found to agree with each other. In the forward and backward strain path tests, the almost identical steady state plateaus affirm the occurrence of dynamic recovery (DRV). On reversal of strain direction at constant [Special characters omitted.] , there was generally negligible Bauschinger effect. Features such as elongated grains with serrations and deformation bands confirmed DRV in forward path specimens by optical microscopy. In reverse path specimens, equiaxed grains were seen. In forward path specimens by low magnification polarized optical microscopy, grain alignment increased with strain whereas it decreased in reverse path specimens. Orientation imaging microscopy revealed during the forward path, elongated grains are broken up as deformation bands rotate and on backward straining grains return to equiaxed appearance. The subgrains remain equiaxed and constant in size and character during the forward and backward paths. During forward straining, the fraction of high angle boundaries increased with respect to low angle boundaries and with backward straining it was vice versa. In as-worked specimens annealed at 400°C, static recrystallisation (SRX) was confirmed by microstructural evidence such as fine recrystallized grains in forward path specimens. The progress of SRX in many specimens was seen as a mixture of recrystallized grains and gains with serrated boundaries