Softening of high purity aluminum and copper processed by high pressure torsion

High purity Al (99.99 wt.%) and high purity Cu (99.99 wt.%) were processed using high pressure torsion. The mechanism for unusual softening in Al after the resultant intense plastic straining was investigated. The pure Cu was used to simulate a thermal effect on the hardness behavior and microstructural evolution after processing. This simulation consists of processing and subsequently keeping the pure Cu at the temperature equivalent to room temperature for pure Al. It is shown that the softening of the processed Cu occurs by static recrystallization. It is then suggested that the softening in Al should be due to recovery and/or recrystallization. Whereas the softening in Cu occurs rather slowly, it is very quick in Al and it may even be dynamic during processing by high pressure torsion.