(1)
where, r = radius of the disc (mm), h = height if disc (mm), φ = angle of rotation (radians) and ԑ = equivalent strain value.
According to the equation the strain is directly proportional to the radius of the disc, which indicates that at the centre the strain is ideally zero, whereas the strain is highest at the edges of the disc. The development of microstructure and mechanical properties have been intensely investigated by various authors on many pure and commercially pure (CP) metals during monotonous deformation [4-11]. Addition of metals like Magnesium in pure Aluminium results in increase in the strength of alloy as Mg influences dislocation generation and work hardening [12, 13]. In addition to it, Al-Mg alloy has a lower propensity for dynamic recovery as compared to CP Aluminium. Studies have shown that the addition of Mg has a considerable amount of effect on mechanical properties and microstructure during HPT processing [14, 15].
The stain path change during HPT can be easily achieved by monotonous and reversal strain deformation through the combination of monotonous (CW) and subsequent strain reverse rotation (CW-CCW) (Fig. 1). The strain path change in the HPT process is a continuous process and the sample remain in the equipment throughout the processing operation.