Strain reversal during HPT on the evolution of hardness and
microstructure has been reported by a few researchers who have proved
significant differences in microstructure and mechanical properties
[5, 16]. It has been reported that disc subjected to strain reversal
show limited increase in the hardness at the centre with increasing
strain values, which is justified upon microstructure observation at the
centre where grain refinement is limited [8]. A study on strain path
change during cold rolling has shown differences in behaviour of
microstructure and texture in Al and Al-Mg alloy [17]. There has
been no studies focussing strain path change in HPT for Al-Mg alloys.
The present study is determined to clarify these issues by studying
microstructure and microhardness evolution during strain reversal of
Aluminium-Magnesium (Al-2.5%Mg) alloy during HPT. It is envisaged that
strain reversal would greatly affect the microstructure-property
evolution in Al-2.5%Mg having lower propensity for dynamic recovery
which essentially remains the main motivation for the present study.
Experimental
Al-2.5%Mg alloy was used for the present study. The as-received
Al-2.5%Mg block (160mm (length) × 60mm (width) × 10mm (thickness)) was
cold rolled to ~80% reduction in thickness and annealed
in air furnace at 673K for one hour. The above material was used as the
starting material for further processing. Disks with the diameter of
10mm were then cut from the sheet using EDM wire cut equipment. A total
of 10 disks were cut for further HPT processing. These disks having 2 mm
starting thickness were manually grinded to ~1.5mm
thickness using SiC grit papers with grit size of 500, 1000 and 1200
respectively. The disks were then designated according to the strain
value or the number of rotations as per the given chart.
The disks were then deformed by HPT to the desired strain levels as
shown in
Table 1.
Table 1: Designation of the samples according to the strain