Characterisation of high pressure torsion processed 7150 Al–Zn–Mg–Cu alloy

Solution treated 7150 Al–Zn–Mg–Cu alloy samples were subjected to high pressure torsion (HPT) at room temperature and artificial ageing. Microhardness of HPT processed samples increases with distance from the centre, saturating near the edge of the disk. The hardness obtained through HPT processing is higher compared to that obtained by conventional solution treatment and artificially ageing of this high strength aluminium alloy. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) revealed the sequence of solid state reactions occurring in the Al–Zn–Mg–Cu system, and the presence of β′ (Al3Zr), η′ (MgZn2) and η (MgZn2) phases, respectively. TEM of HPT processed samples revealed that the grains near the edge of the disk are finer compared to that near the centre of the disk. Electrochemical polarisation studies of the HPT processed 7150 alloy indicated open circuit potential (OCP) and corrosion potential (Ecorr) values are more negative (i.e. anodic), and corrosion current density (icorr) values are about one order higher than the values of artificially aged tempers.

► 7150 Al–Zn–Mg–Cu alloy was subjected to high pressure torsion (HPT). ► Characterisation of HPT by hardness measurement, TEM, electrochemical polarisation. ► Grain refinement by HPT and generation of nano-grained structured alloy. ► Increase of hardness with straining and levelling-off hardness at edges with higher strain. ► Possibility of development of homogeneous structure at higher strains during HPT.