2014 年 64 巻 6 号 p. 241-248
The commercial Al–Zn–Mg–Cu base 7075 alloy has been reported to have significantly high tensile strength after high-pressure torsion (HPT) process, one of the typical methods of severe plastic deformation. This strengthening can be attributed to high dislocation density, grain refinement, nano-scale solute clustering in the interior of grains, and/or solute segregation to grain boundaries. However, the details in the strengthening mechanism remain unknown. In the present study, transmission electron microscopy (TEM) analysis has been made to characterize the change in microstructure during HPT. Disc specimens of 10 mm diameter and 1 mm thick were machined from extruded bar of commercial 7075 alloy, and solution treated for 5 h at 480°C. The solution treated specimen was subjected to HPT process under compression stress of 2 GPa and rotation speed of 1 rpm for 10 turns. The TEM analyses were made on the specimen taken from the place 2.5 mm apart from disc center. Localized concentrations of solute atoms to grain boundaries are observed in the HPTed specimen. The strengthening mechanism will be discussed in relation to the observed changes in deformation microstructure.
