121-127Recently, a new severe plastic deformation
method named constrained groove pressing (CGP) has been invented for producing
ultra-fine grained sheet metals. Here, a multi-pass CGP is carried out on 1060
commercially pure aluminum sheets. Through a series of experimental research,
the evolutions of microstructure, tensile properties, forming load and surface
residual stress during the process are investigated. The grain size is greatly refined
from 29 μm of annealed samples to about 18 μm after pass four. Polygonized and dislocation-free
substructures of submicron level with well-defined boundaries is obtained. The ultimate
tensile strength and yield strength increase continuously until pass three and then
decrease by further deformation. Residual tensile stress is observed on the
surface of all pressed samples due to the unique stress-strain state, and it
increases dramatically during the first pass. The results show that lubrication
reduces the average residual tensile stress and its distribution homogeneity
along the longitudinal direction