1999 Volume 63 Issue 2 Pages 243-251
In order to obtain the ultra-fine grained bulk materials whose grain size is less than 1 μm, 5182 aluminum alloy was heavily rolled up to 98.3% at elevated temperatures (R.T.-573 K). The strength of the rolled specimens increased with increasing strain and decreasing rolling temperature, and the tensile strength of the specimen 98.3% rolled at R.T. reached to 540 MPa. The elongation of the 98.3% rolled specimens was 6 to 8% independent of the rolling temperature. No ultra-fine grains were observed in the as-rolled specimens. The specimens 98.3% rolled below 473 K showed complicated deformation microstructures and large local misorientations, while the 573 K rolled specimen showed an ordinary cell structure with small misorientation. Although ultra-fine grains did not form in the as-rolled specimens, 473 K annealing produced the ultra-fine grained structure in the specimens 98.3% rolled below 473 K. The mean grain size of the ultra-fine grains was about 600 nm, independent of the rolling temperature. Ultra-fine grains were not formed in the specimen rolled at 573 K. Even after annealing at 473 K for 18 ks, the ultra-fine grains were not coarsened and the sub-micrometer grain size remained. The formation of the ultra-fine grains can be explained by growth-inhibited recrystallization-nucleation, owing to both the homogeneous introduction of a number of potential nuclei with large local misorientations by high straining and the limited diffusion during low temperature annealing. Ultra-fine grained materials annealed at 473 K showed a tensile strength of 380 MPa and an elongation of 20%. The large strength of the ultra-fine grained material is due to grain refinement, because the Hall-Petch relation between the Vickers hardness and the grain size of the materials was observed.
