Effect of Strain Loading Process on Grain Refinement in Aluminum Alloy

Grain refinement of aluminum alloy can be achieved by introducing a large amount of lattice dislocations during an intense heavy plastic deformation. In this paper, the effect of the strain loading process on the grain refinement and mechanical properties in aluminum alloy was investigated, in terms of mechanical properties, grain boundary misorientations and microstructures. Uniaxial or biaxial forging was performed at 473 K for the grain refinement of the 1100 aluminum. In biaxial forging, the work pieces were rotated by 90° on the longitudinal axis in each forging process.As the result, the bulk materials with biaxial forging at 473 K showed a significant development in grain refinement; to the grain sizes less than 1 μm. On the other hand, these fine grains of sub-micron size were never obtained through a uniaxial forging even at the same temperature. In the biaxial forged materials, it was shown by using high resolution EBSP and TEM that most of fine grains were surrounded by high-angle and random boundaries whose misorientations are larger than 15°. The formation of these fine grains during the forging and reheating process was deeply associated with the development of the sub-grain boundaries within the larger grains surrounded by high angle boundaries. Tensile test at room temperature showed that strength increases with an increase of strain in biaxial forging and also larger total elongation is obtained in comparison with a uniaxial forging material. The yield stress and tensile strength in the biaxial forged materials are higher than that in the uniaxial forging process, when they are compared under the same amount of pre-deformation.As described above, multi-axial forging technique is one of the most effective methods to produce fine grained structure and enhance strength without a decrease of ductility.