Recystallization of Al at various cold work levers
Introduction The hardness of a metal can be manipulated through cold working and annealing. In this work three different aluminum alloys, commercial purity aluminum (CPAl), aluminum-tibor (Al-TiB), and aluminum-silicon (Al-Si), were rolled and annealed at different times and temperatures. ... Micrographs of the Al-TiB alloy showed the correlation between microstructure, hardness, and respective thermomechanical processes. Cold rolling increases the hardness of metals due to a phenomenon know as strain hardening. ... Cold rolling is an example of plastic deformation, which like all other plastic deformation increases the dislocation density of the metal. ... Cold working also affects the microstructure of metals. Before a metal is cold worked the grains are equiaxed, meaning the grains have approximately the same dimension in all directions (Callister 164). ... Annealing is a heat treatment used to soften a previously cold-worked metal. ... Total recrystallization will occur if a cold rolled metal is annealed at a high enough temperature for an extended period of time. ... Procedure First the hardness and conductivity of a block of Al-TiB alloy was recorded. ... This rolling and annealing process was repeated twice on the block of Al-TiB alloy, resulting in 30 total pieces. ... Other groups performed the same procedure on blocks of CPAl and Al-Si alloys. Micrographs of Al-TiB alloys, having different effective strains and heat-treatments, were printed. Pieces of the Al-TiB alloys were mounted in bakelite and polished. ... illustrates the effect cold rolling has on the hardness of CPAl, Al-TiB, and Al-Si alloys. ... Figures 3 and 4 show similar trends for the Al-TiB and Al-Si alloys. Figures 5-9 are micrographs of Al-TiB alloys that were cold rolled and then annealed. ... This means that any changes in hardness due to cold rolling or annealing will coincide with changes in the microstructure. ... After each subsequent pass through the roller the effective strain of the blocks of CPAl, Al-TiB, and Al-Si alloys was increased. ... The recovery and recrystallization process is governed by alloy composition, degree of cold work, and annealing time and temperature. Recovery is the relief of the internal strain or a previously cold worked metal. ... On the other hand, the last series in Figure 4 shows the hardness of the Al-Si alloy that was cold worked and heat-treated just as the last series in Figure 2. ... The Al-Si alloy did not recrystallize because it was less pure than the CPAl sample.