The effect of heat treatment on anisotropy behavior and formability of three-layer composite sheets using digital image correlation method

The rolling process causes anisotropic behavior in metal sheets. The purpose of this research is to study the influence of annealing heat treatment on the anisotropy properties and its relationship with the formability behavior of three-layer brass (CuZn10)/steel (St14)/brass (CuZn10) composite sheet. The samples were fabricated using the cold roll bonding (CRB) process, annealed at different temperatures for two hours, and cooled in the furnace. The uniaxial tensile test was performed in different directions (0°, 45°, 90°), and the anisotropy value of the samples was obtained using the digital image correlation (DIC) method. The formability of the samples was determined experimentally through the forming limit diagram (FLD) by the Nakazima test. The results indicated that the value of normal anisotropy (r_m) increases with the increase of annealing temperature. This trend for FLD₀ is similar to the anisotropy changes, which shows that increasing the annealing temperature improves the formability behavior of the three-layer composite. However, the changes in FLD₀ and r_m at different annealing temperatures are not the same, which can be attributed to the occurrence of recrystallization in steel and brass layers. For this purpose, the microstructure and grain size of the steel layer were examined by an optical microscope (OM). The emergence of new grains at temperatures higher than 600 ℃ was quite evident in the steel sample, indicating static recovery and recrystallization.