The Effect of Preheating Temperature on the Forming Limit Diagram of AA1050/AA7050 Al Multilayered Sheets Produced by Accumulative Roll Bonding (ARB)

Multilayered sheets of AA1050 and AA7050 Al alloys produced by hot accumulative roll bonding (ARB) are tested to estimate their forming limit diagrams (FLDs). Sheets processed with preheating at 450 and 500 degrees C for up to six ARB cycles are submitted to Nakazima tests with an in situ digital image correlation system and tensile tests to analyze the mechanical behavior. X-ray measurements and electron backscatter diffraction are performed to obtain the crystallographic texture and the mesotexture, respectively, and thus characterize the heterogeneous microstructure. A bimodal grain size distribution is observed in these sheets since AA7050 layers present elongated and fine grain size with nanometric precipitates and AA1050 layers present coarser and equiaxed grains. In addition, texture analysis indicates both rolling and shear components in the sheets. The FLDs show that the forming properties did not follow the expected rule of mixtures when compared with monolithic alloy sheets. Overall, the multilayered AA1050/AA7050 processed by means of ARB at 500 degrees C presents better formability than that at 450 degrees C, due to the combination of lower anisotropy measured by the Lankford coefficients r over bar values close to 1 and low normal anisotropy Delta r values.