A Study of the Microstructure, Crystallographic Texture, and Recrystallization in AA4006 Alloy Strips Produced by Twin Roll Caster and Direct Chill Processes

The aluminum alloy AA4006 belongs to the Al-Fe-Si system, with Si between 0.8 and 1.2 % mass, and Fe between 0.5 and 0.8 % mass. This alloy has been little studied despite its extensive use (patent n° US 2003/0196733 A1 from 2003). A study of the as received sheet microstructures, crystallographic texture evolution (for the as received, cold rolled, and recrystallized samples), and recrystallization after 70% cold rolling has been done for two AA4006 alloy strips produced by two industrial casting processes: twin roll caster (TRC) and direct chill (DC). Polarized optical microscopy, scanning electron microscopy have been used to characterize the microstructure and X-ray diffraction for the texture evolution characterization. It has been detected that the recrystallization of the TRC strip sample occurred at a higher temperature than that of the DC strip sample. The precipitation, in the TRC strip sample, occurs mainly before recrystallization and may occur during recrystallization. Precipitation occurs before and during recrystallization in the DC strip sample. Relevant differences in the grain morphology and in grain and intermetallic particles distribution have been detected and discussed. Through thickness (surface and center) textures of these specimens (as received, cold rolled, and recrystallized) have been analyzed and compared. Results showed significant texture changes across thickness of the as received strips. The texture results also indicated the presence of a shear texture on the surface region and β-fiber in the mid section of the cold rolled (70% area reduction) sample for the TRC strip sample. In the DC strip sample, under the same conditions, the cube component and β fiber occurred through the thickness (at the surface and in the center). A texture with random oriented grains has been detected in the two deformed and recrystallized samples of the two sheet samples (TRC and DC). It has been observed that the TRC strip sample recrystallization occurs at higher temperature than that of the DC strip sample despite the little differences in their softening curves. The absence of β fiber in the recrystallized samples (TRC and DC) has also been observed.