Effect of Heat Treatment Conditions on the Elongation of AA1200 Alloy Sheets

Abstract

It has been reported that the elongation of the AA1050-H26 sheet annealed at 200°C is lower than that of the AA1050-H18 sheet. In this study, the effect of the annealing time at 250°C on the elongation of AA1200 alloy sheets was investigated, and the cause of the low elongation was discussed by observing the change in the microstructures before and after tensile deformation. The elongation of the samples annealed at 250°C for less than 50 min was below 1%, and this elongation was lower than the elongation of the as-rolled and annealed ones at 250°C for more than 150 min. In the samples annealed for a short time, the subgrains with diameters of 0.5~2μm formed, and Fe and Si, which were a solid solution, became segregated at the sub-boundaries. These samples were locally deformed in a stress concentrated area during the tensile deformation, and there was no significant increase in the dislocation density near the fracture part after the deformation. The cause of the low elongation was considered to be due to the dynamic recovery that locally occurred in a stress concentrated area during the tensile deformation, because dislocations introduced into the subgrains by the deformation easily moved to the sub-boundaries due to the low solute levels within the subgrains.