Solubility Limit of Iron in Aluminum and Its Alloys: Role on Recrystallization, Grain Growth, Texture, and Interfacial Segregation Leading to Ductile Failure

Despite the low solubility and low diffusivity of iron in aluminum, industrial annealing of wrought aluminum is done at or above 340 °C for complete recrystallizationRecrystallization. Cube textured aluminum capacitor foils are annealed at ~220 °C followed by second annealing at 530 °C. This study addresses the underlying cause behind such practices. Pure aluminum samples were pre-strained to ~25%, annealed at 230 °C or higher, cold-rolled, and recrystallized. Iron solute content after annealing at 230–300 °C was 0.014–0.170 ppm and cold-rolled samples were recrystallized to ~1 µm grains at 60 °C. Similar studies were done in AA1100, AA6063, and AA5754. The key finding was at 335 °C, in all cases, either ultra-fine Al6Fe precipitates formed or pre-existing ones dissolved. The relationship between texture evolution and Fe segregation to grain boundaries resulting in solute and particle drag and to microparticles that act as nuclei for de-cohesion will be discussed and smart processing guidelines will be described.