Enhancement of Recrystallization Resistance of Al-Zr-Mn by two-step precipitation annealing

Al3Zr dispersoids formed during precipitation annealing can improve the recrystallization resistance in aluminium alloys. However, the dispersoids often distribute inhomogeneously through the alloys and also is in a low number density. This results in rapid recrystallization in areas where the dispersoid density is low. In this work, two-step heat treatments have been investigated and compared with the more common one-step precipitate annealing. It was found that an effective increase in the number density of Al3Zr dispersoids is achieved when applying a two-step heat treatment. The choice of temperature for the pre-annealing step during the two-step treatment was also found to influence the dispersoid distribution. The best result was obtained when the first annealing was performed at 350ºC before increasing the temperature to 450ºC where precipitation was completed. Increased precipitation resulted in increased recrystallization resistance.