Microstructure and Thermal Stability of Al-Mg-Mn Alloys by Equal Channel Angular Pressing at Elevated Temperature
Two Al-Mg-Mn alloys having similar compositions but with and without Zr addition were subjected to equal channel angular pressing (ECAP) at 350°C using route BC and a 90° die, followed by water quenching or air cooling. A series of annealing experiments were conducted at various temperatures from 400°C to 460°C on the water-quenched alloys. Fine structures with grain size of approximately 1~2μm were obtained in these alloys after 6 passes. The water-quenched alloy containing Zr exhibited finer structure compared with the Zr-free alloy in the same cooling condition, which was due to the existence of Al3Zr dispersoids. And in the air cooling condition, it was found that in the Zr-free alloy static recovery occurred, and in partial regions some small grains without dislocation inside appeared suggesting the occurrence of static recrystallization. This demonstrated a fairly restored structure. However, the microstructure of the alloy containing Zr kept stable during the air cooling process. In addition, in the annealing experiments, secondary recrystallization took place in the Zr-free alloy annealed at 410°C for 1h, while the alloy containing Zr kept stable up to 460°C. TEM observation showed that the Al3Zr dispersoids pinned the motion of the grain boundaries, thereby the secondary recrystallization and grain growth were inhibited.
Yafang Han et al.
J. L. Ning et al., "Microstructure and Thermal Stability of Al-Mg-Mn Alloys by Equal Channel Angular Pressing at Elevated Temperature", Materials Science Forum, Vols. 546-549, pp. 929-932, 2007