Role of Mg on Mn-Bearing Dispersoids and Their Impact on Mechanical Properties and Recrystallization Resistance of Cold-Rolled 5xxx Alloys

The evolution of the Mn-bearing dispersoids in two Al-Mg-Mn 5xxx alloys with 3% and 5% Mg and their impact on the mechanical properties and recrystallization resistance have been investigated. A large number of Mn-dispersoids were precipitated in the aluminum matrix by applying a low-temperature homogenization, but the type, size, and number density of these dispersoids after heat treatment were strongly related to the Mg levels: fine Al₆Mn and α-Al(Mn,Fe)Si dispersoids were observed in Al-3 Mg-Mn alloy, while the dispersoids changed to relatively large Al₄Mn and Al₆Mn dispersoids in Al-5 Mg-Mn alloy. The mechanical properties after cold rolling as a function of the annealing temperature were studied. The yield strength after cold rolling and 300 °C annealing reached 233 MPa for low Mg and 253 MPa for high Mg alloys homogenized at low temperature, respectively, showing an improvement of 30% and 20% over the high-temperature homogenization. In addition, the deformed grain structures after cold rolling and annealing were characterized. Results demonstrated that fine and densely distributed Mn-dispersoids generated during low-temperature homogenization could effectively hinder the dislocation and sub-grain boundary migration and improve the recrystallization resistance of cold-rolled sheets.