Significant strengthening in superlight Al-Mg alloy with an exceptionally large amount of Mg (13 wt%) after cold rolling

Abstract

Cold rolling could be successfully applied to an Al-Mg alloy with an exceptionally high amount of Mg (13 wt%) by effectively removing the Al3Mg2 phases; this removal was performed before cold rolling using solid solution treatment before extrusion and re-solid solution treatment after extrusion. The microstructures and the tensile properties of the Al-13Mg alloy were compared with those of the Al-Mg alloys with lower amounts of Mg (5–10 wt%), which were prepared following the same processing route. As the Mg content increased, the density of shear bands crossing each other increased during cold rolling, leading to more effective breakup of the initial coarse grains and development of nanosized cell structures and ultrafine grains, and a higher accumulation of dislocation density in the matrix. This result occurred because dynamic recovery was suppressed by the decrease of stacking fault energy and dislocation slip mobility due to the addition of Mg amount. The cold rolled Al-13Mg alloy, which is lighter than pure aluminum by 8.2%, exhibited a yield stress of 653 MPa, a maximum strength of 733 MPa and a total (uniform) tensile elongation of 5.1%. These strength values are superior to those of the conventional Al-Mg alloys with lower Mg contents (≤7 wt%) processed by severe plastic deformation via equal channel angular pressing. The analysis of the strengthening mechanisms of the cold rolled Al-13Mg alloy indicates that the strengthening effect by generation and arrangement of dislocations is more significant that solid solution strengthening.