Microstructure, superplasticity, and mechanical properties of Al-Mg-Er-Zr alloys

Minor additions of rare-earth elements improve the mechanical properties of aluminum-based alloys due to precipitation strengthening, increased recrystallization resistance, and grain refinement effects. This study investigated the microstructure, room temperature mechanical properties, and superplasticity of Al-Mg-Z-Er alloys with the Mg content in a range of 2.1-4.9 wt%. The alloys' microstructure was presented by an Al-based solid solution matrix enriched with Mg, the (Al,Mg)3Er phase of solidification origin, and nanoscale secondary precipitates of the Al3(Er,Zr) L12-structured phase. The Al3(Er,Zr) precipitates provided the Orowan strengthening mechanism, led to a strong recrystallization resistance and the Zener pinning effect during elevated temperature deformation. An increase of the Mg solute resulted in a solid solution strengthening and facilitated dynamic recrystallization at elevated temperatures. In the alloy with 4.9%Mg, a combined effect of fine L12 precipitates, high solute Mg, and (Al,Mg)3Er particles led to a fine-grained structure formation and super plasticity with the maximum strain rate sensitivity m of 0.51 and the elongation-to-failure of 550-600% at the constant strain rates of (0.8-1) x 10-2 s- 1. The mechanical properties at room temperature were studied after the post-deformation annealing of the thermomechanically treated alloys and after the superplastic deformation. The developed Arrhenius-type mathematical model of superplastic deformation behavior showed excellent predictability for the studied alloys with different solute Mg.