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 superplasticity 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) × 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.