Effects of Erbium and Thermo-mechanical Treatments on the Microstructures and Mechanical Properties of Mg-Li-Al based Alloys

Mg-Li-Al-Rare Earth-based alloys are under constant investigation due to their enhanced mechanical properties. The alloys can activate extra deformation modes and form stable strengthening phases during processing, hence improving the mechanical properties. Mg-Li-Al-based alloys were examined by introducing the Erbium (RE) element with subsequent thermo-mechanical treatments. Grain refinement mechanisms were investigated by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDX). Microstructure phase analysis depicted the presence of dual α+β-phases and intermetallics. Refined microstructures and enhanced tensile strength resulted, along with increased ductility. The as-cast Mg-8Li-3Al-3Er alloy exhibited a yield strength (YS) of 194.8MPa, Ultimate Tensile Strength (UTS) of 224.5MPa, and an elongation of 20.1%. The optimised hot-rolled, aged, and water quenched alloy had a yield stress of 232.9MPa; ultimate tensile strength of 254.5MPa, and 25.1% strain elongation. The hot-rolled and aged Mg-8Li-3Al-3Er alloys exhibited improved tensile strength and hardness. Ageing decreased the elongation of Mg-8Li-3Al-3Er alloy mainly due to the formation of intermetallics. Introduction of Erbium atoms activates the formation of thermally stable second-phase precipitates. Hot-rolling increased the tensile strength of the alloys due to homogeneous distribution and grain refinement. Strain ageing and water quenching processes enhance the alloy's tensile strength and hardness by heterogeneous nucleation of precipitates. Enhanced tensile and mechanical properties attributable to work hardening and solution strengthening mechanisms. Refined microstructure of the alloys occurred as a result of synergistic effects of Erbium addition, hot-rolling deformation, and water quenching processes.