Improved hardness of Mg-0.5Ni-xY alloys via grain refinement and formation of LPSO structures

Abstract

The effect of yttrium addition on the grain refinement, formation of long period stacking ordered (LPSO) structures, and improved hardness in hot extruded Mg99.5-xNi0.5Yx (x = 0, 0.5, and 1 at%) alloys was investigated. It was revealed that with increasing Y content, the volume fraction of the LPSO phase (VLPSO) increased, and the average dynamic recrystallization (DRX) grain size (D) was refined. It was shown and quantified that both VLPSO and D contribute to the improvement of hardness, where the deviation from the Hall-Petch relationship was ascribed to the strengthening effect of VLPSO. The equation of H = 36.7 + 0.64 VLPSO + 35/√D was proposed to quantify the synergistic effects of hardening mechanisms to predict the hardness of Mg99.5-xNi0.5Yx alloys after deformation by hot extrusion.

Keywords

• Magnesium alloys
• LPSO phase
• Thermomechanical processing
• Grain refining
• Hardness
• Hall-Petch equation