Superplasticity in Mg–Li–Zn Alloys Processed by High Ratio Extrusion

Abstract

Superplastic behavior of Mg-8.5Li-1Zn and Mg-8.5Li-3Zn alloys has been investigated. Dynamic recrystallization occurs in the Mg–Li–Zn alloys during extruding with high ratio after stir casting. Mg-8.5Li-1Zn alloy exhibits an elongation of about 400% at the high strain rate of 1.1 × 10⁻² S⁻¹ at 623 K, while the Mg-8.5Li-3Zn alloy shows maximum elongation of more than 540%. The apparent activation energy for superplastic flow of both Mg-8.5Li-1Zn and Mg-8.5Li-3Zn alloys at 573–673 K is about 86 kJ/mol and 79 kJ/mol, respectively, so that the dominant deformation mechanism in Mg–Li–Zn alloys is grain boundary sliding (GBS) controlled by grain boundary diffusion.

Keywords:

• Activation energy
• Elongation
• Extrusion
• Fracture
• Grain boundary
• Magnesium alloys
• Magnesium–lithium alloy
• Metallographic phases
• Plastic flow
• Recrystallization
• Sliding
• Stirring casting
• Strain rate
• Superplasticity
• Tensile testing

ACKNOWLEDGMENT

One of the authors (Shangli Dong) gratefully appreciates the financial support from Japan Society for the Promotion of Science (JSPS).