High-strain-rate superplasticity in magnesium matrix composites containing Mg2Si particles

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Abstract
The superplastic properties have been investigated by constant-strain-rate tensile tests for Mg2Sip[sbnd](Mg[sbnd]Zn) and Mg2Sip[sbnd](Mg[sbnd]Al) composites (where Mg2Sip represents Mg2Si particles). The composites exhibited superplastic behaviour at a high strain rate of 10−1s−1. It is noted that the high-strain-rate superplasticity was attained in a solid state including no liquid phase for the Mg2Sip[sbnd](Mg[sbnd]Zn). This is because the stress concentrations around Mg2Si particles could be sufficiently relaxed by diffusional flow and/or diffusion-controlled dislocation movement. The mechanical properties in a solid state for the magnesium matrix composites were roughly in agreement with those for magnesium alloys, taking into consideration a threshold stress and an increase in the shear modulus due to the presence of hard particles. Calculations based on the critical strain rate for cavity nucleation suggested that magnesium-based materials have high potential for high-strain-rate superplasticity, compared with aluminium-based materials.