Critically designing today’s melt processed bulk magnesium alloys using boron rich nanoparticles

Abstract

Abstract In this work, boron rich nanoparticles (B4C, SiB6 and ZrB2) were added to bulk melt processed Mg–Al, Mg–Zn and Mg–RE (Rare Earth) series contemporary magnesium alloys, respectively. The most obvious positive effect when adding B4C nanoparticles to the Mg–Al alloy was the significant increase in tensile ductility (to about 25%). Here, there was no significant change in grain size or crystallographic texture due to nanoparticle addition. However, it was observed that stacking faults formed more easily in the magnesium matrix due to nanoparticle addition. Also, it was observed that coarser nanoparticles broke down high strain zones (HSZs) during tensile deformation. The addition of SiB6 to Mg–Zn alloy also resulted in similar significant increase in tensile ductility (to about 23%). Tensile deformation induced alignment of more rounded and spherical nanoparticles was observed. Stacking faults forming more easily in the alloy matrix was also observed. However, the formation of nanograins (nanoscale recrystallization) during room temperature tensile deformation was observed in this system. This implied that nanograin rotation during deformation was also responsible for the observed enhanced tensile ductility. When ZrB2 was added to Mg–RE alloy, the tensile strength was significantly enhanced (yield strength >400 MPa) after thermal ageing. Here, the ZrB2 nanoparticles induced the formation of thermal ageing resistant long period stacking/ordered (LPSO) nanograins and nanolayers in the Mg–RE alloy matrix. Regarding the Mg–Al and Mg–Zn nanocomposites having high tensile ductility (>20%), it was also hypothesized that a further 5–10% cold working could significantly increase the tensile strength while maintaining the ductility above 10%. This simple hypothesis could greatly increase the suitability of bulk melt processed magnesium alloy nanocomposites (originally having high ductility) towards multiple structural (including transport) applications beneficial (yet lucrative) to mankind.