Effect of microalloying (Ca, Sr, and Ce) on elevated temperature tensile behavior of AZ31 magnesium sheet alloy

The effect of microalloying with calcium, strontium, and cerium on the microstructure and the elevated temperature deformation behavior of magnesium sheet alloy AZ31 was investigated. Base composition and microalloyed AZ31 materials were cast and rolled into wrought sheet by an identical thermo-mechanical process. A series of hot tensile tests (temperatures of 300 °C, 400 °C, and 450 °C; constant true strain rates of 0.1 s−1, 0.01 s−1, 0.001 s−1, and 0.0003 s−1) were performed to characterize the deformation behavior of the sheet alloys. Interrupted tensile tests were used to study microstructural evolution with strain.A well-dispersed and thermally stable second phase produced by microalloying refines, stabilizes the grain structure, and significantly enhances hot formability of AZ31 sheet. The enhancement is most pronounced under deformation conditions of 450 °C and; 0.0003 s−1 strain rate, with tensile elongation increasing from 347% for the base alloy, to 406% with Ca only, 437% with Ca and Ce, and 552% with Ca, Sr and Ce for microalloyed AZ31 alloys. The second phase particles resist grain coarsening, promote grain boundary sliding, retard strain localization or necking, and postpone cavitation to higher strain levels to achieve this improvement in formability.

Research highlights
► Hot tensile behavior of AZ31 sheet microalloyed with Ca, Sr and Ce was investigated.
► Under superplastic conditions the formability is notably improved by microalloying.
► Second phase particles resist grain coarsening and retard cavitations’ development.
► Under the high Z conditions the deformation is controlled by the dislocation creep.
► Under the low Z conditions the deformation is controlled by grain boundary sliding.