Deformation behavior at room temperature ranges of fine-grained Mg-Mn system alloys

Tensile properties and deformation behavior were investigated on Mg dilute binary alloys (Mg-0.1Bi and Mg-0.1Zr alloys) and Mg-Mn based ternary alloys (Mg-0.3Mn-0.1Bi and Mg-0.3Mn-0.1Zr alloys). These alloys were processed by hot extrusion to obtain fine-grained structures with an average grain size of similar to 1 mu m. Microstructural observations showed that Mn element was segregated at grain boundaries in the ternary alloys. Precipitates consisting of the alpha-Mn and/or Mg3Bi2 phase were dispersed in the matrix in the alloys containing Mn and/or Bi elements. All the extruded alloys showed good tensile property of ductility. The elongation-to-failure in tension of Mg-0.3Mn-0.1Zr alloy was more than 100% even at a quasi-static strain rate of 1 x 10(-3)/s. The Mg-0.1Bi alloy exhibited the largest value of 250% among all in the present examined conditions. These values are superior to those of conventional wrought processed Mg alloys. These superior properties are found to be due to the contribution of grain boundary sliding (GBS) to deformation. Bi and Zr are alternative elements to Mn for use in binary alloys. On the other hand, in low strain rate regimes, a combination of Mn and such micro-alloying elements led to an increase in flow stress, but reduced the elongation-to-failure. This resulted from a high density of precipitates in the matrix, which became cavity nucleation sites. Moreover, non-equilibrium grain boundary structures, which induced atomistic strains, were also unlikely to promote GBS. The normalized stress vs. strain relations including the previous results in the temperature ranges of 298-423 K is found to be fitted by the well-known constitutive equation.