Large elongations in WE54 magnesium alloy by solute-drag creep controlling the deformation behavior

Abstract

Solute-drag creep is a diffusion-controlled process that may govern deformation in coarse-grained materials with solute atoms in solution. Elongation-to-failure tensile tests were conducted in a WE54 alloy containing solutes of Y and Nd in the range 25 to 450 ºC. Elongations of more than 150% were observed at high temperatures and a maximum elongation to failure of 312% was determined at 450 ºC and 10-2 s-1. Microstructural observations show elongated grains and the presence of dislocation bands after deformation under these conditions. Strain-rate-change tests reveal a range at high temperatures showing low stress exponents. Since grain boundary sliding was discarded as a possible controlling mechanism, the observed low stress exponents, high elongations and elongated grains are attributed to solute-drag creep as the principal deformation mechanism.

High Strain Rate Superplasticity of WE54 Mg Alloy after Severe Friction Stir Processing

“…At 450 • C, the elongation to failure drastically drops, pointing to a change in the deformation mechanism as a result of grain growth. This peak and the subsequent drop do not exist in the non-processed WE54 material, since the ductility increases continuously up to the highest temperature of 450 • C [17].…”

“…Figure 5 shows curves of the elongation to failure at 10 −2 s −1 as a function of temperature for the WE54 alloy after FSP under various conditions. For comparison, data from the as-received material in the T6 condition (not subjected to FSP) are included in the figure [17]. The ductility continuously increases with temperature and a strong peak is observed at 400 • C. At this temperature, the ductility values for all samples are around 700% with a maximum of 726% observed in the R14r05v material.…”

“…The flow stress, σ, as a function of temperature at 10 −2 s −1 , is represented in Figure 6. Again, for comparison, data from the as-received material in the T6 condition (not subjected to FSP) are included in the figure [17]. The figure shows a moderate decrease in the stress with temperature up to 200 °C.…”

“…It should be noted the slight stress increase at 450 °C, which is attributed to rapid grain coarsening of all our WE54 processed materials at such a high temperature. This behavior can be compared with that of the material without FSP [17], for which the increase at 450 °C does not exist and the curve continuously decreases from 250 °C. Very low stress values are also observed at high temperatures in most of the tensile tests in the range 350-450 • C. The flow stress, σ, as a function of temperature at 10 −2 s −1 , is represented in Figure 6.…”

“…Very low stress values are also observed at high temperatures in most of the tensile tests in the range 350-450 • C. The flow stress, σ, as a function of temperature at 10 −2 s −1 , is represented in Figure 6. Again, for comparison, data from the as-received material in the T6 condition (not subjected to FSP) are included in the figure [17]. The figure shows a moderate decrease in the stress with temperature up to 200 • C. Above this temperature, the stress strongly drops.…”