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

Abstract

Friction stir processing (FSP) was used on coarse-grained WE54 magnesium alloy plates of as-received material. These were subjected to FSP under two different cooling conditions, refrigerated and non-refrigerated, and different severe processing conditions characterized by low rotation rate and high traverse speed. After FSP, ultrafine equiaxed grains and refinement of the coarse precipitates were observed. The processed materials exhibited high resistance at room temperature and excellent superplasticity at the high strain rate of 10−2 s−1 and temperatures between 300 and 400 °C. Maximum tensile superplastic elongation of 726% was achieved at 400 °C. Beyond 400 °C, a noticeable loss of superplastic response occurred due to a loss of thermal stability of the grain size. Grain boundary sliding is the operative deformation mechanism that can explain the high-temperature flow behavior of the ultrafine grained FSP-WE54 alloy, showing increasing superplasticity with increasing processing severity.

Microstructure Features and Superplasticity of Extruded, Rolled and SPD-Processed Magnesium Alloys: A Short Review

“…The weak texture was attributed to the grain rotation/grain rearrangement during the GBS mechanism. Alvarez-Leal et al [46] reported that the large coarse grains were refined during hightemperature tensile loading, which proposed that the grain refinement led to change in the texture during the recrystallization process; thus, based on the grain refinement after tensile loading, the texture might be changed and facilitate the GBS mechanism. Wang et al [26] processed extruded ZK60 Mg alloy and studied the texture changes at a temperature of 275 °C and a strain rate of 0.001 s −1 .…”

“…Therefore, after a brief analysis, it is concluded that:  During high temperature and high strain rate loading, dynamic recrystallization weakens the texture;  Texture effect is strain rate, temperature and exposure-time dependent;  During high-temperature loading, in the early stages of deformation, the <c + a> slip activity alters the texture, which promotes the GBS phenomenon. Alvarez-Leal et al [46] reported that the large coarse grains were refined during hightemperature tensile loading, which proposed that the grain refinement led to change in the texture during the recrystallization process; thus, based on the grain refinement after tensile loading, the texture might be changed and facilitate the GBS mechanism. Wang et al [26] processed extruded ZK60 Mg alloy and studied the texture changes at a temperature of 275 • C and a strain rate of 0.001 s −1 .…”

High-Temperature Behavior of Metals

“…The effects of microstructure or microstructural stability, either directly correlated to the manufacturing process, or induced by heat treatment or by prolonged high temperature exposure simulating service, have also been considered in other contributions: for the two Al-SiMg alloys differently produced and heat treated by Gariboldi et al [5] and Paoletti et al [6], for the friction stir welded Mg alloy WE54 studied by Álvarez-Leal et al [7], for the dynamic recrystallization in martensitic steels changes reviewed by Derazkola et al [8], the Ni-based alloys investigated by Llizzi et al [9] and Engels [10], and finally the Mo-Si alloys investigated by Krauss et al [11].…”

Wire-based Direct Energy Deposition (DED-wire) used as additive manufacturing technology for industrial Inconel 718 tools for Robotic Friction Stir Welding (R-FSW)

“…The tool is inserted exactly in the contact point between the pieces, reaching the shoulder the material and by frictioning the surface. Then the tool is moved forward while rotating, mixing the plastic material blurring the previous microstructure and recrystallizing the material, generating a fine and equiaxial microstructure [8], [9]. Joining FSW process is considered one of the most innovative developments for metal joining within the last decades, since it offers important advances such as the increase of the energy efficiency, environment friendly and versatility [10].…”