Mechanical properties of ultrafine-grained AX41 magnesium alloy at room and elevated temperatures

Mechanical properties of ultra-fine grained AX41 magnesium alloy were investigated at ambient and elevated temperatures. The study focuses on the effect of the grain size, dislocation density and crystallographic texture on the strength and formability. Commercial AX41 magnesium alloy was processed by hot extrusion followed by eight passes of equal-channel angular pressing at temperatures of 220 and 250 °C. Material was tested in tension in the direction parallel to the ECAP processing at temperatures up to 200 °C. In this temperature range, the ultra-fine grained structure is thermally stable. The strength of the material at room temperature is significantly affected by texture. In particular, basal texture component formed in ECAP samples is tilted by 40° from the processing direction and therefore facilitates plastic deformation by basal slip. In contrast, the texture of extruded material is not suitable for basal slip deformed in the same direction. The effect of texture on strength can outweigh the effect of reduced grain size and increased dislocation density in ultrafine-grained AX41 alloy. At elevated temperatures, starting from 100 °C, the deformation behaviour is controlled simultaneously by dislocation slip and grain boundary sliding (GBS). Mechanical properties of the as-cast coarse grained material are virtually independent of the temperature. On the other hand, the reduced grain size of UFG material caused the progressive decrease of the proof stress and, simultaneously, considerably improves the ductility. The study systematically shows that the effect of microstructural features on mechanical properties of coarse grained and UFG AX41 alloy strongly depends on the dominant mechanism of plastic deformation.