Superplastic Deformation of AZ61 Magnesium Alloy having Fine Grains

Abstract

Extruded Mg-6 mass%Al-1 mass%Zn (AZ61) alloy was grain-refined utilizing Equal Channel Angular Extrusion (ECAE) processing. Initially, the extruded bar of the alloy was ECAE-processed 2-times at 473 K. Subsequently, it was processed 4-times at 448 K. As a result, the grains are refined to less than 1 mm and a large amount of fine Mg 17 Al 12 compound precipitates. Subsequently, the superplastic properties of the ECAE-processed specimens were investigated. Large fracture elongations of over 300% are obtained at 423 K and 448 K, which is below T m =2 (T m : melting point of the alloy), at strain rates above 1 Â 10 À4 s À1 and 1 Â 10 À3 s À1 , respectively. That is, low temperature superplasticity occurs. Furthermore, at a high strain rate of 1 Â 10 À2 s À1 , superplasticity occurs with the elongation of 242% and 398% at relatively low temperatures of 473 K and 523 K, respectively. In the extraordinarily elongated specimens, significant grain boundary sliding is observed with strain rate sensitivity of 0:3$0:4. The activation energy for superplastic deformation is about 91 kJ/mol, which is close to that for grain boundary diffusion of pure magnesium. It is concluded that the superplastic deformation mechanism of the investigated alloy would be grain boundary sliding accommodated by dislocation slip controlled by grain boundary diffusion.

Realization of high strength and high ductility for AZ61 magnesium alloy by severe warm working

“…The results are different from previously reported highly ductile AZ31 magnesium alloys, which show low yield strength and high strain hardening [4][5][6][7][8][9][10]. Hence, operation of some peculiar deformation mechanisms is expected on the ductility of the investigated alloy.…”

“…An ECAE die used for the present study has two equal channels of 15 mm diameter [7,8]. The intersecting angle between the two channels is 908 and the angle of the outer arc at the intersection is 608.…”

“…It has been reported [1][2][3][4] that the strength of magnesium alloys is improved by means of grain refinement according to the Hall-Petch relation. Also, recent research [5][6][7][8][9][10] reveals that high ductility can be obtained by structure control such as grain refinement and texture control even in magnesium alloys. Recently, Koike et al [11][12][13] reported that the ductility is improved in finegrained magnesium AZ31 (Mg-3 mass%Al-1 mass%Zn) alloys due to the activity of non-basal slip, grain boundary sliding (GBS) and recovery at high strained region.…”

Mechanisms of Plastic Deformation in AZ31 Magnesium Alloy Investigated by Acoustic Emission and Electron Microscopy

“…Beneficial effects of ECAP on magnesium alloys have been demonstrated recently by many authors, e.g. (Mabuchi et al, 1997;Kim et al, 2003;Yoshida et al, 2004). Various ECAP conditions were also investigated.…”

Determination of the Cyclic-Tension Fatigue of Extruded Pure Magnesium Using Multiple Ultrasonic Waves

“…Thus, there have been extensive studies on the magnesium alloys in order to improve the fracture reliability [3][4][5] and the grain greater control. [6][7][8] On another front, as well as these efforts, a clarification of the fracture behavior through a nondestructive evaluation could serve a useful role, in both aspects of material science and engineering safety.…”