Eutectic phase strengthening and strain rate sensitivity behavior of AZ80 magnesium alloy

A Mg–8Al-0.5Zn-0.2Mn wt.% (AZ80) alloy, containing a high volume percent of the β eutectic phase, was prepared using extrusion without a homogenization pretreatment (EX-II(F)). The β-eutectic-phase contributions to grain refinement, texture tailoring, and plastic behavior were discussed. Microstructure characterization was presented along with a strengthening mechanism analysis. The β-eutectic-phase strengthening contributions to the yield strength were estimated according to the thermal mismatch, Orowan looping, load transfer, and Hall-Petch mechanisms. In addition, the temperature and strain dependence for strain rate sensitivity (SRS) were investigated, and the influence of aging on the SRS evolution was discussed. The SRS exponent, m, of the EX-II(F) was measured at 298–573 K using strain rate jumps between 10−4 s−1-10−3 s−1. The m-value increased with increasing strain and temperature, and decreased with grain coarsening and Al solute depletion. Aging precipitation exhibited a softening effect on the 473–573 K flow stress and resulted in higher m-values. The β eutectic phase cracking decreased with increasing test temperature, which was attributed to the high deformability of the β eutectic phase above 573 K. Overall, this work has shown that the β eutectic phase can serve as a means to strengthen extruded AZ80.