Reducing the tension-compression yield asymmetry of extruded Mg-Zn-Ca alloy via equal channel angular pressing

The influence of equal channel angular pressing on the tension-compression yield asymmetry of extruded Mg-5.3 Zn-0.6 Ca (weight percent) alloy has been investigated. The microstructure was obviously refined by the large strain during the equal channel angular pressing, accompanied with very fine Ca₂Mg₆Zn₃ phases with average diameter of 70 nm. The weak tension-compression yield asymmetry after equal channel angular pressing is mainly attributed to the reduced volume fraction of extension twinning during the compression, because the slope (k) of twinning in Hall-Petch relationship is higher than that of dislocation slip, and the twinning deformation is difficult to take place with decreasing grain size. The basal slip is more active in the alloy after equal channel angular pressing, due to the non-basal texture components, which hinders the twinning activation and reduces the yield asymmetry. Furthermore, the presence of fine precipitate restricts the twinning activation, which also contributes to the reduction of yield asymmetry.