Asymmetric tension-compression mechanical behavior of the as-cast Mg-4.58Zn-2.6Gd-0.16Zr alloy

Tensile and compressive mechanical behaviors of the as-cast Mg-4.58Zn-2.6Gd-0.16Zr alloy were investigated. It was found that the tensile yield strength was lower than the compressive yield strength, and three stages of strain hardening were both detected under tensile and compressive conditions, however, strain hardening exponent and strain hardening rate in stage II were higher under compressive condition than those in tension. The volume fraction of {101‾2} twin lamellas increased slower in stage II of tensile deformed sample than that of the compressive deformed sample, which was found to be related with the interaction of different {101‾2} twin variants. The lattice rotation played the most significant role in twinning induced strain hardening, therefore, higher strain hardening exponent and strain hardening rate in stage II under compressive condition were explained. A simplified loading model, which was performed within grains with random orientations, was established to calculate the Schmid factor of {101‾2} extension twinning under uniaxial tensile and compressive conditions. The calculated Schmid factor was found to be higher in tension than that in compression, as a result, lead to the lower tensile yield strength.