The dynamic compressive response of a high-strength magnesium alloy and its nanocomposite

The dynamic compressive mechanical properties of the alloy Mg-4Zn-3Gd-1Ca (wt%) and its nanocomposite Mg4Zn3Gd1Ca-2ZnO were investigated at strain rates up to 1×103 s−1, using a Split Hopkinson Pressure Bar (SHPB) tester. Under dynamic loading, the addition of 2 wt% ZnO nanoparticles into the alloy generated a significant strength increase (~100 MPa), attributed largely to grain refinement. Negative strain rate sensitivity of the alloy and its nanocomposite was observed. It is postulated that the strengthening influence of the nanoparticles by retarding twin nucleation/growth at grain boundaries, is significantly weakened as strain rate increases. The yield stress of the materials studied follows the Hall-Petch relationship even when the grain size is less than 1 µm. It is proposed that the strong solute strengthening from Gd and Ca enhances the critical resolved shear stress for slip and preserves tension twinning as the dominant deformation mechanism for yielding.