Decoupling the constitutive parameters of magnesium matrix and LPSO phase in the Mg-Gd-Y-Zn-Zr alloy via targeted nanoindentation and finite element simulation

Reliable constitutive parameters are essential for microstructure-based mechanical modeling of Mg-RE alloys containing long-period stacking ordered (LPSO) phases. However, owing to the in-situ formation and limited size of the LPSO phase, together with the solid-solution nature of the magnesium matrix, their independent constitutive parameters cannot be directly obtained using conventional mechanical testing. To address this challenge, this study decouples the elastic-plastic constitutive parameters of the magnesium matrix and LPSO phase within a Mg-Gd-Y-Zn-Zr alloy by means of the targeted nanoindentation experiment. The load-displacement curves for the magnesium matrix and LPSO phase were obtained from the nanoindentation experiments, which were used to determine their Young’s modulus (E), yield strength (σ y ) strength coefficient (K), and strain-hardening exponent (n), combining the numerical analysis method. Results shows that the magnesium matrix possesses Young’s modulus of 45.7 GPa, yield strength of 335.0 MPa, strength coefficient of 439.1 MPa and strain-hardening exponent of 0.055, while the LPSO phase shows substantially higher corresponding values of 56.7 GPa, 536.5 MPa, 854.7 MPa and 0.100, respectively. In order to verify the accuracy of these parameters, the finite element models were used to simulate the nanoindentation experiment for the magnesium matrix and the LPSO phase. With these parameters, the load-displacement curves and residual indentation morphologies in the simulated models show excellent agreement with that in the experimental results for both the magnesium matrix and the LPSO phase, validating the accuracy of these constitutive parameters. The decoupled parameters provide a reliable independent stress-strain relationship for the magnesium matrix and the LPSO phase, serving as the critical data for multiphase microstructural modeling of the Mg-Gd-Y-Zn-Zr alloy.