High temperature creep behaviors and microstructure evolution of EV31 magnesium alloys

High-temperature creep resistance is a key requirement for structural materials used in aerospace applications. However, this property remains poorly understood for the EV31 alloy. This study investigates the creep mechanisms of EV31 alloy in temperature range from 200 °C to 300 °C through experimental characterization of creep curves and microstructures after creep deformation, combined with extracting the stress exponents and creep activation energies. The results show that the stress exponent (n) is primarily in a range of 4–6, but decreases to approximately 2.5 during creep deformation at 300 °C. The measured activation energy exceeds the lattice self-diffusion activation energy of α-Mg (135 kJ·mol⁻¹). Microstructural observations reveal that the creep samples contain precipitate phases, mainly β′ and β₁ within grains and β phase at grain boundaries, with precipitate-free zones forming on one side of the grain boundaries. Dislocation pile-up and tangle are observed around grain boundaries during creep at 250 °C. At 300 °C, dislocations are present within the grains and are hindered by the β′ phase. Based on these findings, it is concluded that the creep deformation of the EV31 alloy is dominated by mixed mechanisms. The grain-boundary gliding mechanism operates throughout the entire temperature range and dominates creep deformation at temperatures near 200 °C by mixing with dislocation creep. Dislocation climbing is the dominant mechanism at around 250 °C. At 300 °C, creep proceeds via precipitate-induced drag on dislocation motion, accompanied by grain-boundary gliding. This work casts new light on the development of high creep resistant magnesium alloys based on EV31 alloys and also provides critical information for EV31 alloys using at elevated temperatures.