A novel method towards improving the hydrogen storage properties of hypoeutectic Mg-Ni alloy via ultrasonic treatment

Ultrasonic treatment has great contributions on modifying the morphology, dimension and distribution of constituent phases during solidification, which serve as dominate factors influencing the hydrogen storage performance of Mg-based alloys. In this research, ultrasonic treatment is utilized as a novel method to enhance the de-/hydriding properties of Mg-2Ni (at.%) alloy. Due to ultrasonic treatment, the microstructure of as-cast alloy is significantly refined and homogenized. Ascribing to the increased eutectic boundaries and shortened distance inside α-Mg for hydrogen atoms diffusion, the hydrogen uptake capacities and isothermal de-/hydriding rates improve effectively, especially at lower temperature. The peak desorption temperature reduces from 392.99 °C to 345.56 °C, and the dehydriding activation energy decreases from 101.93 kJ mol−1 to 88.65 kJ mol−1. Weakened hysteresis of plateau pressures and slightly optimized thermodynamics are determined from the pressure-composition isotherms. Owing to the refined primary Mg, a larger amount of hydrogen with the higher hydriding proportion is absorbed in the first stage when hydrides nucleate in eutectic region and grow on primary Mg periphery subsequently before MgH2 colonies impinging, resulting in the enhancement of hydrogenation rates and capacities.