Solid solution strengthening and diffusion behaviors in Mg–Bi and Mg–Al–Bi alloys via high-throughput measurements

The diffusion coefficients, hardness, Young's modulus, and creep behaviors of Mg–Bi and Mg–Al–Bi alloys were measured using a high-throughput approach that integrated nanoindentation and diffusion couple techniques. Six groups of solid-solid and three groups of solid-liquid diffusion couples were prepared and subsequently annealed at temperatures ranging from 723 K to 823 K to form the diffusion zones. The composition gradients within the diffusion zones were quantified, followed by the conduct of nanoindentation tests. The interdiffusion coefficients and mobility parameters in hcp Mg–Bi and Mg–Al–Bi alloys were directly determined based on the measured composition distributions, employing a numerical inverse method. Additionally, the composition-dependent hardness, Young's modulus, and creep behaviors were effectively determined. It was observed that both the hardness and Young's modulus of the alloys increased with higher concentrations of Bi and Al. Notably, Bi exhibited a greater influence on hardness than Al, whereas Al had a more pronounced effect on Young's modulus. Furthermore, creep resistance in the alloys improved with increasing levels of Bi and Al, with the combined addition of both elements providing greater enhancement in creep resistance than the addition of Bi alone. The Mg–Al–Bi mobility descriptions were employed to analyze the effects of Al and Bi additions on creep performance under the diffusional creep mechanism.