Diffusion-induced property modifications of magnesium alloy and aluminum.

摘要

Diffusion is an essential process to chemical reaction and physical change. The diffusion modifies various properties of materials, including chemical composition, reactivity, microstructure and mechanical performance. To understand property changes of metals, diffusion-based corrosion layer in Mg alloy and diffusion-induced activation of Al have been investigated.;For ZK60A Mg alloy, a diffusion-based corrosion layer (DCL) as a subsurface damage region is identified. The DCL is composed of partially oxidized alloy and corrosive species, featuring with gradual composition changes and corrosion defects (voids, cracks). Moreover, it is mechanically degraded, including reduced elastic modulus, embrittlement, and increased heterogeneities. The DCL formation is a dynamic interdiffusion process. Metal ions diffuse into the solution while the corrosive species (e.g., chloride, water, oxygen) diffuse into the bulk alloy. Furthermore, the embrittlement of DCL is verified as a dominant factor for the toughness and ductility decrease by tensile tests on the pre-corroded Mg alloy. Cracking is preferably initiated at the corrosion surface, and propagated into the bulk under the promotion of brittle DCL, leading to a catastrophic failure of the entire sample.;For the Al alloy, interdiffusion takes place between liquid Galinstan and solid Al at room temperature, generating a liquid or solid Al-Ga based alloy with high reactivity. Galinstan-activated Al liquid alloy is more reactive than Galinstan, solid Al and Galinstan-Al solid alloy. The concentration of Al at the surface of Galinstan-activated Al liquid alloy is about 0.75 wt% (~2.18 at%). Additionally, Al-rich minor phase is observed due to the excess Al atoms transferred into the liquid alloy by diffusion. The Galinstan-activated solid Al alloy has two major phases, namely Al-rich and Al-poor phases, and the concentration of Al in both phases are higher than the liquid Al alloy. Moreover, Galinstan-activated Al liquid alloy has been proved as a promising anode material used in the rechargeable Al-ion battery for energy storage.