Magnesium and its alloys are characteristic of low density, high strength-to-weight, recyclability and etc., but their poor corrosion resistance and high stress corrosion cracking (SCC) susceptibility have restricted their applications and developments. Based on the evolution of the corrosion interfaces of magnesium and its alloys, the corrosion processes, corrosion and SCC mechanisms of as-cast AZ91 magnesium alloy were systematically investigated.
Environmental scanning electron microscope (ESEM) was first used to in situ and dynamically observe and study the formation and spreading of micro-droplets on magnesium and AZ91 alloy, and the initial corrosion process, which recurred the actual initial corrosion processes. It was found that Al alloying decreased the hydrophilicity of AZ91 alloy, which is one of the reasons that AZ91 alloy had better corrosion resistance. The grain boundary for pure magnesium, and phase for AZ91 magnesium alloy had no influences on the formation and spreading of micro-droplets. The corrosion occurring on surface was parallel to the distribution of droplets or water film.
The effects of surface state and microstructure on the formation and spreading of micro-droplets were first investigated. It was found that the spreading kinetics of micro-droplet and water film follows the relation: D=Atn (0
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