Corrosion behaviour and mechanism of semisolid AZ91D alloys produced by strain induced melt activation (SIMA)

The microstructure and corrosion behavior of semisolid AZ91D magnesium alloys was investigated. The Semisolid microstructures are consisting of primary solid particles and continuous liquid phase around the solid. The Solid particles have the lesser in solute component, and liquid phase with the higher in solute component that is consisting of β-Mg₁₇Al₁₂ and re-solidification αMg. It has been demonstrated that in different microstructure the corrosion resistance of semisolid specimen is higher than as-cast specimen in the whole progress. For as-cast specimens, the β phase discontinuously distribute in the grain boundaries that accelerate the corrosion process. Contrarily, the solid particles surround by β phase that inhibit the overall corrosion of the semisolid specimen. There are three kinds of galvanic corrosion in semisolid specimen, the first one is between solid phase and liquid phase, the second one is in liquid phase, and the third one is in solid phase. The initial breakage present along the interphase of solid phase and liquid phase that bring primary breakage. The effect of corrosion is low in liquid phase owing to the small α-Mg and the barrier effect of β phase. The area around liquid drop is also a place of corrosion nucleation easily in the solid particles that accelerate whole mass loss.