The corrosion properties of AZ91 alloy improved by the addition of trace submicron SiCp

In this work, the 0.5 mu m SiC particles (0.5, 1, 2 vol.%)/AZ91 composites were prepared by ultrasonic-assisted semi-solid stirring casting. The effect of submicron SiC particles (SiCp) on the microstructure and corrosion behavior of AZ91 alloy was studied. It indicated that the introduction of submicron SiCp induced the beta-Mg17Al12 phase to preferentially form by wrapping the SiCp, which breaks the semi-continuous network structure of the beta-Mg17Al12 phase in the alloy. Interestingly, the formation of lamellar (alpha-Mg+beta-Mg17Al12 ) structures and fine beta-Mg17Al12 phase was promoted by adding trace submicron SiCp (0.5 vol.%) into the alloy. During corrosion process, the lamellar (alpha+beta) structure can act as corrosion barrier and fine beta-Mg17Al12 phase can be shed. In addition, the potential difference between alpha-Mg and beta-Mg17Al12 decreased. These can explain this phenomenon that the weight loss corrosion rate of the alloy was reduced from 8.85 mm/y to 1.23 mm/y by adding trace submicron SiCp (0.5 vol.%). However, the precipitation of granular beta-Mg17Al12 phase increased with the increase of SiC(p )content, which inhibits the formation of lamellar (alpha+beta) structure. Concurrently, the content of Al in the matrix reduced gradually, which makes the matrix potential decrease gradually. Consequently, the corrosion resistance of composites decreased gradually with the increase of SiCp content.