Corrosion characteristics of hybrid Al/SiCp/MgAl2O4 composites fabricated with fly ash and recycled aluminum

The corrosion characteristics of Al/SiCp/spinel composites fabricated with SiCp, fly ash (FA) and recycled aluminum were experimentally assessed. For type A composites prepared with the alloy Al–8Si–15Mg (wt.%), the Mg2Si intermetallic precipitated during solidification acted as a microanode coupled to the matrix (in the presence of condensed humidity) and led to catastrophic localized corrosion. Although the potential attack of SiC by liquid aluminum was successfully avoided by the presence of SiO2 in the FA, Al4C3 was still formed due to the reaction of carbon in the FA with aluminum. For type B composites, processed with the alloy Al–3Si–15Mg (wt.%) and calcinated FA, the silicon content was low enough to avoid formation of Mg2Si. Moreover, chemical degradation by Al4C3 hydrolysis did not happen either because of the absence of carbon and the presence of SiO2. This explains the physical integrity of type B composites even after 11 months of exposure to humid environment.