Corrosion behaviour of carbon fibres/magnesium metal matrix composite and electrochemical response of its constituents

The corrosion behaviour of carbon fibres reinforced magnesium metal matrix composite (MMC) was investigated with emphasis on the galvanic corrosion arisen between the magnesium matrix alloy and the carbon fibres. The susceptibility of carbon/magnesium interface to degradation was also ascertained. The corrosion behaviour was studied in both neutral and alkaline aqueous solutions containing different concentrations of NaCl, using electrochemical techniques, hydrogen evolution test, optical microscopy and scanning electron microscopy (SEM) coupled with EDX and WDX capabilities. Two matrix alloys were used, AS41 and AS41(0.5% Ca). The latter monolithic alloy had a significantly higher corrosion resistance marked by Ca-addition, but the presence of carbon fibres in MMCs invalidated the beneficial effect of Ca. Carbon, as an electrically conductive element, is electrochemically unstable despite its almost chemical stability in aqueous chloride environments. Therefore, the polarisation diagrams of MMCs were demonstrated in terms of the electrochemical activity of carbon fibres. This necessitated performing the electrochemical polarisation tests, individually, on both Mg MMC, monolithic magnesium matrix alloy and carbon fibres electrode.