Corrosion behavior of aluminum 2009/SiC composite machined to different conditions

It has been found that when metal matrix composite materials (MMCs) are machined by mechanical means considerable damage to the reinforcement phase(s) and the substrate up to 100 mu m below the surface are common. During machining, the surface layer in particular is highly sheared and the reinforcement phase, in particle or fiber form, can be severely fragmented and dislodged from the metal matrix leaving crevices behind. However, the effects of machined surface condition on corrosion behavior have not been reported in the literature. This information is vital for the prediction of the long-term environmental stability of MMCs. In the previous studies of the corrosion properties of MMCs, the specimens used for testing were mostly surface finished by polishing. It is apparent that, in most situations, this would not be a practical condition for MMCs in service. In this study, the effects of machined surface condition on the corrosion behavior of aluminum 2009/SiC composite material were studied. The aluminum 2009 matrix was reinforced with 20 vol% of silicon carbide (Fig. 1); the nominal particle size was 3.5 mu m