Corrosion Behavior of Novel Al-Al 2 O 3 Composites in Aerated 3.5% Chloride Solution
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JMEPEG DOI: 10.1007/s11665-016-2420-x
Corrosion Behavior of Novel Al-Al2O3 Composites in Aerated 3.5% Chloride Solution P.O. Acevedo-Hurtado and P.A. Sundaram (Submitted September 11, 2016; in revised form October 20, 2016) The corrosion behavior of novel Al-Al2O3 MMCs was evaluated in aerated 3.5% NaCl solution through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). These materials corrode almost spontaneously by pitting in aerated 3.5% NaCl solution. Observations indicate that intermetallic particles in these composites appear to play an important role in this pitting corrosion behavior. Addition of Al2O3 particles to the base alloys did not appear to increase their corrosion resistance significantly, although corrosion rate was affected by these reinforcement particles. In cyclic polarization experiments, the small difference between the pitting potentials and the repassivation potentials for these MMCs indicated their low resistance to pitting corrosion. EIS measurements indicate adsorption/diffusion phenomena at the interface of the composites. Electrically equivalent circuits are proposed to describe and substantiate the corrosion processes occurring in these materials. Keywords
aluminum matrix composites, Al-Al2O3 MMCs, corrosion behavior, EIS, potentiodynamic polarization
1. Introduction The development of metal matrix composites (MMCs) has reflected the need to achieve property combinations beyond those attainable in monolithic metal alone (Ref 1). This material group becomes of interest for construction and functional materials if the property profile of conventional materials either does not reach the higher standard of specific demands, or is not the best solution to the engineering problem at hand. Although MMCs offer significant performance advantages over monolithic ceramic or metals in terms of mechanical properties (Ref 2), unfortunately, the interaction of the MMC with the environment is normally a secondary consideration. The corrosion resistance of the MMC is usually inferior to that of its monolithic matrix alloy, due to one or more of the following reasons (Ref 3): (1) galvanic coupling of reinforcement constituent and matrix, (2) formation of interphase between the reinforcement constituent and matrix, (3) microstructural contaminant and processing residuals in MMC and (4) microstructural changes caused by the presence of the reinforcement constituents. The corrosion behavior of Al-based MMCs has been shown to depend not only on metal-reinforcement combination, but also on manufacturing process parameters (Ref 4). Despite the risk of corrosive attack, most of the research on MMCs has been concentrated on the mechanical properties and the effect of processing route on these properties (Ref 1, 2). However, comprehensive work on the galvanic corrosion of various metal matrix composites has been reported by Hihara and Latanision
(Ref 5, 6). With the current focus of Al-Al2O3 metal matrix composites in nuclear and defense applications, it is important to understand th
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