Corrosion studies on aluminium-based metal matrix composites reinforced with graphite, SiC and fly ash particles
Jarosław Bieniaś
Quarterly No. 3, 2009 pages 286-290
DOI:
keywords: aluminium, metal matrix composites, microstructure, pitting corrosion
abstract Aluminium Matrix Composites reinforced with ceramic particles (e.g. SiC, Al2O3, graphite and fly ash) are actually advanced engineering materials. These materials can be characterised by superior mechanical and thermal properties. However, the addition of the reinforcement particles could significantly changing corrosion behaviour of aluminium matrix composites. The corrosion resistance of aluminium matrix composites is determined by several factors such as: variety of aluminium alloy matrix and reinforcement type combinations, manufacturing technology, microstructure of composite and interfacial reactions reinforcement/matrix. This paper presents microstructural characteristic and susceptibility to pitting corrosion of on aluminium-based metal matrix (Al-Si) composites reinforced with graphite (5.7 wt. %), SiC (20 vol. %) and fly ash (9.0 wt. %) particles. The corrosion resistance experiments were carried out by accelerated electrochemical studies using the potentiodynamic method (in the 3.5 wt. % NaCl aqueous solution, pH 7.0, at 25ºC). The corrosion behaviour of composite with fly ash particles was studied further by immersion tests for 50 days (3.5 wt. % NaCl). The polarisation curves, corrosion potentials (corrosion Ecorr, pitting Epit and repassivation Erp) and surface morphology after corrosion tests were estimated. It was found that: (1) the electrochemical data and microstructure observations after corrosion tests confirms that incorporation of reinforcement particles (graphite, SiC, fly ash) into aluminium matrix causes the increase of susceptibility to pitting corrosion of the composites in comparison with unreinforced matrix alloys, (2) the enhanced pitting corrosion of Al/fly ash, Al/SiC and Al/GR composites is associated with the pores, multiphasic character of composites (e.g. the releases of intermetallic Al3Ni phase), reactions at the interface reinforcement/matrix and formation of galvanic couples favourable to corrosion. The same factors also determine the properties of oxide film forming on the materials surface.