Corrosion behaviour of 359-SiC particles composite
Jarosław Bieniaś, Barbara Surowska Politechnika Lubelska, Katedra Inżynierii Materiałowej, ul. Nadbystrzycka 36, 20-618 Lublin
Annals 3 No. 8, 2003 pages 380-384
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abstract The paper presents results of the studies on the susceptibility of Aluminium Matrix Composite to corrosion. The subject of the examinations was a composite with the 359 aluminium alloy matrix (Aluminium Association) containing 20 vol.% of SiC particles (359/20%SiC). The 359/20%SiC composite has been synthesized at the Foundry Research Institute in Cracow. This material can be applied as a modern construction material in automotive industry, particularly for brake discs and pistons. However, the addition of the reinforcement particles could significantly influence the corrosion behaviour of these materials. Generally published literature on the corrosion of aluminium-based composites is rather limited and often contradictory. This is due to the fact that there is a variety of aluminium alloy matrix and reinforcement type combinations which may exhibit a completely different corrosion behaviour. In addition, processing parameters can heavily affect composite microstructure and, consequently, their corrosion behaviour. The studies on the 359/20%SiC composite corrosion resistance were carried out by accelerated electrochemical studies using the potentiodynamic method. The corrosion analysis of this material was then related to the corrosion characteristics of AK9 (AlSi9Mg) aluminium alloy. The potentiodynamic measurements were taken in the 3.5 wt.% NaCl water solution (pH = = 7 . 0) at the temperature of 25ºC. Microstructure analysis of the specimens was examined using ZEISS model optical microscope and Hitachi S-3500N scanning electron microscopy (SEM). Silicon carbide particles were seen in the matrix on base of the α-Al solid solution, a fine-grained eutectic α+Si (Fig. 1a). Distribution of SiC in the structure was quite uniform. The course of the anodic polarization curves in the 3.5 wt.% NaCl solutions suggests characteristic curves for the metal that undergoes spontaneous passivation (Fig. 2) Potentials of the Ek, Eb, Er, ΔEb, ΔEr determined in electrochemical studies and analyses of the anodic polarisation curves, for both, composite and AK9 alloy, are very similar (Tab. 1). In the microstructure of AK9 alloy (Fig. 3) there are numerous pits whose depth ranges from 8÷16 μm. The pits are located in α+Si eutectic. In the case of the composite material more numerous and deeper pits (10÷24 μm) were observed which also locate in the α+Si eutectic between SiC particles (Figs. 4, 5). The conducted examinations did not show significant influence of SiC particles on the increase of susceptibility to pitting corrosion in comparison to AK9 alloy, what is confirmed by the literature data. Key words: aluminium, metal matrix composites, potentiodynamic polarization, silicon carbide, corrosion behaviour