Corrosion Behavior of SiC Reinforced Al Alloy Composites

초록

Corrosion potential and pitting potential of 15vol.%SiCw/2124 MMCs were measured and galvanic corrosion tests between SiC reinforcing material and AA2124 matrix alloy were accomplished in 3.5% NaCl solutions. Pitting potentials of MMCs and matrix alloy are obtained by -0.69V of equivalent value. It means that there is no variation of pitting resistance of passive film itself on the surface of MMCs by the existance of SiC reinforcing materials. However, pitting potential of MMCs is almost same as corrosion potential, and pitting susceptibility of MMCs is higher than that of matrix alloy. Galvanic current by formation of galvanic couple between SiCw and matrix reveals very low value because of large cathodic polarization of SiC. However, by increasing potential of matrix to pitting potential by this galvanic couple and thus, forming pits easily at the weak passive film near SiC reinforcing phase preferentially, it is concluded that pitting susceptibility of MMCs increases highly than AA2124 alloy of matrix composition. INTRODUCTION Reinforcing material such as SiC and graphite has higher electrode potential than matrix alloy in metal matrix composites, and it can be considered there is a strong possibility of acceleration for corrosion of matrix by galvanic coupling effect. However, there is no agreement about this effect of galvanic corrosion. Lore and Wolf1) are confirming this effect on SiC/AA6061 MMCs, but Aylor and Kain2) and Hihara and Latanision3) are reporting contrarily. Furthermore, there are some arguments among many investigators that the existence of reinforcing material or the formation of galvanic couple could accelerate the formation and the growth of localized corrosion such as pitting4). In this study, the pitting susceptibility of MMCs has been evaluated by measuring pitting potential of SiC reinforced Al alloy MMCs, and the change of galvanic potential and galvanic current has been measured by artificial formation of galvanic couple of r