Corrosive wear of SiC Whisker-and particulate-reinforced 6061 aluminum alloy composites
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I.
INTRODUCTION
M E T A L matrix composites (MMCs) are well-known for their superior mechanical and tribological propertiesY] As for wear of ceramic whisker- or particulate-reinforced aluminum alloy composites, a reasonable amount of data has been published in the literature, t2-~41However, most of the results were obtained in ambient air and little is known about corrosive wear of MMCs.tlS] In practical situations, even when it is not always apparent whether corrosive action is involved, there are many cases where corrosion is jointly responsible for wear of metal components, since the corrosion product would be removed continuously by the wearing action. Thus, it is important to know the degree of the corrosive effect on wear, but this is not yet well established. As for the corrosive wear of MMCs, it is expected that their properties may be greatly different from a prediction derived from those of monolithic alloys, since they are made of two constituents, each having a different electrochemical behavior. The interactive effects of abrasion and corrosion on mild steel plate were studied as a function of abrasive load, corrosion time, and the frequency of abrasive and corrosive treatments by Nrel and Ball.t16] Their results revealed that the initial rate of corrosion was independent of the abrasive load but that the percentage contribution of corrosion to wear decreased with increasing abrasive load. It was also found that when the frequency of exposure to abrasion and
S.Y. YU, Engineer, is with the System-Manufacturing Center, ChungShan Institute of Science and Technology, Taipei, Taiwan, 237, Republic of China. H. ISHII, Professor, is with the Department of Mechanical Engineering, Shizuoka University, Hamamatsu, 432, Japan. T.H. CHUANG, Professor, is with the Institute of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan, 106, Republic of China. Manuscript submitted July 27, 1995. METALLURGICAL AND MATERIALS TRANSACTIONS A
corrosion was increased, the wear loss for a constant total amount of abrasion and corrosion increased. The performance of various aluminum alloys in abrasive-corrosive wear conditions which simulate those encountered in mining environments was investigated by Meyer-Rodenbeck e t al. t~73 Their results indicated that pitting corrosion with low volume losses and corrosion rates occurred for the wrought alloys 1200, 3004, 5083, 5251, 6063, 6082, 6261, and 7071, owing to small localized differences in electrode potential at constituent sites. Furthermore, localized attack with accelerated volume losses occurred for the wrought alloys 2014 and 7075 and A1-Si cast alloys. This was due to electrolytic action between phases and microconstituents which were rich in silicon and copper and, therefore, strongly cathodic with respect to aluminum. Wear-corrosion tests of a composite metal (18Cr 9Ni stainless steel) containing WC particles (150 to 190/.~m in size) were carried out in a water-sand medium containing various concentrations of sulfuric, hydrochloric, and nitric
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