Characterization of Corrosion on Outdoor-Exposed Aluminum Metal-Matrix Composites as a Function of Reinforcement Specie and Volume Fraction

摘要

The Hawaii Corrosion Laboratory and the U.S. Army Research Laboratory collaborated to prepare, environmentally expose for up to 2 years, and evaluate multivariant sets of metal matrix composites (MMCs). The experimental matrix involved variations in particulate volume-percent and particulate reinforcement specie (higher purity green and less-pure black silicon carbide, boron carbide, and alumina). The specific objective of this study was to determine, mainly using x-ray powder diffractometry, how observed gravimetric variations in corrosion behavior of these sets of MMCs (differentiated by four kinds of reinforcing agents with some variations in volume-percent), after relatively heavy-rainfall outdoor exposures in Hawaii, could be related to the crystallographic and morphological characteristics of the resulting corrosion products. Compared to the monolithic aluminum control specimens, the measured corrosion rates for these MMCs were considerably accelerated (by at least an order of magnitude) by the presence and relative amount of these second-phase particulates. The increased kinetics found for these MMCs were nominally proportional to the volume fraction of the particulate phase. Other differentials in gravimetric corrosion rates and corrosion product characteristics were related to the type of reinforcement phase present.