Particle-induced pitting corrosion of aluminum alloys.

摘要

Pitting corrosion has been identified as one of the principal precursors to fatigue crack initiation and growth in aluminum alloys. It has been attributed to the galvanic coupling between the constituent particles in the alloy and the surrounding matrix. To better understand particle induced pitting corrosion, the efforts of this dissertation research were directed toward fuller characterizations or the constituent particles, the morphology of corrosion pits, and the mechanism, processes, and kinetics of pitting. Model alloys were used to estimate their electrochemical properties and to develop information on the galvanic coupling between the alloy and constituent particles. In situ monitoring and pit replication techniques were developed to provide information on the processes of pitting corrosion in real-time and on the morphology of corrosion pits in three dimensions.; Pitting is caused by the matrix dissolution due to the galvanic effect between particle-matrix coupling. Two pit morphology, general pits and severe pits, were induced due to the difference in particle distribution density. General pits are caused by individual particles and severe pits are induced by particle clusters at or beneath the surface. Corrosion of the particle-matrix couples is cathodically controlled and is governed by the particle size. Pit replica technique faithfully duplicated and reflected all of the key features of corrosion pits. This technique provides a 3-dimensional perspective and can aid in the quantitative assessments of the kinetics and the mechanistic understanding of pitting corrosion.; A Conceptual Model was proposed to describe the mechanism of particle induced pitting. This model provides a new framework for understanding and modeling the nucleation and growth of corrosion pits in aluminum alloys. A Model for General Pitting has been established to describe the development of pitting at single particles in terms of the particle size and limiting cathodic current density over the particle. A simplified approach for modeling the growth of severe pits is described.; Suggestions for further research are described, which include the development of mechanistic model that incorporates the potential and current distributions on the particle and the matrix, and methods for characterizing the spatial distribution of particles and clusters in aluminum alloys.