Statistical analysis of constituent particles in 7075-T6 aluminum alloy

Pitting, corrosion is a primary degradation mechanism that affects the durability and integrity of structures made of aluminum alloys, and it is a concern for commercial transport and military aircraft. The heterogeneous nature of aluminum alloys is the reason that pitting, corrosion is an operative damage mechanism. Typically there are about 2,000 constituent particles per mm(2) on polished surfaces. Corrosion pits are shown to commence at these particles and to evolve into severe pits by sustained growth through clusters of particles. The severe pits are nucleation sites for subsequent corrosion fatigue cracking. Thus, the role of heterogeneous clusters of constituent particles is critical to the quality of aluminum alloys subjected to deleterious environments. To formulate a stochastic model of corrosion, as a part of the methodology for structural reliability analysis, it is essential to have quantitative descriptions of the spatial statistics of the particles and particle clusters, including their location, size, density and chemical composition. The primary purpose of this effort is to statistically estimate the distribution functions of the key geometrical properties of the constituent particles in 7075-T6 aluminum alloy and their role in pitting corrosion.