Measuring and Modeling Alloy Effects on AA5xxx Sensitization
Abstract
Al 5xxx alloys (Al 5083 H116, H131 and 5456 H116) are widely used in marine structures and warships. However, when exposed to relatively high temperature for a long time, Mg-rich precipitates will form at the grain boundaries, which will cause the intergranular corrosion and stress corrosion of these alloys. Our previous research on Al 5083 H116, H131 and 5456 H116 alloy reveals that the sensitization behavior of these alloys is highly affected by the size and distribution of intergranular precipitates. Although some research reported the size, concentration, and structure of intergranular precipitates formed in these alloys, the effects of different alloys on intergranular precipitation behavior have not been fully understood. Based on the nucleation density obtained from transmission electron microscopy (TEM), our previous model gives a reasonable prediction of beta phase formed at grain boundaries.[Error! Bookmark not defined.] The current model, which accounts for the factors of different alloys, such as Mg concentration, grain size, dislocation density, and Mg diffusion coefficients within grain matrix etc., provides generally well description of nucleation, growth, and coarsening behavior of intergranular precipitation in different alloys, and can be used to predict the ASTM G-67 mass loss combined with empirical relations. The main objective of this project is to measure and model the effects of alloy treatment on sensitization based on the methods described previously. The tasks for this project are: (1) Evaluate grain size, Mg concentration within matrix, and proportion of different type of grain boundaries (low, high angle grain boundary) in as received Al 5083 H116, H131 and 5456 H116 samples, to provide parameters for beta phase nucleation and growth model. (2) Evaluate Al 5083 H116, H131 and 5456 H116 alloy specimens using TEM and atomic force microscopy (AFM) to obtain dislocation density and effective diffusion coefficients. (3) Evaluate the nucleation density and precipitate size of Al 5083 H116, H131 and 5456 H116 alloy aged at different temperature for different times using TEM and AFM to validate the beta phase growth model. (4) Investigate the effect of different grain size and beta phase formed at different grain boundaries on the corrosion behavior of Al 5083 H116, H131 and 5456 H116 alloy. (5) Utilize the findings from objectives 1-4 to improve the existing sensitization model to facilitate sensitization prediction for more AA5xxx alloys
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141512414
Entities
People
- Michael L. Free
Organizations
- Office of Naval Research
- United States Navy
- University of Utah