Sensitization prediction and validation for Al 5xxx alloys exposed to long term cyclical and constant heating at low temperatures

Abstract

A number of Al 5xxx alloys were aged at constant temperatures (40, 50, 60, 70°C) and cyclic temperatures (40 to 45, 30 to 70, 50 to 70°C) for as long as 57.5 months. ASTM G67 nitric acid mass loss test (NAMLT) results of Al 5050-H32, 5052-H32, 5154-H32, 5083-H116, 5083-H131, and 5456-H116 alloys were obtained to evaluate the degree of sensitization. An intergranular β-phase growth model that considers nucleation, growth, and coarsening processes was developed to predict the formation and continuity of the β phase that leads to sensitization. Results obtained from scanning transmission electron microscopy were used to verify the model. A linear relationship between continuity and mass loss was adopted to predict the mass loss of Al 5083-H116 and -H131 aged at constant and cyclical temperature, and the modeling results agree well with experimental mass loss data.