Effects of the amount of Mg on the precipitation behavior of β phase and its modeling in Al–Mn–Mg alloys

Abstract

Al–Mn–Mg alloys have been considered as the most suitable basket material of transport and storage casks for spent nuclear fuels. However, the Mg content should be defined with consideration of their prospective heat histories; e.g. exponentially decreasing in temperature from about 200 to 100°C during the fuel storage up to 60 years. In this research, precipitation behavior of β phase (Al₃Mg₂) in Al–Mn–Mg alloys was analyzed at various temperatures, focusing on the effects of the amount of Mg. Time-temperature-precipitation (TTP) diagrams for these alloys were depicted by a model which had been developed based on classical nucleation theory. The TTP diagrams were further rebuilt to “degree of supersaturation-diffusion length-precipitation (SLP) diagram”, where the degree of supersaturation (S) and diffusion length multiplied by cubic root of Mg concentration (L*′) were involved for predicting the starting condition of precipitation. From the SLP diagram, Mg content of 1.0 mass% was found to be able to maintain sufficiently the solid solution strengthening for 60 years.