The effect of accumulative roll bonding on the precipitation behavior of a single step artificially aged Al–Ag-Sc alloy

Abstract

In this study, the effect of ARB process on the microstructural evolution and precipitation characteristics of an Al–Ag-Sc alloy was explored. Four and eight cycles of the ARB process were applied on a solution treated Al–Ag-Sc alloy. As well, artificial aging heat treatment was applied on the solution treated and the severe plastically deformed specimens in the temperature range of 100 °C–500 °C. The microstructural characterization, including dislocation characteristic and grain size measurement, were performed using Electron Backscatter Diffraction (EBSD) technique. Moreover, the precipitation behavior of the various conditions was investigated by Transmission Electron Microscopy (TEM). Hardness measurements were performed on the different conditions of this research to evaluate mechanical properties variations. Results showed that applying various cycles of the ARB process leads to the development of ultra/nano grain structure. In that sense, performing eight-cycle of the ARB process transformed the low angle grain boundaries (LAGBs) of the four-cycle ARB process condition to high angle grain boundaries (HAGBs). The sub-grain boundaries developed in the low cycle ARB process were transformed into sharp HAGBs. The grain size was reduced from about 61 μm in the solution treated situation to 600 nm, and 290 nm in the two ARB processed cases. Grain size variation was lower in the low cycle of the ARB situation compared with the high cycle of the ARB case. Aging at 100 °C did not produce any meaningful changes in the microstructure. However, artificial aging at 200 °C led to the precipitation of thin plate-like precursor of Ag2Al precipitates and a limited amount of restoration (mostly recovery). With the effect of the former being dominant, it led to hardness increment. Artificial aging above 300 °C led to the formation of coherent/spherical Al3Sc precipitates and extended recovery. Higher temperature aging dissolved Al/Ag precipitates and caused a full restoration. Hence, it dropped the hardness value of the specimens aged at above 400 °C.