Processing to ultrafine grain structures by conventional routes

The aim of this project was to achieve grain sizes of the order of 1 μm in Al-Mg-Cr alloys by deformation at elevated temperatures to large strains using conventional rolling or plane strain compression. The 'processing window' for generating such ultrafine grain sizes by continuous rccrystallisation has also been investigated. The necessary processing conditions for achieving a 1-3 μm grain size in alloys containing 2-3 wt-%Mg, deformed to strains of 3, were found to be strain rates of less than 10 s^-1 and temperatures between 300 and 350°C. The restricted range of conditions under which such fine grain microstructurcs can be achieved in these alloys by plane strain deformation is seen to be a limiting factor in commercial exploitation of such processing methods.