Processing of an Al-Mg-Li-Zr alloy with ultra-fine grain size

It is now well established that superplasticity requires a very small and stable grain size, of the order of 10 μm or smaller. In general, superplastic metals usually have grain sizes of the order of 1-5 μm. However, it is possible to introduce an ultra-fine grain size into metallic alloys by subjecting the materials to very intense plastic strain through processes such as equal-channel angular (ECA) pressing or torsion straining. This paper describes experiments conducted on an Al-5.5% Mg-2.2% Li-0.12% Zr alloy where there was a fine dispersion of δ′-Al₃Li and β′-Al₃Zr precipitates. Using a material with an initial grain size of ∼400 μm, it is shown that it is possible to use ECA pressing to achieve a grain size in this alloy of the order of 1.2 μm and the grains remain small up to temperatures of ∼700 K.