Ultrafine grain structures formed by thermomechanical processing of spray cast Al–Li alloys

Abstract

Spray casting has been used to produce Al–Li alloys with an initial grain size of about 10–20 μm and higher levels of dispersoid forming elements (zirconium, titanium, scandium) than can be achieved by conventional casting. Materials with a range of dispersoid densities have been investigated. On thermomechanical processing at elevated temperatures, it has been found that the high volume fraction of fine dispersoids prevents discontinuous recrystallisation mechanisms operating. However, on deformation to high strains, the deformed fibrous grains become unstable and can be induced to break up into a highly desirable microstructure of very fine equiaxed grains with a size of 1–2 μm. The intensity of the rolling texture has also been found to reduce greatly with finer dispersoid interparticle spacings, leading to materials with high strengths, an ultrafine equiaxed grain structure, and low anisotropy in the sheet form.