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

Spray costing has been used to produce Al-Li alloys with an initial grain s ize of about 10-20 mu m and higher levels of dispersoid forming elements (z irconium, titanium, scandium) than can be achieved by conventional casting. Materials with a range of dispersoid densities have been investigated. On thermomechanical processing ar elevated temperatures, it has been found tha t the high volume fraction of fine dispersoids prevents discontinuous recry stallisation mechanisms operating. However: on deformation to high strains, the deformed fibrous grains become unstable and can he induced to break up into a highly desirable microstructure of very fine equiaxed grains with a size of 1-2 mu m. 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.