Processing and characterization of continuous-cast AlMgSc(Zr) sheets for improved strength

A processing route is devised to enhance the precipitate strengthening in a continuous-cast/cold-rolled Al-3Mg-0.36Sc-0.14Zr alloy. Retaining sufficient Sc in the solid solution due to a higher cooling rate in a belt-caster, the thin as-cast slab also exhibits a fine-grained, uniformly equiaxed grain structure throughout the thickness. In the absence of any homogenization/solutionising treatment, the cold-rolled sheets are heat treated to produce precipitation either during an intermediate or a final age-hardening treatment. It is shown that the Al3Sc precipitates are considerably more effective in strengthening if precipitation occurs between the cold-roll passes, i.e. through an intermediate anneal process, as opposed to an age-hardening treatment at the final gauge. The strengthening mechanism is suggested to be precipitate-induced work hardening through a hybrid shearable/non-shearable interaction between the coherent Al3Sc precipitates and the moving dislocations. Such interactive deformation conditions create a uniform precipitate/dislocation network across the microstructure, as opposed to a heterogeneous slip structure developed in the absence of precipitates. The processing concept developed here enables one to further maximize the strength for a given Sc content in the alloy, thus not only lowering the overall need for Sc but also enabling potential higher-strength applications.