Backward can extrusion of ultra-fine-grained bulk Al–Mg alloy fabricated by cryomilling and hydrostatic extrusion

Ultra-fine-grained bulk Al–Mg alloy was forged into cup shape product while its grain size and mechanical properties were conserved. Deformation characteristics of the fine-grained material in practical metal forming process were examined with backward can extrusion. The Al–7.5%Mg alloy produced by cryogenic milling and hot isostatic pressing was subjected to hot hydrostatic extrusion as a final consolidation to fabricate the ultra-fine-grained bulk material. The hydrostatic extrusion reduced porosity, and made fibrous structure along the extrusion direction. In the following backward can extrusion with the workpiece prepared by hydrostatic extrusion, severe plastic deformation was achieved successfully. Microstructure of the metal was stabilized and grain size remained under a few hundred nanometer scale during the processes. The material was developed into bimodal structure composed of fine grain matrix and coarse grain cluster inclusions. The coarse grain clusters were distorted according to metal flow and helped enhance formability. There was a slight grain growth during the can forging process in some region where material experienced high temperature provoked by work dissipation.