Friction extrusion processing of aluminum powders: Microstructure homogeneity and mechanical properties

Abstract

Friction extrusion (FE) is a solid-state process categorized as an energy-efficient process, utilizing the intrinsic friction-induced heat to plasticize and manufacture fully consolidated extrudate from various feedstocks, i.e. solid billet, chips and powder. Friction in the relative motion between the feedstock and the non-consumable die generates heat as well as imposes severe plastic deformation; this combination enables dynamic recrystallization and refinement of the microstructure. This study demonstrates the feasibility of directly extruding aluminum alloy powder into fully consolidated wire in a single step process. The extrudate is free of noticeable defects and shows predominantly homogeneous microstructure along the cross-section of the wire. The powder evolution upon passing through the die orifice was investigated in terms of morphology and microstructure. Additionally, the mechanical properties of the extrudate, i.e. microhardness and ultimate tensile strength, were compared to solid billets of AA7075 in different temper states and shows adequate mechanical properties without possible post-heat treatments.