Changes in processing characteristics and microstructural evolution during friction extrusion of aluminum

Abstract

This study focuses on characterizing the microstructural evolution of the aluminum alloy 7075 in the friction extrusion process under different extrusion forces and die angles. Depending on these conditions, two fundamentally different extrusion types are found, showing significant differences in the process characteristics and microstructural evolution. One of the two extrusion types is associated with high extrusion force and low die angle, leading to fully recrystallized wires with average grain size around 1.2 $$\upmu$$ μ m. The microstructural analysis indicates that the microstructure present in the wires is generated in the charge material by the combination of tool geometry, load induced material flow and friction conditions in the initial stages of the friction extrusion process. The identified processing conditions and influencing factors introduce an alternative route for friction extrusion at low extrusion ratios, capable of producing completely refined wires.

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

“…The recrystallization and the grain refinement enabled the improvement of the mechanical properties; however, the precipitate strengthening effect dictated the mechanical properties of 7075 alloys, and the further increase of UTS after artificial aging has been proven [18]. The UTS value is comparable to the FE from AA7075 solid billet feedstock [8,18], indicating full consolidation of the powder during FE.…”

“…The die geometry not only defines extrudate shape but also affects the material flow prior to extrusion. Darshell et al [7] and Halak et al [8] discussed the influence of different die profiles and angles, respectively.…”

Process simulation of friction extrusion of aluminum alloys

“…The quality of the extrudate has been associated with a number of factors. In FE experiments, the extreme changes observed in processing characteristics and microstructural evolution have been attributed in particular to the friction condition [4], where the friction condition controls the introduced strain and thermal evolution [2,4]. For instance, Peng et al [5] ascribed the formation of hot cracks during extrusion to the material flow governed by the temperature gradient across the wire diameter.…”

Grain Structure Evolution Ahead of the Die During Friction Extrusion of AA2024

“…Kalsar et al [7] reported a homogeneous microstructure along the extruded wire manufactured by a scroll-featured 90 degree die angle and a reduction of the subsequent solution treatment time to reach the peak-aged T6 condition, compared to other extrusion techniques. Halak et al [8] discovered two distinct extrusion modes by a lower die angle (60°), in which a fully recrystallized wire was successfully produced when sticking occurred at the die-feedstock interface. However, with processing time and temperature increase, the friction condition at the die-feedstock interfaces changed to sliding, resulting in an inhomogeneous microstructure within the wire.…”