Multiple shearing induced in one-step deformation fabricating gradient-structured aluminium disks

Abstract

Repeated deformation or extended time is generally required in producing ultrafine grained structures, while this applies equally to forming gradient structures with ultrafine grains, which have been developed to evade the strength-ductility trade-off in recent years. This paper reports multiple shearing assisted fabrication of gradient-structured (GS) aluminium disks involving ultrafine grain formation in one step through a new process, called radial extrusion machining (REM). Finite element analysis and microstructural observations revealed that REM introduced multiple shearing, which provided hierarchical combinations of shear effects of different origins, intensities, and ranges of influence, resulting in a structural gradient across the disk thickness. The fabricated GS disks exhibited significant refinement of grains from ∼100 µm to submicron scale in the large-strained layers, which is attributable to the promoted multiple shearing. It was demonstrated that the grain refinement process is accelerated with the evolution of mutually crossing deformation or microshear bands introduced by multiple shearing. The operating structural mechanisms responsible for the dynamic formation of new grains were discussed in detail. This study provides a feasible method to fabricate GS disks with ultrafine grains formed in a straightforward and time-efficient way, and offers insights and guidance to develop new processes by introducing multiple shearing.