Investigation on the Strengthening Mechanism of Flow Control Extrusion by Using Experiment and Numerical Simulation.

Guangshan Wu,Yangqi Li,Fei Chen

doi:10.3390/ma14175001

Abstract

Bimodal grain structure leads to high strength and strain hardening effect of metallic materials. In this study, an effective approach called flow control extrusion (FCE) is proposed to achieve heterostructures of pure copper. Compared with conventional extrusion (CE), FCE shows much stronger grain refine ability and much weaker grain orientation concentration. The significant grain refinement and heterostructures depend on the severe shear strain from FCE. The heterostructures of sample subject to FCE transfer from bimodal structure to gradient structure with the decrease of temperature, as the grains in the surface of sample are all refined to ultrafine scale. Both these two heterostructures can realize the improvement of strength and strain hardening effect simultaneously.

Highlights

One of the main strengthening mechanisms for polycrystalline materials is grain boundary strengthening [1,2,3,4]
There are mainly three categories: bimodal structure with micrometre-sized grains and ultrafine/nano grains distributes in the sample uniformly [19]; gradient structure characterized by the grain size from nano scale at the surface to micro scale in the core; and heterogeneous lamella structure with the soft micrograined lamellae embedded in hard ultrafine-grained lamella matrix [20,21,22,23]
Bimodal structured pure copper with enhanced strength and strain hardening effect was established after flow control extrusion (FCE)

Summary

Introduction

One of the main strengthening mechanisms for polycrystalline materials is grain boundary strengthening [1,2,3,4]. If the metal has a strong texture, it means the anisotropy of the mechanical properties, and limits the following deformation strategies, for scaling-up to industrial size samples [31,32,33,34]. For the traditional deformation process (including severe plastic deformation, such as equal channel angle pressing (ECAP) and high pressure torsion (HPT), the texture is relatively strong, as the metal flow direction is constant and unified [35,36]. The flow direction and path of the sample can be controlled by the designed structure and distribution of these bulges, and affect the grain refinement ability and grain orientations.

Microstructure Characterization and Mechanical Property Test

Mechanical Properties

Strengthening Mechanism

Findings

Conclusions