Using Severe Plastic Deformation to Fabricate Strong Metal Matrix Composites

Megumi Kawasaki,Terence G Langdon

doi:10.1590/1980-5373-mr-2017-0218

Abstract

The processing of bulk metals through the application of severe plastic deformation leads to significant grain refinement and a consequent strengthening of the material. High-pressure torsion (HPT) generally refers to the processing of disk samples and this technique is especially effective in producing extremely small grains. Recently, new experiments were conducted in which disks of two different alloys, based on aluminum and magnesium, were stacked together and then processed by HPT for up to 20 turns at room temperature. Analysis after processing revealed the formation of a multi-layered structure in the central region of the disks but with a true nanoscale microstructure containing different types of intermetallic compounds within an Al matrix leading to the formation of metal matrix nanocomposites at the disk edges. Measurements showed a lowering of density at the disk edges, thereby confirming the potential for using HPT to fabricate materials with exceptionally high strength-to-weight ratios.

Highlights

True nanostructures in bulk materials are difficult to produce using established engineering techniques, especially when considering the practical and societal needs of materials selection
The present study shows the unique microstructure and hardness distributions and provides a detailed analysis of the strengthening mechanism for the Al-Mg hybrid system formed by High-pressure torsion (HPT)
The results demonstrate the feasibility of HPT processing in the preparation of new alloy systems and a wide range of metal matrix nanocomposite (MMNC) exhibiting exceptionally high strength-to-weight ratios

Summary

Introduction

True nanostructures in bulk materials are difficult to produce using established engineering techniques, especially when considering the practical and societal needs of materials selection. An earlier report demonstrated an increase in the strength limit of an aerospace-grade Al-7075 alloy through the application of high-pressure torsion (HPT) while maintaining appropriate formability.[1] Processing by HPT is a most promising severe plastic deformation (SPD) technique producing true nanometer grains leading to and providing an excellent potential for achieving high hardness in most bulk metals.[2] In recent years, because of the introduction of intense plastic strain during processing, HPT has been applied for the consolidation of metallic powders[3,4,5,6,7,8,9,10] and the bonding of machining chips[11,12]. The results demonstrate the feasibility of HPT processing in the preparation of new alloy systems and a wide range of MMNCs exhibiting exceptionally high strength-to-weight ratios

Processing of the Al-Mg system

Formation of MMNCs and the hardening mechanism

Future potential of the HPT technique for synthesized hybrid metals

Summary and conclusions