Deakin Research

Institute for Frontier Materials

Light Metals

Introduction

Reducing the weight of vehicles, for increased fuel efficiency, is now a high priority and this has intensified the focus on lightweight metals. The Light Metals Research Group aims to understand and exploit the metallurgy of deformation in magnesium, aluminium and titanium to optimise processing techniques and final properties.

Van Goph sky pattern in extruded magnesium

Areas of expertise:

  • Thermo-mechanical processing (forging, drawing, rolling, extrusion)
  • Alloy development
  • Deformation mechanisms
  • Crystallographic texture development
  • Formability / ductility
  • Electron Back-Scattering Diffraction

The group is involved in a wide range of research activities including:

  • Extrusion alloy and process development
  • Understanding Hall-Petch behaviour for twining dominated flow
  • Thermo-Mechanical Processing of Powders
  • Extrusion and Properties Tubes
  • Deformation Twinning Phenomena
  • Relationship between formability and deformation mechanisms
  • Modelling Recrystallization (dynamic and static)
  • Crystallographic texture development during deformation and annealing

Current projects include:

Influence of Grain Size on Deformation Behaviour

Values for the Hall-Petch slope in the literature for Mg alloys vary over the range 2 - 15 MPa mm1/2, a spread of nearly an order of magnitude. This project looks into the effect of grain size on the deformation stress of extruded AZ31. Apart from determining the Hall-Petch parameters, this study also examines the influence of grain size on the activation of twinning. The topic is also being explored in other materials such as titanium and TWIP steels.

Some key papers:

Increasing Extrusion Speeds / Extrusion Alloy Development

The slow extrusion speed required to avoid cracking of magnesium extrusions is a significant component of the manufacturing cost. In this project, a method is being developed for the rapid generation of extrusion limit diagrams. This method, which combines engineering equations for temperature rise and extrusion load with small scale laboratory extrusion tests, is then employed to examine the hot extrusion performance of a range of commercial and prototype magnesium alloys. Within these extrusion limits, the influence of the extrusion conditions on the properties of the extruded product is also being investigated.

Key paper:

Recrystallization of Magnesium Alloys

Recrystallization of magnesium occurs during deformation (dynamic recrystallization), during heating between rolling passes and during cooling following extrusion (static recrystallization). This project aims to determine how these mechanisms can be exploited, through optimized processing routes or through different alloy additions, to generate high strength fine uniform grain structures. Equations are developed which, for given deformation and annealing regimes, can determine the grain size that is developed.

Some key papers:

Deformation Modes in Magnesium

The deformation modes activated in magnesium are being studied through conventional and in-situ tensile testing. The in-situ technique enables temperature treatments and deformation to be carried out in an SEM. The work aims to assess the influence of grain size and alloy composition on the active deformation mechanisms. Particular attention is being paid to primary and secondary twinning due to its important role in the ductility of magnesium alloys.

Some key papers:

Crystallographic Texture Development

The combination of the high mechanical anisotropy of the hcp unit cell with typically sharp textures means that the mechanical properties of wrought magnesium are very sensitive to loading path. In some applications this is good but in most it is detrimental to performance. In this project we are exploring ways to randomize the texture to reduce the mechanical anisotropy.

Some key papers:

Ductility of Magnesium

Wrought magnesium alloys generally have superior mechanical properties to those of castings, but they suffer from low room temperature ductility. This restriction can be partly ascribed to mechanical twins formed by deformation. This study examines the effects of twinning and precipitation hardening on the ductility of Mg alloys.

Some key papers:

A new cheap technology for magnesium metal foam production - M. Barnett and C. Wen

The Development of Mg and Al Tubes

Tubes of various dimensions are extruded from magnesium and aluminium billets. These tubes are then subjected to bending and axial compression tests. The aim of this project is to evaluate the suitability of light metal tubes for automotive bumper and crash box applications.



The research is supported by the CAST CRC, the Australian Research Council, ARC Centre of Excellence in Design in Light Metals and Deakin University Funding Schemes.

Deakin University acknowledges the traditional land owners of present campus sites.

19th February 2012