Project A3: Design of structures for enhanced ductility
	Target: Optimising ductility for improved performance (processing & service)
•	Project Chief Investigators: Matthew Barnett (Project leader), Michael Ferry, Christopher Davies
•	Senior Researchers/Research Associates: Deakin: Aiden Beer, Nicole Stanford, Pavel Cizek; Monash: Yong B Chum; UNSW: M. Zakaria Quadir, Kevin Laws
•	Research Students: Deakin: -; Monash: -; UNSW: Aravinda Bommareddy, Lalu Robin, Bulent Gun, Kevin Laws, Nanang Burhan, Oday Al-Buhamad, Hamidreza Mohseni, Julia Sokolova
•	Research Assistants Visiting Scholars, Hons Students etc: UNSW: Timothy Burgess, Kai Dick Lau, Greig Kurniawan
•	External Collaborators: F. John Humphreys (Manchester, UK), W.B. Hutchinson (Stockholm, Sweden)
Project Summary
The object of this project is to determine how to manipulate the structure using alloying addition and process changes so that the final formability and/or ductility of the material is improved. In meeting this objective we acknowledge that we must not compromise on strength.
Project Progress: Technical Details, Targets and Research Outcomes
Advances have been made in the production of metallic glasses and roll bonded sheet. The complex role of twinning in the ductility of magnesium has also been established. It has also been shown that high levels of grain refinement can occur through the application of high strain hot rolling. The structures that are produced display favourable ductility-strength relationships following annealing. The project is divided up into two streams – low and high temperature ductility.
A3 - Stream 1: High temperature ductility
The custom die casting rig built in the early part of the project is continuing to be used to determine optimal processing conditions for the production of bulk metallic glasses. Work is progressing into the production of roll bonded materials with unique property combinations. Key to this process is the ability to achieve high bond strengths. Without this, ductility is impaired. An journal article has been published that reveals the optimum conditions for high bond strength.
A3 - Stream 2: Low temperature ductility (magnesium)
It has been found that the composition of magnesium alloys plays a large role in determining the texture and the propensity for twinning. These in turn impact upon the ductility. It appears that twinning is suppressed in a Mg-Mn binary by a mechanism that is yet to be determined. However, despite this, the material still displays twin induced failure. The nature of the twinning that forms is important. To understand the type of twins that form, an extensive EBSD study was performed. This revealed that the shape of primary twins is an important factor in determining the type of secondary twins that can grow. The secondary twins that most impair the ductility are formed preferentially in thin long primary twins. This shape factor must be accounted for if the effect is to be modelled. And, it is now clear that to improve the ductility it is necessary to prevent the secondary twin from forming. The double twinning mechanism is illustrated in Figure A4.
Figure A4 - Dark field Transmission Electron Microscope image showing the formation of secondary twins in the interior of a primary twin. Such twins play a large role in ductile failure.
It was also found that high strain hot rolling can produce favourable fine structures in a conventional magnesium alloy (AZ31). The structure thus produced reveals a good strength-ductility balance. The results appear in the article below. The optimal structure is shown in Figure A5 along with the associated mechanical properties.
Figure A5 - (a) Grain structure of hot rolled sample A1 (grain size = ~2 μm), (b) mechanical properties and (c) extension of strength/elongation space.