RESEARCH INTERESTS

Associate Professor Davies' research interests lie in the field of thermomechanical processing of metals. Always mindful of the product-process linkage, Dr. Davies tries to combine industrial relevance with the application of fundamental knowledge. The approach has led to the use of empirical and phenomenological models, and simulations in the following areas:

1. Thermomechanical processing of magnesium alloys. If predictions are to be believed, the use of wrought magnesium alloys is set to increase dramatically over the next five to ten years as auto manufacturers and others seek to lightweight components. However, this increased use will rely in part on improved understanding of the deformation of these metals. Wrought magnesium, because of its hexagonal close packed crystal structure, shows a marked anisotropy of yield when comparing compression with tension. The importance of this can be illustrated by imagining a car bumper made from wrought magnesium. In an impact a bumper will typically have a tensile and a compression face, and in wrought magnesium – unlike aluminium and steel - differential yielding will occur, with the compressive face yielding first and a consequent shift in the neutral axis of the bumper. After the initial yielding, the deformation responses of the tensile and compressive faces are quite different. The phenomenon at the heart of this is mechanical twinning. Component designers must be able to model such behaviour if magnesium alloys are to be used in large volumes in automotive applications. The bulk of this work is performed under the auspices of the CAST Cooperative Research Centre investigating the development of magnesium extrusion alloys.

2. Microforming. Microforming is an innovative use of metal forming techniques in miniature, and promises to be a low cost alternative to machining for the production of parts with at least two dimensions in the sub-millimetre range. Successful microforming requires a starting material which can be reliably formed to shape. Our research is aimed at identifying the material characteristics required for successful, efficient microforming, and consequently optimise the pre-treatment of metals for the microforming of components, with particular reference to copper. Furthermore, we are developing a predictive model of the deformation of metals which explicitly incorporates the scale of the microstructure and the scale of the specimen. This work is performed in conjunction with the Victorian Centre for Advanced Materials manufacturing (VCAMM).

3. Microstructural evolution during heat treatment of aluminium alloy 7075. With a growing number of older aircraft remaining in service today, corrosion of peak aged 7xxx series aluminium alloys has become a significant problem for aircraft fleets world wide. The 7xxx series alloys were used because of their high strength, but in the peak aged (or T6 temper) condition they display relatively poor resistance to stress corrosion cracking (SCC), and this can have a significant effect on the airworthiness of the aircraft. Initially corrosion damage is ground out, but if this grind-out goes beyond damage tolerance limits the component must be repaired or replaced. The current method used to increase the corrosion resistance of these alloys is to overage to a T73 temper. However, this improved corrosion resistance comes with a 10-15% strength loss. An alternative to the conventional heat treatments is the so-called retrogression and re-ageing heat treatments (RRA). The RRA treatment is conducted on T6 material in two steps : a retrogression step, which consists in a short heat treatment at a relatively high temperature where the precipitates are unstable, leading to a partial dissolution of the precipitates present; a re-ageing step, consisting in a new low-temperature heat treatment, where the solute available at the end of the retrogression step is used to form a new dispersion of fine-scale precipitates. This type of heat treatment results in a corrosion resistance similar to that of conventional overaged materials, while retaining or even improving the strength compared to peak-aged materials. We use a combination of techniques, including differential scanning calorimetry and small angle neutron scattering to investigate the evolution of microstructure during RRA heat treatment.

4. Computer simulation of recrystallization. The cellular automaton approach has been applied to the simulation of microstructural evolution during recrystallization. This technique differs from current techniques in that the evolution of microstructure is simulated, and from this the kinetics are derived. This is in contrast to commonly used methods which measure the kinetics and fit the data to a known equation. Simulations are calibrated using the microstructural path method, and their results are compared to experimental kinetics and grain size distributions.

Top of Page | Publications