Advanced Materials Research Vols. 29-30

Abstract: This paper provides an overview of the key areas of magnesium research and development being undertaken internationally and consideration of the future challenges confronting the further implementation of magnesium components. This paper will also include a description of some of the technologies that the CAST Cooperative Research Centre has developed and licensed for commercialisation which address some of the future challenges. There will also be a brief overview of the extent of Australia’s commitment to magnesium alloy research through the CAST CRC, the Centre of Excellence for Design in Light Metals and the CSIRO including their Light Metals Flagship program.

Abstract: Use of wood-based-composites technology to create value-added commodities and traditional construction materials is generally accepted worldwide. Engineered wood- and lignocellulosiccomposite technologies allow users to add considerable value to a diverse number of wood- and lignocellulosic feedstocks including small-diameter timber, fast plantation-grown timber, agricultural fibre and lignocellulosic residues, exotic-invasive species, recycled lumber, and timber removals of hazardous forest-fuels. Another potential advantage of this type of economic- and materials-development scenario is that developing industrial composite processing technologies will provide producers an ability to use, and to adapt with, an ever-changing quality level of wood and/or other natural lignocellulosic feedstocks. However, the current level of performance of our state-of-the-art engineered composite products sometimes limit broader application into commercial, non-residential and industrial construction markets because of both real and perceived issues related to fire, structural-performance, and service-life. The worldwide research community has recognized this and is currently addressing each of these issues. From a performance standpoint, this developing knowledge has already and will continue to provide the fundamental understanding required to manufacture advanced engineered composites. From a manufacturing and a resource sustainability standpoint, with this evolving fundamental understanding of the relationships between materials, processes, and composite performance properties we now can in some cases, or may soon be able to, recognize the attributes and quality of an array of bio-based materials then adjust the composite manufacturing process to produce high-performance composite products. As this fundamental understanding is developed, we will increasingly be able to produce advanced, high-performance wood- and bio-composites. Then we must use those technologies as tools to help forest and land managers fund efforts to restore damaged eco-systems and which in turn may further promote sustainable forest management practices.

Abstract: This paper examines processes for the preparation and characterisation of new ceramic membrane materials with potential for gas purification, based on nanostructured anodic alumina. The ultimate research goal is to develop a membrane capable of separating hydrogen from hot synthesis gas so a key factor is the ability of the membrane to operate successfully at temperatures in excess of 800°C. Two membrane materials are compared and contrasted: a commercial Whatman product and a membrane prepared in our laboratory. We have demonstrated that the fabrication conditions, most particularly the acid environment used during membrane fabrication, controls and directs the high temperature behaviour of the membranes. Membranes prepared using sulphuric acid electrolytes have been shown to withstand 800°C without distortion and without compromising their nanostructured pore array.

Abstract: Mechanical milling of Al alloy powder in liquid nitrogen leads to a large reduction in the scale of the microstructure and results in material with high thermal stability and strength. However, it is important to consolidate the powder and achieve bulk material with sufficient toughness and ductility for structural applications. In this investigation, hot isostatic pressing, followed by quasiisostatic forging and hot rolling, were performed to fabricate Al 5083 plate with a predominantly ultra-fine grained microstructure. Plate produced in this way possessed enhanced tensile strength and ductility, exceeding that of conventionally processed material.

Abstract: Powder metallurgy is widely used to produce alloys with low cost of production. The main drawback using powders is the level of residual porosity of final product which often implies the application of a complicated and costly hot isostatic pressing process. However, this issue can be overcome by using equal channel angular pressing (ECAE) with back pressure (BP). The use of severe shear deformation, with imposed hydrostatic pressure, allows a reduction in the range of compaction temperatures compare to those used in conventional practice. The compaction of Ti-6Al-4V powder by the ECAE method has been investigated. The compaction has been performed at temperatures starting from room temperature (RT) and increasing up to 400°C with various back pressures ranging from 0 to 350MPa. A billet processed by ECAE with 43MPa back-pressure at 400°C was found to have improved relative density of 97.5% and increased Vickers hardness of 369HV, compared to values of 96.7% and 325HV respectively obtained at RT. A relative density of 98.2% and 426HV hardness were measured for billets processed with BP = 262MPa at 400°C. A fully compact billet was obtained by applying 350 MPa of BP at 400°C.

Abstract: Extensive CFD modelling of cooling using nitrogen jets showed that an array of high velocity gas jets close to its surface could cool the part at a similar speed to oil. The optimum conditions were: an approximately uniform nozzle field with the jets four to eight times their own diameter apart, at a distance from the part to be quenched of a quarter of the diameter of the jets; and a jet velocity of 100 m/s. When these optimised conditions were applied to an idealised gear form, the model suggested that it could be fully hardened if a nitrogen/hydrogen mixture was used. The model was validated by comparison with physical experiments under exactly the same conditions. Unfortunately, although close to the physical results, the model results had some important differences. Part of the difference was explained by the exclusion of radiation losses from the model and part by the use of values for specific heat that were derived from static, rather than dynamic, experiments. When the model was modified to correct these there was closer, but by no means perfect, agreement. The finite element model used at this stage was thought to model the heat transfer accurately, but not the steel. The heat transfer data was therefore applied to a metallurgical model. The results from this model were superior in some respects, particularly regarding the phase changes occurring, although again not perfect, perhaps because of the experimental technique used.

Abstract: Knowledge on the contact condition at the tool/workpiece interface is essential for understanding many aspects of FSW. In the present study, FSW experiments were conducted using aluminium alloys followed by metallographic examination focusing on the tool shoulder-workpiece interface region. It was observed that an interfacial intermetallic layer and hence metallurgical sticking/soldering readily formed. Temperature measurements have suggested the presence of interface liquid, hence suggesting a mechanical sliding contact condition dominant. This has been supported by the observation on material flow within the shear layer.

Abstract: Multifarious fracture features, such as coarse rive-like, micro holes, rugged and flat fracture surface, were systematically investigated in the monolithic Cu46-xZr45Al7Gd2Agx (x=0, 0.5) bulk metallic glasses. The fracture planes presented different angles with the loading direction. These fracture features were completely different from the typical fracture characteristics of amorphous alloys, i.e. vein-pattern and fracturing approximately along the maximum shear stress plane. On the other hand, some tiny strips with about 50 nm intervals were also detected on the flat fracture plane. The preliminary discussions on the formation mechanisms of these exceptional features were presented.