a b s t r a c tResistance spot welding (RSW) is difficult to apply to aluminium automotive alloys. High power ultrasonic spot welding (HP-USW) is a new alternative method which is extremely efficient, using ∼2% of the energy of RSW. However, to date there have been few studies of the mechanisms of bond formation and the material interactions that take place with this process. Here, we report on a detailed investigation where we have used X-ray tomography, high resolution SEM, and EBSD, and dissimilar alloy welds, to track the interface position and characterise the stages of weld formation, and microstructure evolution, as a function of welding energy. Under optimum conditions high quality welds are produced, showing few defects. Welding proceeds by the development and spread of microwelds, until extensive plastic deformation occurs within the weld zone, where the temperature reaches ∼380 • C. The origin of the weld interface 'flow features' characteristic of HP-USW are discussed.

2008) "Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating". Composites Science and Technology,, [1854][1855][1856][1857][1858][1859][1860][1861] Comparison of the mechanical and physical properties of a carbon fibre epoxy composite manufactured by resin transfer moulding using conventional and microwave heating AbstractMicrowave processing holds great potential for improving current composite manufacturing techniques, substantially reducing cure cycle times, energy requirements and operational costs. In this paper, microwave heating was incorporated into the resin transfer moulding technique. Through the use of microwave heating, a 50% cure cycle time reduction was achieved. The mechanical and physical properties of the produced carbon fibre/epoxy composites were compared to those manufactured by conventional resin transfer moulding. Mechanical testing showed similar values of flexural moduli and flexural strength for the two types of composites after normalisation of the corresponding data to a common fibre volume fraction. A 9% increase of the interlaminar shear strength (ILSS) was observed for the microwave cured composites. This enhancement in ILSS is attributed to a lowering of resin viscosity in the initial stage of the curing process, which was also confirmed via scanning electron microscopy by means of improved fibre wetting and less fibre pull-out. Furthermore, both types of composites yielded minimal void content ( properties of the produced carbon fibre/epoxy composites were compared to those manufactured by conventional resin transfer moulding. Mechanical testing showed similar values of flexural moduli and flexural strength for the two types of composites after normalisation of the corresponding data to a common fibre volume fraction. A 9% increase of the interlaminar shear strength (ILSS) was observed for the microwave cured composites. This enhancement in ILSS is attributed to a lowering of resin viscosity in the initial stage of the curing process, which was also confirmed via scanning electron microscopy by means of improved fibre wetting and less fibre pull-out. Furthermore, both types of composites yielded minimal void content (<2%). Dynamic mechanical thermal analysis revealed comparable glass transition temperatures for composites produced by both methods. A 15 °C shift in the position of the ȕ-transition peak was observed between thermally and microwave cured composites, suggesting an alteration in the cross-linking path followed.

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Friction stir spot welding (FSSW) is a relatively new process, which has not yet been fully optimised. The aim of the work presented was to investigate the influence of pin length and an insulating anvil on FSSW thin (0?9 mm) 6111-T4 aluminium automotive closure panels. A pinless, or 'zero pin length', tool was also tested. With a normal pin tool and a steel anvil the optimum pin length was found to be considerably shorter than conventionally used, being in the range 0?7-1 mm, as opposed to y1?4 mm. The insulated anvil increased the peak temperature in the bottom sheet by 45uC, but there was a 15% reduction in lap shear strength when used with a conventional pin tool. In the case of the pinless tool, successful welds were produced with comparable strengths to the highest values measured with the optimum conventional tool without a retained weld keyhole or top sheet thinning (hooking).