Papers by Author: Nicolas Kamp

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Authors: Marco J. Starink, I. Sinclair, Nong Gao, Nicolas Kamp, Peter J. Gregson, P.D. Pitcher, A. Levers, Simon Gardiner
Authors: A. Sullivan, Nicolas Kamp, Joseph D. Robson
Abstract: The effect of friction stir welding (FSW) and post weld heat treatment (PWHT) on the second phase particle distribution and cross weld hardness profile in AA7449 plate has been investigated. The alloy was received in an underaged condition, welded, then PWHT to give an overaged condition (in the parent material) . The effect of this complex treatment on the precipitate distribution in the weld and parent plate has been investigated over a range of length scales using small angle X-ray scattering (SAXS), TEM and FEGSEM. It is shown that the PWHT does not improve the hardness in the heat affected zone (HAZ), which is the location of the strength minimum after welding, but it does reduce the difference between the hardness in the HAZ and the nugget and parent hardness. The reduction in nugget strength after PWHT is particularly marked and is due to replacement of fine GP zones formed on post weld natural ageing by coarse overaged precipitates.
Authors: Nicolas Kamp, A. Sullivan, R. Tomasi, Joseph D. Robson
Abstract: A numerical model based on the Kampmann and Wagner method was developed to predict the evolution of precipitate distribution in 7xxx aluminium alloy during non-isothermal heat treatments. The model considers the nucleation, growth and coarsening/dissolution of the metastable and equilibrium precipitate phases, η' and η with their stochiometric composition, MgZn2. Constitutive model equations for nucleation were based on the classical theory of nucleation whilst growth and coarsening were treated using classical phase transformation theory. The transition between η' and η, where η' acts as a precursor for η was also accounted for in the model. Differential scanning calorimetry was used to calibrate the homogeneous precipitation kinetics. The model also predicts the evolution of grain boundary precipitates and their effect on precipitate free zone size. Jominy end quench tests were performed to calibrate grain boundary precipitation kinetics. Precipitation on dislocations and dispersoids was considered. The dislocation and dispersoid densities were varied to represent different regions of a grain and therefore account for the spatial distribution of preferential heterogeneous precipitation sites. Comparison between the model prediction and experimental characterisation of the microstructure evolution of a friction stir welded 7449 aluminium alloy was found to be reasonably consistent.
Authors: Nicolas Kamp, I. Sinclair, Marco J. Starink
Authors: Joseph D. Robson, Nicolas Kamp, A. Sullivan, Hugh R. Shercliff
Abstract: Two models to predict the microstructural evolution and post-weld properties of friction stir welds in aerospace aluminium alloys are presented. The first model is a develop- ment of an existing semi-empirical method for the prediction of hardness profiles after welding, calibrated using isothermal hardness data. Post-weld natural ageing is accounted for, and a new method that predicts natural ageing kinetics is introduced. Once calibrated, the model is shown to accurately predict weld hardness profiles. However, this model does not explicitly predict the microstructure and therefore cannot readily be extended to model other properties. It can also only be applied to alloys welded in peak or overaged conditions. The second model aims to explicitly predict the heterogeneous precipitate distributions obtained after welding for any initial condition. It is based on classical kinetic theory and the numerical framework of Kampmann and Wagner. Multiple nucleation sites and multiple phases are accounted for. This model provides detailed microstructural information required for prediction of complex properties.
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