Papers by Author: Chris P. Heason

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Authors: C.M. Allen, G. Verhaeghe, P.A. Hilton, Chris P. Heason, Philip B. Prangnell
Abstract: Fusion welding of 7xxx aluminium alloy plates has been investigated for aerospace applications using autogenous laser welding and hybrid laser-MIG welding. Nd:YAG and Yb-fibre lasers have been used, with two different focussed spot sizes in each case. Autogenous and hybrid welding of 12.7mm thick plate using the Yb-fibre laser with a 0.6mm diameter spot was selected for further development, on the basis of penetration and weld quality achieved. These welds were acceptable to the highest quality class B (stringent) of BS EN ISO 13919-2:2001, with a porosity of only 0.3% of the cross-sectional area of the weld, and close to class A of AWS D17.1. Transverse proof strengths of ~60% of parent material were achieved. Development of hybrid welding is ongoing with novel fillers to refine weld metal grain structure and improve weld properties.
Authors: Joseph D. Robson, Philip B. Prangnell, Brian J. McKay, Chris P. Heason
Abstract: A combined model is presented that predicts the non-uniform distribution of Al3X dispersoid particles in commercial aluminium alloys containing zirconium and scandium and uses these predictions as inputs to a simple recrystallization model. The recrystallization model relies on knowledge of the stored energy in the sub-structure after deformation and this has been measured using electron backscattered diffraction (EBSD) techniques. The recrystallization model is based on the concept that partial recrystallization results from the non-uniform distribution of dispersoid particles due to their precipitation from a segregated cast structure. The model has been used to devise an improved homogenization treatment for AA7050, which uses an isothermal hold during heat up to maximize dispersoid nucleation. It has also been applied to predict the effect of scandium additions on recrystallization, investigate the factors that control the through thickness variation in recrystallized fraction, and interpret the results of experiments where the effect of strain rate have been studied.
Authors: P.J. Apps, Chris P. Heason, Philip B. Prangnell
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