Papers by Author: Philip B. Prangnell

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Authors: Chun Y. Chan, Philip B. Prangnell, Simon J. Barnes
Abstract: Friction Stir Processing (FSP) has potential for locally enhancing the properties of Al-Si alloy castings, for demanding applications within the automotive industry, by greatly refining the second phase particle size. In the present study, the homogeneity of particle refinement and second phase spatial distribution within the process zone, as well as the relationship to the processing parameters, were investigated in a gravity die cast Al-Si LM24/A380 alloy, subjected to a range of FSP conditions. Detailed image analysis and the dirichlet tessellation method were used to quantify particle clustering. ‘Stop-action’ experiments were also used to study the process of particle break up, by following the behaviour through the deformation zone surrounding the tool.
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Authors: Yan Huang, Philip B. Prangnell
Abstract: The feasibility of a novel continuous severe plastic deformation (SPD) technique, continuous frictional angular extrusion (CFAE), for producing ultra-fine grained strip material, has been studied. The CFAE technique takes advantage of facets of rolling and equal channel angular extrusion (ECAE) and is designed to produce bulk ultra-fine grained (UFG) metals with high productivity and low cost. A process setup was established through the modification of a standard rolling mill. CFAE processing of commercially pure aluminium AA1050 sheets was successfully carried out at room temperature, using a 120o die angle. A uniform UFG structure with an average grain size of ~0.6μm was achieved after 10 CFAE passes, at an equivalent strain of ~ 6.6. Evolution of the deformation structure and texture during processing was examined as a function of strain and characterized using high resolution EBSD.
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Authors: Alphons A. Antonysamy, Philip B. Prangnell, Jonathan Meyer
Abstract: In titanium alloys it is known that in bulk sections the solidification conditions in ALM commonly lead to undesirable, coarse, columnar β grain structures. Here, we have investigated the effect of build geometry on the grain structure and associated texture in Ti-6Al-4V ALM components produced by Selective Electron Beam Melting (SEBM). Through reconstruction of the primary β-phase, it has been confirmed that in thick sections large columnar β grains grow with a strong <001>β fibre texture, although there is a significant skin effect. In contrast, in thin walls nucleation off the surrounding powder and growth inwards dominates. Local heterogeneities are also observed within section transitions. It is shown that the weaker α transformation texture arises from a random distribution across the possible habit variants.
205
Authors: Dimitrios Tsivoulas, Philip B. Prangnell, Christophe Sigli, Bernard Bès
Abstract: The present paper focuses on the influence of combined additions of Zr and Mn on the recrystallisation resistance of aluminium alloy 2198 sheet. Dual additions of these dispersoid forming elements have previously been reported to be beneficial for reducing recrystallisation during solution treatment, as they exhibit opposing microsegregation partitioning on solidification. Contrary to expectation, it was found that the addition of Mn, to a standard Zr-containing 2198 sheet material, reduced recrystallisation resistance. The reasons for this behaviour are explored by analysis of the morphology, size, chemistry, and distribution of the dispersoid families formed, as a function of the Mn and Zr level, traced back to the homogenisation stage.
568
Authors: P. Ryan, Philip B. Prangnell, Stewart W. Williams
Abstract: The liquid film re-growth behaviour resulting from pulsed laser surface melting (LSM) has been investigated for typical 2xxx, and 7xxx aerospace alloys, both on parent plate and friction stir welded (FSW) joints. In Zr free alloys, as a result of the high growth rate and steep thermal gradient, the melted layer re-grew with a stable front, epitaxially, from the parent subsurface grains. This caused a thin coarse grained solidified layer to form over the parent material, thermomechanically affected zone (TMAZ) and heat affected zone (HAZ), and fine columnar grains to develop over the FSW nugget zone of the same order in width as the nugget grain size. In the case of the Zr containing alloys, a very fine columnar grain structure was found over the entire surface, independent of the subsurface grain structure. This has been shown to occur by growth selection from a band of nanoscale Al grains epitaxially nucleated on Al3Zr dispersoids, at the melt solid interface, that had not fully dissolved in the melt.
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Authors: David G. Richards, Philip B. Prangnell, Philip J. Withers, Stewart W. Williams, Andrew Wescott, E.C. Oliver
Abstract: Although Friction Stir Welding (FSW) avoids many of the problems encountered when fusion welding high strength Al-alloys, it can still result in substantial residual stresses that have a detrimental impact on service life. An FE model has been developed to investigate the effectives of the mechanical tensioning technique for controlling residual stresses in FSWs. The model purely considered the heat input and the mechanical effects of the tool were ignored. Variables, such as tensioning level, heat input, and plate geometry, have been studied. Good general agreement was found between modelling results and residual stress measurements, justifying the assumption that the stress development is dominated by the thermal field. The results showed a progressive decrease in the residual stresses for increasing tensioning levels and, although affected by the heat input, a relatively low sensitivity to the welding variables. At tensioning levels greater than ~ 50% of the room temperature yield stress, tensile were replaced by compressive residual stresses within the weld.
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Authors: David G. Richards, Philip B. Prangnell, Philip J. Withers, Stewart W. Williams, Andrew Wescott, E.C. Oliver
Abstract: Finite element modelling has proved to be an effective tool for the investigation of trends effected by changing welding conditions. This is especially important in mechanical tensioning of friction stir welds because of the large number of parameters involved. In this paper, an FE model is used to examine the effectiveness of the mechanical tensioning technique for controlling residual stresses in FSWs by the investigation of trends caused by changes to the welding parameters. Comparisons between different geometries, traverse speeds, and welding off-axis angle all produced consistent results, and showed that the peak stresses are most strongly influenced by both the local tensioning and heat input, and not by the more global welding conditions. The results also showed a progressive decrease in the residual stresses for increasing tensioning levels and, although affected by the heat input, a relatively low sensitivity to the welding variables. At tensioning levels greater than ~50% of the room temperature yield stress, tensile stresses were replaced by compressive residual stresses within the weld.
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Authors: A.F. Norman, Ian Brough, Philip B. Prangnell
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