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Sediako D.G.,Canadian Neutron Beam Center | Kasprzak W.,Natural Resources Canada
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Understanding of the kinetics of solid-phase evolution in solidification of hypereutectic aluminum alloys is a key to control their as-cast microstructure and resultant mechanical properties, and in turn, to enhance the service characteristics of actual components. This study was performed to evaluate the solidification kinetics for three P-modified hypereutectic Al-19 pct Si alloys: namely, Al-Si binary alloy and with the subsequent addition of 2.8 pct Cu and 2.8 pct Cu + 0.7 pct Mg. Metallurgical evaluation included thermodynamic calculations of the solidification process using the FactSage™ 6.2 software package, as well as experimental thermal analysis, and in situ neutron diffraction. The study revealed kinetics of solid α-Al, solid Si, Al2Cu, and Mg2Si evolution, as well as the individual effects of Cu and Mg alloying additions on the solidification path of the Al-Si system. Various techniques applied in this study resulted in some discrepancies in the results. For example, the FactSage computations, in general, resulted in 281 K to 286 K (8 °C to 13 °C) higher Al-Si eutectic temperatures than the ones recorded in the thermal analysis, which are also ~278 K (~5 °C) higher than those observed in the in situ neutron diffraction. None of the techniques can provide a definite value for the solidus temperature, as this is affected by the chosen calculation path [283 K to 303 K (10 °C to 30 °C) higher for equilibrium solidification vs non-equilibrium] for the FactSage analysis; and further complicated by evolution of secondary Al-Cu and Mg-Si phases that commenced at the end of solidification. An explanation of the discrepancies observed and complications associated with every technique applied is offered in the paper. © 2015, Published with permission of Her Majesty the Queen in Right of Canada, as represented by the Minister of Natural Resources. Source

Zhu Z.,Ecole Polytechnique de Montreal | Gharghouri M.A.,Canadian Neutron Beam Center | Pelton A.D.,Ecole Polytechnique de Montreal
Journal of Chemical Thermodynamics

All available phase diagram data for the (Nd + Mg + Zn) system were critically assessed. In-situ neutron diffraction (ND) experiments were performed on selected samples to identify phases and transition temperatures. A critical thermodynamic evaluation and optimization of the (Nd + Mg + Zn) system was carried out and model parameters for the thermodynamic properties of all phases were obtained. The phase transformation behaviour of selected samples was well resolved from the ND experiments and experimental values were used to refine the thermodynamic model parameters. © 2015 Elsevier Inc. All rights reserved. Source

Elsayed A.,Ryerson University | Sediako D.,Canadian Neutron Beam Center | Ravindran C.,Ryerson University
Journal of Materials Engineering and Performance

In-situ neutron diffraction was used to examine the solidification behaviors of Mg-Zn and Mg-Zn-Zr alloys by melting the alloy in a graphite crucible and irradiating the sample using monochromatic neutrons at 25 different temperatures as it solidified and cooled from 650 to 300 °C. The microstructure of the solidified Mg-Zn sample after in-situ neutron diffraction consisted of Zn-enriched Mg matrix and had an average grain size of ~1500 μm. The Mg-Zn-Zr alloy had a grain size of ~240 μm. The coarse grain size of the Mg-Zn alloy resulted in a large variation in neutron-scattering intensities between the (101¯0) and (101¯1) planes with the (0002) plane being absent, while the Mg-Zn-Zr alloy had the planes (101¯0), (101¯1), and (0002) which are all clearly represented. The authors determined that finer grain sizes improved counting statistics and that increasing sample dimensions or sample oscillation could further improve the diffraction results. © 2015, ASM International. Source

Tomlinson P.,University of British Columbia | Azizi-Alizamini H.,University of British Columbia | Poole W.J.,University of British Columbia | Sinclair C.W.,University of British Columbia | Gharghouri M.A.,Canadian Neutron Beam Center
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

The multiaxial deformation of magnesium alloys is important for developing reliable, robust models for both the forming of components and also analysis of in-service performance of structures, for example, in the case of crash worthiness. The current study presents a combination of unique biaxial experimental tests and biaxial crystal plasticity simulations using a visco-plastic self-consistent (VPSC) formulation conducted on a relatively weak AZ80 cast texture. The experiments were conducted on tubular samples which are loaded in axial tension or compression along the tube and with internal pressure to generate hoop stresses orthogonal to the axial direction. The results were analyzed in stress and strain space and also in terms of the evolution of crystallographic texture. In general, it was found that the VPSC simulations matched well with the experiments. However, some differences were observed for cases where basal 〈a〉 slip and {101̄2} extension twinning were in close competition such as in the biaxial tension quadrant of the plastic potential. The evolution of texture measured experimentally and predicted from the VPSC simulations was qualitatively in good agreement. Finally, experiments and VPSC simulations were conducted on a second AZ80 material which had a stronger initial texture and a higher level of mechanical anisotropy. In the previous case, the agreement between experiments and simulations was good, but a larger difference was observed in the biaxial tension quadrant of the plastic potential. © The Minerals, Metals & Materials Society and ASM International 2013. Source

Elsayed A.,Ryerson University | Sediako D.,Canadian Neutron Beam Center | Ravindran C.,Ryerson University
Canadian Metallurgical Quarterly

In situ neutron diffraction was used to examine the solidification behaviour of Mg-6 wt-%Al and Mg-9 wt-%Al alloys. Samples of each Mg-Al alloy were heated above their liquidus temperatures and stepwise cooled to 420°C while simultaneously collecting neutron scattering intensities. The solidified alloys were examined using scanning electron microscopy. Mainly blocky Mg17Al12 was found in Mg-6 wt-%Al alloy while branched Mg17Al12 adjacent to a large network of fine lamellar Mg17Al12 was found in the Mg-9 wt-%Al alloy. The neutron diffraction data accurately described the fraction solid growth as represented by the (10-11) crystallographic plane over the entire solidification regime. The fraction solid of the Mg-6 wt-%Al alloy rose quickly at temperatures just below the liquidus point and rapidly approached 100% until solidification was complete while the Mg-9 wt-%Al alloy showed a more linear transition from liquid to solid. Neutron diffraction was also capable of detecting the formation of eutectic Mg17Al12 in the Mg-9 wt-%Al alloy. This research demonstrates unique possibilities in using neutron diffraction for further understanding of nucleation, eutectic formation and solid phase evolution of Mg alloys. © 2015 Canadian Institute of Mining, Metallurgy and Petroleum Published by Maney on behalf of the Institute. Source

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