BURA Collection: BCAST is striving for international excellence on both fundamental and applied research on solidification of metallic materials. BCAST sees itself as a reliable source of both new knowledge and new solidification technologies for the metallurgical industry.

The impact of melt-conditioned twin-roll casting on the downstream processing of an AZ31 magnesium alloy

2013-01-17T10:39:47Z

Title: The impact of melt-conditioned twin-roll casting on the downstream processing of an AZ31 magnesium alloy Authors: Bayandorian, I; Huang, Y; Fan, Z; Pawar, S; Zhou, X; Thompson, GE Abstract: Melt conditioning by intensive shear was used prior to twin-roll casting of AZ31 magnesium alloy strip to promote heterogeneous nucleation and to provide a refined and uniform microstructure without severe macrosegregation. The cast strip was then processed by homogenization, hot rolling, and annealing, and its downstream processing was compared with a similar cast strip produced without melt conditioning. Melt conditioning produced strip with accelerated kinetics of recrystallization during homogenization and improved performance in hot rolling and improved tensile properties. An average tensile elongation of ~28 pct was achieved, which is substantially higher than the ~9 pct obtained for the strip produced without melt conditioning which is consistent with reported values (~6 pct to 16 pct). The as-cast, homogenized, and hot-rolled microstructures of the strip were characterized. The kinetics of homogenization and hot-rolling process have been discussed in detail. Description: Copyright @ 2012 Springer Verlag

Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al-Mg alloys

2012-11-12T09:51:27Z

Title: Mechanisms of enhanced heterogeneous nucleation during solidification in binary Al-Mg alloys Authors: Li, HT; Wang, Y; Fan, Z Abstract: The mechanisms involved in the grain refinement of Al–Mg alloys through varying the Mg content and applying intensive melt shearing were investigated. It was found that the oxide formed in Al–Mg alloys under normal melting conditions is MgAl2O4, which displays an equiaxed and faceted morphology with {1 1 1} planes exposed as its natural surfaces. Depending on the Mg content, MgAl2O4 particles exist either as oxide films in dilute Al–Mg alloys (Mg < 1 wt.%) or as naturally dispersed discrete particles in more concentrated Al–Mg alloys (Mg > 1 wt.%). Such MgAl2O4 particles can act as potent sites for nucleation of α-Al grains, which is evidenced by the well-defined cube-on-cube orientation relationship between MgAl2O4 and α-Al. Enhanced heterogeneous nucleation in Al–Mg alloys can be attributed to the high potency of MgAl2O4 particles with a lattice misfit of 1.4% and the increased number density of MgAl2O4 particles due to either natural dispersion by the increased Mg content or forced dispersion through intensive melt shearing. It was also found that intensive melt shearing leads to significant grain refinement of dilute Al–Mg alloys by effective dispersion of the MgAl2O4 particles entrapped in oxide films, but it has marginal effect on the grain refinement of concentrated Al–Mg alloys, where MgAl2O4 particles have been naturally dispersed into individual particles by the increased Mg content. Description: This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2012 Elsevier

Measuring the viscous flow behaviour of molten metals under shear

2012-10-22T10:43:07Z

Title: Measuring the viscous flow behaviour of molten metals under shear Authors: Ritwik Abstract: The flow behaviour of liquid metals (Sn, Pb and Sn-Pb eutectic) under different shearing conditions is investigated. Experiments were performed with two designs of concentric cylinder viscometers: rotating the inner cylinder (Searle) and rotating the outer cylinder (Couette). The latter technique is uncommon and the equipment was optimised with standard oils. The flow behaviour for the metals differs in the two systems. The curves of “apparent” viscosity versus shear rate may be divided into two regimes: I. At lower shear rates (<200 s-1): a reduction of “apparent” viscosity with shear was observed with both viscometers. It is suggested that the high density and high surface tension of the metals and eccentricity between the cylinders at low shear rates, leads to instabilities. Results at low shear rates were therefore discarded and further detailed analysis would be required for a fuller understanding of this behaviour. II. At higher shear rates: a steady, shear-independent behaviour of “apparent” viscosity with shear rate is observed in the Couette system (upto 600 s-1) whereas in the Searle system the “apparent” viscosity increases with shear rate (upto 2600 s-1). From hydrodynamic theory about Newtonian fluids, it is suggested that in the Searle type viscometer, the fluid is unstable and Taylor vortices are expected at low shear rates (~80 s-1). This gives rise to an increase in the “apparent” viscosity with shear rate. Whereas, in the Couette type, the flow is more stable, resulting in a steady “apparent” viscosity. This interpretation is consistent with liquid metals behaving as Newtonian fluids, but further research is required to confirm this. The author suggests further experiments, with the prime one being the investigation of the fluid with counter and co-rotation of the cylinders in order to observe more complex flows. The results are expected to have implications in the modelling of flow for liquid metal processes, especially the initiation of Taylor vortices under the unstable flow conditions produced by rotating the inner cylinder. Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.

Influence of ultrasonic melt treatment on the formation of primary intermetallics and related grain refinement in aluminum alloys

2012-04-23T12:54:01Z

Title: Influence of ultrasonic melt treatment on the formation of primary intermetallics and related grain refinement in aluminum alloys Authors: Zhang, L; Eskin, DG; Katgerman, L Abstract: Ultrasonic melt treatment (UST) is known to induce grain refining in aluminum alloys. Previous studies have clearly shown that in Al-Zr-Ti alloys, the primary Al(3)Zr intermetallics were dramatically refined by cavitation-assisted fragmentation, and a good refinement effect was achieved. In this article, Al-Ti, Al-Ti-Zr alloys, and some commercial aluminum alloys are used to analyze the effect of UST on primary intermetallics and grain refinement. The addition of a small amount of Al-3Ti-B master alloy is also studied in order to compare with the addition of Ti and Zr in commercial aluminum alloys. Experimental results show that the ultrasonic grain refining effect is not only related to the size of particles which are refined and/or dispersed by UST, but also related to an undercooling available for activation of these particles in the solidification process. Athermal heterogeneous nucleation theory is considered to explain the effect of size and distribution of substrate particles on the grain structure with different undercoolings. The distribution of primary particle sizes results in the distribution of required undercoolings. Grain refining occurs when the undercooling is large enough to activate the refined primary intermetallics or dispersed inoculants. Description: This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited - The article can also be accessed from the link below - Copyright @ 2011 Springer