Mathematical modeling of thermo-mechanical behavior of strip during twin roll casting of an AZ31 magnesium alloy (original) (raw)
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International Journal of Advanced Manufacturing Technology
Twin-roll strip casting is an effective technology to produce magnesium alloy strips economically. The aim of this work is to propose suitable (optimized) process parameters for manufacturing AZ61 strips using the twin-roll strip casting technology. Experiments on twin-roll strip casting of an AZ61 magnesium alloy were carried out. Temperature fields, fluid flow fields, and stress fields accompanying the process were simulated using thermal-fluid and thermal-mechanical finite element methods. The effects of casting speed and pouring temperature on temperature fields, fluid flow fields, and stress fields during the process were analyzed. It was found that the optimum pouring temperature should be in the range 690∼715 °C and the optimum casting speed in the range 2.3 and 2.5 m/min.
Metallurgical and Materials Transactions A, 2011
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.
Direct strip casting and hot rolling of an AZ31 magnesium alloy
Materials Science and Engineering: A, 2010
An AZ31 magnesium alloy was cast by the direct strip casting (DSC) process. Prior to casting, the melt was treated with a commercial Al-Ti-B refiner. By subsequently hot rolling the cast strip at 400 • C, a 1 mm thick sheet was produced. The microstructures of DSC and the hot rolled magnesium were examined by optical microscopy and the hardness was measured. The flow curves of the cast material were determined at 200 • C, 300 • C and 400 • C by compression tests with a deformation dilatometer and dynamic recrystallization was found to take place at 300 • C and 400 • C. The thermal stability of the hot rolled sheet was investigated by an isochronal annealing treatment over a wide range of temperatures between 100 • C and 460 • C.
Magnesium Alloy Strip Produced by a Melt-Conditioned Twin Roll Casting Process
Materials Science Forum, 2011
Melt conditioning by intensive shear was used prior to twin roll casting of an AZ91 magnesium alloy strip to promote heterogeneous nucleation and produce a refined and uniform microstructure without severe macro-segregation. The as-cast strip was then processed by homogenization, hot rolling and annealing and the microstructural behaviour during the downstream processing was examined and compared with the strip of the same alloy produced without melt conditioning. The melt conditioned strip after downstream processing displayed significantly improved mechanical properties with an average tensile elongation of ~16%, compared with ~10% for the strip produced without melt conditioning and the reported values of ~1.5-6.2% in the literature.
Optimization and application of process parameters in an AZ61 alloy twin-roll strip casting
2014
Twin-roll strip casting is a concerned technology for economically producing magnesium alloys sheets. In this paper, numerical simulation of the twin-roll strip casting of an AZ61 magnesium alloy was carried out and the optimal process parameters were obtained. Then, under the conditions obtained through simulation, AZ61 strips of good surface quality were successfully manufactured. The microstructure of the alloy by twin-rolled strip casting is obvious refined compared with that by conventional casting.
MECHANICAL PROPERTIES OF HOMOGENIZED TWIN-ROLL CAST AND CONVENTIONALLY CAST AZ31 MAGNESIUM ALLOYS
Materials Engineering
Resume The improvement of mechanical properties of magnesium alloys nowadays is very important, because of the variety of industrial applications. For this goal, the number of casting techniques and further treatments were developed. Among the continuous casting techniques, which allow producing long strips of the alloys, is twin-roll casting. Using this process one can get the magnesium alloy with finest microstructure and higher specific strength. In this paper the comparison of tensile properties of conventionally cast and twin-roll cast AZ31 magnesium alloys was made. Tensile tests were carried out with constant strain rate 10-3 s-1 at temperatures ranging from 100 to 300 °C. Both materials were tested in as-cast state and after homogenization treatment at 450 °C for 10 hours. The investigation showed that there are no significant changes in ductility of AZ31 conventionally cast alloy even after heat treatment, while the ductility of twin-roll cast alloy increases.
METAL 2021 Conference Proeedings, 2021
With increasing interest in lightweight construction and cost-efficient sheet production methods, the twin roll casting of non-ferrous metals is constantly developing, due to the combination of several different process steps into one process. However, its challenge is the impossibility of direct recording of important process parameters such as temperature and pressure distribution in the rolling gap, in order to control product properties, due to the difficult process conditions. This article will discuss asolution to transform the twin roll casting process into a process that can controls product properties using a softsensor with additional inline measurements for temperature and pressure at the surface of the work rolls and a digital twin. The digital twin is used to predict correlations between the entities at the roll surface and the material properties in the bulk of the strip. The model used in this article is an extension of the layer model proposed by Schmidtchen and Kawalla based on the classical elementary theory of plasticity, which aimed to model the heterogeneous deformation behavior during flat rolling. Its great advantage compared to other simulation methods is a much lower computational effort. The actual extension as casting-rolling tool as proposed by Weiner et al. combines a viscous and a solid region for each layer in one tool. Experimental results were obtained that allows the direct correlation between the shape of temperature distributions and the length of the fully solidified part Ld within the roll-casting zone. This length correlates directly to the effective total equivalent strain. The static recrystallization in a subsequent heat treatment process is improved and results in a better formability of the magnesium strip with increasing strain.
Solidification of AZ31 magnesium alloy plate in a horizontal continuous casting process
Materials Science and Engineering: A, 2005
Magnesium plate of 120 mm width and 30 mm thickness was produced by horizontal continuous casting, and its microstructures were analyzed on the surface and in the plate interior. The defect formation on the surface and subsurface, such as side cracks, buckling, pores and segregation, was very sensitive to the casting condition and processing parameters. Especially, a secondary cooling was effective in refining the microstructure and controlling the grain size distribution across the plate thickness, which means that the cooling rate and curvature of the solid/liquid interface in the mold changed. According to AES analysis on the surface, the thickness of the oxide layer was not more than 0.3 m. However, the cyclic marks on the surface were obvious, because the plate were drawn by four-step cycle. In the case of several defects, they caused side cracks during rolling and survived even after rolling. Thus, it was concluded that pretreatment of the as-cast plate, such as homogenization and surface machining, is necessary to produce sound thin sheet by hot rolling.
A study of the hot and cold deformation of twin-roll cast magnesium alloy AZ31
Http Dx Doi Org 10 1080 14786435 2013 853884, 2014
Recent advances in twin-roll casting (TRC) technology of magnesium have demonstrated the feasibility of producing magnesium sheets in the range of widths needed for automotive applications. However, challenges in the areas of manufacturing, material processing and modelling need to be resolved in order to fully utilize magnesium alloys. Despite the limited formability of magnesium alloys at room temperature due to their hexagonal close-packed crystalline structure, studies have shown that the formability of magnesium alloys can be significantly improved by processing the material at elevated temperatures and by modifying their microstructure to increase ductility. Such improvements can potentially be achieved by processes such as superplastic forming along with manufacturing techniques such as TRC. In this work, we investigate the superplastic behaviour of twin-roll cast AZ31 through mechanical testing, microstructure characterization and computational modelling. Validated by the experimental results, a novel continuum dislocation dynamics-based constitutive model is developed and coupled with viscoplastic self-consistent model to simulate the deformation behaviour. The model integrates the main microstructural features such as dislocation densities, grain shape and grain orientations within a self-consistent viscoplasticity theory with internal variables. Simulations of the deformation process at room temperature show large activity of the basal and prismatic systems at the early stages of deformation and increasing activity of pyramidal systems due to twinning at the later stages. The predicted texture at room temperature is consistent with the experimental results. Using appropriate model parameters at high temperatures, the stress-strain relationship can be described accurately over the range of low strain rates.