The Experts below are selected from a list of 14265 Experts worldwide ranked by ideXlab platform
Terence G Langdon - One of the best experts on this subject based on the ideXlab platform.
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developing grain refinement and superplasticity in a magnesium alloy processed by high pressure torsion
2008Co-Authors: Zenji Horita, Terence G LangdonAbstract:Experiments were conducted on a Mg–9% Al alloy to evaluate the microstructural characteristics and the tensile properties at elevated temperatures after processing by high-pressure torsion (HPT) at room temperature and at 423 K. Ultrafine grain sizes were achieved by processing samples in both an extruded and a Cast Condition. The results demonstrate the viability of using HPT as a processing technique for achieving significant grain refinement in magnesium alloys which are not processed easily by equal-channel angular pressing (ECAP). Superplastic ductilities were achieved in tensile testing at a temperature of 473 K with a maximum measured elongation of 810%. In general, higher superplastic elongations were achieved after processing by HPT at 423 K because of the development of some limited internal cracking when processing at room temperature.
Mark Alan Easton - One of the best experts on this subject based on the ideXlab platform.
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age hardening in die Cast mg al re alloys due to minor mn additions
2016Co-Authors: Trevor B Abbott, Mark A. Gibson, Mark Alan EastonAbstract:Abstract Die-Cast Mg–Al–rare earth (RE) alloys are normally used in the as-Cast Condition without the application of heat treatment because it is a common perception that heat treatment will not provide benefit to these alloys. This paper reports, for the first time, that enhanced age hardenability can be achieved in die-Cast Mg–Al–RE alloys with minor Mn additions. For example, the yield strength of Mg–4 wt%Al–3 wt%La alloy with 0.32 wt% Mn is increased by ∼34 MPa (∼26%) after ageing at 200 °C for 32 h (T5). The enhanced age hardenability is associated with the precipitation of nanoscale Al–Mn particles during ageing.
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on the unexpected formation of rare earth hydrides in magnesium rare earth Casting alloys
2014Co-Authors: Suming Zhu, Mark A. Gibson, Jian Feng Nie, Mark Alan EastonAbstract:There have been reports on the presence of rare earth (RE) hydrides in Mg–RE-based alloys either in the as-Cast Condition or after high-temperature heat treatment. However, the origin of the RE hydrides remains unclear. In this work, the formation of RE hydrides was investigated using binary Mg–La, Mg–Ce and Mg–Nd alloys. It is proposed that the RE hydrides are probably formed as a result of the decomposition of Mg–RE intermetallic phases by hydrogen.
M J Starink - One of the best experts on this subject based on the ideXlab platform.
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evolution of microstructure and mechanical properties of an as Cast mg 8 2gd 3 8y 1 0zn 0 4zr alloy processed by high pressure torsion
2017Co-Authors: C Xu, X G Qiao, M Y Zheng, Shigeharu Kamado, M J StarinkAbstract:Abstract The novel Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy with high content of rare earth elements has been processed successfully by high pressure torsion (HPT) starting from an as-Cast Condition. HPT processing was conducted at room temperature for a range of turns from 1/8 to 16, and the evolutions of microstructure and microhardness were investigated. The average grain size decreases from ~85 µm in the as-Cast Condition to ~55 nm when the equivalent strain reaches ~6.0, and remains almost constant on further strain increase. Meanwhile, the coarse netlike Mg3(Gd,Y) second phase structures are gradually broken into fine dispersed particles and the dislocation density increases. The microhardness of the alloy increases with increasing strain, and when the equivalent strain reaches ~6.0, the microhardness reaches a saturated value of about 115 HV, which is higher than that obtained by conventional extrusion/rolling of this alloy. The full range of possible mechanisms of hardening are analyzed and this reveals that hardening is primarily due to the pronounced grain refinement, which is substantially stronger than that for HPT-processed conventional Mg alloys, and to the homogeneously distributed fine second phase particles and the high dislocation density.
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hardening mechanism of commercially pure mg processed by high pressure torsion at room temperature
2014Co-Authors: Xiao Guang Qiao, Ya Wei Zhao, Wei Min Gan, Ying Chen, Ming Yi Zheng, Nong Gao, M J StarinkAbstract:Coarse-grained Mg in the as-Cast Condition and fine-grained Mg in the extruded Condition were processed by high pressure torsion (HPT) at room temperature for up to 16 turns. Microstructure observation and texture analysis indicate that to fulfil the Von Mises criterion, the non-basal slip is activated in the as-Cast Mg and tension twinning is activated in the as-extruded Mg. Although the deformation mechanism is different in the as-Cast Mg and the as-extruded Mg during HPT, their hardening evolutions are similar, i.e. after 1/8 turn of HPT, microhardness of the as-Cast Mg and the extruded Mg both show a significant increase and further HPT processing does not significantly further increase the microhardness. Texture strengthening can explain the rapid hardening. Hardness anisotropy and texture data results suggest that texture strengthening plays an important role for both types of samples. Texture strengthening weakens with decreasing grain size.
L Katgerman - One of the best experts on this subject based on the ideXlab platform.
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thermal expansion contraction behavior of aa7050 alloy in the as Cast Condition relevant to thermomechanical simulation of residual thermal stresses
2011Co-Authors: M Lalpoor, D G Eskin, L KatgermanAbstract:As-Cast 7xxx series aluminum alloys experience a severe loss in ductility upon cooling and become brittle below 3008C. In order to simulate the thermal stresses arising during Casting, a thorough understanding of the thermal contraction behavior during solidification and cooling is required. In this study, some thermal properties of the AA7050 alloy are determined experimentally in the \asCast" Condition. Solidification contraction tests were performed to determine the onset of thermal contraction in the grain refined alloy and dilatometry tests were conducted to estimate the coefficient of thermal expansion/contraction of the alloy. Our simulation results showed that although the temperature dependence of the coefficients of thermal expansion/contraction obtained from the tests differ from the predictions of thermodynamic data-base, these differences are not crucial to the results of the thermomechanical simulations.
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investigation of fracture behavior of high strength aluminum alloys in the as Cast Condition
2010Co-Authors: M Lalpoor, D G Eskin, L KatgermanAbstract:Vertical direct-chill (DC) Casting process has been the mainstream of aluminium industry for the production of billets and ingots since the late 1930s largely due to its robust nature and relative simplicity [1]. Unfortunately the process can produce distortions in the ingot, and cracks can form owing to the non-uniform, high-rate heat removal due to the direct contact of a bottom block and cooling water with the partially solidified ingot. Further increase of thermal stresses in the solid state accompanied by weaker mechanical properties of the alloy in certain temperature ranges may lead to crack propagation and catastrophic failure [2]. Variation of mechanical properties in different ingot sections which is the result of high temperature gradients in the billet upon solidification can also cause different susceptibility of the material to cracking [3, 4] In contrast to pre-solidification cracks (hot cracks), which form at temperatures above the solidus, post-solidification cracks (cold cracks) propagate in a fully solid material [5]. Cold cracks can damage the entire ingot by splitting it open, which results in complete scrapping of the ingot. Cold cracking is characteristic of alloys which are brittle in the as-Cast Conditions. These alloys (mainly high-strength Al-alloys) are apparently unable of withstanding high stresses generated during DC Casting. In order to study cold cracking phenomenon in more detail, sufficient information on mechanical properties of such alloys in the as-Cast Condition (without stress relieving and homogenization) is required. The data on these properties are, however, seldom available in literature. The alloys in question are wrought alloys and most of the tests are performed on wrought products after deformation and heat treatment. Scattered information is available on the properties of ingots, but then only after homogenizing or stress-relief anneals [4,6]. This lack of experimental data on the mechanical properties of as-Cast high-strength wrought alloys, especially in a range of temperatures and strain rates relevant to DC Casting, makes thermo-mechanical simulations of cold cracking unreliable. This paper is a first step in bridging this gap. The results are reported on mechanical properties of as-Cast 7XXX-series alloys in a wide range of subsolidus temperatures. The structure and fractures are examined in an attempt to interpret the results of mechanical testing.
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fracture behavior and mechanical properties of high strength aluminum alloys in the as Cast Condition
2008Co-Authors: M Lalpoor, D G Eskin, L KatgermanAbstract:Abstract Finding a criterion for cold cracking during direct-chill (DC) Casting of high-strength aluminum alloys seems to be quite necessary in aluminum industry. However, lack of experimental information on the fracture mode and temperature dependence of mechanical properties of such alloys in as-Cast Conditions (without any homogenization or stress relieving) makes computer-simulation results unreliable. Mechanical tests on AA7050 and DC-Cast A7475 revealed that these alloys lose their ductility sharply as the temperature falls and fail in inter/transdendritic mode. Formation of pores and micro-cracks especially at the matrix–intermetallics interfaces apparently results in brittleness of the material in the as-Cast Condition.
Fernando Carreno - One of the best experts on this subject based on the ideXlab platform.
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severe plastic deformation of an as Cast hypoeutectic al si alloy
2008Co-Authors: S Swaminathan, J M Garciainfanta, T R Mcnelley, Oscar Antonio Ruano, Fernando CarrenoAbstract:Different equal channel angular pressing (ECAP) processing routes have been employed to investigate the flow plane microstructures in a hypoeutectic Al–7wt%Si. In the as-Cast Condition, this alloy exhibits equiaxed primary aluminum dendrite cells embedded in an Al–Si eutectic constituent. The observed microstructures have been compared to the predicted distortion of a volume element expected during idealized ECAP. The effect of different processing routes on the microstructure refinement, degree of homogenization of second phase particles, and associated mechanical properties are discussed.