Papers by Keyword: Age Hardening

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Authors: Amporn Wiengmoon, Pattama Apichai, John T.H. Pearce, Torranin Chairuangsri
Abstract: Effects of T6 artificial aging heat treatment on microstructure, microhardness and ultimate tensile strength of Al-4.93 wt% Si-3.47 wt% Cu alloy were investigated. The T6 age hardening treatment consists of solution treatment at 500±5°C for 8 hours followed by quenching into hot water at 80°C and artificial aging at 150, 170, 200 and 230°C for 1-48 hours followed by quenching into hot water. Microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). XRD and SEM revealed that the microstructure in the as-cast condition consists of primary dendritic α-Al, acicular-plate and globular forms of eutectic Si and intermetallic phases including globular Al2Cu and a flake-shape Al5FeSi. By T6 aging hardening, some intermetallics were dissolved and spheroidized. The volume fraction of eutectic phases in the as-cast, solution-treated, and solution-treated plus aging at 170°C for 24 hours is 17%, 12% and 10%, respectively. TEM results showed that precipitates in under-aging condition at 170° C for 6 hours are in the form of disc shape with the diameter in the range of 7-20 nm. At peak aging at 170°C for 24 hours, thin-plate precipitates with about 3-10 nm in thickness and 20-100 nm in length were found, lengthening to about 30-200 nm at longer aging time. The microhardness and ultimate tensile strength were increased from 71 HV0.05 and 227 MPa in the as-cast condition up to 140 HV0.05 and 400 MPa after solution treatment plus aging at 170°C for 24 hours, and decreased at prolong aging time.
Authors: Ji Wen Li, Jing Pei Xie, Zhong Xia Liu, Wen Yan Wang
Abstract: Effects of titanium refining methods on the microstructure and mechanical properties of A356 alloys were studied. The results showed that the A356 alloys refining by electrolytic low titanium Al alloys had excellent grain refinement effect and high age-hardening behavior comparing with the traditional A356 alloys. By means of DSC analyses, the solidification characteristics and the age-hardening behavior were discussed. The results showed that the E-A356 alloys had more powerful nucleation potency than that of the M-A356 alloys. The exothermic peaks of β// phase was shifted to a slightly lower temperature, and the rate of the continuous transition from GP zone to metastable phases increased.
Authors: Peter V. Liddicoat, Tomoyuki Honma, L.T. Stephenson, Simon P. Ringer
Abstract: During age-hardening of certain Al-Zn-Mg-Cu alloys, a 90% hardness increase can occur with 75 seconds. The clustering and precipitation of solute element species during this early rapid hardening (RH) period has been investigated through atom probe tomography, transmission electron microscopy, and Vickers hardness measurements. This study has focussed on the effect of copper by analysing three alloys; Al-2.0Zn-1.8Mg-0.7Cu, Al-2.0Zn-1.7Mg-0.2Cu and Al-1.9Zn-1.7Mg (at.%). The early RH reaction in these alloys accounts for up to 70% of the total hardening (peak hardness minus as-quenched hardness) and takes place during the first 60 seconds of ageing. We report preferred solute-solute interactions in the as-quenched materials. This quenched-in nanostructure acts as a template for subsequent solute clustering, the nature of which we have correlated with ageing.
Authors: Franck Tancret, Philippe Guillemet, Florent Fournier Dit Chabert, René Le Gall, Jean François Castagné
Abstract: A finite element approach is used to simulate the precipitation of Ni3(Al,Ti) intermetallics in nickel-based superalloys containing a low volume fraction of spherical g’ precipitates, in which precipitation occurs following nucleation and growth mechanisms. Classical differential equations of nucleation and growth are implemented in the software Comsol (formerly Femlab), to compute the number of precipitates per unit volume and their mean size. Another originality of the model is the use of thermodynamic quantities coming from phase diagram computations (Thermo-Calc), like the temperature variation of the equilibrium g’ volume fraction, and the evolution of the concentration of g’ forming elements (Al, Ti) in the matrix with the volume fraction of precipitates. Once adjusted to experiment in the case of isothermal ageings, the model can be used to simulate precipitation during complex thermal histories. Finally, automatic heat treatment optimisation procedures are proposed and tested, which can reduce heat treatment times by a factor of more than five.
Authors: Kishore Venkatesan, Wendy Borbidge, Michael Kellam, Daniel R. East, Mark A. Gibson, Daniel Liang
Abstract: The suitability of a twin-roll cast (TRC) age-hardenable alloy for wrought applications is explored. A Mg-4Zn (wt.%) alloy, 3mm thick, was cast using the TRC route. Deviating from the traditional practice of homogenization followed by age-hardening in die/sand cast parts, the TRC sheet, cut into small strips, was hot rolled and annealed after homogenization. They were then deep drawn and subsequently age-hardened. The rollability, mechanical properties and microstructure of the alloy at different stages of processing and after forming, are presented and discussed.
Authors: Yoon Uk Heo, Hu Chul Lee
Abstract: Grain boundary embrittlement and de-embrittlement observed in age hardening iron alloys were reviewed. Fe-Mn-Ni and Fe-Ni-Ti alloys show excellent hardening response during aging treatment. However these alloys all suffer grain boundary embrittlemnt and show no tensile ductility even after very short aging treatment. Precipitation of intermetallic phases, θ-MnNi in Fe-Mn-Ni alloys and η-Ni3Ti in Fe-Ni-Ti alloys, at grain or lath boundaries was suggested as the reason for the weakening of grain boundary strength. Grain boundary strength recovered when these precipitates transform to austenite after extended aging. Dislocation glide or dislocation climb did critical role in conversion of these grain boundary precipitates to austenite.
Authors: Yoon Uk Heo, Seung Ho Mun, Hu Chul Lee
Abstract: The mechanism of grain boundary embrittlement and the improvement of the tensile ductility afforded by alloy addition or heat treatment was investigated in an Fe-Mn-Ni alloy. The precipitation of θ-MnNi intermetallic particles was observed at the prior austenite or interlath boundaries during the aging treatment and this was believed to be responsible for the grain boundary embrittlement of these alloys. After prolonged aging or aging at higher temperatures above 520°C, these metastable intermetallic particles were transformed into the thermodynamically stable austenite phase, thereby leading to the recovery of the grain boundary strength. The addition of Mo caused the grain boundary precipitate to be changed to austenite and resulted in a significant improvement in the tensile ductility after aging.
Authors: D.S. Kim, C.G. Kang, S.M. Lee
Abstract: This study demonstrated nanoindentation techniques of investigating the effects of size and feature in a microstructure on the mechanical properties of rheology-forged aluminum alloy. Mechanical properties and tribological characteristics of rheology-forged Al2024 wrought aluminum alloy in terms of T6 heat treatment were investigated by varying the aging time by nanoindentation and nanoscratch techniques. By nanoindentation/nanoscratch tests and atomic force microscopy, it was demonstrated that the 4 hour aged material exhibites the highest hardness because of the intermediate precipitate phase θ″, which was precipitated by T6 heat treatment at 495°C. Moreover, the friction coefficients in the precipitates in the eutectic phase region were lower than those in the primary α phase region.
Authors: L. Kovarik, Pelagia Irene Gouma, Christian Kisielowski-Kemmerich, S.A. Court, Michael J. Mills
Authors: L. Kovarik, Pelagia Irene Gouma, Christian Kisielowski-Kemmerich, S.A. Court, Michael J. Mills
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