Papers by Keyword: Age Hardening

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Authors: B.J. Kim, S.M. Son, K.S. Park, Young Hoon Moon
Abstract: Modern automobiles are built with a steadily increasing variety of materials and semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature of the specimen very quickly. The specimen applied to the test is AA6061 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of AA6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.
Authors: Minoru Furukawa, Jia Lin Wang, Z. Horita, M. Nemoto, Yuanqing Ma, Terence G. Langdon
Authors: A. Bigot, F. Danoix, P. Auger, D. Blavette, A. Reeves
Authors: Ken Ichi Nishikawa, Satoshi Semboshi, Toyohiko J. Konno
Abstract: Environmentally friendly Cu-based alloys with high strength and low electrical resistivity have been much sought in order to replace deleterious Cu-Be alloys for electrical applications. As one of the candidate systems, we have examined age-hardening behaviors of Cu-Mg alloys by using transmission electron microscopy (TEM). Cu-2.26wt.%Mg alloys were solution-treated and annealed at 723K, and their structural changes have been investigated. The Vickers hardness measurements showed that they aged-harden gradually. Our TEM observations showed that annealing for 6h brings about precipitation of numerous needle-like particles of 10 nm in length. The diffraction studies indicated these precipitates consist of the Cu2Mg phase with {111}Cu habit planes. When annealed for 96h, these precipitates become semi-coherent, which was manifested by moiré fringes; while maintaining the orientation relationship of (111)Cu//(111)Cu2Mg, [110]Cu//[110]Cu2Mg.
Authors: Rimi Nishio, Toyohiko J. Konno, Satoshi Semboshi
Abstract: Phase separation behaviors of a quenched Cu-3.0at%Ti alloy, as well as crystallographic structures of Cu-20.7at%Ti alloy have been studied using transmission electron microscopy. The furnacecooled Cu-20.7at%Ti alloy are composed of a-Cu4Ti (Ni4Mo-type) and b-Cu4Ti (Au4Zr-type) with the orientation relationship of (011)a//(110)b, [100]a//[001]b. As-quenched Cu-3.0at%Ti alloy showed a modulated structure with the modulation length of about 4 nm. When aged at 723K for 8 hr, the a-Cu4Ti phase emerges within the modulated or tweed-like microstructure. Prolonged aging results in the growth of the a-Cu4Ti particles and the loss of coherency. It is likely that asquenched Cu-3.0at%Ti alloy decomposes spinodally at 723K, followed by polymorphous ordering; though the present study did not exclude, as an alternative path, a decomposition mechanism based on the catastrophic nucleation.
Authors: Rafael Ferragut, A. Dupasquier, M.M. Iglesias, C.E. Macchi, Alberto Somoza, Ian J. Polmear
Abstract: Positron annihilation spectroscopy in two versions (lifetime and coincidence Doppler broadening) has been applied to investigate solute/vacancy interactions when minor amounts (<1wt.%) of Ag or Cu are added to the alloy Al-4Zn-3Mg (wt.%) during ageing at 150°C. The results show early clustering of vacancies with Zn (and with Cu, if present). Ag displays a strong interaction with vacancies in competition with Mg and forms clusters that may help further aggregation of the other alloying elements during artificial ageing. High Mg concentration is observed at the misfit interfaces of semi-coherent or incoherent precipitates.
Authors: R.K.W. Marceau, Rafael Ferragut, A. Dupasquier, M.M. Iglesias, Simon P. Ringer
Abstract: This is an initial report of a multi-technique study on the effect of Mg alloying on solute-vacancy interactions during the early stages of ageing of dilute 2xxx Al-Cu-Mg alloys so as to better understand the early rapid hardening (RH) that occurs in certain compositions of these alloys and the more general phenomena of secondary hardening (SH) at ambient temperatures. Therefore, RH at 150 °C and SH at room temperature from the as-quenched condition and after 60 sec ageing at 150 °C were studied in Al-1.1Cu and Al-1.1Cu-0.5Mg (at. %) variously by positron annihilation lifetime spectroscopy (PALS), coincidence Doppler broadening (CDB) spectroscopy and atom probe tomography (APT) and monitored by Vickers hardness measurements. The present results indicate that Cu-Cu, Mg-Mg and Cu-Mg clusters are formed in the ternary alloy already in the asquenched state and that they persist during ageing at 150 °C. The fraction of the solutes Cu and Mg that were associated with vacancies after ageing was increased 10-fold and double, respectively and the strength of the Cu clustering is enhanced greatly after 60 sec at 150 °C.
Authors: Jesper Friis, Bjørn Holmedal, Øyvind Ryen, Erik Nes, Ole R. Myhr, Øystein Grong, Trond Furu, Knut Marthinsen
Abstract: The work hardening of alloys hardened by precipitate heat treatments depends on the distribution of the precipitate sizes and the solute level left in the metal matrix. A mean field theory for precipitation is first applied for the ageing and subsequently it is coupled to a work hardening model to study the stress-strain responses of age hardened conditions of AA6xxx alloys. The predictions are compared to mechanical experiments and to TEM characterisations.
Authors: Shinji Muraishi, Shinji Kumai, Akikazu Sato
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