Papers by Keyword: Secondary Precipitation

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Authors: M. Yin, D.D. Risanti, Jiang Hua Chen, Sybrand van der Zwaag
Abstract: This work utilizes thermoelectric power (TEP) measurement to track secondary precipitation during the interrupted ageing cycle for AA2024 alloys as well as the subsequent re-ageing cycle. Clear evidences of secondary precipitation were observed which affect the further precipitation sequence during re-ageing. The TEM results confirm that S and S” phases co-exist upon re-ageing.
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Authors: D.D. Risanti, Sybrand van der Zwaag
Abstract: The anelastic behavior of AA2024 alloy is studied in the temperature range between room temperature and 325 °C. The internal friction technique is shown to be very sensitive to the microstructural changes that take place at these temperatures. Interrupted aging performed at low temperature induces increase in the peak height at ~230 °C indicating the slow release of vacancies aiding the aggregation of Mg and Cu which further transforms into semicoherent precipitates. Stretched specimens indicate increase in background which is attributed to anelastic or viscoelastic of dislocations. TDIF of T6I4 samples is strongly affected to the point of deformation, whilst TDIF of T6I6 samples is affected by the deformation but irrespective to the point of deformation.
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Authors: Roger N. Lumley, J. Buha, Ian J. Polmear, A.J. Morton, A. Crosky
Abstract: This paper reviews some of the practical outcomes of exploiting secondary precipitation during the heat treatment of aluminium alloys and discusses current understanding of this phenomenon. Recent studies have utilised the techniques of positron annihilation spectroscopy (PAS), 3D atom probe (3DAP) as well as the more traditional transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) to investigate early precipitation events that occur during secondary ageing at low temperatures (~20-65°C). This work has confirmed that clustering and GP zone formation can modify the nature and distribution of precipitates that form when ageing is subsequently resumed at more elevated temperatures. Prospects for achieving further improvements in heat treatment schedules and alloy compositions to take greater advantage of secondary precipitation are also considered.
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Authors: D.D. Risanti, M. Yin, Jiang Hua Chen, Sybrand van der Zwaag
Abstract: A comprehensive and systematic study using hardness, tensile test and Kahn tear test was undertaken to follow property development during the recently promoted interrupted ageing treatment. In contrast to the reported claims hardness remains lower than that of single stage heat treatment. Toughness does not improve substantially and deteriorates further as re-ageing time is prolonged. For most cases, the effect of interrupted ageing could not produce a simultaneous improvement in mechanical properties. TEM observations indicate the size and distribution co-existing S” and S phases upon re-ageing depend on interrupted condition.
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