Examinando por Autor "Robson, J.D"

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Direct observation of the dynamic evolution of precipitates in aluminium alloy 7021 at high strain rates via high energy synchrotron X-rays
(Elsevier, 2020-12-02) Mirihanage, W.U; Robson, J.D; Mishra, S; Hidalgo-Manrique, P; Quinta da Fonseca, J; Daniel, C.S; Prangnell, P.B; Michalik, S; Magdysyuk, O.V; Connolley, T; Drakopoulus, M
An improved understanding of the phenomenon of dynamic precipitation is important to accurately model and simulate many industrial manufacturing processes with high strength Al-alloys. Dynamic ageing in 7xxx Al-alloys can occur as a result of both the strain and heat. Small angle X-ray scattering (SAXS) is an advanced technique that allows the precipitation processes to be studied in situ, but to date this has only been possible at lower than industrially relevant strain rates (e.g. < 10−3). In this contribution, we demonstrate the potential of in-situ SAXS studies of metallic alloys at higher strain rates (10−2) than previously, using a high energy synchrotron X-ray. The time resolved SAXS information has been used to evaluate dynamic precipitate evolution models and has demonstrated that at high strain rates a new regime must be considered which includes the more significant effect of vacancy annihilation, leading to a clear strain rate, rather than just strain, kinetic dependence.
Microstructure and properties of aluminium alloy 6082 formed by the Hot Form Quench process
(Elsevier, 2021-01-07) Hidalgo-Manrique, P; Cao, S; Shercliff, H.R; Hunt, R.D; Robson, J.D
During a process development trial, two identical structural automotive parts were formed from a rolled sheet of commercial 6082 Al alloy by Hot Form Quench (HFQ). The rapid transitional contact between the sheet and the die set during die closing imposed a range of complex cooling histories on different locations in the parts. After in-die quenching, one HFQ part was naturally aged at room temperature, while the other was peak-aged at 185 ºC for 7 h. The microstructure was compared at two extreme locations; the flange, where die contact is instantaneous leading to immediate rapid cooling, and the sidewall, where the material cools more slowly in air before rapid quenching. After HFQ, some small quench induced grain boundary precipitates were observed in the sidewall specimen but not in the flange. However, subsequent artificial ageing led to a convergence of the microstructures. Consequently, hardness was found to be constant at both locations, and no loss of hardening potential was observed in either case compared with T6 sheet. Samples of the as-received material were subjected to selected quench-hold-quench-age experiments to mimic the HFQ microstructures. Tensile tests showed that the ductility and failure mechanism is insensitive to the small differences in grain boundary microstructure as observed in the HFQ component.