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Instruments / Technical Area	Publication Details	Published
I12-JEEP: Joint Engineering, Environmental and Processing	In-situ investigation of dynamic precipitation in pre-aged Al-Zn-Mg-Cu alloy AA7075 Z. Ma , M. Bignon , F. Gao , S. Michalik , J. D. Robson Journal Of Alloys And Compounds 47 DOI: 10.1016/j.jallcom.2023.172098 Diamond Proposal Number(s): [30439] Open Access Show Abstract ▼ Abstract: High strength Al-Zn-Mg-Cu alloys rely for their properties on nano-scaled precipitates formed during artificial ageing. Deformation profoundly affects the evolution of these precipitates. This study investigates the effect of warm deformation on precipitation in a pre-aged AA7075 aluminium alloy. Warm deformation was performed using an electro-thermomechanical testing machine for rapid resistance heating. Transmission electron microscopy showed slightly larger, yet evenly distributed, precipitates in the warm deformed sample compared to the thermally treated condition without deformation. Synchrotron small angle X-ray scattering revealed accelerated growth rates of precipitates due to deformation. At low plastic strains, the growth rate increased linearly with applied strain, while at high plastic strains, a slight deviation from linear behaviour was observed. Temperature and strain rate effects were also examined, with a stronger enhancement effect at low temperature and fast strain rate for a given strain. The deformation enhancement effect disappeared rapidly upon finishing plastic deformation (within 400s for the studied condition). The enhanced growth rate during and after deformation can be reasonably explained by the excess vacancy concentration, indicating the influence of strain-induced excess vacancies. However, the simple excess vacancy model used fails to explain the observed strain rate effect, and possible explanations for this discrepancy are discussed.	Sep 2023
I22-Small angle scattering & Diffraction	Microstructural stability and paint bake response of pre-aged AA7075 Z. Ma , E. Cooksey-Nash , D. Barbier , J. D. Robson Materials Characterization 47 DOI: 10.1016/j.matchar.2023.112862 Diamond Proposal Number(s): [27903] Open Access Show Abstract ▼ Abstract: High strength AA7xxx are attractive for use in the automotive industry, offering significant strength/weight benefits. These alloys are often used in tempers that require long ageing times of several hours. Pre-ageing has been proposed to be effective in suppressing natural ageing, and reducing the total ageing time by integrating the final ageing step into the paint bake cycle. However, the precipitate evolution during the pre-ageing and subsequent paint bake processes remains to be fully understood. In the present work, the pre-ageing process was studied for AA7075 over a wide range of temperatures and times. Small angle X-ray scattering (SAXS) was used as the main technique to investigate the precipitate evolution during the pre-ageing, natural ageing and paint bake, with the support from transmission electron microscopy (TEM) and isothermal calorimetry. For the first time, the results show that 8 h pre-ageing at 80 °C can produce a microstructure consisting of GP zones with an average radius of approximately 0.9 nm, which remains stable up to at least 7 months. After a short paint bake process, 94% of the T6 hardness can be obtained by uniformly distributed precipitates with an average radius of approximately 2.6 nm. The final size and strengthening effect of the precipitates after 20 min baking is found to be insensitive to the heating rate, which has not been reported previously. The present results further suggest this process is robust for industrial application.	Apr 2023
I12-JEEP: Joint Engineering, Environmental and Processing	Direct observation of the dynamic evolution of precipitates in aluminium alloy 7021 at high strain rates via high energy synchrotron X-rays W. U. Mirihanage , J. D. Robson , S. Mishra , P. Hidalgo-Manrique , J. Quinta Da Fonseca , C. S. Daniel , P. B. Prangnell , S. Michalik , O. V. Magdysyuk , T. Connolley , M. Drakopoulos Acta Materialia DOI: 10.1016/j.actamat.2020.116532 Diamond Proposal Number(s): [13828] Open Access Show Abstract ▼ Abstract: 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.	Dec 2020

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